JP2012019045A - Semiconductor rectifier element - Google Patents

Abstract

A Schottky diode using a nitride-based semiconductor material with improved reverse leakage characteristics is provided.
A buffer layer, a GaN layer, and an AlGaN layer are stacked on the surface side of a silicon substrate, and are in ohmic contact with the AlGaN layer on the AlGaN layer in an active region of these semiconductor layers. A cathode electrode 6 and an anode electrode 7 that is in Schottky contact with the AlGaN layer 5 are formed, and a stepped portion 5A in which the peripheral portion of the AlGaN layer 5 is removed and the GaN layer 4 is exposed is formed to circulate. . On the GaN layer 4 of the step portion 5A, an enclosing electrode 7A that is in Schottky contact with the GaN layer 4 is formed so as to surround the active region of the semiconductor layer. Here, the enclosing electrode 7A is set to the same potential as the anode electrode 7.
[Selection] Figure 2

Description

  The present invention relates to a semiconductor rectifier, and more particularly to a semiconductor rectifier using a nitride compound semiconductor.

GaN, formulas such as _{AlGaN Al x In y Ga 1-} x-y As u P v N 1-u-v ( where, 0 ≦ x ≦ 1,0 ≦ y ≦ 1, x + y ≦ 1,0 ≦ u <1 , 0 ≦ v <1, u + v <1), a semiconductor device using a nitride-based compound semiconductor is expected as a next-generation power device. Conventionally, devices using nitride-based compound semiconductors and GaN-based semiconductors have been manufactured using sapphire substrates and SiC substrates that facilitate crystal growth of GaN (see, for example, Patent Document 1).

  However, since the sapphire substrate and the SiC substrate are expensive, there is a problem that the cost of the device is increased. Therefore, it has been studied to use a silicon (Si) substrate that is cheaper than these substrates and that can be increased in diameter.

  As a semiconductor device using a silicon substrate, there is a Schottky diode 100 as shown in FIGS. 5 is a plan view of the Schottky diode 100, and FIG. 6 is a sectional view taken along line VI-VI in FIG. As shown in FIG. 6, the Schottky diode 100 includes a buffer layer 102 made of aluminum gallium nitride (AlGaN), a GaN layer 103, and an AlGaN layer 104 sequentially stacked on the surface side of the silicon substrate 101. An anode electrode 105 in Schottky contact with the AlGaN layer 104 and a cathode electrode 106 in ohmic contact with the AlGaN layer 104 are formed thereon. As shown in FIG. 5, the cathode electrode 106 is formed to surround the anode electrode 105 with a predetermined distance therebetween. A back electrode 107 is formed on the back side of the silicon substrate 101. At the periphery of the Schottky diode 100, an insulating region 108 is formed in which the AlGaN layer 104 is removed and the GaN layer 103 is exposed.

Japanese Patent Laid-Open No. 2004-247709

  However, in the above-described conventional Schottky diode 100, although the AlGaN layer 104 in the peripheral portion is removed and the insulating region (mesa isolation) 108 where the GaN layer 103 is exposed is formed as shown in FIG. The leakage current Ir (indicated by broken line arrows in FIG. 5) flowing through the surface of the insulating region 108 and the end face of the Schottky diode 100 is large, and it is difficult to keep the reverse leakage current low.

  The present invention has been made in view of the above, and an object of the present invention is to provide a semiconductor rectifier element using a nitride-based compound semiconductor material in which reverse leakage current is suppressed.

  In order to solve the above-described problems and achieve the object, the present invention provides a semiconductor rectifier in which an anode electrode and a cathode electrode are formed on the surface of a nitride compound semiconductor layer, the nitride compound An enclosing electrode that is in Schottky contact with the nitride-based compound semiconductor layer is formed so as to surround an outer periphery of an active region including a region where the anode electrode and the cathode electrode are formed in the semiconductor layer. Features.

  In the semiconductor rectifier according to the present invention, in the above invention, the nitride-based compound semiconductor layer is composed of a plurality of layers, and at least the uppermost layer of the nitride-based compound semiconductor layer in the region in contact with the surrounding electrode is It is removed, and at least the lowermost layer is left.

  The semiconductor rectifier according to the present invention is characterized in that, in the above-described invention, the nitride compound semiconductor layer in the portion in contact with the enclosing electrode has a high resistance.

  The semiconductor rectifier according to the present invention is characterized in that, in the above invention, a back electrode is formed on the back surface of the nitride-based semiconductor layer, and the enclosing electrode and the back electrode are set to the same potential. And

  In the semiconductor rectifier according to the present invention as set forth in the invention described above, the enclosing electrode is set to the same potential as the anode electrode.

  In the semiconductor rectifier according to the present invention as set forth in the invention described above, the nitride compound semiconductor layer is made of an AlGaN semiconductor.

  According to the present invention, in the semiconductor rectifying device using the nitride-based compound semiconductor layer, the surrounding electrode is arranged so as to be in Schottky contact with the nitride-based compound semiconductor layer so as to surround the outside of the active layer. There is an effect of reducing the leakage current flowing between the back surfaces.

FIG. 1 is a plan view of a semiconductor rectifying device according to Embodiment 1 of the present invention. 2 is a cross-sectional view taken along the line II-II in FIG. FIG. 3 is a cross-sectional view of a semiconductor rectifier according to Embodiment 2 of the present invention. FIG. 4 is a cross-sectional view of a semiconductor rectifier according to Embodiment 3 of the present invention. FIG. 5 is a plan view of a conventional semiconductor rectifier element. 6 is a cross-sectional view taken along the line VI-VI in FIG.

  Hereinafter, a semiconductor rectifying element as an embodiment for carrying out the present invention will be described with reference to the drawings. However, it should be noted that the drawings are schematic, and the thicknesses and ratios of the layers are different from actual ones. Moreover, the part from which the relationship and ratio of a mutual dimension differ also in between drawings is contained. Therefore, specific dimensions should be determined in consideration of the following description.

(Embodiment 1)
1 and 2 show a semiconductor rectifying device 1 according to a first embodiment of the present invention. FIG. 1 is a plan view of the semiconductor rectifying element 1, and FIG. 2 is a cross-sectional view taken along the line II-II of FIG. As shown in FIG. 2, in this semiconductor rectifier element 1, a buffer layer 3, a GaN layer 4, and an AlGaN layer 5 made of aluminum gallium nitride (AlGaN) are sequentially stacked on the surface side of a silicon substrate 2 by crystal growth. A cathode electrode 6 in ohmic contact with the AlGaN layer 5 and an anode electrode 7 in Schottky contact with the AlGaN layer 5 are formed on the AlGaN layer 5 in the active region of these semiconductor layers. Here, the active region includes a region where a two-dimensional electron gas (2DEG) is formed on the GaN layer 4 side from the interface between the GaN layer 4 and the AlGaN layer 5 and the cathode electrode 6 and the anode electrode 7 are formed. It is an area. As shown in FIG. 1, the cathode electrode 6 is formed so as to surround the anode electrode 7 with a predetermined distance therebetween. The lowermost layer of the cathode electrode 6 uses Ti that makes ohmic contact with the AlGaN layer 5, and the lowermost layer of the anode electrode 7 uses Ni that makes Schottky contact with the AlGaN layer 5.

  A back electrode 8 is formed on the back side of the silicon substrate 2. At the periphery of the semiconductor rectifying element 1, a stepped portion 5A is formed as an insulating region where the AlGaN layer 5 is removed and the GaN layer 4 is exposed. On the GaN layer 4 of the stepped portion 5A, an enclosing electrode 7A made of the same material as the anode electrode 7 is formed so as to surround the active region of the semiconductor layer and is in Schottky contact with the GaN layer 4. As shown in FIG. 1, the surrounding electrode 7 </ b> A is connected by a bonding wire 9 so as to have the same potential as the anode electrode 7. As shown in FIG. 1, the anode electrode 7 is also connected to a wiring 10 connected to an external circuit.

  In the semiconductor rectifying device 1 according to the present embodiment, an enclosing electrode 7A that is in Schottky contact with the underlying GaN layer 4 is provided along the outer peripheral edge, and the enclosing electrode 7A is further at the same potential as the anode electrode 7. Therefore, the remaining carriers in the step portion 5A as the insulating region can be depleted, and the leakage current flowing on the surface of the step portion 5A and the chip end surface can be reduced.

  Further, the potential of the anode electrode 7 and the surrounding electrode 7A and the potential of the back electrode 8 are set to be the same potential. For this reason, the electric field at the chip end face in the step portion 5A becomes weak, and the leakage current can be further reduced.

  Hereinafter, a method for manufacturing the semiconductor rectifying device 1 according to the present embodiment will be described. In the present embodiment, first, a buffer layer 3 made of aluminum gallium nitride (AlGaN), a GaN layer 4 and an AlGaN layer 5 are sequentially epitaxially grown on the silicon substrate 2 by MOCVD. In the present embodiment, the buffer layer 3 has a thickness of 30 nm, the GaN layer 4 has a thickness of 1 μm, and the AlGaN layer 5 has a thickness of 40 nm.

Next, a resist patterned into a shape that exposes the peripheral edge is formed on the AlGaN layer 5 by photolithography. Etching is then performed using this resist as a mask, and the AlGaN layer 5 is removed until the GaN layer 4 is exposed to form a stepped portion 5A. As this etching, reactive ion etching (RIE) using chlorine gas (Cl ₂ ) as an etching gas can be used. Thereafter, the resist mask is removed by ashing.

  Next, using a photolithography technique, a resist that exposes the cathode electrode pattern portion on the AlGaN layer 5 is processed, and Ti / Al / Ni / Au (300/220/40/50 nm) using this resist as a mask. The cathode electrode 6 is formed by vapor deposition. Then, using a lift-off method, unnecessary portions are removed together with the resist using acetone.

  In order to obtain ohmic contact between the cathode electrode 6 and the underlying AlGaN layer 5, annealing is performed at 750 ° C. for 30 seconds in a nitrogen atmosphere.

  Next, using a photolithography technique, a resist is processed into a desired pattern for forming the anode electrode 7 and the surrounding electrode 7A that are in Schottky contact with the base. Using this resist as a mask, Ni / Au (50/200 nm) is evaporated, and unnecessary portions are removed together with the resist by a lift-off method, thereby forming the anode electrode 7 and the enclosing electrode 7A.

  Thereafter, a back electrode 8 made of Ti / Ni / Au (50 nm / 500 nm / 50 nm) is formed on the back surface of the silicon substrate 2 by sputtering.

  Finally, after dicing to a desired chip size, the anode electrode 7 and the enclosing electrode 7A are connected by a bonding wire 9 so that they have the same potential, and mounted on a resin mold package, thereby completing the manufacture of the semiconductor rectifying device 1. .

(Embodiment 2)
FIG. 3 is a cross-sectional view of a semiconductor rectifying device 1A according to the second embodiment of the present invention, and is a cross-sectional view of a portion corresponding to the same position as FIG. 2 in the first embodiment.

  As shown in FIG. 3, the semiconductor rectifying device 1A according to this embodiment has no stepped portion 5A of the semiconductor rectifying device 1 according to the first embodiment, and the peripheral portion of the AlGaN layer 5 has a high resistance. It is a high resistance region 5B. An enclosing electrode 7A made of the same material as that of the anode electrode 7 is formed on the high resistance region 5B. Other configurations of the semiconductor rectifying device 1A according to this embodiment are the same as those of the semiconductor rectifying device 1 according to the first embodiment.

  In the present embodiment, boron (B) is ion-implanted into the AlGaN layer 5 to increase the resistance to form the high resistance region 5B. In this embodiment, since the AlGaN layer 5 is kept in a high resistance state by boron ion implantation, annealing for implant impurity activation is not performed. The method for increasing the resistance of the AlGaN layer 5 is not limited to this.

  In the semiconductor rectifying device 1A according to the present embodiment, the surrounding electrode 7A that is in Schottky contact with the base is provided along the outer peripheral edge, and the AlGaN layer 5 that is the base of the surrounding electrode 7A becomes the high resistance region 5B. Therefore, the leakage current flowing on the surface of the high resistance region 5B and the chip end surface can be reduced. In the present embodiment also, the enclosing electrode 7A is set to have the same potential as the anode electrode 7.

(Embodiment 3)
FIG. 4 shows a semiconductor rectifying device 1B according to a third embodiment of the present invention, in which the semiconductor layer of the portion forming the enclosing electrode 7A is composed of the buffer layer 3, the GaN layer 4, and the AlGaN layer 5, and is formed on the AlGaN layer 5. The enclosing electrode 7A that makes Schottky contact is formed, and has a simple structure as compared with the embodiment in which the step portion 5A and the high resistance region 5B are formed in the semiconductor layer as in the first and second embodiments.

  Also in the semiconductor rectifying device 1B according to this embodiment, the enclosing electrode 7A is set to have the same potential as the anode electrode 7. In addition, the enclosing electrode 7A and the back electrode 8 are set to have the same potential.

  In the semiconductor rectifying device 1B according to this embodiment, when a voltage is applied to the enclosing electrode 7A, the depletion layer spreads in the semiconductor layer including the AlGaN layer 5 and the reverse leakage current is prevented from flowing. There is an effect similar to that of the first and second embodiments.

(Other embodiments)
The embodiment of the present invention has been described above. However, the description and the drawings, which constitute a part of the disclosure of the above embodiment, do not limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, in Embodiments 1 and 2 described above, GaN and AlGaN are used as the nitride-based compound semiconductor layers, but the composition is preferably AlxGa (1-x) N (0 ≦ x ≦ 1). . InAlN may be used instead of AlGaN. In this case, InyAl (1-y) N (0 ≦ y ≦ 1) is preferable.

  In each of the above embodiments, the semiconductor layer has a three-layer structure of the buffer layer 3, the GaN layer 4, and the AlGaN layer 5, but may have a multilayer structure, and in this case, as in the second embodiment In the case of forming the stepped portion 5A, at least the uppermost layer may be removed so that at least the lowermost layer remains.

  As described above, the semiconductor rectifier according to the present invention is useful as a next-generation power device, and is particularly suitable for a Schottky diode.

1, 1A, 1B Semiconductor rectifier 2 Silicon substrate 3 Buffer layer 4 GaN layer 5 AlGaN layer 5A Stepped portion 5B High resistance region 7 Anode electrode 7A Enclosed electrode 8 Back surface electrode 9 Bonding wire

Claims (6)

A semiconductor rectifier in which an anode electrode and a cathode electrode are formed on the surface of a nitride compound semiconductor layer,
An enclosing electrode that is in Schottky contact with the nitride-based compound semiconductor layer is formed so as to surround an outer periphery of an active region including a region where the anode electrode and the cathode electrode are formed in the nitride-based compound semiconductor layer. A semiconductor rectifier element characterized by being made. The nitride-based compound semiconductor layer is composed of a plurality of layers,
2. The semiconductor rectifier according to claim 1, wherein at least an uppermost layer of the nitride-based compound semiconductor layer in a region in contact with the surrounding electrode is removed, and at least the lowermost layer is left.   2. The semiconductor rectifier according to claim 1, wherein the resistance of the nitride-based compound semiconductor layer in a portion in contact with the enclosing electrode is increased. A back electrode is formed on the back surface of the nitride-based compound semiconductor layer,
The semiconductor rectifying device according to claim 1, wherein the enclosing electrode and the back electrode are set to the same potential.   5. The semiconductor rectifier according to claim 1, wherein the enclosing electrode is set to the same potential as the anode electrode.   The semiconductor nitride rectifier according to claim 1, wherein the nitride compound semiconductor layer is made of an AlGaN semiconductor.

Images