JPS6138849B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides indium (In) as a group element,
The present invention relates to the structure and manufacturing method of an ohmic electrode for a compound semiconductor containing phosphorus (P) or arsenic (As) as a group element. Conventionally, an ohmic electrode for the compound semiconductor is produced by depositing a metal layer containing gold (Au), silver (Ag), or indium (In) on the surface of the compound semiconductor, and then heat-treating it in a non-oxidizing atmosphere. Accordingly, the metal film is formed by a method of causing an alloying reaction between the metal film and the compound semiconductor. For example, a gold-zinc (Au-Zn) alloy is often used as an electrode material for P-type indium phosphide (InP) as the compound semiconductor. In order to obtain low contact resistance for InP, heat treatment is performed in a hydrogen atmosphere for about 1 minute at a temperature range of 415°C to 440°C. A cross section of the electrode portion subjected to this heat treatment is shown in FIG. 1a. An Au-In alloy layer 12 is formed on the substrate InP11. A very thin Zn-doped layer is formed between the substrate InP 11 and the Au-In alloy layer 12.

When the heat treatment temperature is selected to be 450°C or higher, the Au-In alloy aggregates and aggregates 13 are locally formed as shown in Figure 1b, and at the same time, InP is exposed on the surface other than the area where the aggregates 13 appear. . For this reason 450
If heat treatment is performed at a temperature higher than 0.degree. C., a good ohmic electrode cannot be produced, so it is necessary to keep the heat treatment temperature within the range of 415.degree. C. to 440.degree. However, products heat-treated in this temperature range have the disadvantage that the reaction between InP and the electrode material is not completed, so the reaction progresses further during various temperature raising processes after electrode formation, and the ohmic electrode characteristics change. It was hot. The inventor has clarified that the progress of the reaction between InP and the electrode material is caused by the fact that P dissociates and evaporates easily because the bond energy between In and P is small. Summer. In order to suppress changes in the ohmic electrode characteristics, it is effective to perform heat treatment at a high temperature of 450° C. or higher while preventing dissociation and evaporation of P.

An object of the present invention is to provide a production method in which dissociation and evaporation of P are reduced. In the present invention, agglomeration of reaction products at temperatures of 450° C. or higher could be prevented by heat treatment in an oxidizing atmosphere. The present invention will be described below based on an example in which InP is used as the semiconductor substrate and Au--Zn alloy is used as the electrode metal material.

3% by weight of Zn with a thickness of 0.3μm on the InP substrate 21
An electrode metal layer made of an Au-Zn alloy was deposited using a commonly used method such as sputtering, and heated at 490°C.
Heat treatment was performed in air for 1 minute. A cross-sectional view of the resulting electrode structure is schematically shown in FIG. 1st
Unlike FIG. b, the reaction product layer 22 does not aggregate. Second
After diagonally polishing the sample shown in the figure at an angle of 1 degree,
FIG. 3 shows the results of examining the element distribution in the reaction generation layer 22 by microprobe Auger electron spectroscopy analysis of the obliquely polished cross section. An Au-In alloy region is in contact with the substrate InP, and a P layer is formed on the Au-In alloy region.
It can be seen that an Au--In alloy region is formed on the accumulation region and the P accumulation region, and further, an oxidized region of Zn and In is formed on the surface. On the other hand, 490 in a non-oxidizing atmosphere
When heat treated at ℃, the agglomerate 13 shown in FIG. 1b is characterized by an Au-In alloy, containing zinc,
Phosphorus and oxygen were not detected in aggregate 13. These results indicate that when heat treatment is performed in air, the surface is covered with In and Zn oxide regions,
Since the evaporation of P is prevented, the pressure of P in the electrode increases, and the decomposition of the substrate InP is inhibited, indicating that the aggregation of reaction products and the exposure of the InP surface do not occur. The Zn and In oxidized regions formed on the surface after the heat treatment can be easily removed with hydrofluoric acid or nitric acid after the heat treatment. In the above example, the heat treatment was performed in air, but according to the inventor's experiments,
No agglomeration of reaction products occurred even in hydrogen gas, nitrogen gas, or argon gas containing 50 ppm or more of oxygen or water. Since the ohmic electrode formed in the above example was heat-treated at a high temperature, it remained thermally stable and no change in device characteristics was observed even after the temperature increase process after the heat treatment process. .

In the above embodiments of the present invention, InP was used as the semiconductor substrate, but the present invention is also effective for manufacturing electrodes for other semiconductor substrates containing V group elements that are easy to understand, such as InGaAsP and InAs.

Also, Au-
In materials other than Zn alloys, when the electrode material contains gold, silver, or indium, the electrode material reacts with the semiconductor to form a melt containing indium, which is normal under a non-oxidizing atmosphere. In the heat treatment method, significant agglomeration of the reaction products occurs due to dissociation and evaporation of P. However, when the heat treatment according to the present invention is performed in an oxidizing atmosphere, an oxide containing indium is formed on the surface of the reactant, preventing dissociation and evaporation of P, and preventing aggregation of the reaction product.

Therefore, as ohmic electrode materials for semiconductors, alloys containing gold such as gold-germanium and gold-tin other than Au-Zn alloys, and materials containing silver such as silver-tin and silver-indium-germanium, and The method according to the present invention is also effective when using a material containing indium such as indium or indium-zinc.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the structure of a conventional ohmic electrode. Figure 1a shows the structure of an electrode heat-treated at 415°C to 440°C in a non-oxidizing atmosphere, and Figure 1b shows the structure at 450°C.
The structure of the electrode heat-treated in a non-oxidizing atmosphere is shown above. In the figure, 11 is an InP substrate, 12 is from 415℃
A reaction layer made of Au-In was formed by heat treatment at 440°C. Reference numeral 13 indicates a reaction product formed by heat treatment at 450°C or higher. FIG. 2 is a cross-sectional view showing the structure of an electrode formed based on an embodiment of the present invention, and 21 in the figure.
2 shows an InP substrate, and 22 shows a reaction layer with InP formed by heat treatment in air at 490°C. Figure 3 shows
The results of measuring the depth distribution of elements in the reaction layer 22 shown in FIG. 2 by microprobe Auger electron spectroscopy are shown.

Claims (1)

[Claims] 1. After depositing a metal layer containing gold, silver, or indium on the surface of a compound semiconductor containing indium as a group element and phosphorus or arsenic as a group element, the compound semiconductor is heat-treated to form a bond between the compound semiconductor and the deposited compound semiconductor. 1. A method for producing an ohmic electrode in which an ohmic electrode is formed by causing a reaction with a metal layer, characterized in that the heat treatment is performed in an oxidizing atmosphere.