WO2022075218A1 - Schottky diode - Google Patents

Schottky diode Download PDF

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WO2022075218A1
WO2022075218A1 PCT/JP2021/036436 JP2021036436W WO2022075218A1 WO 2022075218 A1 WO2022075218 A1 WO 2022075218A1 JP 2021036436 W JP2021036436 W JP 2021036436W WO 2022075218 A1 WO2022075218 A1 WO 2022075218A1
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type semiconductor
semiconductor layer
anode electrode
schottky diode
trench
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PCT/JP2021/036436
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French (fr)
Japanese (ja)
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義昭 中田
公平 佐々木
茂伸 山腰
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株式会社タムラ製作所
株式会社ノベルクリスタルテクノロジー
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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 at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
    • H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
    • H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
    • H01L29/47—Schottky barrier electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
    • H01L29/861—Diodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
    • H01L29/861—Diodes
    • H01L29/868—PIN diodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
    • H01L29/861—Diodes
    • H01L29/872—Schottky diodes

Definitions

  • the present invention relates to a Schottky diode.
  • JBS junction barrier Schottky
  • the JBS diode described in Patent Document 1 has an n - type drift layer made of SiC and a p-type layer obtained by ion-implanting a p-type impurity into the n-type drift layer, and the n - type drift layer and the n - type drift layer.
  • the p-type layer forms a pn junction.
  • Patent Document 2 a trench MOS type Ga 2 O 3 system Schottky diode in which a gate electrode is embedded in a semiconductor layer is known (see, for example, Patent Document 2).
  • Ga 2 O 3 series semiconductor devices are known to have high withstand voltage and low loss due to their physical properties represented by the wide band gap of Ga 2 O 3 .
  • the Schottky diode described in Patent Document 1 uses a trench MOS structure, a higher withstand voltage can be obtained without increasing the resistance of the semiconductor layer.
  • Patent Document 2 when trying to improve the resistance to surge current of a Ga 2 O 3 system Schottky diode as shown in Patent Document 2, it is very difficult to obtain a p-type Ga 2 O 3 . It is not possible to add p-type impurities to the Ga 2 O 3 layer to form a pn junction region.
  • An object of the present invention is to provide a Ga 2 O 3 system Schottky diode having high withstand voltage, low loss, and excellent resistance to surge current.
  • One aspect of the present invention provides the following Schottky diodes [1] to [4] in order to achieve the above object.
  • n - type semiconductor layer composed of a Ga 2 O3 system single crystal and having a plurality of trenches opening on one surface and the adjacent trenches of the n-type semiconductor layer.
  • a p-type semiconductor member composed of a cathode electrode directly or indirectly connected, a part of the mesa-shaped region, and a BN or Al x Ga 1-x N (x> 0) connected to the anode electrode.
  • An n-type semiconductor layer composed of a Ga 2 O 3 system single crystal and having a plurality of trenches opening on one surface, and a BN or Al x Ga 1-x N (x> embedded in the trench.
  • the present invention it is possible to provide a Ga 2 O 3 system Schottky diode having high withstand voltage, low loss, and excellent resistance to surge current.
  • FIG. 1 is a vertical sectional view of a Schottky diode according to the first embodiment.
  • FIG. 2 is a graph schematically showing the current-voltage characteristics when an inrush current flows when the Schottky diode includes a p-type semiconductor member (A) and when it does not (B).
  • FIG. 3 is a diagram schematically showing the band structure of an n-type semiconductor layer composed of a p-type semiconductor member and a Ga 2 O3 system single crystal, and the flow of holes.
  • FIG. 4 shows a band diagram of Ga 2 O 3 , which is a typical material of an n-type semiconductor layer, and BN, Al x Ga 1-x N (x> 0), which is a material of a p-type semiconductor member.
  • FIG. 5 is a vertical sectional view of a modified example of the Schottky diode according to the first embodiment.
  • FIG. 6 is a vertical sectional view of the Schottky diode according to the second embodiment.
  • FIG. 1 is a vertical sectional view of the Schottky diode 1 according to the first embodiment.
  • the Schottky diode 1 is a vertical Schottky diode having a trench MOS structure.
  • the shotkey diode 1 is an n-type having a layer laminated on the n-type semiconductor substrate 10 and the n-type semiconductor substrate 10 and having a plurality of trenches 12 opening on a surface 18 opposite to the n-type semiconductor substrate 10. Formed on the surface of the n-type semiconductor substrate 10 opposite to the n-type semiconductor layer 11 and the anode electrode 13 connected to the mesa-shaped region 110 between the semiconductor layer 11 and the adjacent trench 12 of the n-type semiconductor layer 11.
  • the cathode electrode 14 is embedded in the trench insulating film 15 that covers the inner surface of the trench 12 of the n-type semiconductor layer 11 and the trench 12 of the n-type semiconductor layer 11 so as to be covered with the trench insulating film 15. It has an anode electrode 16 electrically connected to, a part of a mesa-shaped region 110, and a p-type semiconductor member connected to the anode electrode 13.
  • the anode electrode 13 and the n-type semiconductor seen from the n-type semiconductor layer 11 are applied by applying a forward voltage (positive potential on the anode electrode 13 side) between the anode electrode 13 and the cathode electrode 14.
  • the energy barrier at the interface with the layer 11 is lowered, and a current flows from the anode electrode 13 to the cathode electrode 14.
  • the upper limit of the reverse leakage current of the Schottky diode is 1 ⁇ A.
  • the reverse voltage when a leak current of 1 ⁇ A flows is defined as the withstand voltage.
  • the current density of the reverse leakage current is 0.0001 A / cm 2 .
  • the electric field strength immediately below the Schottky electrode is approximately 0.8 MV / cm.
  • 0.0001 A / cm 2 is when a current of 1 ⁇ A flows through the Schottky electrode having a size of 1 mm ⁇ 1 mm. The current density just below the Schottky electrode.
  • the electric field strength directly under the Schottky electrode should be 0.8 MV / cm or less. It is necessary to reduce the donor concentration of the semiconductor layer to 10 15 cm -3 units and make the semiconductor layer very thick. Therefore, the conduction loss becomes very large, and it is difficult to manufacture a Schottky barrier diode having a high withstand voltage and a low loss.
  • the Schottky diode 1 Since the Schottky diode 1 according to the present embodiment has a trench MOS structure, a high withstand voltage can be obtained without increasing the resistance of the semiconductor layer. That is, the Schottky diode 1 is a Schottky diode having a high withstand voltage and a low loss.
  • the n-type semiconductor substrate 10 is made of an n-type Ga 2 O 3 system single crystal containing Group IV elements such as Si and Sn as donors.
  • the donor concentration of the n-type semiconductor substrate 10 is, for example, 1.0 ⁇ 10 18 cm -3 or more and 1.0 ⁇ 10 20 cm -3 or less.
  • the thickness of the n-type semiconductor substrate 10 is, for example, 10 to 600 ⁇ m.
  • the n-type semiconductor substrate 10 is, for example, a Ga 2 O 3 system single crystal substrate.
  • the Ga 2 O 3 system single crystal is a Ga 2 O 3 single crystal or a Ga 2 O 3 single crystal to which one or both of Al and In are added, and (Ga x Aly In (1) . ⁇ X ⁇ y) ) A single crystal of a Ga 2 O 3 system semiconductor having a composition represented by 2 O 3 (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, 0 ⁇ x + y ⁇ 1).
  • Al is added to Ga 2 O 3
  • the band gap widens
  • In is added, the band gap narrows.
  • the Ga 2 O 3 single crystal described above has, for example, a ⁇ -type crystal structure.
  • the n-type semiconductor layer 11 is composed of an n-type Ga 2 O 3 system single crystal containing Group IV elements such as Si and Sn as donors.
  • the donor concentration of the n-type semiconductor layer 11 is lower than the donor concentration of the n-type semiconductor substrate 10.
  • the n-type semiconductor layer 11 is, for example, an epitaxial layer epitaxially grown on the n-type semiconductor substrate 10 which is a Ga 2 O 3 system single crystal substrate.
  • a high-concentration layer containing a high-concentration donor may be formed between the n-type semiconductor substrate 10 and the n-type semiconductor layer 11.
  • This high donor concentration layer is used, for example, when the n-type semiconductor layer 11 is epitaxially grown on the n-type semiconductor substrate 10.
  • the n-type semiconductor layer 10 is on the n-type semiconductor substrate 10.
  • the semiconductor layer 11 is directly grown, the region of the n-type semiconductor layer 11 near the interface with the n-type semiconductor substrate 10 may have high resistance.
  • a high donor concentration layer is used.
  • the concentration of the high donor concentration layer is set to, for example, a higher concentration than that of the n-type semiconductor layer 11, and more preferably set to a higher concentration than that of the n-type semiconductor substrate 10.
  • the donor concentration of the n-type semiconductor layer 11 increases, the electric field strength of each part of the Schottky diode 1 increases.
  • the n-type semiconductor is used.
  • the donor concentration of layer 11 is preferably about 6.0 ⁇ 10 16 cm -3 or less.
  • the resistance of the n-type semiconductor layer 11 increases and the forward loss increases. Therefore, for example, in order to obtain a withstand voltage of 1200 V or less, it is 3.0 ⁇ 10 16 cm -3 or more. It is preferable to have. Further, in order to obtain a higher pressure resistance, it is preferable to reduce the donor concentration to, for example, about 1.0 ⁇ 10 16 cm -3 .
  • the thickness T of the n-type semiconductor layer 11 increases, the maximum electric field strength in the n-type semiconductor layer 11 and the maximum electric field strength in the trench insulating film 15 decrease.
  • the thickness T of the n-type semiconductor layer 11 is preferably about 5.5 ⁇ m or more and 9 ⁇ m or less.
  • the electric field strength of each part of the Schottky diode 1 changes depending on the depth D of the trench 12.
  • the depth D is preferably about 2 ⁇ m or more and 6 ⁇ m or less, and more preferably about 3 ⁇ m or more and 4 ⁇ m or less.
  • the width Wt of the trench 12 is irrelevant to the electric field strength in the region directly below the anode electrode 13, it can be freely set. Since no current flows in the trench 12, it is preferable that the width Wt is as narrow as possible. However, if the width Wt is made too fine, it becomes difficult to embed the trench insulating film 15 and the anode electrode 16 in the trench 12, and the manufacturing yield deteriorates. On the other hand, according to the study by the present inventor, it has been found that when the width Wt is 3 ⁇ m or more, even if the width Wt increases, the embedding property of the anode electrode 16 is hardly affected. Further, when the width W t is less than 0.5 ⁇ m, a special exposure apparatus is required for forming the trench 12, and the manufacturing cost may increase. Therefore, the width W t is preferably 0.5 ⁇ m or more and 3 ⁇ m or less.
  • the width Wm of the mesa-shaped portion 110 between the adjacent trenches 12 of the n -type semiconductor layer 11 decreases, the maximum electric field strength in the region immediately below the anode electrode 13 in the n-type semiconductor layer 11 decreases.
  • the width Wm of the mesa-shaped portion 110 is preferably 2.5 ⁇ m or less.
  • the trench insulating film 15 is preferably made of a material having a high dielectric constant.
  • a material having a high dielectric constant for example, Al 2 O 3 (relative permittivity of about 9.3) and HfO 2 (relative permittivity of about 22) can be used as the material of the trench insulating film 15, but HfO 2 having a high dielectric constant is used. Is particularly preferable.
  • the thickness of the trench insulating film 15 is preferably small, and more preferably 300 nm or less. However, as a matter of course, a thickness such that a direct current hardly flows between the anode electrode 16 and the n-type semiconductor layer 11 is required.
  • the material of the anode electrode 16 is not particularly limited as long as it has conductivity, and for example, polycrystalline Si doped at a high concentration or a metal such as Ni or Au can be used.
  • the electric field strength in the Schottky diode 1 is affected by the width W m of the mesa-shaped portion 110 between the two adjacent trenches 12, the depth D of the trench 12, the thickness of the trench insulating film 15, and the like. However, it is hardly affected by the planar pattern of the trench 12. Therefore, the planar pattern of the trench 12 of the n-type semiconductor layer 11 is not particularly limited.
  • the cathode electrode 14 makes ohmic contact with the n-type semiconductor substrate 10.
  • the cathode electrode 14 is made of a metal such as Ti.
  • the cathode electrode 14 may have a multilayer structure in which different metal films are laminated, for example, Ti / Au or Ti / Al.
  • the layer of the cathode electrode 14 in contact with the n-type semiconductor substrate 10 is made of Ti.
  • the cathode electrode 14 is connected to the side opposite to the anode electrode 13 of the n-type semiconductor layer 11 and makes ohmic contact with the n-type semiconductor layer 11.
  • the p-type semiconductor member 17 is a member used as a countermeasure against surges, and is composed of p-type BN (boron nitride) or Al x Ga 1-x N (x> 0) (aluminum gallium nitride).
  • the p-type semiconductor member 17 made of BN contains additives such as Zn, Mg, Be, and Si as acceptors.
  • the p-type semiconductor member 17 composed of Al x Ga 1-x N (x> 0) contains an additive such as Mg as an acceptor.
  • group III atomic vacancies (pores due to lack of B in the case of BN, Al or Ga in the case of Al x Ga 1-x N (x> 0)). It may have a hole) as an acceptor.
  • the energy at the upper end of the valence band of the p-type semiconductor member 17 is equal to or less than the energy obtained by adding 2 eV to the energy at the upper end of the valence band of the Ga 2 O3 system semiconductor constituting the n - type semiconductor layer 11.
  • the resistance of the drift layer can be reduced when a surge current (also called inrush current, starting current, etc.) that can occur when the shotkey diode 1 is turned on can be reduced, and heat generation and breakage can be suppressed. be able to.
  • the pn diode has a larger on-voltage than the Schottky diode. Therefore, the design can be made so that the pn diode portion composed of the p-type semiconductor member 17 and the n-type semiconductor layer 11 does not turn on at the voltage at which the Schottky diode 1 turns on.
  • the on-voltage of the Schottky diode 1 can be set to about 1V
  • the on-voltage of the pn diode portion can be set to about 2V.
  • the pn diode portion does not turn on in the normal operation of the Schottky diode 1, so that the original high-speed operation of the Schottky diode becomes possible.
  • the inrush current is generated, the voltage of the shotkey diode 1 rises and reaches the voltage at which the pn diode portion is turned on, and holes are injected from the p-type semiconductor member 17 into the n-type semiconductor layer 11.
  • the same number of electrons as the injected holes are injected from the cathode electrode 14 into the n-type semiconductor layer 11, and the resistance of the drift layer is significantly reduced. Therefore, although a large current called an inrush current flows through the Schottky diode 1, the rise in voltage is suppressed, so that the temperature rise is suppressed and damage to the Schottky diode 1 due to the inrush current can be prevented.
  • FIG. 2 is a graph schematically showing the current-voltage characteristics when the inrush current flows when the Schottky diode 1 includes the p-type semiconductor member 17 (A) and when it does not (B).
  • the voltage continues to rise as the current increases, and the temperature of the Schottky diode 1 rises sharply and burns out.
  • the p-type semiconductor member 17 when the p-type semiconductor member 17 is included, when the voltage V pn at which the pn diode portion is turned on is reached, the rate of increase in voltage decreases.
  • the increase in voltage is suppressed, so that the temperature increase is suppressed and the Schottky diode 1 is prevented from being damaged.
  • FIG. 3 is a diagram schematically showing the band structure of the n-type semiconductor layer 11 composed of the p-type semiconductor member 17 and the Ga 2 O3 system single crystal and the flow of holes.
  • the energy EV2 at the upper end of the valence band of the p-type semiconductor member 17 is equal to or less than the energy EV1 obtained by adding 2 eV to the energy EV1 at the upper end of the valence band of the Ga 2 O3 system single crystal.
  • holes can be injected from the p-type semiconductor member 17 into the n-type semiconductor layer 11.
  • the size of the energy EC2 at the lower end of the conduction band of the p-type semiconductor member 17 is limited to a specific range because it does not affect the injection of holes from the p-type semiconductor member 17 into the n-type semiconductor layer 11. Will not be done.
  • the energy E V2 at the upper end of the valence band of the p-type semiconductor member 17 is equal to or less than the energy E V1 at the upper end of the valence band of the Ga 2 O3 system single crystal constituting the n - type semiconductor layer 11. Since the holes are easily transferred from the p-type semiconductor member 17 to the n-type semiconductor layer 11, the resistance to the inrush current can be further improved.
  • FIG. 4 includes a band structure of Ga 2 O 3 , which is a typical material of the n-type semiconductor layer 11, and BN, Al x Ga 1-x N (x> 0), which is a material of the p-type semiconductor member 17. Shows the band lineup.
  • the rectangle in FIG. 4 shows the bandgap of each material, the numerical value in the bandgap is the bandgap size [eV], and the numerical value on the upper side of the bandgap is the band offset (conduction band) of the conduction band with Ga 2 O 3 .
  • the values below the bandgap indicate the band offset [eV] of the valence band with Ga 2 O 3 .
  • AlGaN indicates Al x Ga 1 -x N when 0 ⁇ x ⁇ 1.
  • the closer x is to 1, the closer to AlN, and the closer x is to 0, the closer to GaN.
  • FIG. 4 also shows the bandgap between AlO 2 and In 2 O 3 .
  • the Ga 2 O 3 series single crystal which is the material of the n-type semiconductor layer 11
  • the band structure approaches Al 2 O 3 when the concentration of Al increases
  • the band structure approaches In 2 O 3 when the concentration of In increases.
  • the amount of energy modulation at the upper end of the valence band due to the change in Al concentration and In concentration in the Ga 2 O 3 system single crystal is not large, and the band offset of the valence band with Ga 2 O 3 Is about 0.4 eV at the maximum.
  • the energy at the upper end of the valence band of BN, Al x Ga 1-x N (x> 0), which is the material of the p-type semiconductor member 17, is the energy of the Ga 2 O 3 series single crystal, which is the material of the n-type semiconductor layer 11. It is less than or equal to the energy obtained by adding 2 eV to the energy at the upper end of the valence band.
  • this relationship is understood when the Al concentration of Al x Ga 1-x N (x> 0) and the Al concentration and In concentration of the Ga 2 O 3 system single crystal take. It also holds true.
  • Al x Ga 1-x N (x> 0), which is the material of the p-type semiconductor member 17, has a lower energy at the upper end of the valence band as the Al concentration x is closer to 1, and is a material of the n-type semiconductor layer 11. It approaches the energy of the upper end of the valence band of a certain Ga 2 O 3 series single crystal, or becomes smaller than the energy of the upper end of the valence band of the Ga 2 O 3 series single crystal which is the material of the n-type semiconductor layer 11. Therefore, for example, it is preferable that the p-type semiconductor member 17 is made of Al x Ga 1-x N (x ⁇ 0.8).
  • the energy at the upper end of the valence band of the BN is substantially equal to the energy at the upper end of the valence band of the Ga 2 O3 system single crystal which is the material of the n - type semiconductor layer 11, the BN is used as the p-type semiconductor member 17. By using it as a material, the resistance of the shotkey diode 1 to the inrush current can be particularly enhanced.
  • the size, number, and arrangement of the p-type semiconductor member 17 are not particularly limited.
  • FIG. 5 is a vertical cross-sectional view of the Schottky diode 3 which is a modification of the Schottky diode 1 according to the first embodiment.
  • the Schottky diode 3 differs from the Schottky diode 1 in that it does not have a trench structure, that is, it does not have a trench 12, a trench insulating film 15, and an anode electrode 16 in the n-type semiconductor layer 11. Since the Schottky diode 3 does not have a trench structure, the withstand voltage is inferior to that of the Schottky diode 1, but the p-type semiconductor member 17 has the same resistance to surge current as the Schottky diode 1.
  • FIG. 6 is a vertical sectional view of the Schottky diode 2 according to the second embodiment.
  • the Schottky diode 2 is a vertical junction barrier Schottky (JBS) diode having a trench structure.
  • JBS vertical junction barrier Schottky
  • the shotkey diode 2 includes an n-type semiconductor substrate 20 and an n-type semiconductor layer 21 having a plurality of trenches 25 formed on the n-type semiconductor substrate 20 and having a plurality of trenches 25 opened on the surface 26 opposite to the n-type semiconductor substrate 20.
  • the n-type semiconductor layer 21 and the anode electrode 23 form a Schottky junction, and the Schottky diode 2 utilizes the rectification property of this Schottky junction.
  • a p-type semiconductor member 22 made of BN or Al x Ga 1-x N (x> 0) is used instead of the p-type Ga 2 O 3 which is difficult to form. ..
  • the anode electrode 23 and the n-type seen from the n-type semiconductor layer 21 are applied by applying a forward voltage (positive potential on the anode electrode 23 side) between the anode electrode 23 and the cathode electrode 24.
  • the potential barrier at the interface with the semiconductor layer 21 is lowered, and a current flows from the anode electrode 23 to the cathode electrode 24.
  • the Schottky diode 2 Since the Schottky diode 2 according to the present embodiment has a trench type JBS structure, a high withstand voltage can be obtained without increasing the resistance of the semiconductor layer, as with the Schottky diode 1 according to the first embodiment. be able to. That is, the Schottky diode 2 is a Schottky barrier diode having a high withstand voltage and a low loss.
  • the n-type semiconductor substrate 20 is made of an n-type Ga 2 O 3 system single crystal containing Group IV elements such as Si and Sn as donors.
  • the donor concentration of the n-type semiconductor substrate 20 is, for example, 1.0 ⁇ 10 18 cm -3 or more and 1.0 ⁇ 10 20 cm -3 or less.
  • the thickness of the n-type semiconductor substrate 20 is, for example, 10 to 600 ⁇ m. Is.
  • the n-type semiconductor substrate 20 is, for example, a Ga 2 O 3 system single crystal substrate.
  • the n-type semiconductor layer 21 is composed of an n-type Ga 2 O 3 system single crystal containing Group IV elements such as Si and Sn as donors.
  • the donor concentration of the n-type semiconductor layer 21 is lower than the donor concentration of the n-type semiconductor substrate 20.
  • the n-type semiconductor layer 21 is, for example, an epitaxial layer epitaxially grown on the n-type semiconductor substrate 10 which is a Ga 2 O 3 system single crystal substrate.
  • a high-concentration layer containing a high-concentration donor may be formed between the n-type semiconductor substrate 20 and the n-type semiconductor layer 21.
  • This high donor concentration layer is used, for example, when the n-type semiconductor layer 21 is epitaxially grown on the n-type semiconductor substrate 20.
  • the amount of dopant taken up is unstable and acceptor impurities are diffused from the n-type semiconductor substrate 20, so that the n-type semiconductor layer 21 is placed on the n-type semiconductor substrate 20.
  • the region near the interface between the n-type semiconductor layer 21 and the n-type semiconductor substrate 20 may have high resistance.
  • the concentration of the high donor concentration layer is set to, for example, a higher concentration than that of the n-type semiconductor layer 21, and more preferably set to a higher concentration than that of the n-type semiconductor substrate 20.
  • the donor concentration of the n-type semiconductor layer 21 increases, the electric field strength of each part of the Schottky diode 2 increases.
  • the donor concentration of the n-type semiconductor layer 21 is approximately 2.0 ⁇ . It is preferably 10 17 cm -3 or less.
  • the donor concentration decreases, the resistance of the n-type semiconductor layer 21 increases and the forward loss increases. Therefore, for example, when ensuring a withstand voltage of 1200 V or less, 3.0 ⁇ 10 16 cm -3 or more. Is preferable.
  • the donor concentration may be lowered to, for example, about 1.0 ⁇ 10 16 cm -3 .
  • the thickness T of the n-type semiconductor layer 21 increases, the maximum electric field strength in the n-type semiconductor layer 21 decreases.
  • the thickness of the n-type semiconductor layer 21 is preferably about 3 ⁇ m or more and 9 ⁇ m or less.
  • the electric field strength of each part of the Schottky diode 2 changes depending on the depth D of the trench 25.
  • the depth D of the trench 25 is approximately 1.5 ⁇ m or more and 6 ⁇ m. The following is preferable.
  • the width Wt of the trench 25 is preferably 0.3 ⁇ m or more and 5 ⁇ m or less.
  • the width Wm of the mesa-shaped portion 210 between the adjacent trenches 25 of the n -type semiconductor layer 21 decreases.
  • the width Wm of the mesa-shaped portion 210 is preferably 5 ⁇ m or less.
  • the width Wm of the mesa-shaped portion 210 is 0.25 ⁇ m or more.
  • the anode electrode 23 is made of a material in which the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is in Schottky contact with the n-type semiconductor layer 21. That is, when the anode electrode 23 has a single-layer structure, the whole is made of a material that makes Schottky contact with the n-type semiconductor layer 21, and when it has a multilayer structure, at least the layer in contact with the n-type semiconductor layer 21 is an n-type semiconductor. It consists of a material that makes Schottky contact with layer 21.
  • the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is made of Fe (iron), Cu (copper), Mo (molybdenum), or W (tungsten). Is preferable.
  • the rising voltage of the Schottky diode 2 is 0.4 V or more and 0.6 V or less.
  • the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is made of Fe
  • the rising voltage of the Schottky diode 2 is 0.4 V or more and 0.7 V or less.
  • the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is made of Cu
  • the rising voltage of the Schottky diode 2 is 0.6 V or more and 0.9 V or less.
  • the rising voltage depends on the width W m of the mesa-shaped portion 210, and becomes larger as the width W m becomes smaller.
  • the electric field strength in the Schottky diode 2 is affected by the width W m of the mesa-shaped portion 210 between the two adjacent trenches 25, the depth D of the trench 25, and the like, but the plane of the trench 25. It is hardly affected by the pattern (planar pattern of the p-type semiconductor member 22). Therefore, the planar pattern of the trench 25 of the n-type semiconductor layer 21 (the planar pattern of the p-type semiconductor member 22) is not particularly limited.
  • the cathode electrode 24 is in ohmic contact with the n-type semiconductor substrate 20.
  • the cathode electrode 24 is made of a metal such as Ti.
  • the cathode electrode 24 may have a multilayer structure in which different metal films are laminated, for example, Ti / Au or Ti / Al.
  • the layer of the cathode electrode 24 in contact with the n-type semiconductor substrate 20 is made of Ti.
  • the cathode electrode 24 is connected to the side opposite to the anode electrode 23 of the n-type semiconductor layer 21 and makes ohmic contact with the n-type semiconductor layer 21.
  • the p-type semiconductor member 22 is a member used for surge countermeasures like the p-type semiconductor member 17 according to the first embodiment, and is a p-type BN or Al x Ga 1-x N (x>. It consists of 0).
  • the p-type semiconductor member 22 made of BN contains additives such as Zn, Mg, Be, and Si as acceptors.
  • the p-type semiconductor member 22 made of Al x Ga 1-x N (x> 0) contains additives such as as an acceptor.
  • group III atomic vacancies pores due to lack of B in the case of BN, Al or Ga in the case of Al x Ga 1-x N (x> 0)). It may have a hole) as an acceptor.
  • the energy at the upper end of the valence band of the p-type semiconductor member 22 is less than the energy obtained by adding 2 eV to the energy at the upper end of the valence band of the Ga 2 O3 system semiconductor constituting the n - type semiconductor layer 21, it is p-type.
  • the resistance of the drift layer can be reduced when a surge current (also called inrush current, starting current, etc.) that may occur when the shotkey diode 2 is turned on is generated, and heat generation and breakage are suppressed. be able to.
  • the pn diode has a larger on-voltage than the Schottky diode. Therefore, the design can be made so that the pn diode portion composed of the p-type semiconductor member 22 and the n-type semiconductor layer 21 does not turn on at the voltage at which the Schottky diode 2 turns on.
  • the on-voltage of the Schottky diode 2 can be set to about 1V
  • the on-voltage of the pn diode portion can be set to about 2V.
  • the pn diode portion does not turn on in the normal operation of the Schottky diode 2, so that the original high-speed operation of the Schottky diode becomes possible.
  • the inrush current is generated, the voltage of the shotkey diode 2 rises and reaches the voltage at which the pn diode portion is turned on, and holes are injected from the p-type semiconductor member 22 into the n-type semiconductor layer 21.
  • an inrush current flows through the Schottky diode 2, but the rise in voltage is suppressed, so that the temperature rise is suppressed and damage to the Schottky diode 2 due to the inrush current can be prevented.
  • the p-type semiconductor member 22 When the energy at the upper end of the valence band of the p-type semiconductor member 22 is equal to or less than the energy at the upper end of the valence band of the Ga 2 O3 system single crystal constituting the n - type semiconductor layer 21, the p-type semiconductor member Since the holes are easily transferred from the 22 to the n-type semiconductor layer 21, the resistance to the inrush current can be further improved.
  • the energy at the upper end of the valence band of BN, Al x Ga 1-x N (x> 0), which is the material of the p-type semiconductor member 22, is the energy of the Ga 2 O 3 series single crystal, which is the material of the n-type semiconductor layer 21. It is less than or equal to the energy obtained by adding 2 eV to the energy at the upper end of the valence band.
  • this relationship is understood when the Al concentration of Al x Ga 1-x N (x> 0) and the Al concentration and In concentration of the Ga 2 O 3 system single crystal take. It also holds true.
  • Al x Ga 1-x N (x> 0), which is the material of the p-type semiconductor member 22, has a lower energy at the upper end of the valence band as the Al concentration x is closer to 1, and is a material of the n-type semiconductor layer 21. It approaches the energy of the upper end of the valence band of a certain Ga 2 O 3 series single crystal, or becomes smaller than the energy of the upper end of the valence band of the Ga 2 O 3 series single crystal which is the material of the n-type semiconductor layer 21. Therefore, for example, it is preferable that the p-type semiconductor member 22 is made of Al x Ga 1-x N (x ⁇ 0.8).
  • the energy at the upper end of the valence band of the BN is substantially equal to the energy at the upper end of the valence band of the Ga 2 O3 system single crystal which is the material of the n - type semiconductor layer 21, the BN is used as the p-type semiconductor member 22. By using it as a material, the resistance of the shotkey diode 2 to the inrush current can be particularly enhanced.
  • n-type semiconductor substrate 20 a Ga 2 O 3 series single crystal containing Si as a donor is epitaxially grown on the n-type semiconductor substrate 20 by the VPE method, and an n-type semiconductor layer having a thickness of about 5 mm and a Si concentration of about 6 ⁇ 10 15 cm -3 is formed. 21 is formed.
  • a trench 25 is formed on the surface 26 of the n-type semiconductor layer 21 opposite to the n-type semiconductor substrate 20 by using photolithography and dry etching.
  • a cathode electrode 24 having a Ti / Au laminated structure or the like is formed on the bottom surface of the n-type semiconductor substrate 20 by electron beam vapor deposition. After that, heat treatment is performed to reduce the contact resistance between the cathode electrode 24 and the n-type semiconductor substrate 20.
  • a BN film having Zn added having a thickness sufficient to embed the trench 25 is deposited on the entire surface 26 of the n-type semiconductor layer 21.
  • a sputtering method such as a sputtering method, an MBE method, and a CVD method may be used for forming the BN film.
  • Mg, Be, etc. other than Zn may be added to the BN film as an acceptor.
  • Si can be used as an acceptor by using a laser-assisted plasma CVD method as a method for forming a BN film.
  • these acceptors may be added by ion implantation after the formation of the BN film.
  • the BN film is etched by RIE until the mesa-shaped portion 210 between the adjacent trenches 25 of the n-type semiconductor layer 21 is exposed.
  • an anode electrode 23 having a Mo / Au laminated structure is formed on the surface 26 of the n-type semiconductor layer 21 by electron beam vapor deposition.
  • the anode electrode 23 is patterned into a predetermined shape such as a circle by lift-off.
  • Ga 2 O 3 system Schottky diode having high withstand voltage, low loss, and excellent resistance to surge current.

Abstract

Provided is a Ga2O3-based Schottky diode having a high withstand voltage, low loss, and excellent resistance against surge current.　Provided, according to one embodiment, is a Schottky diode 1 which is made of Ga2O3-based single crystals and comprises: an n-type semiconductor layer 11 having a plurality of trenches 12 opening to one surface 18; an anode electrode 13 connected to mesa-shaped regions 110 between the adjacent trenches 12 of the n-type semiconductor layer 11; an anode electrode 16 embedded in each of the plurality of trenches 12 in a state covered with a trench insulating film 15 and electrically connected to the anode electrode 13; a cathode electrode 14 connected directly or indirectly to the side of the n-type semiconductor layer 11 opposite to the anode electrode 13; and a p-type semiconductor member 17 connected to a part of the mesa-shaped regions 110 and to the anode electrode 16, the p-type semiconductor member being made of BN or AlxGa1-xN (x>0).

Description

ショットキーダイオードSchottky diode
　本発明は、ショットキーダイオードに関する。 The present invention relates to a Schottky diode.
　従来、ジャンクションバリアショットキー（ＪＢＳ）ダイオードと呼ばれる、ｐｎ接合とショットキー接合を組み合わせた構造を有するダイオードが知られている（例えば、特許文献１参照）。ＪＢＳダイオードにおいては、ｐｎダイオード部分にサージ電流を流すことができるため、ｐｎ接合を有しないショットキーバリアダイオードと比較して、サージ電流への耐性に優れる。 Conventionally, a diode having a structure combining a pn junction and a Schottky junction, which is called a junction barrier Schottky (JBS) diode, is known (see, for example, Patent Document 1). In the JBS diode, since a surge current can be passed through the pn diode portion, the resistance to the surge current is excellent as compared with the Schottky barrier diode having no pn junction.
　特許文献１に記載のＪＢＳダイオードは、ＳｉＣからなるｎ－型ドリフト層と、ｎ－型ドリフト層にｐ型不純物をイオン注入することにより得られるｐ型層を有し、ｎ－型ドリフト層とｐ型層がｐｎ接合を形成している。 The JBS diode described in Patent Document 1 has an n - type drift layer made of SiC and a p-type layer obtained by ion-implanting a p-type impurity into the n-type drift layer, and the n - type drift layer and the n - type drift layer. The p-type layer forms a pn junction.
　また、従来、ゲート電極が半導体層に埋め込まれたトレンチＭＯＳ型のＧａ２Ｏ３系ショットキーダイオードが知られている（例えば、特許文献２参照）。Ｇａ２Ｏ３系の半導体デバイスは、Ｇａ２Ｏ３の広いバンドギャップに代表される物性から、高耐圧・低損失であることが知られている。さらに、特許文献１に記載のショットキーダイオードは、トレンチＭＯＳ構造を用いているため、半導体層の抵抗を増加することなく、より高い耐圧を得ることができる。 Further, conventionally, a trench MOS type Ga 2 O 3 system Schottky diode in which a gate electrode is embedded in a semiconductor layer is known (see, for example, Patent Document 2). Ga 2 O 3 series semiconductor devices are known to have high withstand voltage and low loss due to their physical properties represented by the wide band gap of Ga 2 O 3 . Further, since the Schottky diode described in Patent Document 1 uses a trench MOS structure, a higher withstand voltage can be obtained without increasing the resistance of the semiconductor layer.
特開２００８－２８２９７３号公報Japanese Unexamined Patent Publication No. 2008-282973 特開２０１８－１４２５７７号公報Japanese Unexamined Patent Publication No. 2018-142577
　しかしながら、特許文献２に示されるようなＧａ２Ｏ３系ショットキーダイオードのサージ電流への耐性を向上させようとした場合、ｐ型のＧａ２Ｏ３を得ることが非常に困難であるため、Ｇａ２Ｏ３層にｐ型不純物を添加してｐｎ接合領域を形成することができない。 However, when trying to improve the resistance to surge current of a Ga 2 O 3 system Schottky diode as shown in Patent Document 2, it is very difficult to obtain a p-type Ga 2 O 3 . It is not possible to add p-type impurities to the Ga 2 O 3 layer to form a pn junction region.
　本発明の目的は、高耐圧かつ低損失であり、かつサージ電流への耐性に優れたＧａ２Ｏ３系のショットキーダイオードを提供することにある。 An object of the present invention is to provide a Ga 2 O 3 system Schottky diode having high withstand voltage, low loss, and excellent resistance to surge current.
　本発明の一態様は、上記目的を達成するために、下記［１］～［４］のショットキーダイオードを提供する。 One aspect of the present invention provides the following Schottky diodes [1] to [4] in order to achieve the above object.
［１］Ｇａ２Ｏ３系単結晶からなり、一方の面に開口する複数のトレンチを有するｎ型半導体層と、前記ｎ型半導体層の隣接する前記トレンチの間のメサ形状領域に接続されたアノード電極と、絶縁膜に覆われた状態で前記複数のトレンチのそれぞれに埋め込まれ、前記アノード電極に電気的に接続されたトレンチアノード電極と、前記ｎ型半導体層の前記アノード電極と反対側に直接又は間接的に接続されたカソード電極と、前記メサ形状領域の一部及び前記アノード電極に接続された、ＢＮ又はＡｌｘＧａ１－ｘＮ（ｘ＞０）からなるｐ型半導体部材と、を備えた、ショットキーダイオード。
［２］Ｇａ２Ｏ３系単結晶からなり、一方の面に開口する複数のトレンチを有するｎ型半導体層と、前記トレンチ内に埋め込まれた、ＢＮ又はＡｌｘＧａ１－ｘＮ（ｘ＞０）からなるｐ型半導体部材と、前記ｎ型半導体層の隣接する前記トレンチの間のメサ形状領域、及び前記ｐ型半導体部材に接続されたアノード電極と、前記ｎ型半導体層の前記アノード電極と反対側に直接又は間接的に接続されたカソード電極と、を備えた、ショットキーダイオード。
［３］前記ｐ型半導体部材がＡｌｘＧａ１－ｘＮ（ｘ≧０．８）からなる、上記［１］又は［２］に記載のショットキーダイオード。
［４］前記ｐ型半導体部材の価電子帯の上端のエネルギーが、前記Ｇａ２Ｏ３系単結晶の価電子帯の上端のエネルギー以下である、上記［１］～［３］のいずれか１項に記載のショットキーダイオード。 [1] It is connected to a mesa-shaped region between an n - type semiconductor layer composed of a Ga 2 O3 system single crystal and having a plurality of trenches opening on one surface and the adjacent trenches of the n-type semiconductor layer. The anode electrode, the trench anode electrode embedded in each of the plurality of trenches in a state of being covered with an insulating film, and electrically connected to the anode electrode, and the side opposite to the anode electrode of the n-type semiconductor layer. A p-type semiconductor member composed of a cathode electrode directly or indirectly connected, a part of the mesa-shaped region, and a BN or Al x Ga 1-x N (x> 0) connected to the anode electrode. With a shot key anode.
[2] An n-type semiconductor layer composed of a Ga 2 O 3 system single crystal and having a plurality of trenches opening on one surface, and a BN or Al x Ga 1-x N (x> embedded in the trench. A mesa-shaped region between a p-type semiconductor member composed of 0), an adjacent trench of the n-type semiconductor layer, an anode electrode connected to the p-type semiconductor member, and the anode electrode of the n-type semiconductor layer. A Schottky diode with a cathode electrode, which is directly or indirectly connected to the opposite side.
[3] The Schottky diode according to the above [1] or [2], wherein the p-type semiconductor member is made of Al x Ga 1-x N (x ≧ 0.8).
[4] Any one of the above [1] to [ 3 ], wherein the energy at the upper end of the valence band of the p-type semiconductor member is equal to or less than the energy at the upper end of the valence band of the Ga 2 O3 system single crystal. The Schottky diode described in the section.
　本発明によれば、高耐圧かつ低損失であり、かつサージ電流への耐性に優れたＧａ２Ｏ３系のショットキーダイオードを提供することができる。 According to the present invention, it is possible to provide a Ga 2 O 3 system Schottky diode having high withstand voltage, low loss, and excellent resistance to surge current.
図１は、第１の実施の形態に係るショットキーダイオードの垂直断面図である。FIG. 1 is a vertical sectional view of a Schottky diode according to the first embodiment. 図２は、ショットキーダイオードがｐ型半導体部材を含む場合（Ａ）と含まない場合（Ｂ）の、突入電流が流れるときの電流－電圧特性を模式的に示すグラフである。FIG. 2 is a graph schematically showing the current-voltage characteristics when an inrush current flows when the Schottky diode includes a p-type semiconductor member (A) and when it does not (B). 図３は、ｐ型半導体部材とＧａ２Ｏ３系単結晶からなるｎ型半導体層のバンド構造と、正孔の流れを模式的に示す図である。FIG. 3 is a diagram schematically showing the band structure of an n-type semiconductor layer composed of a p-type semiconductor member and a Ga 2 O3 system single crystal, and the flow of holes. 図４は、ｎ型半導体層の典型的な材料であるＧａ２Ｏ３と、ｐ型半導体部材の材料であるＢＮ、ＡｌｘＧａ１－ｘＮ（ｘ＞０）のバンドダイアグラムを示す。FIG. 4 shows a band diagram of Ga 2 O 3 , which is a typical material of an n-type semiconductor layer, and BN, Al x Ga 1-x N (x> 0), which is a material of a p-type semiconductor member. 図５は、第１の実施の形態に係るショットキーダイオードの変形例の垂直断面図である。FIG. 5 is a vertical sectional view of a modified example of the Schottky diode according to the first embodiment. 図６は、第２の実施の形態に係るショットキーダイオードの垂直断面図である。FIG. 6 is a vertical sectional view of the Schottky diode according to the second embodiment.
〔第１の実施の形態〕
（ショットキーダイオードの構成）
　図１は、第１の実施の形態に係るショットキーダイオード１の垂直断面図である。ショットキーダイオード１は、トレンチＭＯＳ構造を有する縦型のショットキーダイオードである。 [First Embodiment]
(Schottky diode configuration)
FIG. 1 is a vertical sectional view of the Schottky diode 1 according to the first embodiment. The Schottky diode 1 is a vertical Schottky diode having a trench MOS structure.
　ショットキーダイオード１は、ｎ型半導体基板１０と、ｎ型半導体基板１０に積層される層であって、そのｎ型半導体基板１０と反対側の面１８に開口する複数のトレンチ１２を有するｎ型半導体層１１と、ｎ型半導体層１１の隣接するトレンチ１２の間のメサ形状領域１１０に接続されたアノード電極１３と、ｎ型半導体基板１０のｎ型半導体層１１と反対側の面上に形成されたカソード電極１４と、ｎ型半導体層１１のトレンチ１２の内面を覆うトレンチ絶縁膜１５と、ｎ型半導体層１１のトレンチ１２内にトレンチ絶縁膜１５に覆われるように埋め込まれ、アノード電極１３に電気的に接続されるアノード電極１６と、メサ形状領域１１０の一部及びアノード電極１３に接続されたｐ型半導体部材と、を有する。 The shotkey diode 1 is an n-type having a layer laminated on the n-type semiconductor substrate 10 and the n-type semiconductor substrate 10 and having a plurality of trenches 12 opening on a surface 18 opposite to the n-type semiconductor substrate 10. Formed on the surface of the n-type semiconductor substrate 10 opposite to the n-type semiconductor layer 11 and the anode electrode 13 connected to the mesa-shaped region 110 between the semiconductor layer 11 and the adjacent trench 12 of the n-type semiconductor layer 11. The cathode electrode 14 is embedded in the trench insulating film 15 that covers the inner surface of the trench 12 of the n-type semiconductor layer 11 and the trench 12 of the n-type semiconductor layer 11 so as to be covered with the trench insulating film 15. It has an anode electrode 16 electrically connected to, a part of a mesa-shaped region 110, and a p-type semiconductor member connected to the anode electrode 13.
　ショットキーダイオード１においては、アノード電極１３とカソード電極１４との間に順方向電圧（アノード電極１３側が正電位）を印加することにより、ｎ型半導体層１１から見たアノード電極１３とｎ型半導体層１１との界面のエネルギー障壁が低下し、アノード電極１３からカソード電極１４へ電流が流れる。 In the Schottky diode 1, the anode electrode 13 and the n-type semiconductor seen from the n-type semiconductor layer 11 are applied by applying a forward voltage (positive potential on the anode electrode 13 side) between the anode electrode 13 and the cathode electrode 14. The energy barrier at the interface with the layer 11 is lowered, and a current flows from the anode electrode 13 to the cathode electrode 14.
　一方、アノード電極１３とカソード電極１４との間に逆方向電圧（アノード電極１３側が負電位）を印加したときは、ショットキー障壁により、電流は流れない。また、アノード電極１３とカソード電極１４との間に逆方向電圧を印加すると、アノード電極１３とｎ型半導体層１１との界面及びトレンチ絶縁膜１５とｎ型半導体層１１との界面から空乏層が拡がる。 On the other hand, when a reverse voltage (negative potential on the anode electrode 13 side) is applied between the anode electrode 13 and the cathode electrode 14, no current flows due to the Schottky barrier. Further, when a reverse voltage is applied between the anode electrode 13 and the cathode electrode 14, a depletion layer is formed from the interface between the anode electrode 13 and the n-type semiconductor layer 11 and the interface between the trench insulating film 15 and the n-type semiconductor layer 11. spread.
　一般的に、ショットキーダイオードの逆方向リーク電流の上限は１μＡとされている。本実施の形態では、１μＡのリーク電流が流れるときの逆方向電圧を耐圧と定義する。 Generally, the upper limit of the reverse leakage current of the Schottky diode is 1 μA. In this embodiment, the reverse voltage when a leak current of 1 μA flows is defined as the withstand voltage.
　例えば、“松波弘之、大谷昇、木本恒暢、中村孝著、「半導体ＳｉＣ技術と応用」、第２版、日刊工業新聞社、２０１１年９月３０日、ｐ．３５５”に記載された、ＳｉＣを半導体層とするショットキーダイオードにおける逆方向リーク電流のショットキー界面電界強度依存性のデータによれば、逆方向リーク電流の電流密度が０．０００１Ａ／ｃｍ２のときのショットキー電極直下の電界強度は、およそ０．８ＭＶ／ｃｍである。ここで、０．０００１Ａ／ｃｍ２は、サイズが１ｍｍ×１ｍｍであるショットキー電極に１μＡの電流が流れたときのショットキー電極直下の電流密度である。 For example, "Hiroyuki Matsunami, Noboru Otani, Tsunenobu Kimoto, Takashi Nakamura," Semiconductor SiC Technology and Applications, "2nd Edition, Nikkan Kogyo Shimbun, September 30, 2011, p. According to the Schottky interface electric field strength dependence data of the reverse leakage current in the Schottky diode having SiC as the semiconductor layer described in 355 ”, the current density of the reverse leakage current is 0.0001 A / cm 2 . The electric field strength immediately below the Schottky electrode is approximately 0.8 MV / cm. Here, 0.0001 A / cm 2 is when a current of 1 μA flows through the Schottky electrode having a size of 1 mm × 1 mm. The current density just below the Schottky electrode.
　このため、半導体材料自体の絶縁破壊電界強度が数ＭＶ／ｃｍあったとしても、ショットキー電極直下の電界強度が０．８ＭＶ／ｃｍを超えると、１μＡを超えるリーク電流が流れることになる。 Therefore, even if the dielectric breakdown electric field strength of the semiconductor material itself is several MV / cm, if the electric field strength directly under the shotkey electrode exceeds 0.8 MV / cm, a leak current exceeding 1 μA will flow.
　例えば、ショットキー電極直下の電界強度を抑制するための特別な構造を有さない従来のショットキーダイオードにおいて１２００Ｖの耐圧を得るためには、ショットキー電極直下の電界強度を０．８ＭＶ／ｃｍ以下に抑えるために、半導体層のドナー濃度を１０１５ｃｍ－３台にまで下げ、かつ半導体層を非常に厚くする必要がある。そのため、導通損失が非常に大きくなり、高耐圧かつ低損失のショットキーバリアダイオードを作製することは困難である。 For example, in order to obtain a withstand voltage of 1200 V in a conventional Schottky diode having no special structure for suppressing the electric field strength directly under the Schottky electrode, the electric field strength directly under the Schottky electrode should be 0.8 MV / cm or less. It is necessary to reduce the donor concentration of the semiconductor layer to 10 15 cm -3 units and make the semiconductor layer very thick. Therefore, the conduction loss becomes very large, and it is difficult to manufacture a Schottky barrier diode having a high withstand voltage and a low loss.
　本実施の形態に係るショットキーダイオード１は、トレンチＭＯＳ構造を有するため、半導体層の抵抗を増加することなく、高い耐圧を得ることができる。すなわち、ショットキーダイオード１は、高耐圧かつ低損失のショットキーダイオードである。 Since the Schottky diode 1 according to the present embodiment has a trench MOS structure, a high withstand voltage can be obtained without increasing the resistance of the semiconductor layer. That is, the Schottky diode 1 is a Schottky diode having a high withstand voltage and a low loss.
　ｎ型半導体基板１０は、ドナーとしてのＳｉ、Ｓｎ等のＩＶ族元素を含むｎ型のＧａ２Ｏ３系単結晶からなる。ｎ型半導体基板１０のドナー濃度は、例えば、１．０×１０１８ｃｍ－３以上かつ１．０×１０２０ｃｍ－３以下である。ｎ型半導体基板１０の厚さは、例えば、１０～６００μｍである。ｎ型半導体基板１０は、例えば、Ｇａ２Ｏ３系単結晶基板である。 The n-type semiconductor substrate 10 is made of an n-type Ga 2 O 3 system single crystal containing Group IV elements such as Si and Sn as donors. The donor concentration of the n-type semiconductor substrate 10 is, for example, 1.0 × 10 18 cm -3 or more and 1.0 × 10 20 cm -3 or less. The thickness of the n-type semiconductor substrate 10 is, for example, 10 to 600 μm. The n-type semiconductor substrate 10 is, for example, a Ga 2 O 3 system single crystal substrate.
　ここで、Ｇａ２Ｏ３系単結晶とは、Ｇａ２Ｏ３単結晶、又は、Ａｌ、Ｉｎの一方若しくは両方が添加されたＧａ２Ｏ３単結晶であり、（ＧａｘＡｌｙＩｎ（１－ｘ－ｙ））２Ｏ３（０＜ｘ≦１、０≦ｙ＜１、０＜ｘ＋ｙ≦１）で表される組成を有するＧａ２Ｏ３系半導体の単結晶である。Ｇａ２Ｏ３にＡｌを添加した場合にはバンドギャップが広がり、Ｉｎを添加した場合にはバンドギャップが狭くなる。なお、上記のＧａ２Ｏ３単結晶は、例えば、β型の結晶構造を有する。 Here, the Ga 2 O 3 system single crystal is a Ga 2 O 3 single crystal or a Ga 2 O 3 single crystal to which one or both of Al and In are added, and (Ga x Aly In (1) . −X −y) ) A single crystal of a Ga 2 O 3 system semiconductor having a composition represented by 2 O 3 (0 <x ≦ 1, 0 ≦ y <1, 0 <x + y ≦ 1). When Al is added to Ga 2 O 3 , the band gap widens, and when In is added, the band gap narrows. The Ga 2 O 3 single crystal described above has, for example, a β-type crystal structure.
　ｎ型半導体層１１は、ドナーとしてのＳｉ、Ｓｎ等のＩＶ族元素を含むｎ型のＧａ２Ｏ３系単結晶からなる。ｎ型半導体層１１のドナー濃度は、ｎ型半導体基板１０のドナー濃度よりも低い。ｎ型半導体層１１は、例えば、Ｇａ２Ｏ３系単結晶基板であるｎ型半導体基板１０上にエピタキシャル成長したエピタキシャル層である。 The n-type semiconductor layer 11 is composed of an n-type Ga 2 O 3 system single crystal containing Group IV elements such as Si and Sn as donors. The donor concentration of the n-type semiconductor layer 11 is lower than the donor concentration of the n-type semiconductor substrate 10. The n-type semiconductor layer 11 is, for example, an epitaxial layer epitaxially grown on the n-type semiconductor substrate 10 which is a Ga 2 O 3 system single crystal substrate.
　なお、ｎ型半導体基板１０とｎ型半導体層１１との間に、高濃度のドナーを含む高ドナー濃度層を形成してもよい。この高ドナー濃度層は、例えば、ｎ型半導体基板１０上にｎ型半導体層１１をエピタキシャル成長させる場合に用いられる。ｎ型半導体層１１の成長初期は、ドーパントの取り込み量が不安定であったり、基板であるｎ型半導体基板１０からのアクセプター不純物の拡散があったりするため、ｎ型半導体基板１０上にｎ型半導体層１１を直接成長させると、ｎ型半導体層１１のｎ型半導体基板１０との界面に近い領域が高抵抗化する場合がある。このような問題を避けるため、高ドナー濃度層が用いられる。高ドナー濃度層の濃度は、例えば、ｎ型半導体層１１よりも高い濃度に設定され、より好ましくは、ｎ型半導体基板１０よりも高い濃度に設定される。 A high-concentration layer containing a high-concentration donor may be formed between the n-type semiconductor substrate 10 and the n-type semiconductor layer 11. This high donor concentration layer is used, for example, when the n-type semiconductor layer 11 is epitaxially grown on the n-type semiconductor substrate 10. At the initial stage of growth of the n-type semiconductor layer 11, the amount of dopant taken up is unstable and acceptor impurities are diffused from the n-type semiconductor substrate 10 which is the substrate. Therefore, the n-type semiconductor layer 10 is on the n-type semiconductor substrate 10. When the semiconductor layer 11 is directly grown, the region of the n-type semiconductor layer 11 near the interface with the n-type semiconductor substrate 10 may have high resistance. To avoid such problems, a high donor concentration layer is used. The concentration of the high donor concentration layer is set to, for example, a higher concentration than that of the n-type semiconductor layer 11, and more preferably set to a higher concentration than that of the n-type semiconductor substrate 10.
　ｎ型半導体層１１のドナー濃度が増加するほど、ショットキーダイオード１の各部の電界強度が増加する。ｎ型半導体層１１中のアノード電極１３直下の領域中の最大電界強度、ｎ型半導体層１１中の最大電界強度、及びトレンチ絶縁膜１５中の最大電界強度を低く抑えるためには、ｎ型半導体層１１のドナー濃度がおよそ６．０×１０１６ｃｍ－３以下であることが好ましい。一方、ドナー濃度が小さくなるほどｎ型半導体層１１の抵抗が大きくなり、順方向損失が増加してしまうため、例えば１２００Ｖ以下の耐圧を得るためには、３．０×１０１６ｃｍ－３以上であることが好ましい。また、より高い耐圧を得るためには、ドナー濃度を例えば１．０×１０１６ｃｍ－３程度まで下げることが好ましい。 As the donor concentration of the n-type semiconductor layer 11 increases, the electric field strength of each part of the Schottky diode 1 increases. In order to keep the maximum electric field strength in the region directly under the anode electrode 13 in the n-type semiconductor layer 11, the maximum electric field strength in the n-type semiconductor layer 11, and the maximum electric field strength in the trench insulating film 15 low, the n-type semiconductor is used. The donor concentration of layer 11 is preferably about 6.0 × 10 16 cm -3 or less. On the other hand, as the donor concentration decreases, the resistance of the n-type semiconductor layer 11 increases and the forward loss increases. Therefore, for example, in order to obtain a withstand voltage of 1200 V or less, it is 3.0 × 10 16 cm -3 or more. It is preferable to have. Further, in order to obtain a higher pressure resistance, it is preferable to reduce the donor concentration to, for example, about 1.0 × 10 16 cm -3 .
　ｎ型半導体層１１の厚さＴが増加するほど、ｎ型半導体層１１中の最大電界強度及びトレンチ絶縁膜１５中の最大電界強度が低減する。ｎ型半導体層１１の厚さＴをおよそ６μｍ以上にすることにより、ｎ型半導体層１１中の最大電界強度及びトレンチ絶縁膜１５中の最大電界強度を効果的に低減することができる。これらの電界強度の低減と、ショットキーダイオード１の小型化の観点から、ｎ型半導体層１１の厚さＴはおよそ５．５μｍ以上かつ９μｍ以下であることが好ましい。 As the thickness T of the n-type semiconductor layer 11 increases, the maximum electric field strength in the n-type semiconductor layer 11 and the maximum electric field strength in the trench insulating film 15 decrease. By setting the thickness T of the n-type semiconductor layer 11 to about 6 μm or more, the maximum electric field strength in the n-type semiconductor layer 11 and the maximum electric field strength in the trench insulating film 15 can be effectively reduced. From the viewpoint of reducing the electric field strength and downsizing the Schottky diode 1, the thickness T of the n-type semiconductor layer 11 is preferably about 5.5 μm or more and 9 μm or less.
　トレンチ１２の深さＤによってショットキーダイオード１の各部の電界強度が変化する。ｎ型半導体層１１中のアノード電極１３直下の領域中の最大電界強度、ｎ型半導体層１１中の最大電界強度、及びトレンチ絶縁膜１５中の最大電界強度を低く抑えるためには、トレンチ１２の深さＤがおよそ２μｍ以上かつ６μｍ以下であることが好ましく、およそ３μｍ以上かつ４μｍ以下であることがより好ましい。 The electric field strength of each part of the Schottky diode 1 changes depending on the depth D of the trench 12. In order to keep the maximum electric field strength in the region directly under the anode electrode 13 in the n-type semiconductor layer 11, the maximum electric field strength in the n-type semiconductor layer 11, and the maximum electric field strength in the trench insulating film 15 low, the trench 12 is used. The depth D is preferably about 2 μm or more and 6 μm or less, and more preferably about 3 μm or more and 4 μm or less.
　トレンチ１２の幅Ｗｔは、アノード電極１３直下の領域の電界強度とは無関係のため、自由に設定できる。トレンチ１２内には電流が流れないため、幅Ｗｔは可能な限り狭い方が好ましい。しかしながら、幅Ｗｔを微細化し過ぎると、トレンチ１２内へのトレンチ絶縁膜１５及びアノード電極１６の埋め込みが困難になり、製造歩留まりが悪化する。一方、本発明者の検討により、幅Ｗｔが３μｍ以上になると幅Ｗｔが増えてもアノード電極１６の埋め込み性にほとんど影響がないことがわかっている。また、幅Ｗｔが０．５μｍ未満になると、トレンチ１２の形成のために特殊な露光装置が必要になり、製造コストが増加する場合がある。よって、幅Ｗｔは、０．５μｍ以上、３μｍ以下であることが好ましい。 Since the width Wt of the trench 12 is irrelevant to the electric field strength in the region directly below the anode electrode 13, it can be freely set. Since no current flows in the trench 12, it is preferable that the width Wt is as narrow as possible. However, if the width Wt is made too fine, it becomes difficult to embed the trench insulating film 15 and the anode electrode 16 in the trench 12, and the manufacturing yield deteriorates. On the other hand, according to the study by the present inventor, it has been found that when the width Wt is 3 μm or more, even if the width Wt increases, the embedding property of the anode electrode 16 is hardly affected. Further, when the width W t is less than 0.5 μm, a special exposure apparatus is required for forming the trench 12, and the manufacturing cost may increase. Therefore, the width W t is preferably 0.5 μm or more and 3 μm or less.
　ｎ型半導体層１１の隣接するトレンチ１２の間のメサ形状部分１１０の幅Ｗｍが低減するほど、ｎ型半導体層１１中のアノード電極１３直下の領域中の最大電界強度が低減する。ｎ型半導体層１１中のアノード電極１３直下の領域中の最大電界強度を低く抑えるためには、メサ形状部分１１０の幅Ｗｍが２．５μｍ以下であることが好ましい。一方、メサ形状部分１１０の幅が小さいほどトレンチ１２の製造難度が上がるため、メサ形状部分１１０の幅Ｗｍが０．５μｍ以上であることが好ましい。 As the width Wm of the mesa-shaped portion 110 between the adjacent trenches 12 of the n -type semiconductor layer 11 decreases, the maximum electric field strength in the region immediately below the anode electrode 13 in the n-type semiconductor layer 11 decreases. In order to keep the maximum electric field strength in the region directly below the anode electrode 13 in the n-type semiconductor layer 11 low, the width Wm of the mesa-shaped portion 110 is preferably 2.5 μm or less. On the other hand, the smaller the width of the mesa-shaped portion 110, the more difficult it is to manufacture the trench 12, so that the width Wm of the mesa-shaped portion 110 is preferably 0.5 μm or more.
　トレンチ絶縁膜１５の誘電率が増加するほど、トレンチ絶縁膜１５中の最大電界強度が低減するため、トレンチ絶縁膜１５は誘電率が高い材料からなることが好ましい。例えば、トレンチ絶縁膜１５の材料としてＡｌ２Ｏ３（比誘電率がおよそ９．３）、ＨｆＯ２（比誘電率がおよそ２２）を用いることができるが、誘電率の高いＨｆＯ２を用いることが特に好ましい。 As the dielectric constant of the trench insulating film 15 increases, the maximum electric field strength in the trench insulating film 15 decreases. Therefore, the trench insulating film 15 is preferably made of a material having a high dielectric constant. For example, Al 2 O 3 (relative permittivity of about 9.3) and HfO 2 (relative permittivity of about 22) can be used as the material of the trench insulating film 15, but HfO 2 having a high dielectric constant is used. Is particularly preferable.
　また、トレンチ絶縁膜１５の厚さが増加するほど、ｎ型半導体層１１中の最大電界強度が低減するが、トレンチ絶縁膜１５中の最大電界強度およびアノード電極１３直下の領域中の最大電界強度が増加する。製造容易性の観点からは、トレンチ絶縁膜１５の厚さは小さい方が好ましく、３００ｎｍ以下であることがより好ましい。ただし、当然ながら、アノード電極１６とｎ型半導体層１１の間に直接電流がほとんど流れない程度の厚さは必要である。 Further, as the thickness of the trench insulating film 15 increases, the maximum electric field strength in the n-type semiconductor layer 11 decreases, but the maximum electric field strength in the trench insulating film 15 and the maximum electric field strength in the region directly under the anode electrode 13 Will increase. From the viewpoint of ease of manufacture, the thickness of the trench insulating film 15 is preferably small, and more preferably 300 nm or less. However, as a matter of course, a thickness such that a direct current hardly flows between the anode electrode 16 and the n-type semiconductor layer 11 is required.
　アノード電極１６の材料は、導電性を有するものであれば特に限定されず、例えば、高濃度でドーピングされた多結晶Ｓｉや、Ｎｉ、Ａｕ等の金属を用いることができる。 The material of the anode electrode 16 is not particularly limited as long as it has conductivity, and for example, polycrystalline Si doped at a high concentration or a metal such as Ni or Au can be used.
　ショットキーダイオード１中の電界強度は、上述のように、隣接する２つのトレンチ１２の間のメサ形状部分１１０の幅Ｗｍ、トレンチ１２の深さＤ、トレンチ絶縁膜１５の厚さ等の影響を受けるが、トレンチ１２の平面パターンにはほとんど影響を受けない。このため、ｎ型半導体層１１のトレンチ１２の平面パターンは特に限定されない。 As described above, the electric field strength in the Schottky diode 1 is affected by the width W m of the mesa-shaped portion 110 between the two adjacent trenches 12, the depth D of the trench 12, the thickness of the trench insulating film 15, and the like. However, it is hardly affected by the planar pattern of the trench 12. Therefore, the planar pattern of the trench 12 of the n-type semiconductor layer 11 is not particularly limited.
　カソード電極１４は、ｎ型半導体基板１０とオーミック接触する。カソード電極１４は、Ｔｉ等の金属からなる。カソード電極１４は、異なる金属膜を積層した多層構造、例えば、Ｔｉ／Ａｕ又はＴｉ／Ａｌ、を有してもよい。カソード電極１４とｎ型半導体基板１０を確実にオーミック接触させるため、カソード電極１４のｎ型半導体基板１０と接触する層がＴｉからなることが好ましい。なお、ショットキーダイオード１がｎ型半導体基板１０を含まない場合は、カソード電極１４は、ｎ型半導体層１１のアノード電極１３と反対側に接続され、ｎ型半導体層１１とオーミック接触する。 The cathode electrode 14 makes ohmic contact with the n-type semiconductor substrate 10. The cathode electrode 14 is made of a metal such as Ti. The cathode electrode 14 may have a multilayer structure in which different metal films are laminated, for example, Ti / Au or Ti / Al. In order to ensure ohmic contact between the cathode electrode 14 and the n-type semiconductor substrate 10, it is preferable that the layer of the cathode electrode 14 in contact with the n-type semiconductor substrate 10 is made of Ti. When the shotkey diode 1 does not include the n-type semiconductor substrate 10, the cathode electrode 14 is connected to the side opposite to the anode electrode 13 of the n-type semiconductor layer 11 and makes ohmic contact with the n-type semiconductor layer 11.
　ｐ型半導体部材１７は、サージ対策のために用いられる部材であり、ｐ型のＢＮ（窒化ホウ素）又はＡｌｘＧａ１－ｘＮ（ｘ＞０）（窒化アルミニウムガリウム）からなる。ＢＮからなるｐ型半導体部材１７は、アクセプターとしてのＺｎ、Ｍｇ、Ｂｅ、Ｓｉなどの添加物を含む。ＡｌｘＧａ１－ｘＮ（ｘ＞０）からなるｐ型半導体部材１７は、アクセプターとしてのＭｇなどの添加物を含む。また、ｐ型半導体部材１７は、上記の不純物の代わりにIII族原子空孔（ＢＮの場合はＢの欠損による空孔、ＡｌｘＧａ１－ｘＮ（ｘ＞０）の場合はＡｌ又はＧａの欠損による空孔）をアクセプターとして有していてもよい。 The p-type semiconductor member 17 is a member used as a countermeasure against surges, and is composed of p-type BN (boron nitride) or Al x Ga 1-x N (x> 0) (aluminum gallium nitride). The p-type semiconductor member 17 made of BN contains additives such as Zn, Mg, Be, and Si as acceptors. The p-type semiconductor member 17 composed of Al x Ga 1-x N (x> 0) contains an additive such as Mg as an acceptor. Further, in the p-type semiconductor member 17, instead of the above impurities, group III atomic vacancies (pores due to lack of B in the case of BN, Al or Ga in the case of Al x Ga 1-x N (x> 0)). It may have a hole) as an acceptor.
　ｐ型半導体部材１７の価電子帯の上端のエネルギーは、ｎ型半導体層１１を構成するＧａ２Ｏ３系半導体の価電子帯の上端のエネルギーに２ｅＶを加えたエネルギー以下であるため、ｐ型半導体部材１７を用いることにより、ショットキーダイオード１をオンにする際に生じ得るサージ電流（突入電流、始動電流などとも呼ばれる）発生時にドリフト層の抵抗を下げることができ、発熱や破損を抑制することができる。 The energy at the upper end of the valence band of the p-type semiconductor member 17 is equal to or less than the energy obtained by adding 2 eV to the energy at the upper end of the valence band of the Ga 2 O3 system semiconductor constituting the n - type semiconductor layer 11. By using the semiconductor member 17, the resistance of the drift layer can be reduced when a surge current (also called inrush current, starting current, etc.) that can occur when the shotkey diode 1 is turned on can be reduced, and heat generation and breakage can be suppressed. be able to.
　通常、ｐｎダイオードはショットキーダイオードよりもオン電圧が大きい。このため、ショットキーダイオード１がオンになる電圧でｐ型半導体部材１７とｎ型半導体層１１で構成されるｐｎダイオード部分がオンしないような設計にすることができる。例えば、ショットキーダイオード１のオン電圧を１Ｖ程度、ｐｎダイオード部分のオン電圧を２Ｖ程度とすることができる。 Normally, the pn diode has a larger on-voltage than the Schottky diode. Therefore, the design can be made so that the pn diode portion composed of the p-type semiconductor member 17 and the n-type semiconductor layer 11 does not turn on at the voltage at which the Schottky diode 1 turns on. For example, the on-voltage of the Schottky diode 1 can be set to about 1V, and the on-voltage of the pn diode portion can be set to about 2V.
　これによって、ショットキーダイオード１の通常動作においてはｐｎダイオード部分がオンしないため、ショットキーダイオード本来の高速動作が可能になる。一方、突入電流発生時はショットキーダイオード１の電圧が上昇し、ｐｎダイオード部分がオンする電圧に達し、ｐ型半導体部材１７からｎ型半導体層１１へ正孔が注入される。 As a result, the pn diode portion does not turn on in the normal operation of the Schottky diode 1, so that the original high-speed operation of the Schottky diode becomes possible. On the other hand, when the inrush current is generated, the voltage of the shotkey diode 1 rises and reaches the voltage at which the pn diode portion is turned on, and holes are injected from the p-type semiconductor member 17 into the n-type semiconductor layer 11.
　そのとき、カソード電極１４からｎ型半導体層１１へはその注入された正孔と同じ数の電子が注入され、ドリフト層の抵抗が大幅に減少する。このため、突入電流という大電流がショットキーダイオード１を流れるが、電圧の上昇は抑えられるため、温度上昇が抑えられ、突入電流によるショットキーダイオード１の損傷を防ぐことができる。 At that time, the same number of electrons as the injected holes are injected from the cathode electrode 14 into the n-type semiconductor layer 11, and the resistance of the drift layer is significantly reduced. Therefore, although a large current called an inrush current flows through the Schottky diode 1, the rise in voltage is suppressed, so that the temperature rise is suppressed and damage to the Schottky diode 1 due to the inrush current can be prevented.
　図２は、ショットキーダイオード１がｐ型半導体部材１７を含む場合（Ａ）と含まない場合（Ｂ）の、突入電流が流れるときの電流－電圧特性を模式的に示すグラフである。図２に示されるように、ｐ型半導体部材１７が含まれない場合、電流の増加とともに電圧が上昇し続け、ショットキーダイオード１の温度が急上昇して燃え尽きてしまう。一方、ｐ型半導体部材１７が含まれる場合、ｐｎダイオード部分がオンする電圧Ｖｐｎに達すると、電圧の上昇率が低下する。このように、突入電流によりショットキーダイオード１を流れる電流は上昇するが、電圧の上昇が抑えられるため、温度上昇が抑えられ、ショットキーダイオード１の損傷が防がれる。 FIG. 2 is a graph schematically showing the current-voltage characteristics when the inrush current flows when the Schottky diode 1 includes the p-type semiconductor member 17 (A) and when it does not (B). As shown in FIG. 2, when the p-type semiconductor member 17 is not included, the voltage continues to rise as the current increases, and the temperature of the Schottky diode 1 rises sharply and burns out. On the other hand, when the p-type semiconductor member 17 is included, when the voltage V pn at which the pn diode portion is turned on is reached, the rate of increase in voltage decreases. As described above, although the current flowing through the Schottky diode 1 increases due to the inrush current, the increase in voltage is suppressed, so that the temperature increase is suppressed and the Schottky diode 1 is prevented from being damaged.
　図３は、ｐ型半導体部材１７とＧａ２Ｏ３系単結晶からなるｎ型半導体層１１のバンド構造と、正孔の流れを模式的に示す図である。図３に示されるように、ｐ型半導体部材１７の価電子帯の上端のエネルギーＥＶ２がＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギーＥＶ１に２ｅＶを加えたエネルギー以下であれば、ｐ型半導体部材１７からｎ型半導体層１１へ正孔が注入され得る。なお、ｐ型半導体部材１７の伝導帯の下端のエネルギーＥＣ２の大きさは、ｐ型半導体部材１７からｎ型半導体層１１への正孔の注入に影響を及ぼさないため、特定の範囲に限定されることはない。 FIG. 3 is a diagram schematically showing the band structure of the n-type semiconductor layer 11 composed of the p-type semiconductor member 17 and the Ga 2 O3 system single crystal and the flow of holes. As shown in FIG. 3 , the energy EV2 at the upper end of the valence band of the p-type semiconductor member 17 is equal to or less than the energy EV1 obtained by adding 2 eV to the energy EV1 at the upper end of the valence band of the Ga 2 O3 system single crystal. For example, holes can be injected from the p-type semiconductor member 17 into the n-type semiconductor layer 11. The size of the energy EC2 at the lower end of the conduction band of the p-type semiconductor member 17 is limited to a specific range because it does not affect the injection of holes from the p-type semiconductor member 17 into the n-type semiconductor layer 11. Will not be done.
　また、ｐ型半導体部材１７の価電子帯の上端のエネルギーＥＶ２が、ｎ型半導体層１１を構成するＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギーＥＶ１以下である場合は、ｐ型半導体部材１７からｎ型半導体層１１への正孔の移動が容易になるため、突入電流への耐性をより高めることができる。 When the energy E V2 at the upper end of the valence band of the p-type semiconductor member 17 is equal to or less than the energy E V1 at the upper end of the valence band of the Ga 2 O3 system single crystal constituting the n - type semiconductor layer 11. Since the holes are easily transferred from the p-type semiconductor member 17 to the n-type semiconductor layer 11, the resistance to the inrush current can be further improved.
　図４は、ｎ型半導体層１１の典型的な材料であるＧａ２Ｏ３と、ｐ型半導体部材１７の材料であるＢＮ、ＡｌｘＧａ１－ｘＮ（ｘ＞０）のバンド構造を含むバンドラインアップを示す。図４中の長方形は各材料のバンドギャップを示し、バンドギャップ内の数値はバンドギャップの大きさ［ｅＶ］、バンドギャップの上側の数値はＧａ２Ｏ３との伝導帯のバンドオフセット（伝導帯の下端のエネルギー差）［ｅＶ］、バンドギャップの下側の数値はＧａ２Ｏ３との価電子帯のバンドオフセット［ｅＶ］をそれぞれ示す。 FIG. 4 includes a band structure of Ga 2 O 3 , which is a typical material of the n-type semiconductor layer 11, and BN, Al x Ga 1-x N (x> 0), which is a material of the p-type semiconductor member 17. Shows the band lineup. The rectangle in FIG. 4 shows the bandgap of each material, the numerical value in the bandgap is the bandgap size [eV], and the numerical value on the upper side of the bandgap is the band offset (conduction band) of the conduction band with Ga 2 O 3 . The energy difference at the lower end of the bandgap) [eV], and the values below the bandgap indicate the band offset [eV] of the valence band with Ga 2 O 3 .
　なお、図中のＡｌＮはｘ＝１であるときのＡｌｘＧａ１－ｘＮ、ＡｌＧａＮは０＜ｘ＜１であるときのＡｌｘＧａ１－ｘＮを示している。ＡｌＧａＮのバンドダイアグラムは、ｘが１に近いほどＡｌＮに近づき、ｘが０に近いほどＧａＮに近づく。また、図４には、ＡｌＯ２とＩｎ２Ｏ３のバンドギャップも示されている。ｎ型半導体層１１の材料であるＧａ２Ｏ３系単結晶は、Ａｌの濃度が高くなるとバンド構造がＡｌ２Ｏ３に近付き、Ｉｎの濃度が高くなるとバンド構造がＩｎ２Ｏ３に近付く。図４に示されるように、Ｇａ２Ｏ３系単結晶におけるＡｌ濃度及びＩｎ濃度の変化による価電子帯の上端のエネルギーの変調量は大きくなく、Ｇａ２Ｏ３との価電子帯のバンドオフセットは最大でも０．４ｅＶ程度である。 In the figure, Al N indicates Al x Ga 1- x N when x = 1, and AlGaN indicates Al x Ga 1 -x N when 0 <x <1. In the band diagram of AlGaN, the closer x is to 1, the closer to AlN, and the closer x is to 0, the closer to GaN. FIG. 4 also shows the bandgap between AlO 2 and In 2 O 3 . In the Ga 2 O 3 series single crystal which is the material of the n-type semiconductor layer 11, the band structure approaches Al 2 O 3 when the concentration of Al increases, and the band structure approaches In 2 O 3 when the concentration of In increases. As shown in FIG. 4, the amount of energy modulation at the upper end of the valence band due to the change in Al concentration and In concentration in the Ga 2 O 3 system single crystal is not large, and the band offset of the valence band with Ga 2 O 3 Is about 0.4 eV at the maximum.
　ｐ型半導体部材１７の材料であるＢＮ、ＡｌｘＧａ１－ｘＮ（ｘ＞０）の価電子帯の上端のエネルギーは、ｎ型半導体層１１の材料であるＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギーに２ｅＶを加えたエネルギー以下である。この関係は、図４から理解されるように、ＡｌｘＧａ１－ｘＮ（ｘ＞０）のＡｌ濃度並びにＧａ２Ｏ３系単結晶のＡｌ濃度及びＩｎ濃度がどのような値をとる場合にも成り立つ。 The energy at the upper end of the valence band of BN, Al x Ga 1-x N (x> 0), which is the material of the p-type semiconductor member 17, is the energy of the Ga 2 O 3 series single crystal, which is the material of the n-type semiconductor layer 11. It is less than or equal to the energy obtained by adding 2 eV to the energy at the upper end of the valence band. As can be understood from FIG. 4, this relationship is understood when the Al concentration of Al x Ga 1-x N (x> 0) and the Al concentration and In concentration of the Ga 2 O 3 system single crystal take. It also holds true.
　ｐ型半導体部材１７の材料であるＡｌｘＧａ１－ｘＮ（ｘ＞０）は、Ａｌ濃度ｘが１に近いほど価電子帯の上端のエネルギーが低くなり、ｎ型半導体層１１の材料であるＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギーに近づく、あるいはｎ型半導体層１１の材料であるＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギーよりも小さくなる。このため、例えば、ｐ型半導体部材１７がＡｌｘＧａ１－ｘＮ（ｘ≧０．８）からなることが好ましい。 Al x Ga 1-x N (x> 0), which is the material of the p-type semiconductor member 17, has a lower energy at the upper end of the valence band as the Al concentration x is closer to 1, and is a material of the n-type semiconductor layer 11. It approaches the energy of the upper end of the valence band of a certain Ga 2 O 3 series single crystal, or becomes smaller than the energy of the upper end of the valence band of the Ga 2 O 3 series single crystal which is the material of the n-type semiconductor layer 11. Therefore, for example, it is preferable that the p-type semiconductor member 17 is made of Al x Ga 1-x N (x ≧ 0.8).
　また、ＢＮの価電子帯の上端のエネルギーは、ｎ型半導体層１１の材料であるＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギーとほぼ等しいため、ＢＮをｐ型半導体部材１７の材料として用いることにより、ショットキーダイオード１の突入電流への耐性を特に高めることができる。 Further, since the energy at the upper end of the valence band of the BN is substantially equal to the energy at the upper end of the valence band of the Ga 2 O3 system single crystal which is the material of the n - type semiconductor layer 11, the BN is used as the p-type semiconductor member 17. By using it as a material, the resistance of the shotkey diode 1 to the inrush current can be particularly enhanced.
　ｐ型半導体部材１７の大きさ、個数、配置は特に限定されない。ｐ型半導体部材１７とｎ型半導体層１１との接触面積が大きいほどサージ電流を効率的に逃がすことができるが、通常動作時に電流が流れにくくなる。このため、ｐ型半導体部材１７とｎ型半導体層１１との総接触面積は、アノード電極１３とｎ型半導体層１１との総接触面積の１０％以上かつ５０％以下であることが好ましい。 The size, number, and arrangement of the p-type semiconductor member 17 are not particularly limited. The larger the contact area between the p-type semiconductor member 17 and the n-type semiconductor layer 11, the more efficiently the surge current can escape, but the less the current flows during normal operation. Therefore, the total contact area between the p-type semiconductor member 17 and the n-type semiconductor layer 11 is preferably 10% or more and 50% or less of the total contact area between the anode electrode 13 and the n-type semiconductor layer 11.
　図５は、第１の実施の形態に係るショットキーダイオード１の変形例であるショットキーダイオード３の垂直断面図である。ショットキーダイオード３は、トレンチ構造を有しない、すなわち、トレンチ１２、トレンチ絶縁膜１５、アノード電極１６をｎ型半導体層１１中に有しない点において、ショットキーダイオード１と異なる。ショットキーダイオード３は、トレンチ構造を有しないためにショットキーダイオード１と比較して耐圧性に劣るが、ｐ型半導体部材１７によってショットキーダイオード１と同様のサージ電流への耐性を有する。 FIG. 5 is a vertical cross-sectional view of the Schottky diode 3 which is a modification of the Schottky diode 1 according to the first embodiment. The Schottky diode 3 differs from the Schottky diode 1 in that it does not have a trench structure, that is, it does not have a trench 12, a trench insulating film 15, and an anode electrode 16 in the n-type semiconductor layer 11. Since the Schottky diode 3 does not have a trench structure, the withstand voltage is inferior to that of the Schottky diode 1, but the p-type semiconductor member 17 has the same resistance to surge current as the Schottky diode 1.
〔第２の実施の形態〕
（ショットキーダイオードの構成）
　図６は、第２の実施の形態に係るショットキーダイオード２の垂直断面図である。ショットキーダイオード２は、トレンチ構造を有する縦型のジャンクションバリアショットキー（ＪＢＳ）ダイオードである。 [Second Embodiment]
(Schottky diode configuration)
FIG. 6 is a vertical sectional view of the Schottky diode 2 according to the second embodiment. The Schottky diode 2 is a vertical junction barrier Schottky (JBS) diode having a trench structure.
　ショットキーダイオード２は、ｎ型半導体基板２０と、ｎ型半導体基板２０上に形成された、ｎ型半導体基板２０と反対側の面２６に開口する複数のトレンチ２５を有するｎ型半導体層２１と、ｎ型半導体層２１のトレンチ２５内に埋め込まれたｐ型半導体部材２２と、ｎ型半導体層２１の面２６上に設けられ、ｎ型半導体層２１の隣接するトレンチ２５の間のメサ形状領域２１０及びｐ型半導体部材２２に接続されたアノード電極２３と、ｎ型半導体基板２０のｎ型半導体層２１と反対側の面上に形成されたカソード電極２４と、を備える。 The shotkey diode 2 includes an n-type semiconductor substrate 20 and an n-type semiconductor layer 21 having a plurality of trenches 25 formed on the n-type semiconductor substrate 20 and having a plurality of trenches 25 opened on the surface 26 opposite to the n-type semiconductor substrate 20. , A mesa-shaped region between the p-type semiconductor member 22 embedded in the trench 25 of the n-type semiconductor layer 21 and the adjacent trench 25 of the n-type semiconductor layer 21 provided on the surface 26 of the n-type semiconductor layer 21. It includes an anode electrode 23 connected to the 210 and the p-type semiconductor member 22, and a cathode electrode 24 formed on a surface of the n-type semiconductor substrate 20 opposite to the n-type semiconductor layer 21.
　ｎ型半導体層２１とアノード電極２３とは、ショットキー接合を形成し、ショットキーダイオード２は、このショットキー接合の整流性を利用している。また、ショットキーダイオード２においては、形成することが困難なｐ型のＧａ２Ｏ３の代わりにＢＮ又はＡｌｘＧａ１－ｘＮ（ｘ＞０）からなるｐ型半導体部材２２を用いている。 The n-type semiconductor layer 21 and the anode electrode 23 form a Schottky junction, and the Schottky diode 2 utilizes the rectification property of this Schottky junction. Further, in the Schottky diode 2, a p-type semiconductor member 22 made of BN or Al x Ga 1-x N (x> 0) is used instead of the p-type Ga 2 O 3 which is difficult to form. ..
　ショットキーダイオード２においては、アノード電極２３とカソード電極２４との間に順方向の電圧（アノード電極２３側が正電位）を印加することにより、ｎ型半導体層２１から見たアノード電極２３とｎ型半導体層２１との界面のポテンシャル障壁が低下し、アノード電極２３からカソード電極２４へ電流が流れる。 In the Schottky diode 2, the anode electrode 23 and the n-type seen from the n-type semiconductor layer 21 are applied by applying a forward voltage (positive potential on the anode electrode 23 side) between the anode electrode 23 and the cathode electrode 24. The potential barrier at the interface with the semiconductor layer 21 is lowered, and a current flows from the anode electrode 23 to the cathode electrode 24.
　一方、アノード電極２３とカソード電極２４との間に逆方向の電圧（アノード電極２３側が負電位）を印加したときは、ショットキー障壁により、電流は流れない。このとき、ｐ型半導体部材２２から空乏層が広がり、隣接するｐ型半導体部材２２間のチャネルが閉じるため、リーク電流が効果的に抑制される。 On the other hand, when a voltage in the opposite direction (negative potential on the anode electrode 23 side) is applied between the anode electrode 23 and the cathode electrode 24, no current flows due to the Schottky barrier. At this time, the depletion layer spreads from the p-type semiconductor member 22, and the channels between the adjacent p-type semiconductor members 22 are closed, so that the leakage current is effectively suppressed.
　本実施の形態に係るショットキーダイオード２は、トレンチ型ＪＢＳ構造を有するため、第１の実施の形態に係るショットキーダイオード１と同様に、半導体層の抵抗を増加することなく、高い耐圧を得ることができる。すなわち、ショットキーダイオード２は、高耐圧かつ低損失のショットキーバリアダイオードである。 Since the Schottky diode 2 according to the present embodiment has a trench type JBS structure, a high withstand voltage can be obtained without increasing the resistance of the semiconductor layer, as with the Schottky diode 1 according to the first embodiment. be able to. That is, the Schottky diode 2 is a Schottky barrier diode having a high withstand voltage and a low loss.
　ｎ型半導体基板２０は、ドナーとしてのＳｉ、Ｓｎ等のＩＶ族元素を含むｎ型のＧａ２Ｏ３系単結晶からなる。ｎ型半導体基板２０のドナー濃度は、例えば、１．０×１０１８ｃｍ－３以上かつ１．０×１０２０ｃｍ－３以下であるｎ型半導体基板２０の厚さは、例えば、１０～６００μｍである。ｎ型半導体基板２０は、例えば、Ｇａ２Ｏ３系単結晶基板である。 The n-type semiconductor substrate 20 is made of an n-type Ga 2 O 3 system single crystal containing Group IV elements such as Si and Sn as donors. The donor concentration of the n-type semiconductor substrate 20 is, for example, 1.0 × 10 18 cm -3 or more and 1.0 × 10 20 cm -3 or less. The thickness of the n-type semiconductor substrate 20 is, for example, 10 to 600 μm. Is. The n-type semiconductor substrate 20 is, for example, a Ga 2 O 3 system single crystal substrate.
　ｎ型半導体層２１は、ドナーとしてのＳｉ、Ｓｎ等のＩＶ族元素を含むｎ型のＧａ２Ｏ３系単結晶からなる。ｎ型半導体層２１のドナー濃度は、ｎ型半導体基板２０のドナー濃度よりも低い。ｎ型半導体層２１は、例えば、Ｇａ２Ｏ３系単結晶基板であるｎ型半導体基板１０上にエピタキシャル成長したエピタキシャル層である。 The n-type semiconductor layer 21 is composed of an n-type Ga 2 O 3 system single crystal containing Group IV elements such as Si and Sn as donors. The donor concentration of the n-type semiconductor layer 21 is lower than the donor concentration of the n-type semiconductor substrate 20. The n-type semiconductor layer 21 is, for example, an epitaxial layer epitaxially grown on the n-type semiconductor substrate 10 which is a Ga 2 O 3 system single crystal substrate.
　なお、ｎ型半導体基板２０とｎ型半導体層２１との間に、高濃度のドナーを含む高ドナー濃度層を形成してもよい。この高ドナー濃度層は、例えば、ｎ型半導体基板２０上にｎ型半導体層２１をエピタキシャル成長させる場合に用いられる。ｎ型半導体層２１の成長初期は、ドーパントの取り込み量が不安定であったり、ｎ型半導体基板２０からのアクセプター不純物の拡散があったりするため、ｎ型半導体基板２０上にｎ型半導体層２１を直接成長させると、ｎ型半導体層２１のｎ型半導体基板２０との界面に近い領域が高抵抗化する場合がある。このような問題を避けるため、高ドナー濃度層が用いられる。高ドナー濃度層の濃度は、例えば、ｎ型半導体層２１よりも高い濃度に設定され、より好ましくは、ｎ型半導体基板２０よりも高い濃度に設定される。 A high-concentration layer containing a high-concentration donor may be formed between the n-type semiconductor substrate 20 and the n-type semiconductor layer 21. This high donor concentration layer is used, for example, when the n-type semiconductor layer 21 is epitaxially grown on the n-type semiconductor substrate 20. At the initial stage of growth of the n-type semiconductor layer 21, the amount of dopant taken up is unstable and acceptor impurities are diffused from the n-type semiconductor substrate 20, so that the n-type semiconductor layer 21 is placed on the n-type semiconductor substrate 20. When the n-type semiconductor layer 21 is directly grown, the region near the interface between the n-type semiconductor layer 21 and the n-type semiconductor substrate 20 may have high resistance. To avoid such problems, a high donor concentration layer is used. The concentration of the high donor concentration layer is set to, for example, a higher concentration than that of the n-type semiconductor layer 21, and more preferably set to a higher concentration than that of the n-type semiconductor substrate 20.
　ｎ型半導体層２１のドナー濃度が増加するほど、ショットキーダイオード２の各部の電界強度が増加する。ｎ型半導体層２１中のアノード電極２３直下の領域中の最大電界強度及びｎ型半導体層２１中の最大電界強度を低く抑えるためには、ｎ型半導体層２１のドナー濃度がおよそ２．０×１０１７ｃｍ－３以下であることが好ましい。一方、ドナー濃度が小さくなるほどｎ型半導体層２１の抵抗が大きくなり、順方向損失が増加してしまうため、例えば１２００Ｖ以下の耐圧を確保する場合には、３．０×１０１６ｃｍ－３以上であることが好ましい。また、より高い耐圧を得るためには、ドナー濃度を例えば１．０×１０１６ｃｍ－３程度まで下げてもよい。 As the donor concentration of the n-type semiconductor layer 21 increases, the electric field strength of each part of the Schottky diode 2 increases. In order to keep the maximum electric field strength in the region directly below the anode electrode 23 in the n-type semiconductor layer 21 and the maximum electric field strength in the n-type semiconductor layer 21 low, the donor concentration of the n-type semiconductor layer 21 is approximately 2.0 ×. It is preferably 10 17 cm -3 or less. On the other hand, as the donor concentration decreases, the resistance of the n-type semiconductor layer 21 increases and the forward loss increases. Therefore, for example, when ensuring a withstand voltage of 1200 V or less, 3.0 × 10 16 cm -3 or more. Is preferable. Further, in order to obtain a higher pressure resistance, the donor concentration may be lowered to, for example, about 1.0 × 10 16 cm -3 .
　ｎ型半導体層２１の厚さＴが増加するほど、ｎ型半導体層２１中の最大電界強度が低減する。ｎ型半導体層２１の厚さをおよそ３μｍ以上にすることにより、ｎ型半導体層２１中の最大電界強度を効果的に低減することができる。これらの電界強度の低減と、ショットキーダイオード２の小型化の観点から、ｎ型半導体層２１の厚さはおよそ３μｍ以上かつ９μｍ以下であることが好ましい。 As the thickness T of the n-type semiconductor layer 21 increases, the maximum electric field strength in the n-type semiconductor layer 21 decreases. By setting the thickness of the n-type semiconductor layer 21 to about 3 μm or more, the maximum electric field strength in the n-type semiconductor layer 21 can be effectively reduced. From the viewpoint of reducing the electric field strength and downsizing the Schottky diode 2, the thickness of the n-type semiconductor layer 21 is preferably about 3 μm or more and 9 μm or less.
　トレンチ２５の深さＤによってショットキーダイオード２の各部の電界強度が変化する。ｎ型半導体層２１中のアノード電極２３直下の領域中の最大電界強度及びｎ型半導体層２１中の最大電界強度を低く抑えるためには、トレンチ２５の深さＤがおよそ１．５μｍ以上かつ６μｍ以下であることが好ましい。 The electric field strength of each part of the Schottky diode 2 changes depending on the depth D of the trench 25. In order to keep the maximum electric field strength in the region directly below the anode electrode 23 in the n-type semiconductor layer 21 and the maximum electric field strength in the n-type semiconductor layer 21 low, the depth D of the trench 25 is approximately 1.5 μm or more and 6 μm. The following is preferable.
　トレンチ２５の幅Ｗｔは、狭いほど導通損失を低減できるが、狭いほど製造難易度が上がり、それに起因して製造歩留まりが低下するため、０．３μｍ以上かつ５μｍ以下であることが好ましい。 The narrower the width Wt of the trench 25, the more the conduction loss can be reduced, but the narrower the width Wt, the higher the manufacturing difficulty, and the lower the manufacturing yield, so that the width Wt is preferably 0.3 μm or more and 5 μm or less.
　ｎ型半導体層２１の隣接するトレンチ２５の間のメサ形状部分２１０の幅Ｗｍが低減するほど、ｎ型半導体層２１中のアノード電極２３直下の領域中の最大電界強度が低減する。ｎ型半導体層２１中のアノード電極２３直下の領域中の最大電界強度を低く抑えるためには、メサ形状部分２１０の幅Ｗｍが５μｍ以下であることが好ましい。一方、メサ形状部分２１０の幅が小さいほどトレンチ２５の製造難度が上がるため、メサ形状部分２１０の幅Ｗｍが０．２５μｍ以上であることが好ましい。 As the width Wm of the mesa-shaped portion 210 between the adjacent trenches 25 of the n -type semiconductor layer 21 decreases, the maximum electric field strength in the region directly below the anode electrode 23 in the n-type semiconductor layer 21 decreases. In order to keep the maximum electric field strength in the region directly below the anode electrode 23 in the n-type semiconductor layer 21 low, the width Wm of the mesa-shaped portion 210 is preferably 5 μm or less. On the other hand, the smaller the width of the mesa-shaped portion 210, the more difficult it is to manufacture the trench 25. Therefore, it is preferable that the width Wm of the mesa-shaped portion 210 is 0.25 μm or more.
　アノード電極２３は、アノード電極２３のｎ型半導体層２１と接触する部分がｎ型半導体層２１とショットキー接触する材料からなる。すなわち、アノード電極２３が単層構造を有する場合はその全体がｎ型半導体層２１とショットキー接触する材料からなり、多層構造を有する場合は少なくともｎ型半導体層２１と接触する層がｎ型半導体層２１とショットキー接触する材料からなる。 The anode electrode 23 is made of a material in which the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is in Schottky contact with the n-type semiconductor layer 21. That is, when the anode electrode 23 has a single-layer structure, the whole is made of a material that makes Schottky contact with the n-type semiconductor layer 21, and when it has a multilayer structure, at least the layer in contact with the n-type semiconductor layer 21 is an n-type semiconductor. It consists of a material that makes Schottky contact with layer 21.
　ショットキーダイオード２の立ち上がり電圧を小さくするためには、アノード電極２３のｎ型半導体層２１と接触する部分がＦｅ（鉄）、Ｃｕ（銅）、Ｍｏ（モリブデン）、又はＷ（タングステン）からなることが好ましい。 In order to reduce the rising voltage of the Schottky diode 2, the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is made of Fe (iron), Cu (copper), Mo (molybdenum), or W (tungsten). Is preferable.
　アノード電極２３のｎ型半導体層２１と接触する部分がＭｏ又はＷからなる場合、ショットキーダイオード２の立ち上がり電圧は０．４Ｖ以上かつ０．６Ｖ以下となる。アノード電極２３のｎ型半導体層２１と接触する部分がＦｅからなる場合は、ショットキーダイオード２の立ち上がり電圧は０．４Ｖ以上かつ０．７Ｖ以下となる。また、アノード電極２３のｎ型半導体層２１と接触する部分がＣｕからなる場合、ショットキーダイオード２の立ち上がり電圧は０．６Ｖ以上かつ０．９Ｖ以下となる。 When the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is made of Mo or W, the rising voltage of the Schottky diode 2 is 0.4 V or more and 0.6 V or less. When the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is made of Fe, the rising voltage of the Schottky diode 2 is 0.4 V or more and 0.7 V or less. When the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is made of Cu, the rising voltage of the Schottky diode 2 is 0.6 V or more and 0.9 V or less.
　ショットキーダイオード２においては、メサ形状部分２１０にポテンシャル障壁が形成されるため、立ち上がり電圧はメサ形状部分２１０の幅Ｗｍに依存し、幅Ｗｍが小さくなるほど大きくなる。 In the Schottky diode 2, since a potential barrier is formed in the mesa-shaped portion 210, the rising voltage depends on the width W m of the mesa-shaped portion 210, and becomes larger as the width W m becomes smaller.
　ショットキーダイオード２中の電界強度は、上述のように、隣接する２つのトレンチ２５の間のメサ形状部分２１０の幅Ｗｍ、トレンチ２５の深さＤ等の影響を受けるが、トレンチ２５の平面パターン（ｐ型半導体部材２２の平面パターン）にはほとんど影響を受けない。このため、ｎ型半導体層２１のトレンチ２５の平面パターン（ｐ型半導体部材２２の平面パターン）は特に限定されない。 As described above, the electric field strength in the Schottky diode 2 is affected by the width W m of the mesa-shaped portion 210 between the two adjacent trenches 25, the depth D of the trench 25, and the like, but the plane of the trench 25. It is hardly affected by the pattern (planar pattern of the p-type semiconductor member 22). Therefore, the planar pattern of the trench 25 of the n-type semiconductor layer 21 (the planar pattern of the p-type semiconductor member 22) is not particularly limited.
　カソード電極２４は、ｎ型半導体基板２０とオーミック接触する。カソード電極２４は、Ｔｉ等の金属からなる。カソード電極２４は、異なる金属膜を積層した多層構造、例えば、Ｔｉ／Ａｕ又はＴｉ／Ａｌ、を有してもよい。カソード電極２４とｎ型半導体基板２０を確実にオーミック接触させるため、カソード電極２４のｎ型半導体基板２０と接触する層がＴｉからなることが好ましい。なお、ショットキーダイオード２がｎ型半導体基板２０を含まない場合は、カソード電極２４は、ｎ型半導体層２１のアノード電極２３と反対側に接続され、ｎ型半導体層２１とオーミック接触する。 The cathode electrode 24 is in ohmic contact with the n-type semiconductor substrate 20. The cathode electrode 24 is made of a metal such as Ti. The cathode electrode 24 may have a multilayer structure in which different metal films are laminated, for example, Ti / Au or Ti / Al. In order to ensure ohmic contact between the cathode electrode 24 and the n-type semiconductor substrate 20, it is preferable that the layer of the cathode electrode 24 in contact with the n-type semiconductor substrate 20 is made of Ti. When the shotkey diode 2 does not include the n-type semiconductor substrate 20, the cathode electrode 24 is connected to the side opposite to the anode electrode 23 of the n-type semiconductor layer 21 and makes ohmic contact with the n-type semiconductor layer 21.
　ｐ型半導体部材２２は、第１の実施の形態に係るｐ型半導体部材１７と同様に、サージ対策のために用いられる部材であり、ｐ型のＢＮ又はＡｌｘＧａ１－ｘＮ（ｘ＞０）からなる。ＢＮからなるｐ型半導体部材２２は、アクセプターとしてのＺｎ、Ｍｇ、Ｂｅ、Ｓｉなどの添加物を含む。ＡｌｘＧａ１－ｘＮ（ｘ＞０）からなるｐ型半導体部材２２は、アクセプターとしてのなどの添加物を含む。また、ｐ型半導体部材２２は、上記の不純物の代わりにIII族原子空孔（ＢＮの場合はＢの欠損による空孔、ＡｌｘＧａ１－ｘＮ（ｘ＞０）の場合はＡｌ又はＧａの欠損による空孔）をアクセプターとして有していてもよい。 The p-type semiconductor member 22 is a member used for surge countermeasures like the p-type semiconductor member 17 according to the first embodiment, and is a p-type BN or Al x Ga 1-x N (x>. It consists of 0). The p-type semiconductor member 22 made of BN contains additives such as Zn, Mg, Be, and Si as acceptors. The p-type semiconductor member 22 made of Al x Ga 1-x N (x> 0) contains additives such as as an acceptor. Further, in the p-type semiconductor member 22, instead of the above impurities, group III atomic vacancies (pores due to lack of B in the case of BN, Al or Ga in the case of Al x Ga 1-x N (x> 0)). It may have a hole) as an acceptor.
　ｐ型半導体部材２２の価電子帯の上端のエネルギーは、ｎ型半導体層２１を構成するＧａ２Ｏ３系半導体の価電子帯の上端のエネルギーに２ｅＶを加えたエネルギー以下であるため、ｐ型半導体部材２２を用いることにより、ショットキーダイオード２をオンにする際に生じ得るサージ電流（突入電流、始動電流などとも呼ばれる）発生時にドリフト層の抵抗を下げることができ、発熱や破損を抑制することができる。 Since the energy at the upper end of the valence band of the p-type semiconductor member 22 is less than the energy obtained by adding 2 eV to the energy at the upper end of the valence band of the Ga 2 O3 system semiconductor constituting the n - type semiconductor layer 21, it is p-type. By using the semiconductor member 22, the resistance of the drift layer can be reduced when a surge current (also called inrush current, starting current, etc.) that may occur when the shotkey diode 2 is turned on is generated, and heat generation and breakage are suppressed. be able to.
　通常、ｐｎダイオードはショットキーダイオードよりもオン電圧が大きい。このため、ショットキーダイオード２がオンになる電圧でｐ型半導体部材２２とｎ型半導体層２１で構成されるｐｎダイオード部分がオンしないような設計にすることができる。例えば、ショットキーダイオード２のオン電圧を１Ｖ程度、ｐｎダイオード部分のオン電圧を２Ｖ程度とすることができる。 Normally, the pn diode has a larger on-voltage than the Schottky diode. Therefore, the design can be made so that the pn diode portion composed of the p-type semiconductor member 22 and the n-type semiconductor layer 21 does not turn on at the voltage at which the Schottky diode 2 turns on. For example, the on-voltage of the Schottky diode 2 can be set to about 1V, and the on-voltage of the pn diode portion can be set to about 2V.
　これによって、ショットキーダイオード２の通常動作においてはｐｎダイオード部分がオンしないため、ショットキーダイオード本来の高速動作が可能になる。一方、突入電流発生時はショットキーダイオード２の電圧が上昇し、ｐｎダイオード部分がオンする電圧に達し、ｐ型半導体部材２２からｎ型半導体層２１へ正孔が注入される。 As a result, the pn diode portion does not turn on in the normal operation of the Schottky diode 2, so that the original high-speed operation of the Schottky diode becomes possible. On the other hand, when the inrush current is generated, the voltage of the shotkey diode 2 rises and reaches the voltage at which the pn diode portion is turned on, and holes are injected from the p-type semiconductor member 22 into the n-type semiconductor layer 21.
　そのとき、カソード電極２４からｎ型半導体層２１へはその注入された正孔と同じ数の電子が注入され、ドリフト層の抵抗が大幅に減少する。このため、突入電流という大電流がショットキーダイオード２を流れるが、電圧の上昇は抑えられるため、温度上昇が抑えられ、突入電流によるショットキーダイオード２の損傷を防ぐことができる。 At that time, the same number of electrons as the injected holes are injected from the cathode electrode 24 into the n-type semiconductor layer 21, and the resistance of the drift layer is significantly reduced. Therefore, a large current called an inrush current flows through the Schottky diode 2, but the rise in voltage is suppressed, so that the temperature rise is suppressed and damage to the Schottky diode 2 due to the inrush current can be prevented.
　また、ｐ型半導体部材２２の価電子帯の上端のエネルギーが、ｎ型半導体層２１を構成するＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギー以下である場合は、ｐ型半導体部材２２からｎ型半導体層２１への正孔の移動が容易になるため、突入電流への耐性をより高めることができる。 When the energy at the upper end of the valence band of the p-type semiconductor member 22 is equal to or less than the energy at the upper end of the valence band of the Ga 2 O3 system single crystal constituting the n - type semiconductor layer 21, the p-type semiconductor member Since the holes are easily transferred from the 22 to the n-type semiconductor layer 21, the resistance to the inrush current can be further improved.
　ｐ型半導体部材２２の材料であるＢＮ、ＡｌｘＧａ１－ｘＮ（ｘ＞０）の価電子帯の上端のエネルギーは、ｎ型半導体層２１の材料であるＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギーに２ｅＶを加えたエネルギー以下である。この関係は、図４から理解されるように、ＡｌｘＧａ１－ｘＮ（ｘ＞０）のＡｌ濃度並びにＧａ２Ｏ３系単結晶のＡｌ濃度及びＩｎ濃度がどのような値をとる場合にも成り立つ。 The energy at the upper end of the valence band of BN, Al x Ga 1-x N (x> 0), which is the material of the p-type semiconductor member 22, is the energy of the Ga 2 O 3 series single crystal, which is the material of the n-type semiconductor layer 21. It is less than or equal to the energy obtained by adding 2 eV to the energy at the upper end of the valence band. As can be understood from FIG. 4, this relationship is understood when the Al concentration of Al x Ga 1-x N (x> 0) and the Al concentration and In concentration of the Ga 2 O 3 system single crystal take. It also holds true.
　ｐ型半導体部材２２の材料であるＡｌｘＧａ１－ｘＮ（ｘ＞０）は、Ａｌ濃度ｘが１に近いほど価電子帯の上端のエネルギーが低くなり、ｎ型半導体層２１の材料であるＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギーに近づく、あるいはｎ型半導体層２１の材料であるＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギーよりも小さくなる。このため、例えば、ｐ型半導体部材２２がＡｌｘＧａ１－ｘＮ（ｘ≧０．８）からなることが好ましい。 Al x Ga 1-x N (x> 0), which is the material of the p-type semiconductor member 22, has a lower energy at the upper end of the valence band as the Al concentration x is closer to 1, and is a material of the n-type semiconductor layer 21. It approaches the energy of the upper end of the valence band of a certain Ga 2 O 3 series single crystal, or becomes smaller than the energy of the upper end of the valence band of the Ga 2 O 3 series single crystal which is the material of the n-type semiconductor layer 21. Therefore, for example, it is preferable that the p-type semiconductor member 22 is made of Al x Ga 1-x N (x ≧ 0.8).
　また、ＢＮの価電子帯の上端のエネルギーは、ｎ型半導体層２１の材料であるＧａ２Ｏ３系単結晶の価電子帯の上端のエネルギーとほぼ等しいため、ＢＮをｐ型半導体部材２２の材料として用いることにより、ショットキーダイオード２の突入電流への耐性を特に高めることができる。 Further, since the energy at the upper end of the valence band of the BN is substantially equal to the energy at the upper end of the valence band of the Ga 2 O3 system single crystal which is the material of the n - type semiconductor layer 21, the BN is used as the p-type semiconductor member 22. By using it as a material, the resistance of the shotkey diode 2 to the inrush current can be particularly enhanced.
（ショットキーダイオードの製造方法）
　以下に、ショットキーダイオード２の製造方法の一例を示す。 (Manufacturing method of Schottky diode)
An example of a method for manufacturing the Schottky diode 2 is shown below.
　まず、ｎ型半導体基板２０上に、ＶＰＥ法によりドナーとしてのＳｉを含むＧａ２Ｏ３系単結晶をエピタキシャル成長させ、厚さ５ｍｍ程度、Ｓｉ濃度６×１０１５ｃｍ－３程度のｎ型半導体層２１を形成する。 First, a Ga 2 O 3 series single crystal containing Si as a donor is epitaxially grown on the n-type semiconductor substrate 20 by the VPE method, and an n-type semiconductor layer having a thickness of about 5 mm and a Si concentration of about 6 × 10 15 cm -3 is formed. 21 is formed.
　次に、フォトリソグラフィとドライエッチングを用いてｎ型半導体層２１のｎ型半導体基板２０と反対側の面２６にトレンチ２５を形成する。 Next, a trench 25 is formed on the surface 26 of the n-type semiconductor layer 21 opposite to the n-type semiconductor substrate 20 by using photolithography and dry etching.
　次に、電子ビーム蒸着により、ｎ型半導体基板２０の底面にＴｉ／Ａｕ積層構造等を有するカソード電極２４を形成する。その後、加熱処理を施して、カソード電極２４とｎ型半導体基板２０の間のコンタクト抵抗を減少させる。 Next, a cathode electrode 24 having a Ti / Au laminated structure or the like is formed on the bottom surface of the n-type semiconductor substrate 20 by electron beam vapor deposition. After that, heat treatment is performed to reduce the contact resistance between the cathode electrode 24 and the n-type semiconductor substrate 20.
　次に、Ａｒ＋イオンアシストを併用したＰＶＤ法により、ｎ型半導体層２１の面２６の全面に、トレンチ２５を埋め込める程度の厚さのＺｎが添加されたＢＮ膜を堆積させる。 Next, by the PVD method using Ar + ion assist in combination, a BN film having Zn added having a thickness sufficient to embed the trench 25 is deposited on the entire surface 26 of the n-type semiconductor layer 21.
　なお、ＢＮ膜の形成には、スパッタ法、ＭＢＥ法、ＣＶＤ法などの他の方法を用いてもよい。また、ＢＮ膜にＺｎ以外のＭｇ、Ｂｅなどをアクセプターとして添加してもよい。また、例えば、ＢＮ膜の成膜方法としてレーザ支援プラズマＣＶＤ法を用いることにより、Ｓｉをアクセプターとして用いることもできる。また、これらのアクセプターは、ＢＮ膜の形成後にイオン注入により添加されてもよい。 In addition, other methods such as a sputtering method, an MBE method, and a CVD method may be used for forming the BN film. Further, Mg, Be, etc. other than Zn may be added to the BN film as an acceptor. Further, for example, Si can be used as an acceptor by using a laser-assisted plasma CVD method as a method for forming a BN film. In addition, these acceptors may be added by ion implantation after the formation of the BN film.
　次に、ｎ型半導体層２１の隣接するトレンチ２５の間のメサ形状部分２１０が露出するまで、ＲＩＥによりＢＮ膜をエッチングする。 Next, the BN film is etched by RIE until the mesa-shaped portion 210 between the adjacent trenches 25 of the n-type semiconductor layer 21 is exposed.
　次に、電子ビーム蒸着により、ｎ型半導体層２１の面２６上にＭｏ／Ａｕ積層構造を有するアノード電極２３を形成する。アノード電極２３は、リフトオフにより、円形等の所定の形状にパターニングされる。 Next, an anode electrode 23 having a Mo / Au laminated structure is formed on the surface 26 of the n-type semiconductor layer 21 by electron beam vapor deposition. The anode electrode 23 is patterned into a predetermined shape such as a circle by lift-off.
（実施の形態の効果）
　上記実施の形態によれば、高耐圧かつ低損失であり、かつサージ電流への耐性に優れたＧａ２Ｏ３系のショットキーダイオードを提供することができる。 (Effect of embodiment)
According to the above embodiment, it is possible to provide a Ga 2 O 3 system Schottky diode having high withstand voltage, low loss, and excellent resistance to surge current.
　以上、本発明の実施の形態を説明したが、本発明は、上記実施の形態に限定されず、発明の主旨を逸脱しない範囲内において種々変形実施が可能である。また、上記に記載した実施の形態は請求の範囲に係る発明を限定するものではない。また、実施の形態の中で説明した特徴の組合せの全てが発明の課題を解決するための手段に必須であるとは限らない点に留意すべきである。 Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be carried out within a range that does not deviate from the gist of the invention. Moreover, the embodiment described above does not limit the invention according to the claims. It should also be noted that not all combinations of features described in the embodiments are essential to the means for solving the problems of the invention.
　高耐圧かつ低損失であり、かつサージ電流への耐性に優れたＧａ２Ｏ３系のショットキーダイオードを提供する。 Provided is a Ga 2 O 3 system Schottky diode having high withstand voltage, low loss, and excellent resistance to surge current.
１、２…ショットキーダイオード、　１０、２０…ｎ型半導体基板、　１１、２１…ｎ型半導体層、　１２、２５…トレンチ、　１３、２３…アノード電極、　１４、２４…カソード電極、　１５…トレンチ絶縁膜　１６…アノード電極、　１７、２２…ｐ型半導体部材 1, 2 ... Schottky diode, 10, 20 ... n-type semiconductor substrate, 11, 21 ... n-type semiconductor layer, 12, 25 ... trench, 13, 23 ... anode electrode, 14, 24 ... cathode electrode, 15 ... trench insulation Film 16 ... anode electrode, 17, 22 ... p-type semiconductor member

Claims (4)

  1. 　Ｇａ２Ｏ３系単結晶からなり、一方の面に開口する複数のトレンチを有するｎ型半導体層と、
    　前記ｎ型半導体層の隣接する前記トレンチの間のメサ形状領域に接続されたアノード電極と、
    　絶縁膜に覆われた状態で前記複数のトレンチのそれぞれに埋め込まれ、前記アノード電極に電気的に接続されたトレンチアノード電極と、
    　前記ｎ型半導体層の前記アノード電極と反対側に直接又は間接的に接続されたカソード電極と、
    　前記メサ形状領域の一部及び前記アノード電極に接続された、ＢＮ又はＡｌｘＧａ１－ｘＮ（ｘ＞０）からなるｐ型半導体部材と、
    　を備えた、ショットキーダイオード。     An n-type semiconductor layer composed of a Ga 2 O 3 system single crystal and having a plurality of trenches opening on one surface, and an n-type semiconductor layer.
    An anode electrode connected to a mesa-shaped region between adjacent trenches of the n-type semiconductor layer,
    A trench anode electrode embedded in each of the plurality of trenches in a state of being covered with an insulating film and electrically connected to the anode electrode, and a trench anode electrode.
    A cathode electrode directly or indirectly connected to the side opposite to the anode electrode of the n-type semiconductor layer,
    A p-type semiconductor member made of BN or Al x Ga 1-x N (x> 0) connected to a part of the mesa-shaped region and the anode electrode, and a p-type semiconductor member.
    With a Schottky diode.
  2. 　Ｇａ２Ｏ３系単結晶からなり、一方の面に開口する複数のトレンチを有するｎ型半導体層と、
    　前記トレンチ内に埋め込まれた、ＢＮ又はＡｌｘＧａ１－ｘＮ（ｘ＞０）からなるｐ型半導体部材と、
    　前記ｎ型半導体層の隣接する前記トレンチの間のメサ形状領域、及び前記ｐ型半導体部材に接続されたアノード電極と、
    　前記ｎ型半導体層の前記アノード電極と反対側に直接又は間接的に接続されたカソード電極と、
    　を備えた、ショットキーダイオード。     An n-type semiconductor layer composed of a Ga 2 O 3 system single crystal and having a plurality of trenches opening on one surface, and an n-type semiconductor layer.
    A p-type semiconductor member made of BN or Al x Ga 1-x N (x> 0) embedded in the trench, and a p-type semiconductor member.
    A mesa-shaped region between adjacent trenches of the n-type semiconductor layer, and an anode electrode connected to the p-type semiconductor member.
    A cathode electrode directly or indirectly connected to the side opposite to the anode electrode of the n-type semiconductor layer,
    With a Schottky diode.
  3. 　前記ｐ型半導体部材がＡｌｘＧａ１－ｘＮ（ｘ≧０．８）からなる、
    　請求項１又は２に記載のショットキーダイオード。     The p-type semiconductor member is made of Al x Ga 1-x N (x ≧ 0.8).
    The Schottky diode according to claim 1 or 2.
  4. 　前記ｐ型半導体部材の価電子帯の上端のエネルギーが、前記Ｇａ２Ｏ３系単結晶の価電子帯の上端のエネルギー以下である、
    　請求項１～３のいずれか１項に記載のショットキーダイオード。     The energy at the upper end of the valence band of the p-type semiconductor member is equal to or less than the energy at the upper end of the valence band of the Ga 2 O3 system single crystal.
    The Schottky diode according to any one of claims 1 to 3.
PCT/JP2021/036436 2020-10-07 2021-10-01 Schottky diode WO2022075218A1 (en)

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