US20010050383A1 - Semiconductor device - Google Patents
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- US20010050383A1 US20010050383A1 US09/835,379 US83537901A US2001050383A1 US 20010050383 A1 US20010050383 A1 US 20010050383A1 US 83537901 A US83537901 A US 83537901A US 2001050383 A1 US2001050383 A1 US 2001050383A1
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- 239000004065 semiconductor Substances 0.000 title claims description 125
- 239000012535 impurity Substances 0.000 claims abstract description 10
- 239000000758 substrate Substances 0.000 claims description 29
- 244000126211 Hericium coralloides Species 0.000 claims description 5
- 230000003071 parasitic effect Effects 0.000 description 21
- 230000015556 catabolic process Effects 0.000 description 12
- 238000011084 recovery Methods 0.000 description 7
- 230000005684 electric field Effects 0.000 description 3
- 230000001939 inductive effect Effects 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 230000008901 benefit Effects 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
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- 230000008569 process Effects 0.000 description 1
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- 229910052710 silicon Inorganic materials 0.000 description 1
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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
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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
- H01L29/02—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
- H01L29/0684—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 characterised by the shape, relative sizes or dispositions of the semiconductor regions or junctions between the regions
- H01L29/0692—Surface layout
- H01L29/0696—Surface layout of cellular field-effect devices, e.g. multicellular 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
- H01L29/02—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
- H01L29/0873—Drain regions
- H01L29/0878—Impurity concentration or distribution
Definitions
- the present invention relates to an insulated gate semiconductor device represented by a MOSFET, an IGBT and the like, and more particularly to an improvement of a reverse bias characteristic thereof.
- FIG. 8 is a plan view showing a typical MOSFET.
- the MOSFET is a so-called vertical type MOSFET in which a gate wire bonding pad 2 and a source wire bonding pad 3 are provided on an upper main surface of a semiconductor substrate 1 .
- a large number of unit cells are arranged along a main surface of the semiconductor substrate 1 .
- Each of the unit cells functions as a single MOSFET.
- a region 40 where the unit cells are to be arranged is referred to as a cell region and a partial region B represents the cell region 40 .
- a gate wiring region 4 is formed around the cell region 40 and a partial region A represents a boundary portion between the cell region 40 and the gate wiring region 4 .
- FIG. 9 is an enlarged plan view showing patterns of various semiconductor layers exposed to the upper main surface of the semiconductor substrate 1 in the region A of FIG. 8. Moreover, FIG. 10 is a sectional view taken along a cutting line E-E in FIG. 9.
- the semiconductor substrate 1 comprises an N + layer 11 exposed to a lower main surface, an N ⁇ layer 10 formed on the N + layer 11 , an N layer 17 having a low resistance which is formed on the N layer 10 and is exposed to the upper main surface, P base layers 6 , 7 and 8 selectively formed in the upper main surface, a P + base layer 20 having a low resistance which is protruded downward in central parts of bottom portions of the P base layers 6 and 7 , and an N source layer 5 selectively formed in the upper main surface more shallowly than the P base layer 6 on the inside thereof.
- the N layer 17 is formed more shallowly than the P base layers 6 , 7 and 8 .
- the P base layers 6 and 7 have polygonal (square in the example of FIG. 9) planar shapes and are isolated from each other and arranged in a matrix. Moreover, the P base layers 6 and 7 are also isolated from the P base region 8 formed under the gate wiring region 4 .
- the N source layer 5 formed in the P base layer 6 has an annular planar shape and forms the same polygon (square in the example of FIG. 9) as the P base layer 6 .
- An annular portion of the P base layer 6 positioned on the outside of the annular N source layer 5 functions as a channel region.
- the N source layer 5 is not formed in the P base layers 7 and 8 . Accordingly, the P base layers 7 and 8 do not have the channel region.
- the P base layer 7 is selectively formed in the vicinity of the P base layer 8 .
- An insulating layer 15 is formed on the upper main surface of the semiconductor substrate 1 , and a source electrode 16 is formed on the insulating layer 15 .
- the source electrode 16 is covered with another insulating layer 30 .
- the P base layers 6 and 7 are connected to the source electrode 16 through an opening 9 selectively formed on the insulating layer 15 .
- the source electrode 16 is also connected to the P base region 8 through an opening 31 selectively formed on the insulating layer 15 . More specifically, the P base layers 6 , 7 and 8 isolated from each other in the semiconductor substrate 1 are connected to each other through only the source electrode 16 .
- a gate electrode 14 is buried in the insulating layer 15 and is opposed to the upper main surface of the semiconductor substrate 1 with a gate insulating film 13 , which is a part of the insulating layer 15 , interposed therebetween.
- the gate electrode 14 is opposed to the channel region of the P base layer 6 and is also opposed to an exposed surface of the N layer 17 (the exposed surface also implies a portion exposed to the upper main surface of the semiconductor substrate 1 ).
- the gate electrode 14 is opposed to a part of an exposed surface of the P base layer 7 and the almost whole region of an exposed surface of the P base region 8 .
- a portion in the gate electrode 14 which is opposed to the almost whole region of the exposed surface of the P base region 8 functions as a gate wiring.
- a drain electrode 12 is connected to the lower main surface of the semiconductor substrate 1 . As shown in FIG. 10, the N + layer 11 is exposed to the lower main surface in the MOSFET. Therefore, the drain electrode 12 is directly connected to the N + layer 11 .
- the MOSFET having the above-mentioned structure, when a gate voltage which is equal to or higher than a threshold voltage is applied to the gate electrode 14 in a state in which a positive voltage is applied to the drain electrode 12 based on the source electrode 16 , an inversion layer is formed in the exposed surface of the P base region 6 positioned under the gate electrode 14 , that is, the channel region and a current flows through the inversion layer. In other words, the MOSFET is turned ON.
- the MOSFET is brought into an OFF state. At this time, a drain voltage is held by a depletion layer extended from a PN junction between each of the P base layers 6 , 7 and 8 and the N ⁇ layer 10 in a reverse bias state toward the inside of the N ⁇ layer 10 .
- a switching loss generated by a switching operation of the MOSFET greatly depends on a feedback capacitance, which is a parasitic capacitance of the MOSFET.
- the feedback capacitance is generated between the gate electrode 14 and the N layer 17 opposed thereto and greatly depends on an area of the exposed surface of the N layer 17 .
- the P base layer 6 belonging to each cell is arranged in a matrix. As a result, there has been a problem in that an occupation ratio of the exposed surface of the N layer 17 is higher than that of the exposed surface of the P base layer 6 in the upper main surface of the semiconductor substrate 1 and the feedback capacitance is large.
- the P base layers 6 and 7 of the conventional MOSFET have polygonal planar shapes. Therefore, a distance between the P base layers 6 and 7 adjacent to each other in a direction of the matrix (in a vertical or transverse direction of FIG. 9) is different from a distance between the P base layers 6 and 7 adjacent to each other in an oblique direction. Furthermore, a comer portion is formed in the planar shapes of the P base layers 6 and 7 in a direction in which they are obliquely adjacent to other P base layers 6 and 7 . The comer portion has a large curvature.
- the depletion layer is extended nonuniformly from the PN junction between each of the P base regions 6 , 7 and 8 and the N ⁇ layer 10 toward the inside of the N ⁇ layer 10 and a critical field strength is reached at a comparatively low source-drain voltage in the comer portion so that an avalanche breakdown is caused.
- the P + base layer 20 is formed in the P base regions 6 and 7 and is protruded downward in the central parts of the bottom portions.
- the P + base layer 20 has a larger depth and a larger curvature than the P base layers 6 and 7 . Since the P + base layer 20 is deeper than the P base layers 6 and 7 , when the source-drain voltage is changed into the reverse bias, an effective distance of the depletion layer capable of being extended from the PN junction between the P + base layer 20 and the N ⁇ layer 10 toward the inside of the N ⁇ layer 10 is shortened in the N ⁇ layer 10 . Furthermore, since the P + base layer 20 has a large curvature, there has been a problem in that a portion where the critical field strength is reached at a comparatively low source-drain voltage is generated, resulting in an avalanche breakdown.
- the N layer 17 having a low resistance is formed under the gate electrode 14 more shallowly than the P base layer 6 .
- the N layer 17 having a low resistance functions to reduce a junction resistance in the PN junction between the P base layer 6 and the N ⁇ layer 10 .
- the N layer 17 is shallower than the P base layer 6 , there has been a problem in that the junction resistance is not sufficiently reduced.
- the P base layers 6 , 7 and 8 are isolated from each other in the semiconductor substrate I and are connected to each other through only the source electrode 16 .
- the PN junction between each of the P base layers 6 , 7 and 8 and the N ⁇ layer 10 corresponds to the diode provided in the MOSFET. Holes generated with the conduction of the internal diode depends on areas of the exposed surfaces of the P base layers 6 , 7 and 8 and a concentration of a P-type impurity contained therein. Therefore, the largest number of holes are generated in the vicinity of the P base layer 8 .
- the holes remaining in the vicinity of the P base layer 8 intensively flows into the P base layer 6 positioned in the vicinity of the P base layer 8 , and furthermore, passes through a contact portion 18 between the P base layer 6 and the source electrode 16 toward the source electrode 16 .
- a parasitic bipolar transistor formed by the N ⁇ layer 10 , the P base layer 6 and the N source region 5 is problematically conducted.
- the P base layer 7 in which the N source region 5 is not formed is provided in the vicinity of the P base layer 8 such that the parasitic bipolar transistor is not formed in the vicinity of the P base layer 8 .
- the holes remaining in the vicinity of the P base layer 8 intensively flows into not only the closest P base layer 7 but also the P base layer 6 provided in the vicinity thereof. Consequently, the holes pass through the contact portion 18 toward the source electrode 16 .
- the parasitic bipolar transistor is conducted in the P base layer 6 positioned in the vicinity of the P base layer 7 .
- a first aspect of the present invention is directed to a semiconductor device comprising a semiconductor substrate having an upper main surface and a lower main surface, the semiconductor substrate including a first semiconductor layer of a first conductivity type, a second semiconductor layer of the first conductivity type which is formed on the first semiconductor layer to be exposed to the upper main surface and has a higher impurity concentration than the first semiconductor layer, a third semiconductor layer of a second conductivity type which is selectively formed in the upper main surface more shallowly than the second semiconductor layer, is divided into and provided as a plurality of band-shaped portions parallel with each other, and is not provided with a downward protrusion having a higher impurity concentration in a bottom portion than a periphery, a fourth semiconductor layer of the first conductivity type which is selectively formed in the upper main surface and is divided into and provided as a plurality of ladder-shaped portions parallel with each other, each of the ladder-shaped portions being formed to be extended more shallowly in and along any of at least a part of the band-shaped portions individually corresponding there
- a second aspect of the present invention is directed to the semiconductor device according to the first aspect of the present invention, wherein the first main electrode is connected to each of the ladder-shaped portions through only the crosspiece portion thereof.
- a third aspect of the present invention is directed to the semiconductor device according to the first or second aspect of the present invention, wherein the fifth semiconductor layer is formed to surround a region where the band-shaped portions are arranged, and couples the band-shaped portions to each other on ends in a direction of extension of the band-shaped portions.
- a fourth aspect of the present invention is directed to the semiconductor device according to any of the first to third aspects of the present invention, wherein at least one of the band-shaped portions does not include any of the ladder-shaped portions on ends in a direction of arrangement thereof.
- a fifth aspect of the present invention is directed to the semiconductor device according to the fourth aspect of the present invention, further comprising a sixth semiconductor layer of the first conductivity type which is selectively formed like a comb tooth in the upper main surface and is extended more shallowly within and along one of the at least one band-shaped portion provided most apart from the end in the direction of arrangement of the at least one band-shaped portion such that the comb tooth faces to the end side, the insulating film being also formed on an end region which is a region interposed between the sixth semiconductor layer and one of the ladder-shaped portions adjacent thereto in the upper main surface, the gate electrode being also formed on a portion of the insulating film provided on the end region and being thereby opposed to the end region, and the first main electrode being also connected to the sixth semiconductor layer through at least the tooth.
- a sixth aspect of the present invention is directed to the semiconductor device according to the fifth aspect of the present invention, wherein the first main electrode is connected to the sixth semiconductor layer through only the tooth.
- a seventh aspect of the present invention is directed to the semiconductor device according to any of the first to sixth aspects of the present invention, wherein the second semiconductor layer is selectively formed shallowly directly under the third semiconductor layer.
- An eighth aspect of the present invention is directed to the semiconductor device according to any of the first to seventh aspects of the present invention, wherein a first boundary portion provided along an outside of each of the ladder-shaped portions is shorter than a second boundary portion provided along an inside in a boundary exposed to the upper main surface between the third and fourth semiconductor layers.
- a ninth aspect of the present invention is directed to the semiconductor device according to any of the first to eighth aspects of the present invention, wherein a beam width of each of the ladder-shaped portions is equal to or smaller than ⁇ fraction (1/10) ⁇ of a beam spacing.
- a tenth aspect of the present invention is directed to the semiconductor device according to any of the first to ninth aspects of the present invention, wherein an area of a surface of the second semiconductor layer which is exposed to the upper main surface is four times as large as an area of a surface of the third semiconductor layer which is exposed to the upper main surface or less.
- the third semiconductor layer is provided as a plurality of band-shaped portions parallel with each other, and furthermore, the downward protrusion having a high impurity concentration is not formed in a bottom portion of the third semiconductor layer. Therefore, there is no portion where a critical field strength is reached under a low reverse bias. Consequently, it is possible to avoid concentration of an avalanche current on a specific portion when the device is turned off under an inductive load.
- the third semiconductor layer is shallower than the second semiconductor layer. Therefore, a junction resistance in a PN junction between the third semiconductor layer and a periphery thereof can be reduced sufficiently.
- the band-shaped portions forming the third semiconductor layer are coupled to each other through the fifth semiconductor layer. Therefore, it is possible to suppress such a phenomenon that remaining minority carriers concentrate on the specific portion of the third semiconductor layer in a recovery operation of a diode provided in the device. Consequently, a parasitic bipolar transistor can be prevented from being conducted.
- the fourth semiconductor layer is ladder-shaped and is connected to the first main electrode through only a crosspiece portion thereof. Therefore, even if the PN junction between the third semiconductor layer and the periphery thereof is brought into a reverse bias state so that an avalanche breakdown is caused and an avalanche current flows, the parasitic bipolar transistor is conducted with difficulty.
- the fifth semiconductor layer is formed to surround the region where the band-shaped portions are to be arranged, and couples the band-shaped portions to each other on the ends in the direction of extension of the band-shaped portions. Therefore, a comer portion having a large curvature is not provided in the band-shaped portion. Consequently, the concentration of the avalanche current is further suppressed. Thus, the parasitic bipolar transistor can be prevented more effectively from being conducted due to the avalanche current.
- At least one of the band-shaped portions does not include any of the ladder-shaped portions on the ends in the direction of arrangement thereof. Therefore, the parasitic bipolar transistor can be prevented more effectively from being conducted during a recovery operation.
- the band-shaped portion including the sixth semiconductor layer corresponding to only a part of the ladder-shaped portion is provided in a position which is the most distant from the end in the at least one band-shaped portion having no ladder-shaped portion. Therefore, the parasitic bipolar transistor can be prevented more effectively from being conducted during the recovery operation.
- the first main electrode is connected to the comb tooth-shaped sixth semiconductor layer through only the tooth. Therefore, even if the PN junction between the third semiconductor layer and the periphery thereof is brought into a reverse bias state so that an avalanche breakdown is caused and an avalanche current flows, the parasitic bipolar transistor is conducted with difficulty.
- the second semiconductor layer is selectively formed shallowly directly under the third semiconductor layer. Therefore, even if the PN junction between the third semiconductor layer and the periphery thereof is brought into a reverse bias state, the concentration of an electric field can be prevented directly under the third semiconductor layer so that a reduction in a breakdown voltage can be suppressed.
- the first boundary portion is set to be shorter than the second boundary portion. Therefore, even if the PN junction between the third semiconductor layer and the periphery thereof is brought into a reverse bias state so that an avalanche breakdown is caused and an avalanche current flows, the parasitic bipolar transistor can be prevented more effectively from being conducted.
- the beam width of each of the ladder-shaped portions is set to be ⁇ fraction (1/10) ⁇ of the beam spacing or less. Therefore, the parasitic bipolar transistor can be prevented more effectively from being conducted.
- the area of the exposed surface of the second semiconductor layer is set to be four times as large as the area of the exposed surface of the third semiconductor layer or less. Therefore, a feedback capacitance can be reduced. As a result, it is possible to reduce a switching loss caused by a switching operation of the device.
- FIG. 1 is a partially enlarged plan view showing a region A of FIG. 8 according to an embodiment
- FIG. 2 is a partially enlarged plan view showing the region A of FIG. 8 in another example of a device according to the embodiment
- FIG. 3 is a partially enlarged plan view showing a region B of FIG. 8 according to the embodiment
- FIG. 4 is a sectional view taken along a line C-C in FIG. 3,
- FIG. 5 is a sectional view taken along a line D-D in FIG. 3,
- FIG. 6 is a sectional view showing a further example of the device according to the embodiment.
- FIG. 7 is a graph showing proven data of the device according to the embodiment.
- FIG. 8 is a plan view which is common to the device according to the embodiment and a conventional device
- FIG. 9 is a partially enlarged plan view showing the region A of FIG. 8 in the conventional device.
- FIG. 10 is a sectional view taken along a line E-E in FIG. 9.
- FIG. 1 is an enlarged plan view showing patterns of various semiconductor layers exposed to an upper main surface of a semiconductor substrate 1 in a region A of FIG. 8.
- the same portions or corresponding portions have the same reference numerals as those in the conventional device shown in FIGS. 8 to 10 and their detailed description will be omitted.
- P base layers 6 and 7 are divided and provided as a plurality of band-shaped portions which are arranged in parallel with each other at regular intervals in the upper main surface of the semiconductor substrate 1 . Therefore, a distance between the respective band-shaped portions is uniform.
- a depletion layer is uniformly extended from a PN junction between each of P base layers 6 , 7 and 8 and an N ⁇ layer 10 toward the inside of the N ⁇ layer 10 and there is no portion where a critical field strength is reached at a comparatively low source-drain voltage.
- the MOSFET according to the embodiment carries out a switching operation under an inductive load and counter electromotive force is generated during turn-off so that an avalanche breakdown is caused and an avalanche current flows, the avalanche current does not intensively flow to a specific portion because there is no portion where the critical field strength is reached at a comparatively low reverse bias.
- FIG. 2 In place of a pattern shown in FIG. 1, a pattern shown in FIG. 2 may be employed.
- the P base layer 7 in which an N source layer 5 is not formed is selectively provided in the vicinity of the P base layer 8 . Consequently, a parasitic bipolar transistor can be prevented from being conducted during a recovery operation.
- FIGS. 1 and 2 are different from each other in that one band-shaped portion adjacent to the P base layer 8 is formed as the P base layer 7 in FIG. 1 and a portion corresponding to 1.5 band-shaped portions adjacent to the P base layer 8 is formed as the P base layer 7 in FIG. 2.
- FIG. 1 one band-shaped portion adjacent to the P base layer 8 is formed as the P base layer 7 in FIG. 1 and a portion corresponding to 1.5 band-shaped portions adjacent to the P base layer 8 is formed as the P base layer 7 in FIG. 2.
- the N source layer 5 is formed like a comb tooth corresponding to half of a ladder-shaped portion in the P base layer 7 adjacent to the P base layer 6 . While an ON-state resistance is advantageously low in the pattern of FIG. 1 because of less P base layer 7 , a di/dt tolerance is high and an avalanche tolerance is advantageously high in the pattern of FIG. 2 because the parasitic bipolar transistor can be prevented more effectively from being conducted.
- FIG. 3 is an enlarged plan view showing patterns of various semiconductor layers exposed to the upper main surface of the semiconductor substrate 1 in a region B of FIG. 8 for the MOSFET according to the embodiment.
- FIG. 4 is a sectional view taken along a cutting line C-C in FIG. 3 and
- FIG. 5 is a sectional view taken along a cutting line D-D in FIG. 3.
- a P + base layer 20 having a high impurity concentration is not formed as a protrusion provided downward in a central part of a bottom portion of the P base layer 6 in the MOSFET according to the embodiment.
- the P base layer 6 is divided and provided as a plurality of band-shaped portions. Therefore, convergence of an electric field can be eliminated. Consequently, even if the P + base layer 20 is removed, the conduction of the parasitic bipolar transistor can be suppressed.
- an N layer 17 having a low resistance which is positioned under a gate electrode 14 is formed more deeply than the P base layer 6 in the MOSFET according to the embodiment. Therefore, a junction resistance in the PNjunction between the P base layer 6 and the N ⁇ layer 10 can be reduced sufficiently.
- the base layers 6 and 7 are formed as the band-shaped portions isolated from each other in the MOSFET according to the embodiment.
- the P base layers 6 and 7 are coupled to each other through the P base region 8 on at least ends in a longitudinal direction thereof.
- the PN junction between each of the P base layers 6 , 7 and 8 and the N ⁇ layer 10 or N layer 17 corresponds to a diode provided in the MOSFET. Holes generated with the conduction of the internal diode depend on an area of each of the P base layers 6 , 7 and 8 and a concentration of a P-type impurity contained therein. Therefore, the largest number of holes are generated in the vicinity of the P base layer 8 .
- the generated holes do not intensively flow into the specific isolated P base layer 6 because the isolated P base layer 6 is not provided in the vicinity of the P base layer 8 . Accordingly, it is possible to prevent such a phenomenon that a parasitic bipolar transistor formed by the N ⁇ layer 10 or N layer 17 , the P base layer 6 and the N source layer 5 is conducted.
- the N source layer 5 selectively formed in the upper main surface of the semiconductor substrate 1 is provided with one to one correspondence within the P base layer 6 and is divided and arranged as a plurality of ladder-shaped portions having ladder-like planar shapes in parallel with each other in the MOSFET according to the embodiment.
- a portion adjacent to the outside of the ladder-shaped portion formed in the exposed surface of each band-shaped portion of the P base layer 6 corresponds to a channel region.
- the gate electrode 14 is opposed to a region interposed between the ladder-shaped portions adjacent to each other in the upper main surface of the semiconductor substrate 1 with a gate insulating film 13 provided therebetween.
- An opening 9 formed on an insulating layer 15 is band-shaped extending along a longitudinal direction of each ladder-shaped portion, and furthermore, is provided apart from the channel region. Accordingly, the N source layer 5 is connected to a source electrode 16 through only a contact portion 19 positioned in an exposed surface of a crosspiece portion (which is also referred to as a beam, rung or step portion) of the ladder-shaped portion. Moreover, the P base layer 6 is connected to the source electrode 16 through only a contact portion 18 positioned in a rectangular exposed surface surrounded by strut (i.e., side rail) portions and the crosspiece portions in each ladder-shaped portion.
- strut i.e., side rail
- a width 5 a of the N source layer 5 (FIG. 4) can be set smaller than a width 5 a in the conventional MOSFET (FIG. 10). Consequently, a resistance is reduced in the P base layer 6 portion provided under the N source layer 5 . Therefore, even if the PN junction between the P base layer 6 and the N layer 17 or N ⁇ layer 10 is brought into a reverse bias state so that an avalanche breakdown is caused and an avalanche current flows, the parasitic bipolar transistor is conducted with more difficulty than the conventional MOSFET.
- a boundary exposed to the upper main surface of the semiconductor substrate 1 between the source layer 5 and the P base layer 6 includes a first boundary portion I and a second boundary portion II.
- the first boundary portion is a portion provided along the outside of each ladder-shaped portion, i.e., a portion forming a boundary with the channel region.
- the second boundary portion II is a portion provided along the inside of each ladder-shaped portion, i.e., a portion forming a boundary with the rectangular exposed surface portion of the P base layer 6 surrounded by the strut portions and the crosspiece portions in each ladder-shaped portion. Lengths of the first and second boundary portions I and II can be compared with each other by using a representative length determined as a length within a pattern repetition unit as shown in FIG. 3.
- the second boundary portion II is set to be longer than the first boundary portion I. Consequently, the width 5 a of the N source layer 5 is reduced.
- a length (i.e., a width of the crosspiece portion ; a beam width) 5 b of the N source layer 5 is limited to be much smaller than a length (i.e., a spacing between the adjacent crosspiece portions ; a beam spacing) 7 a of the exposed surface of the P base layer 6 in a direction of extension of the opening 9 .
- the parasitic bipolar transistor formed by the N ⁇ layer 10 or N layer 17 , the P base layer 6 and the N source layer 5 is conducted with difficulty.
- the beam width 5 b is set to be equal to or smaller than one-tenth of the beam spacing 7 a. Consequently, the parasitic bipolar transistor is conducted with more difficulty.
- the N layer 17 is selectively formed shallowly directly under the P base layer 6 as shown in FIG. 6 illustrating another example of the sectional view taken along the cutting line C-C in FIG. 3.
- a region provided under the P base layer 6 is not a current path.
- the concentration of an electric field is suppressed under the P base layer 6 so that a breakdown voltage can be prevented from being reduced.
- FIG. 7 shows proven data based on the foregoing.
- an axis of abscissa represents a function (WG ⁇ 4 ⁇ m)/(WG+WCD) expressed by a gate width WG and a gate spacing WCD in FIG. 4
- an axis of ordinate represents a feedback capacitance Crss with a source-drain voltage of 25 V and an operating frequency of 1 MHz.
- Data on the conventional MOSFET (the planar shape of the P base layer 6 is not a square but a circle and has no substantial difference) are represented by a white circle and data on the MOSFET according to the embodiment are represented by a black circle.
- the feedback capacitance of the MOSFET according to the embodiment is coincident with that of the conventional MOSFET.
- the gate spacing WCD is 4 ⁇ m and the gate width WG is 16 ⁇ m, that is, a ratio of the areas is four times larger, the feedback capacitances Crss between the two MOSFETs are coincident with each other. Furthermore, if the ratio of the areas is four times or less, the feedback capacitance Crss of the MOSFET according to the embodiment is smaller than that of the conventional MOSFET.
- the present invention can also be executed for a P-channel MOSFET having a conductivity type inverted.
- the present invention can also be applied to an N-channel IGBT in which a P-type semiconductor layer is provided between the N + layer 11 and a lower main surface of the semiconductor substrate 1 as well as the N-channel MOSFET in which the N + layer 11 is exposed to the lower main surface of the semiconductor substrate 1 .
- the present invention can also be applied to a P-channel IGBT having a conductivity type obtained by inverting the conductivity type of the N-channel IGBT.
- the present invention can be applied to a general vertical type insulated gate semiconductor device having a MOS structure on the upper main surface of the semiconductor substrate 1 as well as the MOSFET and the IGBT.
- the N source layer 5 is provided in all the P base layers 6
- the present invention can also be executed for a semiconductor substrate using other semiconductor materials.
Abstract
Description
- 1. Field of the Invention
- The present invention relates to an insulated gate semiconductor device represented by a MOSFET, an IGBT and the like, and more particularly to an improvement of a reverse bias characteristic thereof.
- 2. Description of the Background Art
- In recent years, attention has been given to a MOSFET or an IGBT as a switching element to be used for inverter control or the like. FIG. 8 is a plan view showing a typical MOSFET. The MOSFET is a so-called vertical type MOSFET in which a gate
wire bonding pad 2 and a sourcewire bonding pad 3 are provided on an upper main surface of asemiconductor substrate 1. A large number of unit cells are arranged along a main surface of thesemiconductor substrate 1. Each of the unit cells functions as a single MOSFET. Aregion 40 where the unit cells are to be arranged is referred to as a cell region and a partial region B represents thecell region 40. Moreover, agate wiring region 4 is formed around thecell region 40 and a partial region A represents a boundary portion between thecell region 40 and thegate wiring region 4. - FIG. 9 is an enlarged plan view showing patterns of various semiconductor layers exposed to the upper main surface of the
semiconductor substrate 1 in the region A of FIG. 8. Moreover, FIG. 10 is a sectional view taken along a cutting line E-E in FIG. 9. Thesemiconductor substrate 1 comprises an N+ layer 11 exposed to a lower main surface, an N− layer 10 formed on the N+ layer 11, anN layer 17 having a low resistance which is formed on theN layer 10 and is exposed to the upper main surface,P base layers P base layers N source layer 5 selectively formed in the upper main surface more shallowly than theP base layer 6 on the inside thereof. TheN layer 17 is formed more shallowly than theP base layers - The
P base layers P base layers P base region 8 formed under thegate wiring region 4. - The
N source layer 5 formed in theP base layer 6 has an annular planar shape and forms the same polygon (square in the example of FIG. 9) as theP base layer 6. An annular portion of theP base layer 6 positioned on the outside of the annularN source layer 5 functions as a channel region. On the other hand, theN source layer 5 is not formed in theP base layers P base layers P base layer 7 is selectively formed in the vicinity of theP base layer 8. - An
insulating layer 15 is formed on the upper main surface of thesemiconductor substrate 1, and asource electrode 16 is formed on the insulatinglayer 15. Thesource electrode 16 is covered with anotherinsulating layer 30. TheP base layers source electrode 16 through anopening 9 selectively formed on the insulatinglayer 15. Thesource electrode 16 is also connected to theP base region 8 through anopening 31 selectively formed on theinsulating layer 15. More specifically, theP base layers semiconductor substrate 1 are connected to each other through only thesource electrode 16. - A
gate electrode 14 is buried in theinsulating layer 15 and is opposed to the upper main surface of thesemiconductor substrate 1 with agate insulating film 13, which is a part of theinsulating layer 15, interposed therebetween. Thegate electrode 14 is opposed to the channel region of theP base layer 6 and is also opposed to an exposed surface of the N layer 17 (the exposed surface also implies a portion exposed to the upper main surface of the semiconductor substrate 1). Furthermore, thegate electrode 14 is opposed to a part of an exposed surface of theP base layer 7 and the almost whole region of an exposed surface of theP base region 8. A portion in thegate electrode 14 which is opposed to the almost whole region of the exposed surface of theP base region 8 functions as a gate wiring. - A
drain electrode 12 is connected to the lower main surface of thesemiconductor substrate 1. As shown in FIG. 10, the N+ layer 11 is exposed to the lower main surface in the MOSFET. Therefore, thedrain electrode 12 is directly connected to the N+ layer 11. - In the MOSFET having the above-mentioned structure, when a gate voltage which is equal to or higher than a threshold voltage is applied to the
gate electrode 14 in a state in which a positive voltage is applied to thedrain electrode 12 based on thesource electrode 16, an inversion layer is formed in the exposed surface of theP base region 6 positioned under thegate electrode 14, that is, the channel region and a current flows through the inversion layer. In other words, the MOSFET is turned ON. - If the gate voltage to be applied to the
gate electrode 14 is less than a threshold, the inversion layer is annihilated. Therefore, the MOSFET is brought into an OFF state. At this time, a drain voltage is held by a depletion layer extended from a PN junction between each of theP base layers - When a positive voltage is applied to the
source electrode 16 based on thedrain electrode 12 in a state in which thesource electrode 16 and thegate electrode 14 are short-circuited from each other, holes are injected from each of theP base regions source electrode 16 into the N− layer 10 and an electrons are injected from the N+ layer 11 joined with thedrain region 12 to the N− layer 10. Since the PN junction between each of theP base regions source electrode 16 to thedrain electrode 12. - When a negative voltage is applied to the
source electrode 16 based on thedrain electrode 12 in this state, that is, a source-drain voltage is inverted into a reverse bias, the holes remaining in the N− layer 10 moves to thesource electrode 16 and the electrons remaining in the N− layer 10 moves to thedrain electrode 12. As a result, a current flows from thedrain electrode 12 to thesource electrode 16. A mobility of the hole is half of that of the electron. Therefore, a time required for attenuating the current to zero is equal to a time required for annihilating the holes remaining in the N− layer 10. An operation of the MOSFET which is carried out under the reverse voltage is exactly equivalent to a recovery operation of a diode provided in the MOSFET. - A switching loss generated by a switching operation of the MOSFET greatly depends on a feedback capacitance, which is a parasitic capacitance of the MOSFET. The feedback capacitance is generated between the
gate electrode 14 and theN layer 17 opposed thereto and greatly depends on an area of the exposed surface of theN layer 17. In the conventional MOSFET, theP base layer 6 belonging to each cell is arranged in a matrix. As a result, there has been a problem in that an occupation ratio of the exposed surface of theN layer 17 is higher than that of the exposed surface of theP base layer 6 in the upper main surface of thesemiconductor substrate 1 and the feedback capacitance is large. - Moreover, the
P base layers P base layers P base layers P base layers P base layers P base regions - Furthermore, when the conventional MOSFET carries out a switching operation under an inductive load, counter electromotive force is generated during turn-off so that the avalanche breakdown is caused and an avalanche current flows in some cases. The avalanche current converges on the comer portions of the
P base layers P base layer 6 and theN source layer 5 is turned ON with a comparatively low avalanche current. - In the conventional MOSFET, moreover, the P+ base layer 20 is formed in the
P base regions P base layers P base layers - In the conventional MOSFET, furthermore, the
N layer 17 having a low resistance is formed under thegate electrode 14 more shallowly than theP base layer 6. When the MOSFET is turned ON, theN layer 17 having a low resistance functions to reduce a junction resistance in the PN junction between theP base layer 6 and the N− layer 10. However, since theN layer 17 is shallower than theP base layer 6, there has been a problem in that the junction resistance is not sufficiently reduced. - In the conventional MOSFET, moreover, the P base layers6, 7 and 8 are isolated from each other in the semiconductor substrate I and are connected to each other through only the
source electrode 16. As described above, the PN junction between each of the P base layers 6, 7 and 8 and the N− layer 10 corresponds to the diode provided in the MOSFET. Holes generated with the conduction of the internal diode depends on areas of the exposed surfaces of the P base layers 6, 7 and 8 and a concentration of a P-type impurity contained therein. Therefore, the largest number of holes are generated in the vicinity of theP base layer 8. In the case in which the internal diode is caused to carry out a recovery operation at comparatively high di/dt (i.e., a rate of current change), the holes remaining in the vicinity of theP base layer 8 intensively flows into theP base layer 6 positioned in the vicinity of theP base layer 8, and furthermore, passes through acontact portion 18 between theP base layer 6 and thesource electrode 16 toward thesource electrode 16. During this process, a parasitic bipolar transistor formed by the N−layer 10, theP base layer 6 and theN source region 5 is problematically conducted. - As shown in FIG. 9, the
P base layer 7 in which theN source region 5 is not formed is provided in the vicinity of theP base layer 8 such that the parasitic bipolar transistor is not formed in the vicinity of theP base layer 8. However, when the di/dt is increased to a certain extent, the holes remaining in the vicinity of theP base layer 8 intensively flows into not only the closestP base layer 7 but also theP base layer 6 provided in the vicinity thereof. Consequently, the holes pass through thecontact portion 18 toward thesource electrode 16. As a result, there has been a problem in that the parasitic bipolar transistor is conducted in theP base layer 6 positioned in the vicinity of theP base layer 7. Furthermore, if a large number of P base layers 7 in which theN source layer 5 is not formed are provided to obtain a high di/dt tolerance, the number of cells to be turned ON when the MOSFET is turned ON is decreased; i.e., a channel width of the whole MOSFET is problematically reduced and therefore an ON-state resistance is increased. - In order to solve the above-mentioned problems in the conventional device, it is an object of the present invention to provide a semiconductor device capable of improving a characteristic under a reverse bias.
- A first aspect of the present invention is directed to a semiconductor device comprising a semiconductor substrate having an upper main surface and a lower main surface, the semiconductor substrate including a first semiconductor layer of a first conductivity type, a second semiconductor layer of the first conductivity type which is formed on the first semiconductor layer to be exposed to the upper main surface and has a higher impurity concentration than the first semiconductor layer, a third semiconductor layer of a second conductivity type which is selectively formed in the upper main surface more shallowly than the second semiconductor layer, is divided into and provided as a plurality of band-shaped portions parallel with each other, and is not provided with a downward protrusion having a higher impurity concentration in a bottom portion than a periphery, a fourth semiconductor layer of the first conductivity type which is selectively formed in the upper main surface and is divided into and provided as a plurality of ladder-shaped portions parallel with each other, each of the ladder-shaped portions being formed to be extended more shallowly in and along any of at least a part of the band-shaped portions individually corresponding thereto, and a fifth semiconductor layer of the second conductivity type which is selectively formed in the upper main surface and couples the band-shaped portions to each other, the semiconductor device further comprising an insulating film formed on a region interposed between adjacent sets of the ladder-shaped portions in the upper main surface, a gate electrode formed on the insulating film and opposed to the region, a first main electrode connected to each of the band-shaped portions and connected to each of the ladder-shaped portions through at least a crosspiece portion thereof, and a second main electrode connected to the lower main surface.
- A second aspect of the present invention is directed to the semiconductor device according to the first aspect of the present invention, wherein the first main electrode is connected to each of the ladder-shaped portions through only the crosspiece portion thereof.
- A third aspect of the present invention is directed to the semiconductor device according to the first or second aspect of the present invention, wherein the fifth semiconductor layer is formed to surround a region where the band-shaped portions are arranged, and couples the band-shaped portions to each other on ends in a direction of extension of the band-shaped portions.
- A fourth aspect of the present invention is directed to the semiconductor device according to any of the first to third aspects of the present invention, wherein at least one of the band-shaped portions does not include any of the ladder-shaped portions on ends in a direction of arrangement thereof.
- A fifth aspect of the present invention is directed to the semiconductor device according to the fourth aspect of the present invention, further comprising a sixth semiconductor layer of the first conductivity type which is selectively formed like a comb tooth in the upper main surface and is extended more shallowly within and along one of the at least one band-shaped portion provided most apart from the end in the direction of arrangement of the at least one band-shaped portion such that the comb tooth faces to the end side, the insulating film being also formed on an end region which is a region interposed between the sixth semiconductor layer and one of the ladder-shaped portions adjacent thereto in the upper main surface, the gate electrode being also formed on a portion of the insulating film provided on the end region and being thereby opposed to the end region, and the first main electrode being also connected to the sixth semiconductor layer through at least the tooth.
- A sixth aspect of the present invention is directed to the semiconductor device according to the fifth aspect of the present invention, wherein the first main electrode is connected to the sixth semiconductor layer through only the tooth.
- A seventh aspect of the present invention is directed to the semiconductor device according to any of the first to sixth aspects of the present invention, wherein the second semiconductor layer is selectively formed shallowly directly under the third semiconductor layer.
- An eighth aspect of the present invention is directed to the semiconductor device according to any of the first to seventh aspects of the present invention, wherein a first boundary portion provided along an outside of each of the ladder-shaped portions is shorter than a second boundary portion provided along an inside in a boundary exposed to the upper main surface between the third and fourth semiconductor layers.
- A ninth aspect of the present invention is directed to the semiconductor device according to any of the first to eighth aspects of the present invention, wherein a beam width of each of the ladder-shaped portions is equal to or smaller than {fraction (1/10)} of a beam spacing.
- A tenth aspect of the present invention is directed to the semiconductor device according to any of the first to ninth aspects of the present invention, wherein an area of a surface of the second semiconductor layer which is exposed to the upper main surface is four times as large as an area of a surface of the third semiconductor layer which is exposed to the upper main surface or less.
- According to the first aspect of the present invention, the third semiconductor layer is provided as a plurality of band-shaped portions parallel with each other, and furthermore, the downward protrusion having a high impurity concentration is not formed in a bottom portion of the third semiconductor layer. Therefore, there is no portion where a critical field strength is reached under a low reverse bias. Consequently, it is possible to avoid concentration of an avalanche current on a specific portion when the device is turned off under an inductive load. Moreover, the third semiconductor layer is shallower than the second semiconductor layer. Therefore, a junction resistance in a PN junction between the third semiconductor layer and a periphery thereof can be reduced sufficiently. Furthermore, the band-shaped portions forming the third semiconductor layer are coupled to each other through the fifth semiconductor layer. Therefore, it is possible to suppress such a phenomenon that remaining minority carriers concentrate on the specific portion of the third semiconductor layer in a recovery operation of a diode provided in the device. Consequently, a parasitic bipolar transistor can be prevented from being conducted.
- According to the second aspect of the present invention, the fourth semiconductor layer is ladder-shaped and is connected to the first main electrode through only a crosspiece portion thereof. Therefore, even if the PN junction between the third semiconductor layer and the periphery thereof is brought into a reverse bias state so that an avalanche breakdown is caused and an avalanche current flows, the parasitic bipolar transistor is conducted with difficulty.
- According to the third aspect of the present invention, the fifth semiconductor layer is formed to surround the region where the band-shaped portions are to be arranged, and couples the band-shaped portions to each other on the ends in the direction of extension of the band-shaped portions. Therefore, a comer portion having a large curvature is not provided in the band-shaped portion. Consequently, the concentration of the avalanche current is further suppressed. Thus, the parasitic bipolar transistor can be prevented more effectively from being conducted due to the avalanche current.
- According to the fourth aspect of the present invention, at least one of the band-shaped portions does not include any of the ladder-shaped portions on the ends in the direction of arrangement thereof. Therefore, the parasitic bipolar transistor can be prevented more effectively from being conducted during a recovery operation.
- According to the fifth aspect of the present invention, the band-shaped portion including the sixth semiconductor layer corresponding to only a part of the ladder-shaped portion is provided in a position which is the most distant from the end in the at least one band-shaped portion having no ladder-shaped portion. Therefore, the parasitic bipolar transistor can be prevented more effectively from being conducted during the recovery operation.
- According to the sixth aspect of the present invention, the first main electrode is connected to the comb tooth-shaped sixth semiconductor layer through only the tooth. Therefore, even if the PN junction between the third semiconductor layer and the periphery thereof is brought into a reverse bias state so that an avalanche breakdown is caused and an avalanche current flows, the parasitic bipolar transistor is conducted with difficulty.
- According to the seventh aspect of the present invention, the second semiconductor layer is selectively formed shallowly directly under the third semiconductor layer. Therefore, even if the PN junction between the third semiconductor layer and the periphery thereof is brought into a reverse bias state, the concentration of an electric field can be prevented directly under the third semiconductor layer so that a reduction in a breakdown voltage can be suppressed.
- According to the eighth aspect of the present invention, the first boundary portion is set to be shorter than the second boundary portion. Therefore, even if the PN junction between the third semiconductor layer and the periphery thereof is brought into a reverse bias state so that an avalanche breakdown is caused and an avalanche current flows, the parasitic bipolar transistor can be prevented more effectively from being conducted.
- According to the ninth aspect of the present invention, the beam width of each of the ladder-shaped portions is set to be {fraction (1/10)} of the beam spacing or less. Therefore, the parasitic bipolar transistor can be prevented more effectively from being conducted.
- According to the tenth aspect of the present invention, the area of the exposed surface of the second semiconductor layer is set to be four times as large as the area of the exposed surface of the third semiconductor layer or less. Therefore, a feedback capacitance can be reduced. As a result, it is possible to reduce a switching loss caused by a switching operation of the device.
- These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
- FIG. 1 is a partially enlarged plan view showing a region A of FIG. 8 according to an embodiment,
- FIG. 2 is a partially enlarged plan view showing the region A of FIG. 8 in another example of a device according to the embodiment,
- FIG. 3 is a partially enlarged plan view showing a region B of FIG. 8 according to the embodiment,
- FIG. 4 is a sectional view taken along a line C-C in FIG. 3,
- FIG. 5 is a sectional view taken along a line D-D in FIG. 3,
- FIG. 6 is a sectional view showing a further example of the device according to the embodiment,
- FIG. 7 is a graph showing proven data of the device according to the embodiment,
- FIG. 8 is a plan view which is common to the device according to the embodiment and a conventional device,
- FIG. 9 is a partially enlarged plan view showing the region A of FIG. 8 in the conventional device, and
- FIG. 10 is a sectional view taken along a line E-E in FIG. 9.
- A semiconductor device according to an embodiment will be described below, considering a MOSFET as an example. A plan view showing the MOSFET is equivalent to FIG. 8. FIG. 1 is an enlarged plan view showing patterns of various semiconductor layers exposed to an upper main surface of a
semiconductor substrate 1 in a region A of FIG. 8. In order to avoid redundant description, the same portions or corresponding portions (having the same functions) have the same reference numerals as those in the conventional device shown in FIGS. 8 to 10 and their detailed description will be omitted. - P base layers6 and 7 are divided and provided as a plurality of band-shaped portions which are arranged in parallel with each other at regular intervals in the upper main surface of the
semiconductor substrate 1. Therefore, a distance between the respective band-shaped portions is uniform. As a result, in the case in which a source-drain voltage is changed into a reverse bias, a depletion layer is uniformly extended from a PN junction between each of P base layers 6, 7 and 8 and an N− layer 10 toward the inside of the N− layer 10 and there is no portion where a critical field strength is reached at a comparatively low source-drain voltage. Furthermore, even if the MOSFET according to the embodiment carries out a switching operation under an inductive load and counter electromotive force is generated during turn-off so that an avalanche breakdown is caused and an avalanche current flows, the avalanche current does not intensively flow to a specific portion because there is no portion where the critical field strength is reached at a comparatively low reverse bias. - In place of a pattern shown in FIG. 1, a pattern shown in FIG. 2 may be employed. In both of FIGS. 1 and 2, the
P base layer 7 in which anN source layer 5 is not formed is selectively provided in the vicinity of theP base layer 8. Consequently, a parasitic bipolar transistor can be prevented from being conducted during a recovery operation. FIGS. 1 and 2 are different from each other in that one band-shaped portion adjacent to theP base layer 8 is formed as theP base layer 7 in FIG. 1 and a portion corresponding to 1.5 band-shaped portions adjacent to theP base layer 8 is formed as theP base layer 7 in FIG. 2. In FIG. 2, theN source layer 5 is formed like a comb tooth corresponding to half of a ladder-shaped portion in theP base layer 7 adjacent to theP base layer 6. While an ON-state resistance is advantageously low in the pattern of FIG. 1 because of lessP base layer 7, a di/dt tolerance is high and an avalanche tolerance is advantageously high in the pattern of FIG. 2 because the parasitic bipolar transistor can be prevented more effectively from being conduced. - FIG. 3 is an enlarged plan view showing patterns of various semiconductor layers exposed to the upper main surface of the
semiconductor substrate 1 in a region B of FIG. 8 for the MOSFET according to the embodiment. FIG. 4 is a sectional view taken along a cutting line C-C in FIG. 3 and FIG. 5 is a sectional view taken along a cutting line D-D in FIG. 3. As shown in FIGS. 4 and 5, a P+ base layer 20 having a high impurity concentration is not formed as a protrusion provided downward in a central part of a bottom portion of theP base layer 6 in the MOSFET according to the embodiment. - Consequently, when the source-drain voltage is changed into a reverse bias, an effective distance of the depletion layer capable of being extended from the PN junction between the P− base layer 20 and the N− layer 10 toward the inside of the N− layer 10 is not shortened by the P+ base layer 20 in the N− layer 10, and furthermore, there is no portion where the critical field strength is reached at a comparatively low source-drain voltage. Therefore, there is an advantage that an avalanche breakdown is caused with difficulty. In the conventional MOSFET, moreover, the P+ base layer 20 is formed to serve to suppress the conduction of the parasitic bipolar transistor. In the MOSFET according to the embodiment, the
P base layer 6 is divided and provided as a plurality of band-shaped portions. Therefore, convergence of an electric field can be eliminated. Consequently, even if the P+ base layer 20 is removed, the conduction of the parasitic bipolar transistor can be suppressed. - As shown in FIGS. 4 and 5, moreover, an
N layer 17 having a low resistance which is positioned under agate electrode 14 is formed more deeply than theP base layer 6 in the MOSFET according to the embodiment. Therefore, a junction resistance in the PNjunction between theP base layer 6 and the N− layer 10 can be reduced sufficiently. - As shown in FIGS.1 to 3, the base layers 6 and 7 are formed as the band-shaped portions isolated from each other in the MOSFET according to the embodiment. The P base layers 6 and 7 are coupled to each other through the
P base region 8 on at least ends in a longitudinal direction thereof. The PN junction between each of the P base layers 6, 7 and 8 and the N− layer 10 orN layer 17 corresponds to a diode provided in the MOSFET. Holes generated with the conduction of the internal diode depend on an area of each of the P base layers 6, 7 and 8 and a concentration of a P-type impurity contained therein. Therefore, the largest number of holes are generated in the vicinity of theP base layer 8. Also in the case in which the internal diode carries out a recovery operation with comparatively high di/dt, the generated holes do not intensively flow into the specific isolatedP base layer 6 because the isolatedP base layer 6 is not provided in the vicinity of theP base layer 8. Accordingly, it is possible to prevent such a phenomenon that a parasitic bipolar transistor formed by the N− layer 10 orN layer 17, theP base layer 6 and theN source layer 5 is conducted. - As shown in FIGS.3 to 5, the
N source layer 5 selectively formed in the upper main surface of thesemiconductor substrate 1 is provided with one to one correspondence within theP base layer 6 and is divided and arranged as a plurality of ladder-shaped portions having ladder-like planar shapes in parallel with each other in the MOSFET according to the embodiment. A portion adjacent to the outside of the ladder-shaped portion formed in the exposed surface of each band-shaped portion of theP base layer 6 corresponds to a channel region. Thegate electrode 14 is opposed to a region interposed between the ladder-shaped portions adjacent to each other in the upper main surface of thesemiconductor substrate 1 with agate insulating film 13 provided therebetween. - An
opening 9 formed on an insulatinglayer 15 is band-shaped extending along a longitudinal direction of each ladder-shaped portion, and furthermore, is provided apart from the channel region. Accordingly, theN source layer 5 is connected to asource electrode 16 through only acontact portion 19 positioned in an exposed surface of a crosspiece portion (which is also referred to as a beam, rung or step portion) of the ladder-shaped portion. Moreover, theP base layer 6 is connected to thesource electrode 16 through only acontact portion 18 positioned in a rectangular exposed surface surrounded by strut (i.e., side rail) portions and the crosspiece portions in each ladder-shaped portion. - Therefore, a
width 5 a of the N source layer 5 (FIG. 4) can be set smaller than awidth 5 a in the conventional MOSFET (FIG. 10). Consequently, a resistance is reduced in theP base layer 6 portion provided under theN source layer 5. Therefore, even if the PN junction between theP base layer 6 and theN layer 17 or N− layer 10 is brought into a reverse bias state so that an avalanche breakdown is caused and an avalanche current flows, the parasitic bipolar transistor is conducted with more difficulty than the conventional MOSFET. - As shown in FIG. 3, in the MOSFET according to the embodiment, a boundary exposed to the upper main surface of the
semiconductor substrate 1 between thesource layer 5 and theP base layer 6 includes a first boundary portion I and a second boundary portion II. The first boundary portion is a portion provided along the outside of each ladder-shaped portion, i.e., a portion forming a boundary with the channel region. The second boundary portion II is a portion provided along the inside of each ladder-shaped portion, i.e., a portion forming a boundary with the rectangular exposed surface portion of theP base layer 6 surrounded by the strut portions and the crosspiece portions in each ladder-shaped portion. Lengths of the first and second boundary portions I and II can be compared with each other by using a representative length determined as a length within a pattern repetition unit as shown in FIG. 3. - In the MOSFET according to the embodiment, preferably, the second boundary portion II is set to be longer than the first boundary portion I. Consequently, the
width 5 a of theN source layer 5 is reduced. In addition, a length (i.e., a width of the crosspiece portion ; a beam width) 5 b of theN source layer 5 is limited to be much smaller than a length (i.e., a spacing between the adjacent crosspiece portions ; a beam spacing) 7 a of the exposed surface of theP base layer 6 in a direction of extension of theopening 9. As a result, even if the PN junction between theP base layer 6 and theN layer 17 or N− layer 10 is brought into a reverse bias state so that the avalanche breakdown is caused and the avalanche current flows, the parasitic bipolar transistor formed by the N− layer 10 orN layer 17, theP base layer 6 and theN source layer 5 is conducted with difficulty. - More preferably, the
beam width 5 b is set to be equal to or smaller than one-tenth of the beam spacing 7 a. Consequently, the parasitic bipolar transistor is conducted with more difficulty. - More preferably, the
N layer 17 is selectively formed shallowly directly under theP base layer 6 as shown in FIG. 6 illustrating another example of the sectional view taken along the cutting line C-C in FIG. 3. A region provided under theP base layer 6 is not a current path. Moreover, also in the case in which the PN junction between theP base layer 6 and the N− layer 10 orN layer 17 is brought into the reverse bias state, the concentration of an electric field is suppressed under theP base layer 6 so that a breakdown voltage can be prevented from being reduced. - More preferably, the area of the exposed surface of the
N layer 17 opposed to thegate electrode 14 is controlled to be four times as large as the area of the exposed surface of theP base layer 6 or less. Consequently, a feedback capacitance is reduced. As a result, a switching loss caused by a switching operation can be reduced. FIG. 7 shows proven data based on the foregoing. In a graph of FIG. 7, an axis of abscissa represents a function (WG −4 μm)/(WG+WCD) expressed by a gate width WG and a gate spacing WCD in FIG. 4 and an axis of ordinate represents a feedback capacitance Crss with a source-drain voltage of 25 V and an operating frequency of 1 MHz. Data on the conventional MOSFET (the planar shape of theP base layer 6 is not a square but a circle and has no substantial difference) are represented by a white circle and data on the MOSFET according to the embodiment are represented by a black circle. - As shown in FIG. 7, when a function value is 0.6, the feedback capacitance of the MOSFET according to the embodiment is coincident with that of the conventional MOSFET. This implies the following. When the gate spacing WCD is 4 μm and the gate width WG is 16 μm, that is, a ratio of the areas is four times larger, the feedback capacitances Crss between the two MOSFETs are coincident with each other. Furthermore, if the ratio of the areas is four times or less, the feedback capacitance Crss of the MOSFET according to the embodiment is smaller than that of the conventional MOSFET.
- While the example in which the semiconductor device is an N-channel MOSFET has been taken in the above description, the present invention can also be executed for a P-channel MOSFET having a conductivity type inverted. Furthermore, the present invention can also be applied to an N-channel IGBT in which a P-type semiconductor layer is provided between the N+ layer 11 and a lower main surface of the
semiconductor substrate 1 as well as the N-channel MOSFET in which the N+ layer 11 is exposed to the lower main surface of thesemiconductor substrate 1. Furthermore, the present invention can also be applied to a P-channel IGBT having a conductivity type obtained by inverting the conductivity type of the N-channel IGBT. Moreover, the present invention can be applied to a general vertical type insulated gate semiconductor device having a MOS structure on the upper main surface of thesemiconductor substrate 1 as well as the MOSFET and the IGBT. - Moreover, while the example in which the
N source layer 5 is provided in all the P base layers 6 has been described, it is also possible to generally execute the present invention in such a configuration that theN source layer 5 is not provided in a part of the P base layers 6 arranged on the inside as well as theP base layer 7 positioned on the end. - Furthermore, although a silicon substrate is typically used for the
semiconductor substrate 1, the present invention can also be executed for a semiconductor substrate using other semiconductor materials. - While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.
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JP5011612B2 (en) * | 2000-10-31 | 2012-08-29 | 富士電機株式会社 | Semiconductor device |
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JPS5553462A (en) | 1978-10-13 | 1980-04-18 | Int Rectifier Corp | Mosfet element |
US4680853A (en) | 1980-08-18 | 1987-07-21 | International Rectifier Corporation | Process for manufacture of high power MOSFET with laterally distributed high carrier density beneath the gate oxide |
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US4672407A (en) * | 1984-05-30 | 1987-06-09 | Kabushiki Kaisha Toshiba | Conductivity modulated MOSFET |
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US5321281A (en) * | 1992-03-18 | 1994-06-14 | Mitsubishi Denki Kabushiki Kaisha | Insulated gate semiconductor device and method of fabricating same |
US5489788A (en) * | 1993-03-09 | 1996-02-06 | Mitsubishi Denki Kabushiki Kaisha | Insulated gate semiconductor device with improved short-circuit tolerance |
EP0772242B1 (en) * | 1995-10-30 | 2006-04-05 | STMicroelectronics S.r.l. | Single feature size MOS technology power device |
JP3209091B2 (en) * | 1996-05-30 | 2001-09-17 | 富士電機株式会社 | Semiconductor device having insulated gate bipolar transistor |
GB9726829D0 (en) * | 1997-12-19 | 1998-02-18 | Philips Electronics Nv | Power semiconductor devices |
JP2000077663A (en) * | 1998-09-02 | 2000-03-14 | Mitsubishi Electric Corp | Field-effect semiconductor device |
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2001
- 2001-04-17 US US09/835,379 patent/US6388280B2/en not_active Expired - Lifetime
- 2001-05-23 FR FR0106813A patent/FR2810160B1/en not_active Expired - Fee Related
- 2001-05-28 TW TW090112770A patent/TW523928B/en not_active IP Right Cessation
- 2001-06-06 DE DE10127391A patent/DE10127391B4/en not_active Expired - Lifetime
- 2001-06-06 CN CNB011208805A patent/CN1166005C/en not_active Expired - Lifetime
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EP1450411A1 (en) * | 2003-02-21 | 2004-08-25 | STMicroelectronics S.r.l. | MOS power device with high integration density and manufacturing process thereof |
US20040222483A1 (en) * | 2003-02-21 | 2004-11-11 | Ferruccio Frisina | MOS power device with high integration density and manufacturing process thereof |
US7091558B2 (en) | 2003-02-21 | 2006-08-15 | Stmicroelectronics S.R.L. | MOS power device with high integration density and manufacturing process thereof |
US20060267092A1 (en) * | 2005-05-31 | 2006-11-30 | Lite-On Semiconductor Corp. | High power semiconductor device capable of preventing parasitical bipolar transistor from turning on |
CN100431168C (en) * | 2005-05-31 | 2008-11-05 | 敦南科技股份有限公司 | High power semiconductor device capable of preventing parasitical bipolar transistor |
US9142662B2 (en) | 2011-05-06 | 2015-09-22 | Cree, Inc. | Field effect transistor devices with low source resistance |
US9029945B2 (en) | 2011-05-06 | 2015-05-12 | Cree, Inc. | Field effect transistor devices with low source resistance |
US9673283B2 (en) | 2011-05-06 | 2017-06-06 | Cree, Inc. | Power module for supporting high current densities |
US9373617B2 (en) | 2011-09-11 | 2016-06-21 | Cree, Inc. | High current, low switching loss SiC power module |
US9640617B2 (en) | 2011-09-11 | 2017-05-02 | Cree, Inc. | High performance power module |
US10153364B2 (en) | 2011-09-11 | 2018-12-11 | Cree, Inc. | Power module having a switch module for supporting high current densities |
US11024731B2 (en) | 2011-09-11 | 2021-06-01 | Cree, Inc. | Power module for supporting high current densities |
US11171229B2 (en) | 2011-09-11 | 2021-11-09 | Cree, Inc. | Low switching loss high performance power module |
US9793392B2 (en) * | 2014-12-25 | 2017-10-17 | Fuji Electric Co., Ltd. | Semiconductor device |
Also Published As
Publication number | Publication date |
---|---|
DE10127391A1 (en) | 2002-01-17 |
TW523928B (en) | 2003-03-11 |
CN1328345A (en) | 2001-12-26 |
FR2810160A1 (en) | 2001-12-14 |
CN1166005C (en) | 2004-09-08 |
DE10127391B4 (en) | 2013-12-24 |
JP2001352061A (en) | 2001-12-21 |
FR2810160B1 (en) | 2004-08-13 |
JP4198302B2 (en) | 2008-12-17 |
US6388280B2 (en) | 2002-05-14 |
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