Schottky barrier diode

Abstract

[Problem] To reduce an electrical field applied to an insulating film in trenches in a Schottky barrier diode that uses gallium oxide. [Solution] A Schottky barrier diode 1 comprises a drift layer 30 that is provided on a semiconductor substrate 20 and an anode electrode 40. The drift layer 30 has trenches 61, 62 which are provided at positions overlapping the anode electrode 40. The bottom surfaces of the trenches 61, 62 are covered with a laminated insulating film 70. The laminated insulating film 70 has a structure in which insulating films 71, 72 are laminated. An insulating material constituting the insulating films 71, 72 has a band gap which is not less than the band gap of gallium oxide, and has dielectric constant that is not less than 1 / 2 the dielectric constant of gallium oxide. Thus, an electrical field applied to the laminated insulating film 70 when a reverse voltage is applied is dispersed by the insulating films 71, 72, and therefore the strength of the electrical field applied to the insulating films 71, 72 is reduced.

Description

Schottky barrier diode

[0001] The present disclosure relates to a Schottky barrier diode, and more particularly to a Schottky barrier diode using gallium oxide.

[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 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), gallium oxide (GaO), and other materials with larger band gaps are used. ２ O ３ ) are sometimes 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 approximately 8 MV / cm, so 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 portion of an anode electrode is embedded in the trenches via an insulating film. By providing multiple trenches 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, thereby pinching off the channel region of the drift layer. This significantly reduces leakage current when a reverse voltage is applied.

[0005] Japanese Patent Application Laid-Open No. 2018-142577

[0006] However, when a trench is provided in a gallium oxide layer, a strong electric field is applied to the insulating film located at the bottom of the trench when a reverse voltage is applied.

[0007] This disclosure describes a technique for reducing the electric field applied to an insulating film in a trench in a Schottky barrier diode using gallium oxide.

[0008] A Schottky barrier diode according to one aspect of the present disclosure includes 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, the drift layer having a trench provided at a position overlapping the anode electrode, at least a bottom surface of the trench being covered with a stacked insulating film and filled with a conductive material connected to the anode electrode, the stacked insulating film having a structure in which a plurality of insulating films including first and second insulating films made of mutually different insulating materials are stacked, and the insulating material constituting the first and second insulating films has a band gap equal to or larger than the band gap of gallium oxide and a relative dielectric constant equal to or larger than half the relative dielectric constant of gallium oxide.

[0009] According to the present disclosure, a technique for reducing the electric field applied to an insulating film in a trench in a Schottky barrier diode using gallium oxide is provided.

[0010] FIG. 1A is a schematic plan view showing the configuration of a Schottky barrier diode 1 according to a first embodiment of the technology disclosed herein. FIG. 1B is a schematic cross-sectional view taken along line A-A in FIG. 1A. FIG. 2 is a schematic cross-sectional view illustrating the structure of a stacked insulating film 70. FIG. 3 is a table showing the relative permittivity, band gap, and breakdown field of each insulating material. FIG. 4 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 2 according to a second embodiment of the technology disclosed herein. FIGS. 5A to 5C are schematic cross-sectional views illustrating the positions of the inner walls of a central trench 61 and a peripheral trench 62 that are covered with a stacked insulating film 70. FIG. 6 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 3 according to a third embodiment of the technology disclosed herein. FIG. 7 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 4 according to a fourth embodiment of the technology disclosed herein. FIG. 8 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 5 according to a fifth embodiment of the technology disclosed herein. FIG. 9 is a schematic cross-sectional view illustrating the structure of a stacked insulating film 70. Fig. 10 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 6 according to a sixth embodiment of the technology disclosed herein. Fig. 11 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 7 according to a seventh embodiment of the technology disclosed herein. Fig. 12 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 8 according to a comparative example. Fig. 13 is a table showing the results of examples. Fig. 14 is a table showing the results of examples.

[0011] Hereinafter, embodiments of the technology according to the present disclosure will be described in detail with reference to the accompanying drawings.

[0012] 1A is a schematic plan view showing the configuration of a Schottky barrier diode 1 according to a first embodiment of the technology disclosed herein, and FIG. 1B is a schematic cross-sectional view taken along line AA in FIG. 1A.

[0013] As shown in FIG. 1, the Schottky barrier diode 1 according to the first embodiment is made of gallium oxide (β-Ga ２ O ３The semiconductor substrate 20 and the drift layer 30 are made of 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, so that the semiconductor substrate 20 is made of n-type ＋ layer, and the drift layer 30 is n － It acts as a layer.

[0014] 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.

[0015] 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 element. To ensure a withstand voltage of about 600 V, a thickness of about 10 μm may be used, for example.

[0016] 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 also have a multilayer structure in which different metal films are stacked, such as Ti / Au or Ti / Al.

[0017] 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 material as the anode electrode 40. However, the conductive material filled in the central trench 61 and the peripheral trench 62 does not need to be the same material as the anode electrode 40; it is sufficient that the conductive material filled in the central trench 61 and the peripheral trench 62 is electrically connected to the anode electrode 40. 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 the central trench 61 and the peripheral trench 62 may be connected. The depths of the central trench 61 and the peripheral trench 62 may be the same or different. 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, thereby significantly suppressing leakage current when a reverse voltage is applied.

[0018] The central trench 61 and the peripheral trench 62 are covered with a stacked insulating film 70. In this embodiment, all of the inner walls of the central trench 61 and the peripheral trench 62, i.e., the bottom surfaces 32 and side surfaces 33, are covered with the stacked insulating film 70. In this embodiment, as shown in FIG. 2 , the stacked insulating film 70 has a structure in which two insulating films 71 and 72 are stacked. Of the stacked insulating film 70, the insulating film 71 is located on the outer side and the insulating film 72 is located on the inner side. Therefore, the insulating film 71 contacts the drift layer 30 exposed on the inner wall of the central trench 61 or the peripheral trench 62, and the insulating film 72 contacts the conductive material embedded in the central trench 61 or the peripheral trench 62. The film thicknesses of the insulating films 71 and 72 are defined by the film thicknesses on the bottom surfaces 32 of the central trench 61 and the peripheral trench 62. That is, the film thickness T1 of the insulating film 71 and the film thickness T2 of the insulating film 72 are defined by the thicknesses shown in FIG. 2 .

[0019] The insulating films 71 and 72 are made of different insulating materials. Materials with high band gaps and dielectric constants are selected as the insulating materials for the insulating films 71 and 72. Specifically, it is necessary to select an insulating material whose band gap is equal to or larger than that of gallium oxide and whose dielectric constant is equal to or larger than half that of gallium oxide. This is because if the band gap of the insulating material for the insulating films 71 and 72 is smaller than that of the gallium oxide for the drift layer 30, sufficient insulation cannot be obtained when a reverse voltage is applied. If the dielectric constant of the insulating material for the insulating films 71 and 72 is less than half that of the gallium oxide for the drift layer 30, a high electric field will be generated in the insulating film when a reverse voltage is applied. It is more preferable that the dielectric constant of the insulating material for the insulating films 71 and 72 be equal to or larger than that of gallium oxide.

[0020] However, since there is generally a trade-off between the band gap and the relative dielectric constant, the insulating materials that satisfy the above conditions are limited. ２ O ３ , HfO ２ , Ta ２ O ５ and Si ３ O ４As shown in FIG. ２ O ３ , HfO ２ , Ta ２ O ５ and Si ３ O ４ Each of these has a band gap equal to or larger than that of gallium oxide, and a relative dielectric constant equal to or larger than half that of gallium oxide. ２ Since Al has a relative dielectric constant equal to or greater than that of gallium oxide, it can be preferably selected as the material for the insulating films 71 and 72. ２ O ３ Since Si has a very large band gap, it can be preferably selected as the material for the insulating films 71 and 72. ３ O ４ Although the dielectric constant of SiO2 is not particularly large, it has a high breakdown field and is therefore a preferable material for the insulating films 71 and 72. The dielectric constant values ​​shown in Fig. 3 were measured by a method using an impedance analyzer or a TM cavity resonator, or by a frequency variation method, and the measurement frequency was 1 MHz. The band gap values ​​shown in Fig. 3 were measured by spectroscopic band gap measurement or simple band gap measurement using XPS.

[0021] However, the insulating material constituting the insulating films 71 and 72 is pure Al. ２ O ３ , HfO ２ , Ta ２ O ５ or Si ３ O ４ In other words, even if the insulating material constituting the insulating films 71 and 72 contains impurities, it is sufficient that the band gap is equal to or larger than the band gap of gallium oxide and the relative dielectric constant is equal to or larger than half of the relative dielectric constant of gallium oxide.

[0022] In contrast, SiO ２Although SiO has a large band gap and a large dielectric breakdown field, its relative dielectric constant is as small as 3.9, which is less than half the relative dielectric constant of gallium oxide. ２ If SiO is used, the electric field applied to the laminated insulating film 70 will be increased. ２ is not suitable as a material for the insulating films 71 and 72. ２ O ３ and TiO ２ Although La has a high relative dielectric constant, its band gap is smaller than that of gallium oxide. ２ O ３ or TiO ２ When a reverse voltage is applied, sufficient insulation is not obtained. ２ O ３ and TiO ２ is not suitable as a material for the insulating films 71 and 72.

[0023] Furthermore, when a reverse voltage is applied, an electric field is more easily applied to the insulating film 72 located inside than to the insulating film 71 located outside. Therefore, if there is a difference in the relative dielectric constant of the insulating materials constituting the insulating films 71 and 72, the insulating film with the lower relative dielectric constant may be the insulating film 71, and the insulating film with the higher relative dielectric constant may be the insulating film 72. As an example, Al may be used as the insulating material constituting the insulating films 71 and 72. ２ O ３ and HfO ２ When using Al, which has a lower relative dielectric constant ２ O ３ is used for the insulating film 71, and HfO ２ may be used for the insulating film 72.

[0024] The thickness of the insulating film 71 and the thickness of the insulating film 72 may be the same or different. Here, when a reverse voltage is applied, the electric field strength tends to increase as the thickness of a material with a low relative dielectric constant increases. Therefore, if there is a difference in the thickness of the insulating films 71 and 72, the thickness of the insulating film made of a material with a low relative dielectric constant may be made thinner and the thickness of the insulating film made of a material with a high relative dielectric constant may be made thicker. As an example, Al is used as the insulating material constituting the insulating films 71 and 72. ２O ３ and HfO ２ When using Al, which has a lower relative dielectric constant ２ O ３ The insulating film made of HfO has a higher dielectric constant. ２ It is sufficient to make the insulating film thinner than the insulating film made of

[0025] As described above, in the Schottky barrier diode 1 according to this embodiment, the inner walls of the central trench 61 and the peripheral trench 62 are covered with the stacked insulating film 70 having a two-layer structure, and therefore, when a reverse voltage is applied, the electric field applied to the stacked insulating film 70 is dispersed among the insulating films 71 and 72, thereby mitigating the electric field strength applied to each of the insulating films 71 and 72. This makes it possible to reduce the electric field strength applied to the insulating film 71 compared to when a single-layer insulating film 71 is used, as in the Schottky barrier diode 8 according to the comparative example shown in FIG.

[0026] Second Embodiment FIG. 4 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 2 according to a second embodiment of the technique of the present disclosure.

[0027] 4, the Schottky barrier diode 2 according to the second embodiment differs from the Schottky barrier diode 1 according to the first embodiment in that, among the inner walls of the central trench 61 and the peripheral trench 62, the bottom surfaces 32 are covered with the laminated insulating film 70, while among the inner walls of the central trench 61 and the peripheral trench 62, the side surfaces 33 are not covered with the laminated insulating film 70. Since the other basic configuration is the same as that of the Schottky barrier diode 1 according to the first embodiment, the same elements are designated by the same reference numerals and redundant description will be omitted.

[0028] 5( a), if the bottom surfaces 32 of the central trench 61 and the peripheral trench 62 are horizontal and the portions located 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 the insulating film 70. Also, if the bottom surfaces 32 of the central trench 61 and the peripheral trench 62 are entirely curved as shown in FIG. 5( b), the entire curved bottom surfaces 32 must be covered with the insulating film 70. 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. 5( c), the bottom surfaces 32 and the corners 35 must be covered with the insulating film 70. This is because the electric field strength is particularly high at the peripheral bottoms of the central trench 61 and the peripheral trench 62 when a reverse voltage is applied. 5( a), the electric field strength is high near the curved surface 34, in the example shown in Fig. 5( b), the electric field strength is high near the curved bottom surface 32, and in the example shown in Fig. 5( c), the electric field strength is high near the corners 35. For this reason, at least these portions of the inner walls of the central trench 61 and the outer peripheral trench 62 need to be covered with the stacked insulating film 70.

[0029] Furthermore, in this embodiment, the side surfaces 33 of the central trench 61 and the peripheral trench 62 are not covered with the laminated insulating film 70 and are in Schottky 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 top surface 31 of the drift layer 30 but also at the side surfaces 33 of the central trench 61 and the peripheral trench 62, thereby reducing the on-resistance compared to when the entire inner walls of the central trench 61 and the peripheral trench 62 are covered with the laminated insulating film 70. Furthermore, since the dopant concentration of the drift layer 30 can be suppressed, a decrease in reverse breakdown voltage is also prevented.

[0030] Third Embodiment FIG. 6 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 3 according to a third embodiment of the technique of the present disclosure.

[0031] 6 , the Schottky barrier diode 3 according to the third embodiment differs from the Schottky barrier diode 2 according to the second embodiment in that, of the inner walls of the central trench 61 and the peripheral trench 62, the side surfaces 33 are covered with an insulating film 72. Since the other basic configurations are the same as those of the Schottky barrier diode 2 according to the second embodiment, the same elements are denoted by the same reference numerals and redundant description will be omitted. In this way, the side surfaces 33 of the central trench 61 and the peripheral trench 62 may be covered with a single layer of insulating film 71 or 72.

[0032] Fourth Embodiment FIG. 7 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 4 according to a fourth embodiment of the technique of the present disclosure.

[0033] 7, 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 thickness of the insulating film 72 is selectively thickened in the portion covering the bottom surface 32. Since the other basic configuration is the same as that of the Schottky barrier diode 1 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant description will be omitted. In this way, the thickness of the insulating film 71 or 72 does not need to be constant.

[0034] Fifth Embodiment FIG. 8 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 5 according to a fifth embodiment of the technique of the present disclosure.

[0035] 8, 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 laminated insulating film 70 has a three-layer structure. Since the other basic configurations are the same as those of the Schottky barrier diode 1 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0036] 9 , the stacked insulating film 70 has a structure in which three insulating films 71 to 73 are stacked. Of the stacked insulating film 70, the insulating film 71 is located on the outermost side, the insulating film 73 is located on the innermost side, and the insulating film 72 is located between the insulating films 71 and 73. Therefore, the insulating film 71 contacts the drift layer 30 exposed on the inner wall of the central trench 61 or the outer peripheral trench 62, and the insulating film 73 contacts the conductive material embedded in the central trench 61 or the outer peripheral trench 62.

[0037] The insulating films 71 and 72 are made of different insulating materials, and the insulating films 72 and 73 are made of different insulating materials. The insulating films 71 to 73 may all be made of different insulating materials. As an example, the insulating materials constituting the insulating films 71 to 73 may be Al. ２ O ３ , HfO ２ and Si ３ N ４ In this case, HfO, which has the highest relative dielectric constant, may be selected from the group consisting of ２ As a result, if Al is selected as the insulating material for the insulating film 72, the electric field strength applied to the insulating film 71 located on the outermost side can be reduced. ２ O ３ The insulating film 72 is made of HfO ２ The insulating material constituting the insulating film 73 is Si. ３ N ４ It is also acceptable to use

[0038] Sixth Embodiment FIG. 10 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 6 according to a sixth embodiment of the technique of the present disclosure.

[0039] 10 , the Schottky barrier diode 6 according to the sixth embodiment differs from the Schottky barrier diode 2 according to the second embodiment in that the laminated insulating film 70 has a three-layer structure. Since the other basic configurations are the same as those of the Schottky barrier diode 2 according to the second embodiment, the same elements are denoted by the same reference numerals, and redundant explanations will be omitted. Thus, even when the laminated insulating film 70 has a three-layer structure, the laminated insulating film 70 on the side surface 33 may be removed.

[0040] Seventh Embodiment FIG. 11 is a schematic cross-sectional view showing the configuration of a Schottky barrier diode 7 according to a seventh embodiment of the technique of the present disclosure.

[0041] 11 , the Schottky barrier diode 7 according to the seventh embodiment differs from the Schottky barrier diode 6 according to the sixth embodiment in that, of the inner walls of the central trench 61 and the peripheral trench 62, the side surfaces 33 are covered with an insulating film 73. Since the other basic configurations are the same as those of the Schottky barrier diode 6 according to the sixth embodiment, the same elements are denoted by the same reference numerals and redundant description will be omitted. In this way, the side surfaces 33 of the central trench 61 and the peripheral trench 62 may be covered with a single layer of insulating film 71, 72, or 73.

[0042] The above describes embodiments of the technology according to the present disclosure, but the technology according to the present disclosure is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the technology, and it goes without saying that these modifications are also included within the scope of the technology according to the present disclosure.

[0043] For example, in each of the above-described embodiments, the drift layer 30 is provided with the central trench 61 and the outer periphery trench 62, but one of the central trench 61 and the outer periphery trench 62 may be omitted.

[0044] The technology according to the present disclosure includes, but is not limited to, the following configuration examples.

[0045] A Schottky barrier diode according to one aspect of the present disclosure includes 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, the drift layer having a trench provided at a position overlapping the anode electrode, at least a bottom surface of the trench being covered with a stacked insulating film and filled with a conductive material connected to the anode electrode, the stacked insulating film having a structure in which a plurality of insulating films including first and second insulating films made of mutually different insulating materials are stacked, the insulating materials constituting the first and second insulating films having a band gap equal to or larger than the band gap of gallium oxide and a relative dielectric constant equal to or larger than half the relative dielectric constant of gallium oxide. This allows an electric field applied to the stacked insulating film when a reverse voltage is applied to be dispersed among the plurality of insulating films, thereby reducing the electric field strength applied to each insulating film.

[0046] In the above Schottky barrier diode, the insulating material constituting at least one of the first and second insulating films may have a dielectric constant equal to or greater than that of gallium oxide, thereby enabling the electric field strength applied to each insulating film to be further reduced.

[0047] In the above Schottky barrier diode, the plurality of insulating films may further include a third insulating film, which makes it possible to further reduce the electric field strength applied to each insulating film.

[0048] In the above Schottky barrier diode, the first and second insulating films are each made of Al ２ O ３ , HfO ２ , Ta ２ O ５ and Si ３ O ４ In this case, the electric field strength applied to each insulating film is reduced compared to when a single insulating film made of an insulating material selected from the above group is used.

[0049] This application claims the benefit of Japanese Patent Application No. 2023-027092, filed on February 24, 2023, the entire disclosure of which is incorporated herein by reference.

[0050] 1 and 12, a simulation was performed to determine the electric field strength applied to the insulating films 71 and 72 when a reverse voltage of 1200 V was applied between the anode electrode 40 and the cathode electrode 50. The dopant concentration of the semiconductor substrate 20 was set to 1×10 １８ cm －３ The dopant concentration of the drift layer 30 is set to 1×10 １６ cm －３ The thickness of the drift layer 30 was 10 μm. The depths of the central trench 61 and the peripheral trench 62 were both 2 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 1.0 μm. The material of the anode electrode 40 was Ni, and the material of the cathode electrode 50 was a laminated film of Ti and Au. The materials and film thicknesses of the insulating films 71 and 72 in each simulation model are as shown in FIGS. 13 and 14 .

[0051] As shown in FIG. ２ O ３ Compared with the simulation models A0, B0, and C0 using a single layer insulating film 71 made of HfO ２ or Si ３ O ４ In the simulation models A1 to A6, B1 to B6, and C1 to C6 in which the insulating film 72 made of HfO was added, the electric field strength applied to the insulating film 71 was reduced. The electric field strength applied to the insulating films 71 and 72 tended to decrease as the thickness of the insulating film 71 became thinner, and to decrease as the thickness of the insulating film 72 became thicker. In particular, when the insulating film 72 was made of HfO ２ In the simulation models A1 to A3, B1 to B3, and C1 to C3 using SiO ２In the simulation models A7 to A9, B7 to B9, and C7 to C9 in which the insulating film 72 made of the above was added, the electric field strength applied to the insulating film 71 was actually increased compared to the simulation models A0, B0, and C0 in which the single-layer insulating film 71 was used.

[0052] As shown in FIG. ２ Compared with the simulation models D0, E0, and F0 using a single layer insulating film 71 made of Al ２ O ３ or Si ３ O ４ In the simulation models D1 to D6, E1 to E6, and F1 to F6 in which the insulating film 72 made of SiO was added, the electric field strength applied to the insulating film 71 was reduced. No strong correlation was observed between the film thickness of the insulating films 71 and 72 and the electric field strength applied to the insulating films 71 and 72. ２ In the simulation models D7 to D9, E7 to E9, and F7 to F9 in which the insulating film 72 made of the above was added, the electric field strength applied to the insulating film 71 was actually increased compared to the simulation models D0, E0, and F0 in which the single-layer insulating film 71 was used.

[0053] In addition, several simulation models having the same structure as the Schottky barrier diode 5 shown in FIG. 8 were assumed, and the electric field strength applied to the insulating films 71 to 73 when a reverse voltage of 1200 V was applied between the anode electrode 40 and the cathode electrode 50 was simulated. The material of the insulating film 71 was Al. ２ O ３ The material and thickness of the insulating films 72 and 73 in each simulation model are as shown in FIG.

[0054] As shown in FIG. ２ O ３ Compared with the simulation model B0 using a single layer insulating film 71 made of HfO ２ or Si ３ O ４ In the simulation models G1 to G6 in which the insulating films 72 and 73 made of SiO were added, the electric field strength applied to the insulating film 71 was reduced.２ In the simulation models G7 to G18 using the insulating film 71, the electric field strength applied to the insulating film 71 was actually greater than that in the simulation model B0 using the single-layer insulating film 71.

[0055] 1 to 8 Schottky barrier diode 20 Semiconductor substrate 21 Upper surface of semiconductor substrate 22 Rear surface of semiconductor substrate 30 Drift layer 31 Upper surface of drift layer 32 Bottom surface of trench 33 Side surface of trench 34 Curved surface of trench 35 Corner of trench 40 Anode electrode 50 Cathode electrode 61 Central trench 62 Peripheral trench 70 Stacked insulating film 71 to 73 Insulating films 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 trench provided at a position overlapping the anode electrode, At least a bottom surface of the trench is covered with a laminated insulating film and is filled with a conductive material connected to the anode electrode; the laminated insulating film has a structure in which a plurality of insulating films including first and second insulating films made of different insulating materials are laminated; a Schottky barrier diode, wherein the insulating material constituting the first and second insulating films has a band gap equal to or larger than the band gap of gallium oxide and a relative dielectric constant equal to or larger than half of the relative dielectric constant of gallium oxide.

2. 2. The Schottky barrier diode according to claim 1, wherein the insulating material constituting at least one of said first and second insulating films has a relative dielectric constant equal to or greater than that of gallium oxide.

3. The Schottky barrier diode according to claim 1 , wherein said plurality of insulating films further includes a third insulating film.

4. The relative dielectric constant of the insulating material constituting the second insulating film is higher than the relative dielectric constant of the insulating material constituting the first insulating film; The Schottky barrier diode according to claim 1 , wherein the first insulating film is located between the bottom surface of the trench and the second insulating film.

5. The relative dielectric constant of the insulating material constituting the second insulating film is higher than the relative dielectric constant of the insulating material constituting the first insulating film; 2. The Schottky barrier diode according to claim 1, wherein the second insulating film has a thickness greater than that of the first insulating film.

6. The first and second insulating films are each made of Al ２ O ３ , HfO ２ , Ta ２ O ５ and Si ３ O ４ 6. The Schottky barrier diode according to claim 1, wherein the Schottky barrier diode is made of an insulating material selected from the group consisting of: