JP2014090140A - Nitride semiconductor schottky barrier diode - Google Patents

Abstract

Provided is a nitride semiconductor Schottky barrier diode which can widen a current path between an anode and a cathode to enable a large current or a small size.
A nitride semiconductor Schottky barrier diode (1) is in ohmic contact with a first nitride semiconductor layer, a second nitride semiconductor layer (32) laminated thereon, and a surface of the second nitride semiconductor layer (32). And a plurality of ohmic electrodes 15 arranged in a distributed manner and a Schottky electrode 16 in Schottky contact with the surface of the second nitride semiconductor layer 32. The plurality of ohmic electrodes 15 are formed on the surface of the second nitride semiconductor layer 32 so that six adjacent ohmic electrodes 15 are positioned so as to have a six-fold symmetrical arrangement around the one ohmic electrode 15. Yes. The Schottky electrode 16 is formed in a mesh structure having a honeycomb structure surrounding each ohmic electrode 15 and defining a plurality of diode cells D.
[Selection] Figure 4

Description

  The present invention relates to a nitride semiconductor Schottky barrier diode having a Schottky electrode that forms a Schottky junction with a nitride semiconductor layer.

  Patent Document 1 discloses a Schottky diode using a group III nitride semiconductor. This Schottky diode is composed of a GaN semiconductor layer disposed on a substrate, an AlGaN semiconductor layer that forms a heterojunction with the GaN semiconductor layer, an anode electrode that is in Schottky contact with the AlGaN semiconductor layer, and an ohmic contact with the AlGaN semiconductor layer. A cathode electrode. On the AlGaN semiconductor layer, a plurality of anode electrodes and a plurality of cathode electrodes each formed in a straight strip are arranged, and the anode electrodes and the cathode electrodes are alternately arranged in a direction perpendicular to the longitudinal direction thereof. Yes.

JP-T-2007-522677 (FIGS. 6A and 6B)

  The present invention provides a nitride semiconductor Schottky barrier diode in which a current path between an anode and a cathode is widened to enable a large current or a small size.

  According to a first aspect of the present invention for achieving the above object, a first nitride semiconductor layer made of a nitride semiconductor and the first nitride semiconductor layer are laminated, and the first nitride semiconductor layer has a composition. A second nitride semiconductor layer made of different nitride semiconductors, and a plurality of ohmic electrodes disposed in ohmic contact with the surface of the second nitride semiconductor layer and distributed on the surface of the second nitride semiconductor layer And six adjacent ohmic electrodes so that the plurality of ohmic electrodes are arranged in a six-fold symmetry with one ohmic electrode as the center, and a Schottky electrode in contact with the surface of the second nitride semiconductor layer. Is formed on the surface of the second nitride semiconductor layer, and the Schottky electrode is formed in a mesh structure of a honeycomb structure surrounding each ohmic electrode and defining a plurality of cells. It is a nitride semiconductor Schottky barrier diode.

  According to this configuration, a plurality of ohmic electrodes are positioned on the surface of the second nitride semiconductor layer such that six adjacent ohmic electrodes are positioned so as to have a six-fold symmetrical arrangement around one ohmic electrode. Distributed. Then, a Schottky electrode is formed in a mesh structure having a honeycomb structure so as to surround each ohmic electrode, and thereby, a plurality of cells surrounding each ohmic electrode are partitioned. Thereby, a plurality of cells are spread on the surface of the second nitride semiconductor layer, and a current path is formed between the ohmic electrode of each cell and the Schottky electrode surrounding it. In this way, the current path can be widened as compared with a structure in which straight strip-like anode electrodes and cathode electrodes are alternately arranged. That is, a wider current path can be ensured in the same size chip, thereby increasing the current of the nitride semiconductor Schottky barrier diode. In addition, if a diode chip having the same current capacity is designed, the current capacity per unit area (current density) can be increased, so that the size of the nitride semiconductor Schottky barrier diode can be reduced.

  Further, by arranging the ohmic electrodes in a six-fold symmetrical dispersive arrangement, the Schottky electrodes surrounding each ohmic electrode can have a network structure having a regular hexagonal center line. Thereby, the distance between the ohmic electrode and the Schottky electrode can be made almost uniform everywhere while the electrode width of the Schottky electrode is made almost uniform. Thereby, substantially the entire region in the cell becomes a current path, which can contribute to the expansion of the current path. In addition, since the electric field between the ohmic electrode and the Schottky electrode is substantially uniform around the ohmic electrode, concentration of the electric field can be avoided and the breakdown voltage can be improved.

According to a second aspect of the present invention, the plurality of ohmic electrodes are uniformly distributed on the surface of the active region of the second nitride semiconductor layer, and the plurality of cells have the same shape and size. The nitride semiconductor Schottky barrier diode according to claim 1, wherein one ohmic electrode is arranged at the center of each cell.
According to this configuration, the ohmic electrodes are evenly distributed on the surface of the active region of the second nitride semiconductor layer, and cells having the same shape and the same size are arranged so as to surround each ohmic electrode. It is divided by. As a result, cells of the same size and size can be efficiently spread in the active region, and current flows evenly through all the cells arranged in the active region. Thereby, the current capacity can be further increased. Further, in all the cells, a voltage is evenly applied between the ohmic electrode and the Schottky electrode, so that concentration of the electric field can be avoided and the breakdown voltage can be improved. Further, in each cell, the distance between the central ohmic electrode and the surrounding Schottky electrode is substantially uniform throughout the periphery of the ohmic electrode. As a result, current flows evenly throughout the entire area of the cell, which can contribute to an increase in current capacity. In addition, since the electric field around the ohmic electrode becomes uniform, concentration of the electric field can be avoided, which can contribute to the improvement of the breakdown voltage.

  According to a third aspect of the present invention, in the first or second aspect, the Schottky electrode has an inner edge of a regular polygon having six or more vertices in each cell centered on the ohmic electrode of each cell. The nitride semiconductor Schottky barrier diode described. Since the ohmic electrodes are dispersed on the surface of the second nitride semiconductor layer in a six-fold symmetrical arrangement, the Schottky electrodes surrounding each ohmic electrode can be arranged so as to partition regular hexagonal cells. Therefore, the Schottky electrode can be formed to have a regular hexagonal inner edge in each cell, and can also be formed to have a regular polygonal inner edge having six or more vertices in each cell. Thereby, since the distance from each position of the inner edge of the Schottky electrode to the ohmic electrode can be made substantially uniform, the current flowing between the Schottky electrode and the ohmic electrode passes through almost the entire region in the cell. Thus, the current path can be widened. In addition, since a voltage is applied substantially evenly between each position on the inner edge of the Schottky electrode and the ohmic electrode, concentration of the electric field can be avoided, thereby improving the breakdown voltage.

  According to a fourth aspect of the present invention, the ohmic electrode has a regular polygonal outer shape having six or more vertices, and the Schottky electrode is configured such that the outer shape of the ohmic electrode is formed radially from the center of the ohmic electrode. 4. The nitride semiconductor Schottky barrier diode according to claim 1, wherein each cell has a similar inner edge obtained by enlargement. 5. According to this configuration, the outer edge of the ohmic electrode and the inner edge of the Schottky electrode are both regular polygons having six or more vertices, and the distance from the outer edge of the ohmic electrode to the inner edge of the Schottky electrode is Nearly uniform around. As a result, the current flows more evenly in the cell, so that the current path can be widened, and the electric field around the ohmic electrode becomes almost uniform, so that the breakdown voltage can be improved.

  The invention according to claim 5 is the nitride semiconductor Schottky barrier according to any one of claims 1 to 4, wherein the Schottky electrode has a regular polygonal inner edge with rounded corners in each cell. It is a diode. According to this configuration, the distance from the ohmic electrode to the inner edge of the Schottky electrode can be made substantially uniform around the ohmic electrode. As a result, the current path can be effectively expanded and the breakdown voltage can be improved.

  The invention according to claim 6 is the nitride semiconductor Schottky barrier diode according to claim 1, wherein the Schottky electrode has a circular inner edge centered on the ohmic electrode of each cell in each cell. is there. According to this configuration, since the inner edge of the Schottky electrode is circular, the distance to the Schottky electrode can be made substantially uniform around the ohmic electrode. As a result, the current path can be effectively expanded and the breakdown voltage can be improved.

  According to a seventh aspect of the present invention, a plurality of cells having the same shape and the same size are spread on the surface of the second nitride semiconductor layer without gaps between the cells, and the Schottky electrode is disposed between adjacent cells. Is a nitride semiconductor Schottky barrier diode according to any one of claims 1 to 6. According to this configuration, since a plurality of cells are spread without gaps and the Schottky electrode is shared between adjacent cells, a current path between the Schottky electrode and the ohmic electrode can be formed by efficiently using the chip surface. . Thereby, the current path can be widened.

The invention according to claim 8 is the nitride semiconductor Schottky barrier diode according to any one of claims 1 to 7, wherein a distance between the ohmic electrode and the Schottky electrode in each cell is 1 μm to 10 μm. It is. With this configuration, it is possible to secure a wide current path by laying cells on the surface of the second nitride semiconductor layer at a high density while securing a sufficient breakdown voltage.
The invention according to claim 9 is an insulating film formed on the second nitride semiconductor layer so as to cover the ohmic electrode and the Schottky electrode, and the ohmic via the contact hole formed in the insulating film. The nitride semiconductor Schottky barrier diode according to any one of claims 1 to 8, further comprising a wiring film connected to the electrode and formed on the insulating film. According to this configuration, the ohmic electrodes distributed on the surface of the second nitride semiconductor layer are connected to the wiring film disposed on the insulating film. Thereby, the ohmic electrode surrounded by the Schottky electrode can be connected to the outside. Further, a plurality of distributed ohmic electrodes can be commonly connected to the wiring film on the insulating film.

  A tenth aspect of the present invention is the nitride semiconductor Schottky barrier diode according to the ninth aspect, further comprising a pad electrode disposed on the wiring film on the active region where the cell is disposed. With this configuration, the pad electrode can be disposed so as to overlap the active region where the cell is disposed. Thereby, the surface of the chip can be used efficiently. That is, it is possible to arrange an active region for arranging cells without securing a dedicated region for the pad electrode. As a result, a large number of cells can be arranged, so that the current path can be widened while suppressing the chip size.

  The invention according to claim 11 is the nitride semiconductor Schottky barrier according to any one of claims 1 to 10, wherein the first nitride semiconductor layer is made of GaN and the second nitride semiconductor layer is made of AlGaN. It is a diode. According to this configuration, the first nitride semiconductor layer and the second nitride semiconductor layer form a heterojunction of GaN / AlGaN. Thereby, a two-dimensional electron gas is formed near the interface between the first nitride semiconductor layer made of GaN and the second nitride semiconductor layer made of AlGaN. Since the current path between the Schottky electrode and the ohmic electrode can be formed via the two-dimensional electron gas, a nitride semiconductor Schottky barrier diode that has a wide current path and can operate at high speed can be provided.

FIG. 1 is a perspective view showing the appearance of a nitride semiconductor Schottky barrier diode according to an embodiment of the present invention. FIG. 2 is a plan view of the nitride semiconductor Schottky barrier diode. FIG. 3 is an enlarged plan view for explaining the arrangement of diode cells in the active region of the nitride semiconductor Schottky barrier diode. FIG. 4 is a further enlarged plan view for explaining the arrangement of the plurality of diode cells. FIG. 5 is a cross-sectional view showing the cross-sectional structure taken along the section line VV in FIG. 2 with the intermediate portion omitted. FIG. 6 is an illustrative plan view showing an enlarged structure of one diode cell. FIG. 7A is a cross-sectional view for explaining the manufacturing process for the nitride semiconductor Schottky barrier diode. FIG. 7B is a cross-sectional view showing a step subsequent to FIG. 7A. FIG. 7C is a cross-sectional view showing a step subsequent to FIG. 7B. FIG. 7D is a cross-sectional view showing a step subsequent to FIG. 7C. FIG. 7E is a cross-sectional view showing a step subsequent to FIG. 7D. FIG. 7F is a cross-sectional view showing a step subsequent to FIG. 7E. FIG. 8 is an enlarged plan view for explaining the configuration of a nitride semiconductor Schottky barrier diode according to the second embodiment of the present invention. FIG. 9 is an enlarged plan view for explaining the structure of a nitride semiconductor Schottky barrier diode according to the third embodiment of the present invention. FIG. 10 is an enlarged plan view for explaining a configuration of a nitride semiconductor Schottky barrier diode according to a comparative example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a perspective view showing an appearance of a nitride semiconductor Schottky barrier diode 1 according to an embodiment of the present invention.
The nitride semiconductor Schottky barrier diode 1 is a substantially rectangular parallelepiped chip-like electronic device, and has a rectangular main surface 2 having a vertical and horizontal length of about 1 mm to 2 mm, for example. On one main surface 2 of the nitride semiconductor Schottky barrier diode 1, an anode pad 3 and a cathode pad 4 are arranged. More specifically, the anode pad 3 and the cathode pad 4 are formed in a linear strip shape along two opposite sides 2 a and 2 b of the main surface 2 of the nitride semiconductor Schottky barrier diode 1.

  For example, four nitride semiconductor Schottky barrier diodes 1 can be combined to form a rectifier circuit including a diode bridge. Such a rectifier circuit can be provided, for example, in a power receiving circuit of a wireless power feeding system. A Schottky barrier diode using a nitride semiconductor has a large current value per unit area and can operate at a high speed, and thus can be reduced in size and increased in current.

In the rectifier circuit as described above, for example, four nitride semiconductor Schottky barrier diodes are connected to a wiring board by wire bonding or flip chip bonding, and the four nitride semiconductor Schottky barrier diodes 1 are resin-sealed together with the wiring board. Then, it may be configured as one package.
FIG. 2 is a plan view of the nitride semiconductor Schottky barrier diode 1 and shows a plan view overlooking the main surface 2 on which the anode pad 3 and the cathode pad 4 are formed.

A cathode wiring film 6 is formed on the main surface 2 of the nitride semiconductor Schottky barrier diode 1. In this embodiment, the cathode wiring film 6 is formed in a substantially rectangular shape in a region avoiding the anode pad 3. The cathode wiring film 6 is formed so as to cover most of the region of the main surface 2 of the nitride semiconductor Schottky barrier diode 1.
Below the cathode wiring film 6, an active region 10 in which a large number of diode cells are arranged is provided. In this embodiment, the active region 10 is formed in a comb shape. Specifically, the active region 10 includes a connection region 11 formed in a strip shape along the cathode pad 4 and a plurality of finger-like regions 12 extending linearly parallel to each other from the connection region 11 toward the anode pad 3. And have. The plurality of finger-shaped regions 12 are arranged in parallel to each other at intervals in the longitudinal direction of the connection region 11.

FIG. 3 is an enlarged plan view for explaining the arrangement of the diode cells D in the active region 10.
In the active region 10, a plurality of diode cells D having the same shape and the same size are arranged without gaps. The plurality of diode cells D are formed in a regular hexagon in this embodiment. In the center of each diode cell D, an ohmic electrode 15 is disposed. A Schottky electrode 16 is formed around the ohmic electrode 15 so as to surround the ohmic electrode 15. The Schottky electrode 16 is formed in a knitted pattern having a honeycomb structure that partitions the plurality of diode cells D.

  The Schottky electrode 16 is integrally coupled to an anode electrode lead-out portion 17 formed outside the active region 10. The anode electrode lead-out portion 17 is formed in a comb shape that meshes with the active region 10. Specifically, the anode electrode lead-out portion 17 is provided below the anode pad 3, a connection portion 18 formed in a strip shape along the anode pad 3, and a linear shape from the connection portion 18 toward the cathode pad 4. And a plurality of finger-like portions 19 extending in the direction. The plurality of finger-like portions 19 are arranged at intervals along the longitudinal direction of the connecting portion 18 and extend linearly in parallel with each other. The plurality of finger portions 19 are arranged so as to mesh with the finger regions 12 of the active region 10.

FIG. 4 is a further enlarged plan view for explaining the arrangement of the plurality of diode cells D. FIG. FIG. 5 is a cross-sectional view showing the cross-sectional structure taken along the section line VV in FIG. 2 with the intermediate portion omitted.
The nitride semiconductor Schottky barrier diode 1 includes a substrate 30, a first nitride semiconductor layer 31 formed on the substrate 30, and a second nitride semiconductor layer 32 stacked so as to be in contact with the first nitride semiconductor layer 31. Including. The substrate 30 may be a silicon substrate, for example. The first nitride semiconductor layer 31 is made of non-doped GaN, for example. The second nitride semiconductor layer 32 is made of, for example, AlGaN.

  Thus, the first nitride semiconductor layer 31 and the second nitride semiconductor layer 32 are made of nitride semiconductors having different compositions. Therefore, the first nitride semiconductor layer 31 and the second nitride semiconductor layer 32 form a heterojunction. Thereby, a two-dimensional electron gas 33 is formed in the first nitride semiconductor layer 31 close to the interface between the first nitride semiconductor layer 31 and the second nitride semiconductor layer 32. That is, the first nitride semiconductor layer 31 is an electron transit layer in which electrons as carriers travel, and the second nitride semiconductor layer 32 is an electron supply layer that supplies electrons.

  A plurality of ohmic electrodes 15 are uniformly distributed on the surface of the second nitride semiconductor layer 32. More specifically, the plurality of ohmic electrodes 15 are uniformly distributed on the surface of the second nitride semiconductor layer 32 in the active region 10, and each of them is formed of the second nitride semiconductor layer 32. There is ohmic contact with the surface. The ohmic electrode 15 may be formed of a laminated electrode film of a Ti layer (for example, 200 mm thick) in contact with the second nitride semiconductor layer 32 and an Al layer (for example, 4000 mm thick) laminated on the Ti layer.

  The plurality of ohmic electrodes 15 are arranged on the surface of the second nitride semiconductor layer 32 so as to have a six-fold symmetry arrangement. More specifically, when attention is paid to one ohmic electrode 15, the other six adjacent one ohmic electrodes 15 are arranged so as to have a six-fold symmetrical arrangement around the one ohmic electrode 15. The ohmic electrode 15 is located. That is, there are six other ohmic electrodes 15 that are adjacent to each other with an equal distance (for example, about 20 μm) from one ohmic electrode 15, and these six ohmic electrodes 15 are connected by line segments. Thus, a regular hexagon 21 surrounding one ohmic electrode 15 is formed at the center position (center of gravity position) on the inside.

  A predetermined distance (about 1 to 10 μm, for example, 9 μm) is opened from the ohmic electrode 15 so that each line segment of the regular hexagon 21 is vertically divided into two equal parts, and the Schottky electrode 16 is patterned. Yes. That is, the Schottky electrode 16 is formed in a mesh pattern having a center line 22 of a regular hexagon (six-fold symmetrical shape) disposed around each ohmic electrode 15 and surrounding the ohmic electrode 15. The center line 22 of the Schottky electrode 16 is a virtual line passing through the center of the Schottky electrode 16 in the width direction. In this embodiment, the Schottky electrode 16 is formed in a substantially uniform band shape.

Each ohmic electrode 15 is isolated on the surface of the second nitride semiconductor layer 32 by being surrounded by the Schottky electrode 16. Schottky electrode 16 may be composed of a laminated electrode film of a Ni layer (for example, 100 Å thick) in contact with the surface of second nitride semiconductor layer 32 and an Au layer (for example, 3,000 Å thick) laminated on this Ni layer. .
A protective film 35 that covers a region other than the ohmic electrode 15 and the Schottky electrode 16 is formed on the surface of the second nitride semiconductor layer 32. The protective film 35 is made of an insulating film such as a SiN film (for example, a thickness of about 750 mm). Further, an interlayer insulating film 36 is formed so as to cover the ohmic electrode 15 and the Schottky electrode 16. The thickness of the interlayer insulating film 36 is preferably 300 nm or more. In this embodiment, it is, for example, about 1 μm. In this embodiment, the interlayer insulating film 36 is a laminated film in which a first layer 37 made of, for example, SOG (Spin-on-Glass) and a second layer 38 made of, for example, SiO ₂ are laminated thereon. Consists of. The first layer 37 is a layer for planarization, and has a thickness of about 3000 mm, for example. The thickness of the second layer 38 is, for example, about 7000 mm.

  A cathode contact hole 44 is formed in the interlayer insulating film 36 immediately above each ohmic electrode 16. Further, an anode contact hole 43 is formed in the interlayer insulating film 36 immediately above the connection portion 18 of the anode electrode lead-out portion 17. A cathode wiring film 6 is formed on the interlayer insulating film 36, and the cathode wiring film 6 is commonly connected to all the ohmic electrodes 15 through a cathode contact hole 44. A cathode pad 4 is formed on the cathode wiring film 6. On the other hand, the anode pad 3 is connected to the connection portion 18 of the anode electrode lead-out portion 17 through an anode contact hole 43 formed in the interlayer insulating film 36. The cathode wiring film 6 can be formed of, for example, an Al wiring film, and the film thickness thereof may be about 2 μm. The anode pad 3 and the cathode pad 4 may be formed of, for example, an Au layer of about 500 mm when performing flip bonding and 5000 mm when performing wire bonding.

FIG. 6 is an illustrative plan view showing an enlarged structure of one diode cell D. FIG.
In this embodiment, the ohmic electrode 15 has a regular hexagonal outer edge 23. The size of the ohmic electrode 15 may be, for example, such that the distance (diameter of the inscribed circle) between a pair of opposing parallel sides of a regular hexagon formed by the outer edge 23 is about 4 μm. .
The regular hexagon formed by the outer edge 23 of the ohmic electrode 15 is similar to the regular hexagon formed by the center line 22 of the Schottky electrode 16 surrounding one diode cell D, and they share a center, Each of the six vertices of the regular hexagon is located on six straight lines 24 that extend radially from the center 15c of the ohmic electrode 15 at equal angular intervals. In other words, the center line 22 of the Schottky electrode 16 is formed in a similar shape obtained by radially expanding the shape of the outer edge 23 of the ohmic electrode 15 from the center 15 c of the ohmic electrode 15.

  Further, in this embodiment, the inner edge 25 of the Schottky electrode 16 is formed in a similar shape obtained by radially expanding the shape of the outer edge 23 of the ohmic electrode 15 from the center 15 c of the ohmic electrode 15. Therefore, the inner edge 25 of the Schottky electrode 16 forms a regular hexagon obtained by slightly reducing the regular hexagon formed by the center line 22 of the Schottky electrode 16. The regular hexagon formed by the center line 22 of the Schottky electrode 16 defines one diode cell D. The regular hexagon formed by the inner edge 25 of the Schottky electrode 16 defines a current path through which current flows in the diode cell D. The width of the Schottky electrode 16 may be approximately the same as the size of the ohmic electrode 15 (for example, approximately 4 μm).

  The distance from the ohmic electrode 15 to the Schottky electrode 16 is represented by the distance between the outer edge 23 of the ohmic electrode 15 and the inner edge 25 of the Schottky electrode 16. The shortest distance Lac1 expressed by the distance between one side of the outer edge 23 of the ohmic electrode 15 and one side of the inner edge 25 of the Schottky electrode 16 parallel to the outer edge 23, and one vertex of the outer edge 23 of the ohmic electrode 15 and the Schottky opposite thereto. The longest distance Lac2 represented by the length of a line segment connecting one vertex of the inner edge 25 of the electrode 16 satisfies the relationship Lac2 = (2 / √3) · Lac1. Therefore, since the difference between the shortest distance Lac1 and the longest distance Lac2 can be regarded as almost equal, a current path having a substantially uniform electric resistance is provided between the ohmic electrode 15 and the Schottky electrode 16 around the entire circumference. It can be said that it is formed. As a result, current flows almost evenly around the entire circumference of the ohmic electrode 15, so that almost the entire area in the diode cell D contributes to conductance, and a wide current path can be secured. Furthermore, since the difference between the shortest distance Lac1 and the longest distance Lac2 is negligible, the electric field between the ohmic electrode 15 and the Schottky electrode 16 is substantially uniform over the entire circumference around the ohmic electrode 15, Electric field concentration does not occur. Therefore, the breakdown voltage can be improved. For example, the shortest distance Lac1 may be 1 nm to 10 nm (for example, 9 nm).

  For example, as in the comparative example shown in FIG. 10, a structure in which the active region is filled with the square diode cell D ′ may be considered. However, in such a square diode cell D ′, the relationship between the shortest distance Lac1 and the longest distance Lac2 between the ohmic electrode 15 ′ and the Schottky electrode 16 ′ is Lac2 = √2 · Lac1, which can be regarded as equivalent. It's not about. Therefore, the current concentrates on the path along the shortest distance Lac1, and the area contributing to the conductance in the active region is reduced. Therefore, the substantial current path is narrowed, and the current density is accordingly reduced and the electric resistance is increased. . In addition, since the electric field around the anode electrode is not uniform, the electric field tends to be concentrated, and it is necessary to open a wide gap between the anode electrode and the Schottky electrode in order to obtain a good breakdown voltage. Therefore, the arrangement density of the diode cells is reduced, and the current capacity is reduced.

In addition to regular hexagons, regular polygons of the same size that can lay flat surfaces without gap include squares and regular triangles as described above. However, both the square and the equilateral triangle have a large variation in distance from the center to the side (difference between the shortest distance and the longest distance), and there is the above-described problem described with reference to the comparative example of FIG.
On the other hand, regular hexagons are the same size and have the largest number of vertices among regular polygons that can be stacked and accumulated on a plane without gaps, and are therefore closest to a circle. Therefore, variation in the distance from the center to the side is small, and the area on the plane can be efficiently used and integrated at a high density. Therefore, the structure in which regular hexagonal diode cells D of the same size are spread over the active region 10 on the surface of the second nitride semiconductor layer 32 can contribute almost all the region in the diode cell D to conductance, and As a result of the high density integration, the current capacity can be increased.

  Although it may be considered to use a plurality of types of diode cells having different sizes or shapes, the current concentrates on the path where the distance between the ohmic electrode and the Schottky electrode is the shortest, leading to a decrease in conductance. In addition, the breakdown voltage may decrease due to the concentration of the electric field. Therefore, it is preferable to spread diode cells of the same shape and size in the active region 10.

FIGS. 7A to 7F are cross-sectional views illustrating steps of manufacturing a nitride semiconductor Schottky barrier diode in the order of steps.
First, as shown in FIG. 7A, a first nitride semiconductor layer 31 made of, for example, GaN and a second nitride semiconductor layer 32 made of, for example, AlGaN are epitaxially grown on a silicon substrate in this order. Next, as shown in FIG. 7B, a protective film 35 made of, for example, SiN is formed on the surface of the second nitride semiconductor layer 32.

  Next, as shown in FIG. 7C, ohmic electrode openings 54 that match the pattern of the ohmic electrode 15 are formed in the protective film 35 by, for example, dry etching. The ohmic electrode 15 is formed in the opening 54. As described above, the ohmic electrode 15 may be a laminated electrode film in which a Ti layer in ohmic contact with the second nitride semiconductor layer 32 and an Al layer laminated on the Ti layer are laminated. The ohmic electrode 15 may be formed by a lift-off method. Specifically, after a resist film having a pattern exposing the opening 54 is formed, a Ti layer and an Al layer are sequentially formed by, for example, vapor deposition, and then unnecessary portions of the Ti layer and the Al layer are removed together with the resist film. That's fine.

  Next, as shown in FIG. 7D, the Schottky electrode opening 53 that matches the pattern of the Schottky electrode 16 and the anode electrode lead portion 17 integrated therewith is formed in the protective film 35 by dry etching. This dry etching is performed under the condition that the ohmic electrode 15 is not etched. The opening 53 is formed in the pattern of the Schottky electrode 16 in the active region 10, and is formed in the pattern of the anode electrode lead-out portion 17 outside the active region 10. Next, the Schottky electrode 16 and the anode electrode lead portion 17 are formed in the opening 53. As described above, the Schottky electrode 16 may be a stacked electrode film including a Ni layer that is Schottky bonded to the second nitride semiconductor layer 32 and an Au layer that is stacked on the Ni layer. The formation of the Schottky electrode 16 and the anode electrode lead-out portion 17 may be performed by a lift-off method. Specifically, a resist film having a pattern exposing the opening 53 is formed, and an Ni layer and an Au layer are sequentially formed on the resist film, for example, by vapor deposition, and then the unnecessary Ni layer and Au layer are removed together with the resist film. do it.

Next, as shown in FIG. 7E, an interlayer insulating film 36 is formed so as to cover the ohmic electrode 15 and the Schottky electrode 16. As described above, the interlayer insulating film 36 may be a laminated film of a first layer 37 made of SOG (for example, 3000 Å thick) and a second layer 38 made of an SiO ₂ layer (for example 7000 Å thick). The first layer 37 made of SOG relaxes the step between the protective film 35 and the electrodes 15 and 17 and provides a flat surface. A second layer 38 is formed on the flat surface.

Next, as shown in FIG. 7F, an anode contact hole 43 and a cathode contact hole 44 are opened in the interlayer insulating film 36. Then, after a wiring film made of, for example, aluminum is formed on the entire surface, this wiring film is etched into the pattern of the cathode wiring film 6.
Thereafter, as shown in FIG. 5, the cathode pad 4 is formed on the cathode wiring film 6, and at the same time, the anode pad 3 embedded in the anode contact hole 43 is formed. The cathode pad and the anode pad may be formed, for example, by vapor deposition of gold (Au). Thus, the nitride semiconductor Schottky barrier diode 1 having the above-described structure can be obtained.

  As described above, according to this embodiment, a plurality of ohmic electrodes 15 are formed such that six adjacent ohmic electrodes 15 are positioned so as to have a six-fold symmetrical arrangement around one ohmic electrode 15. The second nitride semiconductor layer 32 is distributed on the surface. A Schottky electrode 16 is formed in a mesh structure having a honeycomb structure so as to surround each ohmic electrode 15, thereby dividing a plurality of diode cells D surrounding each ohmic electrode 15. As a result, a plurality of diode cells D are spread on the surface of the second nitride semiconductor layer 32, and a current path is formed between the ohmic electrode 15 of each diode cell D and the Schottky electrode 16 surrounding it. As a result, a wide current path can be secured, thereby increasing the current of the nitride semiconductor Schottky barrier diode 1. Moreover, since the current capacity (current density) per unit area can be increased, the nitride semiconductor Schottky barrier diode 1 can be reduced in size.

  Further, the Schottky electrode 16 has a mesh structure having a regular hexagonal center line 22 surrounding each ohmic electrode 15. Thereby, the distance between the ohmic electrode 15 and the Schottky electrode 16 can be made almost uniform everywhere while the electrode width of the Schottky electrode 16 is made almost uniform. Thereby, substantially the entire region in the diode cell D becomes a current path, which can contribute to the expansion of the current path. In addition, since the electric field between the ohmic electrode 15 and the Schottky electrode 16 becomes substantially uniform around the ohmic electrode 15, concentration of the electric field can be avoided and the breakdown voltage can be improved.

  The ohmic electrodes 15 are evenly distributed on the surface of the active region 10 of the second nitride semiconductor layer 32, and are equilateral hexagonal diodes having the same shape and the same size so as to surround and surround the respective ohmic electrodes 15. Cell D is partitioned by Schottky electrode 16. As a result, the diode cells D having the same shape and the same size can be efficiently spread in the active region 10, and a current flows equally to all the diode cells D arranged in the active region 10. Thereby, substantially the entire region of the active region 10 becomes a current path, so that the current capacity can be further increased. Further, in all the diode cells D, a voltage is evenly applied between the ohmic electrode 15 and the Schottky electrode 16, which can contribute to an improvement in breakdown voltage.

  In this embodiment, the ohmic electrode 15 has a regular hexagonal outer edge 23, and the Schottky electrode 16 is obtained by radially expanding the outer edge of the ohmic electrode 15 from the center 15 c of the ohmic electrode 15. Each diode cell D has a similar inner edge 25. Thereby, the distance from the outer edge 23 of the ohmic electrode 15 to the inner edge 25 of the Schottky electrode 16 becomes substantially uniform around the ohmic electrode 15. As a result, current flows more evenly in the diode cells D, so that the current path can be widened, and the electric field around the ohmic electrode 15 is almost uniform, so that the breakdown voltage can be improved.

  Furthermore, in this embodiment, a plurality of diode cells D having the same shape and the same size are spread on the surface of the second nitride semiconductor layer 32 without having a gap between the diode cells D, and adjacent diode cells D The Schottky electrode 16 is shared between them. Thereby, a current path between the Schottky electrode and the ohmic electrode can be formed by efficiently using the chip surface. Thereby, the current path can be widened.

In each diode cell D, the distance between the ohmic electrode 15 and the Schottky electrode 16 is preferably 1 μm to 10 μm. As a result, while ensuring a sufficient breakdown voltage (for example, a reverse breakdown voltage of 600 V), the diode cells D are laid on the surface of the second nitride semiconductor layer 32 at a high density, and a wide current path can be secured.
Further, in this embodiment, the ohmic electrodes 15 distributed on the surface of the second nitride semiconductor layer 32 are connected to the cathode wiring film 6 disposed on the interlayer insulating film 36. Thereby, each ohmic electrode 15 surrounded and isolated by the Schottky electrode 16 can be connected to the outside. In addition, a plurality of ohmic electrodes 15 arranged in a distributed manner can be commonly connected to the cathode wiring film 6 on the interlayer insulating film 36.

  In this embodiment, as shown in FIG. 2 and the like, the cathode pad 4 is disposed above the active region 10 with the interlayer insulating film 36 and the like interposed therebetween. Thereby, the surface of the chip can be used efficiently. That is, the active region 10 can be arranged without securing a dedicated region for the cathode pad 4. Thereby, since the active region 10 can be widened and a large number of diode cells D can be arranged, the current path can be widened without increasing the chip size.

  In this embodiment, the first nitride semiconductor layer 31 and the second nitride semiconductor layer 32 form a heterojunction of GaN / AlGaN. Thereby, a two-dimensional electron gas 33 is formed in the vicinity of the interface between the first nitride semiconductor layer 31 and the second nitride semiconductor layer 32. Since the current path between the Schottky electrode 16 and the ohmic electrode 15 can be formed via the two-dimensional electron gas 33, the nitride semiconductor Schottky barrier diode 1 having a wide current path and capable of high-speed operation can be provided.

FIG. 8 is a diagram for explaining the configuration of a nitride semiconductor Schottky barrier diode 60 according to the second embodiment of the present invention, and is a plan view showing the structure of the diode cell D in an enlarged manner. In FIG. 8, the same reference numerals are given to the corresponding parts of the respective parts shown in FIG.
In this embodiment, the Schottky electrode 16 is different from the first embodiment in the shape of the inner edge 25 facing the ohmic electrode 15. That is, in each diode cell D, the inner edge 25 of the Schottky electrode 16 that faces the ohmic electrode 15 is formed in a substantially regular hexagonal shape, and a round portion 25r that protrudes outward at each vertex position of the regular hexagon. Is provided. Corresponding to this, the ohmic electrode 15 has a substantially regular hexagonal planar shape, and round portions 15r convex outward are provided at six vertex positions thereof.

  With this configuration, the difference between the shortest distance Lac1 and the longest distance Lac2 between the ohmic electrode 15 and the Schottky electrode 16 is further reduced, so that an equal current flows in the entire area around the ohmic electrode 15, thereby a substantial current. The route is expanded. Further, since the electric field between the ohmic electrode 15 and the Schottky electrode 16 becomes substantially uniform over the entire circumference of the ohmic electrode 15, concentration of the electric field can be avoided and the breakdown voltage can be improved accordingly.

FIG. 9 is a diagram for explaining the configuration of a nitride semiconductor Schottky barrier diode 70 according to the third embodiment of the present invention, and is a plan view schematically showing the configuration of the diode cell D in an enlarged manner. 9, parts corresponding to those in FIG. 6 are given the same reference numerals.
In this embodiment, the inner edge 25 of the Schottky electrode 16 is formed in a circular shape. Accordingly, the outer edge 23 of the ohmic electrode 15 is also formed in a circular shape concentric with the inner edge 25 of the Schottky electrode 16. As a result, the distance between the ohmic electrode 15 and the Schottky electrode 16 is constant in any direction around the ohmic electrode 15. As a result, a uniform current path is formed over the entire circumference of the ohmic electrode 15, so that the substantial current path can be expanded. Further, since the distance between the ohmic electrode 15 and the Schottky electrode 16 is constant everywhere, the concentration of the electric field can be avoided, and the breakdown voltage can be improved accordingly.

  In the comparative example having the square diode cell shown in FIG. 10, it may be considered that the inner edge of the Schottky electrode 16 'is circular. However, in such a configuration, the width of the Schottky electrode 16 'becomes very large in a region where four square diode cells gather, and a region (dead space) that does not contribute to element operation on the chip becomes wide. As a result, the integration density of the diode cells D is reduced, and there is a possibility that the substantial current path of the entire chip cannot be made too wide.

  As mentioned above, although embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, the shape of the inner edge 25 of the Schottky electrode 16 is a regular hexagon (FIG. 6), a regular hexagon (FIG. 8) in which a round portion is formed at each vertex, and a circle (FIG. 9). Although the example has been described, the inner edge 25 of the Schottky electrode 16 may be formed into another regular polygon having seven or more vertices, for example, a regular octagon, a regular dodecagon, or the like. And you may provide a round shape part in the vertex position of the inner edge of a regular polygon with seven or more vertices. In the above-described embodiment, the outer edge 23 of the ohmic electrode 15 and the inner edge 25 of the Schottky electrode 16 are similar to each other. However, the outer edge 23 of the ohmic electrode 15 and the inner edge 25 of the Schottky electrode 16 are not necessarily similar. It need not be in shape. For example, the outer edge 23 of the ohmic electrode 15 may be circular, and the inner edge 25 of the Schottky electrode 16 may be a regular hexagon. The inner edge 25 of the Schottky electrode 16 may be circular, while the outer edge 23 of the ohmic electrode 15 may be a regular hexagon. Further, the shapes of the outer edge 23 of the ohmic electrode 15 and the inner edge 25 of the Schottky electrode 16 may be regular polygons having six or more vertices and different numbers of vertices.

In the above-described embodiment, the anode pad 3 does not overlap the active region 10, but the anode pad 3 may be disposed on the interlayer insulating film 36 above the active region 10. This eliminates the need for a dedicated arrangement space for the anode pad 3, thereby further widening the active region 10.
In addition, various design changes can be made within the scope of matters described in the claims.

D Diode cell 1 Nitride semiconductor Schottky barrier diode 3 Anode pad 4 Cathode pad 6 Cathode wiring film 10 Active region 15 Ohmic electrode 15c Center of ohmic electrode 15r Round part 16 Schottky electrode 17 Anode electrode lead-out part 21 Regular hexagon formed by ohmic electrode 22 Schottky electrode center line 23 Outer edge of ohmic electrode 24 Line segment connecting between centers of ohmic electrodes 25 Inner edge of Schottky electrode 25r Round portion 30 Substrate 31 First nitride semiconductor layer 32 Second nitride semiconductor layer 33 Two-dimensional electron gas 35 Protective film 36 Interlayer insulating film 37 First layer (SOG)
38 Second layer (SiO ₂ )
43 Anode contact hole 44 Cathode contact hole 53 Schottky electrode opening 54 Ohmic electrode opening 60 Nitride semiconductor Schottky barrier diode 70 Nitride semiconductor Schottky barrier diode

Claims (11)

A first nitride semiconductor layer made of a nitride semiconductor;
A second nitride semiconductor layer that is stacked on the first nitride semiconductor layer and is made of a nitride semiconductor having a composition different from that of the first nitride semiconductor layer;
A plurality of ohmic electrodes disposed in an ohmic contact with the surface of the second nitride semiconductor layer and dispersed on the surface of the second nitride semiconductor layer;
A Schottky electrode in Schottky contact with the surface of the second nitride semiconductor layer,
The plurality of ohmic electrodes are formed on the surface of the second nitride semiconductor layer so that six adjacent ohmic electrodes are positioned so as to have a six-fold symmetrical arrangement around one ohmic electrode;
A nitride semiconductor Schottky barrier diode, wherein the Schottky electrode is formed in a mesh structure having a honeycomb structure surrounding each ohmic electrode and defining a plurality of cells. The plurality of ohmic electrodes are uniformly distributed on the surface of the active region of the second nitride semiconductor layer,
2. The nitride semiconductor Schottky barrier diode according to claim 1, wherein the plurality of cells have the same shape and the same size, and one ohmic electrode is disposed at the center of each cell.   3. The nitride semiconductor Schottky barrier diode according to claim 1, wherein each Schottky electrode has an inner edge of a regular polygon having six or more apexes centered on the ohmic electrode of each cell. 4. .   The ohmic electrode has a regular polygon outer edge having six or more vertices, and the Schottky electrode has a similar shape obtained by radially expanding the outer edge of the ohmic electrode from the center of the ohmic electrode. The nitride semiconductor Schottky barrier diode according to claim 1, wherein each cell has an inner edge.   The nitride semiconductor Schottky barrier diode according to any one of claims 1 to 4, wherein the Schottky electrode has a regular polygonal inner edge with rounded corners in each cell.   3. The nitride semiconductor Schottky barrier diode according to claim 1, wherein the Schottky electrode has a circular inner edge centered on the ohmic electrode of each cell in each cell.   The plurality of cells having the same shape and the same size are spread on the surface of the second nitride semiconductor layer without gaps between the cells, and the Schottky electrode is shared between adjacent cells. The nitride semiconductor Schottky barrier diode according to any one of 1 to 6.   The nitride semiconductor Schottky barrier diode according to any one of claims 1 to 7, wherein a distance between the ohmic electrode and the Schottky electrode in each cell is 1 µm to 10 µm. An insulating film formed on the second nitride semiconductor layer so as to cover the ohmic electrode and the Schottky electrode;
The nitride according to claim 1, further comprising a wiring film connected to the ohmic electrode through a contact hole formed in the insulating film and formed on the insulating film. Semiconductor Schottky barrier diode.   The nitride semiconductor Schottky barrier diode according to claim 9, further comprising a pad electrode disposed on the wiring film on the active region where the cell is disposed.   The nitride semiconductor Schottky barrier diode according to any one of claims 1 to 10, wherein the first nitride semiconductor layer is made of GaN, and the second nitride semiconductor layer is made of AlGaN.

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