US20130224941A1 - Silicon carbide semiconductor device and method of manufacturing thereof - Google Patents
Silicon carbide semiconductor device and method of manufacturing thereof Download PDFInfo
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- US20130224941A1 US20130224941A1 US13/858,904 US201313858904A US2013224941A1 US 20130224941 A1 US20130224941 A1 US 20130224941A1 US 201313858904 A US201313858904 A US 201313858904A US 2013224941 A1 US2013224941 A1 US 2013224941A1
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- silicon carbide
- trench
- semiconductor device
- sidewall
- insulating film
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- 239000004065 semiconductor Substances 0.000 title claims abstract description 155
- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 92
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims abstract description 90
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 40
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 66
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 33
- 238000000137 annealing Methods 0.000 claims description 18
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 16
- 239000007789 gas Substances 0.000 claims description 13
- 238000010438 heat treatment Methods 0.000 claims description 13
- 239000011261 inert gas Substances 0.000 claims description 9
- 229910052786 argon Inorganic materials 0.000 claims description 8
- 239000013078 crystal Substances 0.000 abstract description 30
- 239000010410 layer Substances 0.000 description 131
- 239000012535 impurity Substances 0.000 description 83
- 238000009792 diffusion process Methods 0.000 description 52
- 239000000758 substrate Substances 0.000 description 26
- 238000005530 etching Methods 0.000 description 23
- 238000005468 ion implantation Methods 0.000 description 10
- 230000003647 oxidation Effects 0.000 description 9
- 238000007254 oxidation reaction Methods 0.000 description 9
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 8
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 8
- 238000000206 photolithography Methods 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 7
- 230000007547 defect Effects 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 5
- 239000000969 carrier Substances 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 3
- 230000004913 activation Effects 0.000 description 3
- 238000005275 alloying Methods 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 229910052796 boron Inorganic materials 0.000 description 3
- 238000004544 sputter deposition Methods 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 238000005229 chemical vapour deposition Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 230000005669 field effect Effects 0.000 description 2
- BHEPBYXIRTUNPN-UHFFFAOYSA-N hydridophosphorus(.) (triplet) Chemical compound [PH] BHEPBYXIRTUNPN-UHFFFAOYSA-N 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 238000000059 patterning Methods 0.000 description 2
- 238000001004 secondary ion mass spectrometry Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
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- 230000004048 modification Effects 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
Images
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/0445—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising crystalline silicon carbide
- H01L21/048—Making electrodes
- H01L21/049—Conductor-insulator-semiconductor electrodes, e.g. MIS contacts
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
- H01L21/28008—Making conductor-insulator-semiconductor electrodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a 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
- H01L29/04—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their crystalline structure, e.g. polycrystalline, cubic or particular orientation of crystalline planes
- H01L29/045—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their crystalline structure, e.g. polycrystalline, cubic or particular orientation of crystalline planes by their particular orientation of crystalline planes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a 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 Table
- H01L29/1608—Silicon carbide
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/49—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET
- H01L29/51—Insulating materials associated therewith
- H01L29/518—Insulating materials associated therewith the insulating material containing nitrogen, e.g. nitride, oxynitride, nitrogen-doped material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a 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
- H01L29/66007—Multistep manufacturing processes
- H01L29/66053—Multistep manufacturing processes of devices having a semiconductor body comprising crystalline silicon carbide
- H01L29/66068—Multistep manufacturing processes of devices having a semiconductor body comprising crystalline silicon carbide the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a 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 specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/76—Unipolar devices, e.g. field effect transistors
- H01L29/772—Field effect transistors
- H01L29/78—Field effect transistors with field effect produced by an insulated gate
- H01L29/7801—DMOS transistors, i.e. MISFETs with a channel accommodating body or base region adjoining a drain drift region
- H01L29/7802—Vertical DMOS transistors, i.e. VDMOS transistors
- H01L29/7813—Vertical DMOS transistors, i.e. VDMOS transistors with trench gate electrode, e.g. UMOS transistors
Definitions
- the present invention relates to a silicon carbide semiconductor device and a method of manufacturing thereof, and particularly to a silicon carbide semiconductor device exhibiting excellent electrical characteristics and a method of manufacturing thereof.
- Patent Document 1 discloses a MOS-type field effect transistor (MOSFET) that is formed as a silicon carbide semiconductor device using an SiC substrate of the 4H polytype having a surface orientation of substantially ⁇ 03-38 ⁇ . According to Patent Document 1 disclosing the MOSFET, a gate oxide film is formed by dry oxidation and a high channel mobility (about 100 cm 2 /Vs) can be achieved.
- MOSFET MOS-type field effect transistor
- Patent Document 1 International Patent Publication WO01/018872
- an object of the present invention is to provide a silicon carbide semiconductor device capable of achieving a high channel mobility with high reproducibility, and a method of manufacturing the same.
- the present invention is a silicon carbide semiconductor device including: a semiconductor layer made of silicon carbide and having a surface with a trench having a sidewall formed of a crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to a ⁇ 0001 ⁇ plane; and an insulating film formed to contact the sidewall of the trench, a maximum value of a nitrogen concentration in a region within 10 nm from an interface between the sidewall of the trench and the insulating film is not less than 1 ⁇ 10 21 cm ⁇ 3 , and the silicon carbide semiconductor device has a channel direction in a range of ⁇ 10° relative to a direction orthogonal to a ⁇ 2110> direction in the sidewall of the trench.
- the present invention is a silicon carbide semiconductor device including: a substrate made of silicon carbide of a first conductive type; a semiconductor layer made of silicon carbide of the first conductive type, formed on the substrate, containing a first-conductive-type impurity of a lower concentration than the substrate, and having a surface with a trench having a sidewall formed of a crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to a ⁇ 0001 ⁇ plane; a second-conductive-type impurity diffusion layer formed in the sidewall of the trench; a first-conductive-type impurity diffusion layer formed in the surface of the semiconductor layer; an insulating film formed to contact the sidewall of the trench; a source electrode formed to contact at least a part of a region, except for a portion where the insulating film is formed, of the surface of the semiconductor layer; a gate electrode formed on the insulating film; and a drain electrode formed on a surface of the substrate opposite to a surface of the substrate
- a maximum value of a nitrogen concentration in a region within 10 nm from an interface between the sidewall of the trench and the insulating film is not less than 1 ⁇ 10 21 cm ⁇ 3 , and the silicon carbide semiconductor device has a channel direction in a range of ⁇ 10° relative to a direction orthogonal to a ⁇ 2110> direction in the sidewall of the trench.
- the source electrode has a surface in a stripe pattern.
- the source electrode has a surface in a honeycomb pattern.
- the sidewall of the trench is formed of a crystal plane tilted at an angle of ⁇ 5° relative to a ⁇ 03-38 ⁇ plane.
- the present invention is a method of manufacturing a silicon carbide semiconductor device, including the steps of: forming a trench having a sidewall formed of a crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to a ⁇ 0001 ⁇ plane, in a surface of a semiconductor layer made of silicon carbide; forming an insulating film contacting the sidewall of the trench so that a channel direction is set in a range of ⁇ 10° relative to a direction orthogonal to a ⁇ 2110> direction in the sidewall of the trench; and adjusting a nitrogen concentration so that a maximum value of the nitrogen concentration in a region within 10 nm from an interface between the sidewall of the trench and the insulating film is not less than 1 ⁇ 10 21 cm ⁇ 3 .
- the channel direction is set in a range of ⁇ 10° relative to the direction orthogonal to the ⁇ 2110> direction in the sidewall of the trench, based on an orientation of a defect included in the semiconductor layer.
- the step of adjusting the nitrogen concentration includes the step of performing a heat treatment in an atmosphere of a gas containing nitrogen, on the semiconductor layer where the insulating film is formed.
- the step of adjusting the nitrogen concentration includes the step of performing, on the semiconductor layer having undergone the heat treatment, a heat treatment in an atmosphere of an inert gas.
- the present invention can provide a silicon carbide semiconductor device that can achieve a high channel mobility with high reproducibility, as well as a method of manufacturing the same.
- FIG. 1 is a schematic cross section of an example of a vertical trench gate MOSFET that is an example of the silicon carbide semiconductor device of the present invention.
- FIG. 2 is a schematic plan view of the silicon carbide semiconductor device shown in FIG. 1 as seen from a gate electrode side.
- FIG. 3 is a schematic cross section illustrating a part of a manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention.
- FIG. 4 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention.
- FIG. 5 is a schematic plan view illustrating an example of a surface of a semiconductor layer of the present invention.
- FIG. 6 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention.
- FIG. 7 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention.
- FIG. 8 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention.
- FIG. 9 is a schematic plan view illustrating an example of the sidewall of a trench in the present invention.
- FIG. 10 is a schematic perspective view illustrating an example of a crystal plane of the sidewall of the trench in the present invention.
- FIG. 11 is a schematic cross section illustrating a preferred example of the crystal plane of the sidewall of the trench in the present invention.
- FIG. 12 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention.
- FIG. 13 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention.
- FIG. 14 is a schematic plan view of another example of the silicon carbide semiconductor device of the present invention as seen from the gate electrode side.
- FIG. 15 is a diagram showing an example of a nitrogen concentration distribution in the vicinity of the interface between the sidewall of a trench and an insulating film in an example of the silicon carbide semiconductor device of the present invention.
- FIG. 16 is a diagram showing an example of the relation between an angle (°) relative to the ⁇ 2110> direction and a channel mobility (relative value) in the sidewall of the trench in an example of the silicon carbide semiconductor device of the present invention.
- crystal plane and direction are to be expressed, they should actually be expressed with a bar on a required number. Because of restricted expression means, however, they are expressed in the present invention with “-” added before a required number instead of a bar on the required number.
- an individual orientation is denoted in [ ]
- a group orientation is denoted in ⁇ >
- an individual plane is denoted in ( )
- a group plane is denoted in ⁇ ⁇ .
- FIG. 1 shows a schematic cross section of an example of a vertical trench gate MOSFET (Metal Oxide Semiconductor Field Effect Transistor) that is an example of the silicon carbide semiconductor device of the present invention.
- MOSFET Metal Oxide Semiconductor Field Effect Transistor
- a silicon carbide semiconductor device 1 shown in FIG. 1 includes a substrate 11 made of silicon carbide of n type and 4H-SiC polytype for example, a semiconductor layer 12 made of silicon carbide of n type formed on a surface 11 a of substrate 11 , a trench 20 formed in a surface 12 a of semiconductor layer 12 , a second-conductive-type impurity diffusion layer 14 that is a p-type region formed in surface 12 a of semiconductor layer 12 , a first-conductive-type impurity diffusion layer 15 that is an n-type region formed in a surface of second-conductive-type impurity diffusion layer 14 (also in surface 12 a of semiconductor layer 12 ), an insulating film 13 formed on a part of surface 12 a of semiconductor layer 12 to contact a sidewall 19 of trench 20 , a source electrode 16 formed in a region of surface 12 a of semiconductor layer 12 other than a region where insulating film 13 is formed, a gate electrode 17 formed on a surface of insulating film 13 , and a
- surface 11 a of substrate 11 on which semiconductor layer 12 is formed a crystal plane that is a ⁇ 04-4-3 ⁇ plane for example may be used.
- semiconductor layer 12 a layer such as a layer made of silicon carbide of n type having a lower n-type impurity concentration than substrate 11 for example may be used.
- sidewall 19 of trench 20 formed in surface 12 a of semiconductor layer 12 is formed of a crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to the ⁇ 0001 ⁇ plane.
- Insulating film 13 a film such as an oxide film formed for example by dry oxidation (thermal oxidation) or the like may be used. Insulating film 13 is not limited to a single-layer structure, and may be of a structure including two or more layers.
- second-conductive-type impurity diffusion layer 14 a layer such as a p-type region may be used that is formed by diffusing a p-type impurity serving as a second-conductive-type impurity in surface 12 a of semiconductor layer 12 , for example.
- a p-type impurity serving as a second-conductive-type impurity aluminum, boron, or the like may be used, for example.
- a p+-type region containing a p-type impurity serving as a second-conductive-type impurity and having a higher concentration than second-conductive-type impurity diffusion layer 14 may be formed.
- first-conductive-type impurity diffusion layer 15 a layer such as an n-type region that is formed by diffusing an n-type impurity serving as a first-conductive-type impurity in surface 12 a of semiconductor layer 12 may be used, for example.
- the n-type impurity concentration of first-conductive-type impurity diffusion layer 15 may be made higher than the n-type impurity concentration of semiconductor layer 12 .
- the n-type impurity serving as a first-conductive-type impurity nitrogen, phosphorous or the like may be used, for example.
- source electrode 16 gate electrode 17 , and drain electrode 18 each, a conventionally known metal or the like may be used, for example.
- a maximum value of the nitrogen concentration in a region within 10 nm from the interface between sidewall 19 of trench 20 and insulating film 13 is not less than 1 ⁇ 10 21 cm ⁇ 3 .
- the region within 10 nm from the interface between sidewall 19 of trench 20 and insulating film 13 refers to a region made up of: a region extending from the interface between sidewall 19 of trench 20 and insulating film 13 perpendicularly to the interface toward sidewall 19 side of trench 20 by 10 nm, and a region extending from the interface between sidewall 19 of trench 20 and insulating film 13 perpendicularly to the interface toward insulating film 13 side by 10 nm.
- FIG. 2 shows a schematic plan view of silicon carbide semiconductor device 1 shown in FIG. 1 as seen from gate electrode 17 side.
- the surface of source electrode 16 and the surface of gate electrode 17 are formed to extend in a stripe pattern in the ⁇ 2110> direction. Further, along the ⁇ 03-38> direction which is perpendicular to the ⁇ 2110> direction, source electrode 16 and gate electrode 17 are alternately arranged, and one gate electrode 17 is disposed between two source electrodes 16 . Further, from a gap between source electrode 16 and gate electrode 17 , a surface of insulating film 13 is exposed.
- the channel direction tends to be set easily in a range of ⁇ 10° relative to the direction orthogonal to the ⁇ 2110> direction, in sidewall 19 (crystal plane tilted by an angle in a range of not less than 50° and not more than 65° relative to the ⁇ 0001 ⁇ plane) of trench 20 as described later herein.
- the channel direction means the direction in which carriers move in sidewall 19 of trench 20 .
- the channel direction of silicon carbide semiconductor device 1 with the above-described structure is set to be included in a range of ⁇ 10° relative to the direction orthogonal to the ⁇ 2110> direction, in sidewall 19 of trench 20 that is formed of a crystal plane tilted by an angle in a range of not less than 50° and not more than 65° relative to the ⁇ 0001 ⁇ plane.
- substrate 11 made of silicon carbide (4H-SiC) having surface 11 a formed of a crystal plane that is a ⁇ 04-4-3 ⁇ plane for example is prepared.
- semiconductor layer 12 is formed on surface 11 a of substrate 11 .
- semiconductor layer 12 may be formed for example by epitaxial growth or the like of semiconductor layer 12 made of n-type silicon carbide having an n-type impurity with a lower concentration than substrate 11 , on surface 11 a of substrate 11 .
- semiconductor layer 12 is formed by the above-described epitaxial growth, surface 12 a of semiconductor layer 12 is allowed to have the same crystal plane as surface 11 a of substrate 11 . Therefore, if surface 11 a of substrate 11 is formed for example of a crystal plane that is a ⁇ 04-4-3 ⁇ plane, surface 12 a of semiconductor layer 12 is allowed to have a crystal plane that is a ⁇ 04-4-3 ⁇ plane as well, as shown in the schematic plan view of FIG. 5 for example.
- second-conductive-type impurity diffusion layer 14 is formed in surface 12 a of semiconductor layer 12 .
- second-conductive-type impurity diffusion layer 14 is formed in a stripe pattern extending in the ⁇ 2110> direction.
- Second-conductive-type impurity diffusion layer 14 is not limited to this form.
- second-conductive-type impurity diffusion layer 14 may be formed for example by ion implantation or the like in which ions of a p-type impurity serving as a second-conductive-type impurity are implanted into surface 12 a of semiconductor layer 12 , after an ion implantation block mask is placed in a region other than the region where second-conductive-type impurity diffusion layer 14 is to be formed in surface 12 a of semiconductor layer 12 .
- an oxide film or the like that has been patterned by photolithography and etching for example may be used.
- first-conductive-type impurity diffusion layer 15 is formed in a surface of second-conductive-type impurity diffusion layer 14 formed in the above-described manner.
- first-conductive-type impurity diffusion layer 15 is also formed in a stripe pattern extending in the ⁇ 2110> direction.
- First-conductive-type impurity diffusion layer 15 is not limited to this form.
- first-conductive-type impurity diffusion layer 15 may be formed for example by ion implantation or the like in which ions of an n-type impurity serving as a first-conductive-type impurity are implanted into surface 12 a of semiconductor layer 12 , after an ion implantation block mask is placed in a region other than the region where first-conductive-type impurity diffusion layer 15 is to be formed in surface 12 a of semiconductor layer 12 .
- an oxide film or the like that has been patterned by photolithography and etching for example may be used as well.
- an activation annealing treatment is performed on semiconductor layer 12 in which second-conductive-type impurity diffusion layer 14 and first-conductive-type impurity diffusion layer 15 have been formed in the above-described manner. Accordingly, the p-type impurity serving as a second-conductive-type impurity in second-conductive-type impurity diffusion layer 14 as well as the n-type impurity serving as a first-conductive-type impurity in first-conductive-type impurity diffusion layer 15 that have been introduced by the above-described ion implantation can be activated.
- the activation annealing treatment may be performed for example in an argon gas atmosphere by heating semiconductor layer 12 in which second-conductive-type impurity diffusion layer 14 and first-conductive-type impurity diffusion layer 15 have been formed, at a temperature of approximately 1700° C. for approximately 30 minutes, for example.
- trench 20 having sidewall 19 is formed in surface 12 a of semiconductor layer 12 .
- Trench 20 may be formed for example by providing an etching mask in a region other than the region where trench 20 is to be formed in surface 12 a of semiconductor layer 12 , and thereafter etching and thereby removing the region of surface 12 a of semiconductor layer 12 where the etching mask is not provided.
- the channel direction is to be made coincident with the direction in which sidewall 19 of trench 20 extends
- a defect could be formed at a certain portion of semiconductor layer 12 . Therefore, the position of the defect formed at a certain portion of semiconductor layer 12 may be used as a reference. Then, where the channel direction is to be made coincident with the direction in which sidewall 19 of trench 20 extends for example, trench 20 can be formed easily so that the direction in which sidewall 19 of trench 20 extends is included in a range of ⁇ 10° relative to the direction orthogonal to the ⁇ 2110> direction.
- sidewall 19 of trench 20 is formed of a crystal plane (hatched portion in FIG. 10 ) that is tilted at an angle ⁇ ° in a range of not less than 50° and not more than 65° relative to the ⁇ 0001 ⁇ plane.
- the crystal plane of sidewall 19 of trench 20 is also tilted at an angle in a range of ⁇ 5° relative to the ⁇ 03-38 ⁇ plane as shown for example in a schematic cross section of FIG. 11 .
- sidewall 19 of trench 20 is a crystal plane tilted at an angle in a range of ⁇ 5° relative to the ⁇ 03-38 ⁇ plane
- electrical characteristics such as channel mobility of silicon carbide semiconductor device 1 tend to be improved.
- sidewall 19 of trench 20 is a crystal plane tilted at an angle in a range of ⁇ 3° relative to the ⁇ 03-38 ⁇ plane, and most preferably sidewall 19 of trench 20 is the ⁇ 03-38 ⁇ plane.
- a crystal plane tilted at an angle in a range of ⁇ 5° relative to the ⁇ 03-38 ⁇ plane and a crystal plane tilted at an angle in a range of ⁇ 3° relative to the ⁇ 03-38 ⁇ plane each include the ⁇ 03-38 ⁇ plane.
- Insulating film 13 is formed to contact sidewall 19 of trench 20 formed in the above-described manner.
- Insulating film 13 can be formed to contact sidewall 19 of trench 20 that extends in the direction as controlled so that the direction in which sidewall 19 of trench 20 extends is included in a range of ⁇ 10° relative to the direction orthogonal to the ⁇ 2110> direction, and thereby set the channel direction in a range of ⁇ 10° relative to the direction orthogonal to the ⁇ 2110> direction.
- insulating film 13 an oxide film or the like formed for example by dry oxidation (thermal oxidation) or the like may be used.
- dry oxidation thermal oxidation
- a nitrogen annealing treatment is performed on semiconductor layer 12 where above-described insulating film 13 has been formed.
- the nitrogen concentration is adjusted so that a maximum value of the nitrogen concentration in a region within 10 nm from the interface between sidewall 19 of trench 20 and insulating film 13 is not less than 1 ⁇ 10 21 cm ⁇ 3 .
- semiconductor layer 12 where above-described insulating film 13 has been formed is heated for example in an atmosphere of a gas containing nitrogen such as nitrogen monoxide (NO) gas at a temperature of approximately 1100° C. for approximately 120 minutes for example.
- a maximum value of the nitrogen concentration in the region within 10 nm from the interface between sidewall 19 of trench 20 and insulating film 13 can be set to 1 ⁇ 10 21 cm ⁇ 3 or more.
- an inert gas annealing treatment on semiconductor layer 12 having undergone the above-described nitrogen annealing treatment, in an atmosphere of an inert gas such as argon gas for example.
- an inert gas such as argon gas for example.
- the above-described inert gas annealing treatment may be performed for example in an argon gas atmosphere by heating semiconductor layer 12 having undergone the above-described nitrogen annealing treatment, at a temperature of approximately 1100° C. for approximately 60 minutes for example.
- patterning of insulating film 13 is performed by removing a part of insulating film 13 so that at least a part of the surface of first-conductive-type impurity diffusion layer 15 in surface 12 a of semiconductor layer 12 is exposed.
- a part of insulating film 13 may be removed for example by forming, on the surface of insulating film 13 , an etching mask patterned by means of photolithography and etching for exposing a part to be removed of insulating film 13 , for example, and thereafter etching and thereby removing the exposed part of insulating film 13 .
- source electrode 16 is formed to contact the exposed surface of first-conductive-type impurity diffusion layer 15 in surface 12 a of semiconductor layer 12 that is exposed from the part where insulating film 13 has been removed.
- source electrode 16 may be formed for example by performing sputtering for example to form an electrically conductive film made of a metal such as nickel for example, on surface 12 a of semiconductor layer 12 exposed after the above-described etching of insulating film 13 and on the surface of the above-described etching mask, and thereafter removing this etching mask.
- the conductive film formed on the surface of the etching mask is removed (lifted off) together with the etching mask while only the conductive film formed on surface 12 a of semiconductor layer 12 is left to serve as source electrode 16 .
- a heat treatment for achieving alloying is performed on semiconductor layer 12 on which above-described source electrode 16 has been formed.
- the heat treatment for achieving alloying may be performed for example in an atmosphere of an inert gas such as argon gas by heating semiconductor layer 12 on which above-described source electrode 16 has been formed, at a temperature of approximately 950° C. for approximately two minutes for example.
- an inert gas such as argon gas
- gate electrode 17 is formed on a surface of insulating film 13 .
- gate electrode 17 may be formed for example by performing photolithography and etching or the like to form a resist mask having an opening corresponding to a portion where gate electrode 17 is to be formed and covering respective entire surfaces of insulating film 13 and source electrode 16 , then performing for example sputtering or the like to form an electrically conductive film made of a metal such as aluminum for example, on the surface of the resist mask and on the surface of insulating film 13 that is exposed from the opening of the resist mask, and thereafter removing this resist mask.
- the conductive film formed on the surface of the resist mask is removed (lifted off) together with the resist mask while only the conductive film formed on the surface of insulating film 13 is left to serve as gate electrode 17 .
- drain electrode 18 is formed on the back surface of substrate 11 .
- drain electrode 18 may be formed for example by performing for example sputtering or the like to form an electrically conductive film made of a metal such as nickel for example, on the back surface of substrate 11 .
- silicon carbide semiconductor device 1 with the structure shown in FIG. 1 can be manufactured.
- the surface of source electrode 16 may be formed in a honeycomb pattern and a region except for a partial region surrounding the outer periphery of source electrode 16 may be formed as gate electrode 17 as shown for example in a schematic plan view of FIG. 14 .
- each source electrode 16 is formed in the shape of a hexagon.
- the surface of source electrode 16 is preferably formed in the shape of a regular hexagon.
- the possible number of silicon carbide semiconductor devices 1 to be formed from substrate 11 of the same size can be increased. Therefore, there is a tendency that silicon carbide semiconductor device 1 having a high channel mobility can be fabricated with higher reproducibility and at a higher manufacturing efficiency.
- second-conductive-type impurity diffusion layer 14 and first-conductive-type impurity diffusion layer 15 may also be formed in a hexagonal shape such as regular hexagonal shape.
- silicon carbide semiconductor device 1 having source electrode 16 and gate electrode 17 structured as shown in FIG. 14 may be similar to the above-described ones.
- silicon carbide semiconductor device 1 structured in the above-described manner, when a negative voltage is applied to source electrode 16 and a positive voltage is applied to gate electrode 17 and drain electrode 18 for example, carriers (electrons in the above-described example) injected from source electrode 16 move to drain electrode 18 through the surface of first-conductive-type impurity diffusion layer 15 , sidewall 19 of trench 20 , the inside of semiconductor layer 12 , and the inside of substrate 11 .
- a maximum value of the nitrogen concentration in a region within 10 nm from the interface between sidewall 19 of trench 20 and insulating film 13 is not less than 1 ⁇ 10 21 cm ⁇ 3 as shown for example in FIG. 15 . Therefore, in silicon carbide semiconductor device 1 of the present invention, the number of interface states that occur when insulating film 13 is formed by dry oxidation (thermal oxidation) or the like at the interface between sidewall 19 of trench 20 and insulating film 13 can be reduced. Accordingly, particularly in a channel directly below insulating film 13 (the portion of sidewall 19 of trench 20 contacting insulating film 13 ), the carrier mobility (channel mobility) can stably be improved.
- FIG. 15 shows an example of the nitrogen concentration in the vicinity of the interface between sidewall 19 of trench 20 and insulating film 13 in silicon carbide semiconductor device 1 with the above-described structure.
- the vertical axis represents the nitrogen concentration (cm ⁇ 3 ) and the horizontal axis represents the distance (nm) from the interface between sidewall 19 of trench 20 and insulating film 13 .
- the portion where the distance (nm) on the horizontal axis is 0 (nm) represents the interface between sidewall 19 of trench 20 and insulating film 13 .
- the extension in the leftward direction with respect to the portion of 0 (nm) on the horizontal axis of the distance (nm) represents extension in the direction toward insulating film 13 side, while the extension in the rightward direction with respect to the portion of 0 (nm) on the horizontal axis of the distance (nm) represents extension in the direction toward sidewall 19 side of trench 20 .
- silicon carbide semiconductor device 1 with the above-described structure has the channel direction in a range of ⁇ 10° relative to the direction orthogonal to the ⁇ 2110> direction in sidewall 19 of trench 20 . Carriers therefore move smoothly in this channel direction, and the carrier mobility in this channel direction and electric current characteristics can be improved. Accordingly, the ON resistance of silicon carbide semiconductor device 1 can be reduced.
- FIG. 16 shows an example of the relation between the channel mobility (relative value) and the angle (°) relative to the ⁇ 2110> direction in sidewall 19 of trench 20 (in the crystal plane tilted by an angle in a range of not less than 50° and not more than 65° relative to the ⁇ 0001 ⁇ plane) of silicon carbide semiconductor device 1 with the above-described structure.
- the vertical axis represents the channel mobility (relative value)
- the horizontal axis represents the angle (°) relative to the ⁇ 2110> direction in sidewall 19 of trench 20 .
- the angle (°) on the horizontal axis in FIG. 16 the angle is not distinguished in terms of the direction of tilt relative to the ⁇ 2110> direction. Therefore, 80° on the horizontal axis for example represents both the direction tilted by +80° relative to the ⁇ 2110> direction and the direction tilted by ⁇ 80° relative to the ⁇ 2110> direction.
- the channel mobility (relative value) on the vertical axis in FIG. 16 is indicated by a relative value with respect to 1 of the channel mobility in the direction orthogonal to the ⁇ 2110> direction in sidewall 19 of trench 20 . Further, the portion where the angle is 90° on the horizontal axis in FIG. 16 indicates the direction orthogonal to the ⁇ 2110> direction in sidewall 19 of trench 20 .
- the channel mobility is highest when the channel direction extends in the direction at an angle of 90° relative to the ⁇ 2110> direction (the direction orthogonal to the ⁇ 2110> direction) in sidewall 19 of trench 20 , while the channel mobility tends to be smaller as a deviation is larger from the direction orthogonal to the ⁇ 2110> direction in sidewall 19 of trench 20 .
- the tendency seen from FIG. 16 is also satisfied by any crystal plane of sidewall 19 of trench 20 that is tilted at an angle in a range of not less than 50° and not more than 65° relative to the ⁇ 0001 ⁇ plane.
- the channel direction orthogonal to the ⁇ 2110> direction in sidewall 19 of trench 20 (crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to the ⁇ 0001 ⁇ plane) (namely the direction of ⁇ 0° orthogonal to the ⁇ 2110> direction).
- the channel direction is a direction at an angle of not less than 80° and not more than 90° relative to the ⁇ 2110> direction in sidewall 19 of trench 20 (namely a direction in a range of ⁇ 10° relative to the direction orthogonal to the ⁇ 2110> direction)
- the channel mobility (relative value) is higher than 0.99. Therefore, even when the channel mobility varies to a certain extent due to a problem or the like in manufacture, the channel mobility would unlikely to be deteriorated to a large extent.
- silicon carbide semiconductor device 1 of the present invention having a channel direction in a range of ⁇ 10° relative to the direction orthogonal to the ⁇ 2110> direction in sidewall 19 of trench 20 , a high channel mobility can be achieved with high reproducibility. Further, in order to achieve a high channel mobility with high reproducibility in silicon carbide semiconductor device 1 of the present invention, it is most preferable that the channel direction is set in the direction orthogonal to the ⁇ 2110> direction in sidewall 19 of trench 20 as described above.
- the present invention may be constructed so that the first conductive type is the p-type and the second conductive type is the n-type in the structure of the above-described silicon carbide semiconductor device 1 .
- a silicon carbide semiconductor device was formed as a vertical trench gate MOSFET of an Example in the following way.
- substrate 11 formed of an n-type silicon carbide crystal (4H-SiC) with a thickness of 400 ⁇ m was prepared.
- substrate 11 had surface 11 a formed of a crystal plane that is a ⁇ 04-4-3 ⁇ plane.
- semiconductor layer 12 (n-type impurity concentration: 5 ⁇ 10 15 cm ⁇ 3 ) formed of an n-type silicon carbide crystal doped with nitrogen as an n-type impurity was epitaxially grown to a thickness of 10 ⁇ m on surface 11 a of substrate 11 by means of CVD (Chemical Vapor Deposition).
- surface 12 a of semiconductor layer 12 was formed of a crystal plane that is a ⁇ 04-4-3 ⁇ plane having the ⁇ 2110> direction and the ⁇ 03-38> direction orthogonal to the ⁇ 2110> direction as shown in FIG. 5 .
- second-conductive-type impurity diffusion layer 14 (p-type impurity concentration: 1 ⁇ 10 17 cm ⁇ 3 ) was formed in surface 12 a of semiconductor layer 12 .
- second-conductive-type impurity diffusion layer 14 was formed by using photolithography and etching to form a patterned oxide film in a region other than the region where second-conductive-type impurity diffusion layer 14 was to be formed in surface 12 a of semiconductor layer 12 , and implanting ions of boron as a p-type impurity using the oxide film as an ion implantation block mask.
- Second-conductive-type impurity diffusion layer 14 was formed in a stripe pattern extending in the ⁇ 2110> direction.
- first-conductive-type impurity diffusion layer 15 (n-type impurity concentration: 5 ⁇ 10 19 cm ⁇ 3 ) and a p+-type region (not shown) (p-type impurity concentration: 3 ⁇ 10 19 cm ⁇ 3 ) were formed.
- first-conductive-type impurity diffusion layer 15 was formed in a stripe pattern extending in the ⁇ 2110> direction
- the p+-type region was formed in a stripe pattern extending in the ⁇ 2110> direction on the outside of first-conductive-type impurity diffusion layer 15 shown in FIG. 7 to contact first-conductive-type impurity diffusion layer 15 .
- First-conductive-type impurity diffusion layer 15 was formed by using photolithography and etching to form a patterned oxide film in a region other than the region where first-conductive-type impurity diffusion layer 15 was to be formed in surface 12 a of semiconductor layer 12 , and implanting ions of phosphorous as an n-type impurity using the oxide film as an ion implantation block mask.
- the p+-type region was also formed by using photolithography and etching to form a patterned oxide film in a region other than the region where the p+-type region was to be formed in surface 12 a of semiconductor layer 12 , and implanting ions of boron as a p-type impurity using the oxide film as an ion implantation block mask.
- an activation annealing treatment was performed by heating semiconductor layer 12 in which second-conductive-type impurity diffusion layer 14 , first-conductive-type impurity diffusion layer 15 , and the p+-type region were formed in the above-described manner, in an argon gas atmosphere at 1700° C. for 30 minutes.
- trench 20 having sidewall 19 was formed in surface 12 a of semiconductor layer 12 .
- Trench 20 may be formed for example by providing an etching mask in a region other than the region where trench 20 was to be formed in surface 12 a of semiconductor layer 12 , and thereafter performing etching perpendicularly to surface 12 a of semiconductor layer 12 to remove the region where the etching mask was not provided and thus trench 20 was to be formed in surface 12 a of semiconductor layer 12 .
- trench 20 was formed in the following way. A defect formed in semiconductor layer 12 was used as a reference to specify the direction orthogonal to the ⁇ -2110> direction. As shown in FIG.
- trench 20 was formed so that the direction of extension of sidewall 19 of trench 20 was included in a range of ⁇ 10° relative to the direction orthogonal to the ⁇ 2110> direction. Accordingly, sidewall 19 of trench 20 was formed of the ⁇ 03-38 ⁇ plane which was a crystal plane tilted at an angle of about 55° relative to the ⁇ 0001 ⁇ plane. Further, sidewall 19 of trench 20 extended perpendicularly to surface 12 a ( ⁇ 04-4-3 ⁇ plane) of semiconductor layer 12 .
- surface 12 a of semiconductor layer 12 was heated in oxygen at 1200° C. for 30 minutes to be dry-oxidized (thermally oxidized) and thereby form insulating film 13 contacting the whole of surface 12 a of semiconductor layer 12 .
- a nitrogen annealing treatment was performed by heating semiconductor layer 12 on which insulating film 13 had been formed, in a nitrogen monoxide (NO) gas atmosphere at 1100° C. for 120 minutes.
- NO nitrogen monoxide
- an inert gas annealing treatment was performed by heating semiconductor layer 12 having undergone the above-described nitrogen annealing treatment, in an argon gas atmosphere at 1100° C. for 60 minutes.
- insulating film 13 was patterned by removing a part of insulating film 13 so that a part of the surface of first-conductive-type impurity diffusion layer 15 and the surface of the p+-type region (not shown) in surface 12 a of semiconductor layer 12 were exposed.
- patterning of insulating film 13 was performed by forming, on the surface of insulating film 13 , an etching mask patterned by photolithography and etching in order to expose a part-to-be-removed of insulating film 13 , and thereafter etching and thereby removing the exposed part of insulating film 13 .
- source electrode 16 was formed that was made of nickel and having its surface in the shape of a regular hexagon as shown in FIG. 14 and a thickness of 0.1 ⁇ m.
- semiconductor layer 12 on which above-described source electrode 16 had been formed was heat-treated for alloying, by being heated in an argon gas atmosphere at 950° C. for two minutes.
- gate electrode 17 was formed that was made of aluminum and having a surface shape as shown in FIG. 14 and a thickness of 1 ⁇ m.
- drain electrode 18 of nickel with a thickness of 0.1 ⁇ m was formed.
- silicon carbide semiconductor device 1 was fabricated as a vertical trench gate MOSFET of the Example.
- Silicon carbide semiconductor device 1 to serve as a vertical trench gate MOSFET of the Example fabricated in the above-described manner had a channel length (the length, along the direction in which sidewall 19 extends, of first-conductive-type impurity diffusion layer 15 exposed on sidewall 19 of trench 20 ) was set to 2 ⁇ m.
- a silicon carbide semiconductor device to serve as a vertical trench gate MOSFET of a Comparative Example was fabricated in a manner similar to the above-described one, except that the channel direction of sidewall 19 of trench 20 in surface 12 a was the ⁇ 2110> direction.
- the distribution, in the depth direction, of the nitrogen concentration in the vicinity of the interface between sidewall 19 of trench 20 and insulating film 13 was measured by SIMS (secondary ion mass spectrometry).
- the maximum value of the nitrogen concentration in the vicinity of the interface between sidewall 19 of trench 20 and insulating film 13 was 1 ⁇ 10 21 cm ⁇ 3 or more in both of respective vertical trench gate MOSFETs of the Example and the Comparative Example. It was thus confirmed that the maximum value of the nitrogen concentration in a region within 10 nm from the interface between sidewall 19 of trench 20 and insulating film 13 was not less than 1 ⁇ 10 21 cm ⁇ 3 in each of respective vertical trench gate MOSFETs of the Example and the Comparative Example.
- the channel mobility was evaluated.
- L represents the channel length
- d represents the thickness of insulating film 13
- W represents the channel width
- ⁇ represents the dielectric constant of insulating film 13 .
- the channel mobility of the vertical trench gate MOSFET of the Example was 100 cm 2 /Vs and the channel mobility of the vertical trench gate MOSFET of the Comparative Example was 40 cm 2 /Vs.
- the channel mobility of the vertical trench gate MOSFET of the Example was 2.5 times as high as the channel mobility of the vertical trench gate MOSFET of the Comparative Example, and accordingly the source-drain current value was 2.5 times. Thus, a significant reduction in ON resistance was confirmed.
- the channel mobility is unlikely to considerably decrease even when the channel mobility varies depending on problems in manufacture, and thus a high channel mobility can be achieved with high reproducibility.
- the present invention can provide a silicon carbide semiconductor device that can achieve a high channel mobility with high reproducibility as well as a method of manufacturing the same, the present invention is suitably applicable for example to a vertical trench gate MOSFET and the like in which SiC is used.
- 1 silicon carbide semiconductor device 11 substrate; 11 a surface; 12 semiconductor layer; 12 a surface; 13 insulating film; 14 second-conductive-type impurity diffusion layer; 15 first-conductive-type impurity diffusion layer; 16 source electrode; 17 gate electrode; 18 drain electrode; 19 sidewall; 20 trench.
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Abstract
A silicon carbide semiconductor device is provided that includes a semiconductor layer made of silicon carbide and having a surface with a trench having a sidewall formed of a crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to the {0001} plane, and an insulating film formed to contact the sidewall of the trench. A maximum value of the nitrogen concentration in a region within 10 nm from the interface between the sidewall of the trench and the insulating film is not less than 1×1021 cm−3, and the semiconductor device has a channel direction in a range of ±10° relative to the direction orthogonal to the <−2110> direction in the sidewall of the trench. A method of manufacturing the silicon carbide semiconductor device is also provided.
Description
- This application is a Continuation of U.S. application Ser. No. 13/130,986, filed on May 24, 2011, which is a 371 National Stage Application of International Application No. PCT/JP2010/051034 filed Jan. 27, 2010. The contents of the foregoing applications are incorporated herein by reference.
- The present invention relates to a silicon carbide semiconductor device and a method of manufacturing thereof, and particularly to a silicon carbide semiconductor device exhibiting excellent electrical characteristics and a method of manufacturing thereof.
- Conventionally, silicon carbide semiconductor devices in which silicon carbide (SiC) is used have been known, and an example of them is disclosed in International Patent Publication WO01/018872 (hereinafter “
Patent Document 1”) for example.Patent Document 1 discloses a MOS-type field effect transistor (MOSFET) that is formed as a silicon carbide semiconductor device using an SiC substrate of the 4H polytype having a surface orientation of substantially {03-38}. According toPatent Document 1 disclosing the MOSFET, a gate oxide film is formed by dry oxidation and a high channel mobility (about 100 cm2/Vs) can be achieved. - In order for a silicon carbide semiconductor device in which SiC is used to stably exhibit its excellent electrical characteristics, it is required to achieve a high channel mobility with high reproducibility.
- The inventors of the present invention have conducted studies to found, however, that even the MOSFET disclosed in
Patent Document 1 may not have a sufficiently high channel mobility depending on the case. - In view of the circumstances above, an object of the present invention is to provide a silicon carbide semiconductor device capable of achieving a high channel mobility with high reproducibility, and a method of manufacturing the same.
- The present invention is a silicon carbide semiconductor device including: a semiconductor layer made of silicon carbide and having a surface with a trench having a sidewall formed of a crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to a {0001} plane; and an insulating film formed to contact the sidewall of the trench, a maximum value of a nitrogen concentration in a region within 10 nm from an interface between the sidewall of the trench and the insulating film is not less than 1×1021 cm−3, and the silicon carbide semiconductor device has a channel direction in a range of ±10° relative to a direction orthogonal to a <−2110> direction in the sidewall of the trench.
- Further, the present invention is a silicon carbide semiconductor device including: a substrate made of silicon carbide of a first conductive type; a semiconductor layer made of silicon carbide of the first conductive type, formed on the substrate, containing a first-conductive-type impurity of a lower concentration than the substrate, and having a surface with a trench having a sidewall formed of a crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to a {0001} plane; a second-conductive-type impurity diffusion layer formed in the sidewall of the trench; a first-conductive-type impurity diffusion layer formed in the surface of the semiconductor layer; an insulating film formed to contact the sidewall of the trench; a source electrode formed to contact at least a part of a region, except for a portion where the insulating film is formed, of the surface of the semiconductor layer; a gate electrode formed on the insulating film; and a drain electrode formed on a surface of the substrate opposite to a surface of the substrate on which the semiconductor layer is formed. A maximum value of a nitrogen concentration in a region within 10 nm from an interface between the sidewall of the trench and the insulating film is not less than 1×1021 cm−3, and the silicon carbide semiconductor device has a channel direction in a range of ±10° relative to a direction orthogonal to a <−2110> direction in the sidewall of the trench.
- Preferably, in the silicon carbide semiconductor device of the present invention, the source electrode has a surface in a stripe pattern.
- Preferably, in the silicon carbide semiconductor device of the present invention, the source electrode has a surface in a honeycomb pattern.
- Preferably, in the silicon carbide semiconductor device of the present invention, the sidewall of the trench is formed of a crystal plane tilted at an angle of ±5° relative to a {03-38} plane.
- Further, the present invention is a method of manufacturing a silicon carbide semiconductor device, including the steps of: forming a trench having a sidewall formed of a crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to a {0001} plane, in a surface of a semiconductor layer made of silicon carbide; forming an insulating film contacting the sidewall of the trench so that a channel direction is set in a range of ±10° relative to a direction orthogonal to a <−2110> direction in the sidewall of the trench; and adjusting a nitrogen concentration so that a maximum value of the nitrogen concentration in a region within 10 nm from an interface between the sidewall of the trench and the insulating film is not less than 1×1021 cm−3.
- Preferably, regarding the method of manufacturing a silicon carbide semiconductor device of the present invention, the channel direction is set in a range of ±10° relative to the direction orthogonal to the <−2110> direction in the sidewall of the trench, based on an orientation of a defect included in the semiconductor layer.
- Preferably, regarding the method of manufacturing a silicon carbide semiconductor device of the present invention, the step of adjusting the nitrogen concentration includes the step of performing a heat treatment in an atmosphere of a gas containing nitrogen, on the semiconductor layer where the insulating film is formed.
- Preferably, regarding the method of manufacturing a silicon carbide semiconductor device of the present invention, the step of adjusting the nitrogen concentration includes the step of performing, on the semiconductor layer having undergone the heat treatment, a heat treatment in an atmosphere of an inert gas.
- The present invention can provide a silicon carbide semiconductor device that can achieve a high channel mobility with high reproducibility, as well as a method of manufacturing the same.
-
FIG. 1 is a schematic cross section of an example of a vertical trench gate MOSFET that is an example of the silicon carbide semiconductor device of the present invention. -
FIG. 2 is a schematic plan view of the silicon carbide semiconductor device shown inFIG. 1 as seen from a gate electrode side. -
FIG. 3 is a schematic cross section illustrating a part of a manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention. -
FIG. 4 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention. -
FIG. 5 is a schematic plan view illustrating an example of a surface of a semiconductor layer of the present invention. -
FIG. 6 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention. -
FIG. 7 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention. -
FIG. 8 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention. -
FIG. 9 is a schematic plan view illustrating an example of the sidewall of a trench in the present invention. -
FIG. 10 is a schematic perspective view illustrating an example of a crystal plane of the sidewall of the trench in the present invention. -
FIG. 11 is a schematic cross section illustrating a preferred example of the crystal plane of the sidewall of the trench in the present invention. -
FIG. 12 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention. -
FIG. 13 is a schematic cross section illustrating a part of the manufacturing process of an example of the method of manufacturing a silicon carbide semiconductor device of the present invention. -
FIG. 14 is a schematic plan view of another example of the silicon carbide semiconductor device of the present invention as seen from the gate electrode side. -
FIG. 15 is a diagram showing an example of a nitrogen concentration distribution in the vicinity of the interface between the sidewall of a trench and an insulating film in an example of the silicon carbide semiconductor device of the present invention. -
FIG. 16 is a diagram showing an example of the relation between an angle (°) relative to the <−2110> direction and a channel mobility (relative value) in the sidewall of the trench in an example of the silicon carbide semiconductor device of the present invention. - An embodiment of the present invention will hereinafter be described. In the drawings of the present invention, the same reference characters denote the same or corresponding parts.
- Where crystal plane and direction are to be expressed, they should actually be expressed with a bar on a required number. Because of restricted expression means, however, they are expressed in the present invention with “-” added before a required number instead of a bar on the required number. Further, in the present invention, an individual orientation is denoted in [ ], a group orientation is denoted in < >, an individual plane is denoted in ( ), and a group plane is denoted in { }.
-
FIG. 1 shows a schematic cross section of an example of a vertical trench gate MOSFET (Metal Oxide Semiconductor Field Effect Transistor) that is an example of the silicon carbide semiconductor device of the present invention. - A silicon
carbide semiconductor device 1 shown inFIG. 1 includes asubstrate 11 made of silicon carbide of n type and 4H-SiC polytype for example, asemiconductor layer 12 made of silicon carbide of n type formed on asurface 11 a ofsubstrate 11, atrench 20 formed in asurface 12 a ofsemiconductor layer 12, a second-conductive-typeimpurity diffusion layer 14 that is a p-type region formed insurface 12 a ofsemiconductor layer 12, a first-conductive-typeimpurity diffusion layer 15 that is an n-type region formed in a surface of second-conductive-type impurity diffusion layer 14 (also insurface 12 a of semiconductor layer 12), aninsulating film 13 formed on a part ofsurface 12 a ofsemiconductor layer 12 to contact asidewall 19 oftrench 20, asource electrode 16 formed in a region ofsurface 12 a ofsemiconductor layer 12 other than a region whereinsulating film 13 is formed, agate electrode 17 formed on a surface ofinsulating film 13, and adrain electrode 18 formed on the back surface ofsubstrate 11. - Here, as
surface 11 a ofsubstrate 11 on whichsemiconductor layer 12 is formed, a crystal plane that is a {04-4-3} plane for example may be used. - Further, as
semiconductor layer 12, a layer such as a layer made of silicon carbide of n type having a lower n-type impurity concentration thansubstrate 11 for example may be used. - Further,
sidewall 19 oftrench 20 formed insurface 12 a ofsemiconductor layer 12 is formed of a crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to the {0001} plane. - Further, as
insulating film 13, a film such as an oxide film formed for example by dry oxidation (thermal oxidation) or the like may be used.Insulating film 13 is not limited to a single-layer structure, and may be of a structure including two or more layers. - Further, as second-conductive-type
impurity diffusion layer 14, a layer such as a p-type region may be used that is formed by diffusing a p-type impurity serving as a second-conductive-type impurity insurface 12 a ofsemiconductor layer 12, for example. Here, as the p-type impurity serving as a second-conductive-type impurity, aluminum, boron, or the like may be used, for example. Furthermore, in at least a part of a region excluding the region where first-conductive-typeimpurity diffusion layer 15 is formed in the surface of second-conductive-typeimpurity diffusion layer 14, a p+-type region containing a p-type impurity serving as a second-conductive-type impurity and having a higher concentration than second-conductive-typeimpurity diffusion layer 14 may be formed. - Further, as first-conductive-type
impurity diffusion layer 15, a layer such as an n-type region that is formed by diffusing an n-type impurity serving as a first-conductive-type impurity insurface 12 a ofsemiconductor layer 12 may be used, for example. The n-type impurity concentration of first-conductive-typeimpurity diffusion layer 15 may be made higher than the n-type impurity concentration ofsemiconductor layer 12. Here, as the n-type impurity serving as a first-conductive-type impurity, nitrogen, phosphorous or the like may be used, for example. - Further, for
source electrode 16,gate electrode 17, anddrain electrode 18 each, a conventionally known metal or the like may be used, for example. - In silicon
carbide semiconductor device 1 shown inFIG. 1 , a maximum value of the nitrogen concentration in a region within 10 nm from the interface betweensidewall 19 oftrench 20 and insulatingfilm 13 is not less than 1×1021 cm−3. Here, the region within 10 nm from the interface betweensidewall 19 oftrench 20 and insulatingfilm 13 refers to a region made up of: a region extending from the interface betweensidewall 19 oftrench 20 and insulatingfilm 13 perpendicularly to the interface towardsidewall 19 side oftrench 20 by 10 nm, and a region extending from the interface betweensidewall 19 oftrench 20 and insulatingfilm 13 perpendicularly to the interface toward insulatingfilm 13 side by 10 nm. -
FIG. 2 shows a schematic plan view of siliconcarbide semiconductor device 1 shown inFIG. 1 as seen fromgate electrode 17 side. Here, the surface ofsource electrode 16 and the surface ofgate electrode 17 are formed to extend in a stripe pattern in the <−2110> direction. Further, along the <03-38> direction which is perpendicular to the <−2110> direction,source electrode 16 andgate electrode 17 are alternately arranged, and onegate electrode 17 is disposed between twosource electrodes 16. Further, from a gap betweensource electrode 16 andgate electrode 17, a surface of insulatingfilm 13 is exposed. Thus, where the surface ofsource electrode 16 has the stripe pattern, the channel direction tends to be set easily in a range of ±10° relative to the direction orthogonal to the <−2110> direction, in sidewall 19 (crystal plane tilted by an angle in a range of not less than 50° and not more than 65° relative to the {0001} plane) oftrench 20 as described later herein. In the present invention, the channel direction means the direction in which carriers move insidewall 19 oftrench 20. - Here, the channel direction of silicon
carbide semiconductor device 1 with the above-described structure is set to be included in a range of ±10° relative to the direction orthogonal to the <−2110> direction, insidewall 19 oftrench 20 that is formed of a crystal plane tilted by an angle in a range of not less than 50° and not more than 65° relative to the {0001} plane. - In the following, a description will be given of an example of the method of manufacturing silicon
carbide semiconductor device 1 having the above-described structure. First, as shown in a schematic cross section ofFIG. 3 ,substrate 11 made of silicon carbide (4H-SiC) havingsurface 11 a formed of a crystal plane that is a {04-4-3} plane for example is prepared. - Next, as shown in a schematic cross section of
FIG. 4 ,semiconductor layer 12 is formed onsurface 11 a ofsubstrate 11. - Here,
semiconductor layer 12 may be formed for example by epitaxial growth or the like ofsemiconductor layer 12 made of n-type silicon carbide having an n-type impurity with a lower concentration thansubstrate 11, onsurface 11 a ofsubstrate 11. Wheresemiconductor layer 12 is formed by the above-described epitaxial growth, surface 12 a ofsemiconductor layer 12 is allowed to have the same crystal plane assurface 11 a ofsubstrate 11. Therefore, ifsurface 11 a ofsubstrate 11 is formed for example of a crystal plane that is a {04-4-3} plane, surface 12 a ofsemiconductor layer 12 is allowed to have a crystal plane that is a {04-4-3} plane as well, as shown in the schematic plan view ofFIG. 5 for example. - Next, as shown in a schematic cross section of
FIG. 6 , second-conductive-typeimpurity diffusion layer 14 is formed insurface 12 a ofsemiconductor layer 12. In this example, second-conductive-typeimpurity diffusion layer 14 is formed in a stripe pattern extending in the <−2110> direction. Second-conductive-typeimpurity diffusion layer 14, however, is not limited to this form. - Here, second-conductive-type
impurity diffusion layer 14 may be formed for example by ion implantation or the like in which ions of a p-type impurity serving as a second-conductive-type impurity are implanted intosurface 12 a ofsemiconductor layer 12, after an ion implantation block mask is placed in a region other than the region where second-conductive-typeimpurity diffusion layer 14 is to be formed insurface 12 a ofsemiconductor layer 12. As the ion implantation block mask, an oxide film or the like that has been patterned by photolithography and etching for example may be used. - Next, as shown in a schematic cross section of
FIG. 7 , first-conductive-typeimpurity diffusion layer 15 is formed in a surface of second-conductive-typeimpurity diffusion layer 14 formed in the above-described manner. In this example, first-conductive-typeimpurity diffusion layer 15 is also formed in a stripe pattern extending in the <−2110> direction. First-conductive-typeimpurity diffusion layer 15, however, is not limited to this form. - Here, first-conductive-type
impurity diffusion layer 15 may be formed for example by ion implantation or the like in which ions of an n-type impurity serving as a first-conductive-type impurity are implanted intosurface 12 a ofsemiconductor layer 12, after an ion implantation block mask is placed in a region other than the region where first-conductive-typeimpurity diffusion layer 15 is to be formed insurface 12 a ofsemiconductor layer 12. As the ion implantation block mask, an oxide film or the like that has been patterned by photolithography and etching for example may be used as well. - Next, an activation annealing treatment is performed on
semiconductor layer 12 in which second-conductive-typeimpurity diffusion layer 14 and first-conductive-typeimpurity diffusion layer 15 have been formed in the above-described manner. Accordingly, the p-type impurity serving as a second-conductive-type impurity in second-conductive-typeimpurity diffusion layer 14 as well as the n-type impurity serving as a first-conductive-type impurity in first-conductive-typeimpurity diffusion layer 15 that have been introduced by the above-described ion implantation can be activated. - Here, the activation annealing treatment may be performed for example in an argon gas atmosphere by
heating semiconductor layer 12 in which second-conductive-typeimpurity diffusion layer 14 and first-conductive-typeimpurity diffusion layer 15 have been formed, at a temperature of approximately 1700° C. for approximately 30 minutes, for example. - Next, as shown in a schematic cross section of
FIG. 8 ,trench 20 havingsidewall 19 is formed insurface 12 a ofsemiconductor layer 12.Trench 20 may be formed for example by providing an etching mask in a region other than the region wheretrench 20 is to be formed insurface 12 a ofsemiconductor layer 12, and thereafter etching and thereby removing the region ofsurface 12 a ofsemiconductor layer 12 where the etching mask is not provided. - Here, in the case where the channel direction is to be made coincident with the direction in which sidewall 19 of
trench 20 extends, for example, it is preferable to specify the direction orthogonal to the <−2110> direction with respect to a defect formed insemiconductor layer 12, andform trench 20 as shown for example in a schematic plan view ofFIG. 9 so that the direction in which sidewall 19 oftrench 20 extends (the upward direction inFIG. 9 ) is included in a range of ±10° relative to the direction orthogonal to the <−2110> direction. - The above is for the following reason. In the process of manufacturing silicon
carbide semiconductor device 1, a defect could be formed at a certain portion ofsemiconductor layer 12. Therefore, the position of the defect formed at a certain portion ofsemiconductor layer 12 may be used as a reference. Then, where the channel direction is to be made coincident with the direction in which sidewall 19 oftrench 20 extends for example,trench 20 can be formed easily so that the direction in which sidewall 19 oftrench 20 extends is included in a range of ±10° relative to the direction orthogonal to the <−2110> direction. - Further, as shown for example in a schematic perspective view of
FIG. 10 ,sidewall 19 oftrench 20 is formed of a crystal plane (hatched portion inFIG. 10 ) that is tilted at an angle α° in a range of not less than 50° and not more than 65° relative to the {0001} plane. Preferably, the crystal plane ofsidewall 19 oftrench 20 is also tilted at an angle in a range of ±5° relative to the {03-38} plane as shown for example in a schematic cross section ofFIG. 11 . In the case wheresidewall 19 oftrench 20 is a crystal plane tilted at an angle in a range of ±5° relative to the {03-38} plane, electrical characteristics such as channel mobility of siliconcarbide semiconductor device 1 tend to be improved. In order to further improve electrical characteristics such as channel mobility of siliconcarbide semiconductor device 1, preferably sidewall 19 oftrench 20 is a crystal plane tilted at an angle in a range of ±3° relative to the {03-38} plane, and most preferably sidewall 19 oftrench 20 is the {03-38} plane. As is evident, a crystal plane tilted at an angle in a range of ±5° relative to the {03-38} plane and a crystal plane tilted at an angle in a range of ±3° relative to the {03-38} plane each include the {03-38} plane. - Next, as shown in a schematic cross section of
FIG. 12 , insulatingfilm 13 is formed to contactsidewall 19 oftrench 20 formed in the above-described manner. Insulatingfilm 13 can be formed to contactsidewall 19 oftrench 20 that extends in the direction as controlled so that the direction in which sidewall 19 oftrench 20 extends is included in a range of ±10° relative to the direction orthogonal to the <−2110> direction, and thereby set the channel direction in a range of ±10° relative to the direction orthogonal to the <−2110> direction. - Here, as insulating
film 13, an oxide film or the like formed for example by dry oxidation (thermal oxidation) or the like may be used. Specifically, dry oxidation (thermal oxidation) may be performed for example in oxygen byheating surface 12 a ofsemiconductor layer 12 in whichtrench 20 has been formed as described above, at a temperature of approximately 1200° C. for approximately 30 minutes for example. - Next, a nitrogen annealing treatment is performed on
semiconductor layer 12 where above-described insulatingfilm 13 has been formed. In this way, the nitrogen concentration is adjusted so that a maximum value of the nitrogen concentration in a region within 10 nm from the interface betweensidewall 19 oftrench 20 and insulatingfilm 13 is not less than 1×1021 cm−3. - Here, in the above-described nitrogen annealing treatment,
semiconductor layer 12 where above-described insulatingfilm 13 has been formed is heated for example in an atmosphere of a gas containing nitrogen such as nitrogen monoxide (NO) gas at a temperature of approximately 1100° C. for approximately 120 minutes for example. In this way, a maximum value of the nitrogen concentration in the region within 10 nm from the interface betweensidewall 19 oftrench 20 and insulatingfilm 13 can be set to 1×1021 cm−3 or more. - It is preferable to further perform an inert gas annealing treatment on
semiconductor layer 12 having undergone the above-described nitrogen annealing treatment, in an atmosphere of an inert gas such as argon gas for example. In the case where the above-described inert gas annealing treatment is performed onsemiconductor layer 12 having undergone the above-described nitrogen annealing treatment, there is a higher tendency for siliconcarbide semiconductor device 1 to be able to achieve a high channel mobility with high reproducibility. - Here, the above-described inert gas annealing treatment may be performed for example in an argon gas atmosphere by
heating semiconductor layer 12 having undergone the above-described nitrogen annealing treatment, at a temperature of approximately 1100° C. for approximately 60 minutes for example. - Next, as shown in a schematic cross section of
FIG. 13 , a part of insulatingfilm 13 formed as described above is removed topattern insulating film 13. - Here, patterning of insulating
film 13 is performed by removing a part of insulatingfilm 13 so that at least a part of the surface of first-conductive-typeimpurity diffusion layer 15 insurface 12 a ofsemiconductor layer 12 is exposed. - Further, a part of insulating
film 13 may be removed for example by forming, on the surface of insulatingfilm 13, an etching mask patterned by means of photolithography and etching for exposing a part to be removed of insulatingfilm 13, for example, and thereafter etching and thereby removing the exposed part of insulatingfilm 13. - Next, as shown in
FIG. 1 ,source electrode 16 is formed to contact the exposed surface of first-conductive-typeimpurity diffusion layer 15 insurface 12 a ofsemiconductor layer 12 that is exposed from the part where insulatingfilm 13 has been removed. - Here,
source electrode 16 may be formed for example by performing sputtering for example to form an electrically conductive film made of a metal such as nickel for example, onsurface 12 a ofsemiconductor layer 12 exposed after the above-described etching of insulatingfilm 13 and on the surface of the above-described etching mask, and thereafter removing this etching mask. In other words, the conductive film formed on the surface of the etching mask is removed (lifted off) together with the etching mask while only the conductive film formed onsurface 12 a ofsemiconductor layer 12 is left to serve assource electrode 16. - Preferably, a heat treatment for achieving alloying is performed on
semiconductor layer 12 on which above-describedsource electrode 16 has been formed. - Here, the heat treatment for achieving alloying may be performed for example in an atmosphere of an inert gas such as argon gas by
heating semiconductor layer 12 on which above-describedsource electrode 16 has been formed, at a temperature of approximately 950° C. for approximately two minutes for example. - Next, as shown in
FIG. 1 ,gate electrode 17 is formed on a surface of insulatingfilm 13. Here,gate electrode 17 may be formed for example by performing photolithography and etching or the like to form a resist mask having an opening corresponding to a portion wheregate electrode 17 is to be formed and covering respective entire surfaces of insulatingfilm 13 andsource electrode 16, then performing for example sputtering or the like to form an electrically conductive film made of a metal such as aluminum for example, on the surface of the resist mask and on the surface of insulatingfilm 13 that is exposed from the opening of the resist mask, and thereafter removing this resist mask. In other words, the conductive film formed on the surface of the resist mask is removed (lifted off) together with the resist mask while only the conductive film formed on the surface of insulatingfilm 13 is left to serve asgate electrode 17. - Next, as shown in
FIG. 1 ,drain electrode 18 is formed on the back surface ofsubstrate 11. Here,drain electrode 18 may be formed for example by performing for example sputtering or the like to form an electrically conductive film made of a metal such as nickel for example, on the back surface ofsubstrate 11. - In this way, silicon
carbide semiconductor device 1 with the structure shown inFIG. 1 can be manufactured. - In silicon
carbide semiconductor device 1 of the present invention, the surface ofsource electrode 16 may be formed in a honeycomb pattern and a region except for a partial region surrounding the outer periphery ofsource electrode 16 may be formed asgate electrode 17 as shown for example in a schematic plan view ofFIG. 14 . - In the case where the surface of
source electrode 16 is formed in a honeycomb pattern as described above, the surface of eachsource electrode 16 is formed in the shape of a hexagon. In particular, the surface ofsource electrode 16 is preferably formed in the shape of a regular hexagon. In the case where eachsource electrode 16 has its surface formed in the shape of a regular hexagon, the possible number of siliconcarbide semiconductor devices 1 to be formed fromsubstrate 11 of the same size can be increased. Therefore, there is a tendency that siliconcarbide semiconductor device 1 having a high channel mobility can be fabricated with higher reproducibility and at a higher manufacturing efficiency. In this case, second-conductive-typeimpurity diffusion layer 14 and first-conductive-typeimpurity diffusion layer 15 may also be formed in a hexagonal shape such as regular hexagonal shape. - Other features of silicon
carbide semiconductor device 1 havingsource electrode 16 andgate electrode 17 structured as shown inFIG. 14 may be similar to the above-described ones. - In silicon
carbide semiconductor device 1 structured in the above-described manner, when a negative voltage is applied to sourceelectrode 16 and a positive voltage is applied togate electrode 17 anddrain electrode 18 for example, carriers (electrons in the above-described example) injected fromsource electrode 16 move to drainelectrode 18 through the surface of first-conductive-typeimpurity diffusion layer 15,sidewall 19 oftrench 20, the inside ofsemiconductor layer 12, and the inside ofsubstrate 11. - If a negative voltage is applied to source
electrode 16 and a positive voltage is applied to drainelectrode 18 while the positive voltage is not applied togate electrode 17, carriers (electrons in the above-described example) injected fromsource electrode 16 will be restricted in movement in the surface of second-conductive-typeimpurity diffusion layer 14 insidewall 19 oftrench 20. - In silicon
carbide semiconductor device 1 of the present invention, a maximum value of the nitrogen concentration in a region within 10 nm from the interface betweensidewall 19 oftrench 20 and insulatingfilm 13 is not less than 1×1021 cm−3 as shown for example inFIG. 15 . Therefore, in siliconcarbide semiconductor device 1 of the present invention, the number of interface states that occur when insulatingfilm 13 is formed by dry oxidation (thermal oxidation) or the like at the interface betweensidewall 19 oftrench 20 and insulatingfilm 13 can be reduced. Accordingly, particularly in a channel directly below insulating film 13 (the portion ofsidewall 19 oftrench 20 contacting insulating film 13), the carrier mobility (channel mobility) can stably be improved. -
FIG. 15 shows an example of the nitrogen concentration in the vicinity of the interface betweensidewall 19 oftrench 20 and insulatingfilm 13 in siliconcarbide semiconductor device 1 with the above-described structure. Here, inFIG. 15 , the vertical axis represents the nitrogen concentration (cm−3) and the horizontal axis represents the distance (nm) from the interface betweensidewall 19 oftrench 20 and insulatingfilm 13. Further, inFIG. 15 , the portion where the distance (nm) on the horizontal axis is 0 (nm) represents the interface betweensidewall 19 oftrench 20 and insulatingfilm 13. The extension in the leftward direction with respect to the portion of 0 (nm) on the horizontal axis of the distance (nm) represents extension in the direction toward insulatingfilm 13 side, while the extension in the rightward direction with respect to the portion of 0 (nm) on the horizontal axis of the distance (nm) represents extension in the direction towardsidewall 19 side oftrench 20. - Further, silicon
carbide semiconductor device 1 with the above-described structure has the channel direction in a range of ±10° relative to the direction orthogonal to the <−2110> direction insidewall 19 oftrench 20. Carriers therefore move smoothly in this channel direction, and the carrier mobility in this channel direction and electric current characteristics can be improved. Accordingly, the ON resistance of siliconcarbide semiconductor device 1 can be reduced. -
FIG. 16 shows an example of the relation between the channel mobility (relative value) and the angle (°) relative to the <−2110> direction insidewall 19 of trench 20 (in the crystal plane tilted by an angle in a range of not less than 50° and not more than 65° relative to the {0001} plane) of siliconcarbide semiconductor device 1 with the above-described structure. InFIG. 16 , the vertical axis represents the channel mobility (relative value) and the horizontal axis represents the angle (°) relative to the <−2110> direction insidewall 19 oftrench 20. As to the angle (°) on the horizontal axis inFIG. 16 , the angle is not distinguished in terms of the direction of tilt relative to the <−2110> direction. Therefore, 80° on the horizontal axis for example represents both the direction tilted by +80° relative to the <−2110> direction and the direction tilted by −80° relative to the <−2110> direction. - The channel mobility (relative value) on the vertical axis in
FIG. 16 is indicated by a relative value with respect to 1 of the channel mobility in the direction orthogonal to the <−2110> direction insidewall 19 oftrench 20. Further, the portion where the angle is 90° on the horizontal axis inFIG. 16 indicates the direction orthogonal to the <−2110> direction insidewall 19 oftrench 20. - As shown in
FIG. 16 , it is seen that the channel mobility is highest when the channel direction extends in the direction at an angle of 90° relative to the <−2110> direction (the direction orthogonal to the <−2110> direction) insidewall 19 oftrench 20, while the channel mobility tends to be smaller as a deviation is larger from the direction orthogonal to the <−2110> direction insidewall 19 oftrench 20. The tendency seen fromFIG. 16 is also satisfied by any crystal plane ofsidewall 19 oftrench 20 that is tilted at an angle in a range of not less than 50° and not more than 65° relative to the {0001} plane. - Thus, in order to achieve a high channel mobility, it would be most preferable to have the channel direction orthogonal to the <−2110> direction in
sidewall 19 of trench 20 (crystal plane tilted at an angle in a range of not less than 50° and not more than 65° relative to the {0001} plane) (namely the direction of ±0° orthogonal to the <−2110> direction). - However, as shown in
FIG. 16 , in the case where the channel direction is a direction at an angle of not less than 80° and not more than 90° relative to the <−2110> direction insidewall 19 of trench 20 (namely a direction in a range of ±10° relative to the direction orthogonal to the <−2110> direction), the channel mobility (relative value) is higher than 0.99. Therefore, even when the channel mobility varies to a certain extent due to a problem or the like in manufacture, the channel mobility would unlikely to be deteriorated to a large extent. - As seen from the above, in silicon
carbide semiconductor device 1 of the present invention having a channel direction in a range of ±10° relative to the direction orthogonal to the <−2110> direction insidewall 19 oftrench 20, a high channel mobility can be achieved with high reproducibility. Further, in order to achieve a high channel mobility with high reproducibility in siliconcarbide semiconductor device 1 of the present invention, it is most preferable that the channel direction is set in the direction orthogonal to the <−2110> direction insidewall 19 oftrench 20 as described above. - While the above description refers to the n-type as the first conductive type and the p-type as the second conductive type, the present invention may be constructed so that the first conductive type is the p-type and the second conductive type is the n-type in the structure of the above-described silicon
carbide semiconductor device 1. - Fabrication of Vertical Trench Gate MOSFET
- A silicon carbide semiconductor device was formed as a vertical trench gate MOSFET of an Example in the following way.
- First, as shown in
FIG. 3 ,substrate 11 formed of an n-type silicon carbide crystal (4H-SiC) with a thickness of 400 μm was prepared. Here,substrate 11 hadsurface 11 a formed of a crystal plane that is a {04-4-3} plane. - Next, as shown in
FIG. 4 , semiconductor layer 12 (n-type impurity concentration: 5×1015 cm−3) formed of an n-type silicon carbide crystal doped with nitrogen as an n-type impurity was epitaxially grown to a thickness of 10 μm onsurface 11 a ofsubstrate 11 by means of CVD (Chemical Vapor Deposition). - Here, surface 12 a of
semiconductor layer 12 was formed of a crystal plane that is a {04-4-3} plane having the <−2110> direction and the <03-38> direction orthogonal to the <−2110> direction as shown inFIG. 5 . - Next, as shown in
FIG. 6 , second-conductive-type impurity diffusion layer 14 (p-type impurity concentration: 1×1017 cm−3) was formed insurface 12 a ofsemiconductor layer 12. Here, second-conductive-typeimpurity diffusion layer 14 was formed by using photolithography and etching to form a patterned oxide film in a region other than the region where second-conductive-typeimpurity diffusion layer 14 was to be formed insurface 12 a ofsemiconductor layer 12, and implanting ions of boron as a p-type impurity using the oxide film as an ion implantation block mask. Second-conductive-typeimpurity diffusion layer 14 was formed in a stripe pattern extending in the <−2110> direction. - Next, as shown in
FIG. 7 , in a surface of second-conductive-typeimpurity diffusion layer 14 formed in the above-described manner, first-conductive-type impurity diffusion layer 15 (n-type impurity concentration: 5×1019 cm−3) and a p+-type region (not shown) (p-type impurity concentration: 3×1019 cm−3) were formed. Here, first-conductive-typeimpurity diffusion layer 15 was formed in a stripe pattern extending in the <−2110> direction, and the p+-type region was formed in a stripe pattern extending in the <−2110> direction on the outside of first-conductive-typeimpurity diffusion layer 15 shown inFIG. 7 to contact first-conductive-typeimpurity diffusion layer 15. - First-conductive-type
impurity diffusion layer 15 was formed by using photolithography and etching to form a patterned oxide film in a region other than the region where first-conductive-typeimpurity diffusion layer 15 was to be formed insurface 12 a ofsemiconductor layer 12, and implanting ions of phosphorous as an n-type impurity using the oxide film as an ion implantation block mask. The p+-type region was also formed by using photolithography and etching to form a patterned oxide film in a region other than the region where the p+-type region was to be formed insurface 12 a ofsemiconductor layer 12, and implanting ions of boron as a p-type impurity using the oxide film as an ion implantation block mask. - Next, an activation annealing treatment was performed by
heating semiconductor layer 12 in which second-conductive-typeimpurity diffusion layer 14, first-conductive-typeimpurity diffusion layer 15, and the p+-type region were formed in the above-described manner, in an argon gas atmosphere at 1700° C. for 30 minutes. - Next, as shown in
FIG. 8 ,trench 20 havingsidewall 19 was formed insurface 12 a ofsemiconductor layer 12.Trench 20 may be formed for example by providing an etching mask in a region other than the region wheretrench 20 was to be formed insurface 12 a ofsemiconductor layer 12, and thereafter performing etching perpendicularly to surface 12 a ofsemiconductor layer 12 to remove the region where the etching mask was not provided and thus trench 20 was to be formed insurface 12 a ofsemiconductor layer 12. Here,trench 20 was formed in the following way. A defect formed insemiconductor layer 12 was used as a reference to specify the direction orthogonal to the <-2110> direction. As shown inFIG. 9 , in order to allow the channel direction to be coincident with the direction in which sidewall 19 oftrench 20 extends,trench 20 was formed so that the direction of extension ofsidewall 19 oftrench 20 was included in a range of ±10° relative to the direction orthogonal to the <−2110> direction. Accordingly, sidewall 19 oftrench 20 was formed of the {03-38} plane which was a crystal plane tilted at an angle of about 55° relative to the {0001} plane. Further, sidewall 19 oftrench 20 extended perpendicularly to surface 12 a ({04-4-3} plane) ofsemiconductor layer 12. - Next, as shown in
FIG. 12 ,surface 12 a ofsemiconductor layer 12 was heated in oxygen at 1200° C. for 30 minutes to be dry-oxidized (thermally oxidized) and thereby form insulatingfilm 13 contacting the whole ofsurface 12 a ofsemiconductor layer 12. - Next, a nitrogen annealing treatment was performed by
heating semiconductor layer 12 on which insulatingfilm 13 had been formed, in a nitrogen monoxide (NO) gas atmosphere at 1100° C. for 120 minutes. - Next, an inert gas annealing treatment was performed by
heating semiconductor layer 12 having undergone the above-described nitrogen annealing treatment, in an argon gas atmosphere at 1100° C. for 60 minutes. - Next, as shown in
FIG. 13 , insulatingfilm 13 was patterned by removing a part of insulatingfilm 13 so that a part of the surface of first-conductive-typeimpurity diffusion layer 15 and the surface of the p+-type region (not shown) insurface 12 a ofsemiconductor layer 12 were exposed. Here, patterning of insulatingfilm 13 was performed by forming, on the surface of insulatingfilm 13, an etching mask patterned by photolithography and etching in order to expose a part-to-be-removed of insulatingfilm 13, and thereafter etching and thereby removing the exposed part of insulatingfilm 13. - Next, on the surface of first-conductive-type
impurity diffusion layer 15 and the surface of the p+-type region (not shown) that have been exposed from the portion where insulatingfilm 13 was removed,source electrode 16 was formed that was made of nickel and having its surface in the shape of a regular hexagon as shown inFIG. 14 and a thickness of 0.1 μm. - Next,
semiconductor layer 12 on which above-describedsource electrode 16 had been formed was heat-treated for alloying, by being heated in an argon gas atmosphere at 950° C. for two minutes. - Next, on the surface of insulating
film 13,gate electrode 17 was formed that was made of aluminum and having a surface shape as shown inFIG. 14 and a thickness of 1 μm. - Next, on the whole of the rear surface of
substrate 11,drain electrode 18 of nickel with a thickness of 0.1 μm was formed. - In this way, silicon
carbide semiconductor device 1 was fabricated as a vertical trench gate MOSFET of the Example. - Silicon
carbide semiconductor device 1 to serve as a vertical trench gate MOSFET of the Example fabricated in the above-described manner had a channel length (the length, along the direction in which sidewall 19 extends, of first-conductive-typeimpurity diffusion layer 15 exposed onsidewall 19 of trench 20) was set to 2 μm. - Further, for comparison's sake, a silicon carbide semiconductor device to serve as a vertical trench gate MOSFET of a Comparative Example was fabricated in a manner similar to the above-described one, except that the channel direction of
sidewall 19 oftrench 20 insurface 12 a was the <−2110> direction. - Evaluation of Vertical Trench Gate MOSFET
- For the vertical trench gate MOSFETs of the Example and the Comparative Example fabricated in the above-described manner, the distribution, in the depth direction, of the nitrogen concentration in the vicinity of the interface between
sidewall 19 oftrench 20 and insulatingfilm 13 was measured by SIMS (secondary ion mass spectrometry). - As a result, it was found that the maximum value of the nitrogen concentration in the vicinity of the interface between
sidewall 19 oftrench 20 and insulatingfilm 13 was 1×1021 cm−3 or more in both of respective vertical trench gate MOSFETs of the Example and the Comparative Example. It was thus confirmed that the maximum value of the nitrogen concentration in a region within 10 nm from the interface betweensidewall 19 oftrench 20 and insulatingfilm 13 was not less than 1×1021 cm−3 in each of respective vertical trench gate MOSFETs of the Example and the Comparative Example. - Further, for the vertical trench gate MOSFETs of the Example and the Comparative Example, the channel mobility was evaluated. For evaluating the channel mobility, the following method was used. First, under the condition that the source-drain voltage was VDS=0.1 V, a gate voltage VG was applied to measure a source-drain current IDS (to measure the gate voltage dependency). Then, Expression (1) below where gm=(δIDS)/(δVG) was used to determine the maximum value of the channel mobility for the gate voltage, and the maximum value was calculated as the channel mobility.
-
Channel mobility μ=gm×(L×d)/(W×ε×VDS) (1) - In Expression (1) above, L represents the channel length, d represents the thickness of insulating
film 13, W represents the channel width, and ε represents the dielectric constant of insulatingfilm 13. - Consequently, it was found that the channel mobility of the vertical trench gate MOSFET of the Example was 100 cm2/Vs and the channel mobility of the vertical trench gate MOSFET of the Comparative Example was 40 cm2/Vs.
- As seen from the above, the channel mobility of the vertical trench gate MOSFET of the Example was 2.5 times as high as the channel mobility of the vertical trench gate MOSFET of the Comparative Example, and accordingly the source-drain current value was 2.5 times. Thus, a significant reduction in ON resistance was confirmed.
- It is therefore considered that in the structure of the vertical trench gate MOSFET of the Example, the channel mobility is unlikely to considerably decrease even when the channel mobility varies depending on problems in manufacture, and thus a high channel mobility can be achieved with high reproducibility.
- It should be construed that embodiments and examples disclosed herein are by way of illustration in all respects, not by way of limitation. It is intended that the scope of the present invention is defined by claims, not by the description above, and encompasses all modifications and variations equivalent in meaning and scope to the claims.
- Since the present invention can provide a silicon carbide semiconductor device that can achieve a high channel mobility with high reproducibility as well as a method of manufacturing the same, the present invention is suitably applicable for example to a vertical trench gate MOSFET and the like in which SiC is used.
- 1 silicon carbide semiconductor device; 11 substrate; 11 a surface; 12 semiconductor layer; 12 a surface; 13 insulating film; 14 second-conductive-type impurity diffusion layer; 15 first-conductive-type impurity diffusion layer; 16 source electrode; 17 gate electrode; 18 drain electrode; 19 sidewall; 20 trench.
Claims (10)
1-9. (canceled)
10. A method of manufacturing a silicon carbide semiconductor device, comprising the steps of:
forming an insulating film contacting a semiconductor layer made of silicon carbide; and
adjusting a nitrogen concentration so that a maximum value of the nitrogen concentration in a region within 10 nm from an interface between said semiconductor layer and said insulating film is not less than 1×1021 cm−3.
11. The method of manufacturing a silicon carbide semiconductor device according to claim 10 , further comprising the step of annealing said semiconductor layer in an atmosphere of an inert gas after said adjusting.
12. The method of manufacturing a silicon carbide semiconductor device according to claim 11 , further comprising the step of forming a gate electrode on said insulating film after said annealing.
13. The method of manufacturing a silicon carbide semiconductor device according to claim 11 , further comprising the step of forming an electrode to contact said semiconductor layer after said annealing.
14. The method of manufacturing a silicon carbide semiconductor device according to claim 13 , wherein said electrode is a source electrode.
15. The method of manufacturing a silicon carbide semiconductor device according to claim 11 , wherein said inert gas includes an argon gas.
16. The method of manufacturing a silicon carbide semiconductor device according to claim 11 , wherein said annealing is performed at a temperature of approximately 1100° C.
17. The method of manufacturing a silicon carbide semiconductor device according to claim 10 , wherein said step of adjusting the nitrogen concentration includes the step of performing a heat treatment in an atmosphere of a gas containing nitrogen, on said semiconductor layer where said insulating film is formed.
18. The method of manufacturing a silicon carbide semiconductor device according to claim 10 , further comprising the step of forming a trench having a sidewall, wherein
said step of forming the insulating film is performed so that said insulating film contacts said sidewall of said trench.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US13/858,904 US20130224941A1 (en) | 2008-07-31 | 2013-04-08 | Silicon carbide semiconductor device and method of manufacturing thereof |
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JP2008198351A JP5298691B2 (en) | 2008-07-31 | 2008-07-31 | Silicon carbide semiconductor device and manufacturing method thereof |
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PCT/JP2010/051034 WO2011092808A1 (en) | 2010-01-27 | 2010-01-27 | Silicon carbide semiconductor device and production method therefor |
US201113130986A | 2011-05-24 | 2011-05-24 | |
US13/858,904 US20130224941A1 (en) | 2008-07-31 | 2013-04-08 | Silicon carbide semiconductor device and method of manufacturing thereof |
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US201113130986A Continuation | 2008-07-31 | 2011-05-24 |
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EP (1) | EP2530718B1 (en) |
JP (1) | JPWO2011092808A1 (en) |
KR (1) | KR20120107838A (en) |
CN (1) | CN102725849B (en) |
CA (1) | CA2740244A1 (en) |
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US8872188B2 (en) | 2010-01-19 | 2014-10-28 | Sumitomo Electric Industries, Ltd. | Silicon carbide semiconductor device and method of manufacturing thereof |
US9318558B2 (en) * | 2012-07-09 | 2016-04-19 | Hitachi, Ltd. | MOS field effect transistor |
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JP6119100B2 (en) * | 2012-02-01 | 2017-04-26 | 住友電気工業株式会社 | Silicon carbide semiconductor device |
JP2013165197A (en) * | 2012-02-13 | 2013-08-22 | Sumitomo Electric Ind Ltd | Silicon carbide semiconductor device and silicon carbide semiconductor device manufacturing method |
JP5867134B2 (en) | 2012-02-13 | 2016-02-24 | 住友電気工業株式会社 | Method for manufacturing silicon carbide semiconductor device |
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JP6237046B2 (en) * | 2013-09-25 | 2017-11-29 | 住友電気工業株式会社 | Silicon carbide semiconductor device and manufacturing method thereof |
JP2015072944A (en) * | 2013-10-01 | 2015-04-16 | 住友電気工業株式会社 | Silicon carbide semiconductor device and manufacturing method of the same |
JP2015156429A (en) * | 2014-02-20 | 2015-08-27 | 住友電気工業株式会社 | Silicon carbide semiconductor device and manufacturing method of the same |
JP6301795B2 (en) * | 2014-09-19 | 2018-03-28 | 株式会社東芝 | Semiconductor device |
DE102015103067B3 (en) * | 2015-03-03 | 2016-09-01 | Infineon Technologies Ag | SEMICONDUCTOR DEVICE WITH TRENCHGATE STRUCTURES IN A SEMICONDUCTOR BODY WITH HEXAGONAL CRYSTAL GRILLE |
KR102335489B1 (en) * | 2016-12-13 | 2021-12-03 | 현대자동차 주식회사 | Semiconductor device and method manufacturing the same |
CN115513297B (en) * | 2022-11-09 | 2023-09-22 | 中芯越州集成电路制造(绍兴)有限公司 | Silicon carbide planar MOSFET device and method of manufacturing the same |
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Also Published As
Publication number | Publication date |
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CA2740244A1 (en) | 2011-07-27 |
US8450750B2 (en) | 2013-05-28 |
EP2530718A1 (en) | 2012-12-05 |
JPWO2011092808A1 (en) | 2013-05-30 |
CN102725849B (en) | 2015-09-09 |
EP2530718A4 (en) | 2014-01-01 |
EP2530718B1 (en) | 2019-10-23 |
US20110297963A1 (en) | 2011-12-08 |
CN102725849A (en) | 2012-10-10 |
KR20120107838A (en) | 2012-10-04 |
WO2011092808A1 (en) | 2011-08-04 |
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