Schottky barrier diode

Abstract

To reduce on-resistance while ensuring a sufficient reverse breakdown voltage, in a Schottky barrier diode using a gallium oxide.SOLUTION: A Schottky barrier 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 central trenches 61 in which the anode electrode 40 is embedded. The bottom surfaces of the central trenches 61 are covered with insulating films 70 without being in contact with the anode electrode 40, and at least part of side surfaces of the central trenches 61 is in Schottky contact with the anode electrode 40 without being covered by the insulating films 70. 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 Schottky barrier diode, and more particularly to a Schottky barrier diode using gallium oxide.

Background Art

[0002] A Schottky barrier diode is a rectifying element that utilizes a Schottky barrier generated by the junction of a metal and a semiconductor. It has the characteristics of a lower forward voltage and a faster switching speed compared to a normal diode having a PN junction. Therefore, a Schottky barrier diode may be used as a switching element for power devices.

[0003] When using a Schottky barrier diode as a switching element for power devices, since it is necessary to ensure a sufficient reverse breakdown voltage, instead of silicon (Si), silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), etc. with a larger bandgap may be used. Among them, gallium oxide has a very large bandgap of 4.8 - 4.9 eV and a large breakdown electric field of about 8 MV / cm. Therefore, a Schottky barrier diode using gallium oxide is very promising as a switching element for power devices. An example of a Schottky barrier diode using gallium oxide is described in Patent Document 1.

[0004] The Schottky barrier diode described in Patent Document 1 has a structure in which a plurality of trenches are provided in a gallium oxide layer, and a part of the anode electrode is embedded in the trenches via an insulating film. Thus, when a plurality of trenches are provided in the gallium oxide layer, when a reverse voltage is applied, the mesa region located between the trenches becomes a depletion layer, and the channel region of the drift layer is pinched off. Thereby, the leakage current when a reverse voltage is applied can be significantly suppressed.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-199869 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, a problem arose when trenches with inner walls covered by an insulating layer were provided in the drift layer, resulting in high on-resistance. To lower the on-resistance, the impurity concentration of the drift layer could be increased, but this would reduce the reverse breakdown voltage.

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

[0008] The Schottky barrier 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 that makes Schottky contact with the drift layer, and a cathode electrode that makes ohmic contact with the semiconductor substrate, wherein the drift layer has a central trench in which the anode electrode is embedded, the bottom surface of the central trench is covered with an insulating film without contacting the anode electrode, and at least a portion of the side surface of the central trench makes Schottky contact with the anode electrode.

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

[0010] In the present invention, the anode electrode may include a first anode electrode that makes Schottky contact with the upper surface of the drift layer, and a second anode electrode that makes Schottky contact with the side surface of the central trench and is made of a different metallic material than the first anode electrode. This makes it easier to fabricate an anode electrode without voids.

[0011] In the present invention, the drift layer further has an outer trench surrounding a central trench in which the anode electrode is embedded, and the bottom surface and outer surface of the outer trench may be covered with an insulating film 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 surface of the outer trench may be in Schottky contact with the anode electrode. This increases the area of ​​Schottky contact, making it possible to further reduce the on-resistance.

[0012] In the present invention, the drift layer further comprises an outer trench surrounding the central trench, and the outer trench may be filled with a semiconductor material having a conductivity opposite to that of the drift layer. This allows a depletion layer to spread around the outer trench when a reverse voltage is applied. As a result, the electric field generated at the outer bottom of the outer trench when a reverse voltage is applied is mitigated. [Effects of the Invention]

[0013] Thus, according to the present invention, since the side surface of the central trench makes Schottky contact with the anode electrode, it is possible to reduce the on-resistance of a Schottky barrier diode using gallium oxide. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1(a) is a schematic plan view showing the configuration of a Schottky barrier diode 1 according to the first embodiment of the present invention. Figure 1(b) is a substantially cross-sectional view along line AA shown in Figure 1(a). [Figure 2]Figs. 2(a) to 2(c) are schematic cross-sectional views for explaining positions covered with the insulating film 70 among the inner walls of the center trench 61 and the outer peripheral trench 62. [Figure 3] Fig. 3 is a schematic cross-sectional view showing the configuration of the Schottky barrier diode 2 according to the second embodiment of the present invention. [Figure 4] Fig. 4 is a schematic cross-sectional view showing the configuration of the Schottky barrier diode 3 according to the third embodiment of the present invention. [Figure 5] Fig. 5 is a schematic cross-sectional view showing the configuration of the Schottky barrier diode 4 according to the fourth embodiment of the present invention. [Figure 6] Fig. 6 is a schematic cross-sectional view showing the configuration of the Schottky barrier diode 5 according to the fifth embodiment of the present invention. [Figure 7] Fig. 7 is a schematic cross-sectional view showing the configuration of the Schottky barrier diode 6 according to the sixth embodiment of the present invention. [Figure 8] Fig. 8 is a schematic cross-sectional view showing the configuration of the Schottky barrier diode 7 according to the seventh embodiment of the present invention. [Figure 9] Fig. 9(a) is a schematic plan view showing the configuration of the Schottky barrier diode 8 according to the eighth embodiment of the present invention. Further, Fig. 9(b) is a schematic cross-sectional view taken along the line A-A shown in Fig. 9(a). [Figure 10] Fig. 10 is a schematic cross-sectional view showing the configuration of the Schottky barrier diode 9 according to the ninth embodiment of the present invention. [Figure 11] Fig. 11 is a schematic cross-sectional view showing the configuration of the Schottky barrier diode 10 according to the tenth embodiment of the present invention. [[ID=二十九]] [Figure 12] [[ID=三十]]Fig. 12 is a schematic cross-sectional view showing the configuration of the Schottky barrier diode 11 according to the eleventh embodiment of the present invention. [[ID=三十一]] [[ID=三十二]] [Figure 13] [[ID=三十三]]Fig. 13(a) is a schematic plan view showing the configuration of the Schottky barrier diode 12 according to the twelfth embodiment of the present invention. Further, Fig. 13(b) is a schematic cross-sectional view taken along the line A-A shown in Fig. 13(a). [[ID=三十四]] [[ID=三十五]] [Figure 14]FIG. 14(a) is a schematic plan view showing the configuration of the Schottky barrier diode 13 according to the 13th embodiment of the present invention. FIG. 14(b) is a schematic cross-sectional view taken along the line A-A shown in FIG. 14(a). [Figure 15] FIG. 15(a) is a schematic plan view showing the configuration of the Schottky barrier diode 14 according to the 14th embodiment of the present invention. FIG. 15(b) is a schematic cross-sectional view taken along the line A-A shown in FIG. 15(a). [Figure 16] FIG. 16(a) is a schematic plan view showing the configuration of the Schottky barrier diode 15 according to the 15th embodiment of the present invention. FIG. 16(b) is a schematic cross-sectional view taken along the line A-A shown in FIG. 16(a). [Figure 17] FIG. 17(a) is a schematic plan view showing the configuration of the Schottky barrier diode 16 according to the 16th embodiment of the present invention. FIG. 17(b) is a schematic cross-sectional view taken along the line A-A shown in FIG. 17(a). [Figure 18] FIG. 18 is a graph showing the simulation results of the examples.

Embodiments for Carrying Out the Invention

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

[0016] <The First Embodiment> FIG. 1(a) is a schematic plan view showing the configuration of the Schottky barrier diode 1 according to the first embodiment of the present invention. FIG. 1(b) is a schematic cross-sectional view taken along the line A-A shown in FIG. 1(a).

[0017] As shown in FIG. 1, the Schottky barrier diodes 1 according to the first embodiment all include a semiconductor substrate 20 and a drift layer 30 made of gallium oxide (β-Ga2O3). Silicon (Si) or tin (Sn) is introduced as an n-type dopant into the semiconductor substrate 20 and the drift layer 30. The concentration of the dopant is higher in the semiconductor substrate 20 than in the drift layer 30, whereby the semiconductor substrate 20 is n+ Layer, drift layer 30 is n - It functions as a layer.

[0018] The semiconductor substrate 20 is formed by cutting a bulk crystal created using a method such as melt growth, and its thickness is approximately 250 μm. The planar size of the semiconductor substrate 20 is not particularly limited, but is generally selected according to the amount of current flowing through the device. If the maximum forward current is approximately 20 A, then a planar size of approximately 2.4 mm × 2.4 mm is sufficient.

[0019] The semiconductor substrate 20 has an upper surface 21 that is located on the upper side during mounting, and a back surface 22 that is on the opposite side of the upper surface 21 and located on the lower side during mounting. A drift layer 30 is formed on the entire surface of the upper surface 21. The drift layer 30 is a thin film of gallium oxide epitaxially grown on the upper surface 21 of the semiconductor substrate 20 using reactive sputtering, PLD method, MBE method, MOCVD method, HVPE method, etc. The thickness of the drift layer 30 is not particularly limited, but is generally selected according to the reverse withstand voltage of the device, and for example, a thickness of about 7 μm is sufficient to ensure a withstand voltage of about 600 V.

[0020] An anode electrode 40 is formed on the upper surface 31 of the drift layer 30, which makes 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, for example, Pt / Au, Pt / Al, Pd / Au, Pd / Al, Pt / Ti / Au, or Pd / Ti / Au. On the other hand, a cathode electrode 50 is provided on the back surface 22 of the semiconductor substrate 20, which makes 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, for example, Ti / Au or Ti / Al.

[0021] In this embodiment, a central trench 61 and an outer trench 62 are provided in the drift layer 30. Both the central trench 61 and the outer trench 62 are located in positions that overlap with the anode electrode 40 in a plan view, and their interiors are filled with the same metallic material as the anode electrode 40. The central trench 61 is sandwiched between mesa regions M, which are part of the drift layer 30. The outer trench 62 surrounds the mesa region M and the central trench 61 in a ring shape. The central trench 61 and the outer trench 62 do not need to be completely separated; as shown in Figure 1(a), they may be connected. The depths of the central trench 61 and the outer trench 62 may be the same or different. The mesa region M is part of the drift layer 30 partitioned by the central trench 61 and the outer trench 62, and becomes a depletion layer when a reverse voltage is applied between the anode electrode 40 and the cathode electrode 50. As a result, the channel region of the drift layer 30 is pinched off, significantly suppressing leakage current when a reverse voltage is applied.

[0022] The bottom surface 32 of the inner walls of the central trench 61 and the outer trench 62 is covered with an insulating film 70. In contrast, the side surfaces 33 of the inner walls of the central trench 61 and the outer trench 62 are not covered with the insulating film 70. Therefore, the bottom surface 32 of the central trench 61 and the outer trench 62 does not come into contact with the anode electrode 40, while the side surfaces 33 of the central trench 61 and the outer trench 62, which are not covered with the insulating film 70, make Schottky contact with the anode electrode 40. As a result, the drift layer 30 and the anode electrode 40 make Schottky contact not only on the top surface 31 of the drift layer 30 but also on the side surfaces 33 of the central trench 61 and the outer trench 62, thus reducing the on-resistance compared to the case where the entire inner walls of the central trench 61 and the outer trench 62 are covered with the insulating film 70. Furthermore, the dopant concentration of the drift layer 30 is 3 × 10 16 cm -3 Because the effect can be kept to a certain extent, a decrease in reverse breakdown voltage is also prevented. For the insulating film 70, it is desirable to use an insulating material with a high dielectric constant, such as HfO2 or Al2O3. This enhances the breakdown voltage effect.

[0023] Here, as shown in Figure 2(a), if the bottom surfaces 32 of the central trench 61 and the outer trench 62 are horizontal, and the portion located between the horizontal bottom surface 32 and the vertical side surface 33 is a curved surface 34, then the bottom surface 32 and the curved surface 34 must be covered with the insulating film 70. Also, as shown in Figure 2(b), if the bottom surfaces 32 of the central trench 61 and the outer trench 62 are curved overall, then the entire curved bottom surface 32 must be covered with the insulating film 70. Furthermore, as shown in Figure 2(c), if the bottom surfaces 32 of the central trench 61 and the outer trench 62 are horizontal, and there is a right-angle corner 35 between the horizontal bottom surface 32 and the vertical side surface 33, then the bottom surface 32 and the corner 35 must be covered with the insulating film 70.

[0024] Thus, in the Schottky barrier diode 1 according to this embodiment, the anode electrode 40 makes Schottky contact at the side surfaces 33 of the central trench 61 and the outer trench 62, which makes it possible to reduce the on-resistance compared to the case where the entire surface of the central trench 61 and the outer trench 62 is covered with an insulating film 70.

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

[0026] As shown in Figure 3, the Schottky barrier diode 2 according to the second embodiment differs from the Schottky barrier diode 1 according to the first embodiment in that a portion of the side surface 33 of the central trench 61 and the outer trench 62, closer to the bottom surface 32, is covered with an insulating film 70. Since the other basic configurations are the same as those of the Schottky barrier diode 1 according to the first embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. In this embodiment, the depth T of the anode electrode 40 in contact with the side surface 33 of the central trench 61 and the outer trench 62 can be adjusted by changing the height position of the insulating film 70.

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

[0028] As shown in Figure 4, the Schottky barrier diode 3 according to the third embodiment differs from the Schottky barrier diode 2 according to the second embodiment in that the upper surface of the insulating film 70 is substantially flat and is embedded in the bottom of the central trench 61 and the outer trench 62. Since the other basic configurations are the same as those of the Schottky barrier diode 2 according to the second embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. Thus, when covering a portion of the side surface 33 of the central trench 61 and the outer trench 62 that is close to the bottom surface 32 with the insulating film 70, the entire bottom of the central trench 61 and the outer trench 62 may be embedded with the insulating film 70.

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

[0030] As shown in Figure 5, the Schottky barrier diode 4 according to the fourth embodiment differs from the Schottky barrier diode 1 according to the first embodiment in that the width of the outer trench 62 is wider than the width of the central trench 61. Since the other basic configurations are the same as those of the Schottky barrier diode 1 according to the first embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. By widening the outer trench 62 in this way, it is possible to mitigate the electric field concentrated near the bottom of the outer trench 62 when a reverse voltage is applied.

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

[0032] As shown in Figure 6, the Schottky barrier diode 5 according to the fifth embodiment differs from the Schottky barrier diode 1 according to the first embodiment in that the drift layer 30 located outside the outer trench 62 has been removed. Since the other basic configurations are the same as those of the Schottky barrier diode 1 according to the first embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. Since almost no on-current flows through the portion of the drift layer 30 located outside the outer trench 62, the drift layer 30 located in this portion may be removed, as illustrated in this embodiment.

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

[0034] As shown in Figure 7, the Schottky barrier diode 6 according to the sixth embodiment differs from the Schottky barrier diode 1 according to the first embodiment in that an insulating film 71 is provided between the upper surface 31 of the drift layer 30 located outside the outer peripheral trench 62 and the anode electrode 40. Since the other basic configurations are the same as those of the Schottky barrier diode 1 according to the first embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. According to this embodiment, a so-called field plate structure is obtained by the insulating film 71, which makes it possible to further mitigate the electric field applied to the bottom of the outer peripheral trench 62. It is desirable to use a material with high dielectric breakdown voltage, such as SiO2 or Al2O3, as the material for the insulating film 71. This enhances the breakdown voltage effect.

[0035] <Seventh Embodiment> Figure 8 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 7 according to the seventh embodiment of the present invention.

[0036] As shown in Figure 8, the Schottky barrier diode 7 according to the seventh embodiment differs from the Schottky barrier diode 1 according to the first embodiment in that the anode electrode 41 covering the upper surface of the drift layer 30 and the anode electrodes 42 embedded in the central trench 61 and the outer periphery trench 62 are made of different metal materials. Since the other basic configurations are the same as those of the Schottky barrier diode 1 according to the first embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. Such a structure can be obtained, for example, by forming the anode electrode 42 by electroplating and the anode electrode 41 by vapor deposition. With such a manufacturing method, voids are less likely to occur in the anode electrodes 42 embedded in the central trench 61 and the outer periphery trench 62.

[0037] <Eighth Embodiment> Figure 9(a) is a schematic plan view showing the configuration of a Schottky barrier diode 8 according to the eighth embodiment of the present invention. Figure 9(b) is a substantially cross-sectional view along line AA shown in Figure 9(a).

[0038] As shown in Figure 9, the Schottky barrier diode 8 according to the eighth embodiment differs from the Schottky barrier diode 1 according to the first embodiment in that the entire inner wall of the outer trench 62 is covered with an insulating film 70. Since the other basic configurations are the same as those of the Schottky barrier diode 1 according to the first embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. In Figure 9(a), the surface of the mesa region M that is in Schottky contact with the drift layer 30 is shown with a dashed line, and the surface of the mesa region M covered with the insulating film 70 is shown with a solid line. This makes it possible to further increase the reverse breakdown voltage.

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

[0040] As shown in Figure 10, the Schottky barrier diode 9 according to the ninth embodiment differs from the Schottky barrier diode 8 according to the eighth embodiment in that the height of the insulating film 70 covering the side surface 33 of the outer peripheral trench 62 is lower than that of the Schottky barrier diode 8 according to the eighth embodiment. As a result, a portion of the side surface 33 of the outer peripheral trench 62 makes Schottky contact with the anode electrode 40. The other basic configurations are the same as those of the Schottky barrier diode 8 according to the eighth embodiment, so the same reference numerals are used for the same elements, and redundant explanations are omitted. According to this embodiment, it is possible to increase the reverse breakdown voltage while lowering the on-resistance compared to the Schottky barrier diode 8 according to the eighth embodiment.

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

[0042] As shown in Figure 11, the Schottky barrier diode 10 according to the tenth embodiment differs from the Schottky barrier diode 8 according to the eighth embodiment in that the insulating film 70 on the inner side surface 33a of the outer trench 62 is removed. Of the side surfaces 33 of the outer trench 62, the entire outer side surface 33b is covered with the insulating film 70. Since the other basic configurations are the same as those of the Schottky barrier diode 8 according to the eighth embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. In this embodiment as well, it is possible to increase the reverse breakdown voltage while lowering the on-resistance compared to the Schottky barrier diode 8 according to the eighth embodiment.

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

[0044] As shown in Figure 12, the Schottky barrier diode 11 according to the 11th embodiment differs from the Schottky barrier diode 8 according to the 8th embodiment in that the anode electrode 41 covering the upper surface of the drift layer 30 and the anode electrodes 42 embedded in the central trench 61 and the outer periphery trench 62 are made of different metallic materials. Since the other basic configurations are the same as those of the Schottky barrier diode 8 according to the 8th embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. Such a structure can be obtained, for example, by forming the anode electrode 42 by electroplating and the anode electrode 41 by vapor deposition. With such a manufacturing method, voids are less likely to occur in the anode electrodes 42 embedded in the central trench 61 and the outer periphery trench 62.

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

[0046] As shown in Figure 13, the Schottky barrier diode 12 according to the twelfth embodiment differs from the Schottky barrier diode 2 according to the second embodiment in that another outer trench 63 surrounding the outer trench 62 is provided in the drift layer 30, and the entire inner wall of this outer trench 63 is covered with an insulating film 70. The outer trench 63 is provided independently of the outer trench 62. Since the other basic configurations are the same as those of the Schottky barrier diode 2 according to the second embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. In Figure 13(a), the surface of the mesa region M that is in Schottky contact with the drift layer 30 is shown with a dashed line, and the surface of the mesa region M covered with the insulating film 70 is shown with a solid line. By providing another outer trench 63 in the drift layer 30 in this way, and covering its entire inner wall with the insulating film 70, it is possible to mitigate the electric field concentrated near the bottom of the central trench 61 and the outer trench 62 when a reverse voltage is applied.

[0047] <13th Embodiment> Figure 14(a) is a schematic plan view showing the configuration of a Schottky barrier diode 13 according to the 13th embodiment of the present invention. Figure 14(b) is a substantially cross-sectional view along line AA shown in Figure 14(a).

[0048] As shown in Figure 14, the Schottky barrier diode 13 according to the 13th embodiment differs from the Schottky barrier diode 12 according to the 12th embodiment in that the width of the outer trench 63 is wider than the width of the central trench 61 and the outer trench 62. Since the other basic configurations are the same as those of the Schottky barrier diode 12 according to the 12th embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. By widening the outer trench 63 in this way, it is possible to mitigate the electric field concentrated near the bottom of the outer trench 63 when a reverse voltage is applied.

[0049] <Embodiment 14> Figure 15(a) is a schematic plan view showing the configuration of a Schottky barrier diode 14 according to the 14th embodiment of the present invention. Figure 15(b) is a substantially cross-sectional view along line AA shown in Figure 15(a).

[0050] As shown in Figure 15, the Schottky barrier diode 14 according to the 14th embodiment differs from the Schottky barrier diode 12 according to the 12th embodiment in that the outer periphery trench 63 is filled with a p-type semiconductor material 80. The p-type semiconductor material 80 is in contact with the anode electrode 40. Since the other basic configurations are the same as those of the Schottky barrier diode 12 according to the 12th embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. As the p-type semiconductor material 80, Si, GaAs, GaN, SiC, Ge, ZnSe, CdS, InP, SiGe, AlN, BN, AlGaN, NiO, Cu2O, Ir2O3, and Ag2O can be used, and among these, p-type oxides such as NiO are preferred because they do not have oxidation problems. In this way, if the outer periphery trench 63 is filled with a p-type semiconductor material 80, a depletion layer will spread around the outer periphery trench 63 when a reverse voltage is applied. This reduces the electric field generated at the bottom of the outer circumference trench 63 when a reverse voltage is applied.

[0051] <Embodiment 15> Figure 16(a) is a schematic plan view showing the configuration of a Schottky barrier diode 15 according to the 15th embodiment of the present invention. Figure 16(b) is a substantially cross-sectional view along line AA shown in Figure 16(a).

[0052] As shown in Figure 16, the Schottky barrier diode 15 according to the 15th embodiment differs from the Schottky barrier diode 1 according to the 13th embodiment in that the upper surface 31 of the drift layer 30 located outside the outer peripheral trench 63, the outer side surface 33b of the outer peripheral trench 63, and the outer bottom surface 32b of the outer peripheral trench 63 are covered with an insulating film 71. The inner bottom surface 32a of the outer peripheral trench 63 is covered with the anode electrode 40 via the insulating film 70. Also, the lower part of the inner side surface 33a of the outer peripheral trench 63, which is close to the bottom surface 32, is covered with the insulating film 70, and the upper part is in contact with the anode electrode 40. The other basic configurations are the same as those of the Schottky barrier diode 13 according to the 13th embodiment, so the same elements are denoted by the same reference numerals, and redundant explanations are omitted. The insulating film 70 and the insulating film 71 may be made of the same insulating material, or they may be made of different insulating materials. With this configuration, the on-resistance can be lowered compared to the Schottky barrier diode 13 in the 13th embodiment, and the reverse breakdown voltage can be increased.

[0053] <Embodiment 16> Figure 17(a) is a schematic plan view showing the configuration of a Schottky barrier diode 16 according to the 16th embodiment of the present invention. Figure 17(b) is a substantially cross-sectional view along line AA shown in Figure 17(a).

[0054] As shown in Figure 17, the Schottky barrier diode 16 according to the 16th embodiment differs from the Schottky barrier diode 15 according to the 15th embodiment in that the drift layer 30 located outside the outer trench 63 has been removed. Since the other basic configurations are the same as those of the Schottky barrier diode 15 according to the 15th embodiment, the same reference numerals are used for the same elements, and redundant explanations are omitted. Since almost no on-current flows through the portion of the drift layer 30 located outside the outer trench 63, the drift layer 30 located in this portion may be removed, as illustrated in this embodiment.

[0055] Although preferred embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the invention, and these modifications are also included within the scope of the present invention. [Examples]

[0056] <Example 1> Assuming a simulation model of an embodiment having the same structure as the Schottky barrier diode 2 shown in Figure 3, the resistance value when a forward voltage is applied between the anode electrode 40 and the cathode electrode 50 was simulated. The dopant concentration of the semiconductor substrate 20 was set to 1 × 10⁻¹⁶. 18 cm -3 Therefore, the dopant concentration in the drift layer 30 is 3 × 10⁻¹⁰ 16 cm -3 The thickness of the drift layer 30 was set to 7 μm. The depth of both the central trench 61 and the outer trench 62 was set to 3 μm. The widths of the central trench 61 and the outer trench 62 in the cross-section shown in Figure 3, as well as the width of the upper surface 31 of the drift layer 30 (width of the mesa region M), were all set to 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 outer trench 62 was set to 0.05 μm. The insulating film 70 was a 50 nm thick HfO2 film. The material of the anode electrode 40 was Ni, and the material of the cathode electrode 50 was a multilayer film of Ti and Au. The simulation was performed with the depth T of the anode electrode 40 in contact with the side surface 33 of the central trench 61 and the outer trench 62 as the variable.

[0057] The results are shown in Figure 18. As shown in Figure 18, it was found that the on-resistance decreased as the depth T of the anode electrode 40 in contact with the side surface 33 of the central trench 61 and the outer trench 62 increased. Furthermore, the reverse breakdown voltage was 7.5 MV / cm regardless of the depth T. [Explanation of symbols]

[0058] 1-16 Schottky barrier diodes 20 Semiconductor substrates 21 Top surface of semiconductor substrate 22 Back surface of semiconductor substrate 30 drift layers 31 Upper surface of the drift layer 32 Bottom of the trench 32a Inside bottom of the trench 32b Outer bottom surface of the trench 33 Side of the trench 33a Inside side of the trench 33b Outer side of the trench 34 Curved surface of the trench 35 Corner of the trench 40-42 Anode electrodes 50 Cathode electrodes 61 Center Trench 62,63 Outer perimeter 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 is provided on the semiconductor substrate, The drift layer and the anode electrode that is in Schottky contact with the Schottky layer, The semiconductor substrate and the cathode electrode which make ohmic contact with the semiconductor substrate are provided. The drift layer has a central trench in which the anode electrode is embedded, and an outer trench surrounding the central trench in which the anode electrode is embedded. The bottom surface of the central trench and the bottom surface of the outer trench are covered with an insulating film without contacting the anode electrode. At least a portion of the side surface of the central trench is in Schottky contact with the anode electrode, A portion of the inner and outer surface of the outer trench makes Schottky contact with the anode electrode. A Schottky barrier diode characterized in that the height position of the insulating film covering the inner and outer circumferential sides of the outer trench is higher than the height position of the insulating film covering the side of the central trench.

2. The Schottky barrier diode according to claim 1, characterized in that the anode electrode includes a first anode electrode that makes Schottky contact with the upper surface of the drift layer, and a second anode electrode that makes Schottky contact with the side surface of the central trench and is made of a different metallic material than the first anode electrode.

3. The drift layer has the anode electrode embedded in it and further has an outer periphery trench surrounding the central trench, The Schottky barrier diode according to claim 1 or 2, characterized in that the bottom surface and outer surface of the outer trench are covered with an insulating film without contacting the anode electrode.

4. The Schottky barrier diode according to claim 3, characterized in that at least a portion of the inner surface of the outer trench is in Schottky contact with the anode electrode.

5. The drift layer further comprises an outer trench surrounding the central trench, The Schottky barrier diode according to claim 1 or 2, characterized in that the outer periphery trench is filled with a semiconductor material having a conductivity type opposite to that of the drift layer.

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