WO2010021146A1 - 半導体装置 - Google Patents
半導体装置 Download PDFInfo
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- WO2010021146A1 WO2010021146A1 PCT/JP2009/003990 JP2009003990W WO2010021146A1 WO 2010021146 A1 WO2010021146 A1 WO 2010021146A1 JP 2009003990 W JP2009003990 W JP 2009003990W WO 2010021146 A1 WO2010021146 A1 WO 2010021146A1
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- 239000004065 semiconductor Substances 0.000 title claims abstract description 52
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- H—ELECTRICITY
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- 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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- 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
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- 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
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- 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
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/16—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only elements of Group IV of the Periodic System
- H01L29/1602—Diamond
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- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/16—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only elements of Group IV of the Periodic System
- H01L29/1608—Silicon carbide
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- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/20—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only AIIIBV compounds
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- 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
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/20—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only AIIIBV compounds
- H01L29/2003—Nitride compounds
Definitions
- the present invention relates to a semiconductor device, and more particularly, to a silicon carbide (SiC) metal oxide semiconductor field effect transistor (MOSFET).
- SiC silicon carbide
- MOSFET metal oxide semiconductor field effect transistor
- FIG. 7 schematically shows a cross section in one direction (x direction) of the conventional vertical SiC power MOSFET 100.
- the SiC power MOSFET 100 has the same structure in the direction (y direction) perpendicular to the paper surface of FIG. 7, and unit cells U having a structure sandwiched between alternate long and short dash lines are two-dimensionally arranged in the x and y directions. Yes.
- Each unit cell U includes a SiC semiconductor substrate 102 and an n-type drift layer 103 provided on the SiC semiconductor substrate 102.
- a P-type well 104a is provided from the surface 103s toward the inside.
- an n-type source region 105 and a P-type contact region 104b are further provided.
- the source region 105 and the contact region 104b are in ohmic contact with the source electrode 106 provided on the surface 103s of the drift layer 103.
- a gate insulating film 107a is provided so as to cover the well 104a exposed on the surface 103s of the drift layer 103 and the surface of the drift layer 103 where the well 104a is not provided, and a gate electrode 108 is provided on the gate insulating film 107a. ing.
- a drain electrode 101 is provided on the surface of the SiC semiconductor substrate 102 where the drift layer 103 is not provided, and is in ohmic contact with the semiconductor substrate 102.
- FIG. 8 is a perspective view schematically showing the arrangement of unit cells U in SiC power MOSFET 100. For ease of understanding, a gap is provided between adjacent unit cells U. Further, in FIG. 8, only the well 104a of each unit cell U is shown. The flow of electrons is indicated by dashed arrows.
- each unit cell U of SiC power MOSFET 100 electrons move from the surface 103 s of drift layer 103 to the thickness direction of SiC semiconductor substrate 102 in the vicinity of the boundary with adjacent unit cell U. Moving. Therefore, in the entire vertical SiC power MOSFET 100, electrons move in the thickness direction of the drift layer 103 and the SiC semiconductor substrate 102 between the wells 104a.
- the source electrode 106 and the drain electrode 101 are provided so as to be separated from each other in the thickness direction of the drift layer 103 and the SiC semiconductor substrate 102, and electrons as carriers move in the thickness direction.
- the channel is formed in the vicinity of the outer periphery of the well 104a having a rectangular shape. Therefore, the sum of the lengths of the four sides defining the well 104 on the surface 103s of the drift layer 103 becomes the gate width.
- the vertical SiC power MOSFET 100 having such a structure the smaller the unit cell U, the longer the total gate width.
- the gate width is 4W.
- the unit cell U2 having one side of W / 2 four unit cells U2 can be formed with the same area as the unit cell U1, and the gate width of each unit cell U2 is 2W. Is 8W. Therefore, by reducing the unit cell, the amount of current per unit area, that is, the current density can be increased.
- the on-resistance of the vertical SiC power MOSFET is constituted by the sum of source contact resistance, source sheet resistance, channel resistance, JFET resistance, drift resistance, substrate resistance, and drain contact resistance.
- the key is to effectively reduce channel resistance and JFET resistance.
- the channel resistance is a resistance of a channel formed below the gate insulating film 107a.
- the channel mobility is low and the channel resistance is large due to the reason attributable to the SiC material and the manufacturing process.
- channel mobility of about 30 to 60 cm 2 / Vs can be realized even on the (0001) plane of 4H—SiC.
- the inventors of the present application have examined that in a SiC power MOSFET having a unit cell size of 10 ⁇ m or less, if the channel length is set to 1 ⁇ m or less, the channel resistance can be reduced to about 1.5 to 2 m ⁇ cm 2 . .
- the JFET resistance is the resistance of the JFET region 111 sandwiched between adjacent wells 104a of the drift layer 103, which is a path of electrons moving from the source to the drain, as shown in FIG. .
- the depletion layer 110 is formed by the junction of the P-type well 104a and the n-type drift layer 103, and the current path is narrowed. Therefore, the resistance of the JFET region 111 is increased.
- the depletion layer 110 spreads and does not pinch off the electron path moving through the JFET region 111 when the MOSFET is in the ON state. Thus, it is necessary to set the interval L to 3 ⁇ m or more. Even in this case, the JFET resistance becomes relatively high.
- the unit cell U becomes large and the channel density is reduced. This increases the channel resistance of the entire SiC power MOSFET. Furthermore, the source contact occupancy ratio decreases, and there is a problem that the source contact resistance increases. For this reason, it is difficult to effectively reduce the on-resistance of the SiC power MOSFET.
- Patent Document 1 discloses a technique for suppressing the spread of the depletion layer by increasing the carrier concentration of the JFET region 111 from 1 ⁇ 10 16 cm ⁇ 3 to about 5 ⁇ 10 17 cm ⁇ 3. Is disclosed. Patent Document 1 discloses that a SiC power MOSFET is used as long as the concentration in the JFET region 111 is different from the concentration in the other region of the drift layer, particularly when the concentration in the JFET region 111 is higher than the concentration in the other region of the drift layer. It is described that the effect of improving the on-characteristic can be obtained.
- the distance L can be set as close as possible to 0 ⁇ m.
- the inventor of the present application has made a device in which the concentration of the JFET region 111 is increased and the distance L is shortened, and various studies have been made. As a result, it has been confirmed that the JFET resistance is reduced in the on state. In other words, under the condition where a high voltage is applied to the drain electrode, an increase in drain leakage current, a decrease in source-drain breakdown voltage, and an increase or breakdown of leakage in the gate insulating film due to a high drain electric field may arise as new problems. I understood.
- An object of the present invention is to solve such problems of the prior art, and to provide a semiconductor device that has low on-resistance and can ensure reliability in an off state even when a unit cell is made small. To do.
- the semiconductor device of the present invention is a semiconductor device including a plurality of unit cells arranged at least one dimension, each unit cell is formed on a substrate composed of a wide band gap semiconductor, An n-type drift layer composed of a wide band gap semiconductor, a p-type well provided in the drift layer, a first n-type impurity region provided in the well, and the first n A source electrode electrically connected to the type impurity region and in the drift layer, between the well and the well of the adjacent unit cell, having an impurity concentration higher than that of the drift layer.
- n-type impurity regions at least part of the second n-type impurity region, at least part of the well, and less of the first n-type impurity region
- a gate insulating film provided on a part of the gate insulating film, a gate electrode provided on the gate insulating film, in the drift layer, adjacent to the second n-type impurity region, and A third n-type impurity region formed at a position including the apex of the unit cell when the drift layer is viewed in the thickness direction from the surface of the drift layer, the impurity concentration being the second n-type impurity;
- a third n-type impurity region lower than the region.
- each unit cell further includes a drain electrode provided on the back surface of the substrate opposite to the surface on which the drift layer is formed, and the voltage with a polarity that can maintain a high breakdown voltage in the drain electrode.
- the impurity concentration of the third n-type impurity region is set so that the third n-type impurity region is depleted before the second n-type impurity region is completely depleted. Yes.
- the third n-type impurity region is located at a distance exceeding a / 2 from the outer periphery of the well.
- the unit cells are arranged two-dimensionally.
- the unit cells when the drift layer is viewed from the surface of the drift layer in the thickness direction, the unit cells have a quadrangular shape and are arranged in a staggered manner.
- each unit cell when the drift layer is viewed from the surface of the drift layer in the thickness direction, each unit cell has a quadrangular shape and is arranged in a lattice shape.
- each unit cell when the drift layer is viewed from the surface of the drift layer in the thickness direction, each unit cell has a hexagonal shape, and each unit cell has a vertex of three adjacent unit cells. They are arranged so as to overlap.
- the second n-type impurity region includes an outer periphery defining a well of each unit cell and each unit cell when the drift layer is viewed in a thickness direction from the surface of the drift layer.
- the third n-type impurity region is provided between the wells of each unit cell so as to be in contact with the well only between portions where the outer peripheries defining the wells of adjacent unit cells are substantially parallel to each other. In FIG. 3, the region other than the second n-type impurity region is filled.
- each unit cell is formed on at least part of the second n-type impurity region, on at least part of the well, and on at least part of the first n-type impurity region.
- the semiconductor device further includes a channel layer provided below the gate insulating film.
- the wide band gap semiconductor is SiC.
- the impurity concentration of the third n-type impurity region is less than 1 ⁇ 10 17 cm ⁇ 3 .
- the semiconductor device is turned off by the third n-type impurity region which is lower in impurity concentration than the second n-type impurity region provided between the wells and is provided at a position including the apex of the unit cell.
- the drain electrode when the drain electrode is at a high potential, the electric field in the vicinity of the apex of the unit cell is relaxed, drain leakage can be suppressed, and variations in breakdown voltage of individual semiconductor devices can be suppressed.
- the strength of the electric field applied to the gate insulating film is reduced at the apex of the unit cell, the breakdown of the gate insulating film is suppressed, and the reliability of the gate insulating film can be improved.
- the on-resistance of the semiconductor device can be reduced without impairing the effect of reducing the JFET resistance between the wells. . Therefore, the distance between the wells can be shortened to reduce the size of the unit cell, and a semiconductor device driven with a large current can be realized.
- FIG. 2 is a cross-sectional view taken along line A-A ′ in FIG. 1.
- FIG. 2 is a cross-sectional view taken along the line Q-Q ′ in FIG. 1.
- It is a schematic diagram which expands and shows the structure of the apex vicinity of the unit cell of the SiC power MOSFET of 1st Embodiment.
- It is a top view which shows 2nd Embodiment of SiC power MOSFET by this invention.
- It is a top view which shows 3rd Embodiment of SiC power MOSFET by this invention.
- It is a top view which shows 4th Embodiment of SiC power MOSFET by this invention.
- the SiC power MOSFET 100 when the SiC power MOSFET 100 is in the off state, a large potential difference is generated between the gate electrode 108 and the drain electrode 101.
- the depletion layer 110 is formed in the JFET region 111, the electric field due to the potential difference between the gate electrode 108 and the drain electrode 101 is concentrated in a region other than the depletion layer 110. More specifically, the point R in the JFET region 111 that is approximately the same distance from the two adjacent wells 104a is farthest from the interface between the well 104a and the drift layer 103, so that the depletion layer 110 is formed. Hateful. For this reason, the electric field in the OFF state is concentrated at the position of the point R in the JFET region 111.
- FIG. 10 is a graph showing the relationship between the distance L between the wells 104a at the point R and the concentration n j of the JFET region and the electric field strength applied to the gate insulating film 107a in the off state. As is apparent from FIG.
- each element size and impurity concentration in the unit cell are determined in such a range that the maximum electric field strength at the point R is not problematic for ensuring the reliability of the gate insulating film.
- FIG. 11 shows the arrangement of the unit cells U viewed from the drift layer 103 in the thickness direction from the surface (upper surface) of the drift layer 103.
- the unit cells are arranged in a staggered manner.
- the impurity concentration of the JFET region 111 is uniformly increased, the highest electric field is applied to the gate insulating film in the OFF state not at the point R but at the point S.
- the distance to the well 104a is the longest at the position of the apex of the polygon, and the electric field strength is the highest for the reason described above. Because.
- the standard of the maximum value of the electric field that can be applied to the PN junction in the SiC crystal when the SiC power MOSFET is turned off is about 2 MV / cm.
- the electric field applied to the gate insulating film at this time is about 3 MV / cm.
- the design value is exceeded at the apex of the unit cell, such a design is not preferable in consideration of long-term reliability.
- Such a problem is a problem that has not occurred in the Si power MOSFET in which the maximum value of the electric field is about one digit smaller.
- the inventor of the present application has invented a SiC power MOSFET having a novel structure, which will be described in detail below, based on such studies.
- FIG. 1 is a plan view showing the structure of the SiC power MOSFET 51 according to the first embodiment.
- the drift layer 3a viewed from the surface (upper surface) of the drift layer 3a in the thickness direction is shown in FIG.
- the structure is shown.
- SiC power MOSFET 51 includes a plurality of unit cells U.
- the unit cell U has a quadrangular shape as viewed from the drift layer 3a side, and the quadrangular shapes are arranged in a staggered manner. More specifically, the arrangement of the unit cells U in the y direction is shifted by 1 ⁇ 2 cycle.
- seven unit cells U are shown. When each unit cell U has a square shape when viewed from the surface side of the drift layer 3a, the unit cells can be arranged in a lattice shape without providing a gap between the unit cells, and the density of the unit cells is increased. can do.
- a unit cell is the smallest structural unit having the same structure. Further, when the unit cells are arranged in a lattice shape, the shape of each unit cell viewed from the surface of the drift layer 3a is a line segment connecting the center of each unit cell and the centers of a plurality of adjacent unit cells. It is defined by a region surrounded by a plurality of straight lines that respectively pass through the midpoints and are perpendicular to the line segment. As shown in FIG. 11, the unit cells in the case where the unit cells are arranged in a zigzag pattern are considered to be obtained by shifting the unit cells arranged in a grid pattern.
- the shape of the unit cell defined in this way is a geometrical shape determined from the layout of the unit cell, in the actual SiC power MOSFET 51, the boundary or apex that defines the shape of the unit cell on the surface of the drift layer 3a There is no specific structure. However, the boundaries and vertex positions that define the shape of the unit cell can be uniquely determined by the above-described definition.
- FIG. 2A and 2B show the cross-sectional structure of the unit cell
- FIG. 2A shows the A-A ′ cross section in FIG. 1
- FIG. 2B shows the Q-Q ′ cross section.
- the unit cell U includes a substrate 2 mainly composed of a wide band gap semiconductor, and a drift layer 3a formed on the substrate 2 and mainly composed of a wide band gap semiconductor.
- the substrate 2 and the drift layer 3a may each contain impurities.
- the wide band gap semiconductor refers to a semiconductor such as SiC, GaN, diamond, BN, or GaAs.
- the substrate 2 is a low-resistance SiC substrate containing n-type impurities (nitrogen, phosphorus, arsenic, etc.) of 1 ⁇ 10 18 cm ⁇ 3 or more, for example.
- the drift layer 3a is a SiC semiconductor layer doped with an n-type impurity (for example, nitrogen) of about 1 ⁇ 10 15 cm ⁇ 3 to 1 ⁇ 10 16 cm ⁇ 3 .
- a buffer layer 3b doped with n-type impurities of about 10 17 cm ⁇ 3 to 10 18 cm ⁇ 3 is provided between the drift layer 3 a and the substrate 2.
- Drift layer 3a and buffer layer 3b can be formed, for example, by epitaxial growth on substrate 2 by CVD or the like.
- a p-type well 4a is provided in a part of the drift layer 3a so as to go from the surface to the inside.
- the well 4a is doped with, for example, a p-type impurity of 5 ⁇ 10 17 cm ⁇ 3 to 1 ⁇ 10 19 cm ⁇ 3 .
- a p + -type contact region 4b and a source region 5 that is a first n-type impurity region are formed in a part of the well 4a.
- the contact region 4b and the source region 5 are formed from the surface of the well 4a toward the inside.
- the p + -type contact region 4b is doped with a p-type impurity of about 5 ⁇ 10 19 cm ⁇ 3
- the source region 5 is 1 ⁇ 10 19 cm ⁇ 3 to 1 ⁇ 10 20 cm ⁇ 3 .
- An n-type impurity is doped.
- a JFET region 30 as a second n-type impurity region is provided between the well 4a and the well 4a of the adjacent unit cell U.
- the impurity concentration of the JFET region 30 is higher than the impurity concentration of the drift layer 3a.
- the JFET region 30 is doped with an n-type impurity, for example, 1 ⁇ 10 16 cm ⁇ 3 to 5 ⁇ 10 17 cm ⁇ 3 .
- the third position is located in the drift layer 3a, adjacent to the JFET region 30, and including the apex of the unit cell U when viewed from the surface of the drift layer 3a.
- a low concentration impurity region 31 which is an n-type impurity region is provided.
- the unit cell U of the SiC power MOSFET 51 does not have a specific structure showing a vertex. However, the position of the vertex is uniquely determined from the layout of the unit cell U, and the low concentration impurity region 31 is provided so as to include the position of the vertex.
- the low-concentration impurity region 31 is preferably formed to the same depth as the well 4a or about 10% deeper than the well 4a. Generally, the variation in the depth direction when a well is formed by ion implantation is about 5% including a margin. Therefore, if the low-concentration impurity region 31 is designed to be about 10% deeper than the well 4a, the low-concentration impurity region 31 having a depth equal to or greater than that of the well 4a can be surely formed.
- the low-concentration impurity region 31 is doped with an n-type impurity to about 1 ⁇ 10 16 cm ⁇ 3 , for example.
- the impurity concentration of the low concentration impurity region 31 is preferably lower than that of the JFET region 30.
- the impurity concentration of the low concentration impurity region 31 is not particularly limited in relation to the impurity concentration of the drift layer 3a, and may be higher or lower than the impurity concentration of the drift layer 3a.
- the impurity concentration of the low concentration impurity region 31 and the impurity concentration of the drift layer 3a may be approximately the same.
- Well 4a, contact region 4b, source region 5, JFET region 30 and low-concentration impurity region 31 are formed in drift layer 3a by ion implantation, for example.
- each unit cell in order to realize a low resistance channel, is n-type on at least a part of the JFET region 30, on at least a part of the well 4 a, and on at least a part of the source region 5.
- a channel layer 7b doped with impurities of about 1 ⁇ 10 15 cm ⁇ 3 to 1 ⁇ 10 16 cm ⁇ 3 is provided.
- Channel layer 7b is made of SiC, and is formed, for example, by epitaxial growth by a CVD method.
- the thickness is about 50 nm to 200 nm, and the threshold voltage of the gate voltage is 3V to 6V at this time.
- ion implantation may be performed on the surface of the well 4a in contact with the channel layer 7b.
- the channel layer 7b is not necessarily essential, and may be provided with a channel formed by an inversion layer formed in the vicinity of the surface of the well 4a, as in a normal MOSFET.
- the gate insulating film 7a is provided on the channel layer 7b or on at least a part of the JFET region 30, on at least a part of the well 4a, and on at least a part of the source region 5.
- a gate electrode 6 is provided on the gate insulating film 7a.
- the gate insulating film 7a is made of, for example, silicon oxide, and may be patterned by depositing silicon oxide, or may be patterned by thermally oxidizing the surfaces of the drift layer 3a and the channel layer 7b.
- the gate electrode 6 is made of polysilicon, for example.
- a source electrode 6 is provided so as to be electrically joined to the source region 5 and the contact region 4b.
- a drain electrode 1 is provided on the surface of the substrate 2 on which the drift layer 3a is not provided.
- the source electrode 6 and the drain electrode 1 are made of, for example, a Ni alloy and are in ohmic contact with the source region 5 and the contact region 4b and the substrate 2 by heat treatment.
- An interlayer insulating film 9 is provided so as to cover the gate electrode 8, and a contact is formed on the interlayer insulating film 9 so that the source electrode 6 is exposed.
- the source electrode 6 is electrically connected to the source wiring 10.
- Source electrodes 9 of other unit cells are also connected to the source wiring 10.
- the SiC power MOSFET 51 includes a low concentration impurity region 31.
- the low concentration impurity region 31 can be formed by ion implantation, for example. Specifically, after forming the drift layer 3a, a mask defining the low-concentration impurity region 31 is formed on the surface of the drift layer 3a in the same manner as the well 4a, the contact region 4b, the source region 5 and the JFET region 30. It can be formed by ion implantation. Other structures can be manufactured using a semiconductor device manufacturing technique similar to the conventional one.
- the well 4a, the contact region 4b and the source region 5 are formed in the drift layer 3a by ion implantation, and then the JFET region 30 is formed in a part of the region other than the well 4a of the drift layer 3a. That is, a region other than the well 4 a and the JFET region 30 may be used as the low concentration impurity region 31. In this case, the impurity concentration of the low concentration impurity region 31 matches the impurity concentration of the drift layer 3a.
- each unit cell of the SiC power MOSFET 51 when a bias voltage equal to or higher than the threshold voltage is applied to the gate electrode 8 with a predetermined voltage applied between the source electrode 6 and the drain electrode 1, the source wiring 10 and Electrons are injected from the source electrode 6 into the channel layer 7 b through the source region 5, and electrons move from the channel layer 7 b through the JFET region 30, the drift region 3 a and the substrate 2 to the drain electrode 1. In this way, each unit cell of the SiC power MOSFET 51 is turned on. Although not shown in FIG. 1 and the like, the gate electrode 8 and the drain electrode 1 of each unit cell are continuous with the gate electrode 8 and the drain electrode 1 of other unit cells. For this reason, each unit cell of the SiC power MOSFET 51 operates simultaneously.
- the low concentration impurity region 31 In the conventional SiC power MOSFET, all the JFET regions between the wells are doped with a uniform concentration, but in the SiC power MOSFET 51 of this embodiment, the low concentration impurity region 31 having a lower impurity concentration than the JFET region 30 drifts. In the layer 3a, it is provided at a position adjacent to the JFET region 30 and including the apex of the unit cell U when viewed from the surface of the drift layer 3a.
- the impurity concentration of the low concentration impurity region 31 is determined based on the impurity concentration of the well 4a and the JFET region 30 and the distance between the wells 4a. Specifically, the concentration of the well 4a is generally 5 ⁇ 10 17 cm ⁇ 3 to 2 ⁇ 10 18 cm ⁇ 3 . By setting this concentration range, the well region is depleted when a positive high voltage is applied to the drain electrode 1 in the off state, that is, when a voltage is applied to the drain electrode 1 with a polarity that maintains a high breakdown voltage. The layer can be extended to prevent punch-through with the source region 5. Compared to Si power devices, the well concentration is higher. Note that applying a high voltage to the drain electrode 1 means maintaining the drain electrode 1 at a high potential with respect to the source electrode 6 or the gate electrode 8.
- the distance L between the wells 4a is preferably 0.5 ⁇ m or more because of limitations on mask formation. A practical range is 0.8 ⁇ m or more and 1.5 ⁇ m or less. At this time, the range of the impurity concentration of the JFET region 30 is preferably 1 ⁇ 10 16 cm ⁇ 3 or more and 5 ⁇ 10 17 cm ⁇ 3 or less. However, if the distance L between the wells 4a can be fabricated with a reproducibility of 0.5 ⁇ m, the impurity concentration of the JFET region 30 may be 5 ⁇ 10 17 cm ⁇ 3 or more, for example, 8 ⁇ 10 17 cm ⁇ 3. Good. In this case, even if a high voltage is applied to the drain electrode in the off state, the depletion layer is designed to quickly extend to the JFET region 30 between the wells 4a, so there is no problem as a function.
- the distance L between the wells 4a is preferably set to about 1 ⁇ m when the SiC power MOSFET 51 is manufactured using an i-line stepper. Therefore, in this case, the impurity concentration of the JFET region 30 is preferably set in the range of 1 ⁇ 10 16 cm ⁇ 3 to 5 ⁇ 10 16 cm ⁇ 3 .
- the impurity concentration of the low concentration impurity region 31 is set lower than that of the JFET region 30.
- the impurity concentration of the low concentration impurity region 31 is set such that the low concentration impurity region 31 is depleted before the JFET region 30 is completely depleted.
- the impurity concentration in the well 4a and the JFET region 30 is determined as described above, and the distance L between the wells 4a is determined, the apex of the unit cell is as shown in FIG.
- the depletion layer should extend about 1.4 times longer than when the JFET region 30 is depleted at the point P.
- the impurity concentration at the apex of the unit cell U may be about 1 ⁇ 2 or less of the JFET region 30.
- the impurity concentration of the JFET region 30 is 2.5 ⁇ 10 16 cm ⁇ 3
- the JFET region 30 is completely depleted if the impurity concentration of the low concentration impurity region 31 is set to about 1 ⁇ 10 16 cm ⁇ 3.
- the concentration of the low-concentration impurity region 31 may be designed in accordance with whether to improve the reliability of the unit cell or prioritize the reduction of the on-resistance in the on state. In any case, in the case of the staggered arrangement, the impurity concentration of the low concentration impurity region 31 is appropriately 1 ⁇ 2 or less of the concentration of the JFET region 30.
- FIG. 3 shows the vicinity of the apex Q of the unit cell U in an enlarged manner.
- the low concentration impurity region 31 is preferably located away from the outer periphery of the well 4a by a distance exceeding a / 2. If the position of the low-concentration impurity region 31 satisfies such a relationship and the impurity concentration is lower than that of the JFET region, even if a high breakdown voltage is applied to the drain electrode in the off state, the SiC in the point Q and the gate insulating film The maximum electric field strength can be reduced.
- the low-concentration impurity region 31 shows a minimum area, and the same effect can be obtained even if it is slightly larger than the region shown in FIG.
- the same effect can be obtained by approximating the planar shape of the low-concentration impurity region 31 with a triangular shape connecting the vertices in FIG.
- the impurity concentration of the JFET region 30 is higher than the impurity concentration of the drift layer 4a, the spread of the depletion layer in the JFET region 30 is suppressed, and the JFET resistance is reduced. For this reason, the distance between the wells 4a can be shortened, and the unit cell can be made small. That is, the current density can be increased while reducing the on-resistance in the on-state.
- a low concentration impurity region 31 having an impurity concentration lower than that of the JFET region 30 is provided at the apex of each unit cell. Since the distance between the wells is longer than the other portions in the direction including the apex of the unit cell, it is not easily affected by the JFET resistance. In particular, since the depletion layer spreads from the boundary between the well and the JFET region, if the impurity concentration of the JFET region is increased so that other portions reduce the JFET resistance, the unit cell located between the wells In the vicinity of the apex, the influence of the resistance increase due to the depletion layer is small. For this reason, even if the low concentration impurity region 31 is provided, the JFET resistance in the ON state does not increase.
- the low-concentration impurity region 31 having a low impurity concentration is located in the vicinity of the apex of the unit cell located in the middle between the wells that is not easily affected by the increase in resistance due to the spread of the depletion layer. Therefore, the electric field can be effectively reduced in the portion where the highest electric field is applied to the gate insulating film in the off state. Therefore, drain leakage in the off state can be suppressed, variation in breakdown voltage between unit cells can be reduced, and the reliability of the gate insulating film can be improved.
- each unit cell of the SiC power MOSFET 51 includes the channel layer 7b.
- a channel formed by an inversion layer formed in the vicinity of the surface of the well 4a and a gate insulating film formed by oxidizing the surface of the drift layer 3a may be provided.
- the portion of the gate insulating film located on the low concentration impurity region 31 has a low impurity concentration in the low concentration impurity region 31.
- the quality of the gate insulating film is improved. This is because the crystal concentration in the low concentration impurity region 31 is reduced due to the low impurity concentration in the low concentration impurity region 31, so that an electrical adverse effect is exerted on the channel layer, the gate insulating film and the like located on the low concentration impurity region 31. It is thought that this is because giving is suppressed.
- the electric field strength applied to the gate insulating film at the apex Q of the unit cell U in the on state and the off state is reduced, and the breakdown voltage in the vicinity of the apex Q of the gate insulating film itself is reduced. More enhanced. As a result, the breakdown voltage of the SiC power MOSFET can be further improved and high reliability can be obtained.
- the effect of improving the breakdown voltage of the oxide film generated by oxidizing the semiconductor by reducing the impurity concentration of the semiconductor layer is remarkable when the impurity concentration is smaller than 1 ⁇ 10 17 cm ⁇ 3 .
- the impurity concentration of the low-concentration impurity region 31 smaller than 1 ⁇ 10 17 cm ⁇ 3 , in addition to the above-described effects, it is possible to obtain the effect of improving the breakdown voltage by improving the quality of the gate insulating film.
- FIG. 4 is a plan view showing a second embodiment of the SiC power MOSFET according to the present invention.
- the SiC power MOSFET 52 shown in FIG. 4 includes a plurality of unit cells U having the same structure as that of the first embodiment.
- the second embodiment is different from the first embodiment in that the arrangement of the unit cells U viewed from the drift layer 3a is not a staggered pattern but a lattice pattern.
- the JFET region 30 when viewed from the surface side of the drift layer 3a, the JFET region 30 is located around the well 4a, and the low concentration is at a position where the apexes of the four adjacent unit cells U overlap. Impurity region 31 is located. Since the cell arrangement is point-symmetric with respect to the point where the vertices of the four unit cells U overlap, the element design is easy and the device can be stabilized.
- the SiC power MOSFET 52 of the present embodiment includes the low-concentration impurity region 31, thereby reducing the concentration of the electric field due to the voltage applied to the drain electrode in the off state.
- a SiC power MOSFET with more stable off characteristics can be realized.
- each unit cell U has a quadrangular shape when viewed from the surface side of the drift layer 3a. Therefore, the unit cells are arranged in a lattice pattern without providing a gap between the unit cells. And the density of the unit cell can be increased.
- FIG. 5 is a plan view showing a third embodiment of the SiC power MOSFET according to the present invention.
- the SiC power MOSFET 53 shown in FIG. 5 includes a plurality of unit cells U having the same structure as that of the first embodiment, but is different in that the shape of the unit cell U viewed from the surface side of the drift layer 3a is a hexagon. Different from the first embodiment.
- the JFET region 30 when viewed from the surface side of the drift layer 3a, the JFET region 30 is located around the well 4a, and the low concentration is at a position where the apexes of the adjacent three unit cells U overlap. Impurity region 31 is located. Since the cell arrangement is point-symmetric with respect to the point where the vertices of the three unit cells U overlap, the element design is easy and the device is stabilized.
- the SiC power MOSFET 53 of the present embodiment includes the low-concentration impurity region 31, thereby reducing the concentration of the electric field due to the voltage applied to the drain electrode in the off state. Therefore, it is possible to realize a SiC power MOSFET with more stable off characteristics.
- FIG. 6 is a plan view showing a fourth embodiment of the SiC power MOSFET according to the present invention.
- the SiC power MOSFET 54 shown in FIG. 6 includes a plurality of unit cells U having the same structure as that of the first embodiment.
- the rectangular unit cell U is shown as viewed from the surface side of the drift layer 3a, but the unit cell U may be polygonal.
- the arrangement of the unit cells U may be staggered or latticed as long as it has periodicity, and may be arranged in another pattern.
- each unit cell U includes a well 4a.
- the JFET region is not provided in the entire periphery of the well 4a, but is provided only in the portion closest to the well 4a of the adjacent unit cell U, and the low concentration impurity region 31 is provided in the other regions. Is provided. More specifically, the JFET region 30 has an outer periphery that defines the well 4a of each unit cell U and an outer periphery that defines the well 4a of the adjacent unit cell U when the drift layer 3a is viewed from the surface side. It is provided so as to be in contact with the well 4a only between the substantially parallel portions. This region is a region where the distance between adjacent wells 4a is the shortest.
- the low concentration impurity region 31 is provided so as to fill a region other than the JFET region 30 between the wells 4a of the unit cell U. Since the low-concentration impurity region 31 is provided in a portion where the interval between the wells 4a is wide, the proportion of the low-concentration impurity region 31 is higher than in the first to third embodiments. For this reason, according to the present embodiment, when the SiC power MOSFET 54 is in the OFF state, the electric field due to the voltage applied to the drain can be further reduced.
- the shape of the low concentration impurity region 31 is not limited to that shown in FIG. 6, and the low concentration impurity region 31 having various shapes and sizes may be provided. In this case, the optimum shape changes depending on which of the on-resistance and drain withstand voltage electrical characteristics that are in a trade-off relationship is preferentially considered.
- the present invention has been described by taking the SiC power MOSFET as an example. However, as long as it is a wide band gap semiconductor, a power MOSFET using GaN may be used. The effects of the present invention as described above can be obtained similarly.
- the shape of the unit cell U viewed from the surface side of the drift layer 3a is a square or a hexagon, but may be another polygon.
- the unit cells U are two-dimensionally arranged. However, if the unit cells U are arranged at least one dimension, the same effects as those of the above embodiments can be obtained. Further, the vertexes of the polygons of the unit cell U as viewed from the surface side of the drift layer 3a are not necessarily sharp and may be somewhat rounded.
- the present invention is suitably used for power MOSFETs and various control devices and drive devices using power MOSFETs.
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Abstract
Description
以下に、本発明による半導体装置の第1の実施形態を説明する。図1は、第1の実施形態であるSiCパワーMOSFET51の構造を示す平面図であり、以下において詳細に説明するようにドリフト層3aの表面(上面)から厚さ方向に見たドリフト層3aの構造を示している。SiCパワーMOSFET51は、複数のユニットセルUを含む。ユニットセルUは本実施形態では、ドリフト層3a側から見て四角形状を有しており四角形状が千鳥状に配置されている。より具体的にはy方向へのユニットセルUの配置が1/2周期シフトしている。図1では、ユニットセルUは7つ示されている。ドリフト層3aの表面側から見て各ユニットセルUが四角形状を有している場合、ユニットセル間に隙間を設けることなく格子状にユニットセルを配列させることができ、ユニットセルの密度を高くすることができる。
図4は、本発明によるSiCパワーMOSFETの第2の実施形態を示す平面図である。図4に示すSiCパワーMOSFET52は、第1の実施形態と同じ構造のユニットセルUを複数含む。本第2の実施形態はドリフト層3aから見たユニットセルUの配列が千鳥状ではなく、格子状であるという点で、第1の実施形態と異なっている。
図5は、本発明によるSiCパワーMOSFETの第3の実施形態を示す平面図である。図5に示すSiCパワーMOSFET53は、第1の実施形態と同じ構造のユニットセルUを複数含んでいるが、ドリフト層3aの表面側から見たユニットセルUの形状が六角形である点で第1の実施形態と異なる。
図6は、本発明によるSiCパワーMOSFETの第4の実施形態を示す平面図である。図6に示すSiCパワーMOSFET54は、第1の実施形態と同じ構造のユニットセルUを複数含む。図6では、ドリフト層3aの表面側から見て四角形状のユニットセルUを示しているが、ユニットセルUの形状は多角形であればよい。また、ユニットセルUの配列は、周期性を有していれば、千鳥状や格子状であってもよく、他のパターンで配列されていてもよい。
2、102 基板
3a、103 ドリフト層
3b バッファ層
4a、104a ウェル
4b コンタクト領域
5、105 ソース領域
6、106 ソース電極
7a、107 ゲート絶縁膜
7b チャネル層
8、108 ゲート電極
9 層間絶縁膜
10 ソース配線
30 JFET領域
31 低濃度不純物領域
51、52、53、54 半導体装置
Claims (11)
- 少なくとも一次元に配置された複数のユニットセルを含む半導体装置であって、各ユニットセルは、
ワイドバンドギャップ半導体により構成される基板と、
前記基板上に形成され、前記ワイドバンドギャップ半導体により構成されるn型のドリフト層と、
前記ドリフト層内に設けられたp型のウェルと、
前記ウェル内に設けられた第1のn型不純物領域と、
前記第1のn型不純物領域と電気的に接続されたソース電極と、
前記ドリフト層中であって、前記ウェルと、隣接するユニットセルのウェルとの間に設けられた、不純物濃度が前記ドリフト層よりも高い第2のn型不純物領域と、
前記第2のn型不純物領域の少なくとも一部の上、前記ウェルの少なくとも一部の上、および前記第1のn型不純物領域の少なくとも一部の上に設けられたゲート絶縁膜と、
前記ゲート絶縁膜上に設けられたゲート電極と、
前記ドリフト層中であって、前記第2のn型不純物領域に隣接し、かつ、前記ドリフト層の表面から厚さ方向に前記ドリフト層を見た場合の前記ユニットセルの頂点を含む位置に形成された第3のn型不純物領域であって、不純物濃度が前記第2のn型不純物領域よりも低い第3のn型不純物領域と、
を備えた半導体装置。 - 前記各ユニットセルは、前記基板の前記ドリフト層が形成された面と反対側の裏面に設けられたドレイン電極をさらに有し、
前記ドレイン電極に高耐圧を保持できる極性で電圧を印加し、前記第2のn型不純物領域が完全に空乏化する前に前記第3のn型不純物領域が空乏化するように、前記第3のn型不純物領域の不純物濃度が設定されている請求項1に記載の半導体装置。 - 前記ウェルと隣接するユニットセルのウェルとの最小間隔をaとした場合、前記第3のn型不純物領域は前記ウェルの外周からa/2を超える距離に位置している請求項1に記載の半導体装置。
- 前記ユニットセルが、二次元に配列されている請求項1から3のいずれかに記載の半導体装置。
- 前記ドリフト層の表面から厚さ方向に前記ドリフト層を見た場合、前記各ユニットセルは四角形状を有しており、千鳥状に配置されている請求項4に記載の半導体装置。
- 前記ドリフト層の表面から厚さ方向に前記ドリフト層を見た場合、前記各ユニットセルは四角形状を有しており、格子状に配置されている請求項4に記載の半導体装置。
- 前記ドリフト層の表面から厚さ方向に前記ドリフト層を見た場合、前記各ユニットセルは六角形状を有しており、各ユニットセルは隣接する3つのユニットセルの頂点が重なるように配置されている請求項4に記載の半導体装置。
- 前記第2のn型不純物領域は、前記ドリフト層の表面から厚さ方向に前記ドリフト層を見た場合に、各ユニットセルのウェルを規定する外周と前記各ユニットセルに隣接するユニットセルのウェルを規定する外周とが互いに略平行になっている部分の間にのみ、前記ウェルと接するように設けられ、前記第3のn型不純物領域は、各ユニットセルのウェル間において、前記第2のn型不純物領域以外の領域を埋めるように設けられている請求項5に記載の半導体装置。
- 各ユニットセルは、前記第2のn型不純物領域の少なくとも一部の上、前記ウェルの少なくとも一部の上、および前記第1のn型不純物領域の少なくとも一部の上であって、前記ゲート絶縁膜の下方に設けられたチャネル層をさらに備える請求項1から8のいずれかに記載の半導体装置。
- 前記ワイドバンドギャップ半導体はSiCである請求項1から9のいずれかに記載の半導体装置。
- 前記第3のn型不純物領域の不純物濃度は1×1017cm-3より小さい請求項1から10のいずれかに記載の半導体装置。
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WO2011122670A1 (ja) * | 2010-03-30 | 2011-10-06 | ローム株式会社 | 半導体装置 |
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WO2013161420A1 (ja) * | 2012-04-24 | 2013-10-31 | 富士電機株式会社 | 縦型高耐圧半導体装置およびその製造方法 |
JPWO2013161420A1 (ja) * | 2012-04-24 | 2015-12-24 | 富士電機株式会社 | 縦型高耐圧半導体装置およびその製造方法 |
US9362392B2 (en) | 2012-04-24 | 2016-06-07 | Fuji Electric Co., Ltd. | Vertical high-voltage semiconductor device and fabrication method thereof |
US10361302B2 (en) | 2013-09-20 | 2019-07-23 | Monolith Semiconductor Inc. | High voltage MOSFET devices and methods of making the devices |
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KR20210063491A (ko) * | 2013-09-20 | 2021-06-01 | 모노리스 세미컨덕터 아이엔씨. | 고전압 mosfet 장치 및 상기 장치의 제조방법 |
KR102259531B1 (ko) * | 2013-09-20 | 2021-06-02 | 모노리스 세미컨덕터 아이엔씨. | 고전압 mosfet 장치 및 상기 장치의 제조방법 |
KR102414729B1 (ko) * | 2013-09-20 | 2022-06-29 | 모노리스 세미컨덕터 아이엔씨. | 고전압 mosfet 장치 및 상기 장치의 제조방법 |
WO2016132987A1 (ja) * | 2015-02-20 | 2016-08-25 | 住友電気工業株式会社 | 炭化珪素半導体装置 |
JP7165822B2 (ja) | 2018-07-13 | 2022-11-04 | ウルフスピード インコーポレイテッド | ワイドバンドギャップ半導体デバイス |
JP7447415B2 (ja) | 2019-09-26 | 2024-03-12 | 富士電機株式会社 | 窒化ガリウム半導体装置 |
Also Published As
Publication number | Publication date |
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US20110095305A1 (en) | 2011-04-28 |
JP4698767B2 (ja) | 2011-06-08 |
US8530943B2 (en) | 2013-09-10 |
CN102217073A (zh) | 2011-10-12 |
JPWO2010021146A1 (ja) | 2012-01-26 |
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