WO2001006568A2 - Trench-gate field-effect transistors and their manufacture - Google Patents
Trench-gate field-effect transistors and their manufacture Download PDFInfo
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- WO2001006568A2 WO2001006568A2 PCT/EP2000/006442 EP0006442W WO0106568A2 WO 2001006568 A2 WO2001006568 A2 WO 2001006568A2 EP 0006442 W EP0006442 W EP 0006442W WO 0106568 A2 WO0106568 A2 WO 0106568A2
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- 238000004519 manufacturing process Methods 0.000 title claims description 11
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- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical group [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 2
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/76—Unipolar devices, e.g. field effect transistors
- H01L29/772—Field effect transistors
- H01L29/78—Field effect transistors with field effect produced by an insulated gate
- H01L29/7801—DMOS transistors, i.e. MISFETs with a channel accommodating body or base region adjoining a drain drift region
- H01L29/7802—Vertical DMOS transistors, i.e. VDMOS transistors
- H01L29/7813—Vertical DMOS transistors, i.e. VDMOS transistors with trench gate electrode, e.g. UMOS transistors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
- H01L29/08—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions with semiconductor regions connected to an electrode carrying current to be rectified, amplified or switched and such electrode being part of a semiconductor device which comprises three or more electrodes
- H01L29/0843—Source or drain regions of field-effect devices
- H01L29/0847—Source or drain regions of field-effect devices of field-effect transistors with insulated gate
- H01L29/0852—Source or drain regions of field-effect devices of field-effect transistors with insulated gate of DMOS transistors
- H01L29/0856—Source regions
- H01L29/0865—Disposition
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/76—Unipolar devices, e.g. field effect transistors
- H01L29/772—Field effect transistors
- H01L29/78—Field effect transistors with field effect produced by an insulated gate
- H01L29/7801—DMOS transistors, i.e. MISFETs with a channel accommodating body or base region adjoining a drain drift region
- H01L29/7802—Vertical DMOS transistors, i.e. VDMOS transistors
- H01L29/781—Inverted VDMOS transistors, i.e. Source-Down VDMOS transistors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
- H01L29/10—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions with semiconductor regions connected to an electrode not carrying current to be rectified, amplified or switched and such electrode being part of a semiconductor device which comprises three or more electrodes
- H01L29/1095—Body region, i.e. base region, of DMOS transistors or IGBTs
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/41—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions
- H01L29/423—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions not carrying the current to be rectified, amplified or switched
- H01L29/42312—Gate electrodes for field effect devices
- H01L29/42316—Gate electrodes for field effect devices for field-effect transistors
- H01L29/4232—Gate electrodes for field effect devices for field-effect transistors with insulated gate
- H01L29/42364—Gate electrodes for field effect devices for field-effect transistors with insulated gate characterised by the insulating layer, e.g. thickness or uniformity
- H01L29/42368—Gate electrodes for field effect devices for field-effect transistors with insulated gate characterised by the insulating layer, e.g. thickness or uniformity the thickness being non-uniform
Definitions
- This invention relates to trench-gate field-effect transistors in which an insulated trench-gate structure extends to an underlying source region from a drain region adjacent to a major surface of the semiconductor body.
- the invention also relates to methods of manufacturing such transistors.
- Trench-gate field-effect transistors comprising a semiconductor body into which an insulated gate electrode extends in a trench from a major surface of the body.
- the trench extends through a channel-accommodating portion of a body region of a first conductivity type between drain and source regions of an opposite second conductivity type.
- the source region is adjacent to the said major surface, where it is electrically shorted to a part of the body region.
- United States patent specification US-A-5, 134,448 discloses a trench-gate field-effect transistor of what may be termed an inverted configuration, in which the drain region is adjacent to the said major surface with the insulated gate electrode.
- the insulated gate electrode extends in a trench from a major surface of the body, successively through a drain region, a lower-doped drain drift region, and a transistor body region to reach an underlying source region of the transistor. A part of the body region is electrically shorted to the underlying source region by a buried electrical short.
- US-A-5, 134,448 teaches burying the electrical short at the bottom of a trench, where it is formed by a variety of ohmic-contact means.
- Such means include a metal (for example, Al, Ti, W, Mo, Ta, Ni, Cr, Pt, or alloy thereof), an intermetallic with the semiconductor, and a degenerate semiconductor.
- the layout area of the device is significantly increased when an extra trench (separate from that of the trench-gate) is provided specifically for the electrical short.
- the trench-gate structure becomes complicated when the electrical short is provided at the same trench as the insulated gate electrode.
- a trench-gate transistor of inverted configuration which can have a compact layout of drain and trench-gate structures at the body surface and a buried source-body region short that does not complicate the trench structure of the insulated gate electrode.
- a trench-gate field-effect transistor of inverted configuration in which the insulated gate electrode extends in a trench lined with gate dielectric that insulates the gate electrode from the drain region, a drain drift region, the transistor body region and the underlying source region.
- the gate dielectric is thicker adjacent to the drain region than adjacent to a channel-accommodating portion of the body region.
- a more highly doped bottom portion of the body region forms a leaky p-n junction with the underlying source region at an area that is separated laterally from the insulated gate electrode by an active portion of the source region adjacent to the trench.
- the leaky p-n junction provides the buried electrical short.
- the body region comprises an overlying layer that provides the channel-accommodating portion and that is less highly doped than the bottom portion.
- the active portion of the source region extends across the highly doped bottom portion of the body region to connect with the channel-accommodating portion of the body region adjacent to the trench.
- Such an arrangement of the trench for the insulated gate electrode with respect to the various transistor regions permits a compact layout of the transistor.
- a compact layout of drain and trench-gate structures is achievable at the body surface, and a compact layout of the buried electrical short is achievable with the underlying source region.
- Premature breakdown between gate and drain across the gate dielectric is avoided by making the gate dielectric to be thicker adjacent to the drain region than adjacent to the channel-accommodating portion of the body region.
- a thicker dielectric may also be advantageously provided adjacent to the lower-doped drain drift region, for example in a power device with cells which are so closely packed that the drift region is depleted by RESURF action from neighbouring trench-gate portions in the voltage blocking state of the device.
- the highly doped bottom portion of the body region in the form of a layer that extends laterally to the gate trench where it is overdoped by the said active portion of the source region.
- the active portion of the source region can be formed by dopant implantation and/or diffusion.
- its doping concentration profile of the second conductivity type may be implanted at the bottom of a trench in the semiconductor body before the gate electrode is provided in the trench. Its final doping profile of the second conductivity type may correspond to a dopant diffusion profile from the bottom of the trench.
- the present invention is particularly advantageous for realising power devices with a compact transistor layout geometry.
- Such devices generally comprise a plurality of the body regions that are located side-by-side in the semiconductor body, with grid portions of the trench-gate structure in-between.
- the realisation of the electrical short in accordance with the present invention permits a close spacing of these grid portions, and even permits the active portion of the source region to be provided in a self-aligned manner around the bottom of each grid portion of the gate trench.
- the drain drift region is lower doped than the drain region and so has a lower conductivity. In order to reduce the on-resistance of the device, it is advantageous for the drain drift region to have a doping concentration of the second conductivity type that increases towards the drain region.
- Figure 1 is a cross-sectional view of an active central part of a trench-gate field-effect power transistor in accordance with the invention
- Figure 2 is an enlarged cross-sectional view of the transistor structure of Figure 1 , in the vicinity of a grid portion of the trench-gate structure;
- Figure 3 is a cross-sectional view of the transistor structure of Figure 2, at a stage in the manufacture of the device;
- Figure 4 is an enlarged cross-sectional view, similar to Figure 2, of the transistor structure of another trench-gate field-effect device in accordance with the invention.
- Figure 5 shows doping profiles Nd (for n-type regions) and Na (for the p-type region) in cm "3 through the regions 14, 14a, 15a, 13a for a specific embodiment of a drift region in a transistor device in accordance with the invention. It should be noted that all the Figures are diagrammatic. Relative dimensions and proportions of parts of the drawings have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar features in modified and different embodiments.
- FIG. 1 illustrates an exemplary embodiment of a cellular trench-gate field-effect power transistor in accordance with the invention.
- the transistor comprises a semiconductor body 10 having a top major surface 10a from which an insulated gate electrode 1 1 extends in a trench 20 into the body 10.
- the gate electrode 1 1 is present on a gate dielectric layer 12 that lines the trench 20.
- This insulated trench-gate structure 1 1 ,12 extends through a channel-accommodating portion 15a of a body region 15 of a first conductivity type (p-type in this embodiment), between drain and source regions 14 and 13 of an opposite second conductivity type (n-type in this embodiment).
- the transistor is of the MOSFET type, in which the gate electrode 1 1 is capacitively coupled to the channel-accommodating portion 15a of the body region 15 across the intermediate gate dielectric 12.
- the application of a voltage signal to the gate electrode 11 in the on-state of the device serves in known MOSFET manner for inducing a conduction channel 22 in the region portion 15a and for controlling current flow in this conduction channel 22 between the source and drain regions 13 and 14.
- the transistor is of an inverted configuration, in which the drain region 14 is adjacent to the top surface 10a.
- the gate trench 20 extends successively through the drain region 14, or drain drift region 14a, and the body region 15 into an underlying portion of the source region 13.
- the drain region 14 is contacted at the top major surface 10a by a drain electrode 34.
- the drain electrode 34 extends over the gate electrode 11 from which it is insulated by an intermediate insulating layer 32.
- the drain drift region 14a is of lower doping concentration (n-) than the drain region 14 (n+) and is present between the drain region 14 and the underlying body region 15.
- the gate dielectric 12 insulates the gate electrode 1 1 from the successive regions 14, 14a, 15 and 13 and is thicker adjacent to the drain region 14 than adjacent to a channel-accommodating portion 15a of the body region 15.
- the gate dielectric 12 has a thickness that increases progressively adjacent to the drain drift region 14a with distance from the channel-accommodating portion 15a of the body region 15.
- Figures 1 and 2 illustrate this increase to the thick dielectric layer portion 12a adjacent to the drain region 14.
- a part of the body region 15 is electrically shorted to the underlying source region 13 by a buried electrical short 35 in accordance with the present invention.
- Figure 1 shows a discrete vertical device structure in which the source region 13 is a substrate of high conductivity (n+ in this example), which is contacted by the source electrode 33 at the bottom major surface 10b of the body 10.
- the transistor typically comprises tens of thousands of parallel device cells in the semiconductor body 10 adjacent to the body surface 10a.
- the number of cells is dependent on the desired current-carrying capability of the device.
- Transistors in accordance with the invention may have any one of a variety of known cell geometries, for example an hexagonal close-packed geometry, or a square geometry, or an elongate stripe geometry.
- the device has a plurality of the body regions 15 which are located side-by-side in the semiconductor body 10, and the trench-gate structure 11 ,12 comprises grid portions which extend between the channel-accommodating portions 15a of the neighbouring side-by-side body regions 15, as illustrated in Figure 1.
- the source region 13 is common to all the cells.
- the active cellular area of the device may be bounded around the periphery of the body 10 by various known peripheral termination schemes. Such schemes normally include the formation of a thick field-oxide layer at the peripheral area of the body surface 10a, before the transistor cell fabrication steps.
- a leaky p-n junction 35 provides the buried electrical short between the transistor body region 15 and the underlying source region 13.
- the body region 15 comprises an overlying layer 15a that provides the channel-accommodating portion and that extends over a bottom portion 15b of the body region that is more highly doped (p+) than the overlying layer 15a (p).
- This highly doped bottom portion 15b forms the leaky p-n junction 35 with the underlying source region 13 at an area that is separated laterally from the insulated gate electrode 11 by the gate dielectric 12 and by an active portion 13a of the source region 13 adjacent to the gate trench 20.
- This active portion 134a of the source region 13 extends across the thickness of the highly doped bottom portion 15b of the body region 15 to connect with the channel-accommodating portion 15a.
- This active portion 13a of the source region 13 extends around the bottom of each grid portion of the insulated trench-gate structurel 1 ,12, as illustrated in Figures 1 and 2.
- the body 10 is of monocrystalline silicon
- the gate electrode 1 1 is of doped polycrystalline on a gate insulating layer 12 of silicon dioxide
- the electrodes 33 and 34 are of, for example, aluminium.
- the doping concentration (p+) of the high-doped portion 15b may be, for example, 10 18 to 10 19 boron atoms cm "3
- that (p) of the channel-accommodating portion 15a may be, for example, 10 16 to 10 17 boron atoms cm "3
- that (n+) of the active source portion 13a of the may be, for example, 10 19 to 10 21 phosphorus or arsenic atoms cm "3
- the dopant concentration (n+) of the source and drain regions may be, for example, 10 20 to 10 22 phosphorus or arsenic atoms cm "3 .
- the tunnelling current across the resulting p-n junction 35 is of the order of 10 to 100 amps. cm "2 .
- the total leakage current across the p-n junction 35 with an area of 15mm 2 may be in the range of, for example, 1.5 to 15 amps.
- the lower doped drain drift region 14a may have a doping concentration (n-) that is uniform or that reduces with depth, for example from about 3 x 10 17 at the interface with drain region 14 to about 10 16 at the interface with the body region 15.
- the highly doped bottom portion 15b of the body region 15, the channel-accommodating portion 15a of the body region 15, the drain drift region 14a and the drain region 14 may be formed as a stack of epitaxial layers on the substrate 13.
- the layer that forms the highly doped bottom portion 15b of the body region 15 extends laterally to the trench-gate structure 1 1 ,12 where it is overdoped by the active portion 13a of the source region 13.
- Figure 3 illustrates a step in the manufacture of such a structure.
- Figure 3 illustrates an ion implantation step that is carried out after etching the trench 20 through the stacked epitaxial layers 14, 14a, 15a, 15b and before providing the insulated trench-gate structure 1 1 ,12 in the trench 20.
- the ions 30 may be of arsenic or phosphorus and are implanted at the bottom of a trench 20 in the semiconductor body 10 so as to provide the doping n+ for the active portion 13a of the source region 13.
- the doping n+ for the active portion 13a is self-aligned with the trench 20, because outside the trench 20 the ions are implanted into the n-type drain region 14.
- a range of ion energies may be used to overdope the region portion 15b throughout its thickness, and/or the implanted dopant region 31 may be diffused in subsequent heat treatments, for example during the growth of the gate dielectric 12 and the deposition of the polysilicon gate 11.
- the resulting extension portion 13a of the source region 13 may have an n+ doping profile corresponding to a dopant diffusion profile from the bottom of the trench 20.
- Figure 4 illustrates an alternative device structure in accordance with the invention.
- the doping (p+) of the highly doped portion 15b of the body region 15 is provided only locally in the centre of each cell.
- a part of the substrate region 13 itself adjoins the bottom of the trench 20 and the channel-accommodating portion 15a of the body region 15.
- This part of the substrate region forms the active source portion 13a that laterally separates the leaky p-n junction 35 from the trench-gate structure 11 ,12 and that extends across the highly doped bottom portion 15b of the body region 15 to connect with the channel-accommodating portion 15a.
- the provision of the leaky junction 35 of the Figure 4 device is less easily self-aligned with the trench 20. However, self-alignment can be achieved using spacer technology.
- the doping concentration of the drift region 14a may reduce with depth. Its higher doping concentration towards the drain region 14 can reduce the on-resistance of the device, while still permitting the drift region 14a to be depleted between neighbouring grid portions of the trench-gate structure 11 ,12 in a voltage-blocking state of the device.
- Figure 5 illustrates a specific embodiment in which the doping profile Nd for the drift region 14a decreases substantially linearly from 3x10 17 cm "3 in the vicinity of the drain region 14 to 10 16 cm “3 in the vicinity of the underlying body region 15a. This doping profile may be formed by in situ growth of the doped epitaxial material.
- the inverted configuration of the transistor permits the doping profile of the drift region 14a to be formed by, for example, dopant implantation and/or diffusion from the surface 10a after growing all the epitaxial layers. At least part of the desired doping profile may, alternatively, be formed by dopant implantation and/or diffusion from the surface of an epitaxial layer 14a before growing or diffusing the drain region 14.
- Figure 5 illustrates a linearly graded profile, different doping profiles can easily be produced in this way for the drift region 14a.
- an inverted device structure in accordance with the invention may also be used for low-voltage devices.
- the substrate source 13,33 has a low inductance, and so inverted device structures in accordance with the invention can be used advantageously for high-frequency devices.
- a conductively-doped polycrystalline gate electrode 11 has been described above. However, so as to reduce its resistance, the gate electrode 11 may include a metal suicide layer or may even be entirely of metal.
- n-channel device has been described with reference to Figures 1 to 4.
- a p-channel device is also possible in accordance with the invention, in which the regions 14, 14a, 13a and 13 are p-type, the body region portions 15a and 15b are n-type and the conduction channel 22 is of holes.
- the source region 13 may be a doped buried layer between a device substrate and an epitaxial body region 15a and may be contacted by electrode 33 at the front major surface 10a via a doped peripheral contact region which extends from the surface 10a to the depth of the buried layer.
- a device in accordance with the present invention may be of a so-called silicon-on-insulator (SOI) construction, in which the transistor structure (either vertical or horizontal) is formed in a monocrystalline silicon layer on an insulator.
- SOI silicon-on-insulator
- the semiconductor body 10 of a transistor in accordance with the invention may be a comparatively thin layer of monocrystalline silicon.
- Such a layer that is tens of micrometres (microns) thick can be carried on thicker substrate.
- the carrier substrate may be of, for example, monocrystalline silicon.
- the silicon layer may be bonded to the carrier substrate.
- an insulating interface layer may be present at the carrier substrate surface.
- other monocrystalline semiconductor materials may be adopted for the body 10, for example silicon carbide.
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- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Ceramic Engineering (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Junction Field-Effect Transistors (AREA)
- Insulated Gate Type Field-Effect Transistor (AREA)
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Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP00945893A EP1145325A3 (en) | 1999-07-20 | 2000-07-07 | Trench-gate field-effect transistors and their manufacture |
JP2001510920A JP2003505864A (en) | 1999-07-20 | 2000-07-07 | Trench-gate field-effect transistor and method of manufacturing the same |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GBGB9916868.4A GB9916868D0 (en) | 1999-07-20 | 1999-07-20 | Trench-gate field-effect transistors and their manufacture |
GB9916868.4 | 1999-07-20 |
Publications (2)
Publication Number | Publication Date |
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WO2001006568A2 true WO2001006568A2 (en) | 2001-01-25 |
WO2001006568A3 WO2001006568A3 (en) | 2001-09-07 |
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Application Number | Title | Priority Date | Filing Date |
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PCT/EP2000/006442 WO2001006568A2 (en) | 1999-07-20 | 2000-07-07 | Trench-gate field-effect transistors and their manufacture |
Country Status (5)
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US (1) | US6509608B1 (en) |
EP (1) | EP1145325A3 (en) |
JP (1) | JP2003505864A (en) |
GB (1) | GB9916868D0 (en) |
WO (1) | WO2001006568A2 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2002027800A2 (en) * | 2000-09-28 | 2002-04-04 | General Semiconductor, Inc. | Trench dmos transistor having lightly doped source structure |
US20220140141A1 (en) * | 2019-02-07 | 2022-05-05 | Rohm Co., Ltd. | Semiconductor device |
Families Citing this family (21)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2002270840A (en) * | 2001-03-09 | 2002-09-20 | Toshiba Corp | Power mosfet |
GB0117949D0 (en) * | 2001-07-24 | 2001-09-19 | Koninkl Philips Electronics Nv | Trench-gate semiconductor devices and their manufacture |
US7262461B1 (en) * | 2002-05-20 | 2007-08-28 | Qspeed Semiconductor Inc. | JFET and MESFET structures for low voltage, high current and high frequency applications |
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Also Published As
Publication number | Publication date |
---|---|
US6509608B1 (en) | 2003-01-21 |
JP2003505864A (en) | 2003-02-12 |
EP1145325A3 (en) | 2001-11-28 |
WO2001006568A3 (en) | 2001-09-07 |
EP1145325A2 (en) | 2001-10-17 |
GB9916868D0 (en) | 1999-09-22 |
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