JP2708829B2 - Method of forming electrode of silicon carbide - Google Patents

Description

The present invention relates to a method for forming an electrode of silicon carbide.

(B) Conventional technology Silicon carbide (SiC) has attracted attention as a semiconductor material that can operate at high temperatures and pressures, and is expected to be a blue light emitting device material because of its wide optical band gap and easy formation of a pn junction. ing.

Such a SiC semiconductor device has been conventionally used as an ohmic electrode in the fall meeting of the Japan Society of Applied Physics Fall 1987, 29a-W-1, 586.
As shown on the page, Al / Si is used on p-type SiC and Ni is used on n-type SiC.

FIG. 2 shows the structure of a conventional SiC semiconductor device, for example, a SiC light emitting diode. In the method for manufacturing such a SiC light emitting diode, for example, an n-type SiC layer (9) and a p-type SiC layer (10) are sequentially grown on one main surface of an n-type SiC substrate (8) by using the LPE method. Next, a Ni electrode film (11) is vacuum-deposited on the other main surface of the n-type SiC substrate (8), and this is heat-treated at 1000 ° C. for about 5 minutes. As a result, the n-type SiC substrate (8) and the Ni electrode film (1
1) alloys and obtains ohmic properties. Next, the n-type S
After the surface treatment of the iC substrate (8) by wet etching with hydrofluoric acid (HF), an Al / Si electrode film (12) is vacuum-deposited on the p-type SiC layer (10), and this is applied at 900 to 950 ° C. Heat treat for 5 minutes. As a result, the p-type SiC layer (10) and the Al / Si electrode film (1
2) alloys and obtains ohmic properties. Finally, an Au / Cr electrode film (13), which is well known as a wire bonding electrode, is laminated on the Ni electrode film (11) to obtain a SiC light emitting diode.

However, in such a conventional light emitting diode, the Ni electrode film (11) is slightly oxidized during the surface treatment with HF during the manufacturing process, so that the Au formed as an electrode for wire bonding is used.
Adhesion with Ni / Cr electrode film (13) is reduced, and Ni electrode film (11)
Peeling often occurs at the interface between the electrode and the Au / Cr electrode film (13). In order to solve this problem, for example, as shown in "Electronic Technology" published by Nikkan Kogyo Shimbun, Vol.
Used instead of 1). However, even in this method, during the heat treatment at 1000 ° C. performed after the formation of the Au / Ni electrode film, Au and Ni react and some of the Au moves to the lower layer of the electrode. And Ni appears elsewhere. Then, since a natural oxide film is formed on the Ni appearing on the surface, the bonding strength between the electrode and the Au / Cr electrode film which is a wire bond wire or a wire bond electrode is eventually weakened.

(C) Problems to be Solved by the Invention Therefore, the present invention provides an n-type capable of firmly wire bonding.
An object of the present invention is to provide a method for forming an electrode of SiC.

(D) Means for Solving the Problems The present invention provides a method for forming an electrode on silicon carbide, comprising the steps of: depositing a Ni electrode film on n-type silicon carbide;
A step of applying a Pd electrode film on the electrode film; and a step of heat-treating the Ni electrode film and the Pd electrode film.

(E) Function In the method of the present invention, a Pd electrode film is deposited on a Ni electrode film capable of ohmic contact with n-type SiC. This Pd electrode film is 1200 ℃
Below, it does not react with the Ni electrode film. Further, the Pd electrode film has a property of being hardly oxidized.

(F) Example FIG. 1 is a sectional view of each step showing an example of the method of the present invention. Hereinafter, the method of the present invention will be described in detail with reference to the drawings.

FIG. 1A shows a first step, in which an n-type SiC substrate (1) is first prepared. And on one of the main surfaces, LPE method, C
An n-type SiC layer (2) and a p-type SiC layer (3) are sequentially stacked using a well-known epitaxial method such as a VD method.

FIG. 1 (b) shows a second step, in which a Ni electrode film (4) is formed on the other main surface of the n-type SiC substrate (1) by a vacuum evaporation method at 500 ° and a Pd electrode film (5). Are deposited for 3000 mm each. Thereafter, the laminated substrate is heat-treated at 1000 ° C. for about 5 minutes. Thus, the Ni electrode film (4) becomes the n-type SiC substrate (1)
Alloys to obtain ohmic properties. Further, the Pd electrode film (5) does not react with the Ni electrode film (4) in the heat treatment at 1000 ° C. Therefore, Ni in the Ni electrode film (4) does not appear on the surface of the Pd electrode film (5) through the inside of the Pd electrode film (5).

FIG. 1 (c) shows a third step, in which a p-type SiC layer (3) is used.
After applying a surface treatment by wet etching with hydrofluoric acid (HF), the Si film was 1000 mm thick using a vacuum evaporation method.
An Al film is deposited at 7000 ° to form an Al / Si electrode film (6). Thereafter, the laminated substrate is heated at 900 to 1000 ° C, for example, 950 ° C.
Heat treatment at about 5 minutes. Thereby, the Al / Si electrode film (6) is alloyed with the p-type SiC layer (3) to obtain ohmic properties. P-type SiC layer by hydrofluoric acid in such a process (3)
No oxide film is formed on the surface of the Pd electrode film (5) at the time of the surface treatment. This is because the Pd electrode film (5) has the property of being hardly oxidized and Ni in the lower layer does not appear on the surface of the Pd electrode film (5).

FIG. 1 (d) shows a fourth step, in which, for example, a Ti film is formed on the Pd electrode film (5) by using a vacuum evaporation method to a thickness of 1000 ° and a Pd film.
An Au film is deposited by 2000 mm and an Au film is deposited by 3000 mm to form a well-known Au / Pd / Ti electrode film (7) as a wire bonding electrode. Such Au / Pd /
Since the Ti electrode film (7) has no oxide film on the surface of the Pd electrode film (5), it is strongly bonded to the Pd electrode film (5).

In the present embodiment, the Ni electrode film (4) and the Pd electrode film (5) are formed on the n-type SiC substrate (1), but the same effects can be obtained by forming them on the n-type SiC epitaxial layer.

Further, since the Pd electrode film in the method of the present invention has a high melting point, it does not deform during heat treatment. Along with this, the lower Ni electrode film is less likely to be deformed. For this reason, in the method of the present invention, it is not necessary to increase the thickness of the Ni electrode film to suppress the electric field unevenness in the element due to the deformation of the electrode film, and the thickness of the Ni electrode film can be freely set. Also, since the thickness of the Ni electrode film is related to the diffusion depth of Ni in the Ni electrode film to SiC during the heat treatment, and since the Ni electrode film and the Pd electrode film do not react during the heat treatment, In the method of the present invention, the Ni diffusion depth can be easily controlled by appropriately changing the thickness of the Ni electrode film since the diffusion of Ni in the Ni electrode film occurs only to SiC. Since the SiC in the Ni-diffused portion becomes conductive, the thickness of the SiC on which the Ni electrode film is deposited must be larger than the diffusion depth. In the method of the present invention, the diffusion depth can be made as small as possible by reducing the thickness of the Ni electrode film as described above, so that the thickness of the SiC on which the Ni electrode film is deposited can be reduced. As a result, the specific resistance of the element decreases, so that the amount of heat generated during operation can be suppressed,
Since the element is less likely to deteriorate, the reliability of the element is improved. Furthermore, if the method of the present invention is applied to the formation of a base electrode in a pnp-type SiC bipolar transistor, the thickness of the n-type SiC layer serving as the base layer can be reduced as much as possible for the above-described reason, and the response characteristics are improved. A good bipolar transistor is obtained.

(G) Effects of the Invention According to the method of the present invention, an oxide film is not formed on the surface of the Pd electrode film after the heat treatment by depositing the Pd electrode film on the Ni electrode film. Therefore, the electrode film for wire bonding formed on the Pd electrode film can be strongly bonded to the Pd electrode film. Further, since the diffusion depth of Ni into SiC can be easily controlled, the thickness of the n-type SiC layer can be reduced, and the characteristics of the device can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing steps of an embodiment of the method of the present invention, and FIG. 2 is a sectional view showing a conventional apparatus.

Claims (1)

(57) [Claims] 1. A method for forming an electrode on silicon carbide, comprising the steps of: depositing a Ni electrode film on n-type silicon carbide;
A method for forming an electrode of silicon carbide, comprising: a step of applying a Pd electrode film on an electrode film; and a step of heat-treating the Ni electrode film and the Pd electrode film.