Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D30/00—Field-effect transistors [FET]
  • H10D30/60—Insulated-gate field-effect transistors [IGFET]
  • H10D30/64—Double-diffused metal-oxide semiconductor [DMOS] FETs
  • H10D30/66—Vertical DMOS [VDMOS] FETs
  • H10D30/668—Vertical DMOS [VDMOS] FETs having trench gate electrodes, e.g. UMOS transistors
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D12/00—Bipolar devices controlled by the field effect, e.g. insulated-gate bipolar transistors [IGBT]
  • H10D12/411—Insulated-gate bipolar transistors [IGBT]
  • H10D12/441—Vertical IGBTs
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D12/00—Bipolar devices controlled by the field effect, e.g. insulated-gate bipolar transistors [IGBT]
  • H10D12/411—Insulated-gate bipolar transistors [IGBT]
  • H10D12/441—Vertical IGBTs
  • H10D12/461—Vertical IGBTs having non-planar surfaces, e.g. having trenches, recesses or pillars in the surfaces of the emitter, base or collector regions
  • H10D12/481—Vertical IGBTs having non-planar surfaces, e.g. having trenches, recesses or pillars in the surfaces of the emitter, base or collector regions having gate structures on slanted surfaces, on vertical surfaces, or in grooves, e.g. trench gate IGBTs
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D30/00—Field-effect transistors [FET]
  • H10D30/01—Manufacture or treatment
  • H10D30/021—Manufacture or treatment of FETs having insulated gates [IGFET]
  • H10D30/028—Manufacture or treatment of FETs having insulated gates [IGFET] of double-diffused metal oxide semiconductor [DMOS] FETs
  • H10D30/0291—Manufacture or treatment of FETs having insulated gates [IGFET] of double-diffused metal oxide semiconductor [DMOS] FETs of vertical DMOS [VDMOS] FETs
  • H10D30/0297—Manufacture or treatment of FETs having insulated gates [IGFET] of double-diffused metal oxide semiconductor [DMOS] FETs of vertical DMOS [VDMOS] FETs using recessing of the gate electrodes, e.g. to form trench gate electrodes
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D30/00—Field-effect transistors [FET]
  • H10D30/60—Insulated-gate field-effect transistors [IGFET]
  • H10D30/64—Double-diffused metal-oxide semiconductor [DMOS] FETs
  • H10D30/66—Vertical DMOS [VDMOS] FETs
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/10—Shapes, relative sizes or dispositions of the regions of the semiconductor bodies; Shapes of the semiconductor bodies
  • H10D62/17—Semiconductor regions connected to electrodes not carrying current to be rectified, amplified or switched, e.g. channel regions
  • H10D62/213—Channel regions of field-effect devices
  • H10D62/221—Channel regions of field-effect devices of FETs
  • H10D62/235—Channel regions of field-effect devices of FETs of IGFETs
  • H10D62/299—Channel regions of field-effect devices of FETs of IGFETs having lateral doping variations
  • H10D62/307—Channel regions of field-effect devices of FETs of IGFETs having lateral doping variations the doping variations being parallel to the channel lengths
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/10—Shapes, relative sizes or dispositions of the regions of the semiconductor bodies; Shapes of the semiconductor bodies
  • H10D62/17—Semiconductor regions connected to electrodes not carrying current to be rectified, amplified or switched, e.g. channel regions
  • H10D62/393—Body regions of DMOS transistors or IGBTs 
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
  • H10D62/60—Impurity distributions or concentrations
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D64/00—Electrodes of devices having potential barriers
  • H10D64/20—Electrodes characterised by their shapes, relative sizes or dispositions 
  • H10D64/27—Electrodes not carrying the current to be rectified, amplified, oscillated or switched, e.g. gates
  • H10D64/311—Gate electrodes for field-effect devices
  • H10D64/411—Gate electrodes for field-effect devices for FETs
  • H10D64/511—Gate electrodes for field-effect devices for FETs for IGFETs
  • H10D64/514—Gate electrodes for field-effect devices for FETs for IGFETs characterised by the insulating layers
  • H10D64/516—Gate electrodes for field-effect devices for FETs for IGFETs characterised by the insulating layers the thicknesses being non-uniform

Definitions

• Document US 6 573 561 B1 refers to a vertical MOSFET with an asymmetrically graded channel profile.
• Document US 6 664 594 B2 discloses a power MOS device with an asymmetrical channel structure for enhanced linear operation capability.
• Document US 8 067 797 B2 describes a variable threshold trench IGBT with offset emitter contacts.
• Document US 2016/0064550 A1 refers to power devices.
• Documents US 2021/0111279 A1 and US 2005/0133833 A1 refer to electronic devices.
• Embodiments of the disclosure relate to a power semiconductor device that shows improved electrical behavior and to a corresponding production method. This object is achieved, inter alia, by a production method and by a power semiconductor device as defined in the independent claims. Exemplary further developments constitute the subject-matter of the dependent claims.
• the method for producing a power semiconductor device comprises the following steps, for example, in the stated order: - providing a semiconductor substrate, - epitaxially growing at least one semiconductor layer onto the semiconductor substrate, and - providing a gate insulator and a gate electrode, the gate insulator (4) is located directly between the at least one semiconductor layer and the gate electrode, wherein - the semiconductor substrate and/or the at least one semiconductor layer constitute a semiconductor body having a source region of a first conductivity type and a well region of a second conductivity type different from the first conductivity type, and the well region comprises a channel region directly at the source region, and - the channel region has a non-uniform channel doping profile along the gate insulator, so that a doping concentration N A in the channel region is largest in a first section remote from the source region, the non-uniform channel doping profile is completely or partly formed by the epitaxially growing of the at least one semiconductor layer.
• the power semiconductor device comprises: - a semiconductor body having a source region of a first conductivity type and a well region of a second conductivity type different from the first conductivity type, and the well region comprises a channel region starting directly at the source region, - at least one gate electrode arranged at the semiconductor body and assigned to the at least one channel region, and - at least one gate insulator directly between the semiconductor body and the at least one assigned gate electrode, wherein the channel region has an intentionally non-uniform channel doping profile along the gate insulator, so that a doping concentration in the channel region is largest in a first section remote from the source region.
• the gate electrode is insulated from the semiconductor body by the gate insulator.
• the at least one source region is in direct contact with the assigned gate insulator and/or is directly at the assigned channel region.
• the first conductivity type is, for example, n-conductive and, thus, the at least one source region is n-doped.
• the at least one well region and consequently the at least one channel region are of the second conductivity type different from the first conductivity type.
• the second conductivity type is, for example, p-conductive and, thus, the at least one channel region is p-doped. It is possible that a maximum doping concentration of the at least one well region and/or of the at least one channel region is less than a maximum doping concentration of the at least one source region.
• the semiconductor body further comprises a drift region which may be of the first conductivity type, too.
• the drift region is in direct contact with the gate insulator and/or is directly at the channel region.
• the drift region may be located between the channel region and a drain region or a collector region of the semiconductor body, for example, in a direction perpendicular to the top side of the semiconductor body.
• the optional trench may terminate in the drift region.
• the semiconductor body can comprise an enhancement layer.
• the enhancement layer is located directly between the well region and the drift region and may have a higher maximum doping concentration than the drift region.
• the enhancement layer can also be of the first conductivity type.
• the enhancement layer may work as a hole blocking layer, that is, it enhances plasma concentration near the source side resulting in an improved V ce-sat without increasing E off too much. Additionally, the enhancement layer also helps in controlling a length of the channel region and minimizes manufacturing process-induced variability.
• a thickness of the enhancement layer is at least 1 ⁇ m and/or is at most 5 ⁇ m.
• the doping concentration N A in the channel region is largest at a depth from the top side of the semiconductor body of at least 0.5 ⁇ m or of at least 1.5 ⁇ m. Said maximum doping concentration N A may also be at a distance of at least 0.5 ⁇ m or of at least 1.5 ⁇ m from the source region, seen along the gate insulator.
• the power semiconductor device is a metal–insulator–semiconductor field-effect transistor, MISFET, a metal–oxide–semiconductor field-effect transistor, MOSFET, or an insulated-gate bipolar transistor, IGBT or a reverse-conducting insulated-gate bipolar transistor, RC-IGBT.
• the well region extends from the top side of the semiconductor body to the drift region. The channel region is part of the well region and may have the same doping concentration.
• the electrons flow in the channel region from the source region to the drift region along the gate insulator.
• the channel region has a thickness in a direction perpendicular to an interface between the gate insulator and the well region, for example, in a nanometer range, exemplarily 1 nm to 50 nm.
• the semiconductor body is of Silicon, Si for short.
• the semiconductor body can alternatively be of a wide-bandgap semiconductor material like SiC, Ga 2 O 3 or GaN.
• the gate insulator is made of any insulating material, which may be an oxide.
• the gate insulator may be of at least one of the following materials: SiO 2 , Si 3 N 4 , Al 2 O 3 , Y 2 O 3 , ZrO 2 , HfO 2 , La 2 O 3 , Ta 2 O 5 , TiO 2 .
• the gate insulator may also be referred to as gate oxide.
• the power semiconductor device is a power device.
• the power semiconductor device is configured for a maximum voltage of at least 0.2 kV or of at least 0.6 kV or of at least 1.2 kV.
• the power semiconductor device is, for example, for a power module in a vehicle to convert direct current from a battery or a fuel cell to alternating current for an electric motor, for example, in hybrid vehicles or plug-in electric vehicles.
• the power semiconductor device can be a fuse, for example, in a vehicle like a car.
• the doping concentration increases monotonically or strictly monotonically along the gate insulator, for example, towards the drift region.
• the non-uniform channel doping profile has a first section remote from the source region and next to the drift region. The doping concentration is highest in the first section. Otherwise, the doping concentration is highest in a middle section of the channel region, between the first section and a second section, the second section is close to the assigned source region and remote from the drift region. If there is no such middle section, then the channel region may consist of the first section having the highest doping concentration and of the second section next to the source region.
• a length of the first section and/or of the middle section is at least 5% or is at least 10% or is at least 15% of an overall length of the channel region along the gate insulator. Alternatively or additionally, said length is at most 40% or at most 30% or at most 25% of said overall length. The same may apply to the second section, if present.
• the doping concentration is constant along the gate insulator in the second section and/or in the middle section. Constant means, for example, that there is no intentional variation of the doping concentration so that variations due to manufacturing tolerances may be disregarded.
• constant may mean that there are no changes in the doping concentration in the second section and/or in the middle section exceeding 5% or exceeding 10% or exceeding 15% of the maximum doping concentration present in the channel region.
• the doping concentration varies along the channel region by at least 50% or by at least 65% or by at least 80% of the maximum doping concentration of the non-uniform channel doping profile.
• the second section has a maximum doping concentration of at most 50% or of at most 35% or of at most 20% of the maximum doping concentration of the first section or, if the maximum doping concentration is in the middle section, of the middle section.
• the channel doping profile is configured in a stepped manner so that there is one or a plurality of steps in the channel doping profile along the gate insulator within the channel region. Otherwise, the channel doping profile along the gate insulator may change in a continuous, step-less manner.
• the gate electrode is partially or completely arranged in at least one trench formed in the semiconductor body. The at least one trench and, thus, the assigned gate electrode extends through the well region into the drift region, for example, in a direction away from a top side of the semiconductor body. Consequently, the gate insulator is located partially or completely in the assigned trench, too.
• the power semiconductor device could be a trench-based device.
• the gate electrode and the gate insulator are applied on the top side of the semiconductor body.
• the top side may be a planar face.
• the well region is of multi-layer fashion so that the well region comprises at least two sub-layers.
• the sub-layers may be grown epitaxially or may be produced by ion implantation and/or thermal treatment. It is possible that the sub-layers are of the same material, but differ in their doping concentrations. Hence, between the sub-layers there may be distinct jumps in the doping concentration and within the respective sub-layer the doping concentration can be constant, for example, with a tolerance of at most 5% of a maximum doping concentration of the respective layer.
• a doping concentration is constant throughout the well region.
• the well region is of single-layer fashion and comprises only one layer in which the doping profile is established.
• Such a doping profile may be of a continuous fashion without steps and may be produced, for example, by means of ion implantation and/or thermal treatment. If there is a plurality of sub-layers, the sub-layers may be made by applying different dopants and/or may be grown in different epitaxial growth steps with the respective doping concentration applied during epitaxial growth.
• the applying of dopants may be made in a single step or by more than one applying step, for example, by using different implantation energies or different dopants.
• a mask may be used for applying the dopants to achieve the non-uniform channel doping profile.
• a thermal treatment step may follow after applying dopants or after epitaxial growth.
• the well region outside the channel region and along a depth of the well region, that is, perpendicular to the top side, the well region has a constant doping concentration at least in places. Hence, along at least some vertical intersections the doping concentration may be constant in the well region.
• the non-uniform channel doping profile may be limited to a region next to the gate insulator.
• the non- uniform channel doping profile is limited to the channel region, for example, with a tolerance of at most 0.5 ⁇ m.
• the gate insulator has a non-uniform thickness along the channel region. For example, along the channel region the gate insulator is thickest in the first section.
• the gate electrode has a non-uniform gate electrode work function profile along the channel region, such that a threshold voltage of the gate electrode is highest in the first section.
• a work function ⁇ m of the gate electrode in the first section remote from the source region is largest for devices having a p-type doped well region, and correspondingly a p-type doped channel region, and smallest for devices having an n-type doped well region, and correspondingly an n-type doped channel region.
• the gate insulator has a non-uniform gate insulator thickness profile along the channel region.
• a thickness of the gate insulator varies along the channel region. Said thickness variation may be continuous or non-continuous, that is, stepped.
• the gate insulator is thickest in the first section, and consequently may be thinnest in the second section.
• the gate insulator has a non-uniform gate dielectric constant profile along the channel region, such that a relative dielectric constant of the gate insulator is lowest in the first part of the channel region remote from the source region.
• the non-uniform channel doping profile profile can be combined with the non-uniform gate insulator thickness, the non-uniform gate electrode work function profile or the non-uniform gate dielectric constant profile, or with two of the non-uniform channel doping profile, the non-uniform gate electrode work function profile and the non-uniform gate dielectric constant profile, or with all three other non-uniform profiles.
• the power semiconductor device is configured so that both a saturation current and a short-circuit current are decreased, for example, while a collector-emitter saturation voltage V ce-sat , and consequently on-state losses, may remain unaffected.
• Figure 1 is a schematic sectional view of a reference semiconductor device
• Figure 2 is a schematic sectional view of an exemplary embodiment of a power semiconductor device described herein
• Figure 3 is a top view of the power semiconductor device of Figure 2
• Figures 4 to 7 are schematic representations of electric data of power semiconductor devices described herein and of a reference semiconductor device
• Figure 8 is a schematic representation of doping profiles of power semiconductor devices described herein and of a reference semiconductor device
• Figure 9 shows simulation results of electric data of power semiconductor devices described herein and of a reference semiconductor device
• Figures 10 to 16 are schematic sectional views of exemplary embodiments of power semiconductor devices described herein.
• Figure 1 illustrates a reference semiconductor device 9 that corresponds to exemplary embodiments of power semiconductor devices 1 described herein except for a channel doping profile 6, 69 in a channel region 220 included in a well region 22.
• the reference semiconductor device 9 comprises a semiconductor body 2 which is, for example, of Si.
• the semiconductor body 2 also comprises a source region 21 at a top side 20 of the semiconductor body 2.
• a trench passes both through the well region 22 and through the source region 21.
• the source region 21 is of a first conductivity type, like n-conducting, and the well region 22, and consequently the channel region 220 included by the well region 22, is of a second, different conductivity type, like p-conducting.
• the channel region 220 is doped with a uniform reference doping profile 69. That is, along a direction x away from the source region 21 and towards the drift region 23, there is a constant doping concentration N A .
• x 0.
• L corresponds to a channel length of the channel region 220.
• x runs perpendicular to the top side 20 of the semiconductor layer body 2.
• the length L may correspond to a distance between the source region 21 and the drift region 23 directly at the gate insulator 4.
• the length L may be defined as the length of the second conductivity type layer between the layers of the first conductivity type, that is, the source region 21 and the drift region 23, wherein the drift region 23 may comprise a layer of lower doping concentration, not illustrated.
• a shape of the channel region 220 is drawn only very schematically, and for simplification of the drawings only along one side of the gate electrode 31.
• the well region comprises a non-uniform channel doping profile 6, which may be present in the whole well region 22 or which may be limited to the channel region 220 or to the channel region 220 and to an adjacent region of the well region 22.
• the doping concentration N A changes in a stepped manner so that the doping profile 6 has a step 53.
• the step 53 does not need to exactly follow a theta function or unit step function, but there can be a transitional section 62.
• a length of the transitional section 62 is small and amount, for example, to at most 2% or to at most 5% of the channel length L.
• the doping concentration N A is highest next to the drift region 23 in a first section 61 of the doping profile 6.
• a length of the first section 61 is, for example, a quarter or a third of the channel length L.
• the length of the first section 61 is between 20% and 40% of the channel length L.
• the amount of change of the doping concentration N A at the step 53 is illustrated only schematically in Figure 2.
• a maximum doping concentration N A in the first section 61 exceeds a maximum doping concentration N A in a remainder of the channel region 220, that is, in a second section 64 out of the first section 61 and out of the transitional section 62, by at least a factor 2 or by at least a factor of 5 and/or by at most a factor of 10 or by at most a factor of 8.
• the doping concentration N A may virtually be constant.
• Both the source region 21 and the well region 22 may be electrically connected by means of at least one source electrode 32 which is located at the top side 20.
• the plug 25 may have a different thickness than the well region 22 so that the plug 25 can extend deeper or shallower into the semiconductor body 2 than the well region 22. Further, the thicknesses of the source region 21 and of the plug 25 can be the same or can be different. Further, between the drift region 23 and the well region 22, there is an enhancement layer 27. The enhancement layer 27 is of the first conductivity type, too. Both the source region 21 and the at least one plug 25 may be electrically connected by means of the at least one source electrode 32 which is located at the top side 20. Exemplarily, the plug 25 has a higher maximum doping concentration than the well region 22 or the channel region 220. The depth of the plug may be lower, deeper or the same as of the well region/channel region.
• the source region 21 and the optional at least one plug 25 are located along only one side of the gate electrode 31.
• the source region 21 and the optional at least one plug 25 can also be arranged along both sides of the gate electrode 31, compare, for example, Figure 10, or all around the gate electrode 31.
• the power semiconductor device 1 is an insulated-gate bipolar transistor, IGBT for short.
• IGBT insulated-gate bipolar transistor
• the collector region 26 which is of the second conductivity type, too.
• the doping concentration of such a buffer region can be higher than that of the drift region 26.
• the trench accommodating the gate electrode 31 and the gate insulator 4 may be of extended fashion.
• the source region 21, the at least one plug 25 as well as the channel region 220 may be arranged symmetrically on both sides of the trench, see Figure 3.
• maximum doping concentrations of the source regions 21, the collector region 26 or instead of a drain region 24 and the at least one plug 25 are at least 1 x 10 18 cm -3 or at least 5 x 10 18 cm -3 or at least 1 x 10 19 cm -3 and/or at most 5 x 10 20 cm -3 or at most 2 x 10 20 cm -3 or at most 1 x 10 20 cm -3 .
• a maximum doping concentration of the well region 22 and, thus, of the channel region 220 may be at least 5 x 10 16 cm -3 or at least 1 x 10 17 cm -3 and/or at most 5 x 10 19 cm -3 or at most 5 x 10 18 cm -3 .
• the maximum doping concentration in the first section 61 is at least at least 1.5 x 10 17 cm -3 and/or is at most 3 x 10 18 cm -3 .
• the maximum doping concentration present in the non-uniform channel doping profile 6 is at least at least 5 x 10 16 cm -3 and at most 3 x 10 18 cm -3 and/or a minimum doping concentration present in the non-uniform channel doping profile 6 is at most 2 x 10 17 cm -3 or at most 1 x 10 17 cm -3 .
• a maximum doping concentration of the enhancement layer 27 is at least 10 15 cm -3 and/or is at most 10 18 cm -3 .
• a maximum doping concentration of the drift region 23 may be at least 1 x 10 11 cm -3 or at least 1 x 10 12 cm -3 or at least 1 x 10 13 cm -3 and/or at most 1 x 10 17 cm -3 or at most 5 x 10 16 cm -3 or at most 1 x 10 16 cm -3 .
• the semiconductor body 2 is at least in part produced by epitaxial growth. That is, the doping concentrations of the respective layers of the semiconductor body 2 may be produced during growth and may not be produced after growth, for example, by means of ion implantation. This applies, for example, at least for the enhancement layer 27 and the well region 22 which can thus be doped by means of epitaxial growth.
• the drift region 23 can be partly or completely be part of a growth substrate.
• the concept behind the channel region 220 having the non- uniform channel doping profile 6 is explained in the following.
• a power semiconductor device 1 exemplarily for low frequency applications, it may be desirable to have on-state losses as low as possible in order to minimize the total electrical losses. Further, from a device reliability point of view, it may be advantageous to have a low short circuit current. Thus, a power semiconductor device 1 with minimized on-state losses and improved short circuit capability may be desired.
• Figures 4 and 5 are schematics of typical output characteristics of an IGBT with a uniform threshold profile along the whole channel region, in Figure 4 for a same V th and different channel resistance, and in Figure 5 for different threshold voltages V th .
• Other techniques to reduce the short-circuit current such as: a) increasing the channel length L, b) reducing an anode injection efficiency, by reducing an anode implant dose, c) reducing a channel width, by decreasing a source coverage along the trench, and d) reducing the channel width, by increasing a cell pitch, also undesirably result in higher on-state losses.
• techniques such as d) can also adversely affect the breakdown capability of the power semiconductor device 1.
• Reducing gate biasing in order to reduce short-circuit current may also not be desirable as it leads to unstable dynamic behavior and moreover it is mainly defined by the application requirements.
• the trade-off between on-state losses and short circuit current is improved by improving the latter without adversely affecting the former.
• the described design features a non-uniform threshold voltage profile along the channel region 220 next to the gate insulator 4 to lower down the saturation current for a given V ce-sat .
• the proposed non-uniform V th in the power semiconductor device 1 described herein is achieved by implementing the non-uniform channel doping profile 6 in the channel region 220.
• the described power semiconductor device 1 does not adversely affect the breakdown capability and more so ever the turn-off losses of the power semiconductor device 1.
• the described concept is applicable to any MOS device in general such as power-MOSFET or IGBT or reverse-conducting-IGBT and is even compatible with both planar and trench architectures.
• an improved MISFET, MOSFET or IGBT or RC-IGBT device with an enhanced short circuit capability is introduced without a detrimental effect on the on-state losses.
• the improved design also relaxes the design constraints of the IGBT, enabling the possibility to independently explore the other methods mentioned above to minimize the on-state losses which are normally limited by the short circuit capability of the respective device.
• some theoretical background to the idea of the semiconductor device 1 described herein is presented.
• a channel pinch-off at high V ce is responsible for the current saturation in the output characteristics, which ultimately determines the short circuit current.
• the channel pinch-off voltage V pinch-off is determined by the threshold voltage V th .
• V ce the pinch-off voltage
• V th the local threshold voltage
• V th (L) at the channel end, that is, in the first section 61 near the drift region 23.
• V th (x) can be decreased in the rest of the channel. This is illustrated schematically in Figure 6 where the curve referring to the reference semiconductor device 9 comprises a uniform threshold voltage V th-1 profile along the whole channel.
• the curve for the power semiconductor device 1 on the other hand consists of a non-uniform V th profile along the channel, where V th is locally raised near the channel end, that is, in the first section 61, such that V th-2 (L) > V th-1 in order to lower the pinch-off point, while V th-2' ⁇ V th-1 in the rest of the channel to keep the overall channel resistance the same.
• V th-2 (L) > V th-1 in order to lower the pinch-off point
• V th-2' ⁇ V th-1 in the rest of the channel to keep the overall channel resistance the same.
• N A is the channel body doping, ⁇ s is the permittivity of the semiconductor, C ox is the gate insulator capacitance, and ⁇ B is the semiconductor surface potential and: where k is the Boltzmann constant, T is the temperature and n i is the intrinsic carrier concentration of the semiconductor.
• the focus is on the channel doping profile variation, but said doping concentration variation can of course be combined with a varying gate insulator thickness, a varying gate dielectric and/or a varying gate metal work function.
• Figures 1 and 2 above show schematic cross-sections of the reference semiconductor device 9 with a uniform doping profile 69 and of the power semiconductor device 1 with the non-uniform channel doping profile 6 as implemented in the simulations presented below.
• Three different doping profiles A, B, C were investigated, see Figure 8. That is, the non-uniform channel doping profiles N A (x) have been implemented in technology computer aided design, TCAD, simulations to obtain the locally varying V th profile with the aim of reducing the saturation current without affecting the on-state performance.
• TCAD technology computer aided design
• the uniform doping profile 69 of the reference semiconductor device 9 is illustrated, too.
• the total integral doping concentration along the channel was however kept same in order to maintain the identical V ce-sat .
• the output characteristics, see Figure 9, show the expected effect which is attributed to the local V th variation due to non-uniform channel doping profiles 6.
• the design with boron peak in the first section 61 of the channel region 220, that is, design A shows reduced I sat as compared to that of design C with a peak doping concentration in a second section 64 next to the source region 21.
• Design A is also better compared to the reference uniform doping profile 69 for the same reason, that is, due to higher local V th at the channel region end.
• design C may be undesired for applications where short circuit current needs to be reduced.
• the short circuit problem that is, to reduce the current between the source and the collector, has been solved in the power semiconductor devices 1 described herein by introducing the non-uniform channel doping profile 6 with higher doping near the channel end, that is, with higher doping concentrations in the middle section 63 or in the first section 61 next to the drain region as in designs B and A.
• the overall channel resistance is kept the same by lowering the doping in the other part of the channel which fixes the V ce-sat .
• design B the peak doping concentration in a middle section 63 between the second section 64 and the first section 61, and I sat is already reduced compared with the reference semiconductor device 9.
• the length L of the channel is in each case between 1 ⁇ m and 10 ⁇ m or between 1 ⁇ m and 5 ⁇ m.
• the length L of the channel is in each case 2.5 ⁇ m
• the first section 61 in design A has a length of 0.5 ⁇ m.
• the doping profile 6 again has the one step 53. Because optionally the channel region 220 is produced, for example, grown, with a first sub-layer 51 and a second sub-layer 52 which can be doped, for example, during growth, there is virtually no transitional region in this exemplary embodiment.
• the trench accommodating the gate electrode 31 does not need to have a round end part in the drift region 23, but can be of rectangular shape, or also of other shapes, when seen in cross-section, compare Figure 10, too.
• an outward side of the gate insulator 4 facing the semiconductor body 2 may be of planar fashion, at least along the channel region 220.
• the power semiconductor device 1 of Figure 10 is not an IGBT, but a MISFET or MOSFET. Consequently, the power semiconductor device 1 comprises a drain region 24 instead of the collector region 26.
• the drain region 24 which is of the first conductivity type, too, but, for example, with a maximum doping concentration higher than in the drift region 23.
• the drain region 24 there is a drain electrode 33.
• the doping profile 6 comprises a plurality of the steps 53, for example, two of the steps 53.
• the second step closer to the drift region 23 is larger than the first step closer to the source region 21.
• the first step may define the beginning of the first section 61.
• the non-uniform channel doping profile 6 can be combined with a varying thickness of the gate insulator 4.
• the thickness of the gate insulator 4 is between 20 nm and 80 nm inclusive or is between 40 nm and 80 nm inclusive.
• these two ideas that is, having an asymmetric, non-uniform gate insulator thickness and the non-uniform channel doping profile 6, can be combined with each other.
• the gate insulator 4 may be thickest in the first section 61.
• the thickness of the gate insulator 61 may increase in the same manner as the doping concentration N A , or in a different manner.
• the schematic progressions of the non-uniform channel doping profiles 6 described herein can apply to the non-uniform gate insulator thickness, too, wherein the progressions of the non-uniform channel doping profiles 6 and the non-uniform gate insulator thickness can be the same or can be different.
• said thickness could be between 120 nm and 250 nm inclusive or between 120 nm and 180 nm inclusive.
• these two thicknesses of the gate insulator 4 differ by at least a factor of 1.5 and/or by at most a factor of 5.
• a position J of a gate insulator thickness jump is, for example, within the first section 61.
• said position J is between the two steps 53 in the doping profile 6.
• the same as to Figures 2 to 10 may also apply to Figure 11, and vice versa.
• the doping concentration N A is not fashioned in a stepped manner, but changes continuously at a beginning of the first section 61.
• the transitional section 62, in which the doping concentration N A changes amounts, for example, to at least 2% and/or to at most 15% or to at most 10% or to at most 5% of the length L.
• the doping concentration N A does not increase monotonically.
• the minor peak in the doping concentration N A may be located in the middle section 63. Otherwise, the same as to Figures 2 to 12 may also apply to Figure 13, and vice versa.
• the doping concentration N A increases continuously in a linear manner from the second section 64 till the first section 61. Hence, there is no need for a well-defined interface or dividing line between the first section 61 and the second section 64. Otherwise, the same as to Figures 2 to 13 may also apply to Figure 14, and vice versa.
• the power semiconductor device 1 is of a planar design and not of a trench design like, for example, the power semiconductor device 1 of Figures 2 and 3.
• the top side 20 is planar, and the gate insulator 4 and the gate electrode 31 are applied onto the top side 20.
• the length L between the source region 21 and the drift region 23 is in parallel with the top side 20, and not like in the other exemplary embodiments perpendicular to the top side 20.
• the well region 22 protrudes from the source region 21 in a lateral direction, that is, in parallel with the top side 20, and extends below the gate insulator 4.
• the source region 21 may extend below the gate insulator 4, but less far.
• All the above-mentioned different designs of the doping profile 6 can analogously be applied to the planar concept of Figure 15, both in case of a MISFET or MOSFET as well in case of an IGBT.
• Figures 2 to 13 can also apply to Figure 14.
• FIG. 16 it is illustrated that there is not only the non-uniform channel doping profile, but also a non- uniform gate insulator thickness profile and a non-uniform gate dielectric constant profile of the gate insulator 4 because of optionally present at least two different materials 81, 82, the gate insulator 4 is composed of. That is, the thickness of the gate insulator 4 varies along the channel region 220. For example, a difference of the relative dielectric constant along the channel region 220 because of the at least two different materials 81, 82 is at least 2.0 or is at least 3.0 or is at least 3.5. Alternatively or additionally, said difference is at most 50 or is at most 25.
• a thickness of the first material 81 in the first section 61 exceeds a thickness of the second material 82 in the second section 64, or vice versa.
• a thickness difference between the first material 81 and the second material 82 is at least 20% or at least 40% of a maximum thickness of the gate insulator 4 along the channel region 220. If there is only the non-uniform gate insulator thickness profile and a uniform gate dielectric constant profile, the gate insulator 4 can be of a single material.
• a thickness of the gate insulator 4 in the second section 64 is between 50 nm and 100 nm inclusive and/or a thickness of the gate insulator 4 in the first section 61 is between 100 nm and 240 nm inclusive.
• the thickness of the gate insulator 4 in the first section 61 can alternatively be smaller than in the second section 64, and a maximum thickness can instead be present in the second section 64. Accordingly, there is a step in the non-uniform channel doping profile 6 at the interface between the first section 61 and the second section 64, see the insert in Figure 16.
• the gate electrode 31 can include a first gate material 84 next to the source region 21 and a second gate material 85 next to the drain region 23.
• the gate materials 84, 85 may change where the materials 81, 82 of the gate insulator 4 change.
• the work function ⁇ m of the gate electrode 31 in the first section 61 remote from the source region 21 is largest for devices 1 having a p-doped well region 22 and smallest for devices 1 having an n-doped well region 22.
• a work function difference of the gate electrode along the channel region 220 is at least 0.7 eV or is at least 1.0 eV or is at least 1.1 eV. This applies, for example, when the gate electrode 31 is based on poly-silicon. If metals like Li, Zn, Hf for a low work function, or metals like Pt, Pd or Au for a high work function are also considered, the work function difference may be at least 1.3 eV or at least 1.4 eV. For example, the work function difference is at most 2.0 eV or at most 1.5 eV.
• the second gate material 85 is p + -doped poly- silicon having a work function ⁇ m of about 5.22 eV.
• the first gate material 84 is n + -doped poly-silicon having a work function ⁇ m of about 4.1 eV.
• these first gate materials 84 and second materials 85 may be referred to as different gate electrode metals.
• Such at least one of the non-uniform gate insulator thickness profile, the non-uniform gate insulator dielectric constant profile and the non-uniform gate insulator thickness profile can be present analogously in all the other exemplary embodiments, too. Otherwise, the same as to Figures 2 to 15 may also apply to Figure 16, and vice versa.

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• 2021
  • 2021-07-16 EP EP21186114.1A patent/EP4120357A1/en not_active Withdrawn
• 2022
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