EP4189744A2 - Entwurf und herstellung von verbesserten leistungsbauelementen - Google Patents

Entwurf und herstellung von verbesserten leistungsbauelementen

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Publication number
EP4189744A2
EP4189744A2 EP21862946.7A EP21862946A EP4189744A2 EP 4189744 A2 EP4189744 A2 EP 4189744A2 EP 21862946 A EP21862946 A EP 21862946A EP 4189744 A2 EP4189744 A2 EP 4189744A2
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EP
European Patent Office
Prior art keywords
region
conductivity type
layer
source
sic
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EP21862946.7A
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English (en)
French (fr)
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EP4189744A4 (de
Inventor
Siddarth Sundaresan
Ranbir Singh
Jaehoon Park
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GeneSIC Semiconductor Inc
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GeneSIC Semiconductor Inc
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Publication of EP4189744A2 publication Critical patent/EP4189744A2/de
Publication of EP4189744A4 publication Critical patent/EP4189744A4/de
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    • H10D62/299—Channel regions of field-effect devices of FETs of IGFETs having lateral doping variations
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Definitions

  • This invention relates to power semiconductor devices using a vertical silicon carbide (SiC) Double-Implantation Metal oxide semiconductor field-effect transistor (DMOSFET).
  • SiC vertical silicon carbide
  • DMOSFET Double-Implantation Metal oxide semiconductor field-effect transistor
  • MOSFET power metal oxide semiconductor field-effect transistor
  • this invention relates to 4H-SiC devices, which include diodes and transistors having inter-digitated n-type and P-Type areas such as Junction Barrier Schottky (JBS) diodes, Merged PiN/Schottky (MPS) diodes, Metal oxide semiconductor field effect transistors (MOSFETs) and Junction field effect transistors (JFETs) having inter-digitated N-Type and P- Type areas.
  • JBS Junction Barrier Schottky
  • MPS Merged PiN/Schottky
  • MOSFETs Metal oxide semiconductor field effect transistors
  • JFETs Junction field effect transistors
  • SiC has a higher breakdown electric field (3 x 10 6 V/cm to 5 x 10 6 V/cm) compared to Si (breakdown electric field for Si is 0.3 x 10 6 V/cm) and is a better thermal conductor (3.7 (W/cm-K) for SiC versus 1.6 (W/cm-K) for Si).
  • SiC has been a material of choice for power MOSFETs.
  • SiC exists in a kind of polymorphic crystalline building known as a polytype, e.g., 3C-SiC, 4H-SiC, 6H-SiC.
  • Fig. 1A is the prior art SiC DMOSFET structure reported by B.J. Baliga in Advanced High-Voltage Power Device Concepts (Springer Press, 2011).
  • Fig. IB shows the electric field contours simulated for the prior art SiC DMOSFET structure of Fig. 1A. The electric field distribution near the surface of the 5-kV shielded 4H-SiC inversion-mode power MOSFET structure is shown in Fig. IB to allow examination of the electric field in the junction gate fieldeffect transistor (JFET) region and the gate region.
  • JFET junction gate fieldeffect transistor
  • Fig. 1C shows the electric field distribution in the shielded 4H-SiC inversion-mode MOSFET.
  • the simulated results in the figure show an electric field as high as 4 MV/cm in the gate oxide for the prior art SiC DMOSFET structure of Fig. 1A.
  • a typical SiC MOSFET device structure such as that shown in Fig.
  • Si silicon-doped nitride-doped nitride-doped nitride-doped nitride-doped nitride-doped nitride-doped nitride-doped nitride-doped nitride-doped nitride-doped nitride-doped nitride-doped silicadium silicates.
  • SiC devices are manufactured by ion implantation of both source and p-well regions but ion implantation and deep ion implantation is difficult in SiC. Therefore, there is a long-felt need for improved power devices that address the reliability issues for SiC power MOSFETs.
  • the MOSFET channel region is formed as a result of the offset between the p-well and the N+ source regions in a DMOSFET structure. If the p-well and N+ source regions are formed by two separate masking steps, there will inevitably be a certain amount of lithographic misalignment between these levels, resulting in different (or asymmetric) MOS channel lengths on the two sides of the unit cell.
  • the lithographic misalignment between two masking levels using projection lithography techniques typically used in high-volume semiconductor manufacturing can range from +/- 0.05 pm to +/- 0.2 pm or greater, which sets a lower limit on the practically realizable MOS channel lengths without significant asymmetry.
  • a +/- 0.2 pm misalignment between the N+ source and p-well masking steps can result in a MOS channel length of 0.3 pm on one side of the unit cell and a MOS channel length of 0.7 pm on the other side of the unit cell.
  • the ON resistance of the MOSFET is increased at higher MOS channel lengths, lower than optimal MOS channel lengths can result in undesirable effects such as gate threshold voltage (Vth) degradation and other short-channel effects such as drain-induced barrier lowering (DIBL).
  • Vth gate threshold voltage
  • DIBL drain-induced barrier lowering
  • the metal oxide semiconductor (MOS) channel is formed on the horizontal or 0001 crystal plane of SiC.
  • the channel mobility or field effect mobility on the 0001 crystal plane of SiC tends to be lower as compared to the vertical side wall or what is called as the 11-20 or 10-10 crystal plane.
  • the channel mobility or field effect mobility on the 0001 crystal plane of SiC is in the range of 15 to 25 cm2/ V-sec as compared to silicon MOSFETs where it can be more than 350 cm2/ V-sec.
  • the ON resistance tends to be large and the MOSFET is limited by the field effect channel mobility. Therefore, there is a long-felt need for improved power devices that addresses the low channel mobility and high ON resistance in SiC MOSFET.
  • VG - VT threshold voltage
  • Fig. 22 [source: B.J. Baliga, Silicon Carbide Power Devices, Springer Press (2005), Page 235] shows the threshold voltage of 4H-SiC planar MOSFETSs for the case of a gate oxide thickness of 0.1 microns. The results obtained for a silicon power MOSFET with the same gate oxide thickness is also provided in the figure for comparison. [0014] In the race to achieve lower RDS, ON of planar gate SiC MOSFETs with high breakdown voltage ratings, it is a common practice to make the channel lengths (LCH) as short as possible which reduces a great part of the conduction loss that is associated to the channel.
  • LCH channel lengths
  • the MOSFET devices become susceptible to undesirable phenomena such as the DIBL effect (the Drain Induced Barrier Lowering effect) which is responsible for the poor device performance including but not limited to the roll-off of the threshold voltage (VTH) at high drain bias and the increase of the drain leakage (II) at high drain bias.
  • DIBL effect the Drain Induced Barrier Lowering effect
  • VTH threshold voltage
  • II drain leakage
  • Fig. 27 is the prior art structure of a MPS diode, consisting of interdigitated pin and Schottky diodes connected in parallel as reported in “T. Kimoto and J. A. Cooper, Fundamentals of Silicon Carbide Technology, IEEE Press (2014), page 296]”.
  • the MPS diode as shown in the prior art in Fig. 27 has metal layer on top which forms ohmic contacts to the P+ regions and Schottky contacts to the n- regions, so the overall device consists of interdigitated Schottky and pin diodes connected in parallel.
  • the P+ anode regions are spaced far enough apart that their depletion regions do not touch under zero or forward bias.
  • the series resistance of the drift region is determined by its thickness and doping. This relatively high resistance leads to a voltage drop VDR that dominates the total voltage drop at high currents. In a Schottky diode, this poses a problem under high surge current events, since the pure Schottky diode can go into thermal runaway, with catastrophic consequences.
  • SiC device may include a gate electrode disposed above a SiC semiconductor layer, wherein the SiC semiconductor layer comprises: a drift region having a first conductivity type; a well region disposed adjacent to the drift region, wherein the well region has a second conductivity type; and a source region having the first conductivity type disposed adjacent to the well region, wherein the source region comprises a source contact region and a pinch region, wherein the pinch region is disposed only partially below the gate electrode, wherein a sheet doping density in the pinch region is less than 2.5 x 10 14 cm -2 , and wherein the pinch region is configured to deplete at a current density greater than a nominal current density of the SiC device to increase the resistance of the source region.”
  • Source Silicon carbide device and method of making thereof, Peter Almem Losee, Ljubisa Dragoljub Stevanovic, Gregory Thomas Dunne, Alexander Viktorovich Bolotnikov, published as US9899512B2 on February
  • US20190013312A1 discloses body regions numbered 3, 5, respectively, that accommodate a first and a second source region numbered 4, 6, of the N type, extending from the upper surface 2 A into the interior of the body regions 3, 5 and states: “A first metallization layer extends over the first surface and forms, in direct contact with the implanted structure and with the JFET region, a JBS diode.”
  • source MOSFET device of silicon carbide having an integrated diode and manufacturing process thereof, Mario Giuseppe Saggio, Simone RASCUNA, published at USPTO as US20190013312A1 on January 10, 2019]
  • n-MOSFET device (11) has an n-type channel (2) between a substrate (1) and a gate structure (7, 8), the channel (2) being formed by a layer of n-doped germanium of a thickness such that the channel (2) is fully-depleted with no applied gate voltage whereby the device (11) is operative in accumulation mode.”
  • source Germanium n-mosfet devices and production methods, Daniele Caimi, Athanasios Dimoulas, Jean Fompeyrine, Chiara Marchiori, Christophe P. Rossel, Marilyne Sousa, Axelle M. Tapponnier, David J. Webb, published as W02011013042A1 on February 03, 2011]
  • US9318597B2 discloses that a semiconductor device that includes a vertical field-effect- transistor (FET) and a bypass diode. It further states that the vertical FET device includes a substrate, a drift layer formed over the substrate, a gate contact and a plurality of source contacts located on a first surface of the drift layer opposite the substrate, a drain contact located on a surface of the substrate opposite the drift layer, and a plurality of junction implants, each of the plurality of junction implants laterally separated from one another on the surface of the drift layer opposite the substrate and extending downward toward the substrate and that each of the one or more bypass diodes are formed by placing a Schottky metal contact on the first surface of the drift layer, such that each Schottky metal contact runs between two of the plurality of junction implants, [source: Layout configurations for integrating schottky contacts into a power transistor device, Vipindas Paia, Edward Robert Van Brunt, Lin Cheng, John Williams Palmour, published as US9318597B2 at USPTO
  • US9876104B2 discloses a multi-cell MOSFET device including a MOSFET cell with an integrated Schottky diode wherein the MOSFET includes n-type source regions formed in p-type well regions which are formed in an n-type drift layer, a p-type body contact region is formed on the periphery of the MOSFET, and the source metallization of the device forms a Schottky contact with an n-type semiconductor region adjacent the p-type body contact region of the device, [source: High voltage semiconductor devices and methods of making the devices, Kevin Matocha, Kiran Chatty, Sujit Baneijee, published as US9876104B2 on January 23, 2018],
  • US8436367B1 discloses that a SiC Power Semiconductor device of the Field Effect Type (MOSFET, IGBT or the like) with “muted” channel conduction, negative temperature coefficient of channel mobility, in situ “ballasted” source resistors and optimized thermal management of the cells for increased Safe Operating Area is described. Controlling the location of the Zero Temperature Crossover Point (ZTCP) in relationship to the drain current is achieved by the partition between the “active” and “inactive” channels and by adjusting the mobility of the carriers in the channel for the temperature range of interest.”
  • ZTCP Zero Temperature Crossover Point
  • FIG. 67A shows two implementations of a power MOSFET in the form of a vertical, planar DMOSFET and a vertical trench UMOSFET.
  • DMOSFET derives from the silicon device of the same name, where the n+ source and p-base regions are formed by diffusion of n-type and p-type impurities through the same mask opening (hence “double diffused” MOSFET).
  • SiC the same structure is formed by double implantation.
  • UMOSFET derives from the U-shaped geometry, but the term trench MOSFET is also used.
  • the first SiC power MOSFETs were UMOSFETs, but they were joined soon by ion implanted DMOSFETs. [SOURCE: T. Kimoto, J. A. Cooper in Fundamentals of Silicon Carbide Technology, IEEE Press (2014), pages 320-324.]
  • UMOSFETs Because of their trench geometry, UMOSFETs present both opportunities and challenges relative to planar devices such as the DMOSFETs.
  • the UMOSFET can be fabricated in a smaller surface area than the DMOSFET, since the MOS channel is oriented perpendicular to the surface. It is also easier to form a short sub-micron channel since the channel length is determined by epigrowth.
  • the MOS channel is formed on an etched non-polar face of the crystal, and the properties of the gate oxide are different from those on the (1000) plane.
  • the channel mobility or field effect mobility on the 0001 crystal plane tends to be lower as compared to the vertical side wall or what is called as the 11-20 or 10-10 crystal plane.
  • the channel mobility can be in the range of 15-25 cm2/Vs on the 1000 plane whereas it can be as high as 60-80 cm2/Vs on the 11-20 or 10- 10 crystal planes of SiC.
  • FIG. 67B and 67C show major resistances in the vertical DMOSFET and the UMOSFET respectively and it is apparent that the geometry of the device effectively eliminates the JFET resistance present in the DMOSFET.
  • FIG. 67D illustrates the electric fields in the UMOSFET in the blocking state, the trench corners are significant locations of significant field crowding. Because the oxide field is ⁇ 2.5X higher than the peak field in the semiconductor (due to Gauss’ law of electrostatics), this is a serious problem inherent to the UMOSFET device design. [SOURCE: T. Kimoto, J.A. Cooper in Fundamentals of Silicon Carbide Technology, IEEE Press (2014), pages 320-324.]
  • JBS junction barrier Schottky
  • MPS PiN Schottky
  • a device comprises a unit cell on a SiC substrate.
  • the unit cell comprises a gate insulator film, a trench in a well region, a first sinker region having a second conduction type, and a second sinker region having the second conduction type.
  • the first sinker region has a depth that is equal to or greater than a depth of the well region.
  • Each of the first sinker region and the second sinker region is in contact with a region having a first conduction type to form a p-n junction.
  • the device comprises a semiconductor metal-insulator-semiconductor transistor component.
  • the well region is next to an insulator-semiconductor interface; and a source region of the first conduction type formed within the well region.
  • a depth of the trench is greater than or equal to a thickness of the source region.
  • the first sinker region is located below the trench.
  • a depth of the second sinker region is less than the depth of the first sinker region.
  • a depth of the second sinker region is greater than the depth of the well region.
  • the device has an on-resistance of less than 4 milliohm centimeter squared, a gate threshold voltage of greater than 1.5 Volt, a breakdown voltage of greater than 500 Volt, and an electric field of less than 3.5 megavolt per cm in the gate insulator film.
  • a device comprising a unit cell on a SiC substrate.
  • the unit cell comprises a gate insulator film, a trench in a well region, a first sinker region of a second conduction type, a second sinker region of the second conduction type, and a source region.
  • the source region is in direct contact with the second sinker region.
  • the device comprises a semiconductor metal-insulator-transistor component.
  • the unit cell further comprises a semiconductor body of a first conduction type that comprises a drift zone; the well region of the second conduction type next to an insulator-semiconductor interface; and the source region of the first conduction type formed within the well region.
  • a depth of the trench is greater than or equal to a thickness of the source region.
  • a depth of the trench is greater than a depth of the source region.
  • the device has an avalanche energy of greater than 10 Joule per centimeter squared, calculated by dividing an avalanche energy in Joules by a total die area in centimeter squared.
  • an avalanche failure is located within the unit cell.
  • a device comprising a unit cell on a SiC substrate.
  • the unit cell comprises a gate insulator film, a trench in a well region, a first sinker region of a second conduction type, a second sinker region of the second conduction type, and a source region.
  • the first sinker region has a depth that is greater than a depth of the second sinker region.
  • the second sinker has a width that is greater than that of the first sinker
  • the first sinker region is located below the trench. [0046] In yet another embodiment, the depth of the second sinker region is less than the depth of the first sinker region.
  • the depth of the second sinker region is greater than a depth of the well region.
  • a device comprising a unit cell on a Silicon Carbide (SiC) substrate.
  • the unit cell comprises a first conductivity type first source region; a first conductivity type second source region; a second conductivity type well region; and a silicide layer.
  • the device comprises a vertical Silicon Carbide (SiC) double-implantation metal oxide semiconductor fieldeffect transistor (DMOSFET) comprising a drain terminal on a backside of the SiC substrate and a source terminal on a topside of the SiC substrate.
  • the first conductivity type second source region comprises a thickness lower than a thickness of the first conductivity type first source region.
  • the first conductivity type second source region is interspersed between the second conductivity type well region and the silicide layer.
  • the first conductivity type second source region comprises a sheet of source region located between a recessed SiC trench region and the second conductivity type well region.
  • the sheet of source region comprises a thin sheet of source region.
  • first conductivity type second source region comprises at least one of (a) a target thickness and (b) a target doping concentration.
  • the target thickness of the first conductivity type second source region ranges from 1 nm to 1 pm and the target doping concentration ranges from 10 15 cm' 3 to 10 21 -3 cm .
  • the first conductivity type second source region comprises a sheet of source region located between the silicide layer and the second conductivity type well region.
  • the device is capable of carrying a drain current of less than negative 500 milliamperes at a drain voltage of negative 3 volts.
  • a device comprising a unit cell on a silicon carbide (SiC) substrate.
  • the unit cell comprises a first conductivity type source region; a second conductivity type well region; and a second conductivity type shield region.
  • the second conductivity type shield region is confined within the second conductivity type well region.
  • the second conductivity type shield region is located within a metal oxide semiconductor field-effect transistor (MOSFET) channel.
  • MOSFET metal oxide semiconductor field-effect transistor
  • the second conductivity type shield region is located closer to an edge of the second conductivity type well region.
  • a doping concentration inside the second conductivity type well region is non-uniform in a lateral direction.
  • a doping concentration inside the second conductivity type shield region is higher than a doping concentration inside the second conductivity type well region.
  • the second conductivity type shield region extends beyond a vertical extent of the second conductivity type well region.
  • the device further comprises a trench region in the second conductivity type well region.
  • the trench region comprises a depth of one of greater than and equal to a thickness of the first conductivity type source region.
  • the device comprises a gate oxide layer in contact with the second conductivity type well region and the first conductivity type source region.
  • the device comprises a double-implantation metal oxide semiconductor field-effect transistor (DMOSFET).
  • DMOSFET double-implantation metal oxide semiconductor field-effect transistor
  • the device comprises multiple second conductivity type shield regions within a metal oxide semiconductor field-effect transistor (MOSFET) channel.
  • MOSFET metal oxide semiconductor field-effect transistor
  • the multiple second conductivity type shield regions are located closer to an edge of the second conductivity type well region.
  • the multiple second conductivity type shield regions extend beyond a vertical extent of the second conductivity type well region.
  • the second conductivity type shield region is buried within the second conductivity type well region.
  • a device comprising a unit cell on a silicon carbide (SiC) substrate.
  • the device comprises a first conductivity type source region; a second conductivity type well region; and a second conductivity type shield region.
  • the second conductivity type shield region is confined within the second conductivity type well region.
  • the second conductivity type shield region shields a metal oxide semiconductor field-effect transistor (MOSFET) channel from a high potential applied to a drain terminal.
  • MOSFET metal oxide semiconductor field-effect transistor
  • the device further comprises a trench region in the second conductivity type well region, the trench region comprises a depth of one of greater than and equal to a thickness of the first conductivity type source region.
  • the device comprises a gate threshold voltage of greater than 2.5 volts, a breakdown voltage of greater than 3300 volts at a gate to source voltage of 0 volt, an on- resistance of less than 15 milliohm centimeter squared, and a short-circuit withstand time of greater than 4 microseconds at a drain voltage of 1500 volts.
  • the device comprises a gate threshold voltage of greater than 2 volts, a breakdown voltage of greater than 1200 volts at a gate to source voltage bias of 0 volt, an on-resistance of less than 4.5 milliohm centimeter squared, and a short-circuit withstand time of greater than 2.5 microseconds at a drain voltage of 800 volts.
  • the device comprises a gate threshold voltage of greater than
  • the device comprises a gate threshold voltage of greater than
  • the device comprises a gate threshold voltage of greater than
  • the second conductivity type shield region shields the metal oxide semiconductor field-effect transistor (MOSFET) channel from the high potential applied to the drain terminal during one of an off-state and a blocking operation.
  • MOSFET metal oxide semiconductor field-effect transistor
  • a method comprises forming a silicon carbide (SiC) metal oxide semiconductor field-effect transistor (MOSFET); forming a second conductivity type well region; forming a first conductivity type source region within the second conductivity type well region; and forming a second conductivity type shield region.
  • the second conductivity type shield region is located outside the first conductivity type source region.
  • the second conductivity type shield region is located within the second conductivity type well region.
  • the second conductivity type shield region extends beyond the second conductivity type well region.
  • the SiC MOSFET is manufactured on SiC epi-wafer comprising a doping ranging from 10 14 to 10 18 cm' 3 and a thickness ranging from 1 micrometers (pm) to 300 micrometers (pm).
  • forming the second conductivity type well region comprises: depositing a hard mask comprising at least one of a silicon dioxide layer, a silicon nitride layer, a polysilicon layer, a silicon oxynitride layer, and a metallic layer with a total thickness ranging from 50 nanometers to 5 micrometers; patterning the hard mask; etching the hard mask; and performing one of an ion-implantation and an epitaxial growth using second conductivity type ions.
  • the step of performing the ion-implantation comprises implanting the second conductivity type ions at energies ranging from 10 keV to 1000 keV, and at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 .
  • the second conductivity type ions comprise one of aluminum and boron.
  • forming the second conductivity type shield region comprises forming the second conductivity type shield region closer to an edge of the second conductivity type well region.
  • forming the second conductivity type shield region comprises forming the second conductivity type shield region confined within the second conductivity type well region.
  • the method further comprises forming a metal oxide semiconductor field-effect transistor (MOSFET) channel.
  • MOSFET metal oxide semiconductor field-effect transistor
  • forming the second conductivity type shield region comprises forming the second conductivity type shield region in contact with the metal oxide semiconductor field-effect transistor (MOSFET) channel.
  • MOSFET metal oxide semiconductor field-effect transistor
  • forming the second conductivity type shield region comprises forming multiple second conductivity type shield regions in contact with the metal oxide semiconductor field-effect transistor (MOSFET) channel.
  • MOSFET metal oxide semiconductor field-effect transistor
  • forming the first conductivity type source region comprises forming the first conductivity type source region using one of nitrogen and phosphorus ions.
  • the method further comprises forming a gate oxide layer; forming a polysilicon gate layer; forming an interlayer dielectric (ILD) layer; forming a silicide region; and forming an interconnect metal layer.
  • ILD interlayer dielectric
  • forming the gate oxide layer comprises performing either one or a stacked combination of a thermal oxidation and a chemical vapor deposition (CVD) of a dielectric layer of one of a silicon dioxide layer, a silicon nitride layer, and a silicon oxynitride layer.
  • the gate oxide layer is formed with a thickness ranging from 10 nanometers to 100 nanometers.
  • forming the polysilicon gate layer comprises depositing a polysilicon layer using one of a plasma-enhanced chemical vapor deposition (PECVD) and a low- pressure chemical vapor deposition (LPCVD) through one of an in-situ doping and a subsequent drive-in doping.
  • PECVD plasma-enhanced chemical vapor deposition
  • LPCVD low- pressure chemical vapor deposition
  • forming the interlayer dielectric (ILD) layer comprises depositing one of at least one of a silicon dioxide layer, a silicon nitride layer, and a silicon oxynitride layer; and a stacked combination of the silicon dioxide layer, the silicon nitride layer, and the silicon oxynitride layer.
  • the ILD layer comprises a thickness one of greater than and equal to 50 nanometers.
  • forming the silicide region comprises forming a nickel silicide region on an exposed SiC surface.
  • forming the second conductivity type shield region comprises forming the second conductivity type shield region extending beyond a vertical extent of the second conductivity type well region.
  • a method is described herein.
  • the method comprises forming a silicon carbide (SiC) metal oxide semiconductor field-effect transistor (MOSFET); forming a second conductivity type well region; forming a first conductivity type source region within the second conductivity type well region; and forming a second conductivity type shield region.
  • the second conductivity type shield region is located outside the first conductivity type source region.
  • a doping concentration in the second conductivity type well region within a metal oxide semiconductor field-effect transistor (MOSFET) channel is non-uniform. At least a portion of the second conductivity type shield region is located within the second conductivity type well region.
  • doping concentration profiles of the second conductivity type shield region at different locations are different.
  • doping concentration profiles of the second conductivity type shield region at different locations are not different.
  • a semiconductor component comprises a semiconductor body of a first conduction type comprising a voltage blocking layer; and islands of a second conductivity type on a contact surface; and a metal layer on the voltage blocking layer.
  • the metal layer and the voltage blocking layer includes a Schottky contact, and a first conductivity type layer comprising the first conduction type not in contact with the Schottky contact that is interspersed between the islands of the second conductivity type.
  • a vertical extent of the first conductivity type layer is lower than a bottom of the islands of the second conductivity type.
  • a vertical extent of the first conductivity type layer is higher than a bottom of the islands of the second conductivity type.
  • a doping concentration within the first conductivity type layer is non-uniform in a direction that is perpendicular to the Schottky contact.
  • a vertical extent of the first conductivity type layer is higher or lower than a bottom of the islands of the second conductivity type.
  • the first conductivity type layer has a doping concentration that does not vary in any direction along the contact surface.
  • the first conductivity type layer has a first doping concentration that is higher than a second doping concentration of a drift region. [00101] In yet another embodiment, the first conductivity type layer has a first doping concentration that is lower than a second doping concentration of a drift region.
  • the Schottky contact comprises a metal comprising Al, Ag, Au, Mo, Ni, Ti, W, TixWy, TixNy, or combinations thereof.
  • a diode comprising P+ islands interspersed within a N+ region and a N- region contacts with a Schottky layer.
  • a vertical extent of the N+ region is lower than a bottom of the P+ islands.
  • a vertical extent of the N+ region is higher than a bottom of the P+ islands.
  • a doping concentration within the N+ region is non-uniform in a direction that is perpendicular to the Schottky layer.
  • a vertical extent of the N+ region is higher or lower than a bottom of the P+ islands.
  • a diode comprising N+ islands interspersed within a P+ region and a P- region contacts with a Schottky layer.
  • a vertical extent of the P+ region is lower than a bottom of the N+ islands.
  • a vertical extent of the P+ region is higher than a bottom of the N+ islands.
  • a doping concentration within the P+ region is non-uniform in a direction that is perpendicular to the Schottky layer.
  • a vertical extent of the P+ region is higher or lower than a bottom of the N+ islands.
  • a metal-insulator-semiconductor field effect transistor comprises a unit cell on a SiC substrate.
  • the unit cell comprises a trench in a well region having a second conduction type, a source region of a first conduction type, a first sinker region having a second conduction type, and a second sinker region having the second conduction type.
  • the first sinker region has a depth that is equal to or greater than a depth of the well region.
  • Each of the first sinker region and the second sinker region is in contact with a region having a first conduction type to form a p-n junction.
  • the first sinker region has a depth that is greater than a depth of the second sinker region.
  • the second sinker has a width that is greater than that of the first sinker.
  • a metal-insulator-semiconductor field effect transistor comprises a unit cell on a silicon carbide (SiC) substrate.
  • the unit cell comprises: a first conductivity type source region; a second conductivity type well region; and a second conductivity type shield region.
  • the second conductivity type shield region is located outside the first conductivity type source region.
  • the second conductivity type shield region extends beyond a vertical extent of the second conductivity type well region.
  • the device further comprises a trench region in the second conductivity type well region.
  • the trench region comprises a depth that is greater than and equal to a thickness of the first conductivity type source region.
  • the device further comprises a sinker region of a first conduction type that is located directly below the trench region.
  • a semiconductor component comprises a semiconductor body of a first conduction type comprising a voltage blocking layer; and islands of a second conductivity type on a contact surface; and a metal layer on the voltage blocking layer.
  • the metal layer and the voltage blocking layer includes a Schottky contact, and a first conductivity type layer comprising the first conduction type not in contact with the Schottky contact that is interspersed between the islands of the second conductivity type.
  • a vertical extent of the first conductivity type layer is lower than a bottom of the islands of the second conductivity type.
  • a doping concentration within the first conductivity type layer is non-uniform in a direction that is perpendicular to the Schottky contact.
  • a silicon carbide diode comprises first conduction type islands interspersed within a second region of a first conduction type and a first region of the first conduction type in contact with a metal layer.
  • Fig. 1A shows the prior art SiC DMOSFET structure reported by B.J. Baliga in Advanced High-Voltage Power Device Concepts, Springer Press, 2011.
  • Fig. IB shows the electric field contours simulated for the prior art SiC DMOSFET structure in Fig. 1A.
  • Fig. IC shows the electric field distribution for the prior art SiC DMOSFET structure in Fig. 1A.
  • Fig. 2A shows an embodiment of a SiC DMOSFET with the P+ plug region to ground the p-well region with the N+ source contact.
  • Fig. 2B shows the breakdown simulation of the SiC DMOSFET structure in Fig. 2A.
  • Fig. 3 shows an embodiment of a SiC DMOSFET where the P+ plug region in Fig. 2a is replaced with a deep P-type Sinker# 1 region.
  • Fig. 4A to Fig. 4R are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 3.
  • Fig. 5A shows an embodiment of a SiC DMOSFET where a P-type Sinker#2 region under the N+ source region is formed in addition to the deep P-type Sinker#l region.
  • Fig. 5B shows the breakdown simulation of the SiC DMOSFET structure designed according to embodiments shown in Fig. 3 and Fig. 5A.
  • Fig. 6A to Fig. 6J are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 5A.
  • Fig. 7A shows an embodiment of a SiC DMOSFET where a trench is etched into the N+ source region before implanting the P-type Sinker# 1 region.
  • Fig. 7B shows the breakdown simulation of the SiC MOSFET structure in Fig. 7A.
  • Fig. 8A to Fig. 8BB are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 7A.
  • Fig. 9 shows the prior art SiC DMOSFET process flow for self-aligned MOS channel formation.
  • Fig. 10 shows an embodiment of a SiC DMOSFET structure for removal of a parasitic N+ source region formed in the periphery.
  • Fig. 11A to Fig. 11GG are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 10.
  • Fig. 12 shows an embodiment of a SiC DMOSFET with a dedicated process step utilized for masking the implantation of the N+ source region in the device periphery.
  • Fig. 13A to Fig. 13GG are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 12.
  • Fig. 14 shows an embodiment of a SiC DMOSFET with a dedicated process step for masking the implantation of the N+ source region in the device periphery as well as the N+ source region in the active region to enable ohmic contact to the p-well region
  • Fig. 15A to Fig. 15FF are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 14.
  • Fig. 16 shows an embodiment of a SiC DMOSFET where the polysilicon gate metallization layers are segmented in the peripheral region.
  • Fig. 17A to Fig. 17FF are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 16.
  • Fig. 18 shows an embodiment of a SiC DMOSFET with a portion of the MOS channel on (1000) and a second portion on (11-20) or (11-00) crystal planes.
  • Fig. 19A to Fig. 19U are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 18.
  • Fig. 20 shows an embodiment of a SiC DMOSFET with a portion of the MOS channel on (1000) and a second portion on (11-20) or (11-00) crystal planes and a deeper p-well trench and formation of a second p-well region under the N+ source region
  • Fig. 21A to Fig. 21V are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 20.
  • Fig. 22 is the prior art and shows the plot of threshold voltage versus p-base doping concentration for a 4H-SiC Planar MOSFET.
  • Figs. 23A to Fig. 23D shows embodiments of a SiC DMOSFET structure for field shielding within the p-well region.
  • Figs. 24A to Fig. 24U are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 23 A.
  • Figs. 25A to Fig. 25D show embodiments of a SiC DMOSFET structure for field shielding formed buried within the p-well structure.
  • Figs. 26A to Fig. 26U are cross sectional views showing the process steps for manufacturing the SiC DMOSFET structure in Fig. 25A.
  • Fig. 27 is the cross-sectional schematic of a prior-art SiC MPS diode.
  • Fig. 28A is an embodiment of MPS diode structure with buried N+ regions.
  • Fig. 28B the I-V characteristic for the embodiment described in Fig. 28A.
  • Fig. 28C is the comparison of the cross-sections of the devices in Fig. 28A.
  • Figs. 29A to Fig. 29L are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 28A.
  • Fig. 30 is an embodiment of MPS diode structure where the bottom of the N+ region is higher than the bottom of the P+ region.
  • Figs. 31A to Fig. 31L are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 30.
  • Fig. 32A to Fig 32F are embodiments of MPS diode structures with multiple N subregions, P sub-regions or both
  • Fig. 33AA to Fig. 33AL are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 32A.
  • Fig. 33BA to Fig. 33BL are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 32B.
  • Fig. 33EA to Fig. 33EL are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 32E.
  • Fig. 33FA to Fig. 33FL are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 32F.
  • Fig. 34 is an embodiment of MPS diode structure with two different types of P+ wells depending on their depths which are in comparison to the depth of the N+ layer.
  • Figs. 35A to Fig. 35P are cross sectional views showing the process steps for manufacturing the SiC MPS diode shown in Fig. 34.
  • Fig. 36A is the blocking performances of the devices of this invention with varying ratios ofWl/Dl.
  • Fig. 36B is the blocking I-V curves of the devices of this invention with varying ratios of Wl/Dl.
  • Fig. 36C is the forward I-V curves of the devices of this invention with varying ratios of Wl/Dl.
  • Fig. 36D is the performance of differential specific on-resistances of the devices of this invention with varying ratios ofWl/Dl.
  • Fig. 37A shows the device structure of DMOSFET according to an embodiment.
  • Fig. 37B shows the device structure of junction field effect transistors (JFET) according to an embodiment.
  • Fig. 38 shows an example of the n-type layer formed using ion-implantation according to an embodiment.
  • Fig. 39A to 39C shows the N Layer vertical extent with respect to the P+ gate layer in a JFET according to various embodiments.
  • Fig. 40A to 40C shows the N Layer vertical extent with respect to the p-well layer in a DMOSFET according to various embodiments.
  • Fig. 41A to 41E a cross-sectional schematic of a vertical JFET showing the process steps for the device shown in Fig. 37B.
  • Fig. 42A to 42D a cross-sectional schematic of a power MOSFET structure showing the process steps for the device shown in Fig. 37A.
  • Fig. 43A and Fig. 43B show the output and breakdown I-V characteristics of 1200 V SiC DMOSFETs fabricated using the teachings of this invention.
  • Fig. 44A and Fig. 44B show the transfer (ID v/s VGS) characteristics of 1200 V SiC MOSFETs fabricated using the teachings of this invention.
  • Fig. 45 is a single-pulse avalanche energy measured for a 1200 V SiC MOSFET fabricated using the teachings of this invention.
  • Fig. 46 is a photograph showing a SiC DMOSFET fabricated using the teachings of these inventions and tested for single-pulse avalanche energy test.
  • Fig. 47A and Fig. 47B are output characteristics of two 3.3 kV SiC MOSFETs fabricated using the teachings of these inventions.
  • Fig. 47C is the transfer characteristics of two 3.3 kV SiC MOSFETs fabricated using the teachings of these inventions.
  • Fig. 47D is a short-circuit test measured for two 3.3 kV SiC MOSFETs fabricated using the teachings of this invention.
  • FIG. 48A illustrates an embodiment of a cross sectional structure of a unit cell of a double-implantation metal oxide semiconductor field-effect transistor (DMOSFET) comprising a first conductivity type second source region within a first conductivity type first source region.
  • DMOSFET double-implantation metal oxide semiconductor field-effect transistor
  • FIG. 48B illustrates an embodiment of a cross sectional structure of one or more unit cells of the DMOSFET, comprising one or more unit cells of an integrated Schottky diode, each DMOSFET unit cell comprising the first conductivity type second source region within the first conductivity type first source region.
  • FIG. 48C illustrates an embodiment of a cross sectional structure of one or more unit cells of a trench gate MOSFET, comprising one or more unit cells of the integrated Schottky diode, each MOSFET unit cell comprising the first conductivity type second source region within the first conductivity type first source region.
  • FIG. 49A to 49T illustrates an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 48A.
  • FIG. 50A illustrates an embodiment of a voltage-current characteristic of a SiC DMOSFET with conventional p-n junction vs the SiC DMOSFET with deactivated p-n junction (i.e., the first conductivity type second source region).
  • FIG. 50B is a perspective view that illustrates an embodiment of sides of the DMOSFET in relation to a dice.
  • FIG. 50C and 50D illustrate current flow paths through the MOSFET and through an intrinsic anti-parallel diode region in an H-bridge circuit respectively.
  • FIG. 51A illustrates an embodiment of a cross sectional structure of a unit cell of a double-implantation metal oxide semiconductor field-effect transistor (DMOSFET) comprising a first conductivity type second source region within a first conductivity type first source region.
  • DMOSFET double-implantation metal oxide semiconductor field-effect transistor
  • FIG. 51B illustrates an embodiment of a cross sectional structure of one or more unit cells of the DMOSFET, comprising one or more unit cells of an integrated Schottky diode, each DMOSFET unit cell comprising the first conductivity type second source region within the first conductivity type first source region.
  • FIG. 52A to 52T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 51 A.
  • FIG. 53A illustrates an embodiment of a cross sectional structure of a unit cell of a double-implantation metal oxide semiconductor field effect transistor (DMOSFET) comprising a first metal region in direct contact with a second conductivity type well contact region.
  • DMOSFET metal oxide semiconductor field effect transistor
  • FIG. 53B illustrates an embodiment of a cross sectional structure of one or more unit cells of the DMOSFET, comprising one or more unit cells of an integrated Schottky diode, each DMOSFET unit cell comprising the first metal region in direct contact with the respective second conductivity type well contact region.
  • FIG. 53C illustrates an embodiment of a third quadrant current conduction through an intrinsic p-n junction diode region vs a Schottky diode region connected in parallel to the DMOSFET.
  • FIG. 53D illustrates an embodiment of a third quadrant current conduction through the DMOSFET after connecting the one or more Schottky diode regions in series with the one or more body diode regions of the DMOSFET.
  • FIG. 54A to 54X illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 53 A.
  • FIG. 55A, 55B & 55C illustrate an embodiment of cross-sectional structures of a unit cell of a double-implantation metal oxide semiconductor field effect transistor (DMOSFET) comprising a second conductivity type well contact region that meanders at three different locations respectively.
  • DMOSFET metal oxide semiconductor field effect transistor
  • FIG. 55D, 55E & 55F illustrates an embodiment of cross-sectional structures of one or more unit cells of a diode integrated DMOSFET, each DMOSFET unit cell comprising the second conductivity type well contact region that meanders at three different locations respectively.
  • FIG. 56A to 56T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 55 A.
  • FIG. 57A to 57T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 55B.
  • FIG. 58A to 58T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 55C.
  • FIG. 59A, 59B & 59C illustrate an embodiment of cross sectional structures of a unit cell of a double-implantation metal oxide semiconductor field effect transistor (DMOSFET) comprising a second conductivity type well contact region that meanders at three different locations respectively, allowing a second conductivity type well region to be in contact with a source metal only through the second conductivity type well contact region.
  • DMOSFET metal oxide semiconductor field effect transistor
  • FIG. 59D, 59E & 59F illustrate an embodiment of cross sectional structures of one or more unit cells of a diode integrated DMOSFET, each DMOSFET unit cell comprising the second conductivity type well contact region that meanders at three different locations respectively, allowing the second conductivity type well region to be in contact with the source metal only through the second conductivity type well contact region.
  • FIG. 59G illustrates an embodiment of a cross sectional structure of one or more unit cells of a diode integrated trench gate MOSFET, comprising one or more unit cells of an integrated Schottky diode, each MOSFET unit cell comprising the second conductivity type well contact region at the first location, allowing the second conductivity type well region to be in contact with the source metal only through the second conductivity type well contact region.
  • FIG. 60A to 60T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 59 A.
  • FIG. 61 A to 61T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 59B.
  • FIG. 62A to 62T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 59C.
  • FIG. 63 illustrates an embodiment of a cross-sectional structure of one or more unit cells of a power MOSFET, a first unit cell of the one or more unit cells comprising a first metal oxide semiconductor (MOS) interface on a horizontal surface of a semiconductor substrate and a trench sidewall, and a second unit cell of the one or more unit cells comprising a second metal oxide semiconductor (MOS) interface formed solely on the trench sidewall.
  • MOS metal oxide semiconductor
  • FIG. 64A to 64AB are cross-sectional views illustrating an embodiment of a process of manufacturing the MOSFET structure shown in FIG. 63.
  • FIG. 65 illustrates an embodiment of a cross-sectional structure of one or more unit cells of a power MOSFET, a first unit cell of the one or more unit cells comprising a first metal oxide semiconductor (MOS) interface on a horizontal surface of a semiconductor substrate and a trench sidewall, and a second unit cell of the one or more unit cells comprising a metal region formed adjacent to a first conductivity type drift layer of the MOSFET.
  • MOS metal oxide semiconductor
  • FIG. 66A to 66AA are cross-sectional views illustrating an embodiment of a process of manufacturing the MOSFET structure shown in FIG. 65.
  • FIG. 67A shows two implementations of a power MOSFET in the form of a vertical, planar DMOSFET and a vertical trench UMOSFET.
  • FIG. 67B and 67C show major resistances in a vertical DMOSFET and a UMOSFET respectively and it is apparent that the geometry of the device effectively eliminates JFET resistance present in the DMOSFET.
  • FIG. 67D illustrates electric fields in a UMOSFET in a blocking state, trench corners are significant locations of significant field crowding.
  • unit cell refers to a piece of a pattern in a semiconductor which is repeated in the semiconductor.
  • SiC refers to silicon carbide which is a compound semiconductor and is a mixture of silicon and carbon with the chemical formula SiC. Silicon is covalently bonded with carbon.
  • 4H-SiC 4H is written in the Ramsdell classification scheme here the number indicates the layer, and the letter indicates the Bravais lattice. That means in a 4H- SiC structure four hexagonal layers of SiC are present.
  • SiC exists in a kind of polymorphic crystalline building known as a polytype, e.g., 3C-SiC, 4H-SiC, 6H-SiC. Presently 4H-SiC is used in power device manufacturing.
  • Source A complete analytical potential based solution for a 4H- SiC MOSFET in nanoscale, M K Yadav, K P Pradhan and P K Sahu Published 24 May 2016 • ⁇ 2016 Vietnam Academy of Science & Technology
  • substrate refers to the supporting material on or in which the components of an integrated circuit are fabricated or attached.
  • JFET refers to junction gate field-effect transistor which is a three-terminal semiconductor device that can be used as electronically controlled switches, amplifiers, or voltage-controlled resistors.
  • a FET field-effect transistor
  • a FET field-effect transistor
  • FET field-effect transistor
  • the gate In the junction FET, the gate is isolated from the channel by a pn- junction.
  • an insulated-gate FET the gate is isolated from the channel by an insulating layer so that the gate and channel form a capacitor with the insulating layer as the capacitor dielectric.
  • MOSFET refers to a metal oxide semiconductor field-effect transistor, which is a four-terminal device with source(S), gate (G), drain (D) and body (B) terminals.
  • the body of the MOSFET is frequently connected to the source terminal making it a three-terminal device like field effect transistor.
  • DMOSFET refers to double-implantation metal oxide semiconductor field-effect transistor.
  • a common physical structure of SiC MOSFETs is the planar double-implanted MOSFET in 4H-SiC (SiC-DMOSFET).
  • dopant refers to an impurity added from an external source to a material by diffusion, coating, or implanting into a substrate, such as changing the properties thereof.
  • an impurity may be added to a semiconductor to modify its electrical properties or to a material to produce a semiconductor having desired electrical properties.
  • N-type (negative) dopants e.g., such as phosphorus for a group IV semiconductor
  • n-type dopants When added to a semiconductor, n-type dopants create a material that contains conduction electrons.
  • P-type (positive) dopants typically come from group III and result in conduction holes (i.e., vacancies in the electron shells).
  • drain refers to the electrode of a field effect transistor which receives charge carriers which pass through the transistor channel from the source electrode.
  • source refers to the active region/el ectrode to which the source of charge carriers is connected in a field effect transistor
  • gate refers to the control electrode or control region that exerts an effect on a semiconductor region directly associated therewith, such that the conductivity characteristic of the semiconductor region is altered in a temporary manner, often resulting in an on-off type switching action.
  • the control electrode or control region of a field effect transistor is located between the source and drain electrodes, and regions thereof.
  • impurity refers to A foreign material present in a semiconductor crystal, such as boron or arsenic in silicon, which is added to the semiconductor to produce either p-type or n-type semiconductor material, or to otherwise result in material whose electrical characteristics depend on the impurity dopant atoms.
  • PN junction refers to the interface and region of transition between p-type and n-type semiconductors.
  • polysilicon refers to a polycrystalline form of silicon.
  • P-type refers to extrinsic semiconductor in which the hole density exceeds the conduction electron density.
  • bandgap refers to the difference between the energy levels of electrons bound to their nuclei (valence electrons) and the energy levels that allow electrons to migrate freely (conduction electrons). The band gap depends on the particular semiconductor involved.
  • breakdown refers to a sudden change from high dynamic electrical resistance to a very low dynamic resistance in a reverse biased semiconductor device (e.g., a reverse biased junction between p-type and n-type semiconductor materials) wherein reverse current increases rapidly for a small increase in reverse applied voltage, and the device behaves as if it had negative electrical resistance.
  • a reverse biased semiconductor device e.g., a reverse biased junction between p-type and n-type semiconductor materials
  • channel refers to a path for conducting current between a source and drain of a field effect transistor.
  • chip refers to a single crystal substrate of semiconductor material on which one or more active or passive solid-state electronic devices are formed.
  • a chip may contain an integrated circuit.
  • a chip is not normally ready for use until packaged and provided with external connectors.
  • contact refers to the point or part of a conductor which touches another electrical conductor or electrical component to carry electrical current to or from the conductor or electrical component.
  • die refers to a tiny piece of semiconductor material, separated from a semiconductor slice, on which one or more active electronic components are formed. Sometimes called a chip. N+ substrate.
  • plug refers to the structure used to ground the well and the source contact.
  • drift layer refers to lightly doped region to support the high voltage in power MOSFET
  • well refers certain to regions in a metal-oxide-semiconductor (MOS) transistor. MOS transistors are always created in a “well” region. A PMOS (positivechannel MOS) transistor is made in an N-doped region, called “n-well” region. Similarly, an NMOS transistor (negative-channel MOS) is made in a “P-type” region called “p-well”. This ensures that the leakage between two transistors, through the bottom side, is low due to the reverse bias between the transistor areas and the well region.
  • MOS metal-oxide-semiconductor
  • source interconnect metallization refers to interconnection metallization that interconnects thousands of MOSFETs using fine-line metal patterns.
  • the term “self-aligned” used herein refers to processing steps in manufacturing of semiconductor devices. It is often necessary to achieve precise alignment between structures fabricated at different lithographic stages of integrated circuit fabrication. Stringent requirements on lithographic alignment tolerance can be relaxed if the structures are “self-aligned” which means one is forced into a specific position relative to the other for a wide range of lithographically defined positions.
  • device refers to the physical realization of an individual electrical element in a physically independent body which cannot be further divided without destroying its stated function.
  • trench refers to electrical isolation of electronic components in a monolithic integrated circuit by the use of grooves or other indentations in the surface of the substrate, which may or may not be filled with electrically insulative (i.e., dielectric) material.
  • dielectric refers to a non-conductor of electricity, otherwise known as an insulator.
  • mobility refers to the facility with which carriers move through a semiconductor when subjected to an applied electric field. Electrons and holes typically have different mobilities in the same semiconductor.
  • RIE reactive ion etching which is an etching technology used in microfabrication.
  • RIE is a type of dry etching which has different characteristics than wet etching.
  • RLE uses chemically reactive plasma to remove material deposited on wafers. The plasma is generated under low pressure (vacuum) by an electromagnetic field. High-energy ions from the plasma attack the wafer surface and react with it.
  • the term “ILD” as used herein refers to interlayer dielectric, a dielectric material used to electrically separate closely spaced interconnect lines arranged in several levels (multilevel metallization) in an advanced integrated circuit.
  • CVD chemical vapor deposition is a method used to produce high quality, high-performance, solid materials, typically under vacuum. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber.
  • PECVD plasma-enhanced chemical vapor deposition process used to deposit thin films from a gas state (vapor) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creation of a plasma of the reacting gases.
  • LPCVD low pressure chemical vapor deposition technology that uses heat to initiate a reaction of a precursor gas on the solid substrate. This reaction at the surface is what forms the solid phase material.
  • DIBL drain induced barrier lowering and is a shortchannel effect in MOSFETs referring originally to a reduction of threshold voltage of the transistor at higher drain voltages.
  • the bottleneck in channel formation occurs far enough from the drain contact that it is electrostatically shielded from the drain potential by the combination of the substrate and gate, and so classically the threshold voltage was independent of drain voltage.
  • the drain potential can gate the channel, and so a high drain voltage can open the bottleneck and turn on the transistor prematurely.
  • ICP inductively coupled plasma etching technology often used in specialty semiconductor markets for device manufacturing. This technology can combine both chemical reactions and ion-induced etching. The independent control of ion flux enables high process flexibility.
  • ICP etching is based on the use of an inductively coupled plasma source.
  • the ICP source generates a high-density plasma due to inductive coupling between the RF antenna and the plasma.
  • the antenna located in the plasma generation region, creates an alternating RF magnetic field, and induces RF electric fields, which energize electrons that participate in the ionization of gas molecules and atoms at low pressure. Due to the absence of an electric field near the reactor walls there is virtually no ion bombardment or erosion of the walls.
  • p-shield refers to a carefully designed p-type doped region strategically located close to or within the MOSFET channel region, with the objective of shielding the MOSFET channel from the high potential applied to the drain terminal during off-state or blocking operation.
  • first conductivity type region and “second conductivity type region” as used herein, are used to describe n-type and p-type regions respectively for a N type device.
  • first conductivity type region and “second conductivity type region” are used to describe p-type and n-type regions respectively.
  • I-V Characteristic Curves refers to Current- Voltage Characteristic Curves or simply I-V curves of an electrical device or component, refers to a set of graphical curves which are used to define its operation within an electrical circuit.
  • MV/cm refers to Megavolt per centimeter and refers to unit of electric field.
  • the term “avalanche failure” as used herein refers to a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good insulators. It is a type of electron avalanche. The avalanche process occurs when carriers in the transition region are accelerated by the electric field to energies sufficient to create mobile or free electron-hole pairs via collisions with bound electrons. The voltage at which the breakdown occurs is called the breakdown voltage. Avalanche failure can cause structural damage to a semiconductor device.
  • the term “avalanche energy” as used herein is defined as the amount of energy the MOSFET can withstand when it is set into avalanche mode or its breakdown voltage is exceeded.
  • the term “topside” as used herein refers to the outer side/top of the DMOSFET.
  • the topside of the vertical SiC DMOSFET may comprise a source terminal.
  • bottom side refers to the underside/base of the DMOSFET.
  • the bottom side of the vertical SiC DMOSFET may comprise a drain terminal.
  • front side refers to a side of the DMOSFET which is visible in front.
  • back side refers to the rear side of the DMOSFET.
  • the back side of the vertical SiC DMOSFET may comprise the drain terminal.
  • MOS metal-oxide-semiconductor
  • active region refers to a region of the DMOSFET where the current conduction happens.
  • depletion region refers to a region where flow of charged carriers decreases over a given time.
  • thermal budget refers to the total amount of thermal energy transferred to a wafer during the given elevated temperature operation.
  • work function refers to minimum quantity of energy required to remove an electron to infinity from the surface of a given metal.
  • two or more elements are "integral” if they are comprised of the same piece of material. As defined herein, two or more elements are "non-integral” if each is comprised of a different piece of material.
  • trench sidewalls refers to walls that form sides of the trench region.
  • bottom portion refers to the base of the trench region.
  • crystal plane refers to an imaginary plane inside a crystal of a semiconductor substrate in which large concentrations of atoms are present.
  • MOS interface refers to a region/path that electrically interconnects two regions.
  • horizontal surface refers to an unetched surface on topside of the semiconductor substrate.
  • Radio frequency is an oscillation rate of an alternating electric current or voltage or of a magnetic, electric, or electromagnetic field or mechanical system.
  • Embodiments relate to SiC DMOSFET power devices where the p-well regions effectively shield the sensitive gate oxide from the high electric fields present in SiC especially during high drain bias or blocking mode operation.
  • An embodiment relates to using a P+-plug to ground the p-well region with the N+ source contact.
  • An embodiment relates to making the lateral spacing between the p-well regions narrow enough to suppress the electric field in the gate oxide while ensuring the ON-resistance is not high. [00291] An embodiment relates to replacing the P+ plug region of the DMOSFET with a deep P- type Sinker# 1 region.
  • Embodiments relate to formation of one or more deep implanted sinker regions at certain locations within the MOSFET device structure such as a first P-type sinker region at the center of the MOSFET unit cell whose depth may be equal to or greater than the depth of the p-well region.
  • Embodiment relates to forming a second P-type sinker region under the N+ source region, whose depth may be equal to or greater than the p-well region, but less than or equal to the depth of the first P-type sinker region.
  • Embodiment relates to boron implantation which may be advantageously used for forming the deep sinker regions since boron has a larger implant range than aluminum that can result in deeper implant profiles
  • Embodiment relates to the formation of a first trench with desired shape which may be etched in the N+ source region, prior to the formation of the first P-type sinker region, which may serve to increase the depth of the first P-type sinker region.
  • the depth of the first trench may range from 0.01 pm up to 2 pm.
  • the depth of the resulting first sinker region may be 0% to 100% larger than the depth of the p-well region.
  • the depth of the first P-type sinker region can be as large as the entire epitaxial layer.
  • Embodiment relating to the formation of the first trench in the N+ source region may reduce or eliminate the need for expensive ultra-high energy implantation steps for forming the first P-type sinker region.
  • Embodiment relating to the first trench may be advantageously used to remove the N+ source implant from the first P-type sinker region, which may be desirable to prevent compensation of the first P-type sinker region by the N+ source implant. This is especially useful if the N+ source region is self-aligned to the p-well region.
  • Embodiment relates to a gradually decreasing implant concentration which may be employed for forming the first and second P-type sinker regions in lieu of a box-shaped implant profile, as this may be advantageous in appropriately shaping the electric field under high drain bias.
  • the doping in the P-type sinker regions may be varied linearly from a maximum value close to the SiC surface to a value equal to or slightly higher than the drift layer doping concentration at the other end of the P-type sinker regions.
  • Embodiment of a design of the first and second sinker regions may simplify the design of the p-well region, which can be designed to support metal-oxide-semiconductor (MOS) channel formation and may be advantageously designed for achieving low on-resistance, without compromising other performance metrics, such as reverse leakage current and electric field in gate oxide.
  • MOS metal-oxide-semiconductor
  • SiC devices in power electronics feature fast switching times, high blocking voltage capabilities, and the ability to operate at high temperatures. These characteristics, along with recent advancements in manufacturing processes, suggest that SiC has the potential to revolutionize power electronics as a successor to traditional silicon-based (Si) devices.
  • SiC is a wide band gap material (3.3 eV) and has a higher breakdown electric field (3 x 10 6 V/cm to 5 x 10 6 V/cm) compared to Si (Si band gap is 1.1 eV and breakdown electric field for Si is 0.3 x 10 6 V/cm).
  • SiC is a better thermal conductor (3.7 (W/cm-K) for SiC versus 1.6 (W/cm-K) for Si) which enables SiC devices to operate at extremely high-power levels and still dissipate the large amounts of excess heat generated.
  • These material properties of SiC offer multiple advantages of using SiC instead of Si on power devices.
  • the SiC die In a comparison of SiC and Si semiconductor die with identical structures and dimensions, the SiC die exhibits a lower specific ON resistance and a higher breakdown voltage than the Si die.
  • the disclosed embodiments herein provide novel techniques for SiC DMOSFET design and fabrication for shaping of the electric field over the device structure and reducing concentration of electric fields at singular points.
  • the embodiments herein reduce the electric field in the gate oxide region to less than 3.5 MV/cm and improve the device reliability.
  • SiC devices are manufactured by ion implantation of both source and p-well regions but ion implantation and especially deep ion implantation is difficult in SiC.
  • the ion implantation of source and p-well regions are made deep with novel techniques.
  • SiC devices of the embodiments herein as compared to the silicon devices make them highly desirable in the electric vehicle and renewable energy industries. Traction inverters in electric vehicles are subjected to high thermal (> 150°C) and load cycling and renewable energy converters are subjected to extreme environmental conditions.
  • the embodiments described herein for the SiC devices maximize power conversion efficiency to >98% for example while providing high reliability thus making it an ideal candidate for electric vehicles to minimize maintenance and downtime, which is expensive for the operators of the electric vehicles.
  • the disclosed embodiments change the way in which SiC power DMOSFET devices can effectively shield the sensitive gate oxide from the high electric fields present in 4H-SiC especially during high drain bias (blocking mode operation).
  • SiC power DMOSFET devices overcome the trade-off between achieving a low ON resistance and achieving a robust blocking performance, which implies a low electric field in the structure close to a gate oxide.
  • Embodiments herein include a unit cell of a SiC power DMOSFET comprising a vertical MOSFET. Certain regions of the SiC power DMOSFET device are a p-well region, which is formed by an implantation, an N+ source region, a N- drift layer, and an N+ substrate.
  • the current flows vertically from the drain, through the inversion layer which is formed at the top of the p-well layer, when a gate voltage is applied to this device in through the N+ source region and out through the source metallization.
  • a voltage is supported across the p-well and N- drift layer junction.
  • a power MOSFET has several physical dimensions, including: the pitch of the unit cell, which is the repeat unit for the MOSFET; the channel length, which is the portion of the p-well in which the inversion channels is formed; the distance between two successive p-wells, referred to as the junction gate field-effect transistor (JFET) region or the JFET gap; the thickness of the gate oxide; and an inter-layer dielectric (ILD) layer, which is used to insulate the source interconnect metallization from the poly-silicon gate.
  • JFET junction gate field-effect transistor
  • ILD inter-layer dielectric
  • the advantage of using SiC over Si is that for similar chip sizes, SiC can support much higher power density.
  • the amount of voltage one can support in SiC can be ten times more than in Si, and the current that the SiC chip can carry through the MOSFET can be 10 to 50 times more than in Si.
  • SiC MOSFETs form a convenient switch, because one can achieve much higher power density.
  • the performance advantage relates to the trade-off between voltage and current. Voltage blocking and current conduction capability, is about 200 times better in the case of SiC as compared to Si.
  • the P+ plug which is in the center of the SiC DMOSFET unit cell, is replaced by the PS#1 region.
  • the PS#1 region extends below the p-well region.
  • the electric field, or the main region where the breakdown can happen is at the center of the unit cell of a SiC DMOSFET, which is basically between the PS#1 region and the N- drift layer.
  • SiC structures tend to break down between the p-well and the N- drift layer, and especially at the curvature of the p-well region. In the embodiments herein, the structure will break down between the PS#1 region and the N- drift layer.
  • the embodiments herein have difference in structure, difference in the method of manufacturing, difference in the functionality of the devices, and difference in the results that the devices produce than the prior art SiC devices. Simulation data of the embodiments herein show the differences in performance and results of structures.
  • the devices of the embodiments herein also have a PS#2 region, which is placed under the N+ source region. This improves the electric field profile in the embodiment in a way that during the blocking mode of operation, the voltage is shed across a larger area of the unit cell, which results in even more robust operation.
  • the PS#2 region could be deeper than the p-well region and could be made shallower than the PS#1 region.
  • the deepest of them is the PS#1 region
  • the intermediate one is the PS#2 region
  • the shallower one is the p-well region.
  • the embodiments herein show more appropriate electric field shaping from these PS#1 and PS#2 structures.
  • the PS#2 serves as a secondary p-well region.
  • the design of the p-well region needs to satisfy several different constraints.
  • the electrical dose in the p-well region can be large enough such that the desired breakdown voltage is realized while at the same time, the doping of the p-well region near the gate oxide region where the MOS channel is formed, can be low enough such that a reasonably low threshold voltage is realized.
  • the p-well region could now satisfy conflicting requirements.
  • the PS#2 under the N+ source region, it relaxes the design of the p-well region, whose purpose now is solely for channel definition and channel formation.
  • the p- well does not have to be designed with the objective of supporting the breakdown voltage.
  • the embodiments herein give a lot more flexibility to the designer to design the p-well region suitably only for MOS channel formation.
  • the PS#1 is formed after a trench is etched into the N+ source region which is in the middle of the unit cell of the SiC DMOSFET.
  • the advantage of this trench is that it moves the electric field location farther away from the gate oxide interface and to the middle of the unit cell of the SiC DMOSFET.
  • etching a recess trench into the N+ source region effectively creates a deeper PS#1 region.
  • the electric field moves even further away from the gate oxide region, which would make for more robust blocking capability.
  • one of the reasons for doing the trench is because ion implantation and particularly deep ion implantation in SiC is difficult. Deep PS#1 sinker region can be made because of source trench.
  • etching a trench and then doing the ion implantation allows to make a deeper PS#1 region, which is effective and achieves the functionality.
  • the trench helps in making a deeper PS#1 due to the source trench allows to make a thinner oxide region by reducing the oxide.
  • SiC DMOSFET needs a thicker oxide to prevent them from breaking down in a dielectric field.
  • P-type sinker regions one can use thinner oxide.
  • the SiC DMOSFET devices are made using a series of masking steps followed by either ion implantation or etching and a deposition step.
  • the unit cell is produced where a series of structures are made using photolithography that is used to mask certain portions of the wafer or certain portion of device, and implementing certain steps, and then removing that mask, and doing the other steps.
  • To minimize the number of steps is of great importance to realize cost-effectiveness. That is, the cost structure is lower if one can somehow reduce the number of steps.
  • certain steps in manufacturing of SiC are expensive, and the embodiments herein minimize the number of those expensive steps. For example, ion implantation is a relatively expensive step in SiC.
  • p-well, P-plug, and N+ source regions are made using ion implantation.
  • Ion implantations are expensive steps, particularly deeper ion implantation is even more expensive. So, minimizing deep ion implantation is of importance.
  • P-type Implantation is 5 to 10 times more expensive than doing N-type Implantation, since P-type implantation needs to be performed at higher temperatures (400-1000°C) in contrast to N- type implants which can be performed at room-temperature. So, minimizing P-type implants is also of importance.
  • the wafer goes through a series of ion implantation steps first, which is typically called the front end of the process, then there is a high temperature annealing, which is used to anneal out the implant damage and electrically activate the implants.
  • the back end of the process typically consists of forming the gate oxide, ILD and other metallization steps.
  • photolithography would be used to mask a certain part of the wafer to create a p-well region, following which, a next masking step could be used to realize an N+ source region, followed by another masking step would be used to realize the P+ plug region.
  • a gate oxide or a gate dielectric can be grown by either thermal oxide or using a deposited oxide.
  • a gate metallization can be formed using a polysilicon or other refractory metals. The gate metallization is then selectively patterned and etched to access the N+ source regions, following which the ILD is deposited and then patterned to realize the window for creating these ohmic contacts for the N+ source regions. The ohmic contact can be realized on the backside of the wafer, which is the drain, for the drain region.
  • a source interconnect metallization is used to connect the various unit cells.
  • SiC MOSFET is typically produced in several masking steps. Some of these masking steps could be for forming implanted regions, while other masking steps are for forming structures such as gate oxide, ILD etc.
  • the embodiments herein are all done in 11 masking steps without increasing a masking step for any additional feature like PS#1, PS#2, source trench formations or other structures in the embodiments.
  • ion implantation is a method to introduce dopants since diffusion does not work well. So, to realize the PS#1 region to be deeper than the p-well region, requires higher implantation energy.
  • typically either aluminum or boron is used for realizing P-type regions in SiC. So, for realizing the PS#1 region and a deep PS#1 region, in the embodiments herein boron implantation is used in lieu of aluminum implantation, since for a given energy, the boron implantation can result in deeper regions as compared to aluminum implantation.
  • Another way to realize a deep PS#1 region is to use a much higher energy and still use aluminum as the P-type dope.
  • a p-well region is formed, following which, the N+ source region is formed. While forming the N+ source region, ion implantation is performed to realize the PS#2 region. The same masking step is used for forming the N+ source region and the PS#2 region. In the embodiment herein, this enables one to realize a PS#2 region exactly under the N+ source region.
  • the N+ source implant is made self-aligned to the p-well implant, to reduce or even eliminate misalignment which could occur if the two regions are realized in different masking steps.
  • the first p-well region is formed using a traditional implantation masking step.
  • a dielectric layer of a sufficient thickness is deposited, and then using photolithography, one would selectively pattern this layer, and then perform ion implantation, to realize the p-well region.
  • a second dielectric layer is deposited on top of this patterned first dielectric layer, and then subjected to a blanket etch. This results in a dielectric spacer region which then defines the region which is subjected to the N+ source implant. So, by choosing an appropriate thickness of the second dielectric layer, one can define the MOS channel length.
  • the channel length is formed not by the limitations of lithography techniques, but by the ability of depositing dielectric layers, for example silicon dioxide, where one has much better control.
  • dielectric layers for example silicon dioxide
  • the process first fabricates a N+ source, then deposits a dielectric layer, and then forms the P+ layer through the poly-silicon variation.
  • the embodiments herein do the additive method, where first one does the p-well, and then deposits the dielectric of a controlled thickness, which will define the channel length, and then put the N+ source. So, the order of N+ and p-well is reversed in the embodiments herein when compared to how prior art SiC DMOSFET’s are formed.
  • the embodiments herein avoid implanting N+ source region in the gate region.
  • a SiC MOSFET structure there exists a parasitic NPN transistor, that can get triggered not during normal operation but when you're switching this device from OFF to ON or ON to OFF with extremely high speed.
  • the trench into the N+ source region is formed prior to the implantation of the PS#1 region results in a deeper PS#1 region.
  • another benefit of doing this is that one can also remove the N+ source regions from the portions of the device that do not want the N+ source region to be implanted. So, that is the secondary benefit of having a trench etched into the N+ source region.
  • the same masking step is used for performing the SiC dry etch, and then implanting the PS#1 region. This is achieved with just one masking step.
  • the PS#2 region is formed along with the N+ source region with the same masking step.
  • the SiC trench and the PS#1 region are again formed using the same masking step. In this embodiment, four features are made using two masking steps.
  • the cost of PS#1 sinker is reduced, because one does not have to employ deep ion implantation. Deep ion implantation, which are high doses, is expensive. And on the periphery, having a deep P+ is also beneficial, to prevent breakdown regions that can be formed. In the embodiments herein, one is avoiding the breakdown region at the periphery because one is using a single step for creating PS#1 and the trench. When one forms the MOS channel in a self-aligned fashion, N+ source region is formed everywhere where one has a p-well region, which extends to even the periphery of the device. In the embodiments herein, one avoids the breakdown at the periphery due to formation of trench and PS#1.
  • FIG. 2A An embodiment shown in Fig. 2A is the unit cell of a cross-sectional structure of a SiC DMOSFET.
  • the key regions of this device are a p-well region 203, which is formed by ionimplantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • the ON state when a gate voltage is applied to the polysilicon gate 206 the current flows vertically from the drain 201, through the inversion layer which is formed at the top of the p-well layer 203, through the N+ source region 204, and out through the source metallization 208.
  • a voltage is supported across the p-well 203, N- drift layer 202 junction and there is a PN junction which is formed between the p-well and the N- drift layer.
  • the voltage applied to the structure is supported across this PN junction in the reverse bias.
  • a power MOSFET which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 205.
  • ILD layer 207 which is used to insulate the source interconnect metallization 208 from the poly-silicon gate 206.
  • P+ plug layer 209 which is grounded with the N+ source metallization.
  • the purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.
  • the depth of the P+ plug implant is made shallower than the p-well region as shown in Fig. 2A.
  • the DMOSFET device structure can result in high electric field concentration at the comer of the p-well region 203, which results in a high electric field in the gate oxide layer 205, especially during high drain bias (blocking mode) operation.
  • the high critical electric fields for breakdown in 4H-SiC results in a very high (> 5 MV/cm) electric field in the gate oxide.
  • Fowler- Nordheim tunneling currents are observed at such high electric fields in the gate oxide, which can result in trapped charge in the gate oxide, which leads to poor device reliability.
  • the lateral spacing between p-well regions JFET region is made narrow enough to suppress the electric field in the gate oxide while making sure that the MOSFET ON-resistance is low enough.
  • Fig. 2B is the breakdown simulation of a SiC MOSFET shown in Fig. 2A.
  • the simulation shows the peak electric field located at the comer of the p-well region, which results in a certain high electric field in the gate oxide layer.
  • the electric field is strongly concentrated at the corner of the p-well region because that is the region of maximum curvature, (this embodiment has limitation)
  • FIG. 3 An embodiment shown in Fig. 3 is the cross-sectional unit cell of a SiC DMOSFET.
  • the key regions of this device are a p-well region 303, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • a p-well region 303 which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • N- drift layer 302 There is an N+ substrate 301.
  • the ON state when a gate voltage is applied to the polysilicon gate 306 the current flows vertically from the drain 301, through the inversion layer which is formed at the top of the p-well layer 303, through the N+ source region 304, and out through the source metallization 308.
  • a power MOSFET there are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 305.
  • Another feature is an ILD layer 307 which is used to insulate the source interconnect metallization 308 from the poly-silicon gate 306.
  • the P+ plug region 209 of the SiC DMOSFET from Fig. 2A is replaced with a deep P-type Sinker #1 (PS#1) region 309. The depth of the PS#1 region, is greater than the depth of the p-well region.
  • the structure shown in Fig. 2A will break down between the p-well 203 and the N- drift layer 202 especially at the curvature of the p-well region.
  • the PS#1 region 309 being introduced in Fig. 3 the electric field or the main region where the breakdown will happen, is now at the very center of the drawing, which is basically between the PS#1 region 309 and the N- drift layer 302.
  • the presence of the deeper PS#1 region results in moving the peak electric field location from the corner of the p-well region 303 to the PS#1 region 309.
  • the location of the peak electric field in 4H-SiC during high drain bias operation has been moved farther away from the gate oxide 305.
  • Fig. 4A to Fig. 4R describes the process of manufacturing the structure shown in Fig. 3.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 401 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 402 shown in Fig. 4A.
  • a blanket hard mask 403 (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) is deposited in Fig. 4B and then patterned using photolithography followed by a dry etch (using a reactive ion-etch for example) as shown in Fig. 4C.
  • a P-type implantation 404 (comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 ) in Fig. 4D is performed to create a p-well 405 in Fig. 4E.
  • the mask 403 is removed, and another hard mask layer 406 is deposited (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) and patterned in Fig. 4F to define the N+ source region. Notice that the center of the unit cell is masked for source (SRC) implantation.
  • the SRC (N+ source region) 407 is formed by implantation of the n-type (N+) impurity 408 (comprising nitrogen or phosphorus, at energies ranging from 10 keV to 500 keV, at implant doses ranging from 10 13 cm' 2 to 10 16 cm' 2 ) as shown in Fig.
  • the PS#1 region 411 is formed by implantation of the p-type impurity 410 in Fig. 4H.
  • the deep PS#1 region can be formed using ion-implantation of aluminum or boron, which are commonly used p-type dopants in 4H-SiC. Boron can be advantageously used for forming this deep P-type Sinker region, since it has significantly higher implant range as compared to aluminum, and deep implants using boron can be formed with lower ion-implantation energies.
  • the PS#1 region can be formed with boron implantation with a 20-50% higher depth as compared to the p-well region.
  • the boron implant may comprise of energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 .
  • the doping profile of the PS#1 region can be formed with gradually decreasing doping concentration with a peak value at the SiC surface. This graded doping profile for the PS#1 region can prevent the formation of sharp corners in the 3-Dimensional landscape and is beneficial for spreading the peak electric field during high drain bias operation over a larger area which results in a higher breakdown voltage.
  • the PS#1 region can be formed with a peak doping in the range of 10 19 cm' 3 to IO 20 cm' 3 close to the SiC surface, which linearly decreases as a function of depth into the silicon carbide to the background N-drift layer doping (in the range of 10 14 -10 16 cm' 3 ).
  • a linearly graded doping profile of the PS#1 region results in a sufficient portion of the drain potential being supported within the PS#1 region and not only the N- drift region. This results in a pseudo charge-balanced structure, which promotes breakdown over a larger SiC region, which results in a lower critical electric field at breakdown and consequently a lower electric field in the gate insulator.
  • the oxide layer 412 which is the gate oxide is either thermally grown or deposited using chemical vapor deposition (CVD) in Fig. 4J.
  • the thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth.
  • PECVD plasma-enhanced CVD
  • LPCVD low-pressure CVD
  • a polysilicon gate layer is then deposited on the top 413 in Fig. 4K. The polysilicon layer may be deposited using PECVD or LPCVD.
  • the polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C.
  • a hard mask 414 is deposited on top and patterned as shown in Fig. 4L.
  • the polysilicon gate layer 413 is etched by using the patterned mask layer 414 in Fig. 4M.
  • the mask layer 414 is then removed from the top in Fig. 4N.
  • An interlayer dielectric (ILD) layer 415 (comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof) is deposited on the wafer; a hard mask 416 is deposited and patterned on top to define the ILD opening; the ILD layer is patterned using the hard mask 416 as shown in Fig. 40. Further the gate oxide is etched using the same mask 416 in Fig. 4P. The mask 416 is then removed and a nickel silicide region 417 is formed on the exposed SiC surface in Fig. 4Q. Interconnect metal layers 418 (either Al or Ag or Au) is deposited and patterned on the top and bottom of the chip in Fig. 4R.
  • ILD interlayer dielectric
  • the main problem in the prior art device in Fig. lAas recognized by the authors of this invention is that the p-well regions do not effectively shield the sensitive gate oxide from the high electric fields present in 4H-SiC especially during high drain bias (blocking mode operation).
  • the presence of the deeper PS#1 region results in moving the peak electric field location from the comer of the p-well region to the PS#1 region.
  • the location of the peak electric field in 4H-SiC during high drain bias operation has been moved farther away from the gate oxide.
  • the advantage of this embodiment is that the breakdown location has been moved from the corner of the p-well region to the base of the newly formed PS#1 region, which is both farther away from the gate oxide interface and deeper into the semiconductor.
  • the electric field in the gate oxide for the device structure incorporating the PS#1 region is now significantly lower than the prior art device which is shown using device simulation using SILVACO ATLAS in Fig. 5B.
  • FIG. 5A An embodiment shown in Fig. 5A is the cross-sectional unit cell of a vertical power DMOSFET.
  • the key regions of this device are a p-well region 503, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • the ON state when a gate voltage is applied to the polysilicon gate 506 the current flows vertically from the drain 501, through the inversion layer which is formed at the top of the p-well layer 503, through the N+ source region 504, and out through the source metallization 508.
  • a power MOSFET there are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 505.
  • Another feature is an ILD layer 507 which is used to insulate the source interconnect metallization 508 from the poly-silicon gate 506.
  • a second P-type Sinker #2 (PS#2) region 510 under the N+ source region 504 is formed in addition to the PS#1 region 509 already described in an embodiment shown in Fig. 3.
  • PS#2 P-type Sinker #2
  • the PS#2 region is formed deeper than the p-well region 503 but shallower than the PS#1 region 509.
  • the PS#2 region 510 can be made 20% deeper than the p-well region 503, while the PS#1 region 509 can be made 20% deeper than the PS#2 region 510.
  • the presence of the PS#2 region results in a sharing of the peak electric field under high drain bias operation between the PS#1 and PS#2 regions.
  • the presence of the PS#2 region alleviates a local maximum of the peak electric field in the device structure under high drain bias conditions.
  • the design of the p-well region needs to satisfy conflicting requirements.
  • the electrical dose in the p-well region under the N+ source region must be high enough to prevent reach-through breakdown under off-state (high drain bias) operation. But, at the same time, the surface doping of the p-well region must be low enough to maintain a reasonably low gate threshold voltage and device ON resistance.
  • the PS#2 region introduced in this embodiment can be thought of as a secondary p-well region and can be designed with the main purpose of preventing reach-through breakdown and for appropriately shaping the electric field profile under high drain bias operation.
  • the presence of the PS#2 region frees up the constraint in the design of the primary p-well region, which can be used for ON-state related device metrics such as gate threshold voltage and ON resistance. Since with the introduction of the PS#2 region, p-well region does not have to be designed with the objective of supporting the breakdown voltage it gives a lot more flexibility to the designer to design the p-well region suitably for just MOS channel formation.
  • FIG. 5B of a SiC DMOSFET designed according to the two embodiments described in Fig. 3 and Fig. 5A shows that the peak electric field location has been moved away from the comer of the p-well region to the center of the unit cell, which results in a lower electric field in the gate oxide layer.
  • Fig. 6A to Fig. 6J describes the process of manufacturing the structure shown in Fig. 5a.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 601 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 602 shown in Fig.
  • a blanket hard mask 603 (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) is deposited in Fig. 6B and then patterned using photolithography followed by a dry etch (using a reactive ion-etch for example) as shown in Fig. 6C.
  • a P-type implantation 604 (comprising Boron or Aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 ) is performed in Fig. 6D to create a p-well 605 in Fig. 6E.
  • the mask 603 is removed, and another hard mask layer 606 is deposited (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) and patterned in Fig. 6F to define the N+ source region. Notice that the center of the unit cell is masked for source (SRC) implantation.
  • the SRC (N+ source region) 607 is formed by implantation of the n-type (N+) impurity 608 (comprising nitrogen or phosphorus, at energies ranging from 10 keV to 500 keV, at implant doses ranging from 10 13 cm' 2 to 10 16 cm' 2 ) as shown in Fig.
  • the PS#2 region 609 is formed by implantation of the P type impurity 610 as shown in Fig. 6H.
  • the deep PS#2 region can be formed using ion-implantation of aluminum or boron, which are commonly used p-type dopants in 4H-SiC. Boron can be advantageously used for forming this deep P-type Sinker region, since it has significantly higher implant range as compared to aluminum, and deep implants using boron can be formed with lower ion-implantation energies.
  • the PS#2 region may comprise implant energies ranging from 100 keV to 1 MeV and implant dose ranging from 10 13 cm' 2 to 10 16 cm' 2 .
  • the PS#2 region may comprise implant energies ranging from 50 keV to 800 keV and implant dose ranging from 10 13 cm' 2 to 10 16 cm' 2 .
  • the same hard mask 606 utilized for forming the N+ source region is utilized for defining the ion-implanted PS#2 region. In this case, the PS#2 region is self-aligned under the N+ source region.
  • the hard mask 606 is removed and another hard mask layer 612 is deposited and patterned in Fig. 61.
  • the PS#1 region 611 is formed by implantation of the P-type impurity 613 that may comprise aluminum or boron.
  • the PS#1 region may comprise implant energies ranging from 100 keV to 1 MeV and implant dose ranging from 10 13 cm' 2 to 10 16 cm' 2 .
  • the PS#1 region may comprise implant energies ranging from 50 keV to 800 keV and implant dose ranging from 10 13 cm' 2 to 10 16 cm' 2 .
  • PS#2 region can be formed with a depth higher than that of the p-well region but lower than that of the PS#1 region.
  • the PS#2 region can be made 20% deeper than the p-well region, while the PS#1 region can be made 20% deeper than the PS#2 region.
  • the doping profile of the PS#1 and PS#2 regions can be formed with gradually decreasing doping concentration with a peak value at the SiC surface. This graded doping profile for the PS#1 and PS#2 regions can prevent the formation of sharp corners in the 3-Dimensional landscape and is beneficial for spreading the peak electric field during high drain bias operation over a larger area which results in a higher breakdown voltage.
  • the PS#1 and PS#2 regions can be formed with a peak doping in the range of 10 19 cm' 3 to IO 20 cm' 3 close to the SiC surface and close to the N+ Source region, respectively.
  • the doping concentration in the PS#1 and PS#2 regions may linearly decrease as a function of depth into the silicon carbide to the background N-drift layer doping (in the range of 10 14 - 10 16 cm' 3 ).
  • a linearly graded doping profile of the PS#1/PS#2 regions results in a sufficient portion of the drain potential being supported within the PS#1/PS#2 regions and not only the N- drift region.
  • FIG. 7A An embodiment shown in Fig. 7A is the cross-sectional unit cell of a SiC DMOSFET.
  • the key regions of this device are a p-well region 703, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • a p-well region 703 which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • N- drift layer 702 There is an N+ substrate 701.
  • the current flows vertically from the drain 701, through the inversion layer which is formed at the top of the p-well layer 703, through the N+ source region 704, and out through the source metallization 708.
  • a power MOSFET there are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 705.
  • Another feature is an inter-layer dielectric (ILD) layer 707 which is used to insulate the source interconnect metallization 708 from the poly-silicon gate 706.
  • a trench 711 is etched into the N+ source region 704 before implanting the PS#1 region 709.
  • PS#2 region 710 under the N+ source region 704 is formed in addition to the PS#1 region 709.
  • the PS#2 region is formed deeper than the p-well region 703 but shallower than the PS#1 region 709. It is desirable to move the electric field location as far away from the gate oxide interface for robust blocking capability of the device operation which improves the device reliability. Moving the breakdown location to the middle of the unit cell which is furthest away from the gate oxide 705 is an embodiment and by etching a recess trench 711 into the N+ source region 704, you have effectively created a deeper PS#1 region than what was in Fig. 3 and Fig. 5 A and moved the electric field even further away from the gate oxide region.
  • the PS#1 region is designed with the greatest depth among the P-type Sinker regions. While boron implantation is one technique to create such deep P-type regions in SiC technology, when you consider the maximum range of commercial ion-implanters available it becomes clear that ion implantation in SiC is not an easy process and deep ion implantation is particularly difficult.
  • the function of the N+ source region which is also referred to as source trench is that the PS#1 region can be realized with lower ion-implantation energies, which lowers the cost and time of this implantation step, without any compromise in implantation depth.
  • a trench can be dry etched into SiC after the implantation of the N+ source region but before the implantation of the PS#1 region.
  • the same hard mask layer used for the PS#1 implant can be used for etching the source trench into the SiC.
  • the hard mask layer is first patterned, followed by dry etching the trench into SiC, which is immediately followed by ionimplantation of the PS#1 region.
  • the formation of the source trench naturally extends the depth of the PS#1 region.
  • the PS#1 region can be realized with lower ion-implantation energies, which lowers the cost/time of this implantation step, without any compromise in implant depth.
  • the formation of the source trench also removes the N+ source region and enables a direct connection of the P-well region with the N+ source ohmic contact thereby grounding the p-well and shorting the P-well region with the N+ source region.
  • Fig. 7B is the breakdown simulation of a SiC MOSFET designed according to Embodiment shown in Fig. 7A which shows that the peak electric field location has been moved away from the comer of the p-well region to the center of the unit cell, which results in a lower electric field in the gate oxide layer.
  • Fig. 8A to Fig. 8BB describes the process of manufacturing the SiC DMOSFET structure shown in Fig. 7A.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 801 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 802 shown in Fig. 8A.
  • a blanket hard mask 803 (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) is deposited in Fig.
  • a P-type implantation 804 (comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 ) in Fig. 8D is performed to create a p-well 805 in Fig. 8E.
  • the mask 803 is removed, and another hard mask layer 806 is deposited (comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm) and patterned in Fig. 8F to define the N+ source region.
  • the N+ source region 807 is formed by implantation of the n-type (N+) impurity 808 (comprising Nitrogen or Phosphorus, at energies ranging from 10 keV to 500 keV, at implant doses ranging from 10 13 cm' 2 to 10 16 cm' 2 ) as shown in Fig. 8G.
  • the PS#2 region 809 is formed by the implantation of the P-type impurity 810 in Fig. 8H.
  • the deep PS#2 region can be formed using ion-implantation of aluminum or boron, which are commonly used p- type dopants in 4H-SiC. Boron can be advantageously used for forming this deep P-type Sinker region, since it has significantly higher implant range as compared to aluminum, and deep implants using boron can be formed with lower ion-implantation energies.
  • the patterned hard mask 806 is removed from the top in Fig. 81.
  • Another hard mask layer 811 is formed on the top in Fig. 8 J and patterned in Fig. 8K. The patterned mask 811 is used to etch 812 into the substrate in Fig.
  • the source trench which is the recessed region 813 is formed in the substrate by penetrating the source region in Fig. 8M.
  • a P-type implant 814 in Fig. 8N is performed for creating the PS#1 region.
  • the PS#1 region may comprise implant energies ranging from 100 keV to 1 MeV and implant dose ranging from 10 13 cm' 2 to 10 16 cm' 2 .
  • the PS#1 region may comprise implant energies ranging from 50 keV to 800 keV and implant dose ranging from 10 13 cm' 2 to 10 16 cm' 2 .
  • the PS#1 815 is formed by the self-aligned implantation of the p-type impurity in Fig. 80.
  • a linearly graded doping profile of the PS#1/PS#2 regions may be preferable utilized in lieu of a uniform (abrupt) doping profile, which results in a sufficient portion of the drain potential being supported within the PS#1/PS#2 regions and not only the N- drift region.
  • PS#1 region is designed with the greatest depth among the P-type Sinker regions using Boron implantation and the formation of the trench naturally extends the depth of the PS#1 region.
  • the same hard mask used for etching the source trench 811 is utilized to define the PS#1 region.
  • the SiC trench can be formed using dry etching techniques including reactive ion-etching, inductively coupled plasma (ICP)-RIE, etc. While a 90° sidewall slope is shown for this trench region in Fig. 7A, it is advantageous to form the trench regions with lower angle (60-90°) sidewalls, since this will reduce the curvature of the PS#1 region, and therefore improve the blocking performance of the device.
  • the patterned hard mask 811 is removed from the top in Fig. 8P.
  • An oxide layer 816 for gate oxide is grown in Fig. 8Q.
  • a polysilicon gate layer is deposited on the top 817 in Fig. 8R.
  • the polysilicon layer may be deposited using PECVD or LPCVD.
  • the polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry.
  • Postdeposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C.
  • a hard mask 818 is deposited on top and patterned as shown in Fig. 8S.
  • the polysilicon gate layer 817 is etched by using the patterned mask layer 818 in Fig. 8T.
  • the mask layer 818 is then removed from the top in Fig. 8U.
  • An interlayer dielectric (ILD) layer 819 (comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof) is deposited on the wafer in Fig. 8V.
  • a hard mask 820 is deposited and patterned on top to define the ILD opening in Fig. 8W.
  • the ILD layer is patterned using the hard mask 820 as shown in Fig. 8X.
  • gate oxide 816 is etched using the same mask 820 in Fig. 8Y.
  • the mask 820 is then removed in Fig. 8Z.
  • a nickel silicide region 821 is formed on the exposed SiC surface in Fig. 8AA.
  • Interconnect metal layers 822 are deposited and patterned on the top and bottom of the chip in Fig. 8BB.
  • the advantage of the embodiment herein is that by etching the source trench region, prior to the implantation of the PS#1 region, the breakdown location has been moved further into the semiconductor and farther away from the gate oxide layer. Due to the inherent hardness of silicon carbide, the observed range (depth) of ion-implanted dopants is significantly lower than in silicon. For example, forming deep (> 0.3 pm) ion-implanted layers in silicon carbide requires extremely high implantation energies (> 300 keV), which requires doubly or triply ionized implantation species, which drastically reduces the throughput and increase the cost of these ion-implantation steps. Forming the source trench as described in this embodiment obviates the need for doubly/triply ionized implantation steps, and low-cost with high-throughput singly ionized implantation can be utilized for realizing the PS#1 region.
  • Embodiments relate to SiC DMOSFET power devices that can be used for fabricating self-aligned power MOSFETs.
  • An embodiment relates to increasing MOS channel density.
  • An embodiment relates to increasing effective field-effect mobility.
  • An embodiment relates to improved device reliability. [00351] An embodiment relates to reducing ON resistance for a given chip size.
  • An embodiment relates to design and manufacturing of self-aligned power devices.
  • An embodiment relates to design and manufacturing MOS channels with sub-micron channel lengths.
  • An embodiment relates to removal of the parasitic N+ source region inadvertently formed in the periphery of the device.
  • An embodiment relates to proper grounding of the p-well region with the source ohmic contact in the active region of the device
  • An embodiment relates to removal of the parasitic NPN transistor formed in active and peripheral regions of self-aligned power devices.
  • An embodiment relates to a combination of an appropriately located source trench and ion-implanted P+ plug region to enable proper grounding of the p-well region in the main active MOSFET region and removal of a parasitic N+ source region formed in the periphery of the MOSFET
  • An embodiment relates to the formation of highly doped P+ plug regions in the periphery of the MOSFET, especially under the gate pad and gate bus regions.
  • An embodiment relates to the suppression of false turn-on of the MOSFET during fast switching transitions, at vulnerable locations, due to threshold voltage lowering by the body bias effect.
  • An embodiment relates to the improvement of the maximum dV/dt rating of the MOSFET.
  • An embodiment relates to the improvement of the maximum avalanche energy rating of the MOSFET.
  • An embodiment relates to a dedicated process step being utilized for masking the implantation of the N+ source region in the device periphery.
  • the P+ plug region is formed first in this embodiment, while the source trench is created later on in the process at the ILD etch step.
  • An embodiment relates to a dedicated hard mask applied after the sidewall spacer is formed and before the N+ source implantation. This layer prevents the formation of the N+ source region in the device periphery and hence parasitic NPN structures in the device periphery are avoided.
  • An embodiment relates to a p-well region (P-Well#2) placed under the N+ source region and electrically connected to the main p-well region.
  • the P-Well#2 provides additional electrical dose under the N+ source implant, to prevent reach-through breakdown, especially after the source trench formation.
  • An embodiment relates to a dedicated process step is utilized for masking the implantation of the N+ source region in the device periphery as well as the N+ source region in the middle of the unit cell in the active region to enable ohmic contact to the p-well region.
  • An embodiment relates to the formation of the segmented polysilicon gate metallization in the periphery of the device instead of a contiguous gate bus which will decrease the gate-body capacitance of the MOSFET.
  • An embodiment relates to the decrease of the gate capacitance of the MOSFET.
  • An embodiment relates to the increase of the switching speed of the MOSFET.
  • the embodiments described herein show novel techniques for design and manufacture of self-aligned SiC DMOSFET power devices. Due to limited mobility achievable on SiC planar DMOSFET it is necessary to form n-well channels that are submicron length, so that the overall power and ON resistance of the MOSFET are not degraded.
  • the channel region is formed due to the offset between the p-well and the N+ source region. If the p-well and the N+ source regions are formed by two separate masking steps, there can be lithographic misalignment, which will result in asymmetric MOSFET channel lengths on the two sides of a unit cell. In the embodiments described herein, to minimize this asymmetry in the MOS channel length, the p-well and the N+ source implant are done in a selfaligned fashion. There are several techniques proposed in the literature for achieving self-aligned MOSFET, including ones that use an oxide spacer approach to form a self-aligned p-well and N+ source regions, with the N+ source implant under p-well implant.
  • the embodiments herein describe several innovative techniques during self-aligned channel formation that not only allow for the elimination of the misalignment error during manufacturing of SiC MOSFETs, but also allow the possibility of reducing the channel length.
  • the channel lengths can be made smaller with narrow spacers. While the self-aligning process does provide the benefits of making an arbitrarily short channel length as well as eliminating misalignment, it does create some other problems with respect to the structure of the device outside the unit cells, because n+ regions are co-incident with the p-well regions.
  • a dedicated masking step that will be used for forming the N+ source implant.
  • the various embodiments described herein introduce techniques in which one can get rid of the N+ source implants in the periphery of the device and replace it with some other regions.
  • the active region of the MOSFET is where the current conduction happens while the periphery region of the MOSFET is where the edge termination of the device is provided to block any voltage.
  • the gate pad and gate bus regions are also considered to be part of the peripheral regions of the MOSFET, for the purposes of describing the innovations in this document.
  • a combination of an appropriately located source trench and ion- implanted P+ plug region enables proper grounding of the p-well region in the main active MOSFET region and removal of a parasitic N+ source region formed in the periphery of the MOSFET.
  • a parasitic NPN transistor exists in the active region of the MOSFET unit cell, formed by the N+ source region which acts like the N+ emitter, the p-well region which forms the P-base and the N+ source ohmic contact. In the periphery of the device and also under the gate pad metallization, there is no N+ source ohmic contact, and as a result, the emitter, and base regions of the parasitic NPN transistor are not shorted in this region. The parasitic NPN transistor will not be activated under normal DC or switching operation of the MOSFET, but operating the device under extreme conditions can cause the triggering of the parasitic NPN transistor.
  • the doping concentration of the P+ plug region to be placed in the device periphery can advantageously be made very high. In doing so, another parasitic device effect described here can be avoided.
  • moderately doped P-well regions exist in the device periphery with or without a parasitic N+ Source region, as described above. If the N+ Source region is co-incident with the p-well region in the device periphery (i.e., the n+ source region is not deliberately masked from the peripheral region), this results in a partial compensation of the p-type electrical dose of the p-well region. In either case, the p-well regions in the device periphery can be extremely resistive from an electrical standpoint.
  • the extremely high rate of change of drain voltage can result in capacitive current flow through this resistive peripheral p-well regions, which are only collected by the Source ohmic contact in the active region of the MOSFET.
  • the capacitive current caused by the high dV/dt during device switching has to traverse an extremely long distance from the device periphery to the Source ohmic contact in the active region.
  • the high resistivity of p-well regions in prior art MOSFETs can result in a significant body bias effect, which has the result of lowering the device threshold voltage in those regions.
  • the highly doped P+ plug regions in this embodiment can alleviate the aforementioned effect by reducing the amount of body bias developed in the peripheral regions of the MOSFET, which makes the MOSFET described in this embodiment more resilient to dV/dt induced failure.
  • the MOSFET structure described in this embodiment will have a higher dV/dt rating than prior art MOSFETs. This reduces the switching losses and increases the circuit efficiency.
  • a dedicated process step is utilized for masking the implantation of the N+ source region in the device periphery.
  • the P+ plug region is formed first in this embodiment, while the source trench is created later on in the process at the ILD etch step.
  • a dedicated masking step is interspersed between the formation of the sidewall spacer after the p-well implant and before the N+ source implant to mask the N+ source implant from the peripheral regions of the MOSFET.
  • the masking layer protects the periphery of the device from the source implanted region.
  • a second deeper p- well region (P-Well#2) is formed using the same masking step used for the N+ source implant. P+ plug regions are formed in a later step in both the active regions of the device as well as the device periphery.
  • a trench is later etched through the N+ source regions at discrete locations in the active region to contact the P+ plug regions, which get shorted to the N+ source region by the ohmic or silicide metallization.
  • the source region implantation is masked from the periphery of the device.
  • a dedicated process step is utilized for masking the implantation of the N+ source region in the device periphery as well as the N+ source region in the middle of the unit cell in the active region to enable ohmic contact to the p-well region.
  • the polysilicon metallization has been segmented in the periphery of the device and is not one continuous layer as commonly seen. There is a dedicated masking step interspersed between formation of the sidewall spacer, after the p-well implant and before the implementation of the N+ source implant, to mask the N+ source region, from both the peripheral regions of the device as well as the selected areas in the active region.
  • segmenting the polysilicon metallization reduces the parasitic gate to body or gate to source capacitance which are parasitic capacitances.
  • the islands of polysilicon are not disconnected but are connected at a position orthogonal to the plane of the drawing. Reducing the parasitic capacitance will enable the device to switch faster, which will increase the circuit efficiency by reducing the switching losses.
  • FIG. 10 An embodiment shown in Fig. 10 is the unit cell and the device periphery of a cross- sectional structure of a SiC DMOSFET.
  • the key regions of this device are a p-well region 203, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • the ON state when a gate voltage is applied to the polysilicon gate 208 the current flows vertically from the drain 201, through the inversion layer which is formed at the top of the p-well layer 203, through the N+ source region 204, and out through the source metallization 211.
  • a voltage is supported across the p-well 203, N- drift layer 202 junction and there is a PN junction which is formed between the p-well and the N- drift layer.
  • the voltage applied to the structure is supported across this PN junction in the reverse bias.
  • a power MOSFET which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the junction gate field-effect transistor (JFET) region or the JFET gap and the thickness of the gate oxide 207.
  • JFET junction gate field-effect transistor
  • Another feature is an ILD layer 209 which is used to insulate the source interconnect metallization 211 from the polysilicon gate 208.
  • Source trench regions 205 are realized by dry etching through the N+ source layer at selected locations of the device, followed by a p-type ion-implantation step to realize P+ plug regions 206 under the source trench. At the very center of the unit cell, there is a P+ plug layer 206 which is grounded with the N+ source metallization. The purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact. [00386] The formation of the source trench 205 device structure enables proper grounding of the p-well region in the main active MOSFET region and removal of a parasitic N+ source region 204 formed in the periphery of the MOSFET.
  • the formation of the source trench after the N+ source region formation removes parasitic N+ source regions from the device periphery of the chip and from under the gate pad region.
  • combination of the source trench and the ion-implanted P+ plug region provides three important functions. First it provides proper grounding of the p-well region with the source ohmic contact in the active region of the device and second it helps in the removal of the parasitic N+ source region inadvertently formed in the periphery of the device. Third, the highly doped P+ plug region increases the dV/dt rating of the MOSFET. In the embodiment herein both of the above ensures the removal of the parasitic NPN transistor that would be otherwise formed in those regions.
  • N+ emitter formed by the N+ source region
  • P-base formed by the p-well region
  • the parasitic NPN transistor will not be activated under normal DC or switching operation of the MOSFET, operation of the device under extreme conditions like short-circuit or avalanche-mode results in the simultaneous presence of extremely high junction temperatures, high dV/dt and high current densities, which can cause the triggering of the parasitic NPN transistor.
  • a separate masking step is carried out for masking the N+ source region from being formed at these locations.
  • the source trench can be advantageously used for removing the parasitic N+ source regions and replacing them with a P+ plug region, which is self-aligned with the source trench and electrically connected to the p-well region.
  • Fig. 11 A to Fig. 1 IFF describes the process of manufacturing the structure shown in Fig. 10.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 301 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 302 shown in Fig. 11 A.
  • a blanket hard mask 303 comprising a chemical vapor deposition (CVD) deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig.
  • CVD chemical vapor deposition
  • p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity.
  • a p-type implantation 304 comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 in Fig. 1 ID is performed to create a p-well 305 in Fig. 1 IE.
  • a second hard mask layer 306 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 1 IF on top of the patterned first hard mask layer 303. This is followed by an anisotropic etching 307 in Fig. 11G to form a sidewall spacer 306 as shown in Fig. 11H.
  • a n-type implant 308 is done in Fig. 1 II for creating a N+ source region 309 in Fig. 11 J.
  • a N+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus.
  • the source region 309 is formed in a self-aligned fashion with the p-well region 304.
  • the first and second hard mask layers 303 and 306 respectively, are removed in Fig. 1 IK. While the aforementioned sequence of process steps constitutes one method to form a self-aligned p-well and N+ source region, other methods may be employed to achieve the same result.
  • the N+ source region 309 may first be formed after deposition and patterning of a first hard mask layer, followed by further etch back of the first hard mask layer to then form the p-well region 304.
  • Another mask layer 310 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top in Fig. 1 IL.
  • the mask layer 310 is patterned in Fig. 1 IM.
  • the patterned mask 310 is used to etch into the substrate 311 in Fig. 1 IN using a dry etch method to create a recessed region within the SIC.
  • the recessed region is the source trench 312 formed in the substrate by penetrating the source region in Fig. 110.
  • the entire N+ source region is removed by dry etching at these selected locations of the device.
  • a P+ plug layer is formed in Fig. 1 IQ.
  • the depth of the P+ plug layer 314 may preferably exceed the depth of the N+ source implant and may even exceed the depth of the p-well region, in a particular implementation.
  • a p- type implantation comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 13 cm' 2 to 10 17 cm' 2 in Fig. 11D is performed to create a P+ plug region.
  • the P+ plug region 314 is realized under the source trench 312, which is electrically connected to the p-well region 304.
  • the mask layers are removed in Fig. HR.
  • the wafer is annealed for activating the implanted impurities.
  • the oxide layer 315 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 1 IS.
  • the thickness of the gate oxide could range from 5 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. Plasma-enhanced chemical vapor deposition (PECVD) or low- pressure chemical vapor deposition (LPCVD) could be used for gate oxide deposition.
  • PECVD plasma-enhanced chemical vapor deposition
  • LPCVD low- pressure chemical vapor deposition
  • a polysilicon gate layer 316 is then deposited in Fig. 11T.
  • the polysilicon layer may be deposited using PECVD or LPCVD.
  • the polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 600-900°C.
  • a hard mask 317 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top on top and patterned as shown in Fig. 11U.
  • the polysilicon layer 316 is etched by using the patterned mask layer 317 in Fig. 11V.
  • the mask layer 317 is then removed in Fig. 11W.
  • An ILD layer 318 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 11X.
  • a hard mask 319 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top and patterned on top to define the ILD opening in Fig. 11 Y.
  • the ILD layer 318 is etched using the hard mask 319 as shown in Fig. 11Z. Further the gate oxide 315 is etched using the same mask 319 in Fig. 11 AA.
  • the mask 319 is then removed in Fig. 1 IBB.
  • a nickel silicide region 320 is formed on the exposed SiC surface in Fig. 11CC.
  • a mask layer 321 is formed by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top and patterned in Fig. 11DD.
  • the ILD layer 318 is etched using mask 321 in Fig. 11EE.
  • the mask layer 321 is removed in Fig. 1 IFF.
  • Interconnect metal layers 322 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in. Fig. 11GG.
  • the same final structure for forming the source trench region and P+ plug region may be alternatively realized using a slightly different approach.
  • the p-well region, and the N+ source region is realized using a self-aligned process.
  • the P-plug layer may be formed first using deep boron or aluminum implantation as a buried layer that is placed under the N+ source region. The dry etching for the N+ source trench realization may be performed later on in the process.
  • the N+ source trench may be realized preferably after the high-temperature annealing process in one example implementation.
  • FIG. 12 An embodiment shown in Fig. 12 is the unit cell and the device periphery of a cross- sectional structure of a SiC DMOSFET.
  • the key regions of this device are a p-well region 403, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • the ON state when a gate voltage is applied to the polysilicon gate 407 the current flows vertically from the drain 401, through the inversion layer which is formed at the top of the p-well layer 403, through the N+ source region 404, and out through the source metallization 412.
  • a voltage is supported across the p-well 403, N- drift layer 402 junction and there is a PN junction which is formed between the p-well and the N- drift layer.
  • the voltage applied to the structure is supported across this PN junction in the reverse bias.
  • a power MOSFET which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 407.
  • ILD layer 409 which is used to insulate the source interconnect metallization 412 from the polysilicon gate [00397]
  • a dedicated masking step is interspersed between the formation of the sidewall spacer after the p-well implant and before the N+ source implant to mask the N+ source implant from the peripheral regions of the MOSFET.
  • a second deeper p-well region (P-Well#2) 405 is formed using the same masking step used for the N+ source implant.
  • P+ plug regions 406 are formed in a later step in both the active regions of the device as well as the device periphery.
  • the P+ plug layer 406 is grounded with the N+ source metallization.
  • the purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.
  • a trench 410 is later etched through the N+ source regions at discrete locations in the active region to contact the P+ plug regions, which get shorted to the N+ source region by the ohmic silicide 411 metallization.
  • the source trench 410 is etched into the SiC at selected regions using the same hard mask used for patterning the interlevel dielectric layer (ILD).
  • the source trench 410 serves two functions. First the source trench reveals the surface of the P+ plug layer that was previously buried under the N+ source region for subsequent contact with the ohmic silicide metal and second the source trench reveals the sidewalls of the N+ source region for subsequent contact with the ohmic silicide metal.
  • a dedicated hard mask or photoresist layer is applied after the sidewall spacer is formed and before the N+ source implantation. This layer prevents the formation of the N+ source region in the device periphery and parasitic NPN structures in the device periphery are avoided
  • a second p-well region (P-Well#2) 405 is placed under the N+ source region 404 and electrically connected to the main p-well region provides additional electrical dose under the N+ source implant, for preventing reach-through breakdown, especially after the source trench formation.
  • the etching of the source trench may inadvertently etch part of the primary p-well region under the N+ source region, thereby locally reducing the p-well dose in this region, resulting in undesirable reach through breakdown at these locations.
  • Fig. 13A to Fig. 13GG describes the process of manufacturing the structure shown in Fig. 12.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 501 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 502 shown in Fig. 13A.
  • a blanket hard mask 503 comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig.
  • p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p- type impurity.
  • a p-type implantation 504 comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 in Fig. 13D is performed to create a p-well 505 in Fig. 13E.
  • a second hard mask layer 506 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 13F on top of the patterned first hard mask layer 503. This is followed by an anisotropic etching 507 in Fig, 13G to form a sidewall spacer 506 as shown in Fig. 13H.
  • a patterned mask layer 508 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top alongside the patterned mask layer with the sidewall spacer in Fig. 131.
  • the hard mask layer 508 patterned over the peripheral regions of the device.
  • a n-type implant 509 is done in Fig. 13 J for creating a N+ source region 510 in Fig. 13 J.
  • a N+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus.
  • the N+ source region 510 is formed in a self-aligned fashion with the p-well region 504.
  • the source region is formed in a self-aligned fashion with the p-well region, while it is masked from the peripheral regions of the device.
  • a deep second p-well region (P- Well#2) 511 may be formed at the same time as the N+ source region in Fig. 13K.
  • the buried P- well#2 region may be formed using aluminum or boron, and placed under the N+ source region in the active area of the device.
  • the P-Well#2 region may be preferably formed using the p-type species boron which has a higher ion-implantation range as compared to aluminum in SiC. It may not be necessary to mask the p-well region#2 from the peripheral regions of the device.
  • the first and second hard mask layers 503 and 506 respectively, are removed in Fig. 13L.
  • Another mask layer 512 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top in Fig. 13M.
  • the mask layer 512 is patterned in Fig. 13N.
  • a P+ plug region 514 buried under the N+ source region 510 is realized in Fig. 13P.
  • the P+ plug region 514 is electrically connected to the p-well region 504 and the P-well#2 region 511.
  • the P+ plug region may be formed deeper than the p-well and P-Well#2 regions.
  • the mask layer 512 is then removed in Fig. 13Q and the implants are activated by high -temperature annealing.
  • the oxide layer 515 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 13R.
  • the thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. PECVD or LPCVD could be used for gate oxide deposition.
  • a polysilicon gate layer 516 is then deposited in Fig. 13S.
  • the polysilicon layer may be deposited using PECVD or LPCVD.
  • the polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step.
  • In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry.
  • Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C.
  • a hard mask 517 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top on top and patterned as shown in Fig. 13T.
  • the polysilicon layer 516 is etched by using the patterned mask layer 517 in Fig. 13U.
  • the mask layer 517 is then removed in Fig. 13 V.
  • An ILD layer 518 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 13W.
  • a hard mask 519 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top and patterned on top to define the ILD opening in Fig. 13X.
  • the ILD layer 518 is etched using the hard mask as shown in Fig. 13Y. Further the gate oxide 515 is etched using the same mask 519 in Fig. 13Z.
  • the hard mask that is used for patterning the ILD layer 519 is used to realize the source trench region 520 by etching completely through the N+ source layer and into the P+ plug layer in Fig 13AA.
  • the mask 519 is then removed in Fig. 13BB.
  • a nickel silicide region 521 is formed on the exposed SiC surface in Fig. 13CC.
  • a mask layer 522 is formed by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top which is then patterned in Fig. 13DD.
  • the ILD layer 518 is etched in Fig. 13EE.
  • the mask layer 522 is removed in Fig. 13FF.
  • Interconnect metal layers 523 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in. Fig. 13GG.
  • the ohmic contact to the N+ source regions are made through the etched sidewalls of the source trench regions in this embodiment, as opposed to the horizontal surfaces of the N+ source regions in conventional MOSFETs.
  • An embodiment shown in Fig. 14 is the unit cell and the device periphery of a cross- sectional structure of a SiC DMOSFET.
  • the key regions of this device are a p-well region 603, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • the ON state when a gate voltage is applied to the polysilicon gate 607 the current flows vertically from the drain 601, through the inversion layer which is formed at the top of the p-well layer 603, through the N+ source region 604, and out through the source metallization 610.
  • the OFF state or the blocking state a voltage is supported across the p-well 603, N- drift layer 602 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias.
  • a power MOSFET there are several key features in a power MOSFET, which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 606.
  • Another feature is an ILD layer 608 which is used to insulate the source interconnect metallization 610 from the polysilicon gate 607.
  • a P+ plug layer 605 which is grounded with the N+ source metallization. The purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.
  • a dedicated masking step is interspersed between the formation of the sidewall spacer after the p-well implant and before the N+ source implant to mask the N+ source implant from the peripheral regions of the MOSFET. This also masks the N+ source implant from selected regions in the active area of the device, which enables ohmic contact to the p-well or P+ plug region. This embodiment obviates the need for a source trench that is present in earlier embodiments.
  • a dedicated hard mask or photoresist layer is applied after the sidewall spacer is formed and before the N+ source implantation which prevents the formation of the N+ source region in the device periphery and parasitic NPN structures in the device periphery are avoided.
  • the implantation of the N+ source region is avoided in selected areas in the active region, and this enables ohmic contact to the p-well or P+ plug regions without an intervening N+ source region.
  • Fig. 15A to Fig. 15FF describes the process of manufacturing the structure shown in Fig. 14.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 701 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 702 shown in Fig. 15 A.
  • a blanket hard mask 703 comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 gm is deposited in Fig.
  • p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p- type impurity.
  • a p-type implantation 704 comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 in Fig. 15D is performed to create a p-well 705 in Fig. 15E.
  • a second hard mask layer 706 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 15F on top of the patterned first hard mask layer 703. This is followed by an anisotropic etching 707 in Fig. 15Gto form a sidewall spacer 706 as shown in Fig. 15H.
  • a hard mask layer 708 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm and patterned in Fig. 151.
  • the patterned mask layer is formed on the top alongside the patterned mask layer with the sidewall spacer 706.
  • a n-type implant 709 is done in Fig. 15J for creating a N+ source region 710 in Fig. 15K.
  • a N+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus.
  • the source region 710 is formed in a self-aligned fashion with the p-well region 705 while it is masked from the peripheral regions of the device, as well as selected areas of the active region of the device, to enable contact with the source ohmic metallization.
  • the first and second hard mask layers 703 and 708 respectively, are removed in Fig. 15L.
  • Another mask layer 711 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top in Fig. 15M.
  • the mask layer 711 is patterned in Fig. 15N.
  • a P+ plug region is realized in Fig. 15P.
  • the depth of the P+ plug layer 713 may preferably exceed the depth of the N+ source implant and may even exceed the depth of the p-well region, in a particular implementation.
  • the mask layer 711 is removed in Fig. 15Q. The wafer is annealed for activating the implanted impurities.
  • the oxide layer 714 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 15R.
  • the thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. PECVD or LPCVD could be used for gate oxide deposition.
  • a polysilicon gate layer 715 is then deposited in Fig. 15S.
  • the polysilicon layer may be deposited using PECVD or LPCVD.
  • the polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step.
  • In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry.
  • Post-deposition doping of polysilicon may be performed by depositing a layer of POOL followed by a drive-in step at temperatures ranging from 700-900°C.
  • a hard mask 716 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top on top and patterned as shown in Fig. 15T.
  • the polysilicon layer 715 is etched by using the patterned mask layer 716 in Fig. 15U.
  • the mask layer 716 is then removed in Fig. 15V.
  • An ILD layer 717 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 15W.
  • a hard mask 718 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top and patterned on top to define the ILD opening in Fig. 15X.
  • the ILD layer 717 is etched using the hard mask as shown in Fig. 15Y. Further the gate oxide 714 is etched using the same mask 718 in Fig. 15Z.
  • the mask 718 is then removed in Fig. 15AA.
  • a nickel silicide region 719 is formed on the exposed SiC surface in Fig. 15BB.
  • a mask layer 720 is formed by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top which is then patterned in Fig. 15CC.
  • the ILD layer 717 is etched in Fig. 15DD.
  • the mask layer 720 is removed in Fig. 15EE.
  • Interconnect metal layers 721 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in Fig. 15FF.
  • FIG. 8 An embodiment shown in Fig. 8 is the unit cell and the device periphery of a cross- sectional structure of a SiC DMOSFET.
  • the key regions of this device are a p-well region 803, which is formed by ion- implantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • the ON state when a gate voltage is applied to the polysilicon gate 807 the current flows vertically from the drain 801, through the inversion layer which is formed at the top of the p-well layer 803, through the N+ source region 804, and out through the source metallization 810.
  • a voltage is supported across the p-well 803, N- drift layer 802 junction and there is a PN junction which is formed between the p-well and the N- drift layer.
  • the voltage applied to the structure is supported across this PN junction in the reverse bias.
  • a power MOSFET which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 806.
  • ILD layer 808 which is used to insulate the source interconnect metallization 810 from the polysilicon gate 807.
  • P+ plug layer 805 which is grounded with the N+ source metallization.
  • the purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.
  • a dedicated masking step is interspersed between the formation of the sidewall spacer after the p-well implant and before the N+ source implant to mask the N+ source implant from the peripheral regions of the MOSFET. This also masks the N+ source implant from selected regions in the active area of the device, which enables ohmic contact to the p-well or P+ plug region. This embodiment obviates the need for a source trench that is present in some earlier embodiments.
  • a dedicated hard mask or photoresist layer is applied after the sidewall spacer is formed and before the N+ source implantation which prevents the formation of the N+ source region in the device periphery and parasitic NPN structures in the device periphery are avoided.
  • the implantation of the N+ source region is avoided in selected areas in the active region, and this enables ohmic contact to the p-well or P+ plug regions without an intervening N+ source region.
  • the polysilicon metallization in the peripheral regions of the device 807 are segmented and not a contiguous layer.
  • the formation of the segmented gate metallization in the periphery of the device instead of a contiguous gate bus could significantly decrease the gate-body capacitance of the MOSFET. This could result in a significant increase of the switching speed of the MOSFET.
  • Fig. 17A to Fig. 17FF describes the process of manufacturing the structure shown in Fig. 8.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 901 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 902 shown in Fig. 17 A.
  • a blanket hard mask 903 comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig.
  • p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p- type impurity.
  • a p-type implantation 904 comprising boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 in Fig. 17D is performed to create a p-well 905 in Fig. 17E.
  • a second hard mask layer 906 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 17F on top of the patterned first hard mask layer 903. This is followed by an anisotropic etching 907 in Fig. 17Gto form a sidewall spacer 906 as shown in Fig. 17H.
  • a hard mask layer 908 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm and patterned in Fig. 171.
  • the patterned mask layer 908 is formed on the top alongside the patterned mask layer with the sidewall spacer.
  • a n-type implant 909 is done in Fig. 17J for creating a N+ source region 910 in Fig. 17K.
  • a N+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus.
  • the source region 910 is formed in a self-aligned fashion with the p-well region 905 while it is masked from the peripheral regions of the device, as well as selected areas of the active region of the device, to enable contact with the source ohmic metallization.
  • the first and second hard mask layers 903 and 908 respectively, are removed in Fig. 17L.
  • Another mask layer 911 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top in Fig. 17M.
  • the mask layer 911 is patterned in Fig. 17N.
  • a P+ plug region 913 is realized in Fig. 17P.
  • the mask layer 911 is removed in Fig. 17Q.
  • the wafer is annealed for activating the implanted impurities.
  • the oxide layer 914 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 17R.
  • the thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. PECVD or LPCVD could be used for gate oxide deposition.
  • a polysilicon gate layer 915 is then deposited in Fig. 17S.
  • the polysilicon layer may be deposited using PECVD or LPCVD.
  • the polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step.
  • In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry.
  • Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C.
  • a hard mask 916 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top on top and patterned as shown in Fig. 17T.
  • the polysilicon layer 915 is etched by using the patterned mask layer 916 in Fig. 17U.
  • the masking step used to pattern the polysilicon gate metal results in a partially segmented polysilicon pattern. While not apparent in the cross-sectional schematic, the disjointed gate fingers would be connected at a position orthogonal to the plane of the drawing.
  • the gate insulator 914 is etched in Fig. 17V using the patterned mask 916.
  • the mask layer 916 is then removed in Fig. 17W.
  • An ILD layer 917 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 17X.
  • a hard mask 918 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top and patterned on top to define the ILD opening in Fig. 17Y.
  • the ILD layer 917 is etched using the hard mask as shown in Fig. 17Z.
  • the mask 918 is then removed in Fig. 17AA.
  • a nickel silicide region 919 is formed on the exposed SiC surface in Fig. 17BB.
  • a mask layer 920 is formed by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm on the top which is then patterned in Fig. 17CC.
  • the ILD layer 917 is etched in Fig. 17DD.
  • the mask layer 920 is removed in Fig. 17EE.
  • Interconnect metal layers 921 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in. Fig. 17FF.
  • Embodiments relate to SiC DMOSFET power devices where the p-well regions effectively shield the sensitive gate oxide from the high electric fields present in SiC especially during high drain bias or blocking mode operation.
  • An embodiment relates to using a P+-plug to ground the p-well region with the N+ source contact.
  • An embodiment relates to a p-well trench formed by dry etching into the p-well implanted region immediately preceding the source region formation, resulting in a portion of the MOS channel that is formed on the (0001) or horizontal face and another portion of the MOS channel that is formed on the (11-20/10-10) or vertical crystal plane of SiC which has the benefit of increasing the MOS channel mobility.
  • An embodiment relates to a much deeper vertical MOS channel formed by etching all the way through the p-well region. Subsequently, after the formation of the N+ Source region, a second p-well region (PW#2) is ion-implanted under and around the N+ source region in order to suppress reach-through breakdown.
  • PW#2 second p-well region
  • An embodiment relates to the formation of the p-well trench which offers the flexibility to the device designer to either increase the effective channel length for a given ON resistance target, or reduce the ON resistance for a given chip size
  • SiC devices in power electronics feature fast switching times, high blocking voltage capabilities, and the ability to operate at high temperatures. These characteristics, along with recent advancements in manufacturing processes, suggest that SiC has the potential to revolutionize power electronics as a successor to traditional silicon-based (Si) devices.
  • SiC is a wide band gap material (3.3 eV) and has a higher breakdown electric field (3 x 10 6 V/cm to 5 x 10 6 V/cm) compared to Si (Si band gap is 1.1 eV and breakdown electric field for Si is 0.3 x 10 6 V/cm).
  • SiC is a better thermal conductor (3.7 (W/cm-K) for SiC versus 1.6 (W/cm-K) for Si) which enables SiC devices to operate at extremely high-power levels and still dissipate the large amounts of excess heat generated.
  • These material properties of SiC offer multiple advantages of using SiC instead of Si on power devices.
  • the SiC die In a comparison of SiC and Si semiconductor die with identical structures and dimensions, the SiC die exhibits a lower specific ON resistance and a higher breakdown voltage than the Si die.
  • the disclosed embodiments herein provide novel techniques for SiC DMOSFET design and fabrication to have a higher channel density, which can be advantageous for reducing the ON resistance of the device.
  • the MOS channel is formed on the horizontal or 0001 crystal plane of SiC.
  • the channel mobility or field effect mobility on the 0001 crystal plane of SiC tends to be lower as compared to the vertical side wall or what is called as the 11-20 or 10-10 crystal plane.
  • the ON resistance tends to be large and the DMOSFET is limited by the field effect channel mobility.
  • the channel mobility or field effect mobility on the 0001 crystal plane of SiC is in the range of 15 to 25 cm2/ V-sec as compared to silicon MOSFETs where it can be more than 350 cm2/ V-sec.
  • One way to design lower resistance SiC MOSFETs is to find ways in which you can create very small channel lengths, so that this inversion layer mobility is active only in a smaller region of the current conduction path of this device, but this can lead to problems of short channel effects.
  • reducing the channel alone does not solve the low channel mobility in the 0001 crystal plane because it introduces short channel effects, which results in poor reliability and poor robustness characteristics for this device.
  • one way to combat this problem is by introducing trench MOSFETs in SiC.
  • the channels are now formed on the vertical side wall or on the so called A plane or M plane or also called as 10-10 or the 11-20 planes. Both of these planes have significantly higher channel mobility close to five times higher as compared to the horizontal plane resulting in 110 to 120 cm2/ V-sec for vertical channels.
  • a trench MOSFET can provide a higher channel density as compared to a planar MOSFET so one can increase the packing density. Since channel mobility is higher, it enables devices with small ON resistance. Even though a traditional trench MOSFET has an advantage over DMOSFET, the problem with a traditional trench MOSFET structure in SiC is that at the base of the trench there are high electric fields and a portion of a gate oxide in the trench suffers from high electric fields in the blocking mode of operation. This will become a failure point of a typical trench MOSFET structure and to overcome this issue it is necessary to shield the gate oxide at the base of the trench. P-type implantations used to shield gate oxide and approaches like a W-trench MOSFET are used to shield the gate oxide.
  • the device is neither pure DMOSFET nor is it a pure trench MOSFET.
  • the MOS channel is formed on both the 0001 plane as well as the vertical side wall or 11-20 (or 10-10) plane so it is a hybrid between a DMOSFET and a trench MOSFET.
  • the device has a shorter overall channel length as compared to a pure DMOSFET but with the same effective channel mobility. By increasing the channel length in this way enables you to overcome some of the robustness and reliability problems associated with making short channel DMOSFETs.
  • the device has the trench which is completely surrounded or encompassed in a p-type implanted region. This provides a natural shielding to the high electric fields. Since the trench is completely formed inside a p-well there is no region where the trench is exposed to n-type epilayer which mitigates the issue of high electric fields at the trench comers.
  • the structure of this device is distinguished by a trench which is etched into the p-well region and this trench is referred to as the p-well trench.
  • the p-well region is formed and then the trench is etched into the p-well region, so all sides of this trench are encompassed in this p-well region.
  • This trench also immediately precedes the formation of the N+ source region.
  • the device has a portion of the MOS channel which is formed on the 0001 phase and another portion of the channel is formed on the 11-20 or 10-10 plane.
  • the main steps to form a device described in the embodiment is forming the p-well region, by either ion implantation or epitaxial growth with aluminum or boron as the p-type impurity. Then the p-well trench is formed by controlled etching into the p-well region by using either reactive ion etching (RIE), or higher power inductively coupled plasma (ICP) source with an appropriate hard mask layer for forming this trench.
  • RIE reactive ion etching
  • ICP inductively coupled plasma
  • this trench maybe formed with a sidewall angle between 70° and 90°. That is the approximate angle with which the trench is formed.
  • the depth of this trench as an example may range between 0.1 pm to 0.5 pm.
  • the depth of the p-well trench maybe adjusted to be smaller than the depth of the p-well region where the bottom of the p-well trench is completely enclosed within the p-well region.
  • a N+ source region is formed by ion implantation or by epitaxial re-growth by using an impurity such as nitrogen or phosphorus. The N+ source is fully contained within the p-well region and N+ source does not extend beyond the p-well region.
  • the p-well trench region maybe formed using the same masking step as what may be used for forming the N+ source region even though it is not required.
  • a P+ plug layer for grounding the p-well is formed by implantation of either aluminum or boron.
  • the depth of the P+ plug layer may exceed the depth of the source implant layer such that it can both short the source implant with the ohmic layer that is put on top and also provides the grounding for the p-well region.
  • the remainder of the process constitutes heat treatment of the wafers for electrical activation, the electric formation, gate metal formation, interlayer dielectric (ILD), patterning ILD, ohmic metallization, putting down a thick pad metallization.
  • ILD interlayer dielectric
  • the gate insulator for forming the gate insulator either thermal oxidation or chemical vapor deposition (CVD) of a dielectric layer such as silicon dioxide, silicon nitride or oxynitride is used.
  • CVD chemical vapor deposition
  • the oxidation rates are different for the 0001 plane as compared to the 11-20 or 10-10 plane which means oxidation rates are different for the horizontal side wall and the vertical side wall. This can lead to thicker gate oxide on the vertical side wall as compared to the horizontal side wall.
  • the p-well trench is formed preceding the source region formation and after the p-well region formation in an embodiment with SiC DMOSFETs described herein.
  • a portion of the MOS channel in the device is now formed parallel to the 0001 plane and another portion is formed parallel to the 11-20 plane.
  • a MOSFET which is fabricated according to this embodiment as compared to a planar device for the same lateral footprint will have a higher channel density, hence enabling for a tighter packing.
  • the embodiment herein can also take advantage of the higher channel mobility of the vertical side wall.
  • devices have higher channel density and higher channel mobility and lower ON resistance. For a given ON resistance target you can increase the effective channel length.
  • the device in this embodiment can have the same channel length as the planar DMOSFET but because of the higher channel mobility of 11-20 and 10-10 direction one can afford a longer channel in the vertical side wall and still have a shorter, horizontal channel. Due to higher channel mobility, the device in the embodiment will have a lower ON resistance. It allows you to then have a smaller chip size for the same ON resistance and design a device as in the embodiment which has a longer channel in the vertical and shorter on the horizontal, allowing to make a lower ON resistance MOSFET.
  • the embodiments described herein can be distinguished from a prior art disclosed by Tega et al from Hitachi in a US patent application: US 2018/0331174 Al, published in November of 2018.
  • the prior art structure described by Tega et al from Hitachi in the US patent describes a SiC MOSFET structure in which the MOS channel is formed on both the horizontal and vertical p-well surfaces and the p-well trench which creates this MOS channel on the vertical and horizontal side walls is not formed contiguously.
  • the p-well trench is only formed at orthogonal locations in the 3D landscape. If it were formed contiguously a cross section anywhere in the device will show the same structure.
  • the second difference is that the construction of the MOS channel in the prior art structure described by Tega et al from Hitachi is completely different when compared to what is described in the embodiments here.
  • the MOS channel in the prior art is formed between an N+ source region and a separate N+ accumulation region.
  • the p- well region is formed first followed by a trench into the p-well region, and then the source implant.
  • the p-well region is formed followed by the source implant, an accumulation region, the heat treatment and then a p-well trench.
  • the difference lies in how and when the MOS channel is formed during the process.
  • the third difference is that the process of trench creation for realizing MOS channel on the vertical SiC crystal planes is conducted after all implantation steps are completed in the prior art described by Tega et al from Hitachi. As a result, the N+ Source region is elevated as compared to the MOS channel formed on the vertical sidewall.
  • the p-well trench is etched immediately following the p-well implantation and prior to the N+ source implantation which is formed on the recessed region created by the etching of the p- well trench.
  • the structure proposed by Tega et all along with a P+ plug region, N+ source region, and p-well region has N+ accumulation region and a P+ shielding region.
  • An embodiment described herein enables you to form an extremely long channel on the vertical side wall.
  • the p-well trench can be formed significantly deeper so that the bottom of the p-well trench can extend beyond the p-well region.
  • p-well region is formed followed by a deep p-well trench and source implantation. After the source implantation a second p-well region is formed. The second p-well region extends below the source region and has a cover around the corner to prevent any reliability issues of having a sharp edge.
  • tilted implantation is used to extend the p-well region beyond the lateral extent of the p-well region and shield the gate oxide from any drain induced electric field.
  • the structure in the embodiment provides a natural way to shield the drain potential from the channel region by extending the second p-well region beyond the source region
  • the process to form the device described in the embodiment includes forming a p-well region by ion implantation or epitaxial growth using aluminum or boron. This is followed by a p- well trench that is formed by control etching into the p-well region by RIE or ICP based etching.
  • the p-well trench may be formed with a sidewall angle between 75° and 90°.
  • the depth of the p- well trench region may range anywhere from 0.1 pm to 2 pm.
  • a N+ Source region is then formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus.
  • a second p-well region is formed.
  • the second p-well is formed with a sufficient depth under the N+ source region while making sure that the lateral extent of the p-well region is then now larger than the original p-well region.
  • a dedicated hard mask layer may be deposited and patterned with a slightly larger extent than the original p-well region, and then the ion-implantation for PW#2 may be performed.
  • tilted ion-implantation may be advantageously used for realizing PW#2.
  • the same hard mask may be used for creating the p-well trench, N+ source region and then the PW#2 region, whose lateral extent is made larger than the original PW region using tilted ion-implantation of a p-type impurity.
  • the remainder of the process constitutes heat treatment of the wafers for electrical activation of the implanted impurities, gate insulator formation, gate electrode formation, inter-level dielectric formation, Source/Drain Ohmic metallization and finally the formation of pad or interconnect metals compatible with die probing and packaging.
  • the gate insulator is formed either by thermal oxidation of the silicon carbide or by CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc.
  • FIG. 18 An embodiment shown in Fig. 18 is the unit cell of a cross-sectional structure of a SiC DMOSFET.
  • the key regions of this device are a p-well region 203, which is formed by ionimplantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • the ON state when a gate voltage is applied to the polysilicon gate 206 the current flows vertically from the drain 201, through the inversion layer which is formed at the top of the p-well layer 203, through the N+ source region 204, and out through the source metallization 208.
  • a voltage is supported across the p-well 203, N- drift layer 202 junction and there is a PN junction which is formed between the p-well and the N- drift layer.
  • the voltage applied to the structure is supported across this PN junction in the reverse bias.
  • a power MOSFET which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 205.
  • ILD layer 207 which is used to insulate the source interconnect metallization 208 from the poly-silicon gate 206.
  • P+ plug layer 209 which is grounded with the N+ source metallization.
  • the purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.
  • the p-well region 203 is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity. Then, a p-well trench 210 is formed by controlled etching into the p-well region 203 by either RIE or ICP etching using an appropriately patterned hard mask layer.
  • the p-well trench may be formed with a sidewall angle between 70° and 90°.
  • the depth of the p-well trench region 210 may range from 0.1 pm to 0.5 pm. The depth of the p-well trench can be adjusted to be shallower than the depth of the p-well region.
  • the bottom of the p- well trench may be enclosed within the p-well region.
  • a N+ source region is then formed by ionimplantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus.
  • the p-well trench region may be preferably formed using the same masking step used for performing the ion-implantation necessary for forming the N+ source region 204.
  • a P+ plug layer 209 may be formed by implantation of a controlled dose of a p-type impurity such as aluminum or boron. The depth of the P+ plug layer may exceed the depth of the N+ source implant and may even exceed the depth of the p-well region, in a particular implementation.
  • the gate insulator 205 is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc.
  • the trench is formed into the p-well region immediately preceding the formation of the N+ source region
  • a portion of the MOS channel is formed parallel to the (0001) crystal plane, while another portion of the MOS channel is formed parallel to the (11- 20) or (1-100) crystal plane of SiC.
  • the DMOSFET fabricated according to this embodiment will have a higher channel density, which can be advantageous for reducing the ON resistance of the device. It is well-known to those in the field of the invention that MOS channels formed on vertical sidewalls, parallel to (11-20) or (10-10) crystal planes of 4H-SiC, can achieve much high fieldeffect mobility as compared to the MOS channels formed on the flat (0001) crystal planes.
  • the effective channel mobility for a DMOSFET fabricated according to this embodiment is expected to be higher than for a DMOSFET fabricated with its MOS channel always parallel to the (0001) crystal plane of 4H-SiC. This desirable feature can be exploited for increasing the effective channel length for a given ON resistance target or reducing the ON resistance for a given chip size, whichever may be of interest to the device designer.
  • Fig. 19A to Fig. 19U describes the process of manufacturing the structure shown in Fig. 18.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 301 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 302 shown in Fig. 19 A.
  • a blanket hard mask 303 comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig.
  • p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p- type impurity.
  • a p-type implantation 304 comprising of boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 in Fig. 19D is performed to create a p-well 305 in Fig. 19E.
  • the mask 303 is removed, and another hard mask layer 306 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm and then patterned as in Fig. 19F.
  • a p-well trench 308 is formed by controlled etching process 307 into the p-well region by RIE or ICP etching using the appropriately patterned hard mask layer 306 in Fig. 19G.
  • the p-well trench 308 is formed with a sidewall angle between 70° and 90°. The depth of the p-well trench region ranges from 0.1 pm to 0.5 pm.
  • the depth of the p-well trench may be adjusted to be shallower than the depth of the p-well region 305.
  • the bottom of the p-well trench 308 may be enclosed within the p-well region 305.
  • a n-type implant 309 is done for creating a N+ source region 310 in Fig. 19H.
  • AN+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus.
  • the same hard mask layer 306 used for etching the p-well trench may be advantageously used for patterning the N+ source implant so the source implant is perfectly aligned under the p-well trench.
  • the masking layer 306 is removed in Fig. 191.
  • FIG. 19J Another hard mask layer 311 is deposited in Fig. 19J.
  • the hard mask layer 311 is patterned in Fig. 19K.
  • a P+ plug layer may be formed by implantation of a controlled dose of a p-type impurity 312 such as aluminum or boron in Fig. 19L.
  • the depth of the P+ plug layer 313 may preferably exceed the depth of the N+ source implant and may even exceed the depth of the p-well region, in a particular implementation in Fig. 19M. This is followed by the removal of the hard mask 311 using either dry or wet etching techniques commonly practiced by those in the field in Fig. 19N.
  • the oxide layer 314 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 190.
  • the thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. Plasma-enhanced chemical vapor deposition (PECVD) or low-pressure chemical vapor deposition (LPCVD) could be used for gate oxide deposition.
  • PECVD plasma-enhanced chemical vapor deposition
  • LPCVD low-pressure chemical vapor deposition
  • a polysilicon gate layer 315 is then deposited in Fig. 19P.
  • the polysilicon layer may be deposited using PECVD or LPCVD.
  • the polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C. A hard mask 316 is deposited on top and patterned as shown in Fig. 19Q. The polysilicon gate layer 315 is etched by using the patterned mask layer 316. The mask layer 316 is then removed in Fig. 19R.
  • An ILD layer 317 comprising of 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer; a hard mask is deposited and patterned on top to define the ILD opening; the ILD layer 317 is patterned using the hard mask as shown in Fig. 19S. Further the gate oxide 314 is etched using the same mask. The mask is then removed and a nickel silicide region 318 is formed on the exposed SiC surface in Fig. 19T. Interconnect metal layers 319 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the chip in Fig. 19U
  • FIG. 20 An embodiment shown in Fig. 20 is the unit cell of a cross-sectional structure of a SiC DMOSFET.
  • the key regions of this device are a p-well region 403, which is formed by ionimplantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • the ON state when a gate voltage is applied to the polysilicon gate 406 the current flows vertically from the drain 401, through the inversion layer which is formed at the top of the p-well layer 403, through the N+ source region 404, and out through the source metallization 408.
  • a voltage is supported across the p-well 403, N- drift layer 402 junction and there is a PN junction which is formed between the p-well and the N- drift layer.
  • the voltage applied to the structure is supported across this PN junction in the reverse bias.
  • a power MOSFET which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the JFET region or the JFET gap and the thickness of the gate oxide 405.
  • ILD layer 407 which is used to insulate the source interconnect metallization 408 from the poly-silicon gate 406.
  • P+ plug layer 409 which is grounded with the N+ source metallization.
  • the purpose of the P+ plug in SiC DMOSFET is to ground the p-well region with the N+ source contact.
  • a p-well trench 410 is formed by dry etching into the p-well implanted region immediately preceding the source region 404 formation, resulting in a portion of the MOS channel that is formed on the (0001) or horizontal face and another portion of the MOS channel that is formed on the (11-20/10-10) or vertical crystal plane of SiC.
  • a much deeper vertical MOS channel is formed by etching all the way through the p- well region.
  • a second p-well region indicated as PW#2411 is ion-implanted under and around the N+ source region in order to suppress reach-through breakdown.
  • the p-well region 403 is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity. Then, a p-well trench 410 is formed by controlled etching into the p-well region by RIE or ICP etching using an appropriately patterned hard mask layer. The p-well trench 410 may be formed with a sidewall angle between 75° and 90°. The depth of the p-well trench region may range from 0.5 pm to 2 pm. Compared to the device shown in Fig. 18 the device in Fig. 20 has the depth of the p-well trench which may be adjusted to be of the same depth or even slightly deeper than the p-well region.
  • a N+ source region is then formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus.
  • a second p-well region (PW#2) 411 is then formed to a sufficient depth under the N+ source region, such that the lateral extent of the PW#2 region is larger than that of the original p-well region. Two methods for forming the PW#2 411 regions are identified. (1) A dedicated hard mask layer may be deposited and patterned with a slightly larger extent than the original p-well region, and then the ion-implantation for PW#2 may be performed.
  • Tilted ion-implantation may be advantageously used for realizing PW#2.
  • the same hard mask may be used for creating the trench, N+ source region and then the PW#2 region, whose lateral extent is made larger than the original p-well region 403 using tilted ion-implantation of a p-type impurity.
  • the remainder of the process constitutes heat treatment of the wafers for electrical activation of the implanted impurities, gate insulator formation, gate electrode formation, inter-level dielectric formation, source/drain ohmic metallization and finally the formation of pad or interconnect metals compatible with die probing and packaging.
  • the gate insulator 405 is formed either by thermal oxidation of the silicon carbide or by CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc.
  • the device described in this embodiment in Fig. 20 is an enhancement to the device described in the embodiment in Fig. 18 and has several additional functions and advantages.
  • the vertical portion of the MOS channel of the embodiment in Fig. 20 can be made much larger than the device shown in Fig. 18, due to a deeper p-well trench 410 for the MOSFET in Fig. 20.
  • a larger percentage of the MOS channel can be realized on the higher channel mobility capable vertical sidewall as compared to the horizontal surface. For example, for a total channel length of 1 pm, 0.25 pm of the MOS channel can be realized on the horizontal surface and 0.75 pm of the MOS channel can be realized on the vertical sidewall.
  • a longer channel MOSFET can be fabricated using embodiment in Fig. 20 as compared to the MOSFET fabricated using embodiment in Fig. 18.
  • a longer channel MOSFET offers higher device robustness, including lower drain saturation current, higher short-circuit robustness, lower Vth roll-off with drain voltage, immunity from drain induced barrier lowering (DIBL) effects.
  • a larger extent for the PW#2 411 as compared to the original p-well 403 is necessary and beneficial for reducing the channel length of the horizontal portion of the MOS channel.
  • the drain potential during the high-voltage blocking condition is effectively shielded from the original p-well region by the PW#2 region.
  • This enables a significantly reduced lateral extent (electrical dose) for the original p-well region that extends beyond the p-well trench, without risk of reach- through breakdown.
  • a reduced lateral extent for the p-well region beyond the p-well trench leads to a smaller portion of the MOSFET channel formed on the horizontal surface.
  • Fig. 21A to Fig. 21V describes the process of manufacturing the structure shown in Fig. 20.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 501 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 502 shown in Fig. 21 A.
  • a blanket hard mask 503 comprising a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig.
  • p- well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity.
  • a p-type implantation 504 comprising of boron or aluminum, at energies ranging from 10 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 in Fig. 21D is performed to create a p-well 505 in Fig. 2 IE.
  • the mask 503 is removed, and another hard mask layer 506 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm and then patterned as in Fig. 21F.
  • a deep p-well trench 508 is formed by controlled etching process 507 into the p-well region by RLE or ICP etching using the appropriately patterned hard mask layer 506 in Fig. 21G.
  • the p-well trench 508 may be formed with a sidewall angle between 75° and 90°. The depth of the p-well trench region for example may range from 0.5 pm to 2 pm.
  • a N-type implant 509 is done for creating a N+ source region 510 in Fig. 21H.
  • a N+ source region is formed by ion-implantation or by epitaxial re-growth by a n-type impurity such as nitrogen or phosphorus.
  • a second p-well region (PW#2) 511 is then formed to a sufficient depth under the N+ source region, such that the lateral extent of the PW#2 region is larger than that of the original p-well region in Fig. 211.
  • a dedicated hard mask layer may be deposited and patterned with a slightly larger extent than the original p-well region, and then the ion-implantation for PW#2 may be performed.
  • Tilted ion-implantation may be advantageously used for realizing PW#2.
  • the same hard mask 506 may be used for creating the p-well trench 508, N+ source region 510 and then the PW#2 region 511, whose lateral extent is made larger than the original p-well region using tilted ion-implantation of a p-type impurity.
  • the masking layer 506 is removed in Fig. 21 J.
  • Another hard mask layer 512 is deposited in Fig. 2 IK.
  • the hard mask layer 512 is patterned in Fig. 2 IL.
  • a P+ plug layer may be formed by implantation of a controlled dose of a p-type impurity 513 such as aluminum or boron in Fig. 2 IM.
  • the depth of the P+ plug layer 514 may preferably exceed the depth of the N+ source implant and may even exceed the depth of the p-well region, in a particular implementation in Fig. 2 IN. This is followed by the removal of the hard mask 512 using either dry or wet etching techniques commonly practiced by those in the field in Fig. 210.
  • the oxide layer 515 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 2 IP.
  • the thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. PECVD or LPCVD could be used for gate oxide deposition.
  • a polysilicon gate layer 516 is then deposited in Fig. 2 IQ.
  • the polysilicon layer may be deposited using PECVD or LPCVD.
  • the polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step.
  • In- situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry.
  • Post-deposition doping of polysilicon may be performed by depositing a layer of POCL followed by a drive-in step at temperatures ranging from 700-900°C.
  • a hard mask 517 is deposited and patterned as shown in Fig. 21R.
  • the polysilicon gate layer 516 is etched by using the patterned mask layer 517.
  • the mask layer 517 is then removed in Fig. 21 S.
  • An ILD layer 518 comprising of 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer; a hard mask is deposited and patterned on top to define the ILD opening; the ILD layer 518 is patterned using the hard mask as shown in Fig. 2 IT. Further the gate oxide 515 is etched using the same mask. The mask is then removed and a nickel silicide region 519 is formed on the exposed SiC surface in Fig. 21U. Interconnect metal layers 520 of either aluminum, silver or gold is deposited and patterned on the top and bottom of the chip in Fig. 21V.
  • An embodiment described herein relates to design and manufacturing of a short-channel SiC MOSFET.
  • An embodiment described herein relates to minimizing the DIBL effect of the high voltage, short-channel SiC MOSFETs.
  • An embodiment described herein relates to design and manufacturing MOS channels with sub-micron channel lengths.
  • the embodiments described herein relate to increasing the doping concentration of the channel locally in certain regions of the channel.
  • the non-uniformly doped channels for SiC MOSFET provide better tradeoff between ON resistance, threshold voltage and short circuit withstand time.
  • a p-type shielding layer called the p-shield is formed within the p-well region.
  • the p-shield always originates within the p-well region, but it can extend beyond the vertical extent of the p-well region.
  • the bottom of the p-shield region can extend beneath the p-well.
  • the doping concentrations in the different p-shield region can be different from each other.
  • the embodiment described herein relates to a device where a p-shield region is formed buried within the p-well structure.
  • the p-shield region always originates within the p-well region, but can extend beyond the vertical extent of the p-well region.
  • device structures can have multiple p-shield regions.
  • their doping concentration profiles of the different p-shield regions do not necessarily have to be the same and can be different from each other.
  • One associated problem is a roll off of the threshold voltage at high drain bias where the designed device achieves a certain desired threshold voltage only at very low drain bias. But, as the drain bias approaches it's blocking value, the threshold voltage gets reduced substantially which is undesirable since the channel could inadvertently turn on.
  • a device suffering the DIBL effect has extremely large saturation currents under high drain bias, which results in excessive power dissipation under short circuit load conditions. This results in a low short circuit withstand time. While limited MOS channel mobility of SiC MOSFETS can be overcome with short channel lengths, it is associated with problems due to DIBL effects.
  • the embodiments described herein can help achieve a device with both low enough ON resistance as well as high enough short circuit withstand time. While the conventional approach is to just uniformly increase the doping concentration in the channel region, the embodiments described herein do not increase the doping concentration of the other channel uniformly but increases it locally in certain regions of the channel.
  • the non-uniformly doped channels for SiC MOSFET provide better tradeoff between ON resistance, threshold voltage and short circuit withstand time.
  • the doping concentration is increased such that they do not increase the threshold voltage too much, but at the same time reduce the DIBL effect and hence achieving a better trade off.
  • a p-type shielding layer called the p-shield is formed within the p-well region.
  • the p-shield always originates within the p-well region, but in certain examples of this embodiment, it can extend beyond the vertical extent of the p-well region.
  • the bottom of the p-shield region can be extended further down and can reach beneath the p-well. In an embodiment herein there can be multiple p-shield regions. The doping concentrations in the different p-shield region can be different from each other.
  • a p-type shielding layer called the p-shield is formed buried within the p-well region. The p-shield always originates within the p-well region, but in certain examples of this embodiment, it can extend beyond the vertical extent of the p-well region.
  • the bottom of the p-shield region can be extended further down and can reach beneath the p-well.
  • a p-shield region is formed buried within the p-well structure re-enforces” the doping of the p-well region locally and provides better shielding of the MOSFET channel at the surface, while minimizing the DIBL effect.
  • the p-shield since the p-shield is not directly connected to the channel, the p-shield does not change the VTH.
  • FIG. 23 A An embodiment shown in Fig. 23 A is the half unit cell of a cross-sectional structure of a SiC DMOSFET.
  • the key regions of this device are a p-well region 203, which is formed by ionimplantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • the ON state when a gate voltage is applied to the polysilicon gate 207 the current flows vertically from the drain 201, through the inversion layer which is formed at the top of the p-well layer 203, through the N+ source region 205, and out through the source metallization 210.
  • a voltage is supported across the p-well 203, N- drift layer 202 junction and there is a PN junction which is formed between the p-well and the N- drift layer.
  • the voltage applied to the structure is supported across this PN junction in the reverse bias.
  • a power MOSFET which include the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the junction gate field-effect transistor (JFET) region or the JFET gap and the thickness of the gate oxide 206.
  • JFET junction gate field-effect transistor
  • Another feature is an ILD layer 208 which is used to insulate the source interconnect metallization 210 from the polysilicon gate 207.
  • a p-type shielding layer which is called p-shield 204a is formed within the p-well region.
  • the p-shield can be located inside the p-well such that its lateral location of the point whose doping concentration is the highest as compared to the average background doping concentration of the p-well is positioned within the boundary of the p-well.
  • the p-shield region always originates within the p-well region.
  • Points A and B are given as the reference points for describing how the doping profile of the implanted p-shield region looks like.
  • the embodiment shown in Fig. 23B is similar to that of Fig. 23 A except that the bottom of the p-shield region is extended further down into the p-well and can reach outside the p-well region.
  • Fig. 23C and Fig. 23D the devices are similar to Fig. 23 A.
  • the devices in Fig. 23C and Fig. 23D exemplify the case where there are multiple p-shield regions. In these cases, their doping concentration profiles of the different p-shield regions do not necessarily have to be the same and can be different from each other.
  • the p-shield that is formed in the middle of the channel can help in mitigating the expansion of the drain bias-induced depletion region, which eliminates the DIBL effect.
  • the p-shield region also provides a simple way for controlling the VTH of the MOSFET, which enables improving the short circuit time (tsc).
  • the p-shield enables a local increase of the doping concentration of the p- well at critical locations in the device structure, as opposed to an uniform increase of the p-well doping concentration. A better trade-off with respect to lower Vth, ON resistance and better immunity to short-channel effects is obtained by methods described in the embodiment.
  • the p-shield can also provide better shielding of the electric field to the channel region which further mitigates the DIBL effect in the channel.
  • the device structure with multiple p-shield regions can be designed with different doping concentrations in the different p-shield regions. In an embodiment described herein, a higher doping concentration can be applied to the p-shield region/s close to the edge of the p-well (POINT A), while the p-shield regions closer to POINT B can be made with lower doping concentrations. This structure will have the benefit of a lower gate threshold voltage as well as excellent immunity to short-channel effects, for a given channel length.
  • Fig. 24A to Fig. 24U describes the process of manufacturing the structure shown in Fig. 23 A.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 301 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 302 shown in Fig. 24A.
  • a blanket hard mask 303 comprising a chemical vapor deposition (CVD) deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig.
  • CVD chemical vapor deposition
  • the p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity.
  • a p-type implantation 304 comprising boron or aluminum, at energies ranging from 10 keV to 1000 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 is performed to create a p-well 305 in Fig. 24D.
  • the patterned mask layer 303 is removed in Fig. 24E.
  • a hard mask layer 306 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 24F.
  • the mask layer 306 is patterned using photolithography followed by a dry etch using RTE for example in Fig. 24G.
  • a p-type implant 307 is done as shown in Fig. 24H for creating a p-type region inside the p-well called p-shield 308.
  • the p-shield region 308 can be formed using aluminum or boron as the p-type impurity.
  • the doping concentration in the p-shield region may be in the range of 1E16 cm- 3 to 1E21 cm-3.
  • the patterned mask layer 306 is removed in Fig. 241.
  • a blanket hard mask 309 comprising a chemical vapor deposition (CVD) deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 24J and then patterned using photolithography followed by a dry etch using RIE for example as shown in Fig. 24K.
  • CVD chemical vapor deposition
  • a N+ source region 311 is formed by ion-implantation or by epitaxial re-growth by a n- type impurity such as nitrogen or phosphorus 310 in Fig. 24L.
  • the patterned mask layer 309 is removed in Fig. 24M.
  • the oxide layer 312 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 24N.
  • the thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. Plasma-enhanced chemical vapor deposition (PECVD) or low- pressure chemical vapor deposition (LPCVD) could be used for gate oxide deposition.
  • PECVD plasma-enhanced chemical vapor deposition
  • LPCVD low- pressure chemical vapor deposition
  • a polysilicon gate layer 313 is then deposited in Fig. 240.
  • the polysilicon layer may be deposited using PECVD or LPCVD.
  • the polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POCh followed by a drive-in step at temperatures ranging from 700-900°C.
  • the polysilicon layer 313 is patterned in Fig. 24P.
  • An ILD layer 314 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 24Q.
  • the ILD layer 314 is patterned in Fig. 24R.
  • the gate oxide 312 is patterned in Fig. 24S.
  • Nickel silicide regions 315 are formed on the exposed SiC surface in Fig. 24T.
  • Interconnect metal layers 316 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in.
  • An embodiment shown in Fig. 25A is the half unit cell of a cross-sectional structure of a SiC DMOSFET.
  • the key regions of this device are a p-well region 403, which is formed by ionimplantation or epitaxial re-growth of a p-type species such as aluminum or boron.
  • the current flows vertically from the drain 401, through the inversion layer which is formed at the top of the p-well layer 403, through the N+ source region 405, and out through the source metallization 410.
  • a voltage is supported across the p-well 403, N- drift layer 402 junction and there is a PN junction which is formed between the p-well and the N- drift layer. The voltage applied to the structure is supported across this PN junction in the reverse bias.
  • a power MOSFET which includes the pitch of the unit cell, which is the repeat unit for the MOSFET, the channel length, which is the portion of the p-well in which the inversion channel is formed, the distance between two successive p-wells, which is referred to as the junction gate field-effect transistor region (JFET region) or the JFET gap and the thickness of the gate oxide 406.
  • JFET region junction gate field-effect transistor region
  • ILD layer 408 is used to insulate the source interconnect metallization 410 from the polysilicon gate 407.
  • a p-shield region 404a is formed buried within the p-well structure.
  • the p-shield is formed beneath the SiC surface, where the MOSFET channel is located.
  • the p-shield region always originates within the p-well region as seen in Fig. 25 A, but may in certain examples of this embodiment extend beyond the vertical extent of the p-well region as shown in Fig. 25B.
  • the embodiment shown in Fig. 25B is similar to that of Fig. 25 A except that the bottom of the p-shield region is extended further down into the p-well and can reach outside the p-well region.
  • FIG. 25C and Fig. 25D Device structures shown in Fig. 25C and Fig. 25D are also similar to the device in Fig. 25A, but they exemplify the case where there are multiple p-shield regions. In these cases, their doping concentration profiles of the different p-shield regions do not necessarily have to be the same and can be different from each other. Points A and B in each of these figures are given as the reference points for describing how the doping profile of the implanted p-shield region looks like. [00509] The p-shield in Fig. 25 A to Fig.
  • Fig. 25D “re-enforces” the doping of the p-well region locally and provides better shielding of the MOSFET channel at the surface, while minimizing the DIBL effect. Since the p-shield is not directly connected to the channel, the p-shield in this case does not change the threshold voltage.
  • the device shown in Fig. 25A provides the same kind of field shielding for mitigating the DIBL but does not require the change of the threshold voltage value where it is inevitable for the device of Fig. 23 A.
  • Fig. 26A to Fig. 26U describes the process of manufacturing the structure shown in Fig. 25A.
  • the manufacturing process for a SiC DMOSFET is on a SiC substrate 501 and starts with using a 4H-SiC Si-face epi-wafer with suitable doping (10 14 - 10 18 cm' 3 ) and thickness (1 pm to 300 pm) for the epilayer 502 shown in Fig. 26A.
  • a blanket hard mask 503 comprising a chemical vapor deposition (CVD) deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 26B and then patterned using photolithography followed by a dry etch using reactive ion etching (RIE) for example as shown in Fig. 26C.
  • CVD chemical vapor deposition
  • p-well region is first formed by ion-implantation or epitaxial growth using aluminum or boron as the p-type impurity.
  • a p-type implantation 504 comprising boron or aluminum, at energies ranging from 10 keV to 1000 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 is performed to create a p-well 505 in Fig. 26D.
  • the patterned mask layer 503 is removed in Fig. 26E.
  • a hard mask layer 506 is deposited by a CVD deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm in Fig. 26F.
  • the mask layer 506 is patterned using photolithography followed by a dry etch using RIE for example in Fig. 26G.
  • a p-type implant 507 is done in Fig. 26H for creating a p-type region inside the p-well called p-shield 508.
  • the p-shield region 508 can be formed using aluminum or boron as the p-type impurity.
  • a p-shield region is formed buried within the p-well structure. In other words, the p- shield is formed beneath the SiC surface, where the MOSFET channel is located. The p-shield region always originates within the p-well region. The location of the p-shield region, which is controlled by careful adjustment of the implant energies used for realizing the p-shield region.
  • the p-shield region may be created by a p-type ion-implantation step comprising boron or aluminum, at energies ranging from 25 keV to 800 keV, at implant doses ranging from 10 12 cm' 2 to 10 15 cm' 2 .
  • the patterned mask layer 506 is removed in Fig. 261.
  • a blanket hard mask 509 comprising a chemical vapor deposition (CVD) deposited layer of silicon dioxide, silicon nitride, silicon oxynitride, or a metallic layer such as nickel, with thickness ranging from 50 nm to 5 pm is deposited in Fig. 261 and then patterned using photolithography followed by a dry etch using RIE for example as shown in Fig. 26K.
  • CVD chemical vapor deposition
  • a N+ source region 511 is formed by ion-implantation or by epitaxial re-growth by a n- type impurity such as nitrogen or phosphorus 510 in Fig. 26L.
  • the patterned mask layer 509 is removed in Fig. 26M.
  • the oxide layer 512 which is the gate oxide is formed by thermal oxidation or using CVD of a dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, etc. in Fig. 26N.
  • the thickness of the gate oxide could range from 10 nm to 100 nm. Either dry or wet thermal oxidation could be used for oxide growth. Plasma-enhanced chemical vapor deposition (PECVD) or low- pressure chemical vapor deposition (LPCVD) could be used for gate oxide deposition.
  • PECVD plasma-enhanced chemical vapor deposition
  • LPCVD low- pressure chemical vapor deposition
  • a polysilicon gate layer 513 is then deposited in Fig. 260.
  • the polysilicon layer may be deposited using PECVD or LPCVD.
  • the polysilicon layer may be degenerately doped using boron or phosphorus, either in-situ or in a subsequent step. In-situ doping may be performed by the addition of PH3 precursor to the polysilicon deposition chemistry. Post-deposition doping of polysilicon may be performed by depositing a layer of POOL followed by a drive-in step at temperatures ranging from 700-900°C.
  • the polysilicon layer 513 is patterned in Fig. 26P.
  • An ILD layer 514 comprising 50 nm - 1000 nm thick silicon dioxide, silicon nitride, silicon oxynitride layers or a stacked combination thereof is deposited on the wafer in Fig. 26Q.
  • the ILD layer 514 is patterned in Fig. 26R.
  • the gate oxide 512 is patterned in Fig. 26S.
  • Nickel silicide regions 515 are formed on the exposed SiC surface in Fig. 26T.
  • Interconnect metal layers 516 of either aluminum or silver or gold is deposited and patterned on the top and bottom of the substrate in. Fig. 26U.
  • the device described in an embodiment herein has a buried N+ region, which is located in between that P+ islands.
  • the buried N+ region is formed in a way that it is physically separated from the wafer surface because it does not contact the Schottky layer. There is a portion of the N- drift layer in contact with the Schottky surface.
  • the physical separation of the N+ region from the wafer surface is a critical feature of this embodiment since SiC devices at the Schottky metal have the N- doping concentration, not the N+ doping concentration.
  • the silicon carbide surfaces in contact with a Schottky metal has the N- doping concentration which is critical for reducing the strength of the electric field at the Schottky metal interface with the SiC.
  • the vertical extent of the buried N+ region is lower than the bottom of the P+ region and covers the bottom of the P+ region.
  • the spacing between the P+ islands are narrower and the depth of the P+ islands is deeper when compared to prior art MPS diodes.
  • the presence of the N+ region allows the spacing between the P+ islands to be narrower.
  • the P+ islands shield the electric field that develops during the high voltage operation from the Schottky interface.
  • the P+ regions interspersed with the N+ regions are designed such as to achieve a certain level of charge balance between the P+ islands and N+ regions which provides the benefit of further reducing the ON resistance of this device and also keeping a low electric field.
  • the bottom of the N+ region is higher than the bottom of the P+ region.
  • the bottom of the P+ region is in contact with the N- drift layer which is a trade off as this will enable lower leakage currents but higher ON resistance.
  • Better ON resistance can be achieved in an embodiment of the device where the N+ region located in between the P+ islands is buried while lower leakage currents can be achieved in an embodiment of the device where the N+ region does not enclose the bottom of the P+ islands completely.
  • both buried N+ region located in between the P+ islands and N+ region that do not enclose the bottom of the P+ islands completely can exist on the same device.
  • the N+ region is formed of several sub N regions while the P+ is formed of many sub P regions such that the doping concentration in each of these different layers or slices could be different.
  • either the final slice of the N+ region is underneath the P+ islands and covers around the P+ islands completely or the bottom of the N+ slice is higher than the bottom of the P+ region.
  • the doping concentration of N+ types sub regions farther away from the silicon carbide surface could be progressively higher which may have a benefit of lower conduction losses.
  • the doping concentration of the p- type sub regions farther away from the SiC surface could be made progressively lower which may enable better blocking characteristics.
  • the varying doping concentration described in the embodiments herein allows freedom to appropriately tune the device design towards a lower leakage currents, better conduction losses, lowered resistance etc. Better trade off can be achieved with layered and differently doped N+ and P+ regions as opposed to just having one P+ layer and one N+ layer and this can be achieved by using multiple ion implantation steps or multiple epi growth.
  • the N+ region which is interspersed between a set of multiple P+ wells are formed in such a way that it is physically separated from the wafer surface and extends all the way into the N- drift region.
  • the physical separation of the N+ region from a SiC wafer surface in the embodiments herein distinguishes it from other similar inventions.
  • a part of the SiC wafer which is in contact with a Schottky metal (METAL 1) and is an n-type semiconductor has the same doping concentration of the N- drift since the doping concentration of the n-type SiC semiconductor which is in direct contact with the Schottky metal (METAL 1) is critical for reducing the strength of the electric field at the wafer surface, during the high-voltage blocking mode of operation of the SiC MPS diode.
  • the device of embodiment shown in Fig. 28A is the cross-sectional schematic of the SiC MPS diode.
  • the key regions of this device are an N+ substrate 201 at the bottom which gives mechanical support of the wafer and is -350 pm-thick.
  • An N- drift region 202 which is usually an epi layer and is on top of the N+ substrate.
  • the device has a first metal layer 205 denoted as METAL 1, which is the Schottky metal to an n-type SiC semiconductor region and forms Schottky contact to its underlying n-type regions.
  • the device has a second metal layer 206 denoted as METAL 2 on the front side of the wafer which is in contact with the METAL 1.
  • METAL 2 is often called “power metal” and is usually in Aluminum.
  • silicide layer 207 under the bottom of the N+ substrate.
  • METAL 3 under the back side of the wafer which is in contact with the silicide layer.
  • the device shown in Fig. 28A has a N+ region 203 which is interspersed between a set of multiple P+ wells 204.
  • the N+ region 203 is formed in such a way that it is physically separated from the wafer surface and extends all the way into the N- drift region 202.
  • the physical separation of the N+ region from a SiC wafer surface is a critical feature of the embodiment described herein and distinguishes it from other similar inventions.
  • a part of the SiC wafer which is in contact with a Schottky metal 205 denoted as METAL 1 and is an n-type semiconductor has the same doping concentration of the N- drift 202.
  • the doping concentration of the n-type SiC semiconductor which is in direct contact with the Schottky metal 205 labeled METAL 1 is critical for reducing the strength of the electric field at the wafer surface, during the high-voltage blocking mode of operation of the SiC MPS diode.
  • the vertical extent of the N+ region 203 is lower than the bottom of the P+ region 204.
  • the buried N+ region completely surrounds the P+ region which provides Schottky-injected majority carriers a more conductive travel path and reduces the total forward conduction loss.
  • the embodiment described in the device herein uses a different kind of Schottky metal for the METAL 1 layer when compared to the METAL 1 of the prior art.
  • the choice of METAL 1 205 of the device described in Fig. 28A is made so that the barrier height of its Schottky contact is lower than that of the prior art. Due to the smaller Schottky barrier height, the injection of the majority carrier over the Schottky barrier becomes more efficient and this reflects as a lower Knee Voltage (VKnee) in the forward I-V characteristics as shown in Fig. 28B.
  • the new devices with lower VKnee marked as #2 and #3) have lower forward conduction loss than their counterpart (marked as #1).
  • the lower Schottky barrier height leads to higher reverse leakage current as shown in the reverse I-V curves - marked as #2 and #3.
  • the amount of the leakage current can be kept under control in the embodiment described here by fine tuning the barrier height which is dependent on various design elements including but not limited to the annealing temperature of the Schottky contact, the pitch of the device, depth and doping of the P+ region, the doping and depth of the N+ region, and the doping of the N- drift region.
  • N+ substrate of the new device is thinner (which is usually 100 ⁇ 200 pm) than its counterpart (which is usually - 350 pm).
  • the thinned N+ substrate directly impacts on the forward I-V characteristics that the linear region of the forward I-V curves where VF > VKnee becomes steeper because the thinned substrate contributes less series resistance to the total amount of the forward conduction loss.
  • the diode with the lower VKnee and thinned substrate (marked #3) must have less conduction loss than another diode with the exact lower VKnee and thick substrate (marked #2).
  • the Differential On-Resistance (RON, Diff) which is the inverse of the slope of the linear segment of the forward I-V curve is significantly reduced by thinning the N+ substrate.
  • the lower VKnee and RON, Diff of the diode in the embodiment herein enables significant reduction of the forward conduction loss while maintaining the reverse leakage low enough for suitable needs in the market.
  • Fig. 29A to Fig. 29L describes the process of manufacturing the structure shown in Fig. 28A.
  • the manufacturing process of the device includes preparing a SiC wafer in Fig. 29A which consists of a highly conductive N+ substrate 301 and an N- drift region 302, where the N- drift region is typically epi-grown.
  • the N- drift region 302 is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance.
  • an ion implantation step with an n-type species 303 such as nitrogen and/or phosphorus is performed onto the active region of the device in Fig. 29B forming an N+ region within the N- drift region.
  • the edge termination which is not shown needs to be masked during the n-type ion implantation step. It is important to note that the n-type ion implantation step 303 needs to be performed in such a fashion that the N+ region 304 is completely buried inside the N- drift region in Fig. 29C. The ion implantation step should form the N+ region 304 where the top of the N+ region is physically off from the wafer surface.
  • a patterned mask 305 which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 29D.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a p-type ion implantation step with a p-type impurity 306 such as aluminum and/or boron is performed in Fig. 29E to form a set of multiple P+ wells 307 in Fig. 29F.
  • the bottoms of the set of multiple P+ wells 307 are formed such that they are above the bottom of the N+ region 304.
  • the depth of the set of multiple P+ wells are less than the depth of the N+ region.
  • the set of multiple P+ wells leads to a P+ region as a whole in Fig. 29F.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 305 is removed by dry or wet etching process in Fig. 29G. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 308 marked as METAL 1 directly on the wafer surface in Fig. 29H.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA (Rapid Thermal Anneal).
  • a first pad metal 309 marked as METAL 2 is then deposited on top of the wafer in Fig. 291 and patterned by dry etching, wet etching, or lift-off.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 29J. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by Chemical Mechanical Polishing (CMP), wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • CMP Chemical Mechanical Polishing
  • a silicide region 310 on the back side of the wafer is then formed in Fig. 29K.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 311 marked as METAL 3 is formed on the back side of the wafer in Fig. 29L.
  • the second pad metal can be of Aluminum or Aluminum-based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with.
  • the SiC wafer consists of three n-type epi-grown layers in Fig. 29C with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer.
  • the three n-type epi-grown layers should be formed in such a way that an N- layer 302 is meeting a device side of the wafer and an N+ layer 304 is positioned right underneath the N- layer, where the N+ layer is on top of a second N- layer also labeled 302 which serves as a drift region and the second N- layer is positioned on top of the N+ substrate 301.
  • a patterned mask 305 which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 29D.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a p-type ion implantation step with a p-type impurity 306 such as aluminum and/or boron is performed in Fig. 29E to form a set of multiple P+ wells 307 in Fig. 29F.
  • the bottoms of the set of multiple P+ wells 307 are formed such that they are above the bottom of the N+ region 304. In the embodiments herein, the depth of the set of multiple P+ wells are less than the depth of the N+ region.
  • the set of multiple P+ wells lead to a P+ region as a whole in Fig. 29F.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 305 is removed by dry or wet etching process in Fig. 29G. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 308 marked as METAL 1 directly on the wafer surface in Fig. 29H.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 309 marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 29J. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 310 on the back side of the wafer is then formed in Fig. 29K.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 311 marked as METAL 3 is formed on the back side of the wafer in Fig. 29L.
  • the second pad metal can be of Aluminum or Aluminum-based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • the P+ region 204 of the SiC MPS diode of this invention is formed in such a way that the set of multiple P+ wells are spaced narrower in lateral direction and extend vertically deeper into the N- drift region 202 when compared to the case of the prior art.
  • the P+ region of this invention in conjunction with the aforementioned N+ region, is designed to provide a robust shielding to the Schottky barrier formed on the wafer surface.
  • the device of the prior art is vulnerable to the high stress of the electric field at its Schottky contact which easily results in temporary/permanent degradation of the Schottky contact leading to the high leakage current and/or irreversible destruction of the device.
  • the device in the prior art has the N- drift region as the sole conduction path only, and it is clear that the majority carriers flowing through the JFET-like region between the P+ wells near the wafer surface will suffer in the carrier transport and increase the total forward conduction loss.
  • Fig. 28C compares key dimensions of the device structure of this invention. Regardless of the types of the devices, the lateral spacing between two adjacent P+ wells are defined to be W1 and the vertical depth of the P+ wells measured from the surface of the SiC wafer is defined to be DI. It should be noted that the ratio of W1 over DI (or Wl/Dl) for the device of this invention is less than 3.0 (or Wl/Dl ⁇ 3.0).
  • the device of embodiment shown in Fig. 30 is the cross-sectional schematic of the SiC MPS diode.
  • the key regions of this device are an N+ substrate 401 at the bottom which gives mechanical support of the wafer and is -350 pm-thick.
  • An N- drift region 402 which is usually an epi layer and is on top of the N+ substrate.
  • the device has a first metal layer 405 denoted as METAL 1, which is the Schottky metal to an n-type SiC semiconductor region and forms Schottky contact to its underlying n-type regions.
  • the device has a second metal layer 406 denoted as METAL 2 on the front side of the wafer which is in contact with the METAL 1.
  • METAL 2 is often called “power metal” and is usually in Aluminum.
  • silicide layer 407 under the bottom of the N+ substrate.
  • METAL 3 under the back side of the wafer which is in contact with the silicide layer.
  • the device shown in Fig. 30 has a N+ region 403 which is interspersed between a set of multiple P+ wells 404.
  • the N+ region 403 is formed in such a way to extend near the vicinity of the P+ region 404 but not completely cover the bottom of the P+ region.
  • the physical separation of the N+ region from a SiC wafer surface is a critical feature of the embodiment described herein and distinguishes it from other similar inventions.
  • a part of the SiC wafer which is in contact with a Schottky metal 405 denoted as METAL 1 and is an n-type semiconductor has the same doping concentration of the N- drift 402.
  • the doping concentration of the n-type SiC semiconductor which is in direct contact with the Schottky metal 405 labeled METAL 1 is critical for reducing the strength of the electric field at the wafer surface, during the high-voltage blocking mode of operation of the SiC MPS diode.
  • the vertical extent of the N+ region 403 is above the bottom of the P+ region 404.
  • the buried N+ region does not completely cover the bottom of the P+ region.
  • Fig. 31A to Fig. 3 IL describes the process of manufacturing the structure shown in Fig. 30.
  • the manufacturing process of the device includes preparing a SiC wafer in Fig. 31A which consists of a highly conductive N+ substrate 501 and an N- drift region 502, where the N- drift region is typically epi-grown.
  • the N- drift region 502 is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance.
  • an ion implantation step with an n-type species 503 such as nitrogen and/or phosphorus is performed onto the active region of the device in Fig. 3 IB forming an N+ region within the N- drift region.
  • the edge termination which is not shown needs to be masked during the n-type ion implantation step. It is important to note that the n-type ion implantation step 503 needs to be performed in such a fashion that the N+ region 504 is completely buried inside the N- drift region in Fig. 31C. The ion implantation step should form the N+ region 504 where the top of the N+ region is physically off from the wafer surface.
  • a patterned mask 505 which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 3 ID.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a p-type ion implantation step with a p-type impurity 506 such as aluminum and/or boron is performed in Fig. 3 IE to form a set of multiple P+ wells 507 in Fig. 3 IF.
  • the bottoms of the set of multiple P+ wells 507 are formed such that they are below the bottom of the N+ region 504.
  • the depth of the set of multiple P+ wells are greater than the depth of the N+ region.
  • the set of multiple P+ wells lead to a P+ region as a whole in Fig. 3 IF.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 505 is removed by dry or wet etching process in Fig. 31G. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 508 marked as METAL 1 directly on the wafer surface in Fig. 31H.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 509 marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 31 J. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 510 on the back side of the wafer is then formed in Fig. 3 IK.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 511 marked as METAL 3 is formed on the back side of the wafer in Fig. 3 IL.
  • the second pad metal can be of Aluminum or Aluminum-based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with.
  • the SiC wafer consists of three n-type epi-grown layers in Fig. 31C with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer.
  • the three n-type epi-grown layers should be formed in such a way that an N- layer 502 is meeting a device side of the wafer and an N+ layer 504 is positioned right underneath the N- layer, where the N+ layer is on top of a second N- layer also labeled 502 which serves as a drift region and the second N- layer is positioned on top of the N+ substrate 501.
  • a patterned mask 505 which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 3 ID.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a p-type ion implantation step with a p-type impurity 506 such as aluminum and/or boron is performed in Fig. 3 IE to form a set of multiple P+ wells 507 in Fig. 3 IF.
  • the bottoms of the set of multiple P+ wells 507 are formed such that they are below the bottom of the N+ region 504. In the embodiments herein, the depth of the set of multiple P+ wells are greater than the depth of the N+ region.
  • the set of multiple P+ wells lead to a P+ region as a whole in Fig. 3 IF.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 505 is removed by dry or wet etching process in Fig. 31G. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 508 marked as METAL 1 directly on the wafer surface in Fig. 31H.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 509 marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 31 J. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 510 on the back side of the wafer is then formed in Fig. 3 IK.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 511 marked as METAL 3 is formed on the back side of the wafer in Fig. 3 IL.
  • the second pad metal can be of Aluminum or Aluminum-based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • FIG. 30 affords lower leakage current and better blocking performance than embodiment shown in Fig. 28A, by further reducing the electrical field at the Schottky metal interface, but may trade-off a higher on-state voltage drop as compared to the embodiment shown in Fig. 28A.
  • the devices of embodiments shown in Fig. 32A to Fig. 32F are the cross-sectional schematic of the SiC MPS diode.
  • the key regions of these devices are an N+ substrate 601 at the bottom which gives mechanical support of the wafer and is -350 pm-thick.
  • An N- drift region 602 which is usually an epi layer and is on top of the N+ substrate.
  • the device has a first metal layer 605 denoted as METAL 1, which is the Schottky metal to an n-type SiC semiconductor region and forms Schottky contact to its underlying n-type regions.
  • the device has a second metal layer 606 denoted as METAL 2 on the front side of the wafer which is in contact with the METAL 1.
  • METAL 2 is often called “power metal” and is usually in Aluminum.
  • silicide layer 607 under the bottom of the N+ substrate.
  • METAL 3 under the back side of the wafer which is in contact with the silicide layer.
  • the devices of embodiments in Fig. 32A to Fig. 32F differs from the ones shown in embodiments Fig. 28A and Fig. 30 because the N+ region in the previous embodiments is replaced by a set of multiple N sub-regions 603 arranged in layers. The thickness and doping concentration in each of these sub-regions may be different.
  • the devices in embodiments shown in Fig. 32A to Fig. 32F have the N+ region 603 which is interspersed between a set of multiple P+ wells 604.
  • the embodiment shown in Fig. 32A to Fig. 32F including a device with a set of multiple n-type sublayers with different thicknesses and doping concentrations but a set of multiple p-type wells which are of the same kind as in Fig. 32A and Fig.
  • Devices in Fig. 32A, Fig. 32C and Fig. 32E have the N+ region 603 surrounding and under the P+ wells 604, and devices in Fig. 32B, Fig. 32D and Fig.
  • N+ region 603 placed in between the P+ wells but not surrounding the P+ wells 604.
  • the physical separation of the N+ region from a SiC wafer surface is a critical feature of the embodiment described herein and distinguishes it from other similar inventions.
  • a part of the SiC wafer which is in contact with a Schottky metal 605 denoted as METAL 1 and is an n-type semiconductor has the same doping concentration of the N- drift 602.
  • the doping concentration of the n-type SiC semiconductor which is in direct contact with the Schottky metal 605 labeled METAL 1 is critical for reducing the strength of the electric field at the wafer surface, during the high-voltage blocking mode of operation of the SiC MPS diode.
  • Fig. 33AA to Fig. 33AL describes the process of manufacturing the structure shown in Fig. 32A.
  • the manufacturing process of the device includes preparing a SiC wafer in Fig. 33AA which consists of a highly conductive N+ substrate 701a and an N- drift region 702a, where the N- drift region is typically epi-grown.
  • the N- drift region 702a is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance.
  • a set of multiple ion implantation steps with an n-type species 703a such as nitrogen and/or phosphorus is performed onto the active region of the device in Fig. 33 AB.
  • the set of multiple ion implantation steps with the n-type species forms a set of sub n-type regions 704a in Fig. 33 AC where each sub region is defined by the dotted line in the schematic for indicating the top and bottom of the sub region and all sub regions are interconnected.
  • the interconnected sub regions consist of the N+ region as a whole.
  • the edge termination which is not shown needs to be masked during the set of n-type ion implantation steps.
  • the n-type ion implantation steps 703a needs to be performed in such a fashion that the N+ region 704a is completely buried inside the N- drift region in Fig. 33AC.
  • the ion implantation steps should form the N+ region 704a where the top of the N+ region is physically off from the wafer surface.
  • a patterned mask 705a which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33 AD.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a p-type ion implantation step with a p-type impurity 706a such as aluminum and/or boron is performed in Fig. 33AE to form a set of multiple P+ wells 707a in Fig. 33AF.
  • the bottoms of the set of multiple P+ wells 707a are formed such that they are above the bottom of the N+ region 704a.
  • the depth of the set of multiple P+ wells are less than the depth of the N+ region.
  • the set of multiple P+ wells lead to a P+ region as a whole in Fig. 33AF.
  • the edge termination region which is not shown may be formed by the p- type ion implantation step.
  • the patterned mask 705a is removed by dry or wet etching process in Fig. 33AG. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 708a marked as METAL 1 directly on the wafer surface in Fig. 33AH.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 709a marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 33 AJ.
  • the thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 710a on the back side of the wafer is then formed in Fig. 33AK.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 711a marked as METAL 3 is formed on the back side of the wafer in Fig. 33AL.
  • the second pad metal can be of Aluminum or Aluminum- based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with.
  • the SiC wafer consists of multiple n-type epi-grown layers in Fig. 33AC with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer.
  • an N- drift layer 702a can be epi- grown for serving as a drift/blocking layer.
  • a number of n-type epilayers can be grown to form an N+ region 704a as a whole which consists of a set of sub n-type regions where each sub region is defined by different doping concentration and thickness and all sub regions are interconnected.
  • an N- layer can be formed which reaches to the surface of the SIC wafer 702a.
  • a patterned mask 705a which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33AD.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a p-type ion implantation step with a p-type impurity 706a such as aluminum and/or boron is performed in Fig. 33AE to form a set of multiple P+ wells 707a in Fig. 33AF.
  • the bottoms of the set of multiple P+ wells 707a are formed such that they are above the bottom of the N+ region 704a. In the embodiments herein, the depth of the set of multiple P+ wells are less than the depth of the N+ region.
  • the set of multiple P+ wells lead to a P+ region as a whole in Fig. 33AF.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 705a is removed by dry or wet etching process in Fig. 33 AG. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 708a marked as METAL 1 directly on the wafer surface in Fig. 33AH.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 709a marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 gm in Fig. 33 AJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 710a on the back side of the wafer is then formed in Fig. 33AK.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 711a marked as METAL 3 is formed on the back side of the wafer in Fig. 33 AL.
  • the second pad metal can be of Aluminum or Aluminum- based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • Fig. 33BA to Fig. 33BL describes the process of manufacturing the structure shown in Fig. 32B.
  • the manufacturing process of the device includes preparing a SiC wafer in Fig. 33BA which consists of a highly conductive N+ substrate 701b and an N- drift region 702b, where the N- drift region is typically epi-grown.
  • the N- drift region 702b is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance.
  • a set of multiple ion implantation steps with an n-type species 703b such as nitrogen and/or phosphorus is performed onto the active region of the device in Fig. 33BB.
  • the set of multiple ion implantation steps with the n-type species forms a set of sub n-type regions 704b in Fig. 33BC where each sub region is defined by the dotted line in the schematic for indicating the top and bottom of the sub region and all sub regions are interconnected.
  • the interconnected sub regions consist of the N+ region as a whole.
  • the edge termination which is not shown needs to be masked during the set of n-type ion implantation steps.
  • the n-type ion implantation steps 703b needs to be performed in such a fashion that the N+ region 704b is completely buried inside the N- drift region in Fig. 33BC.
  • the ion implantation steps should form the N+ region 704b where the top of the N+ region is physically off from the wafer surface.
  • a patterned mask 705b which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33BD.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a p-type ion implantation step with a p-type impurity 706b such as aluminum and/or boron is performed in Fig. 33BE to form a set of multiple P+ wells 707b in Fig. 33BF.
  • the bottoms of the set of multiple P+ wells 707b are formed such that they are below the bottom of the N+ region 704b.
  • the depth of the set of multiple P+ wells are greater than the depth of the N+ region.
  • the set of multiple P+ wells lead to a P+ region as a whole in Fig. 33BF.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 705b is removed by dry or wet etching process in Fig. 33BG. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 708b marked as METAL 1 directly on the wafer surface in Fig. 33BH.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 709b marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 33BJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 710b on the back side of the wafer is then formed in Fig. 33BK.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 711b marked as METAL 3 is formed on the back side of the wafer in Fig. 33BL.
  • the second pad metal can be of Aluminum or Aluminum- based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with.
  • the SiC wafer consists of multiple n-type epi-grown layers in Fig. 33BC with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer.
  • an N- drift layer 702b can be epi- grown for serving as a drift/blocking layer.
  • N- drift layer On top of the N- drift layer, a number of n-type epilayers can be grown to form an N+ region 704b as a whole which consists of a set of sub n-type regions where each sub region is defined by different doping concentration and thickness and all sub regions are interconnected. On top of the buried N+ region, an N- layer can be formed which reaches to the surface of the SIC wafer 702b.
  • a patterned mask 705b which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33BD.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a p-type ion implantation step with a p-type impurity 706b such as aluminum and/or boron is performed in Fig. 33BE to form a set of multiple P+ wells 707b in Fig. 33BF.
  • the bottoms of the set of multiple P+ wells 707b are formed such that they are below the bottom of the N+ region 704b. In the embodiments herein, the depth of the set of multiple P+ wells are greater than the depth of the N+ region.
  • the set of multiple P+ wells lead to a P+ region as a whole in Fig. 33BF.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 705b is removed by dry or wet etching process in Fig. 33BG. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 708b marked as METAL 1 directly on the wafer surface in Fig. 33BH.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 709b marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 33BJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 710b on the back side of the wafer is then formed in Fig. 33BK.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 711b marked as METAL 3 is formed on the back side of the wafer in Fig. 33BL.
  • the second pad metal can be of Aluminum or Aluminum- based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • Fig. 33EA to Fig. 33EL describes the process of manufacturing the structure shown in Fig. 32E.
  • the manufacturing process of the device includes preparing a SiC wafer in Fig. 33EA which consists of a highly conductive N+ substrate 701e and an N- drift region 702e, where the N- drift region is typically epi-grown.
  • the N- drift region 702e is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance.
  • a set of multiple ion implantation steps with an n-type species 703e such as nitrogen and/or phosphorus is performed onto the active region of the device in Fig. 33EB.
  • the set of multiple ion implantation steps with the n-type species forms a set of sub n-type regions 704e in Fig. 33EC where each sub region is defined by the dotted line in the schematic for indicating the top and bottom of the sub region and all sub regions are interconnected.
  • the interconnected sub regions consist of the N+ region as a whole.
  • the edge termination which is not shown needs to be masked during the set of n-type ion implantation steps.
  • the n-type ion implantation steps 703e needs to be performed in such a fashion that the N+ region 704e is completely buried inside the N- drift region in Fig. 33EC.
  • the ion implantation steps should form the N+ region 704e where the top of the N+ region is physically off from the wafer surface.
  • a patterned mask 705e which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33ED.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a set of multiple ion implantation steps with a p-type impurity 706e such as aluminum and/or boron is performed in Fig. 33EE to form a set of multiple P+ wells 707e in Fig. 33EF.
  • the set of multiple ion implantation steps with the p-type species forms a set of sub p-type regions 707e in Fig.
  • the P+ region 707e is formed by multiple P sub-regions.
  • the bottoms of the set of multiple P+ wells 707e are formed such that they are above the bottom of the N+ region 704e. In the embodiments herein, the depth of the set of multiple P+ wells are less than the depth of the N+ region.
  • the set of multiple P+ wells lead to a P+ region as a whole in Fig. 33EF.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 705e is removed by dry or wet etching process in Fig. 33EG.
  • a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 708e marked as METAL 1 directly on the wafer surface in Fig. 5FEH.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 709e marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 33EJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 710e on the back side of the wafer is then formed in Fig. 33EK.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 711e marked as METAL 3 is formed on the back side of the wafer in Fig. 33EL.
  • the second pad metal can be of Aluminum or Aluminum- based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with.
  • the SiC wafer consists of multiple n-type epi-grown layers in Fig. 33EC with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer.
  • an N- drift layer 702e can be epi- grown for serving as a drift/blocking layer.
  • N- drift layer On top of the N- drift layer, a number of n-type epilayers can be grown to form an N+ region 704e as a whole which consists of a set of sub n-type regions where each sub region is defined by different doping concentration and thickness and all sub regions are interconnected. On top of the buried N+ region, an N- layer can be formed which reaches to the surface of the SIC wafer 702e.
  • a patterned mask 705e which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33ED.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a set of multiple ion implantation steps with a p-type impurity 706e such as aluminum and/or boron is performed in Fig. 33EE to form a set of multiple P+ wells 707e in Fig. 33EF.
  • the set of multiple ion implantation steps with the p-type species forms a set of sub p-type regions 707e in Fig. 33EF where each sub region is defined by the dotted line in the schematic for indicating the top and bottom of the sub region and all sub regions are interconnected.
  • the P+ region 707e is formed by multiple P sub-regions.
  • the bottoms of the set of multiple P+ wells 707e are formed such that they are above the bottom of the N+ region 704e. In the embodiments herein, the depth of the set of multiple P+ wells is less than the depth of the N+ region.
  • the set of multiple P+ wells leads to a P+ region as a whole in Fig. 33EF.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 705e is removed by dry or wet etching process in Fig. 33EG. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 708e marked as METAL 1 directly on the wafer surface in Fig. 33EH.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 709e marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 33EJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 710e on the back side of the wafer is then formed in Fig. 33EK.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 711e marked as METAL 3 is formed on the back side of the wafer in Fig. 33EL.
  • the second pad metal can be of Aluminum or Aluminum- based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • Fig. 33FA to Fig. 33FL describes the process of manufacturing the structure shown in Fig. 32F.
  • the manufacturing process of the device includes preparing a SiC wafer in Fig. 33FA which consists of a highly conductive N+ substrate 701f and an N- drift region 702f, where the N- drift region is typically epi-grown.
  • the N- drift region 702f is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance.
  • a set of multiple ion implantation steps with an n-type species 703f such as nitrogen and/or phosphorus is performed onto the active region of the device in Fig. 33FB.
  • the set of multiple ion implantation steps with the n-type species forms a set of sub n-type regions 704f in Fig. 33FC where each sub region is defined by the dotted line in the schematic for indicating the top and bottom of the sub region and all sub regions are interconnected.
  • the interconnected sub regions consist of the N+ region as a whole.
  • the edge termination which is not shown needs to be masked during the set of n-type ion implantation steps. It is important to note that the n-type ion implantation steps 703f needs to be performed in such a fashion that the N+ region 704f is completely buried inside the N- drift region in Fig. 33FC.
  • the ion implantation steps should form the N+ region 704f where the top of the N+ region is physically off from the wafer surface.
  • a patterned mask 705f which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33FD.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a set of multiple ion implantation steps with a p-type impurity 706f such as aluminum and/or boron is performed in Fig. 33FE to form a set of multiple P+ wells 707f in Fig. 33FF.
  • the set of multiple ion implantation steps with the p-type species forms a set of sub p-type regions 707f in Fig.
  • the P+ region 707f is formed by multiple P sub-regions.
  • the bottoms of the set of multiple P+ wells 707f are formed such that they are below the bottom of the N+ region 704f. In the embodiments herein, the depth of the set of multiple P+ wells is greater than the depth of the N+ region.
  • the set of multiple P+ wells leads to a P+ region as a whole in Fig. 33FF.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 705f is removed by dry or wet etching process in Fig. 33FG.
  • a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 708f marked as METAL 1 directly on the wafer surface in Fig. 33FH.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 709f marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 33FJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 710f on the back side of the wafer is then formed in Fig. 33FK.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 711f marked as METAL 3 is formed on the back side of the wafer in Fig. 33FL.
  • the second pad metal can be of Aluminum or Aluminum- based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with.
  • the SiC wafer consists of multiple n-type epi-grown layers in Fig. 33FC with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer.
  • an N- drift layer 702f can be epi- grown for serving as a drift/blocking layer.
  • N- drift layer On top of the N- drift layer, a number of n-type epilayers can be grown to form an N+ region 704f as a whole which consists of a set of sub n-type regions where each sub region is defined by different doping concentration and thickness and all sub regions are interconnected. On top of the buried N+ region, an N- layer can be formed which reaches to the surface of the SIC wafer 702f.
  • a patterned mask 705f which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 33FD.
  • the patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a set of multiple ion implantation steps with a p-type impurity 706f such as aluminum and/or boron is performed in Fig. 33FE to form a set of multiple P+ wells 707f in Fig. 33FF.
  • the set of multiple ion implantation steps with the p-type species forms a set of sub p-type regions 707f in Fig. 33FF where each sub region is defined by the dotted line in the schematic for indicating the top and bottom of the sub region and all sub regions are interconnected.
  • the P+ region 707f is formed by multiple P sub-regions.
  • the bottoms of the set of multiple P+ wells 707f are formed such that they are below the bottom of the N+ region 704f. In the embodiments herein, the depth of the set of multiple P+ wells is greater than the depth of the N+ region.
  • the set of multiple P+ wells leads to a P+ region as a whole in Fig. 33FF.
  • the edge termination region which is not shown may be formed by the p-type ion implantation step.
  • the patterned mask 705f is removed by dry or wet etching process in Fig. 33FG. This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 708f marked as METAL 1 directly on the wafer surface in Fig. 33FH.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 709f marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 33FJ. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 710f on the back side of the wafer is then formed in Fig. 33FK.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 711f marked as METAL 3 is formed on the back side of the wafer in Fig. 33FL.
  • the second pad metal can be of Aluminum or Aluminum- based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • the doping concentration of the sub-regions can be appropriately fine-tuned to realize more optimum trade-off between the reverse leakage current and on-state voltage drop.
  • the doping concentration in the n-type subregions farther away from the SiC surface can be made progressively higher, which may benefit from lower conduction losses.
  • the doping concentration in the p-type sub-regions farther away from the SiC surface can be made progressively lower, which may enable better blocking characteristics.
  • Fig. 34 In the device of shown in Fig. 34 is the cross-sectional schematic of the SiC MPS diode.
  • the key regions of this device are an N+ substrate 801 at the bottom which gives mechanical support of the wafer and is -350 pm-thick.
  • An N- drift region 802 which is usually an epi layer and is on top of the N+ substrate.
  • P+ wells 804 There are two different types of P+ wells depending on their depths which are in comparison to the depth of the N+ layer.
  • the P+ wells 804 whose depths are less than the depth of the N+ layer 803 is called a first P+ wells while other P+ wells 805 whose depths are greater than the depth of the N+ layer 803 is called a second P+ wells.
  • the N+ layer 803 is formed in such a way to completely surround the first P+ wells 804 and allow the second P+ wells 805 to completely penetrate the N+ layer which exposes the bottom of the second P+ wells 805 to the N- drift region 802.
  • the device has a first metal layer 806 denoted as METAL 1, which is the Schottky metal to an n-type SiC semiconductor region and forms Schottky contact to its underlying n-type regions.
  • the device has a second metal layer 807 denoted as METAL 2 on the front side of the wafer which is in contact with the METAL 1.
  • METAL 2 is often called “power metal” and is usually in Aluminum.
  • silicide layer 808 under the bottom of the N+ substrate.
  • the device shown in Fig. 34 has a N+ region 803 which is interspersed between a set of two different types of P+ wells depending on their depths which are in comparison to the depth of the N+ layer.
  • the P+ wells 804 whose depths are less than the depth of the N+ layer 803 is called a first P+ wells while other P+ wells 805 whose depths are greater than the depth of the N+ layer 803 is called a second P+ wells.
  • the N+ layer 803 is formed in such a way to completely surround the first P+ wells 804 and allow the second P+ wells 805 to completely penetrate the N+ layer which exposes the bottom of the second P+ wells 805 to the N- drift region 802.
  • the physical separation of the N+ region from a SiC wafer surface is a critical feature of the embodiment described herein and distinguishes it from other similar inventions.
  • a part of the SiC wafer which is in contact with a Schottky metal 806 denoted as METAL 1 and is an n-type semiconductor has the same doping concentration of the N- drift 802.
  • the doping concentration of the n-type SiC semiconductor which is in direct contact with the Schottky metal 806 labeled METAL 1 is critical for reducing the strength of the electric field at the wafer surface, during the high-voltage blocking mode of operation of the SiC MPS diode.
  • Fig. 35 A to Fig. 35P describes the process of manufacturing the structure shown in Fig. 34.
  • the manufacturing process of the device includes preparing a SiC wafer in Fig. 35 A which consists of a highly conductive N+ substrate 901 and an N- drift region 902, where the N- drift region is typically epi-grown.
  • the N- drift region 902 is designed in such a way that the doping concentration and thickness of the N- drift region are primarily selected based on the required blocking performance.
  • an ion implantation step with an n-type species 903 such as nitrogen and/or phosphorus is performed onto the active region of the device in Fig. 35B forming an N+ region within the N- drift region.
  • the edge termination which is not shown needs to be masked during the n-type ion implantation step. It is important to note that the n-type ion implantation step 903 needs to be performed in such a fashion that the N+ region 904 is completely buried inside the N- drift region in Fig. 35C. The ion implantation step should form the N+ region 904 where the top of the N+ region is physically off from the wafer surface.
  • a first patterned mask 905 which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 35D.
  • the first patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a first p-type ion implantation step with a p-type impurity 906 such as aluminum and/or boron is performed in Fig. 35E to form a first set of multiple P+ wells 907 in Fig. 35F.
  • the depths of the first set of multiple P+ wells 907 are formed such that they are completely surrounded by the N+ region 904. In the embodiments herein, the depth of the first set of multiple P+ wells is less than the depth of the N+ region.
  • the first patterned mask 909 is removed by dry or wet etching process in Fig. 35G.
  • a second patterned mask 908 which preferably is a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 35H.
  • the second patterned 908 mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a second p-type ion implantation step 909 with a p-type impurity such as aluminum and/or boron is performed in Fig. 351 in such a way to form a second multiple P+ wells where the bottom of the second set of multiple P+ wells 910 is below the bottom of the N+ region 904 in Fig. 35 J.
  • the first set of multiple P+ wells and the second set of multiple P+ wells lead to a P+ region as a whole.
  • the edge termination region which is not shown may be formed by the first p-type ion implantation step and/or the second p-type ion implantation step.
  • the second patterned mask 908 is removed by dry or wet etching process in Fig. 35K. [00589] This is followed by a process step to electrically activate all the implanted impurity species by coating the wafer with a suitable coating material such as a carbon cap and annealing at high temperature such as 1700°C.
  • the active region is then defined by forming a field oxide layer on the entire wafer surface and clearing out a part of the field oxide where the conduction current needs to flow for on-state operation of the device.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 911 marked as METAL 1 directly on the wafer surface in Fig. 35L.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 912 marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 35N. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer. [00591]
  • a silicide region 913 on the back side of the wafer is then formed in Fig. 350.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 914 marked as METAL 3 is formed on the back side of the wafer in Fig. 35P.
  • the second pad metal can be of Aluminum or Aluminum-based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • Another method to fabricate this embodiment is to use a SiC wafer with multiple n-type epi-grown layers to start with.
  • the SiC wafer consists of three n-type epi-grown layers in Fig. 35C with different doping concentrations and thicknesses and the N+ substrate at the bottom of the SiC wafer.
  • the three n-type epi-grown layers should be formed in such a way that an N- layer 902 is meeting a device side of the wafer and an N+ layer 904 is positioned right underneath the N- layer, where the N+ layer is on top of a second N- layer also labeled 902 which serves as a drift region and the second N- layer is positioned on top of the N+ substrate 901.
  • a first patterned mask 905 which is preferably a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 35D.
  • the first patterned mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a first p-type ion implantation step with a p-type impurity 906 such as aluminum and/or boron is performed in Fig. 35E to form a first set of multiple P+ wells 907 in Fig. 35F.
  • the depths of the first set of multiple P+ wells 907 are formed such that they are completely surrounded by the N+ region 904. In the embodiments herein, the depth of the first set of multiple P+ wells is less than the depth of the N+ region.
  • the first patterned mask 909 is removed by dry or wet etching process in Fig. 35G.
  • a second patterned mask 908 which preferably is a hard mask made of such as an oxide, a nitride, a polysilicon layer, or a combination of these, is formed on the wafer surface in Fig. 35H.
  • the second patterned 908 mask must be thick enough to completely block any high energy impurities during the subsequent ion implant step.
  • a second p-type ion implantation step 909 with a p-type impurity such as aluminum and/or boron is performed in Fig. 351 in such a way to form a second multiple P+ wells where the bottom of the second set of multiple P+ wells 910 is below the bottom of the N+ region 904 in Fig. 35 J.
  • the first set of multiple P+ wells and the second set of multiple P+ wells lead to a P+ region as a whole.
  • the edge termination region which is not shown may be formed by the first p-type ion implantation step and/or the second p-type ion implantation step.
  • the second patterned mask 908 is removed by dry or wet etching process in Fig. 35K.
  • the Schottky contact is formed on the wafer surface by depositing a Schottky metal 911 marked as METAL 1 directly on the wafer surface in Fig. 35L.
  • the deposited Schottky metal layer is then patterned by using dry etching, wet etching, or lift-off process and annealed at a certain temperature for a certain amount of time by using a furnace or RTA.
  • the thermal budget of the annealing step after the Schottky metal deposition needs to be carefully designed and controlled because it directly affects the barrier height of the Schottky contact.
  • a first pad metal 912 marked as METAL 2 is then deposited on top of the wafer in Fig.
  • the first pad metal can be of Aluminum/ Aluminum-based alloy.
  • the wafer is then thinned from its back side until its thickness reaches to a target thickness of 100 ⁇ 200 pm in Fig. 35N. The thickness may be further reduced in the future when the wafer thinning technology improves and provides the target thickness less than the aforementioned 100 ⁇ 200 pm.
  • the wafer thinning can be accomplished by CMP, wet etching, dry etching, or a combination of the aforementioned grinding techniques with a proper protective coating at the front side of the wafer.
  • a silicide region 913 on the back side of the wafer is then formed in Fig. 350.
  • the silicide region is required to form a good ohmic contact on the back side of the wafer.
  • the silicide region is formed by depositing ohmic metal stack and annealing the wafer by using a laser annealing technique as an example.
  • a second pad metal 914 marked as METAL 3 is formed on the back side of the wafer in Fig. 35P.
  • the second pad metal can be of Aluminum or Aluminum-based alloy.
  • a protective coating process step may be followed on top of the wafer to form a moisture barrier.
  • the device of embodiment shown in Fig. 34 combines the desirable features of the devices shown in embodiments described in Fig. 28A and Fig. 30.
  • the first P+ wells that are formed deeper than the N+ layer may serve to inject minority carriers into the N+ drift layer under surge current conditions and the second P+ wells that are completely enclosed by the N+ layer reduce the spreading resistance of the diode current as it spreads vertically from the region in-between the p-type wells to the N- drift layer.
  • the device of embodiment is constructed with both first and second type P+ wells to exploit both aforementioned benefits of the first and second P+ wells, respectively.
  • the proportion of the first and second type P+ wells may be appropriately adjusted to yield a diode that is either tuned for lower conduction losses or one that is designed for withstanding higher surge currents.
  • Fig. 36A shows blocking performances of the devices of this invention with varying ratio of Wl/Dl that ranges from 1.0 to 3.0 and blocking performance of the device of the prior art with a fixed ratio of Wl/Dl which is equal to 3.0.
  • Fig. 36A shows the statistical distribution of the measured blocking voltages of the devices described the various embodiments herein. With a targeted breakdown voltage for these devices at 650 V, the median value of each distribution is highlighted. A leakage current of 10 pA is used as a criteria to measure the blocking voltages and the blocking voltages are greater than the target of 650 V. The measured blocking voltages of the devices of this invention whose ratio of Wl/Dl is varied from 1.0 to 2.5 are greater than 650 V. The case when the ratio of Wl/Dl equals to 3.0, however, shows its blocking voltage distribution spreads out from 500 V to 730 V where a large portion of the distribution is below the targeted 650 V.
  • Fig. 36B shows the blocking I-V curves of the devices of this invention with varying ratio of Wl/Dl (i.e., 2.0, 2.5 and 3.0).
  • Fig. 36B shows that all the devices with the exception of the device of this invention where the radio of Wl/Dl equals to 3.0 block at 650 V with their leakage current kept less than 10 pA which is used as the blocking criterion as mentioned earlier.
  • the device of this invention with the ratio of Wl/Dl that equals to 3.0 shows high leakage current of 22 pA which is above 10 pA.
  • the device of this invention with the ratio of Wl/Dl of 3.0 Due to the high leakage current density of the device of this invention with the ratio of Wl/Dl of 3.0 at the targeted rated voltage of 650 V, the device of this invention with the ratio of Wl/Dl of 3.0 is not adequate for the use. Based on the discussion on the blocking performance, it is clear that the ratio of Wl/Dl of the devices of this invention should be less than 3.0 to meet the targeted blocking voltage of 650 V.
  • Fig. 36C is the forward I-V curves of the devices of this invention with varying ratio of Wl/Dl that ranges from 2.0 to 3.0.
  • Fig. 36C shows that increasing the ratio of Wl/Dl from 2.0 to 3.0 decreases the forward conduction loss.
  • the device of this invention of the ratio of Wl/Dl of 3.0 shows the best forward conduction performance, however due to the aforementioned poor blocking performance of the device, the device is not suitable for the use of 650 V applications.
  • Fig. 36D shows the performance of differential specific on-resistances of the devices of this invention with varying ratio of Wl/Dl that ranges from 2.0 to 3.0.
  • Fig. 36D shows the statistical distribution of the measured differential specific on-resistances of the devices of this invention. The median value of each distribution is highlighted in bold.
  • the differential specific on-resistance drops as the ratio of W 1/DI increases. This trend agrees with the observation made on the forward I-V curves in Fig. 36C.
  • the device of this invention of the ratio of Wl/Dl of 3.0 shows the best forward conduction performance, the device should not be considered to be appropriate due to its poor blocking performance as mentioned earlier.
  • the devices of this invention show improvement in both the forward and blocking performance is only valid when the ratio of Wl/Dl is less than 3.0.
  • FIG. 37A shows a cross-sectional device structure of a double-implanted MOSFET or DMOSFET.
  • the DMOSFET structure comprises a N+ substrate 1101, N-Drift (or Voltage Blocking) Region 1102, p-well Region 1109, N+ source 1108 and P+ Body (or p-well contact) regions 1104.
  • a silicide layer 1107 is formed on the N+ and P+ regions to form the source ohmic contact.
  • the gate dielectric 1110 and gate metal layers 1111 are successively formed on the SiC surface 1107, which together constitute the metal-oxide- semiconductor (MOS) structure.
  • An inter-level dielectric or ILD layer 1112 separates the Gate metal 1 111 from the metal 1 layer 1113 which contacts the interspersed Source ohmic contact regions.
  • An additional n-type layer 1103 is formed that is not in contact with the gate dielectric layer 1110.
  • the additional n-type layer 1103 is formed such that in vertical direction, it is completely enclosed by the N-drift layer 1105.
  • the doping concentration of the n-type layer 1103 should be higher than that of the N-drift layer 1105.
  • the doping concentration of the n-type layer 1103 could be in the range of 1E15 cm-3 to 1E19 cm-3. Except for the gate dielectric layer 1110 in DMOSFET, the design of this n-type layer follows identical considerations.
  • the vertical extent of this n-type layer 1103 is greater than the p-well region 1109, but the n-type layer 1103 could also be designed such that its vertical extent is smaller than the vertical extent of the p-well region.
  • Figs. 40A to 40C show the vertical extent of n-type layer 1103 with respect to the vertical extent of the p-well region 1109. In an embodiment, according to Fig. 40A, the n-type layer 1103 vertical extent is smaller than the vertical extent of the p-well region 1109. In another embodiment, according to Fig. 40B, the vertical extent of n-type layer 1103 is greater than the vertical extent of the p-well region 1109. In another embodiment, according to Fig. 40C, the n-type layer 1103 vertical extent is greater than the vertical extent of the p-well region 1109 but lateral extent is smaller and is non-continuous or interrupted i.e., having gaps.
  • Figs. 42A to 42D depicts the process steps for fabrication of Power DMOSFET.
  • the starting silicon carbide wafer comprises a N-drift layer 1602 formed on top of a N+ substrate 1601.
  • the N-Layer 1603 can be formed either by ion-implantation or by epitaxial growth. If the N- layer 1603 is formed using epitaxial growth, this needs to be followed by the growth of an additional n-type layer 1603 with the same doping concentration as the N-drift layer 1602.
  • the n-type layer 1603 may be formed using either Nitrogen or Phosphorus as the n-type implanted species.
  • the implant energy may be in the range of 50 keV to 4 MeV and the implanted dose may be in the range of 1E10 cm-2 to 1E14 cm-2.
  • An example of the n-type 1603 formed using ion-implantation is shown in Fig. 38. Notice that the n-type layer 1603 is completely buried within the N-drift layer 1602. Following this, appropriate ion-implantation steps may be utilized to realize the p-well 1609, N+ source 1608 and P+ regions 1604. Fig.
  • 42C and 42D shows the remainder of the steps for the DMOSFET fabrication which include post-implantation annealing, gate dielectric 1610 and gate metal 1611 formation, silicide 1607 formation for ohmic contacts, ILD layer 1612 and final pad metal layer deposition 1613.
  • the incorporation of the additional n-type layer into the DMOSFET structures enables a better trade-off between reducing the on-state resistance of the device and maintaining a low electric field in the gate dielectric layer.
  • the DMOSFET device structure can result in high electric field concentration at the corner of the P-well region, which results in a high electric field in the gate oxide layer, especially during high drain bias (blocking mode) operation.
  • the high critical electric fields for breakdown in 4H-SiC ( ⁇ 3 MV/cm) results in a very high (> 5 MV/cm) electric field in the gate oxide.
  • FIG. 37B shows a cross-sectional schematic of a vertical JFET structure.
  • Fig. 37B shows a cross-sectional schematic of a vertical JFET.
  • the JFET comprises a N+ substrate 1120, N- Drift (or Voltage Blocking) Region 1121, P+ gate Region 1123, N+ source 1126, ohmic contact and pad metallization layers.
  • An inter-level dielectric or ILD layer 1124 separates the Gate Metal from the metal 1 layer 1127 which contacts the interspersed Source ohmic contact regions.
  • an additional n-type layer 1122 is formed that is not in contact with the N+ source layer 1126.
  • the additional n-type layer 1122 is formed such that in a vertical direction, it is completely enclosed by the N-drift layer 1121.
  • the doping concentration of the n-type layer 1122 should be higher than that of the N-drift layer 1121.
  • the doping concentration of the n-type layer could be in the range of 1E15 cm-3 to 1E19 cm-3. Except for the N+ source layer 1126 in vertical JFET, the design of this n-type layer follows identical considerations.
  • the vertical extent of this n-type layer 1112 is smaller the P+ gate region 1123, but the n-type layer 1112 could also be designed such that its vertical extent is larger than the vertical extent of the P+ gate region 1123.
  • Figs. 39A to 39C show the vertical extent of n-type layer with respect to the vertical extent of the P+ gate region.
  • the n- type layer 1303 vertical extent is smaller than the vertical extent of the P+ gate region 1304.
  • the n-type layer 1303 vertical extent is greater than the vertical extent of the P+ gate region 1304.
  • the n-type layer 1303 vertical extent is greater than the vertical extent of the P+ gate region 1304 but lateral extent is smaller and is non-continuous or interrupted i.e., having gaps.
  • Figs. 41 A to 41E depicts the process steps for fabrication of Vertical JFET.
  • the starting silicon carbide wafer comprises a N-drift layer 1502 formed on top of a N+ substrate 1501.
  • the n-type Layer 1503 can be formed either by ion-implantation or by epitaxial growth. If the n-type layer 1503 is formed using epitaxial growth, this needs to be followed by the growth of an additional n-type layer with the same doping concentration as the N-drift layer 1502.
  • the n-type layer 1503 may be formed using either Nitrogen or Phosphorus as the n-type implanted species.
  • the implant energy for the n-type layer 1503 may be in the range of 50 keV to 4 MeV and the implanted dose may be in the range of 1E10 cm-2 to 1E14 cm-2.
  • Appropriate ion-implantation steps may be utilized to realize the P+ gate 1504, N+ source regions 1508.
  • the N+ source region 1508 may also be formed using epitaxial growth, as part of the starting wafer.
  • the remainder of the steps for the JFET fabrication include post-implantation annealing, silicide formation 1507 for gate and source ohmic contacts, ILD layer 1506 formation and final pad metal layer 1509 deposition.
  • n-type layer is strategically placed in the so-called channel region of the JFET, and we will refer to this doping concentration as Nch or the channel doping concentration.
  • VGS is the gate-to- source voltage (a negative voltage for a reverse-biased PN junction)
  • Vbi the built-in potential barrier
  • Vpo is the internal pinch-off voltage. This voltage is not the gate-to-source voltage to obtain the pinch-off condition. From the above equations, the pinch-off voltage (threshold voltage) is defined by Equation (3) and Equation (4).
  • the built-in potential is approximately 2.5 V at room temperature.
  • Equation (4) is the basis for designing the channel of the JFET.
  • the channel doping (N C h) has to be chosen according to Equation (4).
  • the above analysis assumes a uniform JFET channel.
  • the n-type channel doping can be designed in a non-uniform manner.
  • the highest doping in this layer can be advantageously realized, where the JFET channel is at its narrowest, with a lower doping in other regions of the JFET channel. Ion -implantation enables the realization of such arbitrary doping profiles.
  • Fig. 43 A and Fig. 43B show the output and breakdown I-V characteristics of 1200 V SiC DMOSFETs fabricated using the teachings of this invention. A specific on-resistance of 2.9 mQ- cm2, gate threshold voltage of 3.0 V and breakdown voltages in the 1400 V - 1500 V range are achieved.
  • Fig. 44A and Fig. 44B show the transfer (ID v/s VGS) characteristics of 1200 V SiC MOSFETs fabricated using the teachings of this invention are shown.
  • the devices feature a gate threshold voltage of 2.9 V, a sub-threshold slope of 150 mV/decade and a transconductance of 9.2 S measured at a drain current of 20 A.
  • Fig. 45 shows a single-pulse avalanche energy of 1.05 J is measured for a 1200 V SiC MOSFET fabricated using the teachings of this invention. This corresponds to an energy density of 15.4 J/cm 2 , when normalized to the total chip size (Avalanche Energy/Chip Size).
  • Fig. 46 is a photograph showing a SiC DMOSFET fabricated using the teachings of these inventions and tested for single-pulse avalanche energy test.
  • Fig. 47A and Fig. 47B are output characteristics of two 3.3 kV SiC MOSFETs fabricated using the teachings of this invention are shown.
  • the Fig. 15a device features a gate threshold voltage of 2.5 V
  • the Fig. 15b device features a gate threshold voltage of 3.8 V.
  • the higher gate threshold voltage is achieved by employing the novel non-uniformly doped channel concept introduced in this invention.
  • Fig. 47C is the transfer characteristics of two 3.3 kV SiC MOSFETs fabricated using the teachings of these inventions.
  • Fig. 47D is a short-circuit test measured for two 3.3 kV SiC MOSFETs fabricated using the teachings of this invention.
  • Embodiments relate to silicon carbide (SiC) DMOSFET power devices having increased third quadrant cross over current.
  • An embodiment relates to tuning the turn-on voltage of one or more body diode regions of the DMOSFET.
  • An embodiment relates to reducing injection of minority carriers during conduction of the one or more body diode regions.
  • An embodiment relates to tuning source contact resistance of the one or more body diode regions of the DMOSFET.
  • An embodiment relates to mitigate basal plane dislocation (BPD).
  • An embodiment relates to formation of a first conductivity type second source region between a silicide layer and a second conductivity type well region of the DMOSFET.
  • An embodiment relates to formation of a first metal region in direct contact with a second conductivity type well contact region.
  • An embodiment relates to connecting one or more Schottky diode regions in series with the one or more body diode regions of the DMOSFET.
  • An embodiment relates to formation of the second conductivity type well contact region that meanders and comprises a periodic spacing between the first conductivity type source region and the second conductivity type well contact region.
  • An embodiment relates to formation of the second conductivity type well contact region that meanders and enables the second conductivity type well region to be contact in with a source metal only through the second conductivity type well contact region.
  • An embodiment relates to a power DMOSFET device structure designed to handle significant power level includes an intrinsic anti-parallel p-n junction diode, formed between the body and well regions, respectively.
  • the anti-parallel p-n junction diode within the power DMOSFET structure conducts during third quadrant operation of the power DMOSFET.
  • the third quadrant operation occurs when source terminal is biased positively with respect to drain terminal, a situation that is commonly encountered when power MOSFETs are utilized in motor control related power conversion applications.
  • a Schottky diode is either externally or internally connected in an anti-parallel with the intrinsic p-n body diode of the DMOSFET. In this scenario, there exists a specific crossover current, above which the current still flows mainly through the p-n diode, despite the connection of the Schottky diode.
  • An embodiment relates to a Silicon Carbide (SiC) double-implantation metal oxide semiconductor field effect transistor (DMOSFET) with increased cross over current.
  • the magnitude of the cross over current of the DMOSFET is increased by at least one of increasing built-in potential (e.g., turn-on voltage) of the one or more body diode regions of the DMOSFET and reducing injection of minority carriers during conduction of the one or more body diode regions.
  • the SiC DMOSFET is a n-type planar gate DMOSFET.
  • the SiC DMOSFET is a p-type planar gate DMOSFET.
  • the SiC DMOSFET is a n-type trench gate DMOSFET. In yet another embodiment, the SiC DMOSFET is a p-type trench gate DMOSFET.
  • the magnitude of the cross over current is increased by performing below embodiments. The below embodiments are described specifically with respect to the n-type planar gate DMOSFET.
  • each unit cell of the DMOSFET comprises a second N+ source region between a silicide layer and a p-well region to impact the turn-on voltage of the one or more body diode regions of the DMOSFET.
  • each unit cell of the DMOSFET comprises a first metal region in direct contact with a P+ region to connect one or more Schottky diode regions in series with the one or more body diode regions of the DMOSFET to impact the turn-on voltage of the one or more body diode regions of the DMOSFET.
  • each unit cell of the DMOSFET comprises the P+ region that meanders and comprises a periodic spacing between a N+ source region and the P+ region to form periodic contacts to a first pad metal (e.g., a source metal) via the silicide layer between interlayer dielectric bumps (ILD) to impact the differential on-resistance of the one or more body diode regions of the DMOSFET.
  • a first pad metal e.g., a source metal
  • ILD interlayer dielectric bumps
  • each unit cell of the DMOSFET comprises the P+ region that meanders and enables the P-well region to be in contact with the silicide layer (i.e., the first pad metal) only through the meandering P+ region to impact the differential on-resistance of the one or more body diode regions of the DMOSFET.
  • FIG. 48A illustrates an embodiment of a cross sectional structure of a unit cell of a double-implantation metal oxide semiconductor field-effect transistor (DMOSFET) comprising a first conductivity type second source region within a first conductivity type first source region.
  • the DMOSFET (shown in FIG. 48A) is a n-type planar gate DMOSFET. In an embodiment, the DMOSFET is a p-type planar gate DMOSFET.
  • the DMOSFET (shown in FIG. 48A) comprises a silicon carbide (SiC) substrate.
  • the SiC substrate comprises aN+ substrate 102 and aN- drift layer 104.
  • the DMOSFET also comprises a P-well region 106, a first N+ source region 108 (i.e., the first conductivity type first source region) and a second N+ source region 110 (i.e., the first conductivity type second source region).
  • the first N+ source region 108 is formed within the P- well region 106.
  • the second N+ source region 110 is formed within each first N+ source region 108 by etching the SiC substrate to remove a portion of the SiC substrate and form a recessed SiC trench 112.
  • the second N+ source region 110 is a depletion region when the DMOSFET is operated in the third quadrant.
  • the recessed SiC trench 112 leaves the remnant thin first N+ source region 108 as the second N+ source region 110.
  • the second N+ source region 110 comprises a thickness less than a thickness of the first N+ source region 108 which enables the second N+ source region 110 to get depleted easily compared to the first N+ source region 108.
  • the second N+ source region 110 may comprise the thickness ranging from 1% to 90% lower than the thickness of the first N+ source region 108.
  • the second N+ source region 110 comprises a doping concentration less than a doping concentration of the first N+ source region 108.
  • the second N+ source region 110 may comprise the doping concentration ranging from 1% to 90% lower than the doping concentration of the first N+ source region 108.
  • the DMOSFET also comprises a gate insulator 114, a polysilicon layer 116 and an interlayer dielectric (ILD) 118 on both sides of top surface of the SiC substrate.
  • the DMOSFET further comprises a first silicide layer 120 on top of the recessed SiC trench 112 and a second silicide layer 122 on bottom side/back side of the SiC substrate to form ohmic contacts for a source terminal and a drain terminal respectively.
  • the DMOSFET further comprises a first pad metal 124 (e.g., a source metal) and a second pad metal 126 (e.g., a drain metal) on top of the first silicide layer 120 and bottom of the second silicide layer 122 respectively.
  • an intrinsic p-n junction between the second N+ source region 110 and the p-well region 106 is reverse biased as electric potential of the first pad metal 124 is low when compared to electric potential of the second pad metal 126.
  • the second N+ source region 110 starts depleting during the third quadrant operation.
  • the first pad metal 124 e.g., the source metal
  • the first pad metal 124 is directly short circuited (e.g., connected) with the P-well region 106, when the second N+ source region 110 is completely depleted.
  • the second N+ source region 110 enables one or more body diode regions of the DMOSFET to have an increased turn-on voltage and the one or more body diode regions turn on only when the second N+ source region 110 is completely depleted.
  • the increased turn-on voltage is due to intrinsic bandgap of the SiC.
  • the turn-on voltage of the second N+ source region 110 also depends on the thickness and the doping concentration of the second N+ source region 110.
  • the turn-on voltage of the one or more body diode regions is tuned by controlling/adjusting the thickness and the doping concentration of the second N+ source region 110 to a target thickness and a target doping concentration respectively.
  • the target thickness ranges from 1 nm to 1 pm.
  • the target doping concentration ranges from 10 15 cm' 3 to 10 21 cm' 3 .
  • the target thickness and the target doping concentration of the second N+ source region 110 is achieved by monitoring and controlling precisely the etching performed onto the SiC substrate.
  • FIG. 48B illustrates an embodiment of a cross sectional structure of one or more unit cells of the DMOSFET, comprising one or more unit cells of an integrated Schottky diode, each DMOSFET unit cell comprising the first conductivity type second source region within the first conductivity type first source region.
  • the DMOSFET (shown in FIG. 48B) is a n-type planar gate SiC DMOSFET.
  • the DMOSFET shown in FIG. 48B operates in a similar way to FIG. 48A.
  • the DMOSFET shown in FIG.
  • the DMOSFET comprises each second N+ source region 110 between the respective silicide SiC trench 112 and the respective P-well region 106.
  • FIG. 48C illustrates an embodiment of a cross sectional structure of one or more unit cells of a trench gate MOSFET, comprising one or more unit cells of the integrated Schottky diode, each MOSFET unit cell comprising the first conductivity type second source region within the first conductivity type first source region.
  • the trench gate MOSFET shown in FIG. 48C is a n-type trench gate SiC MOSFET.
  • the trench gate MOSFET is a p-type trench gate SiC MOSFET.
  • the trench gate MOSFET shown in FIG. 48C operates in a similar way to planar gate DMOSFET shown in FIG. 48 A and FIG. 48B.
  • the main difference between the trench gate MOSFET and the planar gate DMOSFET is that the trench gate MOSFET comprises one or more trench gate structures instead of one or more planar gate structures.
  • the one or more trench gate structures of the trench gate MOSFET comprises sidewalls that are exposed to the first N+ source region 108 and the one or more P-well regions 106.
  • the bottom of the one or more trench gate structures is in vicinity of the bottom of the one or more P-well regions 106.
  • the bottom of the one or more trench gate structures is adjusted appropriately depending on electrical properties of the MOSFET device.
  • Each trench gate structure of the trench gate MOSFET comprises the gate insulator 114 as liner along the sidewall and the bottom of the respective trench gate structure.
  • Each trench gate structure comprises the polysilicon layer 116 that fills the gateinsulator lined trenches and serves as gate electrode.
  • the trench gate MOSFET further comprises the interlayer dielectric (ILD) 118 over each poly silicon layer 116 to open short circuitry between the first pad metal 124 (e.g., the source metal) and the gate electrode.
  • ILD interlayer dielectric
  • FIG. 49A to 49T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 48A.
  • the process of manufacturing the DMOSFET structure comprises preparing a Silicon Carbide (SiC) substrate having a N+ substrate 202 and a N- drift layer 204 as shown in FIG. 49A.
  • the N- drift layer 204 of the SiC substrate is epi -grown and prepared such that a doping concentration and a thickness of the N- drift layer 204 are selected primarily based on blocking voltage and forward conduction loss.
  • the N+ substrate 202 is highly conductive when compared to the N- drift layer 204 and the N+ substrate 202 is in direct contact with the N- drift layer 204.
  • a first patterned hard mask layer 205 is formed on top of the SiC substrate as shown in FIG. 49B.
  • the first patterned hard mask layer 205 is thick enough for completely blocking high energy impurities during implantation.
  • the first patterned hard mask layer 205 is a hard mask of at least one of oxide, nitride, and a polysilicon.
  • a first p-type ion implantation is formed in FIG. 49C through the first patterned hard mask layer 205 to form a p-well region 206.
  • the first p-type ion implantation is performed with one or more p-type impurities (e.g., aluminum, boron, etc.).
  • first p-type ion implantation may comprise a screen oxide layer.
  • the first patterned hard mask layer 205 is then removed, after the first p-type ion implantation, by at least one of dry etching and wet etching process as shown in FIG. 49D.
  • a second patterned hard mask layer 207 is then formed on the top of the SiC substrate as shown in FIG. 49E for subsequent ion implantation.
  • the second patterned hard mask layer 207 is a photoresist based material and thick enough for preventing any unwanted high energy impurity particles penetrating the second patterned hard mask layer 207.
  • a first n-type ion implantation is performed through the second patterned hard mask layer 207 to form a first N+ source region 208 within the p-well region 206 as shown in FIG. 49F.
  • the first n-type ion implantation is performed with one or more n-type impurities (e.g., nitrogen, phosphorous etc.).
  • the second patterned hard mask layer 207 is then removed after the first n-type ion implantation by at least one of dry etching and wet etching process as shown in FIG. 49G.
  • a third patterned hard mask layer 209 is formed on top of the SiC substrate as shown in FIG. 49H.
  • An etching is performed onto the SiC substrate through the third patterned hard mask layer 209.
  • the SiC etching performed consumes a central portion of each first N+ source region 208 and forms a recessed SiC trench region 212 per each first N+ source region 208.
  • the recessed SiC trench region 212 does not fully penetrates the first N+ source region 208 in vertical direction and leaves a remnant of the first N+ source region 208 to form a second N+ source region 210 under the bottom of the recessed SiC trench region 212 as shown in FIG. 491.
  • the SiC etching is controlled accurately and precisely considering plausible loss of the Sic Substrate, during at least one of thermal activation annealing, sacrificial oxidation, and dry oxidation for one of a gate oxide formation and a silicide layer formation for ohmic contacts, when target SiC trench depth is reached.
  • the target SiC trench depth leaves at least one of a target thickness and a target doping concentration of the second N+ source region 210 under the bottom of the recessed SiC trench region 212.
  • the target thickness ranges from 1 nm to 1 gm.
  • the target doping concentration ranges from 10 15 cm' 3 to 10 21 cm' 3 .
  • the third patterned hard mask layer 209 is then removed as shown in FIG. 49J by at least one of a dry etching and a wet etching process once the target SiC trench depth is reached.
  • the SiC substrate undergoes thermal activation annealing with a carbon-based protection coating at a predefined temperature.
  • the predefined temperature is 1700-degree Celsius.
  • the SiC substrate then may undergo an additional ion implantation for forming a current spreading layer to improve on-state resistance.
  • Ion implantations (e.g., the first p-type implantation, the first n-type impanation, the second p-type implantation, edge termination implantation, current spreading layer implantation etc.) undergone by the SiC substrate is performed prior to the thermal activation annealing step.
  • the carbon-based protection coating is then removed from the SiC substrate once the thermal activation annealing is completed.
  • the SiC substrate then undergoes a sacrificial oxide growth and subsequently the sacrificial oxide removal.
  • An active region of the DMOSFET is then patterned by forming and patterning field oxide layer on the SiC substrate.
  • a gate insulator 214 is then deposited/formed on top of the SiC substrate as shown in FIG. 49K.
  • the gate insulator 214 is then patterned as shown in FIG. 49L.
  • a polysilicon layer 216 is then formed on top of the SiC substrate as shown in FIG. 49M.
  • the polysilicon layer 216 is then patterned as shown in FIG. 49N.
  • the contacts for the polysilicon layer are kept open before pad metal deposition for forming a gate pad region and the gate bus region(s).
  • An interlayer dielectric (ILD) 218 is then formed on top of the SiC substrate as shown in FIG. 490.
  • the interlayer dielectric (ILD) 218 is then patterned for exposing the portions of the SiC substrate via the openings of the ILD 218 as shown in FIG. 49P.
  • a first silicide layer 220 is then formed on the exposed portions on top of the SiC substrate for forming a first Ohmic contact (e.g., a source terminal contact) as shown in FIG. 49Q.
  • the first silicide layer 220 is a nickel-based silicide layer.
  • the nickel-based silicide is formed by Nickel deposition on the top of the SiC substrate, thermal activation annealing of the deposited Nickel for silicide formation, and removal of any un-reacted Nickel from the SiC substrate.
  • a first pad metal 224 is then formed on top of the first silicide layer 220 of the SiC substrate as shown in FIG. 49R.
  • a second silicide layer 222 is then formed on bottom of the SiC substrate for forming a second Ohmic contact as shown in FIG. 49S.
  • the second silicide layer 222 is then formed on back of the SiC substrate for forming the second Ohmic contact (e.g., a drain terminal contact).
  • the second silicide layer 222 is also the nickel-based silicide layer.
  • a second pad metal 226 is then formed on bottom of the second silicide layer 222 of the SiC substrate as shown in FIG. 49T.
  • the second pad metal formation is performed by at least one of e-beam and sputtering.
  • a fourth patterned hard mask layer 211 is then formed on the SiC substrate once the first Ohmic contact and the second Ohmic contact are formed on topside and bottom side/back side of the SiC substrate respectively.
  • the fourth patterned hard mask layer 211 is formed for selectively removing the exposed portions of the ILD layer 218 and forming a metal region (i.e., a Schottky metal region 228) shown in FIG. 48B.
  • the fourth patterned hard mask layer 211 is used for both etching the portion of the ILD layer 218 and lifting off the Schottky metal region 228 when Schottky metal is deposited.
  • the Schottky metal region 228 is in direct contact with the N- drift layer 204 and bridge two adjacent P-well regions 206 (i.e., bridges the adjacent unit cells).
  • the Schottky metal region 228 is then annealed with a predefined thermal budget for forming a Schottky metal contact between the Schottky metal region 228 and the portion of the N- drift layer 204 exposed at the top surface of the SiC substrate.
  • the predefined thermal budget ranges from 55°C to 1100°C.
  • the first pad metal and the second pad metal formation are performed once the Schottky metal region 228 formation is completed.
  • FIG. 50A illustrates an embodiment of a voltage-current characteristic of a SiC DMOSFET with conventional p-n junction vs the SiC DMOSFET with deactivated p-n junction (i.e., the first conductivity type second source region).
  • the voltage-current characteristic shown in FIG. 50 A depicts that at a drain current -16A, the SiC planar DMOSFET with conventional p-n junction shows a voltage drop of ⁇ -4v and the SiC DMOSFET with deactivated p-n junction (i.e., the first conductivity type second source region) shows a voltage drop of ⁇ -7V.
  • the SiC DMOSFET comprise the p-n junction with increased built-in potential and increased differential on-resistance when the SiC DMOSFET comprises the first conductivity type second source region 110.
  • FIG. 50B is a perspective view that illustrates an embodiment of sides of the DMOSFET in relation to a dice.
  • the DMOSFET may comprise a structure similar to the dice as shown in FIG. 50B.
  • the DMOSFET comprises at least the topside 340, the bottom side 342, a front side 344, the back side 346, a left side 348 and a right side 350.
  • the topside 340 of the DMOSFET refers to an outer side/top of the DMOSFET.
  • the topside 340 comprises the source terminal.
  • the bottom side 342 refers to a base of the DMOSFET. In an embodiment, the bottom side 342 of the DMOSFET comprises the drain terminal.
  • the back side 346 of the DMOSFET is hidden in FIG.
  • the back side 346 of the DMOSFET comprises the drain terminal.
  • the front side 344 and the right side 350 of the DMOSFET is visible in FIG. 50B, whereas the left side 348 and the back side 346 of the DMOSFET is hidden in FIG. 50B.
  • FIG. 50C and 50D shows the operation of the anti-parallel diode in a half-bridge inverter feeding an inductive load.
  • the left picture i.e., FIG. 50C
  • FIG. 50D shows the state when the upper switch feeds the inductor. However, when that switch turns off, inductor's current continues its path through the anti-parallel diode of the bottom switch (right picture i.e., FIG. 50D).
  • source Re: Why are diodes connected anti-parallel across the MOSFET or IGBT in Inverter Module? Heydari, Gholamali, published on Research gate, July 25, 2013]
  • FIG. 51A illustrates an embodiment of a cross sectional structure of a unit cell of a double-implantation metal oxide semiconductor field-effect transistor (DMOSFET) comprising a first conductivity type second source region within a first conductivity type first source region.
  • the DMOSFET (shown in FIG. 51 A) is a n-type planar gate DMOSFET. In an embodiment, the DMOSFET is a p-type planar gate DMOSFET. In another embodiment, the DMOSFET is one of a n-type trench gate DMOSFET and a p-type trench gate DMOSFET.
  • the DMOSFET (shown in FIG. 51 A) comprises a Silicon Carbide (SiC) substrate.
  • the SiC substrate comprises aN+ substrate 402 and a N- drift layer 404.
  • the DMOSFET also comprises a P-well region 406, a first N+ source region 408 (i.e., the first conductivity type first source region) and a second N+ source region 410 (i.e., the first conductivity type second source region).
  • the first N+ source region 408 is formed within the P-well region 406.
  • the second N+ source region 410 is formed within the first N+ source region 408 by performing a n-type implantation with controlled dosage and energy level.
  • the second N+ source region 410 is a depletion region during third quadrant MOSFET operation.
  • the second N+ source region 410 comprises a thickness and a doping concentration which is significantly less than a thickness and a doping concentration of the first N+ source region 408 respectively which enables the second N+ source region 410 to get depleted easily compared to the first N+ source region 408.
  • the second N+ source region 410 comprises the thickness ranging from 1% to 90% lower than the thickness of the first N+ source region 408.
  • the second N+ source region 410 comprises the doping concentration ranging from 1% to 90% lower than the doping concentration of the first N+ source region 408.
  • the DMOSFET also comprises a gate insulator 414, a polysilicon layer 416 and an interlayer dielectric (ILD) 418 on both sides of top surface of the SiC substrate.
  • the DMOSFET further comprises a first silicide layer 420 on top of the SiC substrate and a second silicide layer 422 on bottom side/back side of the SiC substrate to form ohmic contacts for a source terminal and a drain terminal respectively.
  • the DMOSFET further comprises a first pad metal 424 (e.g., a source metal) and a second pad metal 426 (e.g., a drain metal) on top of the first silicide layer 420 and bottom of the second silicide layer 422 respectively.
  • an intrinsic p-n junction between the second N+ source region 410 and the p-well region 406 is reverse biased as electric potential of the first pad metal 424 is low when compared to electric potential of the second pad metal 426.
  • the second N+ source region 410 starts depleting during the third quadrant operation.
  • the first pad metal 424 e.g., the source metal
  • the first pad metal 424 is directly short circuited (i.e., connected) with the P-well region 406, when the second N+ source region 410 is completely depleted.
  • the second N+ source region 410 enables one or more body diode regions of the DMOSFET to have an increased turn-on voltage and the one or more body diode regions turn on only when the second N+ source region 410 is completely depleted.
  • the increased turn-on voltage is due to intrinsic bandgap of the SiC.
  • the turn-on voltage of the one or more body diode regions also depends on the thickness and the doping concentration of the second N+ source region 410.
  • the turn-on voltage of the one or more body diode regions is tuned by controlling/adjusting the thickness and the doping concentration of the second N+ source region 410 to a target thickness and a target doping concentration respectively.
  • the target thickness ranges from 1 nm to 1 pm.
  • the target doping concentration ranges from 10 15 cm' 3 to 10 21 cm' 3 .
  • the target thickness and the target doping concentration of the second N+ source region 410 is achieved by monitoring and controlling the dosage and the energy level of the n-type implantation.
  • FIG. 51B illustrates an embodiment of a cross sectional structure of one or more unit cells of the DMOSFET, comprising one or more unit cells of an integrated Schottky diode, each DMOSFET unit cell comprising the first conductivity type second source region within the first conductivity type first source region.
  • the DMOSFET (shown in FIG. 5 IB) is a n-type planar gate DMOSFET.
  • the DMOSFET shown in FIG. 5 IB operates in a similar way to FIG. 51 A.
  • the DMOSFET (shown in FIG. 5 IB) comprises a metal region (i.e., a Schottky metal region 428) and one or more P-well regions 406.
  • the Schottky metal region 428 is in direct contact with the N- drift layer 404 and bridges the adjacent P-well regions 406 (i.e., bridges the adjacent unit cells) of the one or more P-well regions 406.
  • the DMOSFET comprises each second N+ source region 410 between the first silicide layer 420 and the respective P-well region 406.
  • FIG. 52A to 52T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 51 A.
  • the process of manufacturing the DMOSFET structure comprises preparing a Silicon Carbide (SiC) substrate having a N+ substrate 502 and a N- drift layer 504 as shown in FIG. 52A.
  • the N- drift layer 504 of the SiC substrate is epi -grown and prepared such that a doping concentration and a thickness of the N- drift layer 504 are selected primarily based on blocking voltage and forward conduction loss.
  • the N+ substrate 502 is highly conductive when compared to the N- drift layer 504 and the N+ substrate 502 is in direct contact with the N- drift layer 504.
  • a first patterned hard mask layer 505 is formed on top of the SiC substrate as shown in FIG. 52B.
  • the first patterned hard mask layer 505 is thick enough for completely blocking high energy impurities during implantation.
  • the first patterned hard mask layer 505 is a hard mask of at least one of oxide, nitride, and a polysilicon.
  • a first p-type ion implantation is formed in FIG. 52C through the first patterned hard mask layer 505 to form a p-well region 506.
  • the first p-type ion implantation is performed with one or more p-type impurities (e.g., aluminum, boron, etc.).
  • first p-type ion implantation may comprise a screen oxide layer.
  • the first patterned hard mask layer 505 is then removed, after the first p-type ion implantation, by at least one of dry etching process and wet etching process as shown in FIG. 52D.
  • a second patterned hard mask layer 507 is then formed on the top of the SiC substrate as shown in FIG.
  • the second patterned hard mask layer 507 is a photoresist based material and thick enough for preventing any unwanted high energy impurities particles penetrating the second patterned hard mask layer 507.
  • a first n-type ion implantation is formed through the second patterned hard mask layer 507 to form a first N+ source region 508 (i.e., the first conductivity type first source region) within the p-well region 506 as shown in FIG. 52F.
  • the first n-type ion implantation is performed with one or more n-type impurities (e.g., nitrogen, phosphorous etc.).
  • the second patterned hard mask layer 507 is then removed after the first n-type ion implantation by at least one of dry etching and wet etching process as shown in FIG. 52G.
  • a third patterned hard mask layer 509 is then formed on top of the SiC substrate as shown in FIG. 52H.
  • a second n-type implantation is performed through the third patterned hard mask layer 509 to form a second N+ source region 510 within the first N+ source region 508 within each p-well region 506 as shown in FIG. 521.
  • the dosage and energy level of the second n-type implantation is controlled accurately and precisely to form the second N+ source region 510 having a target thickness and a target doping concentration.
  • the target thickness may range from 1 nm to 1 pm.
  • the target doping concentration may range from 10 15 cm' 3 to 10 21 cm'3.
  • a doping concentration, and a thickness of the second N+ source region 510 is less than a doping concentration and a thickness of the first N+ source region 508 respectively.
  • the doping concentration of the second N+ source region 510 is 1% to 90% lower than the doping concentration of the first N+ source region 508.
  • the thickness of the second N+ source region 510 is 1% to 90% lower than the thickness of the first N+ source region 508.
  • the third patterned hard mask layer 509 is then removed as shown in FIG. 52J by at least one of a dry etching and a wet etching process once the second N+ source region 510 having the target thickness and the target doping concentration is achieved.
  • the SiC substrate undergoes thermal activation annealing with a carbon-based protection coating at a predefined temperature.
  • the predefined temperature for performing the thermal activation annealing is 1700-degree Celsius.
  • the SiC substrate then may undergo an additional ion implantation for forming a current spreading layer to improve on-state resistance.
  • Ion implantations (e.g., the first p-type implantation, the first n-type impanation, the second p-type implantation, edge termination implantation, current spreading layer implantation etc.) undergone by the SiC substrate is performed prior to the thermal activation annealing step.
  • the carbon-based protection coating is then removed from the SiC substrate.
  • the SiC substrate then undergoes a sacrificial oxide growth and subsequently the sacrificial oxide removal.
  • An active region of the SiC DMOSFET is then patterned by forming and patterning field oxide layer on the SiC substrate.
  • a gate insulator 514 is then formed on top of the SiC substrate as shown in FIG. 52K.
  • the gate insulator is then patterned as shown in FIG. 52L.
  • a polysilicon layer 516 is then formed on top of the SiC substrate as shown in FIG. 52M.
  • the polysilicon layer 516 is then patterned as shown in FIG. 52N. Contacts for the polysilicon layer are kept open for pad metal deposition for forming a gate pad region and one or more gate bus regions.
  • An interlayer dielectric (ILD) 518 is then formed on top of the SiC substrate as shown in FIG. 520.
  • the interlayer dielectric (ILD) 518 is then patterned for exposing the portions of the SiC substrate via the openings of the ILD 518 as shown in FIG.
  • a first silicide layer 520 is then formed on the exposed portions of top of the SiC substrate for forming a first Ohmic contact (e.g., a source terminal contact) as shown in FIG. 52Q.
  • the first silicide layer 520 is a nickel-based silicide layer.
  • the nickel-based silicide is formed by Nickel deposition on the top of the SiC substrate, thermal activation annealing of the deposited Nickel for silicide formation, and removal of any un-reacted Nickel from the SiC substrate.
  • a first pad metal 524 is then formed on top of the first silicide layer 520 of the SiC substrate as shown in FIG. 52R.
  • a second silicide layer 522 is then formed on bottom of the SiC substrate for forming a second Ohmic contact (e.g., a drain terminal contact) as shown in FIG. 52S.
  • the second silicide layer 522 is then formed on back of the SiC substrate for forming the second Ohmic contact (e.g., the drain terminal contact).
  • the second silicide layer 522 is also the nickel-based silicide layer.
  • a second pad metal 526 is then formed on bottom of the second silicide layer 522 of the SiC substrate as shown in FIG. 52T.
  • the second pad metal formation is performed by at least one of e-beam and sputtering.
  • a fourth patterned hard mask layer 511 is then formed on the SiC substrate once the first Ohmic contact and the second Ohmic contact are formed on top and bottom side/back side of the SiC substrate respectively.
  • the fourth patterned hard mask layer 511 is formed for selectively removing the exposed portions of the ILD layer 518 and forming a metal region 528 (i.e., a Schottky metal region 528) shown in FIG. 5 IB.
  • the fourth patterned hard mask layer 511 is used for both etching the portion of the ILD layer 518 and lifting off the Schottky metal region 528 when Schottky metal is deposited.
  • the Schottky metal region 528 is in direct contact with the top of the N- drift layer 504 and bridge two adjacent P-well regions 506 (e.g., bridges the adjacent unit cells).
  • the Schottky metal region 528 is then annealed with a predefined thermal budget for forming a Schottky metal contact between the second Schottky metal region 528 and the portion of the N- drift layer 504 exposed at the top surface of the SiC substrate.
  • the predefined thermal budget ranges from 55°C to 1100°C.
  • the first pad metal and the second pad metal formation are performed once the Schottky metal region 528 formation is completed.
  • FIG. 53A illustrates an embodiment of a cross sectional structure of a unit cell of a double-implantation metal oxide semiconductor field effect transistor (DMOSFET) comprising a first metal region in direct contact with a second conductivity type well contact region.
  • the DMOSFET (shown in FIG. 53A) is a n-type planar gate SiC DMOSFET.
  • the DMOSFET is a p-type planar gate DMOSFET.
  • the DMOSFET is a p-type trench gate DMOSFET.
  • the DMOSFET is a n-type trench gate DMOSFET.
  • the DMOSFET (shown in FIG.
  • the 53A comprises a Silicon Carbide (SiC) substrate.
  • the SiC substrate comprises a N+ substrate 602 and a N- drift layer 604.
  • the DMOSFET also comprises a P-well region 606, a first N+ source region 608 and a P+ region 603 (i.e., the second conductivity type well contact region).
  • the first N+ source region 608 is formed within the P-well region 606.
  • the P+ region 603 i.e., the second conductivity type well contact region
  • the second conductivity type well contact region specifically refers to the P+ region 603.
  • the first metal region 613 (e.g., a first Schottky metal region 613) is then formed in direct contact with the P+ region 603 to connect one or more Schottky diode regions in series with one or more body diode regions of the DMOSFET.
  • the first Schottky metal region 613 comprises a target work function.
  • the target work function of the first Schottky metal region 613 ranges from 3.5 electron volts to 6 electron volts.
  • the work function of the first Schottky metal region 613 and the series connection of the Schottky diode regions with the body diode regions allows the one or more body diode regions to turn-on only when significant number of carriers from the first Schottky metal region 613 is thermionically injected over Schottky barrier during third quadrant operation of the DMOSFET. Since the one or more Schottky diode regions are connected in series with the one or more body diode regions, the one or more Schottky diode regions consumes the voltage of the one or more body diode regions and the one or more Schottky diode regions turn on first before the one or more body diode regions.
  • any additional applied voltage that is greater than turn-on voltage of the one or more Schottky diode regions contributes to turn-on the one or more body diode regions. Due to the series connection of the one or more Schottky diode regions with the body diode regions, the body diode regions consume additional turn-on voltage compared to typical turn-on voltage.
  • the one or more body diode regions get turn-on only when the first Schottky metal region 613 turn on with a forward voltage which corresponds at least to the barrier height of a first Schottky contact region for starting the on-set of the carrier injection over the Schottky barrier (i.e., when the first Schottky metal region 613 comprises the target work function).
  • the forward voltage initiates the carrier injection to turn-on the Schottky diode regions. Any additional forward voltage that is greater than the turn-on voltage of the Schottky diode regions contributes to turn-on the body diode regions.
  • the turn-on voltage of the body diode regions is tuned by at least one of controlling a Schottky barrier height and selecting a Schottky metal with an appropriate work function utilized in forming the first Schottky metal region 613.
  • the turn-on voltage of the body diode regions is also tuned by adjusting thermal budget for annealing the first Schottky contact region once the first Schottky metal region 613 is formed on top of the SiC substrate.
  • the predefined thermal budget may range from 55°C to 1100°C.
  • the DMOSFET comprises a second metal region 628 (e.g., a second Schottky metal region 628) directly on top of the N- drift layer 604 and bridge adjacent P-well regions 606 of the one or more P-well regions 606 (i.e., bridges the adjacent unit cells) shown in FIG. 53B.
  • the work function of the first Schottky metal region 613 is less than a work function of the second Schottky metal region 628.
  • FIG. 53B illustrates an embodiment of a cross sectional structure of one or more unit cells of the DMOSFET, comprising one or more unit cells of an integrated Schottky diode, each DMOSFET unit cell comprising the first metal region in direct contact with the respective second conductivity type well contact region.
  • the DMOSFET (shown in FIG. 53B) is a n-type planar gate SiC DMOSFET.
  • the DMOSFET shown in FIG. 53B operates in a similar way to FIG. 53A.
  • the DMOSFET (shown in FIG. 53B) comprises the second Schottky metal region 628 and one or more P-well regions 606.
  • the second Schottky metal region 628 is in direct contact with the N- drift layer 604 and bridges the adjacent P-well regions 606 (i.e., the adjacent unit cells) of the one or more P-well regions 606.
  • the work function of the first Schottky metal region 613 is less than the work function of the second Schottky metal region 628.
  • FIG. 53C illustrates an embodiment of a third quadrant current conduction through an intrinsic p-n junction diode region vs a Schottky diode region connected in parallel to DMOSFET.
  • the third quadrant current of the body diode region is indicated as 630 in FIG. 53C.
  • the third quadrant current of the anti-parallel Schottky diode region is indicated as 632 in FIG. 53C.
  • the third quadrant current passing through the body diode region intersects with the third quadrant current passing through the Schottky diode region which is indicated as 634 in FIG. 53C.
  • the third quadrant current is bipolar in nature which results in performance and reliability issues.
  • 53D illustrates an embodiment of a third quadrant current conduction through the DMOSFET after connecting the one or more Schottky diode regions in series with the one or more body diode regions of the DMOSFET.
  • the third quadrant current of the body diode region is indicated as 636 in FIG. 53D. Due to the existence of the one or more Schottky diode regions in series connection with the one or more body diode regions, the magnitude of the third quadrant current is shifted by the additional current required for the one or more Schottky diode regions to turn-on first.
  • the shift in the magnitude of the third quadrant current (i.e.) the increased third quadrant current), after connecting the one or more Schottky diode regions in series with the one or more body diode regions, is indicated as 638 in FIG. 53D. It is evident from FIG. 53C and FIG. 53D, the magnitude of the third quadrant current is increased when the one or more Schottky Diode regions is connected in series with the one or more body diode regions of the DMOSFET.
  • FIG. 54A to 54X illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 53 A.
  • the process of manufacturing the DMOSFET structure comprises preparing a Silicon Carbide (SiC) substrate having a N+ substrate 702 and a N- drift layer 704 as shown in FIG. 54A.
  • the N- drift layer 704 of the SiC substrate is epi-grown and prepared such that a doping concentration and a thickness of the N- drift layer 704 are selected primarily based on blocking voltage and forward conduction loss.
  • the N+ substrate 702 is highly conductive when compared to the N- drift layer 704 and the N+ substrate 702 is in direct contact with the N- drift layer 704.
  • a first patterned hard mask layer 705 is formed on top of the SiC substrate as shown in FIG. 54B.
  • the first patterned hard mask layer 705 is thick enough for completely blocking high energy impurities during implantation.
  • the first patterned hard mask layer 705 is a hard mask of at least one of oxide, nitride, and polysilicon.
  • a first p-type ion implantation is formed in FIG. 54C through the first patterned hard mask layer 705 to form a p-well region 706.
  • the first p-type ion implantation is performed with one or more p-type impurities (e.g., aluminum, boron, etc.).
  • first p-type ion implantation may comprise a screen oxide layer.
  • the first patterned hard mask layer 705 is then removed, after the first p-type ion implantation, by at least one of dry etching process and wet etching process as shown in FIG. 54D.
  • a second patterned hard mask layer 707 is then formed on the top of the SiC substrate as shown in FIG.
  • the second patterned hard mask layer 707 is a photoresist based material and thick enough for preventing any unwanted high energy impurities particles penetrating the second patterned hard mask layer 707.
  • a first n-type ion implantation is formed through the second patterned hard mask layer 707 to form a N+ source region 708 within the p-well region 706 as shown in FIG. 54F.
  • the first n-type ion implantation is performed with one or more n-type impurities (e.g., nitrogen, phosphorous etc.).
  • the second patterned hard mask layer 707 is then removed after the first n-type ion implantation by at least one of dry etching and wet etching process as shown in FIG. 54G.
  • a third patterned hard mask layer 709 is then formed on top of the SiC substrate as shown in FIG. 54H.
  • a second p-type implantation is performed through the third patterned hard mask layer 709 to form a P+ region 703 within the p-well region 706 as shown in FIG. 541.
  • the third patterned hard mask layer 709 is then removed as shown in FIG. 54J by at least one of a dry etching and a wet etching process once the P+ region 703 is formed.
  • the SiC substrate undergoes thermal activation annealing with a carbon-based protection coating at a predefined temperature.
  • the predefined temperature for performing the thermal activation annealing is 1700-degree Celsius.
  • the SiC substrate then may undergo an additional ion implantation for forming a current spreading layer to improve on-state resistance.
  • Ion implantations (e.g., the first p-type implantation, the first n-type impanation, the second p-type implantation, edge termination implantation, current spreading layer implantation etc.) undergone by the SiC substrate is performed prior to the thermal activation annealing step.
  • the carbon-based protection coating is then removed from the SiC substrate.
  • the SiC substrate then undergoes a sacrificial oxide growth and subsequently the sacrificial oxide removal.
  • An active region of the SiC DMOSFET is then patterned by forming and patterning field oxide layer on the SiC substrate.
  • a gate insulator 714 is then formed on top of the SiC substrate as shown in FIG. 54K.
  • the gate insulator is then patterned as shown in FIG. 54L.
  • a polysilicon layer 716 is then formed on top of the SiC substrate as shown in FIG. 54M.
  • the polysilicon layer 716 is then patterned as shown in FIG. 54N. Contacts for the polysilicon layer are kept open for pad metal deposition for forming a gate pad region and one or more gate bus regions.
  • An interlayer dielectric (ILD) 718 is then formed on top of the SiC substrate as shown in FIG. 540.
  • the interlayer dielectric (ILD) 718 is then patterned for exposing the portions of the SiC substrate via the openings of the ILD 718 as shown in FIG.
  • a first silicide layer 720 is then formed on the exposed portions of top of the SiC substrate for forming a first Ohmic contact as shown in FIG. 54Q.
  • the first silicide layer 720 is a nickel-based silicide layer.
  • the nickel-based silicide is formed by Nickel deposition on the top of the SiC substrate, thermal activation annealing of the deposited Nickel for silicide formation, and removal of any un-reacted Nickel from the SiC substrate.
  • a fourth patterned hard mask layer 711 is formed on top of the SiC substrate as shown in FIG. 54R. An ILD etching is formed on the SiC substrate through the fourth patterned hard mask layer 711 to selectively remove the exposed portions of the ILD layer 718 as shown in FIG.
  • a first metal is deposited on top of the SiC substrate through the fourth patterned hard mask layer 711 as shown in FIG. 54T.
  • the first metal is lifted off and annealed to form a first metal region 713 (e.g., the first Schottky metal region 713) to be in direct contact with the P+ region 703 as shown in FIG. 54U.
  • the first Schottky metal region 713 comprises a target work function.
  • the target work function may range from 3.5 electron volts to 6 electron volts.
  • the first Schottky metal region 713 is then annealed with a predefined thermal budget for forming a first Schottky contact region between the first Schottky metal region 713 and the top of each P+ region 703.
  • the predefined thermal budget ranges from 55°C to 1100°C.
  • the thermal budget for forming the first Schottky contact region is precisely designed and controlled as it directly impacts electrical properties of the first Schottky contact regions.
  • a first pad metal 724 is formed on top of the SiC substrate as shown in FIG. 54V.
  • a second silicide layer 722 is then formed on bottom of the SiC substrate for forming a second Ohmic contact as shown in FIG. 54W.
  • the second silicide layer 722 is then formed on back of the SiC substrate for forming the second Ohmic contact (e.g., a drain terminal contact).
  • the second silicide layer 722 is the nickel-based silicide layer.
  • a second pad metal 726 is then formed on bottom of the second silicide layer 722 of the SiC substrate.
  • the second pad metal formation is performed by at least one of e- beam and sputtering.
  • a fifth patterned hard mask layer 715 is then formed on the SiC substrate once the first Ohmic contact and the second Ohmic contact are formed on topside and bottom side/back side of the SiC substrate respectively.
  • the fifth patterned hard mask layer 715 is formed for selectively removing the exposed portions of the ILD layer 718 and depositing a second metal region 728 (i.e., a second Schottky metal region 728) (shown in FIG. 52B) on top of the SiC substrate.
  • the fifth patterned hard mask layer 715 is used for both etching the portion of the ILD layer 718 and lifting off the second Schottky metal region 728 when second Schottky metal is deposited.
  • the second Schottky metal region 728 is in direct contact with the N- drift layer 704 and bridge two adjacent P-well regions 706 (i.e., bridges the adjacent unit cells).
  • the second Schottky metal region 728 is then annealed with a predefined thermal budget for forming a second Schottky metal contact between the second Schottky metal region 728 and the portion of the N- drift layer 704 exposed at the top surface of the SiC substrate.
  • the predefined thermal budget ranges from 55°C to 1100°C.
  • the first pad metal and the second pad metal formation are performed once the second Schottky metal region 728 formation is completed.
  • FIG. 55A, 55B & 55C illustrate an embodiment of cross-sectional structures of a unit cell of a DMOSFET comprising a second conductivity type well contact region that meanders at three different locations respectively.
  • the DMOSFET shown in FIG. 55A, 55B and 55C is a n-type planar gate SiC DMOSFET.
  • the DMOSFET is a p-type planar gate DMOSFET.
  • the DMOSFET is a n-type trench gate DMOSFET.
  • the DMOSFET is a p-type trench gate DMOSFET.
  • the DMOSFET (shown in FIG.
  • the 55A, 55B and 55C comprises a Silicon Carbide (SiC) substrate.
  • the SiC substrate comprises a N+ substrate 802 and a N- drift layer 804.
  • the DMOSFET also comprises a P-well region 806, a N+ source region 808 and a P+ region 803 (i.e., the second conductivity type well contact region).
  • the N+ source region 808 i.e., a first conductivity type source region
  • the P+ region 803 is meandering within the P-well region 806 by performing a p-type implantation at respective locations.
  • the P+ region 803 comprise a periodic spacing with the successive P+ region 803(i.e., non-contiguous).
  • the lateral extent of the P+ region 803 varies with a non-zero value in a direction orthogonal to the unit cell.
  • the meandering P+ region 803 periodically forms ohmic contacts to a first pad metal 824 (e.g., a source metal) via a first silicide layer 820 between two interlayer dielectric (ILD) bumps 817 located between metal oxide semiconductor gate stack and the first pad metal 824.
  • the meandering P+ region 803 follows Zigzag path, where corners of the zigzag path is right angled.
  • the Zigzag path of the meandering P+ region 803 comprises dimensions a, P, and y.
  • the meandering P+ region 803 comprise a target size and are a target spacing between adjacent junction points located between the meandering P+ region 803.
  • Contact resistance to the first pad metal 824 varies when the P+ region 803 under the ILD bumps 817 do not have direct contact with the first pad metal 824 and when the P+ region 803 have direct contact with the first pad metal 824 through the first silicide layer 820.
  • the portions of the meandering P+ region 803 which are directly under the ILD bumps 817 functions as networks of distributed ballast resistors and provides an additional source resistance to the source contact resistance.
  • the additional contact resistance provided directly impacts the differential on-resistance of one or more body diode regions of the DMOSFET.
  • the impacted differential-on resistance of the body diode regions suppresses increase of forward conduction current of the one or more body diode regions.
  • the limited forward conduction current mitigates basal plane dislocation (BPD).
  • BPD basal plane dislocation Since the source contact resistance is dependent on the sizing, the spacing between adjacent junction points located between the meandering P+ region 803, and the silicide region between the adjacent ILD bumps 817, the source contact resistance is tuned by sizing the P+ region 803 to a target size and controlling the spacing to a target spacing.
  • the target size ranges from 10 nm to 10 pm. In another embodiment, the target spacing ranges from 10 nm to 10 pm.
  • width (a) of the meandering P+ region 803 when width (a) of the meandering P+ region 803 is reduced, the resistance of each ballast resistor network is increased which degrades the differential on-resistance of the one or more body diode regions.
  • the reduction of the width (a) also shrinks the area where the Ohmic contacts are formed, degrades the differential on- resistance of the one or more body diode regions.
  • the periodic spacing (y) between the meandering P+ region 803 is increased, the resistance of each ballast resistor network is increased which degrades the differential on-resistance of the one or more body diode regions.
  • FIG. 55D, 55E & 55F illustrate an embodiment of cross-sectional structures of one or more unit cells of a diode integrated DMOSFET, each DMOSFET unit cell comprising the second conductivity type well contact region that meanders at three different locations respectively.
  • the DMOSFET (shown in FIG. 55D, 55E & 55F) is a n-type planar gate SiC DMOSFET.
  • the DMOSFET shown in FIG. 55D, 55E & 55F operates in a similar way to FIG. 55A, 55B & 55C.
  • the DMOSFET shown in FIG.
  • 55D, 55E & 55F comprises a metal region (i.e., a Schottky metal region 828) in direct contact with the N- drift layer 804 and bridges adjacent P-well regions 806 of the one or more P-well regions 806 (i.e., bridges the adjacent unit cells).
  • the DMOSFET comprises the P+ region 803 that meanders within each P-well region 806.
  • FIG. 56A to 56T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 55A.
  • the process of manufacturing the DMOSFET structure comprises preparing a Silicon Carbide (SiC) substrate having a N+ substrate 902 and a N- drift layer 904 as shown in FIG. 56A.
  • the N- drift layer 904 of the SiC substrate is epi -grown and prepared such that a doping concentration and a thickness of the N- drift layer 904 are selected primarily based on blocking voltage and forward conduction loss.
  • the N+ substrate 902 is highly conductive when compared to the N- drift layer 904 and the N+ substrate 902 is directly located under the N- drift layer 904.
  • a first patterned hard mask layer 905 is formed on top of the SiC substrate as shown in FIG. 56B.
  • the first patterned hard mask layer 905 is thick enough for completely blocking high energy impurities during implantation.
  • the first patterned hard mask layer 905 is a hard mask of at least one of oxide, nitride, and a polysilicon layer.
  • a first p-type ion implantation is formed in FIG. 56C through the first patterned hard mask layer 905 to form a p-well region 906.
  • the first p-type ion implantation is performed with one or more p-type impurities (e.g., aluminum, boron, etc.).
  • first p-type ion implantation may comprise a screen oxide layer.
  • the first patterned hard mask layer 905 is then removed, after the first p-type ion implantation, by at least one of dry etching process and wet etching process as shown in FIG. 56D.
  • a second patterned hard mask layer 907 is then formed on the top of the SiC substrate as shown in FIG.
  • the second patterned hard mask layer 907 is a photoresist based material and thick enough for preventing any unwanted high energy impurities particles penetrating the second patterned hard mask layer 907.
  • a first n-type ion implantation is formed through the second patterned hard mask layer 907 to form a N+ source region 908 within the p-well region 906 as shown in FIG. 56F.
  • the first n-type ion implantation is performed with one or more n-type impurities (e.g., nitrogen, phosphorous etc.).
  • the second patterned hard mask layer 907 is then removed after the first n-type ion implantation by at least one of dry etching and wet etching process as shown in FIG. 56G.
  • a third patterned hard mask layer 909 is then formed on top of the SiC substrate as shown in FIG. 56H.
  • a second p-type implantation is performed through the third patterned hard mask layer 909 to form a P+ region 903, at a first location within the p-well region 906 as shown in FIG. 561.
  • the third patterned hard mask layer 909 is then removed as shown in FIG. 56J by at least one of a dry etching and a wet etching process once the P+ region 903 is formed.
  • the SiC substrate undergoes thermal activation annealing with a carbon-based protection coating at a predefined temperature.
  • the predefined temperature for performing the thermal activation annealing is 1700-degree Celsius.
  • the SiC substrate then may undergo an additional ion implantation for forming a current spreading layer to improve on-state resistance.
  • Ion implantations (e.g., the first p-type implantation, the first n-type impanation, the second p-type implantation, edge termination implantation, current spreading layer implantation etc.) undergone by the SiC substrate is performed prior to the thermal activation annealing step.
  • the carbon-based protection coating is then removed from the SiC substrate.
  • the SiC substrate then undergoes a sacrificial oxide growth and subsequently the sacrificial oxide removal.
  • An active region of the SiC DMOSFET is then patterned by forming and patterning field oxide layer on the SiC substrate.
  • a gate insulator 914 is then formed on top of the SiC substrate as shown in FIG. 56K.
  • the gate insulator 914 is then patterned as shown in FIG. 56L.
  • a polysilicon layer 916 is then formed on top of the SiC substrate as shown in FIG. 56M.
  • the polysilicon layer 916 is then patterned as shown in FIG. 56N. Contacts for the polysilicon layer are kept open for pad metal deposition for forming a gate pad region and one or more gate bus regions.
  • An interlayer dielectric (ILD) 918 is then formed on top of the SiC substrate as shown in FIG. 560.
  • the interlayer dielectric (ILD) 918 is then patterned for exposing the portions of the SiC substrate via the openings of the ILD 918 and leaving one or more ILD bumps 917 as shown in FIG. 56P.
  • a first silicide layer 920 is then formed between the one or more ILD bumps 917 on the exposed portions of top of the SiC substrate for forming a first Ohmic contact as shown in FIG. 56Q.
  • the first silicide layer 920 is a nickel-based silicide layer.
  • the nickel-based silicide is formed by Nickel deposition on the top of the SiC substrate, thermal activation annealing of the deposited Nickel for silicide formation, and removal of any un-reacted Nickel from the SiC substrate.
  • a first pad metal 924 is formed on top of the SiC substrate as shown in FIG. 56R.
  • a second silicide layer 922 is then formed on bottom of the SiC substrate for forming a second Ohmic contact as shown in FIG. 56S.
  • the second silicide layer 922 is then formed on back of the SiC substrate for forming the second Ohmic contact.
  • the second silicide layer 922 is also the nickel-based silicide layer.
  • a second pad metal 926 is then formed on bottom of the second silicide layer 922 of the SiC substrate as shown in FIG. 56T.
  • the second pad metal formation is performed by at least one of e-beam and sputtering.
  • a fourth patterned hard mask layer 911 is then formed on the SiC substrate once the first Ohmic contact and the second Ohmic contact are formed on topside and bottom side/back side of the SiC substrate respectively.
  • the fourth patterned hard mask layer 911 is formed for selectively removing the exposed portions of the ILD layer 918 and depositing a metal region (i.e., a Schottky metal region 928) (shown in FIG. 55D, 55E & 55F) on top of the SiC substrate.
  • the fourth patterned hard mask layer 911 is used for both etching the portion of the ILD layer 918 and lifting off the Schottky metal region 928 when Schottky metal is deposited.
  • the Schottky metal region 928 is in direct contact with the N- drift layer 904 and bridge two adjacent P-well regions 906 (i.e., bridges the adjacent unit cells).
  • the Schottky metal region 928 is then annealed with a predefined thermal budget for forming a Schottky metal contact between the Schottky metal region 928 and the portion of the N- drift layer 904 exposed at the top surface of the SiC substrate.
  • the predefined thermal budget ranges from 55°C to 1100°C. In fig. 55D, 55E & 55F, the first pad metal and the second pad metal formation are performed once the Schottky metal region 928 formation is completed.
  • FIG. 57A to 57T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 55B.
  • the process of manufacturing the DMOSFET structure comprises preparing a silicon carbide (SiC) substrate having a N+ substrate 1002 and a N- drift layer 1004 as shown in FIG. 57 A.
  • the N- drift layer 1004 of the SiC substrate is epi-grown and prepared such that a doping concentration and a thickness of the N- drift layer 1004 are selected primarily based on blocking voltage and forward conduction loss.
  • the N+ substrate 1002 is highly conductive when compared to the N- drift layer 1004 and the N+ substrate 1002 is in direct contact with the N- drift layer 1004.
  • a first patterned hard mask layer 1005 is formed on top of the SiC substrate as shown in FIG. 57B.
  • the first patterned hard mask layer 1005 is thick enough for completely blocking high energy impurities during implantation.
  • the first patterned hard mask layer 1005 is a hard mask of at least one of oxide, nitride, and a polysilicon layer.
  • a first p-type ion implantation is formed in FIG. 57C through the first patterned hard mask layer 1005 to form a p-well region 1006.
  • the first p-type ion implantation is performed with one or more p-type impurities (e.g., aluminum, boron, etc.).
  • first p-type ion implantation may comprise a screen oxide layer.
  • the first patterned hard mask layer 1005 is then removed, after the first p-type ion implantation, by at least one of dry etching process and wet etching process as shown in FIG. 57D.
  • a second patterned hard mask layer 1007 is then formed on the top of the SiC substrate as shown in FIG. 57E for subsequent ion implantation.
  • the second patterned hard mask layer 1007 is a photoresist based material and thick enough for preventing any unwanted high energy impurities particles penetrating the second patterned hard mask layer 1007.
  • a first n-type ion implantation is formed through the second patterned hard mask layer 1007 to form a N+ source region 1008 within the p-well region 1006 as shown in FIG. 57F.
  • the first n-type ion implantation is performed with one or more n-type impurities (e.g., nitrogen, phosphorous etc.).
  • the second patterned hard mask layer 1007 is then removed after the first n-type ion implantation by at least one of dry etching and wet etching process as shown in FIG. 57G.
  • a third patterned hard mask layer 1009 is then formed on top of the SiC substrate as shown in FIG. 57H.
  • a second p-type implantation is performed through the third patterned hard mask layer 1009 to form a P+ region 1003, at a second location, within the p-well region 1006 as shown in FIG. 571.
  • the third patterned hard mask layer 1009 is then removed as shown in FIG. 57J by at least one of a dry etching and a wet etching process once the P+ region 1003 is formed at the second location.
  • the SiC substrate undergoes thermal activation annealing with a carbon-based protection coating at a predefined temperature.
  • the predefined temperature for performing the thermal activation annealing is 1700-degree Celsius.
  • the SiC substrate then may undergo an additional ion implantation for forming a current spreading layer to improve on-state resistance.
  • Ion implantations (e.g., the first p-type implantation, the first n-type impanation, the second p-type implantation, edge termination implantation, current spreading layer implantation etc.) undergone by the SiC substrate is performed prior to the thermal activation annealing step.
  • the carbon-based protection coating is then removed from the SiC substrate.
  • the SiC substrate then undergoes a sacrificial oxide growth and subsequently the sacrificial oxide removal.
  • An active region of the SiC DMOSFET is then patterned by forming and patterning field oxide layer on the SiC substrate.
  • a gate insulator 1014 is then formed on top of the SiC substrate as shown in FIG. 57K.
  • the gate insulator 1014 is then patterned as shown in FIG. 57L.
  • a polysilicon layer 1016 is then formed on top of the SiC substrate as shown in FIG. 57M.
  • the polysilicon layer 1016 is then patterned as shown in FIG. 57N. Contacts for the polysilicon layer are kept open for pad metal deposition for forming a gate pad region and one or more gate bus regions.
  • An interlayer dielectric (ILD) 1018 is then formed on top of the SiC substrate as shown in FIG. 570.
  • the interlayer dielectric (ILD) 1018 is then patterned for exposing the portions of the SiC substrate via the openings of the ILD 1018 and leaving one or more ILD bumps 1017 on top of the SiC substrate as shown in FIG. 57P.
  • a first silicide layer 1020 is then formed between the one or more ILD bumps 1017 on the exposed portions of top of the SiC substrate for forming a first Ohmic contact as shown in FIG. 57Q.
  • the first silicide layer 1020 is a nickel-based silicide layer.
  • the nickel-based silicide is formed by Nickel deposition on the top of the SiC substrate, thermal activation annealing of the deposited Nickel for silicide formation, and removal of any un-reacted Nickel from the SiC substrate.
  • a first pad metal 1024 is formed on top of the SiC substrate as shown in FIG. 57R. The P+ region 1003, formed at the second location, is under the one or more ILD bumps 1017 and do not form any direct contact with the first silicide layer 1020.
  • a second silicide layer 1022 is then formed on bottom of the SiC substrate for forming a second Ohmic contact as shown in FIG. 57S.
  • the second silicide layer 1022 is then formed on back of the SiC substrate for forming the second Ohmic contact.
  • the second silicide layer 1022 is also the nickel -based silicide layer.
  • a second pad metal 1026 is then formed on bottom of the second silicide layer 1022 of the SiC substrate as shown in FIG. 57T.
  • the second pad metal formation is performed by at least one of e-beam and sputtering.
  • a fourth patterned hard mask layer 1011 is then formed on the SiC substrate once the first Ohmic contact and the second Ohmic contact are formed on topside and bottom side /back side of the SiC substrate respectively.
  • the fourth patterned hard mask layer 1011 is formed for selectively removing the exposed portions of the ILD layer 1018 and depositing a metal region 1028 (e.g., a Schottky metal region 1028) (shown in FIG. 55D, 55E & 55F) on top of the SiC substrate.
  • the fourth patterned hard mask layer 1011 is used for both etching the portion of the ILD layer 1018 and lifting off the Schottky metal region 1028 when Schottky metal is deposited.
  • the Schottky metal region 1028 is in direct contact with the N- drift layer 1004 and bridge two adjacent P-well regions 1006 (i.e., bridges the adjacent unit cells).
  • the Schottky metal region 1028 is then annealed with a predefined thermal budget for forming a Schottky metal contact between the Schottky metal region 1028 and the portion of the N- drift layer 1004 exposed at the top surface of the SiC substrate.
  • the predefined thermal budget ranges from 55°C to 1100°C.
  • the first pad metal and the second pad metal formation are performed once the Schottky metal region 1028 formation is completed.
  • the process of manufacturing the DMOSFET structure comprises preparing a silicon carbide (SiC) substrate having a N+ substrate 1102 and a N- drift layer 1104 as shown in FIG. 58A.
  • the N- drift layer 1104 of the SiC substrate is epi-grown and prepared such that a doping concentration and a thickness of the N- drift layer 1104 are selected primarily based on blocking voltage and forward conduction loss.
  • the N+ substrate 1102 is highly conductive when compared to the N- drift layer 1104 and the N+ substrate 1102 is in direct contact with the N- drift layer 1104.
  • a first patterned hard mask layer 1105 is formed on top of the SiC substrate as shown in FIG. 58B.
  • the first patterned hard mask layer 1105 is thick enough for completely blocking high energy impurities during implantation.
  • the first patterned hard mask layer 1105 is a hard mask of at least one of oxide, nitride, and a polysilicon layer.
  • a first p-type ion implantation is formed in FIG. 58C through the first patterned hard mask layer 1105 to form a p-well region 1106.
  • the first p-type ion implantation is performed with one or more p-type impurities (e.g., aluminum, boron, etc.).
  • first p-type ion implantation may comprise a screen oxide layer.
  • the first patterned hard mask layer 1105 is then removed, after the first p-type ion implantation, by at least one of dry etching process and wet etching process as shown in FIG. 58D.
  • a second patterned hard mask layer 1107 is then formed on the top of the SiC substrate as shown in FIG.
  • the second patterned hard mask layer 1107 is a photoresist based material and thick enough for preventing any unwanted high energy impurities particles penetrating the second patterned hard mask layer 1107.
  • a first n-type ion implantation is formed through the second patterned hard mask layer 1107 to form a first N+ source region 1108 within the p-well region 1106 as shown in FIG. 58F.
  • the first n-type ion implantation is performed with one or more n-type impurities (e.g., nitrogen, phosphorous etc.).
  • the second patterned hard mask layer 1107 is then removed after the first n-type ion implantation by at least one of dry etching and wet etching process as shown in FIG. 58G.
  • a third patterned hard mask layer 1109 is then formed on top of the SiC substrate as shown in FIG. 58H.
  • a second p-type implantation is performed through the third patterned hard mask layer 1109 to form a P+ region 1103, at a third location, within the p-well region 1106 as shown in FIG. 581.
  • the third patterned hard mask layer 1109 is then removed as shown in FIG. 58J by at least one of a dry etching and a wet etching process once the P+ region 1103 is formed at the second location.
  • the SiC substrate undergoes thermal activation annealing with a carbon-based protection coating at a predefined temperature.
  • the predefined temperature for performing the thermal activation annealing is 1700-degree Celsius.
  • the SiC substrate then may undergo an additional ion implantation for forming a current spreading layer to improve on-state resistance.
  • Ion implantations (e.g., the first p-type implantation, the first n-type impanation, the second p-type implantation, edge termination implantation, current spreading layer implantation etc.) undergone by the SiC substrate is performed prior to the thermal activation annealing step.
  • the carbon-based protection coating is then removed from the SiC substrate.
  • the SiC substrate then undergoes a sacrificial oxide growth and subsequently the sacrificial oxide removal.
  • An active region of the SiC DMOSFET is then patterned by forming and patterning field oxide layer on the SiC substrate.
  • a gate insulator 1114 is then formed on top of the SiC substrate as shown in FIG. 58K.
  • the gate insulator 1114 is then patterned as shown in FIG. 58L.
  • a polysilicon layer 1116 is then formed on top of the SiC substrate as shown in FIG. 58M.
  • the polysilicon layer 1116 is then patterned as shown in FIG. 58N. Contacts for the poly silicon layer are kept open for pad metal deposition for forming a gate pad region and one or more gate bus regions.
  • An interlayer dielectric (ILD) 1118 is then formed on top of the SiC substrate as shown in FIG. 580.
  • the interlayer dielectric (ILD) 1118 is then patterned for exposing the portions of the SiC substrate via the openings of the ILD 1118 and leaving one or more ILD bumps 1117 on top of the SiC substrate as shown in FIG. 58P.
  • a first silicide layer 1120 is then formed between the one or more ILD bumps 1117 on the exposed portions of top of the SiC substrate for forming one or more first Ohmic contacts as shown in FIG. 58Q.
  • the first silicide layer 1120 is a nickel-based silicide layer.
  • the nickel-based silicide is formed by Nickel deposition on the top of the SiC substrate, thermal activation annealing of the deposited Nickel for silicide formation, and removal of any un-reacted Nickel from the SiC substrate.
  • a first pad metal 1124 is formed on top of the SiC substrate as shown in FIG. 58R. The P+ region 1103, formed at the third location, is under the one or more ILD bumps 1117 and do not form any direct contact with the first silicide layer 1120.
  • a second silicide layer 1122 is then formed on bottom of the SiC substrate for forming a second Ohmic contact as shown in FIG. 58 S.
  • the second silicide layer 1122 is then formed on back of the SiC substrate for forming the second Ohmic contact.
  • the second silicide layer 1122 is also the nickel-based silicide layer.
  • a second pad metal 1126 is then formed on bottom of the second silicide layer 1122 of the SiC substrate.
  • the second pad metal formation is performed by at least one of e-beam and sputtering.
  • a fourth patterned hard mask layer 1111 is then formed on the SiC substrate once the first Ohmic contact and the second Ohmic contact are formed on topside and bottom side/back side of the SiC substrate respectively.
  • the fourth patterned hard mask layer 1111 is formed for selectively removing the exposed portions of the ILD layer 1118 and depositing a metal region 1128 (i.e., a Schottky metal region 1128) shown in FIG. 55D, 55E & 55F on top of the SiC substrate.
  • the fourth patterned hard mask layer 1111 is used for both etching the portion of the ILD layer 1118 and lifting off the Schottky metal region 1128 when Schottky metal is deposited.
  • the Schottky metal region 1128 is in direct contact with the top of the N- drift layer 1104 and bridge two adjacent P- well regions 1106 (i.e., bridges the adjacent unit cells).
  • the Schottky metal region 1128 is then annealed with a predefined thermal budget for forming a Schottky metal contact between the Schottky metal region 1128 and the portion of the N- drift layer 1104 exposed at the top surface of the SiC substrate.
  • the predefined thermal budget ranges from 55°C to 1100°C. In fig. 55D, 55E & 55F, the first pad metal and the second pad metal formation are performed once the Schottky metal region 1128 formation is completed.
  • FIG. 59A, 59B & 59C illustrate an embodiment of cross sectional structures of a unit cell of a double-implantation metal oxide semiconductor field effect transistor (DMOSFET) comprising a second conductivity type well contact region that meanders at three different locations respectively, allowing a second conductivity type well region to be in contact with a source metal only through the second conductivity type well contact region.
  • the DMOSFET shown in FIG. 59A, 59B and 59C is a n-type planar gate SiC DMOSFET.
  • the DMOSFET is a p-type planar gate DMOSFET.
  • the DMOSFET (shown in FIG.
  • the 59 A, 59B and 59C comprises a Silicon Carbide (SiC) substrate.
  • the SiC substrate comprises a N+ substrate 1202 and a N- drift layer 1204.
  • the DMOSFET also comprises a P-well region 1206, a N+ source region 1208 and a P+ region 1203 (i.e., the second conductivity type well contact region).
  • the N+ source regions 1208 is formed within the P-well region 1206.
  • the P+ region 1203 is meandering within the P-well region 1206 by performing a p-type implantation.
  • the P+ region 1203 comprise a periodic spacing with the successive P+ region 1203 (i.e., non-contiguous).
  • the lateral extent of the P+ region 1203 varies with a non-zero value in a direction orthogonal to the unit cell.
  • the meandering P+ region 1203 periodically forms ohmic contacts to a first pad metal 1224 (e.g., the source metal) via a first silicide layer 1220 between two interlayer dielectric (ILD) bumps 1217 located between metal oxide semiconductor gate stack and the first pad metal 1224.
  • the P-well region 1206 contacts with the first pad metal 1224 (e.g., the source metal) only through the meandering P+ region 1203.
  • the P-well region 1206 do not have a direct contact with the first pad metal 1224.
  • the meandering P+ region 1203 follows Zigzag path, where comers of the zigzag path is right angled.
  • the Zigzag path of the meandering P+ region 1203 comprises dimensions a, P, and y.
  • the meandering P+ region 1203 comprise a target size and a target spacing between adjacent junction points located between the meandering P+ region 803.
  • Contact resistance to the first pad metal 1224 varies when the P+ region 1203 under the ILD bumps 1217 do not have direct contact with the first pad metal 1224 and when the P+ region 1203 have direct contact with the first pad metal 1224 through the first silicide layer 1220.
  • the portions of the meandering P+ region 1203 which are directly under the ILD bumps 1217 functions as networks of distributed ballast resistors and provides an additional source resistance to the source contact resistance.
  • the additional contact resistance provided directly impacts the differential on- resistance of one or more body diode regions of the DMOSFET. Since, the p-well region 1206 contacts the first pad metal 1224 only through the meandering P+ region 1203, flow of carriers is confined within the meandering P+ region 1203. The confined flow of carriers increases source contact resistance of each ballast resistor network and further impacts differential on-resistance of the one or more body diode regions of the DMOSFET.
  • the source contact resistance is dependent on the sizing, the spacing between adjacent junction points located between the meandering P+ region 1203, and the silicide region between the adjacent ILD bumps 1217, the source contact resistance is tuned by sizing the P+ region 1203 to a target size and controlling the spacing to a target spacing.
  • the target size ranges from 10 nm to 10 pm.
  • the target spacing ranges from 10 nm to 10 pm.
  • the reduction of the width (a) also shrinks the area where the Ohmic contacts are formed so degrades the differential on-resistance of the body diode regions.
  • the resistance of each ballast resistor network is increased which degrades the differential on-resistance of the body diode regions.
  • spacing (P) between two adjacent junction points between the meandering featured P+ region 1203, and the straight silicide region between two adjacent ILD bumps 1217 is increased, the resistance of each ballast resistor network is increased which degrades the differential on- resistance of the one or more body diode regions.
  • FIG. 59D, 59E & 59F illustrate an embodiment of cross sectional structures of one or more unit cells of a diode integrated DMOSFET, each DMOSFET unit cell comprising the second conductivity type well contact region that meanders at three different locations respectively, allowing the second conductivity type well region to be in contact with the source metal only through the second conductivity type well contact region.
  • the DMOSFET (shown in FIG. 59D, 59E & 59F) is a n-type planar gate SiC DMOSFET.
  • the DMOSFET shown in FIG. 59D, 59E & 59F operates in a similar way to FIG. 59A, 59B & 59C.
  • FIG. 59D, 59E & 59F illustrate an embodiment of cross sectional structures of one or more unit cells of a diode integrated DMOSFET, each DMOSFET unit cell comprising the second conductivity type well contact region that meanders at three different locations respectively, allowing
  • the DMOSFET (shown in FIG. 59D, 59E & 59F) comprises a metal region 1228 (e.g., a Schottky metal region 1228) in direct contact with the N- drift layer 1204 and bridges adjacent P-well regions 1206 of the one or more P-well regions 1206 (i.e., bridges the adjacent unit cells).
  • a metal region 1228 e.g., a Schottky metal region 1228
  • FIG. 59G illustrate an embodiment of a cross sectional structure of one or more unit cells of a diode integrated trench gate MOSFET, comprising one or more unit cells of an integrated Schottky diode, each MOSFET unit cell comprising the second conductivity type well contact region at the first location, allowing the second conductivity type well region to be in contact with the source metal only through the second conductivity type well contact region.
  • the trench gate MOSFET shown in FIG. 59G is a n-type trench gate SiC MOSFET.
  • the trench gate MOSFET is a p-type trench gate SiC MOSFET.
  • the trench gate MOSFET shown in FIG. 59G operates in a similar way to planar gate MOSFET shown in FIG. 59A and FIG. 59D.
  • the trench gate MOSFET comprises one or more trench gate structures instead of one or more planar gate structures.
  • the one or more trench gate structures of the trench gate MOSFET comprises sidewalls that are exposed to the first N+ source region 1208 and the one or more P-well regions 1206.
  • the bottom of the one or more trench gate structures is in vicinity of the bottom of the one or more P- well regions 1206.
  • the bottom of the one or more trench gate structures is adjusted appropriately depending on electrical properties of the MOSFET device.
  • Each trench gate structure of the trench gate MOSFET comprises a gate insulator as liner along the sidewall and the bottom of the respective trench gate structure.
  • the trench gate MOSFET also comprises the polysilicon layer that fills each gate-insulator lined trenches and serves as gate electrode.
  • the trench gate MOSFET further comprises the interlayer dielectric (ILD) 1218 over each polysilicon layer to open short circuitry between the first pad metal 1224 (e.g., the source metal) and the gate electrode.
  • ILD interlayer dielectric
  • FIG. 60A to 60T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 59 A.
  • the process of manufacturing the DMOSFET structure comprises preparing a silicon carbide (SiC) substrate having a N+ substrate 1302 and a N- drift layer 1304 as shown in FIG. 60 A.
  • the N- drift layer 1304 of the SiC substrate is epi-grown and prepared such that a doping concentration and a thickness of theN- drift layer 1304 are selected primarily based on blocking voltage and forward conduction loss.
  • the N+ substrate 1302 is highly conductive when compared to the N- drift layer 1304 and the N+ substrate 1302 is directly located under the N- drift layer 1304.
  • a first patterned hard mask layer 1305 is formed on top of the SiC substrate as shown in FIG. 60B.
  • the first patterned hard mask layer 1305 is thick enough for completely blocking high energy impurities during implantation.
  • the first patterned hard mask layer 1305 is a hard mask of at least one of oxide, nitride, and a polysilicon layer.
  • a first p-type ion implantation is formed in FIG. 60C through the first patterned hard mask layer 1305 to form a p-well region 1306.
  • the first p-type ion implantation is performed with one or more p-type impurities (e.g., aluminum, boron, etc.).
  • first p-type ion implantation may comprise a screen oxide layer.
  • the first patterned hard mask layer 1305 is then removed, after the first p-type ion implantation, by at least one of dry etching process and wet etching process as shown in FIG. 60D.
  • a second patterned hard mask layer 1307 is then formed on the top of the SiC substrate as shown in FIG.
  • the second patterned hard mask layer 1307 is a photoresist based material and thick enough for preventing any unwanted high energy impurities particles penetrating the second patterned hard mask layer 1307.
  • a first n-type ion implantation is formed through the second patterned hard mask layer 1307 to form a N+ source region 1308 within the p-well region 1306 as shown in FIG. 60F.
  • the first n-type ion implantation is performed with one or more n-type impurities (e.g., nitrogen, phosphorous etc.).
  • the second patterned hard mask layer 1307 is then removed after the first n-type ion implantation by at least one of dry etching and wet etching process as shown in FIG. 60G.
  • a third patterned hard mask layer 1309 is then formed on top of the SiC substrate as shown in FIG. 60H.
  • a second p-type implantation is performed through the third patterned hard mask layer 1309 to form a P+ region 1303, at a first location, within the p-well region 1306 as shown in FIG. 601.
  • the P+ region 1303 formed at the first location allows the P-well region 1306 to be in contact with a first pad metal 1324 (e.g., a source metal) only through the P+ region 1303 formed at the first location.
  • a first pad metal 1324 e.g., a source metal
  • the third patterned hard mask layer 1309 is then removed as shown in FIG. 60J by at least one of a dry etching and a wet etching process once the P+ region 1303 is formed.
  • the SiC substrate undergoes thermal activation annealing with a carbon-based protection coating at a predefined temperature.
  • the predefined temperature for performing the thermal activation annealing is 1700-degree Celsius.
  • the SiC substrate then may undergo an additional ion implantation for forming a current spreading layer to improve on-state resistance.
  • Ion implantations (e.g., the first p-type implantation, the first n-type impanation, the second p-type implantation, edge termination implantation, current spreading layer implantation etc.) undergone by the SiC substrate is performed prior to the thermal activation annealing step.
  • the carbon-based protection coating is then removed from the SiC substrate.
  • the SiC substrate then undergoes a sacrificial oxide growth and subsequently the sacrificial oxide removal.
  • An active region of the SiC DMOSFET is then patterned by forming and patterning field oxide layer on the SiC substrate.
  • a gate insulator 1314 is then formed on top of the SiC substrate as shown in FIG. 60K.
  • the gate insulator 1314 is then patterned as shown in FIG. 60L.
  • a polysilicon layer 1316 is then formed on top of the SiC substrate as shown in FIG. 60M.
  • the polysilicon layer 1316 is then patterned as shown in FIG. 60N. Contacts for the polysilicon layer 1316 is kept open for pad metal deposition for forming a gate pad region and one or more gate bus regions.
  • An interlayer dielectric (ILD) 1318 is then formed on top of the SiC substrate as shown in FIG. 600.
  • ILD interlayer dielectric
  • the interlayer dielectric (ILD) 1318 is then patterned for exposing the portions of the SiC substrate via the openings of the ILD 1318 and leaving one or more ILD bumps 1317 as shown in FIG. 60P.
  • a first silicide layer 1320 is then formed between the one or more ILD bumps 1317 on the exposed portions of top of the SiC substrate for forming a first Ohmic contact as shown in FIG. 60Q.
  • the first silicide layer 1320 is a nickel -based silicide layer.
  • the nickel-based silicide is formed by Nickel deposition on the top of the SiC substrate, thermal activation annealing of the deposited Nickel for silicide formation, and removal of any un-reacted Nickel from the SiC substrate.
  • the first pad metal 1324 is formed on top of the SiC substrate as shown in FIG. 60R.
  • a second silicide layer 1322 is then formed on bottom of the SiC substrate for forming a second Ohmic contact as shown in FIG. 60S.
  • the second silicide layer 1322 is then formed on back of the SiC substrate for forming the second Ohmic contact.
  • the second silicide layer 1322 is also the nickel -based silicide layer.
  • a second pad metal 1326 is then formed on bottom of the second silicide layer 1322 of the SiC substrate as shown in FIG. 60T.
  • the second pad metal formation is performed by at least one of e-beam and sputtering.
  • a fourth patterned hard mask layer 1311 is then formed on the SiC substrate once the first Ohmic contact and the second Ohmic contact are formed on topside and bottom side/back side of the SiC substrate respectively.
  • the fourth patterned hard mask layer 1311 is formed for selectively removing the exposed portions of the ILD layer 1318 and depositing a metal region (e.g., the Schottky metal region 1328) shown in FIG. 60D, 60E & 60F on top of the SiC substrate.
  • the fourth patterned hard mask layer 1311 is used for both etching the portion of the ILD layer 1318 and lifting off the Schottky metal region 1328 when Schottky metal is deposited.
  • the Schottky metal region 1328 is in direct contact with the top of the N- drift layer 1304 and bridge two adjacent P- well regions 1306 (i.e., bridges the adjacent unit cells).
  • the Schottky metal region 1328 is then annealed with a predefined thermal budget for forming a Schottky metal contact between the Schottky metal region 1328 and the portion of the N- drift layer 1304 exposed at the top surface of the SiC substrate.
  • the predefined thermal budget ranges from 55°C to 1100°C.
  • the first pad metal and the second pad metal formation are performed once the Schottky metal region 1328 formation is completed.
  • 61A to 61T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 59B.
  • the process of manufacturing the DMOSFET structure comprises preparing a silicon carbide (SiC) substrate having a N+ substrate 1402 and a N- drift layer 1404 as shown in FIG. 61 A.
  • the N- drift layer 1404 of the SiC substrate is epi-grown and prepared such that a doping concentration and a thickness of the N- drift layer 1404 are selected primarily based on blocking voltage and forward conduction loss.
  • the N+ substrate 1402 is highly conductive when compared to the N- drift layer 1404 and the N+ substrate 1402 is directly located under the N- drift layer 1404.
  • a first patterned hard mask layer 1405 is formed on top of the SiC substrate as shown in FIG. 61B.
  • the first patterned hard mask layer 1405 is thick enough for completely blocking high energy impurities during implantation.
  • the first patterned hard mask layer 1405 is a hard mask of at least one of oxide, nitride, and a polysilicon layer.
  • a first p-type ion implantation is formed in FIG. 61C through the first patterned hard mask layer 1405 to form a p-well region 1406.
  • the first p-type ion implantation is performed with one or more p-type impurities (e.g., aluminum, boron, etc.).
  • first p-type ion implantation may comprise a screen oxide layer.
  • the first patterned hard mask layer 1405 is then removed, after the first p-type ion implantation, by at least one of dry etching process and wet etching process as shown in FIG. 61D.
  • a second patterned hard mask layer 1407 is then formed on the top of the SiC substrate as shown in FIG.
  • the second patterned hard mask layer 1407 is a photoresist based material and thick enough for preventing any unwanted high energy impurities particles penetrating the second patterned hard mask layer 1407.
  • a first n-type ion implantation is formed through the second patterned hard mask layer 1407 to form a N+ source region 1408 within the p-well region 1406 as shown in FIG. 61F.
  • the first n-type ion implantation is performed with one or more n-type impurities (e.g., nitrogen, phosphorous etc.).
  • the second patterned hard mask layer 1407 is then removed after the first n-type ion implantation by at least one of dry etching and wet etching process as shown in FIG. 61G.
  • a third patterned hard mask layer 1409 is then formed on top of the SiC substrate as shown in FIG. 61H.
  • a second p-type implantation is performed through the third patterned hard mask layer 1409 to form a P+ region 1403, at a second location, within the p-well region 1406 as shown in FIG. 611.
  • the third patterned hard mask layer 1409 is then removed as shown in FIG. 61 J by at least one of a dry etching and a wet etching process once the P+ region 1403 is formed at the second location.
  • the SiC substrate undergoes thermal activation annealing with a carbon-based protection coating at a predefined temperature.
  • the predefined temperature for performing the thermal activation annealing is 1700-degree Celsius.
  • the SiC substrate then may undergo an additional ion implantation for forming a current spreading layer to improve on-state resistance.
  • Ion implantations (e.g., the first p-type implantation, the first n-type impanation, the second p-type implantation, edge termination implantation, current spreading layer implantation etc.) undergone by the SiC substrate is performed prior to the thermal activation annealing step.
  • the carbon-based protection coating is then removed from the SiC substrate.
  • the SiC substrate then undergoes a sacrificial oxide growth and subsequently the sacrificial oxide removal.
  • An active region of the SiC DMOSFET is then patterned by forming and patterning field oxide layer on the SiC substrate.
  • a gate insulator 1414 is then formed on top of the SiC substrate as shown in FIG. 61K.
  • the gate insulator 1414 is then patterned as shown in FIG. 61L.
  • a polysilicon layer 1416 is then formed on top of the SiC substrate as shown in FIG. 61M.
  • the polysilicon layer 1416 is then patterned as shown in FIG. 6 IN. Contacts for the poly silicon layer are kept open for pad metal deposition for forming a gate pad region and one or more gate bus regions.
  • An interlayer dielectric (ILD) 1418 is then formed on top of the SiC substrate as shown in FIG. 610.
  • the interlayer dielectric (ILD) 1418 is then patterned for exposing the portions of the SiC substrate via the openings of the ILD 1418 and leaving one or more ILD bumps 1417 on top of the SiC substrate as shown in FIG. 61P.
  • a first silicide layer 1420 is then formed between the one or more ILD bumps 1417 on the exposed portions of top of the SiC substrate for forming a first Ohmic contacts as shown in FIG. 61Q.
  • the first silicide layer 1420 is a nickel-based silicide layer.
  • the nickel -based silicide is formed by Nickel deposition on the top of the SiC substrate, thermal activation annealing of the deposited Nickel for silicide formation, and removal of any un-reacted Nickel from the SiC substrate.
  • a first pad metal 1424 is formed on top of the SiC substrate as shown in FIG. 61R. The P+ region 1403, formed at the second location, is under the one or more ILD bumps 1417 and do not form any direct contact with the first silicide layer 1420.
  • a second silicide layer 1422 is then formed on bottom of the SiC substrate for forming a second Ohmic contact as shown in FIG. 61 S.
  • the second silicide layer 1422 is then formed on back of the SiC substrate for forming the second Ohmic contact.
  • the second silicide layer 1422 is also the nickel-based silicide layer.
  • a second pad metal is then formed on bottom of the second silicide layer 1422 of the SiC substrate as shown in FIG. 61T.
  • the second pad metal formation is performed by at least one of e-beam and sputtering.
  • a fourth patterned hard mask layer 1411 is then formed on the SiC substrate once the first Ohmic contact and the second Ohmic contact are formed on topside and bottom side/back side of the SiC substrate respectively.
  • the fourth patterned hard mask layer 1411 is formed for selectively removing the exposed portions of the ILD layer 1418 and depositing a metal region (i.e., a Schottky metal region 1428) shown in FIG. 59D, 59E & 59F on top of the SiC substrate.
  • the fourth patterned hard mask layer 1411 is used for both etching the portion of the ILD layer 1418 and lifting off the Schottky metal region 1428 when Schottky metal is deposited.
  • the Schottky metal region 1428 is in direct contact with the N- drift layer 1404 and bridge two adjacent P-well regions 1406 (i.e., bridges the adjacent unit cells).
  • the Schottky metal region 1428 is then annealed with a predefined thermal budget for forming a Schottky metal contact between the Schottky metal region 1428 and the portion of the N- drift layer 1404 exposed at the top surface of the SiC substrate.
  • the predefined thermal budget ranges from 55°C to 1100°C.
  • the first pad metal and the second pad metal formation are performed once the Schottky metal region 1428 formation is completed.
  • FIG. 62A to 62T illustrate an embodiment of a process of manufacturing the DMOSFET structure shown in FIG. 59C.
  • the process of manufacturing the DMOSFET structure comprises preparing a silicon carbide (SiC) substrate having a N+ substrate 1502 and a N- drift layer 1504 as shown in FIG. 62 A.
  • the N- drift layer 1504 of the SiC substrate is epi-grown and prepared such that a doping concentration and a thickness of the N- drift layer 1504 are selected primarily based on blocking voltage and forward conduction loss.
  • the N+ substrate 1502 is highly conductive when compared to the N- drift layer 1504 and the N+ substrate 1502 is directly located under the N- drift layer 1504.
  • a first patterned hard mask layer 1505 is formed on top of the SiC substrate as shown in FIG. 62B.
  • the first patterned hard mask layer 1505 is thick enough for completely blocking high energy impurities during implantation.
  • the first patterned hard mask layer 1505 is a hard mask of at least one of oxide, nitride, and a polysilicon layer.
  • a first p-type ion implantation is formed in FIG. 62C through the first patterned hard mask layer 1505 to form a p-well region 1506.
  • the first p-type ion implantation is performed with one or more p-type impurities (e.g., aluminum, boron, etc.).
  • first p-type ion implantation may comprise a screen oxide layer.
  • the first patterned hard mask layer 1505 is then removed, after the first p-type ion implantation, by at least one of dry etching process and wet etching process as shown in FIG. 62D.
  • a second patterned hard mask layer 1507 is then formed on the top of the SiC substrate as shown in FIG.
  • the second patterned hard mask layer 1507 is a photoresist based material and thick enough for preventing any unwanted high energy impurities particles penetrating the second patterned hard mask layer 1507.
  • a first n-type ion implantation is formed through the second patterned hard mask layer 1507 to form a N+ source region 1508 within the p-well region 1506 as shown in FIG. 62F.
  • the first n-type ion implantation is performed with one or more n-type impurities (e.g., nitrogen, phosphorous etc.).
  • the second patterned hard mask layer 1507 is then removed after the first n-type ion implantation by at least one of dry etching and wet etching process as shown in FIG. 62G.
  • a third patterned hard mask layer 1509 is then formed on top of the SiC substrate as shown in FIG. 62H.
  • a second p-type implantation is performed through the third patterned hard mask layer 1509 to form a P+ region 1503, at a third location, within the p-well region 1506 as shown in FIG. 621.
  • the third patterned hard mask layer 1509 is then removed as shown in FIG. 62J by at least one of a dry etching and a wet etching process once the P+ region 1503 is formed at the second location.
  • the SiC substrate undergoes thermal activation annealing with a carbon-based protection coating at a predefined temperature.
  • the predefined temperature for performing the thermal activation annealing is 1700-degree Celsius.
  • the SiC substrate then may undergo an additional ion implantation for forming a current spreading layer to improve on-state resistance.
  • Ion implantations (e.g., the first p-type implantation, the first n-type impanation, the second p-type implantation, edge termination implantation, current spreading layer implantation etc.) undergone by the SiC substrate is performed prior to the thermal activation annealing step.
  • the carbon-based protection coating is then removed from the SiC substrate.
  • the SiC substrate then undergoes a sacrificial oxide growth and subsequently the sacrificial oxide removal.
  • An active region of the SiC DMOSFET is then patterned by forming and patterning field oxide layer on the SiC substrate.
  • a gate insulator 1514 is then formed on top of the SiC substrate as shown in FIG. 62K.
  • the gate insulator 1514 is then patterned as shown in FIG. 62L.
  • a polysilicon layer 1516 is then formed on top of the SiC substrate as shown in FIG. 62M.
  • the polysilicon layer 1516 is then patterned as shown in FIG. 62N. Contacts for the polysilicon layer are kept open for pad metal deposition for forming a gate pad region and one or more gate bus regions.
  • An interlayer dielectric (ILD) 1518 is then formed on top of the SiC substrate as shown in FIG. 620.
  • the interlayer dielectric (ILD) 1518 is then patterned for exposing the portions of the SiC substrate via the openings of the ILD 1518 and leaving one or more ILD bumps 1517 on top of the SiC substrate as shown in FIG. 62P.
  • a first silicide layer 1520 is then formed between the one or more ILD bumps 1517 on the exposed portions on top of the SiC substrate for forming a first Ohmic contact as shown in FIG. 62Q.
  • the first silicide layer 1520 is a nickel -based silicide layer.
  • the nickel -based silicide is formed by Nickel deposition on the top of the SiC substrate, thermal activation annealing of the deposited Nickel for silicide formation, and removal of any un-reacted Nickel from the SiC substrate.
  • a first pad metal 1524 is formed on top of the SiC substrate as shown in FIG. 62R.
  • the P+ region 1503, formed at the third location, is under the one or more ILD bumps 1517 and do not form any direct contact with the first silicide layer 1520.
  • a second silicide layer 1522 is then formed on bottom of the SiC substrate for forming a second Ohmic contact as shown in FIG. 62S.
  • the second silicide layer 1522 is then formed on back of the SiC substrate for forming the second Ohmic contact.
  • the second silicide layer 1522 is also the nickel -based silicide layer.
  • a second pad metal 1526 is then formed on bottom of the second silicide layer 1522 of the SiC substrate as shown in FIG. 62T.
  • the second pad metal formation is performed by at least one of e-beam and sputtering.
  • a fourth patterned hard mask layer 1511 is then formed on the SiC substrate once the first Ohmic contact and the second Ohmic contact are formed on topside and bottom side/back side of the SiC substrate respectively.
  • the fourth patterned hard mask layer 1511 is formed for selectively removing the exposed portions of the ILD layer 1518 and depositing a metal region (e.g., a Schottky metal region 1528) shown in FIG. 59D, 59E & 59F on top of the SiC substrate.
  • the fourth patterned hard mask layer 1511 is used for both etching the portion of the ILD layer 1518 and lifting off the Schottky metal region 1528 when Schottky metal is deposited.
  • the Schottky metal region 1528 is in direct contact with the N- drift layer 1504 and bridge two adjacent P-well regions 1506 (i.e., bridges the adjacent unit cells).
  • the Schottky metal region 1528 is then annealed with a predefined thermal budget for forming a Schottky metal contact between the Schottky metal region 1528 and the portion of the N- drift layer 1504 exposed at the top surface of the SiC substrate.
  • the predefined thermal budget ranges from 55°C to 1100°C.
  • the first pad metal and the second pad metal formation are performed once the Schottky metal region 1528 formation is completed.
  • Embodiments relate to MOSFET power device having inversion channels.
  • An embodiment relates to the MOSFET comprising a first metal oxide semiconductor (MOS) interface at a first section and a second metal oxide semiconductor (MOS) interface at a second section.
  • MOS metal oxide semiconductor
  • An embodiment relates to the MOSFET comprising the first metal oxide semiconductor (MOS) interface at the first section and a metal region formed adjacent to a first conductivity type layer at the second section.
  • MOS metal oxide semiconductor
  • An embodiment relates to the MOSFET comprising the first section and the second section arranged in at least one sequence along a lateral direction.
  • An embodiment relates to the MOSFET comprising a higher channel density.
  • An embodiment relates to the MOSFET for minimizing specific on-resistance.
  • An embodiment relates to the MOSFET for adjusting short-circuit withstand time. [00731] An embodiment relates to the MOSFET for adjusting unclamped inductive switching energy.
  • An embodiment relates to the MOSFET for adjusting gate threshold voltage stability.
  • An embodiment relates to the MOSFET for increasing effective channel length for a given on-resistance target.
  • An embodiment relates to the MOSFET comprising the first metal region in direct contact with a first conductivity type drift layer.
  • An embodiment relates to the MOSFET comprising the first MOS interface comprising a first contact with a horizontal surface of a semiconductor substrate and a second contact with a trench sidewall of a trench region.
  • An embodiment relates to the MOSFET comprising the second MOS interface comprising a third contact solely with the trench sidewall of the trench region.
  • An embodiment relates to the formation of the second MOS interface at the second section, in which the trench region is in contact with the first conductivity type drift layer through a gap between a second conductivity type first well region and a second conductivity type second well region.
  • An embodiment relates to the MOSFET comprising the metal region at the second section, in which the trench region is not in contact with the first conductivity type drift layer.
  • An embodiment relates to the MOSFET comprising the metal region at the second section, in which the second conductivity type first well region and the second conductivity type second well region encloses bottom portion of the trench region.
  • An embodiment relates to the MOSFET, in which the second conductivity type first well region and the second conductivity type second well region overlaps at the first section.
  • An embodiment relates to the MOSFET, in which the second conductivity type first well region and the second conductivity type second well region overlaps at the first section and the second section.
  • FIG. 63 illustrates an embodiment of a cross-sectional structure of one or more unit cells of a power MOSFET, a first unit cell of the one or more unit cells comprising a first metal oxide semiconductor (MOS) interface on a horizontal surface of a semiconductor substrate and a trench sidewall, and a second unit cell of the one or more unit cells comprising a second metal oxide semiconductor (MOS) interface formed solely on the trench sidewall.
  • the MOSFET (shown in FIG. 63) is a n-type MOSFET.
  • the terms "first conductivity type” and "second conductivity type” are used to describe n-type and p-type respectively.
  • the MOSFET is a p-type MOSFET.
  • the MOSFET (shown in FIG. 63) comprises the semiconductor substrate.
  • the semiconductor substrate comprises aN+ substrate 102 (i.e., a first conductivity type substrate) and aN- drift layer 104 (i.e., a first conductivity type drift layer).
  • the semiconductor substrate comprises a silicon carbide (SiC) substrate.
  • the MOSFET comprises a first section and a second section that are contiguously located along a lateral direction within the MOSFET.
  • the first section comprises the first metal oxide semiconductor (MOS) interface
  • the second section comprises the second metal oxide semiconductor (MOS) interface.
  • the first section and the second section are arranged in at least one sequence from left to right or right to left.
  • the at least one sequence comprises the first section (i.e., section A as shown in FIG. 63) at a first location and the second section (i.e., section B as shown in FIG. 63) at a second location along the lateral direction.
  • the at least one sequence comprises the second section at the first location and the first section at the second location along the lateral direction.
  • the at least one sequence comprises the first section at the first location and the second location along the lateral direction.
  • the at least one sequence comprises the second section at the first location and the second location along the lateral direction.
  • At the least one sequence comprises the first section at the first location and a third location, and the second section at the second location along the lateral direction. In yet another embodiment, at the least one sequence comprises the second section at the first location and the third location, and the first section at the second location along the lateral direction. For example, assume the first section as ‘A’ and the second section as ‘B’, then the at least one sequence comprises ‘AB’, ‘BA’, ‘AA’, ‘BB’, ‘ABA’, ‘AAB’, ‘BAA’, ‘ABB’, ‘BAB’, ‘BBA’, ‘ABAB’, ‘ABBA’, ‘BAAB’, etc.
  • the MOSFET comprises a first P-well region 106 (i.e., a second conductivity type first well region), a second P-well region 112 (i.e., a second conductivity type second well region), a first source region 108, a second source region 114 and a trench region 110.
  • the first source region 108 and the second source region 114 are two distinct source regions.
  • the first P-well region 106 and the second P-well region 112 are two distinct well regions.
  • the first source region 108 is positioned (e.g., confined) within the first P-well region 106.
  • the second source region 114 is positioned (e.g., confined) within the second P-well region 112.
  • the second source region 114 and the second P-well region 112 are positioned closer to the first section and far away from the second section.
  • the second P-well region 112 overlaps the first P-well region 106 at the first section.
  • the MOSFET comprises a gap between the first P-well region 106 and the second P-well region 112 at the second section.
  • the second P-well region 112 does not overlap the first P-well region 106 at the second section.
  • the trench region 110 is extended through the first P-well region 106 and the first source region 108.
  • the trench region 110 comprises a contact with the N-drift layer 104 through the gap between the first P-well region 106 and the second P-well region 112.
  • the MOSFET comprises silicide layers 122, 124 on top of the first source region 108, the second source region 114 and bottom of the N+ substrate 102.
  • the silicide layer 122 on top of the second source region 114 is partly positioned on top of the second P-well region 112.
  • the first section comprises the first metal oxide semiconductor (MOS) interface.
  • the first MOS interface comprises a first portion and a second portion.
  • the first portion comprises a first contact with a horizontal surface (e.g., an unetched surface) of the semiconductor substrate.
  • the first portion of the first MOS interface is positioned parallel to 0001 crystal plane of the semiconductor substrate.
  • the first portion of the first MOS interface is positioned parallel to 11-20 crystal plane of the semiconductor substrate.
  • the second portion of the first MOS interface comprises a second contact with the trench sidewall of the trench region 110.
  • the second portion of the first MOS interface is positioned parallel to one of 11-20 crystal plane and 1-100 crystal plane of the semiconductor substrate.
  • the first section comprises a combination of a planar MOSFET structure and a trench MOSFET structure.
  • the second section comprises the second MOS interface.
  • the second MOS interface comprises a third contact with the trench sidewall of the trench region 110.
  • the second section comprises solely the trench MOSFET structure.
  • the MOSFET (shown in FIG. 63), comprising the first section and the second section, comprises a higher channel density and reduced on-resistance of the MOSFET.
  • the trench region comprises the trench sidewall.
  • the trench sidewall of the trench region 110 comprises a sloped sidewall.
  • the sloped sidewall comprises a sidewall angle ranging from 30° to 90°.
  • the trench region 110 comprises a depth ranging from 0.2 pm to 2.0 pm.
  • a slope of the sloped sidewall is selected appropriately to orient the first MOS interface along a predefined crystal plane that comprises a low trap density.
  • the first portion of the first MOS interface is positioned parallel to one of 11-20 crystal plane and 0338 crystal plane of the sloped sidewall of the semiconductor substrate, when the trench sidewall comprises the sloped sidewall.
  • the MOSFET comprising the sloped sidewall further comprises a higher channel mobility in addition to the higher channel density.
  • the MOSFET structure provides flexibility to a designer to increase/lower density of the first section comprising at least one of the trench MOSFET structure and the planar MOSFET structure, and the second section comprising the trench MOSFET structure alone.
  • the density of the first section and the second section is increased or lowered depending on requirement of at least one of a specific on-resistance of the MOSFET and robustness metric such as a short-circuit withstand time, an unclamped inductive switching energy and a gate threshold voltage stability.
  • the MOSFET shown in FIG. 63 further provides the flexibility to at least one of (a) increase an effective channel length for the given on-resistance and (b) reduce the on-resistance for a given chip size based on requirement.
  • FIG. 64A to 64AB are cross-sectional views illustrating an embodiment of a process of manufacturing the MOSFET structure shown in FIG. 63.
  • the process of manufacturing the MOSFET structure shown in FIG. 63 comprises preparing a semiconductor substrate having a N+ substrate 202 (i.e., a first conductivity type substrate) and a N- drift layer 204 (i.e., a first conductivity type drift layer) as shown in FIG. 64A.
  • the N- drift layer 204 is grown on top of the N+ substrate 202.
  • the N+ substrate 202 comprises a heavily doped substrate.
  • a first patterned hard mask layer 205 is formed on topside of the semiconductor substrate as shown in FIG. 64B.
  • a first p-type ion implantation (e.g., Aluminum, Boron) is formed on the topside of the semiconductor substrate through the first patterned hard mask layer 205 to form a first p-well region 206 as shown in FIG. 64C.
  • the first patterned hard mask layer 205 is then removed from the topside of the semiconductor substrate as shown in FIG. 64D.
  • the first p-well region 206 is formed by a first epitaxial growth using a p-type impurity (e.g., Aluminum, Boron) into the N- drift layer 204.
  • the first P-well region 206 comprises a first predefined implantation energy and a first predefined dosage.
  • the first predefined implantation energy ranges from 5 keV to 5 MeV and the first predefined dosage ranges from 1E13 cm -2 to 5E16 cm-2.
  • the first P-well region 206 is formed using a first single ion-implantation step comprising combination of the predefined implantation energy and the predefined dosage.
  • the first P-well region 206 is formed using a first sequence of multiple ionimplantation steps. An ion-implantation step of the first sequence of multiple ion-implantation steps is performed with a different implantation energy or a different dosage.
  • the first P-type ion implantation i.e., second conductivity type first ion implantation
  • a second patterned masking layer 207 is formed on the topside of the semiconductor substrate as shown in FIG. 64E.
  • a first n-type ion (e.g., Nitrogen, Phosphorous) implantation is formed on the topside of the semiconductor substrate through the second patterned masking layer 207 to form a first source region 208 within the first P-well region 206 as shown in FIG. 64F.
  • the second patterned masking layer 207 is then removed from the semiconductor substrate as shown in FIG. 64G.
  • the first source region 208 is formed by a second epitaxial growth using a n-type impurity (e.g., Nitrogen, Phosphorous) into the first P-well region 206.
  • a n-type impurity e.g., Nitrogen, Phosphorous
  • the first source region 208 comprises a second predefined implantation energy and a second predefined dosage.
  • the second predefined implantation energy ranges from 5 keV to 1 MeV and the second predefined dosage ranges from 5E13 cm-2 to 5E16 cm-2.
  • the first source region 208 is formed using a second single ion-implantation step comprising combination of the second predefined implantation energy and the second predefined dosage.
  • the first source region 208 is formed using a second sequence of multiple ion-implantation steps. An ion-implantation step of the second sequence of multiple ionimplantation steps is performed with a different implantation energy or a different dosage.
  • the first n-type ion implantation is performed at one of the room temperature and at the elevated temperature up to 1000°C.
  • a third patterned hard mask layer 209 is formed on the topside of the semiconductor substrate as shown in FIG. 64H.
  • a trench region 210 is then formed by performing etching onto the topside (e.g., a top surface) of the semiconductor substrate through the third patterned hard mask layer 209 as shown in FIG. 641.
  • the etching is performed using one of a reactive ion etching (RIE) and an inductively coupled plasma (ICP) etching.
  • RIE reactive ion etching
  • ICP inductively coupled plasma
  • the etching is controlled appropriately to form the trench region 210.
  • the trench region 210 comprises a predefined depth and a predefined sidewall angle. The predefined depth of the trench region 210 ranges from 0.2 pm to 2.0 pm.
  • the predefined sidewall angle ranges from 30° to 90°.
  • the predefined depth of the trench region 210 is deeper than a depth of the first P-well region 206 (i.e., bottom portion of the trench region 210 may be in contact with the N- drift layer 204).
  • the trench region 210 comprises a first section and a second section.
  • a first spacer 211 (i.e., sidewall spacer) is then formed on the semiconductor substrate along the trench sidewalls of the trench region 210 and the third patterned hard mask layer 209 as shown in FIG. 64J.
  • the first spacer 211 is formed using a dielectric material (e.g., silicon dioxide, silicon nitride).
  • the first spacer 211 and the hard mask layers e.g., the first patterned hard mask layer 205, the second patterned hard mask layer 207) are formed using dis-similar dielectric materials to enable selective removal of one or more portions of the first spacer 211 without removal of the hard mask layers.
  • the one or more portions of the first spacer 211, that are not in contact with the first source region 208, are selectively removed as shown in FIG. 64K.
  • a second p-type ion implantation (e.g., Aluminum, Boron) is then performed to form a second P-well region 212 below the first P-well region 206 as shown in FIG. 64L.
  • the second p-type ion implantation i.e., second conductivity type second ion implantation
  • comprises an angled implantation i.e., at a predefined angle to electrically short a portion of the second P-well region 212 and the first P-well region 206 at the first section.
  • the angled implantation is performed using a tilt angle away from normal incidence. The tilt angle for the angled implantation may range from 0° (normal incidence) to 60°.
  • the second P-well region 212 comprises a third predefined implantation energy and a third predefined dosage.
  • the third predefined implantation energy ranges from 5 keV to 5 MeV and the third predefined dosage ranges from 5E13 cm-2 to 5E16 cm-2.
  • the second P-well region 212 is formed using a third single ion-implantation step comprising combination of the third predefined implantation energy and the third predefined dosage.
  • the second P-well region 212 is formed using a third sequence of multiple ionimplantation steps. An ion-implantation step of the third sequence of multiple ion-implantation steps is performed with a different implantation energy or a different dosage.
  • the second P-type ion implantation i.e., the second conductivity type second ion implantation
  • a second spacer 213 (i.e., sidewall spacer) is then formed on the semiconductor substrate along the trench sidewalls of the trench region 210 and the third patterned hard mask layer 209 as shown in FIG. 64M.
  • a second n-type ion implantation e.g., Nitrogen, Phosphorous
  • the second source region 214 and the second P-well region 212 are formed closer to the first section and far away from the second section.
  • the second source region 214 comprises a fourth predefined implantation energy and a fourth predefined dosage.
  • the fourth predefined implantation energy ranges from 5 keV to 1 MeV and the fourth predefined dosage ranges from 5E13 cm-2 to 5E16 cm-2.
  • the second source region 214 is formed using a fourth single ion-implantation step comprising combination of the fourth predefined implantation energy and the fourth predefined dosage.
  • the second source region 214 is formed using a fourth sequence of multiple ionimplantation steps.
  • An ion-implantation step of the fourth sequence of multiple ion-implantation steps is performed with a different implantation energy or a different dosage.
  • the second n-type ion implantation is performed at one of the room temperature and the elevated temperature up to 1000°C.
  • the hard mask layers (e.g., the first spacer 211, the second spacer 213, the third patterned hard mask layer 209) are removed as shown in FIG. 64P.
  • the semiconductor substrate e.g., wafers
  • the heat treatment or annealing is performed at a temperature ranging from 1700°C - 2000°C, for a duration ranging from 10 min to 2 hours.
  • a gate dielectric layer 216 is then formed onto the topside of exposed portions of the semiconductor substrate as shown in FIG. 64Q.
  • the gate dielectric layer 216 is an oxide layer.
  • the gate dielectric layer 216 is formed by one of a thermal oxidation and a chemical vapor deposition (CVD) of a dielectric layer (e.g., silicon dioxide, silicon nitride, silicon oxynitride, etc.). Then a poly silicon layer 218 is formed onto the topside of the semiconductor substrate as shown in FIG. 64R.
  • the poly silicon layer 218 comprises a n-type doped layer. The n-type doped layer is doped using a n-type dopant (e.g., phosphorous).
  • a fourth patterned masking layer 215 is then formed on top of the poly silicon layer 218 as shown in FIG. 64S.
  • the poly silicon layer 218 is then selectively etched using the fourth patterned masking layer 215 to form one or more poly silicon regions as shown in FIG. 64T.
  • the fourth patterned masking layer 215 is removed as shown in FIG. 64U.
  • an interlayer dielectric (ILD) 220 is formed onto the topside of the semiconductor substrate as shown in FIG. 64V.
  • a fifth patterned masking layer 217 is formed on top of the interlayer dielectric (ILD) 220 as shown in FIG. 64W.
  • the interlayer dielectric (ILD) 220 is then selectively etched using the fifth patterned masking layer 217 as shown in FIG. 64X.
  • the gate dielectric layer 216 is also selectively etched using the fifth patterned masking layer 217 as shown in FIG. 64Y.
  • the fifth patterned masking layer 217 is then removed from the semiconductor substrate and the semiconductor substrate is exposed to air as shown in FIG. 64Z.
  • a first silicide region 222 and a second silicide region 224 are then formed on the topside and bottom side of the semiconductor substrate to form a source terminal and a drain terminal respectively as shown in FIG. 64AA.
  • the first silicide region 222 is formed on top of the first source region 208 and the second source region 214.
  • the second silicide region 224 is formed on bottom of the N+ substrate 202.
  • a first inter-connect metal layer 226 and a second inter-connect metal layer 228 is then formed on the topside and the bottom side of the semiconductor substrate respectively as shown in FIG. 64 AB.
  • FIG. 65 illustrates an embodiment of a cross-sectional structure of one or more unit cells of a power MOSFET, a first unit cell of the one or more unit cells comprising a first metal oxide semiconductor (MOS) interface on a horizontal surface of a semiconductor substrate and a trench sidewall, and a second unit cell of the one or more unit cells comprising a metal region 330 formed adjacent to a first conductivity type drift layer of the MOSFET.
  • the MOSFET (shown in FIG. 65) is a n-type MOSFET.
  • the terms “first conductivity type” and “second conductivity type” are used to describe n-type and p-type respectively.
  • the MOSFET is a p-type MOSFET.
  • the terms "first conductivity type” and “second conductivity type” are used to describe p-type and n-type respectively.
  • the MOSFET (shown in FIG. 65) comprises the semiconductor substrate.
  • the semiconductor substrate comprises aN+ substrate 302 (i.e., a first conductivity type substrate) and a N- drift layer 304 (i.e., a first conductivity type drift layer).
  • the semiconductor substrate comprises a silicon carbide (SiC) substrate.
  • the MOSFET comprises a first section and a second section that are contiguously located along a lateral direction within the MOSFET.
  • the first section comprises the first metal oxide semiconductor (MOS) interface
  • the second section comprises the metal region 330.
  • the metal region comprises a junction barrier Schottky (JBS) diode region.
  • the first section and the second section are arranged in at least one sequence from left to right or right to left.
  • the at least one sequence comprises the first section at a first location and the second section at a second location along the lateral direction. In another embodiment, the at least one sequence comprises the second section at the first location and the first section at the second location along the lateral direction. In yet another embodiment, the at least one sequence comprises the first section at the first location and the second location along the lateral direction. In yet another embodiment, the at least one sequence comprises the second section at the first location and the second location along the lateral direction. In yet another embodiment, the at least one sequence comprises the first section at the first location and a third location, and the second section at the second location along the lateral direction.
  • the at least one sequence comprises the second section at the first location and the third location, and the first section at the second location along the lateral direction.
  • the at least one sequence comprises ‘AB’, ‘BA’, ‘AA’, ‘BB’, ‘ABA’, ‘AAB’, ‘BAA’, ‘ABB’, ‘BAB’, ‘BBA’, ‘ABAB’, ‘ABBA’, ‘BAAB’, etc.
  • the MOSFET comprises a first P-well region 306 (i.e., a second conductivity type first well region), a second P-well region 312 (i.e., a second conductivity type second well region), a source region 314, a metal region 330 and a trench region 310.
  • the first P-well region 306 and the second P-well region 312 are two distinct well regions.
  • the source region 314 is positioned (e.g., confined) within the second P-well region 312.
  • the source region 314 and the second P-well region 312 are positioned closer to the first section and far away from the second section.
  • the second P- well region 312 overlaps the first P-well region 306 at the first section and the second section.
  • the trench region 310 is completely contained within the second P-well region 312.
  • the trench region 310 is extended through the first P-well region 306.
  • the first P-well region 306 and the second P- well region 312 completely enclose bottom portion (i.e., base) of the trench region 310 to shield the bottom portion from first high electric fields in off-state or during high-voltage blocking operation of the MOSFET.
  • the metal region i.e., the junction barrier Schottky diode region
  • the metal region is shielded from second high electric fields present during high-voltage blocking condition.
  • spacing between the first P-well region 306 and the second P-well region 312 at the second section and the first section is adjusted suitably for maintaining a good trade-off between an on-state resistance, and a third electric field at the metal region and the first MOS interface.
  • a depth, and a doping concentration of the first P-well region 306 and the second P-well region 312 are adjusted for maintaining the good trade-off between the on-state resistance, and the third electric field at the metal region and the first MOS interface.
  • a width, and a depth of the trench region 310, and the implantation energy and the dosage of the first P-well region 306 and the second P-well region 312 are adjusted to control total extent and distribution of the first MOS interface.
  • the MOSFET further comprises silicide layers 322, 324 on top of the source region 314, and bottom of the N+ substrate (302).
  • the silicide layer 322 on top of the source region 314 is partly positioned on top of the second P-well region 312 and the first P-well region 306.
  • the first section comprises the first metal oxide semiconductor (MOS) interface.
  • the first MOS interface comprises a first portion and a second portion.
  • the first portion comprises a first contact with a horizontal surface (e.g., an unetched surface) of the semiconductor substrate.
  • the first portion of the first MOS interface is positioned parallel to 0001 crystal plane of the semiconductor substrate.
  • the first portion of the first MOS interface is positioned parallel to 11-20 crystal plane of the semiconductor substrate.
  • the second portion of the first MOS interface comprises a second contact with a trench sidewall of the trench region 310.
  • the second portion of the first MOS interface is positioned parallel to one of 11-20 crystal plane and 1-100 crystal plane of the semiconductor substrate.
  • the first section comprises a combination of a planar MOSFET structure and a trench MOSFET structure.
  • the second section comprises the metal region 330 (e.g., the junction barrier Schottky diode region).
  • the metal region 330 comprises a fourth contact with the N- drift layer 404 of the semiconductor substrate.
  • the metal region 330 comprises a predefined work function.
  • the metal region 330 comprises one of Ti, W, Mo, Au, Pt, TiW, TiN, etc.
  • the trench region 310 comprises the trench sidewall.
  • the trench sidewall of the trench region 310 comprises a sloped sidewall.
  • the sloped sidewall comprises a sidewall angle ranging from 30° to 90°.
  • the trench region 310 comprises a depth ranging from 0.2 pm to 2.0 pm.
  • a slope of the sloped sidewall is selected appropriately to orient the first MOS interface along a predefined crystal plane that comprises a low trap density.
  • the first portion of the first MOS interface is positioned parallel to 11 -20 crystal plane and 0338 crystal plane of the sloped sidewall of the semiconductor substrate, when the trench sidewall comprises the sloped sidewall.
  • the MOSFET turns on when a drain terminal is biased positively as compared to a source terminal and the metal region turns on when the drain terminal is biased negatively with respect to the source terminal.
  • the MOSFET shown in FIG. 65 depicts an equal number of unit cells of the metal regions and unit cells of the first MOS interfaces.
  • the MOSFET comprises an unequal number of the unit cells of the metal regions and the unit cells of the first MOS interfaces based on requirements.
  • a ratio of the number of the unit cells of the metal regions to the unit cells of first MOS interfaces is varied (e.g., increased, decreased) based on application.
  • FIG. 66 to 66AA are cross-sectional views illustrating an embodiment of a process of manufacturing the MOSFET structure shown in FIG. 65.
  • the process of manufacturing the MOSFET structure shown in FIG. 65 comprises preparing a semiconductor substrate having a N+ substrate 402 and a N- drift layer 404 as shown in FIG. 66A.
  • the N- drift layer 404 is grown on top of the N+ substrate 402.
  • the N+ substrate 402 comprises a heavily doped substrate.
  • a first patterned hard mask layer 405 is formed on topside of the semiconductor substrate as shown in FIG. 66B.
  • a first p-type ion (e.g., Aluminum, Boron) implantation is formed on the topside of the semiconductor substrate through the first patterned hard mask layer 405 to form a first p-well region 406 as shown in FIG. 66C.
  • the first patterned hard mask layer 405 is removed from the topside of the semiconductor substrate as shown in FIG. 66D.
  • the first p-well region 406 is formed by a first epitaxial growth using a p-type impurity (e.g., Aluminum, Boron) into the N- drift layer 404.
  • the first P-well region 406 comprises a first predefined implantation energy and a first predefined dosage.
  • the first predefined implantation energy ranges from 5 keV to 5 MeV and the first predefined dosage ranges from 1E13 cm-2 to 5E16 cm- 2.
  • the first P-well region 406 is formed using a first single ion-implantation step comprising combination of the predefined implantation energy and the predefined dosage.
  • the first P-well region 406 is formed using a first sequence of multiple ion-implantation steps. An ion-implantation step of the first sequence of multiple ion-implantation steps is performed with a different implantation energy or a different dosage.
  • the first P-type ion implantation i.e., second conductivity type first ion implantation
  • a second patterned hard mask layer 407 is formed on the topside of the semiconductor substrate as shown in FIG. 66E.
  • a trench region 410 is formed by performing etching onto the topside (e.g., a top surface) of the semiconductor substrate through the second patterned hard mask layer 407 as shown in FIG. 66F.
  • the etching is performed using one of a reactive ion etching (RIE) and an inductively coupled plasma (ICP) etching.
  • RIE reactive ion etching
  • ICP inductively coupled plasma
  • the etching is controlled appropriately to form the trench region 410.
  • the trench region 410 comprises a predefined depth and a predefined sidewall angle. The predefined depth of the trench region 410 ranges from 0.2 pm to 2.0 pm.

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