Schottky Barrier Diode

Abstract

To prevent dielectric breakdown of a Schottky barrier diode containing gallium oxide.SOLUTION: A Schottky barrier diode 11 comprises: a drift layer 30 provided on a semiconductor substrate 20; an anode electrode 40 and a cathode electrode 50. Parts of the anode electrode 40 are embedded in outer peripheral trenches 61 and center trenches 62 via an insulating film 63. The insulating film 63 becomes thicker in a depth direction of the outer peripheral trench 61 as it goes outward. Thereby, an outer peripheral wall S1 of the anode electrode 40 embedded in the outer peripheral trench 61 has a curved shape that becomes closer to vertical as it goes outward. As a result, an electric field generated at an outer peripheral bottom part of the outer peripheral trench 61 is relaxed when a reverse voltage is applied.SELECTED DRAWING: Figure 2

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 technology]

[0002] A Schottky barrier diode is a rectifying element that uses the Schottky barrier created by the junction between a metal and a semiconductor, and has the characteristics of 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 for power devices.

[0003] When using Schottky barrier diodes as switching elements for power devices, it is necessary to ensure sufficient reverse breakdown voltage. Therefore, instead of silicon (Si), silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (GaO) with larger band gaps are used. 2 O 3 ) may be used. Among them, gallium oxide has a very large band gap of 4.8 to 4.9 eV and a large dielectric breakdown field of about 8 MV / cm, so that Schottky barrier diodes using gallium oxide are 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] The Schottky barrier diode described in Patent Document 1 has a structure in which multiple trenches are provided in a gallium oxide layer, and a part of an anode electrode is embedded in the trenches via an insulating film. If multiple trenches are provided in the gallium oxide layer in this way, 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. This makes it possible to significantly suppress the leakage current when a reverse voltage is applied. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-199869 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional Schottky barrier diodes having trenches have a problem in that when a reverse voltage is applied, an electric field concentrates at the outer bottom of the trench located at the outermost periphery, making this portion susceptible to dielectric breakdown.

[0007] Therefore, an object of the present invention is to prevent dielectric breakdown in a Schottky barrier diode using gallium oxide by mitigating the electric field that occurs when a reverse voltage is applied. [Means for solving the problem]

[0008] A 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 in Schottky contact with the drift layer, a cathode electrode in ohmic contact with the semiconductor substrate, and an insulating film covering an inner wall of a trench provided in the drift layer, the trench including a peripheral trench formed in a ring shape and a central trench formed in a region surrounded by the peripheral trench, a part of the anode electrode is embedded in the peripheral trench and the central trench via the insulating film, the insulating film becomes thicker in the depth direction of the peripheral trench toward the outside, and as a result, the peripheral wall of the anode electrode embedded in the peripheral trench has a curved shape that becomes closer to vertical toward the outside.

[0009] According to the present invention, the peripheral wall of the anode electrode embedded in the peripheral trench has a curved shape that becomes closer to vertical toward the outside, thereby mitigating the electric field generated at the peripheral bottom of the peripheral trench when a reverse voltage is applied.

[0010] In the present invention, the inner peripheral wall of the anode electrode embedded in the outer peripheral trench may be closer to vertical than the outer peripheral wall, which makes it possible to reliably pinch off the mesa region between the central trench and the outer peripheral trench.

[0011] In the present invention, the width of the peripheral trench may be wider than the width of the central trench, which can further reduce the electric field generated at the bottom of the peripheral trench.

[0012] In the present invention, the peripheral trench may be deeper than the central trench, which can further reduce the electric field generated at the peripheral bottom of the peripheral trench.

[0013] In the present invention, the upper surface of the drift layer located outside the outer periphery trench may be covered with an insulating film, whereby the upper surface of the drift layer is protected by the insulating film.

[0014] In the present invention, at least the portion of the insulating film that covers the inner wall of the outer periphery trench may have a multi-layer structure, which makes it easier to adjust the film thickness and characteristics of the insulating film. Effect of the Invention

[0015] As described above, according to the present invention, the electric field generated when a reverse voltage is applied is alleviated, making it possible to prevent dielectric breakdown in a Schottky barrier diode using gallium oxide. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic plan view showing the configuration of a Schottky barrier diode 11 according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view taken along the line AA shown in FIG. [Diagram 3] FIG. 3 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 10 according to a comparative example. [Figure 4] FIG. 4 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 12 according to a second embodiment of the present invention. [Diagram 5] FIG. 5 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 13 according to a third embodiment of the present invention. [Figure 6] FIG. 6 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 14 according to a fourth embodiment of the present invention. [Figure 7] FIG. 7 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 14a according to a modification of the fourth embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 15 according to a fifth embodiment of the present invention. [Figure 9] FIG. 9 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 16 according to a sixth embodiment of the present invention. [Figure 10] FIG. 10 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 17 according to the seventh embodiment of the present invention. [Figure 11] FIG. 11 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 18 according to an eighth embodiment of the present invention. [Figure 12] FIG. 12 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 18a according to a modification of the eighth embodiment. [Figure 13] FIG. 13 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 19 according to a ninth embodiment of the present invention. [Figure 14] FIG. 14 is a schematic diagram for explaining parameters according to the first embodiment. [Figure 15] FIG. 15 is a graph showing the simulation results of the first embodiment. [Figure 16]FIG. 16 is a graph showing the simulation results of the second embodiment. [Figure 17] FIG. 17 is a table showing the simulation results of the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0018] <First embodiment> Fig. 1 is a schematic plan view showing the configuration of a Schottky barrier diode 11 according to a first embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view taken along the line AA shown in Fig. 1.

[0019] As shown in FIGS. 1 and 2, the Schottky barrier diode 11 according to the present embodiment is made of gallium oxide (β-Ga 2 O 3 The semiconductor substrate 20 and the drift layer 30 are made of n-type tin (Si) or n-type dopant. The semiconductor substrate 20 and the drift layer 30 are doped with silicon (Si) or tin (Sn) as an n-type dopant. The concentration of the dopant is higher in the semiconductor substrate 20 than in the drift layer 30. As a result, the semiconductor substrate 20 is made of n-type tin (Sn). + The drift layer 30 is n - It functions as a layer.

[0020] 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 according to 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.

[0021] The semiconductor substrate 20 has an upper surface 21 located on the upper surface side when mounted, and a back surface 22 located on the lower surface side when mounted, opposite the upper surface 21. 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 reactive sputtering, PLD method, MBE method, MOCVD method, HVPE method, or the like. The film thickness of the drift layer 30 is not particularly limited, but is generally selected according to the reverse withstand voltage of the element. In order to ensure a withstand voltage of about 600 V, for example, it may be about 7 μm.

[0022] An anode electrode 40 is formed on the upper surface 31 of the drift layer 30, and is in 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), copper (Cu), or the like. 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 rear surface 22 of the semiconductor substrate 20, and is in 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.

[0023] In this embodiment, trenches 61 and 62 are provided in the drift layer 30. Both of the trenches 61 and 62 are provided at positions overlapping with the anode electrode 40 in a plan view. Of these, the trench 61 is a peripheral trench formed in a ring shape, and the trench 62 is a central trench formed in a region surrounded by the peripheral trench. The peripheral trench 61 and the central trench 62 do not need to be completely separated, and as shown in FIG. 1, the peripheral trench 61 and the central trench 62 may be connected. In this embodiment, the peripheral trench 61 and the central trench 62 have the same depth.

[0024] The inner walls of the trenches 61 and 62 are made of HfO 2and the like, and the insides of the trenches 61, 62 are filled with the same material as the anode electrode 40 via the insulating film 63. In this embodiment, since the drift layer 30 is provided with a plurality of trenches 61, 62, the anode electrode 40 may be made of a material having a low work function, such as molybdenum (Mo) or copper (Cu). In addition, since the drift layer 30 is provided with a plurality of trenches 61, 62, the dopant concentration of the drift layer 30 is set to 4×10 16 cm -3 can be increased to a certain extent.

[0025] The portion of the drift layer 30 defined by the trenches 61 and 62 constitutes a mesa region M. When a reverse voltage is applied between the anode electrode 40 and the cathode electrode 50, the mesa region M becomes a depletion layer, and the channel region of the drift layer 30 is pinched off. This significantly suppresses the leakage current when a reverse voltage is applied.

[0026] In this embodiment, when the width of the peripheral trench 61 along the line AA is W1 and the width of the central trench 62 is W2, W1>W2 Here, the width W1 of the peripheral trench 61 refers to the width in the radial direction, and the width W2 of the central trench 62 refers to the width in the mesa width direction.

[0027] Furthermore, the insulating film 63 covering the inner wall of the outer circumferential trench 61 has a thickness in the depth direction (i.e., vertical direction) that increases toward the outside in the radial direction. In other words, the thickness of the insulating film 63 in the direction perpendicular to the outer circumferential wall of the outer circumferential trench 61 (i.e., horizontal direction) increases as the depth position increases. The increase in thickness is quadratic, and as a result, the outer circumferential wall S1 of the anode electrode 40 embedded in the outer circumferential trench 61 has a gently curved shape that becomes closer to vertical toward the outside. In contrast, the thickness in the horizontal direction of the insulating film 63 formed on the inner circumferential wall of the outer circumferential trench 61 is almost constant, and as a result, the inner circumferential wall S2 of the anode electrode 40 is closer to vertical than the outer circumferential wall S1 of the anode electrode 40. In other words, the angle of the outer circumferential wall S1 of the anode electrode 40 with respect to the upper surface 31 of the drift layer 30 is small near the boundary with the inner circumferential wall S2, but the angle of the outer circumferential wall S1 of the anode electrode 40 with respect to the upper surface 31 of the drift layer 30 gradually increases toward the outside, and becomes almost vertical near the upper surface 31 of the drift layer 30. In contrast, the inner peripheral wall S2 of the anode electrode 40 is slightly curved near the boundary with the outer peripheral wall S1 but is substantially vertical.

[0028] Thus, in this embodiment, the cross section in the radial direction of the anode electrode 40 embedded in the peripheral trench 61 is asymmetric. Here, one of the reasons why the width W1 of the peripheral trench 61 is set larger than the width W2 of the central trench 62 is to ensure a sufficient radial space for gently curving the peripheral wall S1 of the anode electrode 40. The insulating film 63 having such a shape can be formed, for example, by multi-stage film deposition or etching using multiple masks.

[0029] FIG. 3 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 10 according to a comparative example.

[0030] 3, the thickness of the insulating film 63 is constant in the direction perpendicular to the wall surface of the peripheral trench 61. As a result, the cross section in the radial direction of the anode electrode 40 embedded in the peripheral trench 61 is symmetrical, and the peripheral wall S1 and the inner wall S2 are both approximately perpendicular. In the case of such a structure, the radius of curvature of the peripheral bottom portion A located between the peripheral wall S1 and the bottom portion S3 of the anode electrode 40 becomes small, so that an electric field is concentrated in this portion, and in some cases, dielectric breakdown occurs.

[0031] In contrast, in the Schottky barrier diode 11 according to the present embodiment, the cross section in the radial direction of the anode electrode 40 embedded in the outer trench 61 is asymmetric, and the outer peripheral wall S1 of the anode electrode 40 itself forms a gently curved surface having a large radius of curvature, so that the electric field is widely dispersed. In the present embodiment, the radius of curvature of the inner peripheral bottom B located at the boundary between the outer peripheral wall S1 and the inner peripheral wall S2 is relatively small, but the outer peripheral wall S1 itself having a large radius of curvature disperses the electric field, so that the electric field is hardly concentrated at the inner peripheral bottom B. Moreover, since the inner peripheral wall S2 is almost perpendicular to the upper surface 31 of the drift layer 30, the distance between the anode electrode 40 embedded in the outer peripheral trench 61 and the anode electrode 40 embedded in the central trench 62 does not become too wide. Therefore, when a reverse voltage is applied, the channel region of the drift layer 30 can be pinched off reliably.

[0032] As described above, in the Schottky barrier diode 11 according to this embodiment, the outer peripheral wall S1 of the anode electrode 40 itself forms a curved surface having a large radius of curvature by controlling the film thickness of the insulating film 63, so that local concentration of an electric field is unlikely to occur even when a reverse voltage is applied. This makes it possible to prevent dielectric breakdown at the outer bottom of the outer peripheral trench 61, which is likely to occur when a reverse voltage is applied. Moreover, the outer peripheral trench 61 and the central trench 62 have the same shape except for their widths, so that both can be formed simultaneously.

[0033] <Second embodiment> FIG. 4 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 12 according to a second embodiment of the present invention.

[0034] 4, the Schottky barrier diode 12 according to the second embodiment differs from the Schottky barrier diode 11 according to the first embodiment in that the anode electrode 40 has a substantially flat bottom surface S3. Since the other basic configurations are the same as those of the Schottky barrier diode 11 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0035] As exemplified in this embodiment, in the present invention, the anode electrode 40 may have a substantially flat bottom surface portion S3 between the outer peripheral wall S1 and the inner peripheral wall S2.

[0036] <Third embodiment> FIG. 5 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 13 according to a third embodiment of the present invention.

[0037] 5, the Schottky barrier diode 13 according to the third embodiment differs from the Schottky barrier diode 11 according to the first embodiment in that the depth D1 of the peripheral trench 61 is deeper than the depth D2 of the central trench 62. Since the other basic configurations are the same as those of the Schottky barrier diode 11 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0038] If the depth D1 of the peripheral trench 61 is made deeper than the depth D2 of the central trench 62 as in this embodiment, the radius of curvature of the peripheral wall S1 of the anode electrode 40 becomes larger, and the concentration of the electric field is further alleviated. However, if the depth D1 of the peripheral trench 61 is too deep, the remaining film of the drift layer 30 located at the bottom of the peripheral trench 61 becomes too thin, and the electric field becomes stronger. For this reason, it is preferable to set the depth D1 of the peripheral trench 61 to a range in which the thickness of the drift layer 30 located at the bottom of the peripheral trench 61 is 1 μm or more.

[0039] <Fourth embodiment> FIG. 6 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 14 according to a fourth embodiment of the present invention.

[0040] 6, the Schottky barrier diode 14 according to the fourth embodiment differs from the Schottky barrier diode 11 according to the first embodiment in that the upper surface 31 of the drift layer 30 located outside the peripheral trench 61 is covered with an insulating film 63. Since the other basic configurations are the same as those of the Schottky barrier diode 11 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0041] As in this embodiment, if the insulating film 63 is formed not only on the inner walls of the trenches 61 and 62 but also on the upper surface 31 of the drift layer 30 located outside the outer periphery trench 61, it is possible to protect the upper surface 31 of the drift layer 30.

[0042] FIG. 7 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 14a according to a modification of the fourth embodiment.

[0043] 7, a portion of the anode electrode 40 located at the upper portion of the peripheral trench 61 is removed, and an insulating film 63 is provided in the portion from which the anode electrode 40 has been removed. As described above, in the present invention, the upper surface of the anode electrode 40 does not need to be flat, and it is acceptable for a portion of it to be removed.

[0044] <Fifth embodiment> FIG. 8 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 15 according to a fifth embodiment of the present invention.

[0045] 8, the Schottky barrier diode 15 according to the fifth embodiment differs from the Schottky barrier diode 11 according to the first embodiment in that a portion of the anode electrode 40 extends beyond the peripheral trench 61 and is formed on the insulating film 63. Since the other basic configurations are the same as those of the Schottky barrier diode 11 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0046] As exemplified in this embodiment, in the present invention, a portion of the anode electrode 40 may be formed on the insulating film 63 beyond the peripheral trench 61 .

[0047] <Fifth embodiment> FIG. 9 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 16 according to a sixth embodiment of the present invention.

[0048] 9, the Schottky barrier diode 16 according to the sixth embodiment differs from the Schottky barrier diode 11 according to the first embodiment in that a portion of the anode electrode 40 located in the outer circumferential trench 61 is removed. Since the other basic configurations are the same as those of the Schottky barrier diode 11 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0049] As illustrated in this embodiment, in the present invention, the inside of the outer circumferential trench 61 does not need to be filled with the anode electrode 40, and a cavity may be present partially therein.

[0050] Seventh embodiment FIG. 10 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 17 according to the seventh embodiment of the present invention.

[0051] 10, the Schottky barrier diode 17 according to the seventh embodiment differs from the Schottky barrier diode 16 according to the sixth embodiment in that a part of the insulating film 63 covering the outer peripheral wall of the outer peripheral trench is exposed. Since the other basic configuration is the same as that of the Schottky barrier diode 16 according to the sixth embodiment, the same elements are denoted by the same reference numerals and duplicated explanations will be omitted.

[0052] As illustrated in this embodiment, in the present invention, the insulating film 63 covering the outer peripheral wall of the outer peripheral trench 61 does not need to be entirely covered by the anode electrode 40, and a portion of it may be exposed.

[0053] <Eighth embodiment> FIG. 11 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 18 according to an eighth embodiment of the present invention.

[0054] 11, the Schottky barrier diode 18 according to the eighth embodiment differs from the Schottky barrier diode 17 according to the seventh embodiment in that the upper part of the outer peripheral wall of the outer peripheral trench 61 is exposed without being covered with the insulating film 63. Since the other basic configuration is the same as that of the Schottky barrier diode 17 according to the seventh embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0055] As illustrated in this embodiment, in the present invention, it is not necessary for the entire outer peripheral wall of the outer peripheral trench 61 to be covered with the insulating film 63, and the upper portion may be partially exposed.

[0056] FIG. 12 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 18a according to a modification of the eighth embodiment.

[0057] 12, the anode electrode 40 is formed on the upper surface of the insulating film 63 located inside the peripheral trench 61. As described above, as long as the anode electrode 40 and the drift layer 30 do not contact each other inside the peripheral trench 61, there may be a portion between them where the insulating film 63 does not exist.

[0058] <Ninth embodiment> FIG. 13 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 19 according to a ninth embodiment of the present invention.

[0059] 13, the Schottky barrier diode 19 according to the ninth embodiment differs from the Schottky barrier diode 11 according to the first embodiment in that an insulating film 64 separate from the insulating film 63 is provided inside the peripheral trench 61. Since the other basic configurations are the same as those of the Schottky barrier diode 11 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0060] The insulating film 64 is made of SiO 2 The insulating film 63 is made of an insulating material different from that of the insulating film 63, and has a thickness in the depth direction (i.e., the vertical direction) that increases toward the outside in the radial direction. In contrast, the thickness of the insulating film 63 is almost constant in the direction perpendicular to the inner wall of the outer periphery trench 61.

[0061] In this way, by covering the inner wall of the outer periphery trench 61 with an insulating film having a multi-layer structure, it becomes easy to adjust the film thickness and characteristics of the insulating film.

[0062] Although a preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention. EXAMPLES

[0063] <Example 1> A simulation model of Example 1 having the same structure as the Schottky barrier diode 19 shown in FIG. 13 was assumed, and the electric field strength was simulated when a reverse voltage of 600 V was applied between the anode electrode 40 and the cathode electrode 50. The dopant concentration of the semiconductor substrate 20 was 1×10 18 cm -3 The dopant concentration of the drift layer 30 is 4×10 16 cm -3 The thickness of the drift layer 30 was 7 μm. The depths of the peripheral trench 61 and the central trench 62 were both 3 μm. The width W1 of the peripheral trench 61 was 10 μm, and the width W2 of the central trench 62 and the width of the drift layer 30 in the portion in contact with the anode electrode 40, i.e., the width of the mesa region M, were all 1.5 μm. The insulating film 63 was a 50 nm-thick HfO 2 The anode electrode 40 was made of Cu, and the cathode electrode 50 was made of a laminated film of Ti and Au. The insulating film 64 covering the bottom and outer wall of the peripheral trench 61 was made of SiO 2 Simulations were performed using a membrane as a variable.

[0064] Fig. 14 is a schematic diagram for explaining parameters of Example 1. As shown in Fig. 14, the maximum width in the radial direction of the anode electrode 40 embedded in the outer circumferential trench 61 was defined as a, and the maximum depth was defined as b. In addition, the thickness of the insulating film 63 covering the inner wall of the outer circumferential trench 61 was defined as t1, the minimum thickness of the insulating films 63, 64 covering the bottom portion of the outer circumferential trench 61 was defined as t2, and the minimum thickness of the insulating films 63, 64 covering the outer circumferential wall of the outer circumferential trench 61 was defined as t3.

[0065] In Example 1, the width a and the thickness t3 were variables, while the depth b was fixed at 2.4 μm, the thickness t1 at 0.05 μm, and the thickness t2 at 0.6 μm.

[0066] The results are shown in Figure 15. As shown in Figure 15, when the width a of the anode electrode 40 is less than 1.5 µm, which is the width W2 of the central trench 62 and the mesa width, the maximum electric field strength (Emax) applied to the insulating film 64 exceeded 10 MV / cm, which is the dielectric breakdown field strength of silicon oxide. Conversely, when the width a of the anode electrode 40 exceeds 9.3 µm, the maximum electric field strength applied to the insulating film 64 exceeded 10 MV / cm, which is the dielectric breakdown field strength of silicon oxide. In contrast, the maximum electric field strength applied to the drift layer 30 was equal to or less than 8 MV / cm, which is the dielectric breakdown field strength of gallium oxide, regardless of the width a of the anode electrode 40.

[0067] <Comparative Example> A simulation was performed under the same conditions as in Example 1, assuming a simulation model of Comparative Example 1 having the same structure as the Schottky barrier diode 10 shown in Fig. 3. The shape of the anode electrode 40 embedded in the peripheral trench 61 was symmetrical, with a width a of 9.9 µm, a depth b of 2.95 µm, and film thicknesses t1 to t3 of 0.05 µm each. As a result, the maximum electric field strength at the peripheral bottom A shown in Fig. 3 was 8.6 MV / cm.

[0068] <Example 2> The simulation was performed under the same conditions as in Example 1, except that the width b and the thickness t2 were fixed to 4.95 μm, the thickness t1 to 0.05 μm, and the thickness t3 to 5 μm, with the width b and the thickness t2 being variables.

[0069] The results are shown in Fig. 16. As shown in Fig. 16, when film thickness t2 is less than 1 / 10 (less than 0.3 µm) of depth D1 of peripheral trench 61, the maximum electric field strength applied to insulating film 64 exceeded 10 MV / cm, which is the dielectric breakdown field strength of silicon oxide. Conversely, when depth b of anode electrode 40 is less than 1.5 µm, the maximum electric field strength applied to drift layer 30 exceeded 8 MV / cm, which is the dielectric breakdown field strength of gallium oxide.

[0070] <Example 3> The simulation was performed under the same conditions as in Example 2, except that the depth D1 of the peripheral trench 61 was set to 4 μm, 5 μm, or 6 μm.

[0071] The results are shown in Figure 17. As shown in Figure 17, when film thickness t2 is less than 1 / 10 of depth D1 of peripheral trench 61, the maximum electric field strength applied to insulating film 64 exceeded 10 MV / cm, which is the dielectric breakdown field strength of silicon oxide. Moreover, the electric field strength applied to drift layer 30 became more relaxed as depth D1 of peripheral trench 61 became deeper. [Explanation of symbols]

[0072] 10~19,14a,18a Schottky Barrier Diodes 20 Semiconductor substrate 21 Upper surface of semiconductor substrate 22 Back side of semiconductor substrate 30 Drift Layer 31 Top surface of drift layer 40 Anode electrode 50 Cathode Electrode 61 Periphery Trench 62 Central Trench 63,64 Insulating film A Bottom of outer periphery B Inner bottom M Mesa Region S1 outer wall S2 Inner wall S3 bottom part

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; an insulating film covering an inner wall of a trench provided in the drift layer; The trench includes a peripheral trench formed in a ring shape and a central trench formed in a region surrounded by the peripheral trench, a portion of the anode electrode is embedded in the outer circumferential trench and the central trench via the insulating film; the insulating film formed between the outer circumferential wall of the anode electrode embedded in the outer circumferential trench and the outer circumferential wall of the outer circumferential trench has a thickness that increases outward in a depth direction of the outer circumferential trench, so that the outer circumferential wall of the anode electrode embedded in the outer circumferential trench has a curved shape that becomes closer to vertical outward; a first insulating layer formed on the first anode electrode and a second insulating layer formed on the second anode electrode;

2. 2. The Schottky barrier diode according to claim 1, wherein the width of the peripheral trench is wider than the width of the central trench.

3. 3. The Schottky barrier diode according to claim 1, wherein the peripheral trench is deeper than the central trench.

4. 4. The Schottky barrier diode according to claim 1, wherein an upper surface of the drift layer located outside the outer periphery trench is covered with the insulating film.

5. 5. The Schottky barrier diode according to claim 1, wherein at least a portion of the insulating film covering an inner wall of the outer circumferential trench has a multi-layer structure.

6. 6. The Schottky barrier diode according to claim 1, wherein a radius of curvature of a curved surface constituting the outer peripheral wall of the anode electrode is larger than a radius of curvature of an inner peripheral bottom portion located at a boundary portion between the outer peripheral wall of the anode electrode and the inner peripheral wall of the anode electrode.

7. 7. The Schottky barrier diode according to claim 1, wherein a cross section of the anode electrode embedded in the central trench in a radial direction is symmetrical.

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