Schottky Diode

Abstract

To provide a Ga2O3-based Schottky diode with high breakdown voltage, low loss, and excellent resistance against surge current.SOLUTION: A Schottky diode 1 includes an n-type semiconductor layer 11 formed of Ga2O3-based single crystal and including a plurality of trenches 12 that open to one surface 18, an anode electrode 13 connected to a mesa shape region 110 between the adjacent trenches 12 of the n-type semiconductor layer 11, an anode electrode 16 embedded in each of the trenches 12 in a state of being covered with a trench insulating film 15 and electrically connected to the anode electrode 13, a cathode electrode 14 directly or indirectly connected to the n-type semiconductor layer 11 on the side opposite to the anode electrode 13, and a p-type semiconductor member 17 connected to a part of the mesa shape region 110 and the anode electrode 16 and formed of BN or AlxGa1-xN (x>0).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a Schottky diode. [Background technology]

[0002] Conventionally, a diode having a structure combining a pn junction and a Schottky junction, called a junction barrier Schottky (JBS) diode, has been known (see, for example, Patent Document 1). In a JBS diode, a surge current can be passed through the pn diode portion, and therefore the JBS diode has superior resistance to surge current compared to a Schottky barrier diode that does not have a pn junction.

[0003] The JBS diode described in Patent Document 1 is a n-type diode made of SiC. - A n-type drift layer and - A p-type layer is obtained by ion-implanting p-type impurities into the n-type drift layer, - The n-type drift layer and the p-type layer form a pn junction.

[0004] Also, a trench MOS type Ga2O3-based Schottky diode in which a gate electrode is embedded in a semiconductor layer has been known (see, for example, Patent Document 2). Ga2O3-based semiconductor devices are known to have high breakdown voltage and low loss due to physical properties such as the wide band gap of Ga2O3. Furthermore, the Schottky diode described in Patent Document 1 uses a trench MOS structure, and therefore can obtain a higher breakdown voltage without increasing the resistance of the semiconductor layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-282973 A [Patent Document 2] JP 2018-142577 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when attempting to improve the surge current resistance of a Ga2O3-based Schottky diode as shown in Patent Document 2, it is extremely difficult to obtain p-type Ga2O3, and therefore it is not possible to form a p-n junction region by adding p-type impurities to the Ga2O3 layer.

[0007] An object of the present invention is to provide a Ga2O3-based Schottky diode that has high breakdown voltage, low loss, and excellent resistance to surge current. [Means for solving the problem]

[0008] In order to achieve the above object, one aspect of the present invention provides the following Schottky diodes [1] to [4].

[0009] [1] An n-type semiconductor layer made of Ga2O3-based single crystal and having a plurality of trenches opening on one surface, 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 while being covered with an insulating film and electrically connected to the anode electrode, a cathode electrode directly or indirectly connected to the side of the n-type semiconductor layer opposite to the anode electrode, and a BN or Al layer connected to a part of the mesa-shaped region and to the anode electrode. x Ga 1-x N(x>0) and a p-type semiconductor member. [2] An n-type semiconductor layer made of Ga2O3-based single crystal and having a plurality of trenches opening on one side, and BN or Al buried in the trenches. x Ga 1-x N(x>0), a mesa-shaped region between adjacent trenches of the n-type semiconductor layer, and an anode electrode connected to the p-type semiconductor member, and a cathode electrode directly or indirectly connected to the side of the n-type semiconductor layer opposite the anode electrode. [3] The p-type semiconductor member is Al x Ga 1-x The Schottky diode according to the above [1] or [2], wherein N(x≧0.8). [4] The Schottky diode according to any one of the above [1] to [3], wherein the energy of the upper end of the valence band of the p-type semiconductor member is equal to or lower than the energy of the upper end of the valence band of the Ga2O3-based single crystal. Effect of the Invention

[0010] According to the present invention, it is possible to provide a Ga2O3-based Schottky diode that has high breakdown voltage, low loss, and excellent resistance to surge current. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a vertical cross-sectional view of a Schottky diode according to a first embodiment. [Diagram 2] FIG. 2 is a graph showing a schematic diagram of current-voltage characteristics when an inrush current flows in a Schottky diode when (A) the diode includes a p-type semiconductor member and when (B) the diode does not include a p-type semiconductor member. [Diagram 3] FIG. 3 is a diagram showing a band structure of a p-type semiconductor member and an n-type semiconductor layer made of a Ga2O3-based single crystal, and a schematic diagram showing the flow of holes. [Figure 4] FIG. 4 shows a band diagram of Ga2O3, a typical material for an n-type semiconductor layer, and BN and AlxGa1-xN (x>0), which are materials for p-type semiconductor components. [Diagram 5] FIG. 5 is a vertical cross-sectional view of a modified example of the Schottky diode according to the first embodiment. [Figure 6] FIG. 6 is a vertical cross-sectional view of a Schottky diode according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First Embodiment (Schottky diode configuration) 1 is a vertical cross-sectional view of a Schottky diode 1 according to a first embodiment. The Schottky diode 1 is a vertical Schottky diode having a trench MOS structure.

[0013] The Schottky diode 1 includes an n-type semiconductor substrate 10, an n-type semiconductor layer 11 which is a layer stacked on the n-type semiconductor substrate 10 and has a plurality of trenches 12 opening on a surface 18 opposite to the n-type semiconductor substrate 10, an anode electrode 13 connected to a mesa-shaped region 110 between adjacent trenches 12 of the n-type semiconductor layer 11, a cathode electrode 14 formed on the surface of the n-type semiconductor substrate 10 opposite to the n-type semiconductor layer 11, a trench insulating film 15 covering the inner surfaces of the trenches 12 in the n-type semiconductor layer 11, an anode electrode 16 which is embedded in the trenches 12 of the n-type semiconductor layer 11 so as to be covered by the trench insulating film 15 and is electrically connected to the anode electrode 13, and a p-type semiconductor member connected to a part of the mesa-shaped region 110 and the anode electrode 13.

[0014] In Schottky diode 1, 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 between the anode electrode 13 and the n-type semiconductor layer 11 as viewed from the n-type semiconductor layer 11 is lowered, and a current flows from the anode electrode 13 to the cathode electrode 14.

[0015] On the other hand, when a reverse voltage (anode electrode 13 side has a negative potential) is applied between the anode electrode 13 and the cathode electrode 14, no current flows due to the Schottky barrier. Also, when a reverse voltage is applied between the anode electrode 13 and the cathode electrode 14, a depletion layer spreads 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.

[0016] Generally, the upper limit of the reverse leakage current of a Schottky diode is set to 1 A. In this embodiment, the reverse voltage when a leakage current of 1 A flows is defined as the withstand voltage.

[0017] For example, according to the data on the Schottky interface electric field strength dependence of reverse leakage current in Schottky diodes using SiC as a semiconductor layer, described in "Hiroyuki Matsunami, Noboru Otani, Tsunenobu Kimoto, Takashi Nakamura, Semiconductor SiC Technology and Applications, 2nd Edition, Nikkan Kogyo Shimbun, September 30, 2011, p. 355," the current density of reverse leakage current is 0.0001 A / cm 2 The electric field strength directly below the Schottky electrode at this time is approximately 0.8MV / cm. Here, 0.0001A / cm 2 is the current density directly below the Schottky electrode when a current of 1 μA flows through the Schottky electrode with dimensions of 1 mm × 1 mm.

[0018] For this reason, even if the dielectric breakdown field strength of the semiconductor material itself is several MV / cm, if the electric field strength directly below the Schottky electrode exceeds 0.8 MV / cm, a leakage current exceeding 1 μA will flow.

[0019] For example, in order to obtain a breakdown voltage of 1200 V in a conventional Schottky diode that does not have a special structure for suppressing the electric field strength directly under the Schottky electrode, the donor concentration of the semiconductor layer must be reduced to 10 15 cm -3 This requires a very thick semiconductor layer, which results in very large conduction loss, making it difficult to fabricate a Schottky barrier diode with high breakdown voltage and low loss.

[0020] The Schottky diode 1 according to the present embodiment has a trench MOS structure, and therefore can achieve a high breakdown voltage without increasing the resistance of the semiconductor layer. In other words, the Schottky diode 1 is a Schottky diode with high breakdown voltage and low loss.

[0021] The n-type semiconductor substrate 10 is made of an n-type Ga2O3-based single crystal containing a Group IV element such as Si or Sn as a donor. The donor concentration of the n-type semiconductor substrate 10 is, for example, 1.0×10 18 cm -3 Greater than or equal to 1.0×1020 cm -3 The following applies. 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 Ga2O3-based single crystal substrate.

[0022] Here, the Ga2O3-based single crystal is a Ga2O3 single crystal or a Ga2O3 single crystal doped with one or both of Al and In, and is a single crystal of a Ga2O3-based semiconductor having a composition represented by (Ga x Al y In (1-x-y) )2O3 (0 < x ≤ 1, 0 ≤ y < 1, 0 < x + y ≤ 1). When Al is added to Ga2O3, the bandgap widens, and when In is added, the bandgap narrows. The above Ga2O3 single crystal has, for example, a β-type crystal structure.

[0023] The n-type semiconductor layer 11 is made of an n-type Ga2O3-based 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 that 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 Ga2O3-based single crystal substrate.

[0024] Note that a high donor concentration layer containing a high concentration of donors 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 epitaxially growing the n-type semiconductor layer 11 on the n-type semiconductor substrate 10. In the initial stage of growth of the n-type semiconductor layer 11, the amount of dopant incorporation is unstable or there is diffusion of acceptor impurities from the n-type semiconductor substrate 10 which is the substrate. Therefore, when the n-type semiconductor layer 11 is directly grown on the n-type semiconductor substrate 10, the region near the interface of the n-type semiconductor layer 11 with the n-type semiconductor substrate 10 may have increased resistance. To avoid such problems, a high donor concentration layer is used. The concentration of the high donor concentration layer is set to a concentration higher than that of the n-type semiconductor layer 11, and more preferably, a concentration higher than that of the n-type semiconductor substrate 10.

[0025] 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 below 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 donor concentration of the n-type semiconductor layer 11 should be about 6.0×10 16 cm -3 On the other hand, as the donor concentration decreases, the resistance of the n-type semiconductor layer 11 increases, and the forward loss increases. 16 cm -3 In order to obtain a higher breakdown voltage, the donor concentration is preferably 1.0×10 16 cm -3 It is preferable to reduce it to a certain extent.

[0026] As the thickness T of n-type semiconductor layer 11 increases, the maximum electric field strength in n-type semiconductor layer 11 and the maximum electric field strength in trench insulating film 15 decrease. By making the thickness T of n-type semiconductor layer 11 approximately 6 μm or more, it is possible to effectively reduce the maximum electric field strength in n-type semiconductor layer 11 and the maximum electric field strength in trench insulating film 15. From the viewpoint of reducing these electric field strengths and reducing the size of Schottky diode 1, it is preferable that the thickness T of n-type semiconductor layer 11 be approximately 5.5 μm or more and 9 μm or less.

[0027] The electric field strength in each part of Schottky diode 1 varies depending on depth D of trench 12. In order to keep low the maximum electric field strength in the region directly below anode electrode 13 in n-type semiconductor layer 11, the maximum electric field strength in n-type semiconductor layer 11, and the maximum electric field strength in trench insulating film 15, depth D of trench 12 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.

[0028] Width W of trench 12 t Since the width W tIt is preferable that the width W be as narrow as possible. t If the width W is made too fine, it becomes difficult to fill the trench 12 with the trench insulating film 15 and the anode electrode 16, and the manufacturing yield decreases. t When the width W becomes 3μm or more, t It has been found that an increase in width W has almost no effect on the embedding of the anode electrode 16. t If the width W is less than 0.5 μm, a special exposure device is required to form the trench 12, which may increase the manufacturing cost. t It is preferable that the thickness is 0.5 μm or more and 3 μm or less.

[0029] The width W of the mesa-shaped portion 110 between adjacent trenches 12 of the n-type semiconductor layer 11 m The more the width W of the mesa-shaped portion 110 is reduced, the more the maximum electric field strength in the region immediately below the anode electrode 13 in the n-type semiconductor layer 11 is reduced. m On the other hand, the smaller the width of the mesa-shaped portion 110, the more difficult it is to manufacture the trench 12. Therefore, the width W of the mesa-shaped portion 110 is preferably 2.5 μm or less. m It is preferable that the thickness is 0.5 μm or more.

[0030] As the dielectric constant of the trench insulating film 15 increases, the maximum electric field strength in the trench insulating film 15 decreases, and therefore, it is preferable that the trench insulating film 15 be made of a material with a high dielectric constant. For example, Al2O3 (relative dielectric constant: approximately 9.3) and HfO2 (relative dielectric constant: approximately 22) can be used as materials for the trench insulating film 15, and it is particularly preferable to use HfO2, which has a high dielectric constant.

[0031] Furthermore, as the thickness of trench insulating film 15 increases, the maximum electric field strength in n-type semiconductor layer 11 decreases, but the maximum electric field strength in trench insulating film 15 and the maximum electric field strength in the region directly below anode electrode 13 increase. From the viewpoint of ease of manufacture, it is preferable that the thickness of trench insulating film 15 is small, and more preferably 300 nm or less. However, it goes without saying that the thickness must be such that almost no current flows directly between anode electrode 16 and n-type semiconductor layer 11.

[0032] The material of the anode electrode 16 is not particularly limited as long as it is conductive, and for example, highly doped polycrystalline Si, or metals such as Ni and Au can be used.

[0033] As described above, the electric field strength in the Schottky diode 1 is determined by the width W of the mesa-shaped portion 110 between two adjacent trenches 12. m It is affected by the depth D of the trench 12, the thickness of the trench insulating film 15, etc., but is hardly affected by the planar pattern of the trench 12. For this reason, the planar pattern of the trench 12 in the n-type semiconductor layer 11 is not particularly limited.

[0034] The cathode electrode 14 is in 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 stacked, for example, Ti / Au or Ti / Al. In order to ensure that the cathode electrode 14 and the n-type semiconductor substrate 10 are in ohmic contact with each other, it is preferable that the layer of the cathode electrode 14 in contact with the n-type semiconductor substrate 10 is made of Ti. Note that when the Schottky diode 1 does not include the n-type semiconductor substrate 10, the cathode electrode 14 is connected to the side of the n-type semiconductor layer 11 opposite to the anode electrode 13 and is in ohmic contact with the n-type semiconductor layer 11.

[0035] The p-type semiconductor member 17 is a member used for surge protection, and is made of p-type BN (boron nitride) or Al x Ga 1-xThe p-type semiconductor member 17 made of BN contains additives such as Zn, Mg, Be, and Si as acceptors. x Ga 1-x The p-type semiconductor member 17 made of N(x>0) contains an additive such as Mg as an acceptor. In addition, the p-type semiconductor member 17 contains a group III atomic vacancy (a vacancy due to a B vacancy in the case of BN, or an Al x Ga 1-x In the case of N(x>0), vacancies due to Al or Ga deficiencies may be present as acceptors.

[0036] The energy of the upper end of the valence band of the p-type semiconductor material 17 is equal to or less than the energy obtained by adding 2 eV to the upper end of the valence band of the Ga2O3-based semiconductor constituting the n-type semiconductor layer 11. Therefore, by using the p-type semiconductor material 17, the resistance of the drift layer can be reduced when a surge current (also called an inrush current or starting current) occurs that may occur when the Schottky diode 1 is turned on, and heat generation and damage can be suppressed.

[0037] Normally, a pn diode has a higher on-voltage than a Schottky diode. For this reason, it is possible to design the pn diode portion, which is made up of the p-type semiconductor member 17 and the n-type semiconductor layer 11, so that it does not turn on at the voltage that turns on the Schottky diode 1. 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.

[0038] As a result, the pn diode portion does not turn on during normal operation of Schottky diode 1, enabling the inherent high-speed operation of a Schottky diode. On the other hand, when an inrush current occurs, the voltage of Schottky diode 1 rises and reaches a voltage at which the pn diode portion turns on, and holes are injected from p-type semiconductor member 17 to n-type semiconductor layer 11.

[0039] 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 greatly reduced. Therefore, although a large current called an inrush current flows through the Schottky diode 1, the increase in voltage is suppressed, and therefore the increase in temperature is suppressed, and damage to the Schottky diode 1 due to the inrush current can be prevented.

[0040] 2 is a graph showing a schematic diagram of the current-voltage characteristics when an inrush current flows when the Schottky diode 1 includes (A) the p-type semiconductor member 17 and when it does not include (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, causing it to burn out. On the other hand, when the p-type semiconductor member 17 is included, the voltage V at which the pn diode portion turns on is pn When the inrush current reaches 1 V, the rate of voltage rise slows down. In this way, the current flowing through the Schottky diode 1 increases due to the inrush current, but the voltage rise is suppressed, so the temperature rise is suppressed and damage to the Schottky diode 1 is prevented.

[0041] 3 is a diagram showing the band structure of the p-type semiconductor member 17 and the n-type semiconductor layer 11 made of a Ga2O3-based single crystal, and the flow of holes. As shown in FIG. 3, the energy E V2 is the energy E of the top of the valence band of Ga2O3 single crystal. V1 If the energy E C2 Since the size of does not affect the injection of holes from the p-type semiconductor member 17 to the n-type semiconductor layer 11, it is not limited to a specific range.

[0042] In addition, the energy E V2 The upper energy E of the valence band of the Ga2O3 single crystal constituting the n-type semiconductor layer 11 is V1If it is equal to or less than this, holes can easily move from the p-type semiconductor member 17 to the n-type semiconductor layer 11, so that the resistance to inrush current can be further improved.

[0043] FIG. 4 shows a typical material for the n-type semiconductor layer 11, Ga2O3, and a typical material for the p-type semiconductor member 17, BN, Al x Ga 1-x The band lineup including the band structure of N(x>0) is shown. The rectangles in Figure 4 indicate the band gap of each material, the numbers inside the band gap indicate the size of the band gap [eV], the numbers above the band gap indicate the band offset of the conduction band with Ga2O3 (energy difference at the bottom of the conduction band) [eV], and the numbers below the band gap indicate the band offset of the valence band with Ga2O3 [eV].

[0044] In addition, AlN in the figure is Al when x=1. x Ga 1-x N, AlGaN is 0 <x<1であるときのAl x Ga 1-x N is shown. In the band diagram of AlGaN, the closer x is to 1, the closer it is to AlN, and the closer x is to 0, the closer it is to GaN. FIG. 4 also shows the band gaps of AlO2 and In2O3. In the Ga2O3-based single crystal, which is the material of the n-type semiconductor layer 11, the band structure approaches Al2O3 as the Al concentration increases, and the band structure approaches In2O3 as the In concentration increases. As shown in FIG. 4, the amount of energy modulation at the top of the valence band due to changes in the Al concentration and In concentration in the Ga2O3-based single crystal is not large, and the band offset of the valence band with Ga2O3 is at most about 0.4 eV.

[0045] BN, Al, which are materials for the p-type semiconductor component 17 x Ga 1-x The energy of the top of the valence band of N(x>0) is equal to or less than 2 eV added to the energy of the top of the valence band of the Ga2O3-based single crystal, which is the material of the n-type semiconductor layer 11. As can be seen from FIG. x Ga 1-xThis holds true regardless of the values ​​of the Al concentration in N(x>0) and the Al and In concentrations in the Ga2O3-based single crystal.

[0046] Al, the material of p-type semiconductor component 17 x Ga 1-x As the Al concentration x approaches 1, the energy of the upper end of the valence band N(x>0) becomes lower, approaching the energy of the upper end of the valence band of the Ga2O3-based single crystal that is the material of the n-type semiconductor layer 11, or becoming smaller than the energy of the upper end of the valence band of the Ga2O3-based single crystal that is the material of the n-type semiconductor layer 11. For this reason, for example, when the p-type semiconductor member 17 is Al x Ga 1-x It is preferable that the number of x is N(x≧0.8).

[0047] In addition, the energy of the upper end of the valence band of BN is approximately equal to the energy of the upper end of the valence band of a Ga2O3-based single crystal that is the material of the n-type semiconductor layer 11. Therefore, by using BN as the material of the p-type semiconductor member 17, the resistance of the Schottky diode 1 to inrush current can be particularly improved.

[0048] 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 be released, but the more difficult it is for the current to flow during normal operation. For this reason, 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.

[0049] 5 is a vertical cross-sectional view of a Schottky diode 3 which is a modified example 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, i.e., it does not have a trench 12, a trench insulating film 15, or an anode electrode 16 in the n-type semiconductor layer 11. The Schottky diode 3 is inferior in withstand voltage compared to the Schottky diode 1 because it does not have a trench structure, but has the same surge current resistance as the Schottky diode 1 due to the p-type semiconductor member 17.

[0050] Second Embodiment (Schottky diode configuration) 6 is a vertical cross-sectional view of a Schottky diode 2 according to a second embodiment. The Schottky diode 2 is a vertical junction barrier Schottky (JBS) diode having a trench structure.

[0051] The Schottky diode 2 comprises an n-type semiconductor substrate 20, an n-type semiconductor layer 21 formed on the n-type semiconductor substrate 20 and having a plurality of trenches 25 opening on a surface 26 opposite to the n-type semiconductor substrate 20, a p-type semiconductor member 22 embedded in the trenches 25 of the n-type semiconductor layer 21, an anode electrode 23 provided on the surface 26 of the n-type semiconductor layer 21 and connected to a mesa-shaped region 210 between adjacent trenches 25 of the n-type semiconductor layer 21 and the p-type semiconductor member 22, and a cathode electrode 24 formed on the surface of the n-type semiconductor substrate 20 opposite to the n-type semiconductor layer 21.

[0052] The n-type semiconductor layer 21 and the anode electrode 23 form a Schottky junction, and the Schottky diode 2 utilizes the rectification of this Schottky junction. In addition, the Schottky diode 2 uses BN or Al instead of p-type Ga2O3, which is difficult to form. x Ga 1-x The p-type semiconductor member 22 is made of N(x>0).

[0053] In the Schottky diode 2, 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 between the anode electrode 23 and the n-type semiconductor layer 21 as viewed from the n-type semiconductor layer 21 is lowered, and a current flows from the anode electrode 23 to the cathode electrode 24.

[0054] On the other hand, when a reverse voltage (anode electrode 23 side has a negative potential) is applied between the anode electrode 23 and the cathode electrode 24, no current flows due to the Schottky barrier. At this time, a depletion layer spreads from the p-type semiconductor member 22, and the channel between the adjacent p-type semiconductor members 22 is closed, so that the leakage current is effectively suppressed.

[0055] The Schottky diode 2 according to the present embodiment has a trench-type JBS structure, and therefore can obtain a high breakdown voltage without increasing the resistance of the semiconductor layer, similar to the Schottky diode 1 according to the first embodiment. In other words, the Schottky diode 2 is a Schottky barrier diode with high breakdown voltage and low loss.

[0056] The n-type semiconductor substrate 20 is made of an n-type Ga2O3-based single crystal containing a Group IV element such as Si or Sn as a donor. The donor concentration of the n-type semiconductor substrate 20 is, for example, 1.0×10 18 cm -3 Greater than or equal to 1.0×10 20 cm -3 The thickness of the n-type semiconductor substrate 20 is, for example, 10 to 600 μm. The n-type semiconductor substrate 20 is, for example, a Ga2O3-based single crystal substrate.

[0057] The n-type semiconductor layer 21 is made of an n-type Ga2O3-based single crystal containing a Group IV element such as Si or Sn as a donor. 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 Ga2O3-based single crystal substrate.

[0058] A high donor concentration layer containing a high concentration of donors 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. In the initial stage of growth of the n-type semiconductor layer 21, the amount of dopant taken in may be unstable, or acceptor impurities may diffuse from the n-type semiconductor substrate 20. Therefore, if the n-type semiconductor layer 21 is directly grown on the n-type semiconductor substrate 20, the region of the n-type semiconductor layer 21 close to the interface with the n-type semiconductor substrate 20 may become highly resistive. To avoid such problems, a high donor concentration layer is used. The concentration of the high donor concentration layer is set to a higher concentration than that of the n-type semiconductor layer 21, for example, and more preferably, to a higher concentration than that of the n-type semiconductor substrate 20.

[0059] 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 under 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 should be set to about 2.0×10 17 cm -3 On the other hand, as the donor concentration decreases, the resistance of the n-type semiconductor layer 21 increases, and the forward loss increases. 16 cm -3 In order to obtain a higher breakdown voltage, the donor concentration is preferably 1.0×10 16 cm -3 It may be reduced to a certain extent.

[0060] As the thickness T of n-type semiconductor layer 21 increases, the maximum electric field strength in n-type semiconductor layer 21 decreases. By making the thickness of n-type semiconductor layer 21 approximately 3 μm or more, it is possible to effectively reduce the maximum electric field strength in n-type semiconductor layer 21. From the viewpoint of reducing the electric field strength and reducing the size of Schottky diode 2, it is preferable that the thickness of n-type semiconductor layer 21 be approximately 3 μm or more and 9 μm or less.

[0061] The electric field strength in each part of Schottky diode 2 varies depending on depth D of trench 25. In order to keep low the maximum electric field strength in the region directly below anode electrode 23 in n-type semiconductor layer 21 and the maximum electric field strength in n-type semiconductor layer 21, depth D of trench 25 is preferably about 1.5 μm or more and 6 μm or less.

[0062] Trench 25 width W t The narrower the width, the lower the conduction loss can be. However, the narrower the width, the more difficult the manufacturing process becomes, which in turn reduces the manufacturing yield. Therefore, the width is preferably 0.3 μm or more and 5 μm or less.

[0063] The width W of the mesa-shaped portion 210 between adjacent trenches 25 of the n-type semiconductor layer 21 m The more the width W of the mesa-shaped portion 210 is reduced, the more the maximum electric field strength in the region immediately below the anode electrode 23 in the n-type semiconductor layer 21 is reduced. m 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, the width W m It is preferable that the thickness is 0.25 μm or more.

[0064] The anode electrode 23 is made of a material that makes Schottky contact with the n-type semiconductor layer 21 at a portion thereof that is in contact with the n-type semiconductor layer 21. That is, when the anode electrode 23 has a single-layer structure, the entire anode electrode 23 is made of a material that makes Schottky contact with the n-type semiconductor layer 21, and when the anode electrode 23 has a multi-layer structure, at least the layer that is in contact with the n-type semiconductor layer 21 is made of a material that makes Schottky contact with the n-type semiconductor layer 21.

[0065] In order to reduce the turn-on voltage of the Schottky diode 2, the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is preferably made of Fe (iron), Cu (copper), Mo (molybdenum), or W (tungsten).

[0066] When the portion of the anode electrode 23 in contact with the n-type semiconductor layer 21 is made of Mo or W, the turn-on 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 turn-on 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 turn-on voltage of the Schottky diode 2 is 0.6 V or more and 0.9 V or less.

[0067] In the Schottky diode 2, a potential barrier is formed in the mesa-shaped portion 210, so the turn-on voltage is increased by the width W of the mesa-shaped portion 210. m Depends on the width W m The smaller is the larger.

[0068] As described above, the electric field strength in the Schottky diode 2 is determined by the width W of the mesa-shaped portion 210 between two adjacent trenches 25. m , but is affected by the depth D of the trench 25, etc., but is hardly affected by the planar pattern of the trench 25 (planar pattern of the p-type semiconductor member 22). For this reason, the planar pattern of the trench 25 in the n-type semiconductor layer 21 (planar pattern of the p-type semiconductor member 22) is not particularly limited.

[0069] 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 multi-layer structure in which different metal films are stacked, for example, Ti / Au or Ti / Al. In order to ensure that the cathode electrode 24 and the n-type semiconductor substrate 20 are in ohmic contact with each other, it is preferable that the layer of the cathode electrode 24 in contact with the n-type semiconductor substrate 20 is made of Ti. Note that when the Schottky diode 2 does not include the n-type semiconductor substrate 20, the cathode electrode 24 is connected to the side of the n-type semiconductor layer 21 opposite to the anode electrode 23 and is in ohmic contact with the n-type semiconductor layer 21.

[0070] The p-type semiconductor member 22 is a member used for surge protection, similar to the p-type semiconductor member 17 according to the first embodiment, and is made of p-type BN or Al. x Ga 1-x The p-type semiconductor member 22 made of BN contains additives such as Zn, Mg, Be, and Si as acceptors. x Ga 1-x The p-type semiconductor member 22 made of N(x>0) contains an additive such as an acceptor. In addition, the p-type semiconductor member 22 contains a group III atomic vacancy (a vacancy due to a B vacancy in the case of BN, an Al vacancy due to a B vacancy in the case of AlN) instead of the above impurities. x Ga 1-x In the case of N(x>0), vacancies due to Al or Ga deficiencies may be present as acceptors.

[0071] The energy of the upper end of the valence band of the p-type semiconductor material 22 is equal to or less than the energy of the upper end of the valence band of the Ga2O3-based semiconductor constituting the n-type semiconductor layer 21 plus 2 eV. Therefore, by using the p-type semiconductor material 22, the resistance of the drift layer can be reduced when a surge current (also called an inrush current or starting current) occurs that may occur when the Schottky diode 2 is turned on, and heat generation and damage can be suppressed.

[0072] Normally, a pn diode has a higher on-voltage than a Schottky diode. For this reason, it is possible to design the pn diode portion, which is made up of the p-type semiconductor member 22 and the n-type semiconductor layer 21, so that it does not turn on at the voltage that turns on the Schottky diode 2. 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.

[0073] As a result, the pn diode portion does not turn on during normal operation of the Schottky diode 2, enabling the high-speed operation inherent to a Schottky diode. On the other hand, when an inrush current occurs, the voltage of the Schottky diode 2 rises and reaches a voltage at which the pn diode portion turns on, and holes are injected from the p-type semiconductor member 22 to the n-type semiconductor layer 21.

[0074] 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 greatly reduced. Therefore, although a large current called an inrush current flows through the Schottky diode 2, the increase in voltage is suppressed, and therefore the increase in temperature is suppressed, and damage to the Schottky diode 2 due to the inrush current can be prevented.

[0075] Furthermore, when the energy of the upper end of the valence band of the p-type semiconductor member 22 is equal to or lower than the energy of the upper end of the valence band of the Ga2O3-based single crystal constituting the n-type semiconductor layer 21, holes can easily move from the p-type semiconductor member 22 to the n-type semiconductor layer 21, thereby making it possible to further improve resistance to inrush current.

[0076] The material of the p-type semiconductor member 22 is BN, Al x Ga 1-x The energy of the top of the valence band of N(x>0) is equal to or less than 2 eV added to the energy of the top of the valence band of the Ga2O3-based single crystal that is the material of the n-type semiconductor layer 21. As can be seen from FIG. x Ga 1-x This holds true regardless of the values ​​of the Al concentration in N(x>0) and the Al and In concentrations in the Ga2O3-based single crystal.

[0077] The material of the p-type semiconductor member 22 is Al x Ga 1-x As the Al concentration x approaches 1, the energy of the upper end of the valence band N(x>0) becomes lower, approaching the energy of the upper end of the valence band of the Ga2O3-based single crystal that is the material of the n-type semiconductor layer 21, or becoming smaller than the energy of the upper end of the valence band of the Ga2O3-based single crystal that is the material of the n-type semiconductor layer 21. For this reason, for example, when the p-type semiconductor member 22 is Al x Ga 1-x It is preferable that the number of x is N(x≧0.8).

[0078] In addition, since the energy of the upper end of the valence band of BN is approximately equal to the energy of the upper end of the valence band of a Ga2O3-based single crystal that is the material of the n-type semiconductor layer 21, by using BN as the material of the p-type semiconductor member 22, it is possible to particularly improve the resistance of the Schottky diode 2 to inrush current.

[0079] (Manufacturing method of Schottky diode) An example of a method for manufacturing the Schottky diode 2 will be described below.

[0080] First, a Ga2O3-based single crystal containing Si as a donor is epitaxially grown on an n-type semiconductor substrate 20 by the VPE method to a thickness of about 5 mm and a Si concentration of 6×10 15 cm -3 The n-type semiconductor layer 21 having a thickness of about 100 nm is formed.

[0081] Next, a trench 25 is formed in a surface 26 of the n-type semiconductor layer 21 opposite to the n-type semiconductor substrate 20 by photolithography and dry etching.

[0082] Next, a cathode electrode 24 having a Ti / Au laminated structure or the like is formed by electron beam evaporation on the bottom surface of the n-type semiconductor substrate 20. Thereafter, a heat treatment is performed to reduce the contact resistance between the cathode electrode 24 and the n-type semiconductor substrate 20.

[0083] Next, Ar + A BN film doped with Zn is deposited on the entire surface of the surface 26 of the n-type semiconductor layer 21 by ion-assisted PVD to a thickness sufficient to fill the trenches 25.

[0084] The BN film may be formed by other methods such as sputtering, MBE, or CVD. Also, Mg, Be, or the like other than Zn may be added to the BN film as an acceptor. For example, by using a laser-assisted plasma CVD method as a method for forming the BN film, Si can be used as an acceptor. Also, these acceptors may be added by ion implantation after the BN film is formed.

[0085] 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.

[0086] Next, by electron beam evaporation, the anode electrode 23 having a Mo / Au laminated structure is formed on the surface 26 of the n-type semiconductor layer 21. The anode electrode 23 is patterned into a predetermined shape such as a circle by lift-off.

[0087] (Effects of the embodiment) According to the above-described embodiment, it is possible to provide a Ga2O3-based Schottky diode that has high breakdown voltage, low loss, and excellent resistance to surge current.

[0088] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention. Furthermore, the above-described embodiment does not limit the invention according to the claims. Furthermore, it should be noted that not all of the combinations of features described in the embodiment are essential to the means for solving the problems of the invention. [Explanation of symbols]

[0089] 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 insulating film, 16... anode electrode, 17, 22... p-type semiconductor member

Claims

1. G ２ O ３ an n-type semiconductor layer made of a silicon-based single crystal and having a plurality of trenches opening on one surface thereof; an anode electrode connected to a mesa-shaped region between adjacent trenches of the n-type semiconductor layer; a trench anode electrode that is embedded in each of the trenches while being covered with an insulating film and is electrically connected to the anode electrode; a cathode electrode connected directly or indirectly to the n-type semiconductor layer on the opposite side to the anode electrode; A BN or Al layer is connected to a portion of the mesa-shaped region and to the anode electrode. ｘ G １－ｘ N (x>0) p-type semiconductor member; A Schottky diode having

2. G ２ O ３ an n-type semiconductor layer made of a silicon-based single crystal and having a plurality of trenches opening on one surface thereof; BN or Al embedded in the trench. ｘ G １－ｘ N (x>0) p-type semiconductor member; an anode electrode connected to a mesa-shaped region between adjacent trenches of the n-type semiconductor layer and to the p-type semiconductor member; a cathode electrode connected directly or indirectly to the n-type semiconductor layer on the opposite side to the anode electrode; A Schottky diode having

3. The p-type semiconductor member is Al ｘ G １－ｘ N (x≧0.8), 3. The Schottky diode according to claim 1 or 2.

4. The upper end energy of the valence band of the p-type semiconductor member is ２ O ３ The energy is equal to or lower than the upper end of the valence band of the single crystal of the The Schottky diode according to any one of claims 1 to 3.

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