US20180366571A1 - Semiconductor device - Google Patents
Semiconductor device Download PDFInfo
- Publication number
- US20180366571A1 US20180366571A1 US15/912,028 US201815912028A US2018366571A1 US 20180366571 A1 US20180366571 A1 US 20180366571A1 US 201815912028 A US201815912028 A US 201815912028A US 2018366571 A1 US2018366571 A1 US 2018366571A1
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- United States
- Prior art keywords
- semiconductor layer
- region
- semiconductor device
- semiconductor
- electrode
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 239000004065 semiconductor Substances 0.000 title claims abstract description 250
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims abstract description 28
- 229910010271 silicon carbide Inorganic materials 0.000 claims abstract description 26
- 150000004767 nitrides Chemical class 0.000 claims abstract description 11
- 239000012535 impurity Substances 0.000 claims description 22
- 229910052782 aluminium Inorganic materials 0.000 claims description 8
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- 229910052719 titanium Inorganic materials 0.000 claims description 5
- 229910052737 gold Inorganic materials 0.000 claims description 4
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical group [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 claims description 2
- 230000000149 penetrating effect Effects 0.000 claims 2
- 229910002601 GaN Inorganic materials 0.000 description 22
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 17
- 230000015556 catabolic process Effects 0.000 description 16
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 12
- 238000000034 method Methods 0.000 description 12
- 230000005533 two-dimensional electron gas Effects 0.000 description 10
- 229910052751 metal Inorganic materials 0.000 description 8
- 239000002184 metal Substances 0.000 description 8
- 239000010936 titanium Substances 0.000 description 8
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 7
- 239000000969 carrier Substances 0.000 description 6
- 239000010931 gold Substances 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 239000013078 crystal Substances 0.000 description 5
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 4
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 4
- RNQKDQAVIXDKAG-UHFFFAOYSA-N aluminum gallium Chemical compound [Al].[Ga] RNQKDQAVIXDKAG-UHFFFAOYSA-N 0.000 description 4
- 230000005684 electric field Effects 0.000 description 4
- 229910052710 silicon Inorganic materials 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- PIGFYZPCRLYGLF-UHFFFAOYSA-N Aluminum nitride Chemical compound [Al]#N PIGFYZPCRLYGLF-UHFFFAOYSA-N 0.000 description 3
- 229910052581 Si3N4 Inorganic materials 0.000 description 3
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 2
- 238000009825 accumulation Methods 0.000 description 2
- AJNVQOSZGJRYEI-UHFFFAOYSA-N digallium;oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Ga+3].[Ga+3] AJNVQOSZGJRYEI-UHFFFAOYSA-N 0.000 description 2
- 229910001195 gallium oxide Inorganic materials 0.000 description 2
- 229910052735 hafnium Inorganic materials 0.000 description 2
- VBJZVLUMGGDVMO-UHFFFAOYSA-N hafnium atom Chemical compound [Hf] VBJZVLUMGGDVMO-UHFFFAOYSA-N 0.000 description 2
- 229910000449 hafnium oxide Inorganic materials 0.000 description 2
- WIHZLLGSGQNAGK-UHFFFAOYSA-N hafnium(4+);oxygen(2-) Chemical compound [O-2].[O-2].[Hf+4] WIHZLLGSGQNAGK-UHFFFAOYSA-N 0.000 description 2
- 238000005468 ion implantation Methods 0.000 description 2
- 229910052749 magnesium Inorganic materials 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 2
- 239000000395 magnesium oxide Substances 0.000 description 2
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 2
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 2
- 229910052814 silicon oxide Inorganic materials 0.000 description 2
- 238000004544 sputter deposition Methods 0.000 description 2
- 229910052726 zirconium Inorganic materials 0.000 description 2
- 229910001928 zirconium oxide Inorganic materials 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 239000000370 acceptor Substances 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- NWAIGJYBQQYSPW-UHFFFAOYSA-N azanylidyneindigane Chemical compound [In]#N NWAIGJYBQQYSPW-UHFFFAOYSA-N 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005669 field effect Effects 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 238000001020 plasma etching Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
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- 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
- H01L29/41—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions
- H01L29/423—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions not carrying the current to be rectified, amplified or switched
- H01L29/42312—Gate electrodes for field effect devices
- H01L29/42316—Gate electrodes for field effect devices for field-effect transistors
- H01L29/4232—Gate electrodes for field effect devices for field-effect transistors with insulated gate
- H01L29/42356—Disposition, e.g. buried gate electrode
- H01L29/4236—Disposition, e.g. buried gate electrode within a trench, e.g. trench gate electrode, groove gate electrode
Definitions
- the embodiment of the present invention relates to a semiconductor device.
- a power semiconductor device is used for a switching circuit and an inverter circuit for power control.
- the breakdown voltage and the carrier mobility of the power semiconductor device using silicon has reached the limit based on physical characteristics of Si.
- silicon carbide and nitride semiconductors which have wider bandgap than Si, are expected to be used widely as materials of the power semiconductor device.
- a vertical type semiconductor device using silicon carbide has a high breakdown voltage, but a carrier mobility thereof is lower than that of the semiconductor device using Si.
- a lateral type semiconductor device having a heterojunction interface using a nitride semiconductor has a high carrier mobility exceeding that of Si, but there is a problem in that it is difficult to allow the lateral type semiconductor device to have a high breakdown voltage. Therefore, a power semiconductor device having both a high breakdown voltage and a high carrier mobility is desired.
- FIG. 1 is a schematic cross-sectional view of a semiconductor device according to a first embodiment
- FIG. 2 is a schematic cross-sectional view of a semiconductor device according to a second embodiment
- FIG. 3 is a schematic cross-sectional view of a semiconductor device according to a third embodiment
- FIGS. 4A and 4B are schematic cross-sectional views of a semiconductor device according to a fourth embodiment.
- FIGS. 5A and 5B are schematic cross-sectional views of a semiconductor device according to a fifth embodiment.
- GaN-based semiconductor is a generic name of gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), and semiconductors having an intermediate composition thereof.
- FIG. 1 is a schematic sectional view of a semiconductor device 100 .
- the semiconductor device 100 is a field effect transistor (FET) made of a GaN-based semiconductor formed on silicon carbide (SiC).
- FET field effect transistor
- the semiconductor device 100 is a vertical type GaN-based FET in which a GaN-based semiconductor is formed on SiC.
- a channel through which carriers flow is formed in an AlGaN/GaN heterointerface above the SiC. This channel electrically conducts with the SiC through a conduction electrode provided in the semiconductor device 100 .
- the SiC becomes a drift layer, and thus, carriers move between the channel of the AlGaN/GaN heterointerface and the SiC drift layer.
- the semiconductor device 100 achieves a high breakdown voltage by the SiC and realizes a high carrier mobility by the GaN-based semiconductor FET on the SiC.
- the semiconductor device 100 includes a first semiconductor layer 1 , a second semiconductor layer 2 , a third semiconductor layer 3 , a drain electrode 4 , a source electrode 5 , a conduction electrode 6 , a gate electrode 7 , a first insulating layer 8 , and a buffer layer 12 .
- the first semiconductor layer 1 includes a first region 14 , a second region 9 , a third region 10 , and a fourth region 11 .
- the first semiconductor layer 1 is, for example, silicon carbide (SiC).
- the thickness of the first semiconductor layer 1 is, for example, 1 ⁇ m or more and 100 ⁇ m or less.
- the first semiconductor layer 1 includes the first region 14 , the second region 9 , the third region 10 , and the fourth region 11 .
- the second semiconductor layer 2 is a nitride semiconductor.
- the second semiconductor layer 2 is, for example, aluminum gallium nitride (Al x Ga (1-x) N, 0 ⁇ x ⁇ 1).
- AlGaN aluminum gallium nitride
- the thickness of the second semiconductor layer 2 is, for example, 1 nm or more and 100 nm or less.
- the third semiconductor layer 3 is in contact with the second semiconductor layer 2 .
- the third semiconductor layer 3 is located between the first semiconductor layer 1 and the second semiconductor layer 2 .
- the third semiconductor layer 3 is, for example, gallium nitride (GaN).
- the third semiconductor layer 3 is preferably i-GaN which is not intentionally doped with impurities.
- the i-GaN has an impurity concentration of 10 17 cm ⁇ 3 or less.
- the thickness of the third semiconductor layer 3 is desirably, for example, 100 nm or more and 10 ⁇ m or less.
- the second semiconductor layer 2 is a material having a bandgap wider than that of the third semiconductor layer 3 .
- the buffer layer 12 is provided between the first semiconductor layer 1 and the third semiconductor layer 3 .
- the buffer layer 12 is a layer for reducing distortion caused by a difference between a lattice constant of the nitride semiconductor layer formed on the buffer layer 12 and a lattice constant of the SiC.
- the material of the buffer layer 12 include at least aluminum nitride (AlN) or aluminum gallium nitride (AlGaN).
- the thickness of the buffer layer 12 is 1 nm or more and 1 ⁇ m or less. In order to grow the GaN with low crystal dislocation on the SiC, the thickness of the buffer layer is preferably 10 nm or more and 100 nm or less.
- the drain electrode 4 is provided in the first semiconductor layer 1 on the side opposite to the side of the first semiconductor layer 1 which is in contact with the third semiconductor layer 3 .
- the drain electrode 4 is, for example, a metal electrode.
- the metal electrode includes an element selected from, for example, nickel (Ni), titanium (Ti), and aluminum (Al).
- the source electrode 5 is provided on the second semiconductor layer 2 on the side opposite to the side of the second semiconductor layer 2 which is in contact with the third semiconductor layer 3 .
- the source electrode 5 has a projection portion.
- the projection portion of the source electrode 5 penetrates the first semiconductor layer 1 and the second semiconductor layer 2 , and the tip of the projection portion is located inside the third semiconductor layer 3 .
- the source electrode 5 is, for example, a metal electrode.
- the metal electrode includes an element selected from, for example, nickel (Ni), titanium (Ti), aluminum (Al), and gold (Au).
- the conduction electrode 6 is provided on the second semiconductor layer 2 on the side opposite to the side of the second semiconductor layer 2 which is in contact with the third semiconductor layer 3 .
- the conduction electrode 6 has a projection portion.
- the projection portion of the conduction electrode 6 penetrates through the second semiconductor layer 2 , the third semiconductor layer 3 , and the buffer layer 12 .
- the tip of the projection portion of the conduction electrode 6 is located inside the first semiconductor layer 1 .
- the conduction electrode 6 is, for example, a metal electrode.
- the metal electrode includes an element selected from, for example, nickel (Ni), titanium (Ti), aluminum (Al), and gold (Au).
- the first gate electrode 7 is located between the source electrode 5 and the conduction electrode 6 in the direction from the source electrode 5 to the conduction electrode 6 .
- the first gate electrode 7 is provided on the side opposite to the side of the second semiconductor layer 2 which is in contact with the third semiconductor layer 3 in the stacking direction.
- the first gate electrode 7 is, for example, a metal electrode.
- the first gate electrode 7 may be a material including an element selected from, for example, nickel (Ni), titanium (Ti), aluminum (Al), and gold (Au).
- the first gate electrode 7 may be a polycrystalline semiconductor material doped with impurities, for example, may be silicon, silicon carbide, or gallium nitride.
- the first gate electrode 7 may be, for example, TiN.
- the source electrode 5 , the conduction electrode 6 and the first gate electrode 7 are provided on a first side (first plane) of the second semiconductor layer 2 respectively.
- the drain electrode 4 is provided on a second side (second plane) of the first semiconductor layer 1 .
- the first insulating layer 8 is provided between the second semiconductor layer 2 and the first gate electrode 7 .
- the first insulating layer 8 is, for example, silicon oxide, silicon nitride, silicon oxynitride, gallium oxide, aluminum oxide, aluminum oxynitride, hafnium oxide, zirconium oxide, magnesium oxide, or the like. Also, nitride and oxynitride of hafnium, zirconium or magnesium may be used.
- the first region 14 of the first semiconductor layer 1 has a first conductivity type.
- the first conductivity type is, for example, n type with a low doping concentration.
- the conductivity type of the first region 14 has an impurity concentration of, for example, 10 15 cm ⁇ 3 or more and 10 17 cm ⁇ 3 or less.
- the second region 9 is provided in the first semiconductor layer 1 in the vicinity of the interface where the first semiconductor layer 1 and the drain electrode 4 are in contact with each other.
- the second region 9 has a first conductivity type.
- the first conductivity type is, for example, n type with a high doping concentration.
- the second region 9 has an impurity concentration of 10 18 cm ⁇ 3 or more and 10 20 cm ⁇ 3 or less.
- the thickness of the second region 9 in the direction from the first semiconductor layer to the drain electrode 4 is, for example, 10 ⁇ m or more and 1 mm or less.
- the third region 10 is provided around the projection portion of the conduction electrode 6 .
- the third region 10 has a first conductivity type.
- the first conductivity type of the third region 10 is, for example, n type with a high doping concentration.
- the third region 10 has an impurity concentration of 10 18 cm ⁇ 3 or more and 10 20 cm ⁇ 3 or less.
- the thickness of the third region 10 in the direction from the first semiconductor layer to the drain electrode 4 is, for example, 10 nm or more and 1 ⁇ m or less.
- the fourth region 11 is provided in the first semiconductor layer 1 on the side where the third semiconductor layer 3 exists in the direction from the first semiconductor layer 1 to the third semiconductor layer 3 .
- the fourth region 11 is provided between the source electrode 5 and the conduction electrode 6 in the direction from the source electrode 5 to the conduction electrode 6 .
- the fourth region 11 is provided around the projection portion of the source electrode 5 .
- the fourth region 11 has a second conductivity type.
- the second conductivity type of the fourth region 11 is, for example, p type.
- the fourth region 11 has an impurity concentration of 10 15 cm ⁇ 3 or more and 10 20 cm ⁇ 3 or less.
- the thickness of the fourth region 11 is, for example, 1 ⁇ m or more and 2 ⁇ m or less in the direction from the first semiconductor layer 1 to the third semiconductor layer 3 .
- the thickness of the fourth region 11 is larger than that of the third region 10 .
- a depletion layer is formed between the fourth region 11 and the first region 14 .
- the depletion layer extends in the direction from the fourth region 11 to the first region 14 , so that the breakdown voltage of the semiconductor device 100 is maintained.
- the first semiconductor layer 1 has a crystal orientation of the (0001) plane (Si plane) on the side where the second semiconductor layer 2 exists.
- the crystal orientation may not be perpendicular to the (0001) direction and may have an off angle.
- the crystal orientation has an off angle of 4°.
- a two-dimensional electron gas layer is formed in the third semiconductor layer 3 .
- a two-dotted dash line in FIG. 1 indicates the position where the two-dimensional electron gas layer exists.
- a channel through which electrons flow is formed in an arrow direction indicated by a dotted line in FIG. 1 .
- the electrons flow in the direction from the source electrode 5 to the conduction electrode 6 .
- the electrons flow in the direction from the conduction electrode 6 to the drain electrode 4 through the first semiconductor layer 1 . Since the first semiconductor layer 1 which is the SiC has a high breakdown voltage, a large portion of the voltage applied to the semiconductor device 100 is applied to the first semiconductor layer 1 between the conduction electrode 6 and the drain electrode 4 .
- the semiconductor device 100 is a normally-on device.
- a negative voltage is applied to the gate electrode 7 in order to stop the electrons from flowing in the channel and turn off the semiconductor device 100 . That is, when a negative voltage is applied to the gate electrode 7 , the band structure of the interface between the second semiconductor layer 2 and the third semiconductor layer 3 is raised, and the two-dimensional electron gas layer is depleted. Therefore, it is possible to stop the electrons from flowing in the channel of the third semiconductor layer 3 .
- the voltage applied to the gate electrode 7 allowing electrons in the two-dimensional electron gas layer to flow is determined by a work function of a metal constituting the gate electrode 7 , a dielectric constant of the first insulating layer 8 , a thickness of the first insulating layer 8 , concentrations of donors and acceptors contained in the third semiconductor layer 3 , and a surface potential of the third semiconductor layer 3 .
- a semiconductor device that is compatible with a high breakdown voltage and a high carrier mobility is obtained.
- a channel is formed between the source electrode 5 and the conduction electrode 6 at the AlGaN/GaN heterointerface above the SiC substrate. Electrons flow from the source electrode 5 to the conduction electrode 6 , and the electrons further flow from the conduction electrode 6 to the drain electrode 4 through the first semiconductor layer 1 which is the SiC.
- a high breakdown voltage is realized by the first semiconductor layer 1 which is the SiC, and a high carrier mobility is realized by the GaN-based semiconductor FET on the first semiconductor layer 1 .
- a method of manufacturing the semiconductor device 100 will be described.
- a preparation process of the second region 9 which is the SiC is performed.
- an epitaxial growth layer forming process is performed.
- a SiC layer which is the first region 14 is formed on the (0001) plane of the second region 9 by epitaxial growth.
- an ion implantation process is performed.
- p type impurities are implanted into the SiC layer, and thus, the fourth region 11 is formed.
- the p type impurities to be ion-implanted are, for example, aluminum (Al) or boron (B).
- n type impurities are implanted into the SiC layer, and thus, the third region 10 having a high doping concentration is formed.
- the n type impurities to be ion-implanted are, for example, phosphorus (P) or nitrogen (N).
- an impurity activation annealing process is performed. By heating the first semiconductor layer 1 at a high temperature, desired carriers are generated in the impurity region.
- a process of forming the buffer layer 12 made of aluminum nitride (AlN) or aluminum gallium nitride (AlGaN) is performed on the first semiconductor layer 1 .
- the buffer layer 12 is formed, for example, by sputtering.
- an epitaxial growth process of the third semiconductor layer 3 and the second semiconductor layer 2 , which are nitride semiconductors, is performed on the buffer layer 12 .
- a process of forming the insulating layer 8 is performed.
- a process of forming the gate electrode 7 is performed.
- a process of forming a projection portion for burying the source electrode 5 and the conduction electrode 6 in the nitride semiconductor layer is performed.
- the process is performed by, for example, reactive ion etching.
- a process of forming the source electrode 5 and the conduction electrode 6 is performed.
- the drain electrode 4 is formed on the side opposite to the side of the first semiconductor layer 1 where the buffer layer 12 exists by, for example, sputtering.
- FIG. 2 illustrates a semiconductor device 101 .
- the gate electrode 7 has a projection portion.
- the projection portion of the gate electrode 7 is located inside the second semiconductor layer 2 , and the projection portion reaches the third semiconductor layer 3 .
- the semiconductor device 101 is a normally-off device.
- the third semiconductor layer 3 is an i-GaN which is not intentionally doped with impurities, the third semiconductor layer 3 exhibits n type conduction with a low impurity concentration.
- the third semiconductor layer 3 on the gate electrode 7 side is in an accumulation state where electrons are induced. Therefore, the electrons induced in the accumulation state are connected to the two-dimensional electron gas layer existing at the interface between the second semiconductor layer 2 and the third semiconductor layer 3 . Therefore, the electrons flow in the arrow direction indicated by a dotted line in FIG. 2 . Accordingly, the semiconductor device 101 operates as an FET.
- the semiconductor device 101 since the projection portion of the gate electrode 7 is buried in the second semiconductor layer 2 , the concentration of electrons in the two-dimensional electron gas layer included in the semiconductor layer 3 at the position of the gate electrode 7 decreases as compared with the semiconductor device 100 of FIG. 1 . For this reason, the threshold voltage shifts to the positive direction. Therefore, the semiconductor device 101 performs a normally-off operation that has a positive threshold voltage. Accordingly, the semiconductor device 101 is a normally-off device realizing a high breakdown voltage by the first semiconductor layer 1 which is the SiC and a high carrier mobility by the GaN-based semiconductor FET on the first semiconductor layer 1 .
- FIG. 3 illustrates a semiconductor device 102 .
- the semiconductor device 102 further includes a second insulating layer 13 between the projection portion of the conduction electrode 6 and the third semiconductor layer 3 and between the projection portion of the conduction electrode 6 and the buffer layer 12 .
- the second insulating layer 13 is made of, for example, silicon oxide, silicon nitride, silicon oxynitride, gallium oxide, aluminum oxide, aluminum oxynitride, hafnium oxide, zirconium oxide, magnesium oxide, or the like. Also, nitride and oxynitride of hafnium, zirconium or magnesium may be used.
- the conduction electrode 6 electrically conducts only with the channel portion of the third semiconductor layer 3 .
- the second insulating layer 13 there is a method of manufacturing an insulating region by implanting ions into the third semiconductor layer 3 and the buffer layer 12 in the vicinity of the conduction electrode 6 .
- the elements used for ion implantation are, for example, argon (Ar) and fluorine (F).
- Ar argon
- F fluorine
- the third semiconductor layer 3 and the buffer layer 12 in the vicinity of the conduction electrode 6 can be allowed to have an insulating property.
- the third semiconductor layer 3 and the buffer layer 12 in the vicinity of the conduction electrode 6 which are ion-implanted to have an insulating property, can be used as the second insulating layer 13 .
- the conduction electrode 6 is prevented from electrically conducting with a portion other than the portion of the third semiconductor layer 3 that becomes a channel, and further, the conduction electrode 6 is prevented from electrically conducting with the buffer layer 12 . Therefore, it is possible to prevent the carriers passing through the conduction electrode 6 from leaking into the buffer layer 12 and a portion of the third semiconductor layer 3 that is not channel. Accordingly, in the semiconductor device 102 , the leakage of carriers from the conduction electrode 6 is suppressed, and thus, a high breakdown voltage by the first semiconductor layer 1 which is the SiC and a high carrier mobility by the GaN-based semiconductor FET are realized.
- the leakage of carriers of the conduction electrode 6 can be prevented.
- FIG. 4A illustrates a semiconductor device 103
- FIG. 4B illustrates an enlarged view of a portion enclosed by a dotted line in FIG. 4A .
- the fifth region 10 a having a first conductivity type and the sixth region 10 b having a second conductivity type are alternately located in the direction (lateral direction) from the source electrode 5 to the conduction electrode 6 .
- the length of the fifth region 10 a is, for example, 10 nm or more and 1 ⁇ m or less
- the length of the sixth region 10 b is, for example, 10 nm or more and 1 ⁇ m or less.
- the first conductivity type of the fifth region 10 a is, for example, n type doped with a high concentration.
- the second conductivity type of the sixth region 10 b is, for example, p type.
- the interface between the n type first region 14 having a low doping concentration and the p type sixth region 10 b has a pn junction.
- a depletion layer exists in the pn junction at the interface between the first region 14 and the sixth region 10 b . Therefore, depletion layers between the first region 14 and the sixth regions 10 b are connected to each other, and a depletion layer exists in the first region 14 around the third region 10 .
- the semiconductor device 103 can improve the breakdown voltage of the first semiconductor layer 1 , and thus, a high breakdown voltage of the first semiconductor layer 1 which is the SiC and a high carrier mobility by the GaN-based semiconductor FET are realized.
- FIG. 5A illustrates a semiconductor device 104 and FIG. 5B illustrates a semiconductor device 105 .
- the semiconductor device 104 of FIG. 5A includes a plurality of the fourth regions 11 separated from each other in the first semiconductor layer 1 .
- the fourth regions 11 are located on the side opposite to the side of the first semiconductor layer 1 where the second region 9 exists.
- the fourth regions 11 are located on the side opposite to the side where the conduction electrode 6 exists as viewed from the source electrode 5 .
- the first semiconductor layer 1 on the side opposite to the side where the conduction electrode 6 exists as viewed from the source electrode 5 becomes a terminated end portion of the semiconductor device 104 .
- a plurality of the fourth regions 11 are separated from each other with the first region 14 interposed therebetween.
- the fourth regions 11 are formed by implanting ions into the first semiconductor layer 1 .
- the thickness of the fourth regions 11 in the direction from the first semiconductor layer 1 to the drain electrode 4 is, for example, 1 ⁇ m or more and 2 ⁇ m or less.
- the fourth regions 11 are guard ring layers.
- the fourth regions 11 At a position close to the source electrode 5 , a plurality of the fourth regions 11 exist at narrow intervals. At a position away from the source electrode 5 , a plurality of the fourth regions 11 exist at wide intervals. Besides, as described before, the fourth regions 11 of this embodiment are the second conductivity type, that is, p type. The fourth regions 11 have an impurity concentration of 10 15 cm ⁇ 3 or more and 10 20 cm ⁇ 3 or less.
- a plurality of the fourth regions 11 are located not only on the side of the first semiconductor layer 1 where the third semiconductor layer 3 exists but also at the terminated end portion of the semiconductor device 104 . Therefore, it is possible to extend the depletion layer in the direction from the conduction electrode 6 to the source electrode 5 , on the side opposite to the side of the first semiconductor layer 1 where the drain electrode 4 exists. Thus, it is possible to prevent an electric field from being concentrated on the terminated end portion of the semiconductor device 104 . In addition, a current of the source electrode and a current of the channel are prevented from leaking into the first semiconductor layer 1 and other devices.
- the semiconductor device 105 of FIG. 5B includes a seventh region 15 which is p type with a low impurity concentration, adjacent to the fourth region 11 .
- the seventh region 15 is on the side opposite to the side of the first semiconductor layer 1 where the drain electrode 4 exists.
- the seventh region 15 is located on the side opposite to the side where the conduction electrode 6 exists as viewed from the source electrode 5 .
- the seventh region 15 is located adjacent to the fourth region 11 .
- the seventh region 15 contains impurities having a second conductivity type having a concentration lower than that of the fourth region 11 .
- the second conductivity type is, for example, p type.
- the seventh region 15 is a reduced surface field (RESURF) layer.
- RESURF reduced surface field
- the seventh region 15 is located adjacent to the fourth region 11 , so that it is possible to extend the depletion layer in the direction from the conduction electrode 6 to the source electrode 5 , on the side opposite to the side of the n type first region 14 where the drain electrode 4 exists. Therefore, it is possible to prevent an electric field from being concentrated on the terminated end portion of the semiconductor device 105 . Accordingly, it is possible to improve the breakdown voltage of the first semiconductor layer 1 .
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Abstract
Description
- This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-118990, filed on Jun. 16, 2017, and the entire contents of which are incorporated herein by reference.
- The embodiment of the present invention relates to a semiconductor device.
- A power semiconductor device is used for a switching circuit and an inverter circuit for power control.
- Although the power semiconductor device is required to have a high breakdown voltage and a high carrier mobility, the breakdown voltage and the carrier mobility of the power semiconductor device using silicon has reached the limit based on physical characteristics of Si.
- In recent years, silicon carbide and nitride semiconductors, which have wider bandgap than Si, are expected to be used widely as materials of the power semiconductor device.
- A vertical type semiconductor device using silicon carbide has a high breakdown voltage, but a carrier mobility thereof is lower than that of the semiconductor device using Si.
- On the other hand, a lateral type semiconductor device having a heterojunction interface using a nitride semiconductor has a high carrier mobility exceeding that of Si, but there is a problem in that it is difficult to allow the lateral type semiconductor device to have a high breakdown voltage. Therefore, a power semiconductor device having both a high breakdown voltage and a high carrier mobility is desired.
-
FIG. 1 is a schematic cross-sectional view of a semiconductor device according to a first embodiment; -
FIG. 2 is a schematic cross-sectional view of a semiconductor device according to a second embodiment; -
FIG. 3 is a schematic cross-sectional view of a semiconductor device according to a third embodiment; -
FIGS. 4A and 4B are schematic cross-sectional views of a semiconductor device according to a fourth embodiment; and -
FIGS. 5A and 5B are schematic cross-sectional views of a semiconductor device according to a fifth embodiment. - Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same components are denoted by the same reference numerals. In addition, the drawings are schematic or conceptual, and a relationship between the thickness and the width of each portion, a ratio coefficient of the size between portions, and the like are not necessarily the same as the actual ones. In addition, even in the case of representing the same portions, the dimensions and the ratio coefficients of the portions may be different from each other depending on the drawing.
- In this specification, in order to indicate positional relationships of parts and the like, the upward direction of the drawings is described as “upper” and the downward direction of the drawings is described as “lower”. In this specification, the concepts of “upper” and “lower” are not necessarily terms indicating the relationship with the direction of gravity.
- In this specification, a “GaN-based semiconductor” is a generic name of gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), and semiconductors having an intermediate composition thereof.
-
FIG. 1 is a schematic sectional view of asemiconductor device 100. Thesemiconductor device 100 is a field effect transistor (FET) made of a GaN-based semiconductor formed on silicon carbide (SiC). - The
semiconductor device 100 is a vertical type GaN-based FET in which a GaN-based semiconductor is formed on SiC. In an AlGaN/GaN heterointerface above the SiC, a channel through which carriers flow is formed. This channel electrically conducts with the SiC through a conduction electrode provided in thesemiconductor device 100. The SiC becomes a drift layer, and thus, carriers move between the channel of the AlGaN/GaN heterointerface and the SiC drift layer. Thesemiconductor device 100 achieves a high breakdown voltage by the SiC and realizes a high carrier mobility by the GaN-based semiconductor FET on the SiC. Thesemiconductor device 100 includes afirst semiconductor layer 1, asecond semiconductor layer 2, athird semiconductor layer 3, adrain electrode 4, asource electrode 5, aconduction electrode 6, agate electrode 7, a firstinsulating layer 8, and abuffer layer 12. Thefirst semiconductor layer 1 includes afirst region 14, asecond region 9, athird region 10, and afourth region 11. - The
first semiconductor layer 1 is, for example, silicon carbide (SiC). The thickness of thefirst semiconductor layer 1 is, for example, 1 μm or more and 100 μm or less. Thefirst semiconductor layer 1 includes thefirst region 14, thesecond region 9, thethird region 10, and thefourth region 11. - The
second semiconductor layer 2 is a nitride semiconductor. Thesecond semiconductor layer 2 is, for example, aluminum gallium nitride (AlxGa(1-x)N, 0<x≤1). Hereinafter, the aluminum gallium nitride is denoted by AlGaN. The thickness of thesecond semiconductor layer 2 is, for example, 1 nm or more and 100 nm or less. - The
third semiconductor layer 3 is in contact with thesecond semiconductor layer 2. Thethird semiconductor layer 3 is located between thefirst semiconductor layer 1 and thesecond semiconductor layer 2. Thethird semiconductor layer 3 is, for example, gallium nitride (GaN). Thethird semiconductor layer 3 is preferably i-GaN which is not intentionally doped with impurities. For example, the i-GaN has an impurity concentration of 1017 cm−3 or less. The thickness of thethird semiconductor layer 3 is desirably, for example, 100 nm or more and 10 μm or less. - The
second semiconductor layer 2 is a material having a bandgap wider than that of thethird semiconductor layer 3. - Since the
first semiconductor layer 1 is the SiC and is a material different from the GaN of thethird semiconductor layer 3, thebuffer layer 12 is provided between thefirst semiconductor layer 1 and thethird semiconductor layer 3. Thebuffer layer 12 is a layer for reducing distortion caused by a difference between a lattice constant of the nitride semiconductor layer formed on thebuffer layer 12 and a lattice constant of the SiC. The material of thebuffer layer 12 include at least aluminum nitride (AlN) or aluminum gallium nitride (AlGaN). The thickness of thebuffer layer 12 is 1 nm or more and 1 μm or less. In order to grow the GaN with low crystal dislocation on the SiC, the thickness of the buffer layer is preferably 10 nm or more and 100 nm or less. - The
drain electrode 4 is provided in thefirst semiconductor layer 1 on the side opposite to the side of thefirst semiconductor layer 1 which is in contact with thethird semiconductor layer 3. Thedrain electrode 4 is, for example, a metal electrode. The metal electrode includes an element selected from, for example, nickel (Ni), titanium (Ti), and aluminum (Al). - The
source electrode 5 is provided on thesecond semiconductor layer 2 on the side opposite to the side of thesecond semiconductor layer 2 which is in contact with thethird semiconductor layer 3. Thesource electrode 5 has a projection portion. The projection portion of thesource electrode 5 penetrates thefirst semiconductor layer 1 and thesecond semiconductor layer 2, and the tip of the projection portion is located inside thethird semiconductor layer 3. Thesource electrode 5 is, for example, a metal electrode. The metal electrode includes an element selected from, for example, nickel (Ni), titanium (Ti), aluminum (Al), and gold (Au). - The
conduction electrode 6 is provided on thesecond semiconductor layer 2 on the side opposite to the side of thesecond semiconductor layer 2 which is in contact with thethird semiconductor layer 3. Theconduction electrode 6 has a projection portion. The projection portion of theconduction electrode 6 penetrates through thesecond semiconductor layer 2, thethird semiconductor layer 3, and thebuffer layer 12. The tip of the projection portion of theconduction electrode 6 is located inside thefirst semiconductor layer 1. Theconduction electrode 6 is, for example, a metal electrode. The metal electrode includes an element selected from, for example, nickel (Ni), titanium (Ti), aluminum (Al), and gold (Au). - The
first gate electrode 7 is located between thesource electrode 5 and theconduction electrode 6 in the direction from thesource electrode 5 to theconduction electrode 6. Thefirst gate electrode 7 is provided on the side opposite to the side of thesecond semiconductor layer 2 which is in contact with thethird semiconductor layer 3 in the stacking direction. Thefirst gate electrode 7 is, for example, a metal electrode. Thefirst gate electrode 7 may be a material including an element selected from, for example, nickel (Ni), titanium (Ti), aluminum (Al), and gold (Au). Alternatively, thefirst gate electrode 7 may be a polycrystalline semiconductor material doped with impurities, for example, may be silicon, silicon carbide, or gallium nitride. Thefirst gate electrode 7 may be, for example, TiN. - The
source electrode 5, theconduction electrode 6 and thefirst gate electrode 7 are provided on a first side (first plane) of thesecond semiconductor layer 2 respectively. Thedrain electrode 4 is provided on a second side (second plane) of thefirst semiconductor layer 1. - The first insulating
layer 8 is provided between thesecond semiconductor layer 2 and thefirst gate electrode 7. The first insulatinglayer 8 is, for example, silicon oxide, silicon nitride, silicon oxynitride, gallium oxide, aluminum oxide, aluminum oxynitride, hafnium oxide, zirconium oxide, magnesium oxide, or the like. Also, nitride and oxynitride of hafnium, zirconium or magnesium may be used. - The
first region 14 of thefirst semiconductor layer 1 has a first conductivity type. The first conductivity type is, for example, n type with a low doping concentration. The conductivity type of thefirst region 14 has an impurity concentration of, for example, 1015 cm−3 or more and 1017 cm−3 or less. - The
second region 9 is provided in thefirst semiconductor layer 1 in the vicinity of the interface where thefirst semiconductor layer 1 and thedrain electrode 4 are in contact with each other. Thesecond region 9 has a first conductivity type. The first conductivity type is, for example, n type with a high doping concentration. Thesecond region 9 has an impurity concentration of 1018 cm−3 or more and 1020 cm−3 or less. The thickness of thesecond region 9 in the direction from the first semiconductor layer to thedrain electrode 4 is, for example, 10 μm or more and 1 mm or less. - The
third region 10 is provided around the projection portion of theconduction electrode 6. Thethird region 10 has a first conductivity type. The first conductivity type of thethird region 10 is, for example, n type with a high doping concentration. Thethird region 10 has an impurity concentration of 1018 cm−3 or more and 1020 cm−3 or less. The thickness of thethird region 10 in the direction from the first semiconductor layer to thedrain electrode 4 is, for example, 10 nm or more and 1 μm or less. - The
fourth region 11 is provided in thefirst semiconductor layer 1 on the side where thethird semiconductor layer 3 exists in the direction from thefirst semiconductor layer 1 to thethird semiconductor layer 3. Thefourth region 11 is provided between thesource electrode 5 and theconduction electrode 6 in the direction from thesource electrode 5 to theconduction electrode 6. Thefourth region 11 is provided around the projection portion of thesource electrode 5. Thefourth region 11 has a second conductivity type. The second conductivity type of thefourth region 11 is, for example, p type. Thefourth region 11 has an impurity concentration of 1015 cm−3 or more and 1020 cm−3 or less. The thickness of thefourth region 11 is, for example, 1 μm or more and 2 μm or less in the direction from thefirst semiconductor layer 1 to thethird semiconductor layer 3. The thickness of thefourth region 11 is larger than that of thethird region 10. By providing thefourth region 11, a depletion layer is formed between thefourth region 11 and thefirst region 14. The depletion layer extends in the direction from thefourth region 11 to thefirst region 14, so that the breakdown voltage of thesemiconductor device 100 is maintained. For example, thefirst semiconductor layer 1 has a crystal orientation of the (0001) plane (Si plane) on the side where thesecond semiconductor layer 2 exists. The crystal orientation may not be perpendicular to the (0001) direction and may have an off angle. For example, the crystal orientation has an off angle of 4°. - In the vicinity of the interface between the
second semiconductor layer 2 and thethird semiconductor layer 3, a two-dimensional electron gas layer is formed in thethird semiconductor layer 3. A two-dotted dash line inFIG. 1 indicates the position where the two-dimensional electron gas layer exists. - A channel through which electrons flow is formed in an arrow direction indicated by a dotted line in
FIG. 1 . The electrons flow in the direction from thesource electrode 5 to theconduction electrode 6. In addition, the electrons flow in the direction from theconduction electrode 6 to thedrain electrode 4 through thefirst semiconductor layer 1. Since thefirst semiconductor layer 1 which is the SiC has a high breakdown voltage, a large portion of the voltage applied to thesemiconductor device 100 is applied to thefirst semiconductor layer 1 between theconduction electrode 6 and thedrain electrode 4. - The
semiconductor device 100 is a normally-on device. A negative voltage is applied to thegate electrode 7 in order to stop the electrons from flowing in the channel and turn off thesemiconductor device 100. That is, when a negative voltage is applied to thegate electrode 7, the band structure of the interface between thesecond semiconductor layer 2 and thethird semiconductor layer 3 is raised, and the two-dimensional electron gas layer is depleted. Therefore, it is possible to stop the electrons from flowing in the channel of thethird semiconductor layer 3. - The voltage applied to the
gate electrode 7 allowing electrons in the two-dimensional electron gas layer to flow is determined by a work function of a metal constituting thegate electrode 7, a dielectric constant of the first insulatinglayer 8, a thickness of the first insulatinglayer 8, concentrations of donors and acceptors contained in thethird semiconductor layer 3, and a surface potential of thethird semiconductor layer 3. - According to the embodiment, a semiconductor device that is compatible with a high breakdown voltage and a high carrier mobility is obtained.
- As described above, in the
semiconductor device 100 according to this embodiment, a channel is formed between thesource electrode 5 and theconduction electrode 6 at the AlGaN/GaN heterointerface above the SiC substrate. Electrons flow from thesource electrode 5 to theconduction electrode 6, and the electrons further flow from theconduction electrode 6 to thedrain electrode 4 through thefirst semiconductor layer 1 which is the SiC. In thesemiconductor device 100, a high breakdown voltage is realized by thefirst semiconductor layer 1 which is the SiC, and a high carrier mobility is realized by the GaN-based semiconductor FET on thefirst semiconductor layer 1. Hereinafter, a method of manufacturing thesemiconductor device 100 will be described. - First, a preparation process of the
second region 9 which is the SiC is performed. Next, an epitaxial growth layer forming process is performed. In this process, a SiC layer which is thefirst region 14 is formed on the (0001) plane of thesecond region 9 by epitaxial growth. Next, an ion implantation process is performed. In this process, p type impurities are implanted into the SiC layer, and thus, thefourth region 11 is formed. The p type impurities to be ion-implanted are, for example, aluminum (Al) or boron (B). Next, n type impurities are implanted into the SiC layer, and thus, thethird region 10 having a high doping concentration is formed. The n type impurities to be ion-implanted are, for example, phosphorus (P) or nitrogen (N). Next, an impurity activation annealing process is performed. By heating thefirst semiconductor layer 1 at a high temperature, desired carriers are generated in the impurity region. - Next, a process of forming the
buffer layer 12 made of aluminum nitride (AlN) or aluminum gallium nitride (AlGaN) is performed on thefirst semiconductor layer 1. Thebuffer layer 12 is formed, for example, by sputtering. Next, an epitaxial growth process of thethird semiconductor layer 3 and thesecond semiconductor layer 2, which are nitride semiconductors, is performed on thebuffer layer 12. Next, a process of forming the insulatinglayer 8 is performed. Then, a process of forming thegate electrode 7 is performed. Next, a process of forming a projection portion for burying thesource electrode 5 and theconduction electrode 6 in the nitride semiconductor layer is performed. The process is performed by, for example, reactive ion etching. Next, a process of forming thesource electrode 5 and theconduction electrode 6 is performed. Furthermore, in the stacking direction, thedrain electrode 4 is formed on the side opposite to the side of thefirst semiconductor layer 1 where thebuffer layer 12 exists by, for example, sputtering. -
FIG. 2 illustrates asemiconductor device 101. - The same components as those of the
semiconductor device 100 inFIG. 1 are denoted by the same reference numerals, and description thereof is omitted. - The
gate electrode 7 has a projection portion. The projection portion of thegate electrode 7 is located inside thesecond semiconductor layer 2, and the projection portion reaches thethird semiconductor layer 3. - Between the projection portion of the
gate electrode 7 and thethird semiconductor layer 3, thesecond semiconductor layer 2 is not exist or may exist as long as the thickness is such that a two-dimensional electron gas layer is not induced. For this reason, a two-dimensional electron gas layer does not exist in thethird semiconductor layer 3 that is located at the position of thegate electrode 7. Therefore, in the state where no voltage is applied to thegate electrode 7, no electron flows in the channel. Accordingly, thesemiconductor device 101 is a normally-off device. - In the vicinity of the interface between the
second semiconductor layer 2 and thethird semiconductor layer 3, there is a two-dimensional electron gas layer in thethird semiconductor layer 3 excluding the position where thegate electrode 7 exists. A two-dotted dash line inFIG. 2 indicates the position where the two-dimensional electron gas layer exists. - Since the
third semiconductor layer 3 is an i-GaN which is not intentionally doped with impurities, thethird semiconductor layer 3 exhibits n type conduction with a low impurity concentration. In a case where a positive voltage is applied to thegate electrode 7, thethird semiconductor layer 3 on thegate electrode 7 side is in an accumulation state where electrons are induced. Therefore, the electrons induced in the accumulation state are connected to the two-dimensional electron gas layer existing at the interface between thesecond semiconductor layer 2 and thethird semiconductor layer 3. Therefore, the electrons flow in the arrow direction indicated by a dotted line inFIG. 2 . Accordingly, thesemiconductor device 101 operates as an FET. - In the
semiconductor device 101, since the projection portion of thegate electrode 7 is buried in thesecond semiconductor layer 2, the concentration of electrons in the two-dimensional electron gas layer included in thesemiconductor layer 3 at the position of thegate electrode 7 decreases as compared with thesemiconductor device 100 ofFIG. 1 . For this reason, the threshold voltage shifts to the positive direction. Therefore, thesemiconductor device 101 performs a normally-off operation that has a positive threshold voltage. Accordingly, thesemiconductor device 101 is a normally-off device realizing a high breakdown voltage by thefirst semiconductor layer 1 which is the SiC and a high carrier mobility by the GaN-based semiconductor FET on thefirst semiconductor layer 1. -
FIG. 3 illustrates asemiconductor device 102. - The same components as those of the
semiconductor device 100 inFIG. 1 are denoted by the same reference numerals, and description thereof is omitted. - The
semiconductor device 102 further includes a second insulatinglayer 13 between the projection portion of theconduction electrode 6 and thethird semiconductor layer 3 and between the projection portion of theconduction electrode 6 and thebuffer layer 12. - The second insulating
layer 13 is made of, for example, silicon oxide, silicon nitride, silicon oxynitride, gallium oxide, aluminum oxide, aluminum oxynitride, hafnium oxide, zirconium oxide, magnesium oxide, or the like. Also, nitride and oxynitride of hafnium, zirconium or magnesium may be used. - By providing the second insulating
layer 13 between theconduction electrode 6 and thethird semiconductor layer 3 and between theconduction electrode 6 and thebuffer layer 12, it is possible to prevent theconduction electrode 6 from electrically conducting with a portion other than the portion of thethird semiconductor layer 3 which is to be a channel, and further, it is possible to prevent theconduction electrode 6 from electrically conducting with thebuffer layer 12. Therefore, theconduction electrode 6 electrically conducts only with the channel portion of thethird semiconductor layer 3. - Alternatively, instead of the second insulating
layer 13 described above, there is a method of manufacturing an insulating region by implanting ions into thethird semiconductor layer 3 and thebuffer layer 12 in the vicinity of theconduction electrode 6. The elements used for ion implantation are, for example, argon (Ar) and fluorine (F). By implanting ions into thethird semiconductor layer 3 and thebuffer layer 12 in the vicinity of theconduction electrode 6, thethird semiconductor layer 3 and thebuffer layer 12 in the vicinity of theconduction electrode 6 can be allowed to have an insulating property. Thethird semiconductor layer 3 and thebuffer layer 12 in the vicinity of theconduction electrode 6, which are ion-implanted to have an insulating property, can be used as the second insulatinglayer 13. - Accordingly, the
conduction electrode 6 is prevented from electrically conducting with a portion other than the portion of thethird semiconductor layer 3 that becomes a channel, and further, theconduction electrode 6 is prevented from electrically conducting with thebuffer layer 12. Therefore, it is possible to prevent the carriers passing through theconduction electrode 6 from leaking into thebuffer layer 12 and a portion of thethird semiconductor layer 3 that is not channel. Accordingly, in thesemiconductor device 102, the leakage of carriers from theconduction electrode 6 is suppressed, and thus, a high breakdown voltage by thefirst semiconductor layer 1 which is the SiC and a high carrier mobility by the GaN-based semiconductor FET are realized. - Even if the second insulating
layer 13 is used for thesemiconductor device 101 according to the second embodiment, the leakage of carriers of theconduction electrode 6 can be prevented. -
FIG. 4A illustrates asemiconductor device 103, andFIG. 4B illustrates an enlarged view of a portion enclosed by a dotted line inFIG. 4A . - The same components as those of the
semiconductor device 100 inFIG. 1 are denoted by the same reference numerals, and description thereof is omitted. - In the
third region 10 ofFIG. 4B , thefifth region 10 a having a first conductivity type and thesixth region 10 b having a second conductivity type are alternately located in the direction (lateral direction) from thesource electrode 5 to theconduction electrode 6. - In the direction from the
source electrode 5 to theconduction electrode 6, the length of thefifth region 10 a is, for example, 10 nm or more and 1 μm or less, and the length of thesixth region 10 b is, for example, 10 nm or more and 1 μm or less. - The first conductivity type of the
fifth region 10 a is, for example, n type doped with a high concentration. The second conductivity type of thesixth region 10 b is, for example, p type. - The interface between the n type
first region 14 having a low doping concentration and the p typesixth region 10 b has a pn junction. In a case where no voltage is applied to thegate electrode 7, a depletion layer exists in the pn junction at the interface between thefirst region 14 and thesixth region 10 b. Therefore, depletion layers between thefirst region 14 and thesixth regions 10 b are connected to each other, and a depletion layer exists in thefirst region 14 around thethird region 10. - In a case where no voltage is applied to the
gate electrode 7, electric field concentration tends to occur at the tip of the projection portion of theconduction electrode 6, that is, the projection portion of theconduction electrode 6 surrounded by thethird region 10. Herein, since the depletion layer exists in thefirst region 14 around thethird region 10, the load of electric field concentration is distributed over the entire depletion layer, so that it is possible to prevent the crystal of thefirst semiconductor layer 1 from being destroyed. Therefore, thesemiconductor device 103 can improve the breakdown voltage of thefirst semiconductor layer 1, and thus, a high breakdown voltage of thefirst semiconductor layer 1 which is the SiC and a high carrier mobility by the GaN-based semiconductor FET are realized. - In addition, it is possible to improve the breakdown voltage of the
first semiconductor layer 1 by using thethird region 10 of this embodiment for thesemiconductor devices -
FIG. 5A illustrates asemiconductor device 104 andFIG. 5B illustrates asemiconductor device 105. - The same components as those of the
semiconductor device 100 inFIG. 1 are denoted by the same reference numerals, and description thereof is omitted. - The
semiconductor device 104 ofFIG. 5A includes a plurality of thefourth regions 11 separated from each other in thefirst semiconductor layer 1. - The
fourth regions 11 are located on the side opposite to the side of thefirst semiconductor layer 1 where thesecond region 9 exists. Thefourth regions 11 are located on the side opposite to the side where theconduction electrode 6 exists as viewed from thesource electrode 5. Thefirst semiconductor layer 1 on the side opposite to the side where theconduction electrode 6 exists as viewed from thesource electrode 5, becomes a terminated end portion of thesemiconductor device 104. A plurality of thefourth regions 11 are separated from each other with thefirst region 14 interposed therebetween. Thefourth regions 11 are formed by implanting ions into thefirst semiconductor layer 1. The thickness of thefourth regions 11 in the direction from thefirst semiconductor layer 1 to thedrain electrode 4 is, for example, 1 μm or more and 2 μm or less. Thefourth regions 11 are guard ring layers. At a position close to thesource electrode 5, a plurality of thefourth regions 11 exist at narrow intervals. At a position away from thesource electrode 5, a plurality of thefourth regions 11 exist at wide intervals. Besides, as described before, thefourth regions 11 of this embodiment are the second conductivity type, that is, p type. Thefourth regions 11 have an impurity concentration of 1015 cm−3 or more and 1020 cm−3 or less. - A plurality of the
fourth regions 11 are located not only on the side of thefirst semiconductor layer 1 where thethird semiconductor layer 3 exists but also at the terminated end portion of thesemiconductor device 104. Therefore, it is possible to extend the depletion layer in the direction from theconduction electrode 6 to thesource electrode 5, on the side opposite to the side of thefirst semiconductor layer 1 where thedrain electrode 4 exists. Thus, it is possible to prevent an electric field from being concentrated on the terminated end portion of thesemiconductor device 104. In addition, a current of the source electrode and a current of the channel are prevented from leaking into thefirst semiconductor layer 1 and other devices. - The
semiconductor device 105 ofFIG. 5B includes aseventh region 15 which is p type with a low impurity concentration, adjacent to thefourth region 11. - The
seventh region 15 is on the side opposite to the side of thefirst semiconductor layer 1 where thedrain electrode 4 exists. Theseventh region 15 is located on the side opposite to the side where theconduction electrode 6 exists as viewed from thesource electrode 5. In thefirst semiconductor layer 1, theseventh region 15 is located adjacent to thefourth region 11. Theseventh region 15 contains impurities having a second conductivity type having a concentration lower than that of thefourth region 11. The second conductivity type is, for example, p type. Theseventh region 15 is a reduced surface field (RESURF) layer. - The
seventh region 15 is located adjacent to thefourth region 11, so that it is possible to extend the depletion layer in the direction from theconduction electrode 6 to thesource electrode 5, on the side opposite to the side of the n typefirst region 14 where thedrain electrode 4 exists. Therefore, it is possible to prevent an electric field from being concentrated on the terminated end portion of thesemiconductor device 105. Accordingly, it is possible to improve the breakdown voltage of thefirst semiconductor layer 1. - Even when the
fourth regions 11 and theseventh region 15 are provided in the above-describedsemiconductor devices 100 to 103, the same effect can be obtained. - While several embodiments of the present invention have been described, these embodiments have been provided by way of examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as being included in the scope and spirit of the description.
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