Classifications

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  • 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
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  • 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
  • H10D30/0293—Manufacture or treatment of FETs having insulated gates [IGFET] of double-diffused metal oxide semiconductor [DMOS] FETs of vertical DMOS [VDMOS] FETs using formation of insulating sidewall spacers
• • 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
  • H10D30/663—Vertical DMOS [VDMOS] FETs having both source contacts and drain contacts on the same surface, i.e. up-drain VDMOS
• • 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
  • H10D30/665—Vertical DMOS [VDMOS] FETs having edge termination structures
• • 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
  • H10D62/102—Constructional design considerations for preventing surface leakage or controlling electric field concentration
  • H10D62/103—Constructional design considerations for preventing surface leakage or controlling electric field concentration for increasing or controlling the breakdown voltage of reverse-biased devices
  • H10D62/105—Constructional design considerations for preventing surface leakage or controlling electric field concentration for increasing or controlling the breakdown voltage of reverse-biased devices by having particular doping profiles, shapes or arrangements of PN junctions; by having supplementary regions, e.g. junction termination extension [JTE] 
  • H10D62/109—Reduced surface field [RESURF] PN junction structures
  • H10D62/111—Multiple RESURF structures, e.g. double RESURF or 3D-RESURF structures
• • 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
  • H10D62/13—Semiconductor regions connected to electrodes carrying current to be rectified, amplified or switched, e.g. source or drain regions
  • H10D62/149—Source or drain regions of field-effect devices
  • H10D62/151—Source or drain regions of field-effect devices of IGFETs 
  • H10D62/156—Drain regions of DMOS transistors
• • 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
  • H10D62/13—Semiconductor regions connected to electrodes carrying current to be rectified, amplified or switched, e.g. source or drain regions
  • H10D62/149—Source or drain regions of field-effect devices
  • H10D62/151—Source or drain regions of field-effect devices of IGFETs 
  • H10D62/156—Drain regions of DMOS transistors
  • H10D62/157—Impurity concentrations or distributions
• • 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
  • H10D62/80—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials
  • H10D62/83—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials being Group IV materials, e.g. B-doped Si or undoped Ge
• • 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
  • H10D64/60—Electrodes characterised by their materials
  • H10D64/66—Electrodes having a conductor capacitively coupled to a semiconductor by an insulator, e.g. MIS electrodes
  • H10D64/661—Electrodes having a conductor capacitively coupled to a semiconductor by an insulator, e.g. MIS electrodes the conductor comprising a layer of silicon contacting the insulator, e.g. polysilicon having vertical doping variation
  • H10D64/662—Electrodes having a conductor capacitively coupled to a semiconductor by an insulator, e.g. MIS electrodes the conductor comprising a layer of silicon contacting the insulator, e.g. polysilicon having vertical doping variation the conductor further comprising additional layers, e.g. multiple silicon layers having different crystal structures
  • H10D64/663—Electrodes having a conductor capacitively coupled to a semiconductor by an insulator, e.g. MIS electrodes the conductor comprising a layer of silicon contacting the insulator, e.g. polysilicon having vertical doping variation the conductor further comprising additional layers, e.g. multiple silicon layers having different crystal structures the additional layers comprising a silicide layer contacting the layer of silicon, e.g. polycide gates
• • 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
  • H10D64/60—Electrodes characterised by their materials
  • H10D64/62—Electrodes ohmically coupled to a semiconductor

Definitions

• the present invention generally relates to field effect transistors (FETS), and more particularly to TMOS type FETS.
• MOS metal-oxide-semiconductor
• FIG. 1 illustrates prior art super-junction TMOS device 20.
• TMOS device 20 is formed in and on substrate 21 having N+ drain region 22 of, for example, 0.01 Ohm-cm resistivity and with thickness Ddram of about 350 micrometers thickness, and with its lower surface coupled to drain contact 23.
• N-Epi region 24 lies above drain region 22 and has thickness Depi typically about 30-50 micrometers.
• P-body regions 26 extend distance Dbody about 1-3 micrometers into N-Epi region 24 from upper surface 25 of substrate 21.
• P+ body contact regions 28 and N+ source regions 30 extend into P- body regions 26 from upper surface 25.
• N+ source regions 30 have thickness D s typically about 0.3 micrometers.
• Gate insulator 32 covered by gate 34 extends between source regions 30 over channel regions 27 in P-body regions 26 and inter-body region 36 located between P- body regions 26.
• Contact 31 is provided to P+ body contact regions 28 and N+ source regions 30, and connection 35 is provided to gate 34.
• Beneath P-body regions 26 and extending through N-epi region 24 to drain 22 are P-partition regions 38 of lateral width Lp.
• Beneath inter-body N regions 36 are N-drift regions 39 of depth Ddnft and of lateral width L N extending through N-epi region 24 to drain 22.
• Lp and L N are typically about 5-8 micrometers.
• the quantities of impurities in N-drift regions 38 should be within 100 % to 150 % of the quantity of impurities in P-partition regions 39.
• W G is the gate length and L acc is the length between facing P-body regions 26.
• the channel lengths LcH are approximately (1/2)*(W G -L acc ).
• W G is typically of the order of about four micrometers or more and L acc about 2.4 micrometers or more.
• TMOS devices are very useful, they suffer from a number of limitations well known in the art.
• the on-resistance R DS(ON) is often higher than desired
• the gate-source and gate-drain capacitances C GS and C GD are often larger than desired
• the gate charge Q G can be larger than desired
• other device properties may also be less than optimum.
• various improvements have been made in the past to attempt to ameliorate these and other problems, such as employing superjunction structures (see for example, U.S. Patent 6,291,856 Bl to Yasushi Miyasaka et al)
• R DS(ON) can be improved by increasing the doping in epi-region 24, this tends to undesirably increase C GD and/or Q G , and/or undesirably reduce the break-down voltage BVD SS - Conversely, while C G D and Q G can be reduced by thickening the gate oxide above region 36 this tends to increase R DS(ON) and/or undesirably perturb the threshold voltage. While use of a superjunction structure like that shown in FIG.
• charge balanced drift region 38, 39 may avoid some of these complications by forming charge balanced drift region 38, 39, it is difficult and expensive to fabricate the required side-by-side arrangement of P and N closely packed parallelepipeds 38, 39 whose heights (Dd ⁇ ft) are generally 4-5 times their width (Lp, L N ), such as is illustrated in FIG. 1.
• MOS devices For higher frequency operation when lateral device dimensions (e.g., W G , L P , L N , etc.) generally must be made smaller, this is even more difficult to accomplish since smaller values of Lp and L N are often associated with larger values of Dd ⁇ ft •
• FIG. 1 is a simplified schematic cross-sectional view through a superjunction TMOS device according to the prior art
• FIG. 2 is a simplified schematic cross-sectional view through a superjunction TMOS device according to an embodiment of the present invention
• FIGS. 3-12 are simplified schematic cross-sectional views showing further detail and according to further embodiments of the present invention, illustrating sequential steps in methods of fabricating devices of the type illustrated in FIG. 2.
• MOS devices may be P-channel type devices referred to as PMOS devices or N- channel type devices, referred to as NMOS devices.
• This invention relates usefully to NMOS devices and is described herein for such structures. However, this is for convenience of illustration and not intended to be limiting and the principles taught herein also apply to PMOS devices.
• P -type and N-type are intended to be equivalent to and include the more general terms "first conductivity type” and “second conductivity type” respectively, where “first” and “second” can refer to either P or N conductivity types.
• N a refers to the number of acceptors per unit volume and Nd refers to the number of donors per unit volume
• N first and Nsecond may be used to refer to the number of donor or acceptor per unit volume, where “first” and “second” can refer to either donors or acceptors.
• MOS metal-oxide-semiconductor
• FIG. 2 is a simplified schematic cross-sectional view through TMOS device 40 according to an embodiment of the present invention.
• Device 40 comprises substrate 41, conveniently of silicon but other semiconductors may also be used, having lower surface 43 and upper surface 45.
• N++ drain region 42 of typically 0.004 Ohm-cm resistivity, is generally provided at or adjacent lower surface 41. Drain contact 45 is conveniently provided on lower surface 41 of N++ drain region 42 with connection D. However, this is not intended to be limiting since drain region 42 can be contacted from either lower surface 43 or if formed as a buried layer be contacted from upper surface 45.
• N-Epi region 44 extends upwardly from N++ drain region 42.
• P-body regions 46 extend downwardly into N-Epi region 44 from upper surface 45 and are laterally separated by distance L acc .
• P++ body contact regions 48 and N++ source regions 50 extend into P-body regions 46.
• Gate dielectric 52 e.g., of silicon dioxide
• Conductive gate electrode 53 of width W G overlies gate dielectric 52.
• Gate electrode 53 is desirably a composite sandwich wherein layer 54 is conveniently of doped poly-silicon and layer 55 is conveniently of a polycide such as, for example, tungsten-silicide WSi x where, generally, 1.5 ⁇ x ⁇ 2, but other composition ranges and other polycides can also be used.
• the combination of poly-Si layer 54 and polycide layer 55 provides low gate resistance, which assists in obtaining good switching speed.
• External gate contact 162 is remotely provided to gate electrode 53.
• Dielectric layer 60 (e.g., of silicon oxide) is provided over gate electrode 53 so that source and body contact metallization 64 of, for example, Al, Cu, Au, Si and/or alloys thereof may bridge over gate electrode 53 above active channel regions 47 and JFET region 56, and be coupled to source regions 50 and body region contacts 48 on either side of gate electrode 53.
• source and body contact metallization 64 of, for example, Al, Cu, Au, Si and/or alloys thereof may bridge over gate electrode 53 above active channel regions 47 and JFET region 56, and be coupled to source regions 50 and body region contacts 48 on either side of gate electrode 53.
• Al with a trace of Cu is preferred for metallization 64 but this is not intended to be limiting.
• the abbreviation "Al:Cu" used herein in referring to metallization 64 is intended to refer not only to the preferred combination but also to the many other possible metal combinations that can be used, including but not limited to those listed above.
• External contact 65 is made remotely to source metallization 64. .
• conductive barrier material 51 of, for example, Ti/TiN or other conductive intermetallic, between source and body contact regions 50, 48 and source/body metallization 64 to retard inter-diffusion of polycide 55 and metallization 64. This helps maintain low resistance connection to source/body contact regions 50, 48.
• other conductive materials may be used for source/body metallization 64.
• metallization 64 may be applied directly to source/body contact regions 50, 48, but this is less desirable.
• Side -wall spacers 61, 62 are provided to separate the lateral edges of gate electrode 53 from source/body contacts 51 and source/body metallization 64.
• L C H are approximately ( 1/2)* (W G - Lacc).
• L acc and L CH (channel 47) are each of the order of about 0.2-0.3 microns so that W G is of the order of about 0.6-1.0 micrometers or less.
• L acc can be less than 0.2 micrometers.
• Using small values of L acc and W G can substantially enhance the high speed switching performance.
• FIGS. 3-12 are simplified schematic cross-sectional views showing further detail and according to further embodiments of the present invention, illustrating sequential steps 101-110 of methods of fabricating device 40 of FIG. 2.
• FIG. 3 shows sequential step 101 wherein there is provided semiconductor wafer or substrate 41 of preferably silicon and comprising N++ doped layer 42 surmounted by N-type layer 44.
• the combination of highly doped layer 42 surmounted by substantially uniformly doped layer 44 may be achieved in various ways well known in the art.
• layer 42 may be the starting substrate on which layer 44 is formed by epitaxial growth or layer 44 may be the starting substrate in which layer 42 is formed by doping or other means.
• layer or region 42 may a buried layer provided within layer 44 at a predetermined depth and contacted by a highly doped sinker region from surface 45 or elsewhere. Either arrangement is useful.
• Layer 44 is preferably an epi-layer but this is not essential, and the identification of layer 44 on FIGS. 3-12 as an "N-Epi" layer is merely by way of example and not intended to be limiting.
• Layer 42 is conveniently arsenic doped to about 0.004 Ohm-cm, but larger or smaller doping levels may also be used.
• Layer 44 is conveniently phosphorous doped to about 0.1 to 1.0 Ohm-cm with about 0.3 Ohm-cm being preferred, but higher and lower doping can also be used.
• Layer 44 is preferably about 3-4 micrometers in thickness, but thinner or thicker layers can also be used.
• Initial oxide layer 111 typically of a few thousand Angstrom units thickness, is provided on upper surface 45.
• Mask layer 115 of, for example, photoresist is applied on initial oxide layer 111 and patterned to provide opening 113 extending to semiconductor surface 45.
• P-type edge region 123 is introduced into N-type layer 44 through opening 113, thereby providing the structure illustrated in FIG. 3.
• Ion implantation 117 utilizing boron is a preferred doping method but other doping arrangements well known in the art for providing P-type edge region 123 may also be used. Persons of skill in the art will understand that FIGS.
• step 102 of FIG. 4 mask layer 115 is removed, and field oxide layer 120 grown or otherwise formed to a thickness about twice that of initial oxide 111, but larger or smaller thickness values may also be used.
• Mask layer 126 is applied and patterned to expose portion 119 of field oxide layer 120. Portion 119 is conveniently removed by etching via opening 125 in mask layer 126.
• the higher temperatures encountered during deposition or growth of field oxide 120 cause initial edge region 123 to diffuse downwardly and laterally in N-layer 44, thereby providing expanded P-type edge region 124', as shown in FIG. 4.
• screen oxide 130 is formed on surface 45 and masking layer 127 of, for example, photoresist, is conveniently provided over screen oxide 130 and field oxide 120 and patterned to have openings 129 where N-doped regions 56 are desired to be located.
• N-type implant 133 is provided to form initial N-doped regions 56' in N-epi layer 44 under mask openings 129.
• a dose about 1E13 to 1E14 atoms per sq cm is convenient with about 3El 3 atoms per sq cm being preferred.
• Implant energies in the range of about 100-350 keV are convenient with about 200 keV being preferred.
• step 105 screen oxide 130 is preferably removed by a brief etch and gate oxide 52 is conveniently formed in its place, but this is not essential and screen oxide 130 may also serve as the gate oxide.
• Gate oxide 52 is preferably formed by thermal growth to a thickness depending upon the desired voltage capabilities and gate capacitance of the device. Gate oxide thicknesses in the range of 100-500 Angstroms units are convenient with thicknesses in range of 350-500 Angstrom units being preferred for higher voltage power devices, but larger or smaller thicknesses can also be used.
• Polysilicon or other blanket polycrystalline semiconductor (SC) layer 112 is provided over oxide layers 120, 52.
• Layers 112, 114, 116 are conveniently but not essentially formed by chemical vapor deposition (CVD) or plasma enhance chemical vapor deposition (PECVD). However, other formation techniques may also be used. Sputtering and evaporation are non-limiting examples of alternative deposition methods for any and all of layers 112, 114, 116.
• the thicknesses of conductive layers 112, 114 should be chosen in conjunction with the choice of materials for these layers so as to provide relatively low resistance gate electrodes 53.
• dielectric layer 116 In general, thicknesses of the order of a few thousand Angstrom units are convenient.
• the thickness of dielectric layer 116 is chosen by the device designer so as to limit capacitive coupling between the source and gate conductors 49, 53 (see FIG. 2) to acceptable levels without producing an overly thick device superstructure. Persons of skill in the art will understand how to make such choices.
• Masking layer 128 of, for example, photoresist is applied over dielectric layer 116 and patterned to provide openings 121, 122 wherein underlying portions of layers 112, 114, 116 are removed, conveniently by etching, thereby producing the structure of FIG. 6.
• Layers 112, 114, 116 correspond to layers 54, 55, 60 of FIGS. 2 and 12.
• step 106 of FIG. 8 P-type implant 136 of, for example, boron is provided through openings 121, 122 to a dose usefully in the range of about lE12 to 1E13 atoms per sq cm at energies in the range of about 40 to 100 KeV, with a dose of about 6El 2 atoms per sq cm at energies in the range of about 60 KeV being preferred.
• Implant 136 forms doped regions 46' beneath openings 121, 122, thereby providing the structure illustrated in FIG. 8. It is desirable to use a range of energies so as to achieve the substantially uniform doping eventually desired for P-body regions 46 which form from implanted regions 46'. In step 107 of FIG.
• a high temperature drive is provided at, for example, about 900 to 1200 degrees centigrade, with about 950 to 1100 degrees centigrade for about 70 minutes being preferred
• Drive step 107 redistributes the various N and P dopants so that P-doped regions 46' expand to form P-doped body regions 46, N-doped regions 56' expand further to form JFET regions 56, and region 124' expands further to form P-edge region 124 of FIGS 2 and 13.
• step 108 of FIG. 10 mask regions 166 located approximately centrally in openings 121, 122 are provided, thereby leaving openings 170 between mask regions 166 and first side-wall spacers 61.
• N+ implant 163 of, for example, arsenic is applied at an energy usefully in the range of about 40 to 120 keV to a dose usefully in the range of about IEl 5 to 5El 5 atoms per sq cm, preferably at about 90 keV to a dose of about 4El 5 atoms per sq cm.
• Implant 163 is conveniently carried out through oxide layer 52 to form source regions 50', as shown in FIG. 10. While ion implantation is preferred, other doping means well known in the art may also be used.
• a blanket layer of dielectric such as, for example, silicon oxide, is deposited over the structure of FIG. 10 (e.g., by CVD, PECVD, evaporation or sputtering) and then differentially etched using means well known in the art to provide second side -wall spacers 62 on the lateral edges of layers 112, 114, 116 and first sidewall spacers 61 in openings 121, 122.
• This anisotropic etch also removes oxide layer 52 in openings 121, 122 between sidewall spacers 62.
• P-type implant 186 is provided into surface 45 through openings 121, 122 to form P-type regions 48'. Any convenient P-type dopant may be used but boron is preferred.
• Implant 186 is usefully carried out at energies in the range of about 20 to 60 keV to a dose of about 5El 4 to 5El 5 atoms per sq cm. An energy of about 40 keV and a dose of about IE 15 atoms per sq cm are preferred. This provides the structure illustrated in FIG. 11.
• step 110 of FIG. 12 opening 193 is etched through dielectric layer 116 to permit contact to polycide layer 114. Then an inter-metallic conductive barrier layer is deposited through openings 121, 122 and 193, masked and etched to leave inter-metallic barrier regions 51 in contact with source regions 50 and body contact region 48 under openings 121, 122, and inter-metallic barrier region 192 in contact with polycide layer 114 under opening 193. Then layer 64 of Al: Cu or other highly conductive material is deposited over the structure and masked and etched to provide source/body metallization 64 in contact with conductive barrier layer regions 51 and gate lead 196 in contact with conductive barrier layer region 192, as shown in FIG. 12. The structure illustrated in FIG.
• FIG. 12 illustrates how connection is usefully made to gate metallization 53.
• conductive regions 112, 114 under gate contact 196 are electrically coupled to regions 54, 55 outside the plane of FIGS. 2 and 13.
• the foregoing conditions are accomplished by suitably adjusting the energy and dose of implant 133 in step 103 of FIG.
• an MOS device comprising, a semiconductor substrate of a first conductivity type and having a first principal surface, a first region of the first conductivity type extending a first distance into the substrate from the first principal surface and of length L acc in a directions substantially parallel to the first principal surface and having a net active dopant concentration of about N first , at least a pair of spaced-apart body regions of a second opposite conductivity type extending a second distance into the substrate from the first principal surface and separated by the first region of the first conductivity type and each having length Lbody in a direction substantially parallel to the first principal surface and having a net active dopant concentration of about Nsecond, channel regions located in the spaced-apart body regions substantially at the first surface and extending to the first region, source regions of the first conductivity type located substantially at the first surface in the spaced-apart body regions and separated from the first region by the channel regions, an insulated gate located above the first surface overlying the channel regions and the first region
• ki has a value in the range of about 0.8 ⁇ ki ⁇ 1.2. According to a still further embodiment, ki has a value in the range of about 0.9 ⁇ ki ⁇ 1.1.
• an MOS device made by a process comprising, providing a substrate of a first conductivity type, forming a drain region of a first conductivity type in the substrate, forming multiple first regions of the first conductivity type at a first surface and of first length L acc measured substantially parallel to the first surface, and separated from the drain region, and extending into the substrate a first distance D JFET , and having net active dopant concentration Nf irst in at least some of said multiple regions, forming in the substrate at the first surface, multiple body regions of second length Lbody measured substantially parallel to the first surface and of a second, opposite conductivity type, and extending from the first surface into the substrate a second distance Dbody, and having net active dopant concentration N seC ond in at least some of said multiple body regions, wherein spaced-apart pairs of said body regions are separated by the first region, wherein for at least a pair of said multiple body regions and an intervening first region, the relationship (Lbody * N
• the method of forming the first region further comprises implanting dopant ions of the first conductivity type into the first region.
• the method of forming the first region further comprises implanting said dopant ions using more than one implant energy.
• the method of forming the multiple body regions further comprises implanting dopant ions using more than one implant energy.
• Dbody k 2 * D JFET where k 2 is desirably in the range 0.8 ⁇ k 2 ⁇ 1.2.
• a region between D body and D JFET and the drain region is of a single conductivity type.
• L acc is ⁇ about 0.3 micrometers.
• L acc is ⁇ about 0.2 micrometers.
• a method for forming an MOS device comprising, providing a semiconductor substrate of a first conductivity type having an upper surface, first implanting through the upper surface a first dose of a first conductivity type to form a first doped region, forming a gate dielectric on the upper surface, depositing a gate conductor and an overlying dielectric layer on the gate dielectric, masking and etching the gate conductor and overlying dielectric layer to provide at least two first spaced-apart openings extending to the gate dielectric and defining the lateral extent of the gate, second implanting through the upper surface in the at least two first spaced-apart openings a second dose of a second opposite conductivity type to form second regions of a second opposite conductivity type in the substrate, anytime after the second implanting step, heat treating the device so that, in combination with the first and second doses, the first and second doped regions expand to meet, and so that the net active impurity concentration N first in the first doped region
• a further embodiment comprising, prior to the second implanting step, forming first dielectric spacers on lateral edges of the gate conductor.
• a still further embodiment comprising, after the second implanting step providing a mask defining second spaced-apart openings within the at least two first spaced-apart openings, and third implanting source regions of the first conductivity type in the second regions through the second spaced-apart openings.
• a yet further embodiment comprising, after the third implanting step, fourth implanting body contact regions of the second conductivity type in the second region between the source regions.

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