Junction Barrier Schottky Diode

Abstract

To reduce on-resistance while ensuring a sufficient reverse breakdown voltage, in a junction barrier Schottky diode using a gallium oxide.SOLUTION: A junction barrier Schottky diode 1 includes: a semiconductor substrate 20 comprising a gallium oxide; a drift layer 30 comprising a gallium oxide, the drift layer being provided on the semiconductor substrate 20; an anode electrode 40 coming in Schottky contact with the drift layer 30; and a cathode electrode 50 coming in Ohmic contact with the semiconductor substrate 20. The drift layer 30 includes center trenches 61 in which the anode electrode 40 and a semiconductor material 80 of a conductivity type opposite to that of the drift layer 30 are embedded. The bottom surfaces 32 of the center trenches 61 is in contact with the semiconductor material 80 without being in contact with the anode electrode 40, and at least part of side surfaces 33 of the central trenches 61 is in Schottky contact with the anode electrode 40. Thus, on-resistance can be reduced without increasing the concentration of impurities in the drift layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a junction barrier Schottky diode, and more particularly to a junction barrier Schottky diode using gallium oxide. [Background technology]

[0002] A Schottky barrier diode is a rectifying element that utilizes the Schottky barrier created by the junction between a metal and a semiconductor, and is characterized by a lower forward voltage and a faster switching speed than a normal diode with a PN junction. For this reason, Schottky barrier diodes are sometimes used as switching elements in power devices.

[0003] When a Schottky barrier diode is used as a switching element for a power device, it is necessary to ensure sufficient reverse breakdown voltage, and therefore, instead of silicon (Si), silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), or the like, which have a larger band gap, may be used. Among these, gallium oxide has a very large band gap of 4.8 to 4.9 eV and a large dielectric breakdown field of approximately 8 MV / cm, making Schottky barrier diodes using gallium oxide very promising as switching elements for power devices. An example of a Schottky barrier diode using gallium oxide is described in Patent Document 1.

[0004] Patent Document 1 discloses a junction barrier Schottky diode having a structure in which multiple trenches formed in a gallium oxide layer are filled with a p-type semiconductor material. By forming multiple trenches in the gallium oxide layer and filling the multiple trenches with a p-type semiconductor material in this way, when a reverse voltage is applied, the mesa region located between the trenches becomes a depletion layer, thereby pinching off the channel region of the drift layer. This significantly reduces leakage current when a reverse voltage is applied. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-036593 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the junction barrier Schottky diode described in Patent Document 1 has a problem of high on-resistance due to the small area of ​​Schottky contact between the anode electrode and the drift layer. To lower the on-resistance, the impurity concentration in the drift layer can be increased, but this reduces the reverse breakdown voltage.

[0007] Therefore, an object of the present invention is to reduce the on-resistance while ensuring a sufficient reverse breakdown voltage in a junction barrier Schottky diode using gallium oxide. [Means for solving the problem]

[0008] A junction barrier Schottky diode according to the present invention comprises a semiconductor substrate made of gallium oxide, a drift layer made of gallium oxide provided on the semiconductor substrate, an anode electrode in Schottky contact with the drift layer, and a cathode electrode in ohmic contact with the semiconductor substrate, wherein the drift layer has a central trench filled with a semiconductor material having an opposite conductivity type to that of the anode electrode and the drift layer, the bottom surface of the central trench being in contact with the semiconductor material without being in contact with the anode electrode, and at least a portion of the side surface of the central trench being in Schottky contact with the anode electrode.

[0009] According to the present invention, the anode electrode embedded in the central trench makes Schottky contact with the side surface of the central trench, so that it is possible to reduce the on-resistance without increasing the impurity concentration in the drift layer.

[0010] In the present invention, the anode electrode may include a first anode electrode in Schottky contact with the top surface of the drift layer and a second anode electrode in Schottky contact with the side surface of the central trench and made of a metal material different from that of the first anode electrode, which makes it easier to fabricate a void-free anode electrode.

[0011] In the present invention, the drift layer may further include an outer trench surrounding the central trench, and the bottom and outer side surfaces of the outer trench may be in contact with the semiconductor material without contacting the anode electrode. This reduces the electric field generated at the outer bottom of the outer trench when a reverse voltage is applied. In this case, at least a portion of the inner side surface of the outer trench may be in Schottky contact with the anode electrode. This increases the area of ​​Schottky contact, thereby further reducing the on-resistance.

[0012] In the present invention, the drift layer may further include an outer trench in which an anode electrode is embedded and which surrounds the central trench, and the inner wall of the outer trench may be covered with an insulating film without contacting the anode electrode, thereby mitigating the electric field generated at the outer bottom of the outer trench when a reverse voltage is applied. [Effects of the Invention]

[0013] As described above, according to the present invention, the side surface of the central trench makes Schottky contact with the anode electrode, so that it is possible to reduce the on-resistance of the junction barrier Schottky diode using gallium oxide. [Brief explanation of the drawings]

[0014] [Figure 1] Fig. 1(a) is a schematic plan view showing the configuration of a junction barrier Schottky diode 1 according to a first embodiment of the present invention, and Fig. 1(b) is a schematic cross-sectional view taken along line AA shown in Fig. 1(a). [Figure 2]2(a) to 2(c) are schematic cross-sectional views illustrating the positions of the inner walls of the central trench 61 and the outer peripheral trench 62 that are covered with a p-type semiconductor material 80. FIG. [Figure 3] FIG. 3 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 2 according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 3 according to a third embodiment of the present invention. [Figure 5] FIG. 5 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 4 according to a fourth embodiment of the present invention. [Figure 6] FIG. 6 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 5 according to a fifth embodiment of the present invention. [Figure 7] FIG. 7 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 6 according to a sixth embodiment of the present invention. [Figure 8] Fig. 8(a) is a schematic plan view showing the configuration of a junction barrier Schottky diode 7 according to a seventh embodiment of the present invention, and Fig. 8(b) is a schematic cross-sectional view taken along line AA shown in Fig. 8(a). [Figure 9] FIG. 9 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 8 according to an eighth embodiment of the present invention. [Figure 10] FIG. 10 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 9 according to a ninth embodiment of the present invention. [Figure 11] FIG. 11 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 10 according to a tenth embodiment of the present invention. [Figure 12] FIG. 12 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 11 according to an eleventh embodiment of the present invention. [Figure 13]Fig. 13(a) is a schematic plan view showing the configuration of a junction barrier Schottky diode 12 according to a twelfth embodiment of the present invention, and Fig. 13(b) is a schematic cross-sectional view taken along line AA shown in Fig. 13(a). [Figure 14] Fig. 14(a) is a schematic plan view showing the configuration of a junction barrier Schottky diode 13 according to a thirteenth embodiment of the present invention, and Fig. 14(b) is a schematic cross-sectional view taken along line AA shown in Fig. 14(a). [Figure 15] Fig. 15(a) is a schematic plan view showing the configuration of a junction barrier Schottky diode 14 according to a fourteenth embodiment of the present invention, and Fig. 15(b) is a schematic cross-sectional view taken along line AA shown in Fig. 15(a). [Figure 16] FIG. 16 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 15 according to a fifteenth embodiment of the present invention. [Figure 17] FIG. 17 is a graph showing the simulation results of the example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0016] First Embodiment Fig. 1(a) is a schematic plan view showing the configuration of a junction barrier Schottky diode 1 according to a first embodiment of the present invention, and Fig. 1(b) is a schematic cross-sectional view taken along line AA shown in Fig. 1(a).

[0017] As shown in Fig. 1, the junction barrier Schottky diode 1 according to the first embodiment includes a semiconductor substrate 20 and a drift layer 30, both of which are made of gallium oxide (β-Ga2O3). Silicon (Si) or tin (Sn) is introduced into the semiconductor substrate 20 and the drift layer 30 as an n-type dopant. The dopant concentration is higher in the semiconductor substrate 20 than in the drift layer 30, so that the semiconductor substrate 20 is an n-type+ layer, drift layer 30 is n - It acts as a layer.

[0018] The semiconductor substrate 20 is cut from a bulk crystal formed by a melt growth method or the like, and has a thickness of about 250 μm. The planar size of the semiconductor substrate 20 is not particularly limited, but is generally selected depending on the amount of current to be passed through the element. If the maximum forward current is about 20 A, the size should be about 2.4 mm × 2.4 mm in plan view.

[0019] The semiconductor substrate 20 has an upper surface 21 that is located on the upper surface side when mounted, and a back surface 22 that is opposite the upper surface 21 and is located on the lower surface side when mounted. A drift layer 30 is formed on the entire upper surface 21. The drift layer 30 is a thin film formed by epitaxially growing gallium oxide on the upper surface 21 of the semiconductor substrate 20 using a method such as reactive sputtering, PLD, MBE, MOCVD, or HVPE. The film thickness of the drift layer 30 is not particularly limited, but is generally selected depending on the reverse withstand voltage of the device. To ensure a withstand voltage of about 600 V, the thickness may be, for example, about 7 μm.

[0020] An anode electrode 40 is formed on the upper surface 31 of the drift layer 30, making Schottky contact with the drift layer 30. The anode electrode 40 is made of a metal such as platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), molybdenum (Mo), or copper (Cu). The anode electrode 40 may have a multilayer structure in which different metal films are stacked, such as Pt / Au, Pt / Al, Pd / Au, Pd / Al, Pt / Ti / Au, or Pd / Ti / Au. Meanwhile, a cathode electrode 50 is provided on the rear surface 22 of the semiconductor substrate 20, making ohmic contact with the semiconductor substrate 20. The cathode electrode 50 is made of a metal such as titanium (Ti). The cathode electrode 50 may have a multilayer structure in which different metal films are stacked, such as Ti / Au or Ti / Al.

[0021] In this embodiment, a central trench 61 and a peripheral trench 62 are provided in the drift layer 30. Both the central trench 61 and the peripheral trench 62 are provided at positions overlapping the anode electrode 40 in a plan view, and are filled with the same metal material as the anode electrode 40 and a p-type semiconductor material 80. The p-type semiconductor material 80 is in contact with the anode electrode 40. Examples of the p-type semiconductor material 80 include Si, GaAs, GaN, SiC, Ge, ZnSe, CdS, InP, SiGe, AlN, BN, AlGaN, NiO, CuO, IrO, and AgO. Among these, p-type oxides such as NiO are preferred because they are free from oxidation problems. The central trench 61 is sandwiched between mesa regions M, which are part of the drift layer 30. The peripheral trench 62 surrounds the mesa region M and the central trench 61 in a ring shape. The central trench 61 and the peripheral trench 62 do not need to be completely separated, and as shown in FIG. 1( a), the central trench 61 and the peripheral trench 62 may be connected. The central trench 61 and the peripheral trench 62 may have the same depth or different depths. The mesa region M is a part of the drift layer 30 defined by the central trench 61 and the peripheral trench 62, and becomes a depletion layer when a reverse voltage is applied between the anode electrode 40 and the cathode electrode 50. This pinches off the channel region of the drift layer 30, significantly suppressing leakage current when a reverse voltage is applied.

[0022] A p-type semiconductor material 80 is buried in the bottoms of the central trench 61 and the peripheral trench 62, and an anode electrode 40 is buried in the upper parts of the central trench 61 and the peripheral trench 62. Therefore, the bottom surface 32 and the lower parts of the side surfaces 33 of the inner walls of the central trench 61 and the peripheral trench 62 are in contact with the p-type semiconductor material 80, and the upper parts of the side surfaces 33 of the inner walls of the central trench 61 and the peripheral trench 62 are in contact with the anode electrode 40. As a result, the drift layer 30 and the anode electrode 40 are in Schottky contact not only at the upper surface 31 of the drift layer 30 but also at the upper parts of the side surfaces 33 of the central trench 61 and the peripheral trench 62. This reduces the on-resistance compared to when the central trench 61 and the peripheral trench 62 are entirely buried with the p-type semiconductor material 80. In addition, the dopant concentration of the drift layer 30 is 3×10 16 cm -3 Since the amount of reverse breakdown voltage can be kept to a minimum, a decrease in reverse breakdown voltage is also prevented.

[0023] 2(a), if the bottom surfaces 32 of the central trench 61 and the peripheral trench 62 are horizontal and the portions between the horizontal bottom surfaces 32 and the vertical side surfaces 33 are curved surfaces 34, the bottom surfaces 32 and the curved surfaces 34 must be covered with a p-type semiconductor material 80. Also, if the bottom surfaces 32 of the central trench 61 and the peripheral trench 62 are curved as a whole, as shown in FIG. 2(b), the entire curved bottom surfaces 32 must be covered with a p-type semiconductor material 80. Furthermore, if the bottom surfaces 32 of the central trench 61 and the peripheral trench 62 are horizontal and there are right-angled corners 35 between the horizontal bottom surfaces 32 and the vertical side surfaces 33, as shown in FIG. 2(c), the bottom surfaces 32 and the corners 35 must be covered with a p-type semiconductor material 80.

[0024] In this way, in the junction barrier Schottky diode 1 according to this embodiment, the anode electrode 40 makes Schottky contact with the upper portions of the side surfaces 33 of the central trench 61 and the peripheral trench 62, and therefore, it is possible to reduce the on-resistance compared to when the central trench 61 and the peripheral trench 62 are all filled with the p-type semiconductor material 80.

[0025] <Second embodiment> FIG. 3 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 2 according to a second embodiment of the present invention.

[0026] As shown in FIG. 3 , the junction barrier Schottky diode 2 according to the second embodiment differs from the junction barrier Schottky diode 1 according to the first embodiment in that the p-type semiconductor material 80 covering the bottom surface 32 and the lower part of the side surface 33 of the inner walls of the central trench 61 and the peripheral trench 62 is thin, thereby allowing the anode electrode 40 to be embedded in the bottom portions of the central trench 61 and the peripheral trench 62 as well. Since the other basic configurations are the same as those of the junction barrier Schottky diode 1 according to the first embodiment, the same elements are denoted by the same reference numerals, and redundant description will be omitted. As illustrated in this embodiment, the p-type semiconductor material 80 does not need to embed the entire bottom portions of the central trench 61 and the peripheral trench 62, and may instead only cover their surfaces.

[0027] <Third embodiment> FIG. 4 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 3 according to a third embodiment of the present invention.

[0028] 4, the junction barrier Schottky diode 3 according to the third embodiment differs from the junction barrier Schottky diode 1 according to the first embodiment in that the width of the peripheral trench 62 is wider than the width of the central trench 61. Since the other basic configurations are the same as those of the junction barrier Schottky diode 1 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted. Increasing the width of the peripheral trench 62 in this way makes it possible to reduce the electric field that concentrates near the bottom of the peripheral trench 62 when a reverse voltage is applied.

[0029] <Fourth embodiment> FIG. 5 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 4 according to a fourth embodiment of the present invention.

[0030] 5, the junction barrier Schottky diode 4 according to the fourth embodiment differs from the junction barrier Schottky diode 1 according to the first embodiment in that the drift layer 30 located outside the peripheral trench 62 is removed. Other basic configurations are the same as those of the junction barrier Schottky diode 1 according to the first embodiment, and therefore the same elements are denoted by the same reference numerals and redundant explanations will be omitted. Because almost no on-current flows through the portion of the drift layer 30 located outside the peripheral trench 62, the drift layer 30 located in this portion may be removed, as exemplified in this embodiment.

[0031] <Fifth embodiment> FIG. 6 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 5 according to a fifth embodiment of the present invention.

[0032] As shown in FIG. 6 , the junction barrier Schottky diode 6 according to the fifth embodiment differs from the junction barrier Schottky diode 1 according to the first embodiment in that an insulating film 71 is provided between the anode electrode 40 and the upper surface 31 of the drift layer 30 located outside the peripheral trench 62. Since the other basic configurations are the same as those of the junction barrier Schottky diode 1 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted. The insulating film 71 is preferably made of a material with a high dielectric strength, such as SiO2 or Al2O3. This enhances the withstand voltage effect. According to this embodiment, the insulating film 71 provides a so-called field plate structure, which further reduces the electric field applied to the bottom of the peripheral trench 62.

[0033] Sixth Embodiment FIG. 7 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 6 according to a sixth embodiment of the present invention.

[0034] As shown in FIG. 7 , the junction barrier Schottky diode 6 according to the sixth embodiment differs from the junction barrier Schottky diode 1 according to the first embodiment in that the anode electrode 41 covering the top surface of the drift layer 30 and the anode electrode 42 embedded in the central trench 61 and the peripheral trench 62 are made of different metal materials. Since the other basic configurations are the same as those of the junction barrier Schottky diode 1 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant description will be omitted. This structure can be obtained, for example, by forming the anode electrode 42 by electroplating and the anode electrode 41 by vapor deposition. This manufacturing method reduces the likelihood of voids occurring in the anode electrode 42 embedded in the central trench 61 and the peripheral trench 62.

[0035] Seventh Embodiment Fig. 8(a) is a schematic plan view showing the configuration of a junction barrier Schottky diode 7 according to a seventh embodiment of the present invention, and Fig. 8(b) is a schematic cross-sectional view taken along line AA shown in Fig. 8(a).

[0036] As shown in FIG. 8, the junction barrier Schottky diode 7 according to the seventh embodiment differs from the junction barrier Schottky diode 1 according to the first embodiment in that the entire peripheral trench 62 is filled with a p-type semiconductor material 80. Other basic configurations are the same as those of the junction barrier Schottky diode 1 according to the first embodiment, so the same elements are denoted by the same reference numerals and redundant explanations will be omitted. In FIG. 8(a), the surface of the mesa region M that makes Schottky contact with the drift layer 30 is indicated by a dashed line, and the surface of the mesa region M that is covered with the p-type semiconductor material 80 is indicated by a solid line. This makes it possible to further increase the reverse breakdown voltage.

[0037] Eighth Embodiment FIG. 9 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 8 according to an eighth embodiment of the present invention.

[0038] 9 , the junction barrier Schottky diode 8 according to the eighth embodiment differs from the junction barrier Schottky diode 7 according to the seventh embodiment in that the height position of the p-type semiconductor material 80 embedded in the peripheral trench 62 is lower than that of the junction barrier Schottky diode 7 according to the seventh embodiment, thereby making Schottky contact with a portion of the side surface 33 of the peripheral trench 62 and the anode electrode 40. Since the other basic configurations are the same as those of the junction barrier Schottky diode 7 according to the seventh embodiment, the same elements are denoted by the same reference numerals and redundant description will be omitted. According to this embodiment, it is possible to increase the reverse breakdown voltage while lowering the on-resistance compared to the junction barrier Schottky diode 7 according to the seventh embodiment.

[0039] <Ninth embodiment> FIG. 10 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 9 according to a ninth embodiment of the present invention.

[0040] As shown in FIG. 10 , the junction barrier Schottky diode 9 according to the ninth embodiment differs from the junction barrier Schottky diode 7 according to the seventh embodiment in that the portion of the side surface 33 of the peripheral trench 62 that contacts the inner side surface 33 a is replaced with an anode electrode 40 instead of the p-type semiconductor material 80. Of the side surfaces 33 of the peripheral trench 62, the outer side surface 33 b is entirely covered with the p-type semiconductor material 80. Since the other basic configuration is the same as that of the junction barrier Schottky diode 7 according to the seventh embodiment, the same elements are denoted by the same reference numerals and redundant description will be omitted. This embodiment also enables a higher reverse breakdown voltage and a lower on-resistance than the junction barrier Schottky diode 7 according to the seventh embodiment.

[0041] <Tenth embodiment> FIG. 11 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 10 according to a tenth embodiment of the present invention.

[0042] As shown in FIG. 11 , the junction barrier Schottky diode 10 according to the tenth embodiment differs from the junction barrier Schottky diode 7 according to the seventh embodiment in that the anode electrode 41 covering the top surface of the drift layer 30 and the anode electrode 42 embedded in the central trench 61 are made of different metal materials. Since the other basic configurations are the same as those of the junction barrier Schottky diode 7 according to the seventh embodiment, the same reference numerals are used for the same elements, and redundant explanations will be omitted. This structure can be obtained, for example, by forming the anode electrode 42 by electroplating and the anode electrode 41 by vapor deposition. This manufacturing method reduces the likelihood of voids occurring in the anode electrodes 42 embedded in the central trench 61 and the peripheral trench 62.

[0043] <Eleventh embodiment> FIG. 12 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 11 according to an eleventh embodiment of the present invention.

[0044] As shown in FIG. 12 , the junction barrier Schottky diode 11 according to the eleventh embodiment differs from the junction barrier Schottky diode 7 according to the seventh embodiment in that the inner wall of the peripheral trench 62 is covered with an insulating film 70, and the peripheral trench 62 is filled with an anode electrode 40 via the insulating film 70. Since the other basic configurations are the same as those of the junction barrier Schottky diode 7 according to the seventh embodiment, the same elements are denoted by the same reference numerals, and redundant explanations will be omitted. As with the seventh embodiment, this embodiment also enables a further increase in reverse breakdown voltage. It is desirable to use an insulating material with a high dielectric constant, such as HfO2 or Al2O3, as the material for the insulating film 70. This improves the breakdown voltage effect.

[0045] <Twelfth embodiment> Fig. 13(a) is a schematic plan view showing the configuration of a junction barrier Schottky diode 12 according to a twelfth embodiment of the present invention, and Fig. 13(b) is a schematic cross-sectional view taken along line AA shown in Fig. 13(a).

[0046] As shown in FIG. 13 , the junction barrier Schottky diode 12 according to the twelfth embodiment differs from the junction barrier Schottky diode 1 according to the first embodiment in that another periphery trench 63 surrounding the periphery trench 62 is provided in the drift layer 30, and the entire periphery trench 63 is filled with a p-type semiconductor material 80. The periphery trench 63 is provided independently of the periphery trench 62. Since the other basic configurations are the same as those of the junction barrier Schottky diode 1 according to the first embodiment, the same elements are denoted by the same reference numerals, and redundant description will be omitted. In FIG. 13( a), the surface of the surface of the mesa region M that makes Schottky contact with the drift layer 30 is indicated by a dashed line, and the surface of the surface of the mesa region M that is covered with the p-type semiconductor material 80 is indicated by a solid line. In this way, by providing another peripheral trench 63 in the drift layer 30 and filling the entire interior thereof with p-type semiconductor material 80, it is possible to alleviate the electric field that concentrates near the bottoms of the central trench 61 and the peripheral trench 62 when a reverse voltage is applied.

[0047] <Thirteenth embodiment> Fig. 14(a) is a schematic plan view showing the configuration of a junction barrier Schottky diode 13 according to a thirteenth embodiment of the present invention, and Fig. 14(b) is a schematic cross-sectional view taken along line AA shown in Fig. 14(a).

[0048] 14 , the junction barrier Schottky diode 13 according to the thirteenth embodiment differs from the junction barrier Schottky diode 12 according to the twelfth embodiment in that the width of the peripheral trench 63 is wider than the widths of the central trench 61 and the peripheral trench 62. Since the other basic configurations are the same as those of the junction barrier Schottky diode 12 according to the twelfth embodiment, the same elements are denoted by the same reference numerals, and redundant explanations will be omitted. Increasing the width of the peripheral trench 63 in this way makes it possible to reduce the electric field that concentrates near the bottom of the peripheral trench 63 when a reverse voltage is applied.

[0049] <Fourteenth embodiment> Fig. 15(a) is a schematic plan view showing the configuration of a junction barrier Schottky diode 14 according to a fourteenth embodiment of the present invention, and Fig. 15(b) is a schematic cross-sectional view taken along line AA shown in Fig. 15(a).

[0050] 15 , the junction barrier Schottky diode 14 according to the fourteenth embodiment differs from the junction barrier Schottky diode 12 according to the twelfth embodiment in that the inner wall of the peripheral trench 63 is covered with an insulating film 70 made of HfO or the like, and the peripheral trench 63 is filled with an anode electrode 40 via the insulating film 70. Since the other basic configurations are the same as those of the junction barrier Schottky diode 12 according to the twelfth embodiment, the same elements are denoted by the same reference numerals, and redundant explanations will be omitted. As with the twelfth embodiment, this embodiment also enables an increase in reverse breakdown voltage.

[0051] <Fifteenth embodiment> FIG. 16 is a schematic cross-sectional view showing the configuration of a junction barrier Schottky diode 15 according to a fifteenth embodiment of the present invention.

[0052] As shown in FIG. 16 , the junction barrier Schottky diode 15 according to the fifteenth embodiment differs from the junction barrier Schottky diode 2 according to the second embodiment in that the anode electrode 41, which makes Schottky contact with the drift layer 30, is made of a Cu single layer film or a Cu / Al laminate film, and the anode electrode 42, which makes ohmic contact with the p-type semiconductor material 80, is made of Ni, for example. Since the other basic configurations are the same as those of the junction barrier Schottky diode 2 according to the second embodiment, the same elements are denoted by the same reference numerals, and redundant explanations will be omitted. In this way, if the anode electrode 42, which makes contact with the p-type semiconductor material 80, is made of a material different from that of the anode electrode 41, which makes contact with the drift layer 30, ohmic contact between the p-type semiconductor material 80 and the anode electrode 42 can be achieved, thereby reducing contact resistance. For example, if the p-type semiconductor material 80 is NiO, using Ni for the anode electrode 42 can achieve ohmic contact between them. Furthermore, when the p-type semiconductor material 80 is made of a material with a wider band gap than NiO, it is preferable to use a metal such as Pt, which has a larger work function than Ni, as the anode electrode 42.

[0053] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention. [Example]

[0054] Example 1 A simulation model of an example having the same structure as the junction barrier Schottky diode 1 shown in FIG. 1 was assumed, and the resistance value when a forward voltage was applied between the anode electrode 40 and the cathode electrode 50 was simulated. The dopant concentration of the semiconductor substrate 20 was 1×10 18 cm -3 The dopant concentration of the drift layer 30 is 3×10 16 cm -3The thickness of the drift layer 30 was 7 μm. The depths of the central trench 61 and the peripheral trench 62 were both 3 μm. The widths of the central trench 61 and the peripheral trench 62 in the cross section shown in FIG. 1(b) and the width of the upper surface 31 of the drift layer 30 (the width of the mesa region M) were both 1.5 μm. The radius of curvature of the curved surface 34 located between the flat bottom surface 32 and the side surface 33 of the central trench 61 and the peripheral trench 62 was 0.2 μm. NiO was used as the p-type semiconductor material 80. The material of the anode electrode 40 was Ni, and the material of the cathode electrode 50 was a stacked film of Ti and Au. Simulations were performed using the depth T of the anode electrode 40 in contact with the side surface 33 of the central trench 61 and the peripheral trench 62 as a variable.

[0055] The results are shown in Figure 17. As shown in Figure 17, it was found that the on-resistance decreased as the depth T of the anode electrode 40 in contact with the side surfaces 33 of the central trench 61 and the peripheral trench 62 increased. Furthermore, the reverse breakdown voltage was 7.8 MV / cm regardless of the depth T. [Explanation of symbols]

[0056] 1~15 Junction Barrier Schottky Diodes 20 Semiconductor substrate 21 Upper surface of semiconductor substrate 22 Backside of semiconductor substrate 30 Drift Layer 31 Top surface of the drift layer 32 Bottom of the trench 33 Trench Side 33a Inner side of trench 33b Outer side of trench 34 Curved surface of trench 35 Trench corner 40~42 Anode electrode 50 cathode electrode 61 Central Trench 62,63 Periphery trench 70,71 Insulating film 80 Semiconductor Materials M Mesa region

Claims

1. a semiconductor substrate made of gallium oxide; a drift layer made of gallium oxide provided on the semiconductor substrate; an anode electrode in Schottky contact with the drift layer; a cathode electrode in ohmic contact with the semiconductor substrate; the drift layer has a central trench filled with a semiconductor material having an opposite conductivity type to that of the anode electrode and the drift layer, and an outer peripheral trench surrounding the central trench; a bottom surface of the central trench contacts the semiconductor material without contacting the anode electrode; At least a portion of a side surface of the central trench makes Schottky contact with the anode electrode; a bottom surface and a peripheral side surface of the peripheral trench are in contact with the semiconductor material without being in contact with the anode electrode; a junction barrier Schottky diode, wherein at least a portion of an inner peripheral side surface of the outer peripheral trench is in Schottky contact with the anode electrode;

2. 2. The junction barrier Schottky diode according to claim 1, wherein the anode electrode includes a first anode electrode in Schottky contact with the top surface of the drift layer, and a second anode electrode in Schottky contact with the side surface of the central trench and made of a metal material different from that of the first anode electrode.

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