JPS6159656B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses indium (In) and V as group elements.
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.

The ohmic electrode for the compound semiconductor has conventionally been a metal layer containing gold (Au), silver (Ag), or indium (In) (in this invention, a reaction layer and an alloy are also referred to as a metal film or metal layer). ) is deposited on the surface of the compound semiconductor and heat-treated in a non-oxidizing atmosphere to cause an alloying reaction between the metal film and the compound semiconductor. For example, the above-
Gold-zinc (Au-Zn) alloy is often used as an electrode material for P-type indium phosphide (InP) as a 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. The cross section of the electrode part that has been subjected to this heat treatment is
Shown in Figure a. 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,
If heat treatment is performed at a temperature higher than 450℃, a good ohmic electrode cannot be produced.For this reason, the heat treatment temperature was changed to 415℃.
It was necessary to keep the temperature within the range of ~440℃. However, products heat-treated in such a temperature range have the disadvantage that the reaction between InP and the electrode material is not completed, and the reaction progresses further during various temperature raising processes after electrode formation, resulting in changes in the ohmic electrode characteristics. Ta. 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 ohmic electrode characteristics, the heat treatment temperature during electrode formation must be adjusted.
It is necessary to carry out the process at a high temperature of 450° C. or higher, or to prevent dissociation and evaporation of P during various temperature raising processes after electrode formation. Therefore, the first object of the present invention is to provide an electrode structure in which reaction products with the substrate semiconductor do not agglomerate even during heat treatment at high temperatures, and the second object is to provide an electrode structure that does not cause aggregation of reaction products with the substrate semiconductor even after heat treatment at high temperatures. The object of the present invention is to provide a method for manufacturing an ohmic electrode that prevents dissociation and evaporation of P during the temperature raising process. In the present invention, the second metal film forming a phosphorus compound with a high dissociation temperature is made of Au or Ag.
Alternatively, by forming the first electrode metal layer containing In as a main component, the dissociated P can be transferred to the second electrode metal layer.
InP is trapped in the metal film, increasing the pressure of P in the electrode and preventing the decomposition of InP. Hereinafter, an embodiment of the present invention will be described in detail using an Au--Zn alloy as a semiconductor substrate and an InP first electrode metal material.

Figure 2 a shows Zn deposited on an InP substrate 21 with a thickness of 0.15 μm.
A first electrode metal layer 22 made of an Au--Zn alloy containing 3% by weight of is deposited. of the above composition as a deposition source.
When depositing by vacuum evaporation using an Au-Zn alloy, the composition in the first electrode metal layer 22 is not uniform due to the difference in vapor pressure between Au and Zn, and the InP substrate 2
In the part in contact with 1, the composition is mainly Zn, and InP
Although the portion away from the substrate 21 shows a composition mainly composed of Au, such compositional non-uniformity does not pose a problem for the alloying reaction of the electrode with InP.
Next, a second metal film 23, which provides the improved effect of the invention, is deposited on the first metal layer 22 to a thickness of 0.15 μm (FIG. 2a). The second metal film 23 is made of a material containing one or more elements from the metal group consisting of tungsten W, molybdenum Mo, tantalum Ta, and hafnium Hf. The structure of the ohmic electrode shown in FIG. 2b is obtained by heat-treating FIG. 2a at 490 DEG C. for 1 minute in a hydrogen atmosphere. Unlike FIG. 1b, the reaction product 24 in FIG. 2b does not aggregate and reacts uniformly with the InP substrate 21. In FIG. FIG. 3 shows the results of measuring the elemental distribution in the depth direction from the surface of the heat-treated sample shown in FIG. 2b using Auger electron spectroscopy. In this sample, tungsten is used as the material for the second metal film 23. The heat-treated electrode has an Au-In alloy part in contact with the InP substrate, and P on the Au-In alloy part.
It can be seen that it shows a structure consisting of two parts separated into a W part containing . That is, the second metal film W23 is formed on the first metal film (Au-Zn) 22.
When Au-Zn 22 and InP 21 react and dissociate, P is captured in W.

Therefore, the pressure of P in the reaction product 24 increases, and significant decomposition of InP 21 is suppressed. On the other hand, when the W film is not deposited, the Au-In alloy formed by reaction with the InP substrate is molten, and the molten Au-In liquid is directly exposed to the heat treatment atmosphere, so that P evaporates. This facilitates the decomposition of InP. In fact, no P was detected in the aggregate 14 of FIG. 1b. As a result, the InP substrate is significantly decomposed, and the molten InP aggregates to form an electrode structure as shown in FIG. 1b. In Figure 3, W is used as the second metal film material, but any metal element that forms a compound that is difficult to dissociate with P is effective.
Mo, Ta, and Hf were effective as elements other than W. The appropriate thickness of the second metal film was 0.5 to 2 times the thickness of the first metal film. In other words, if the second metal film is too thin, the reaction product between the first metal film and the semiconductor substrate will wave when it solidifies, and if the second metal film is too thick, it will cause mechanical damage in the electrode after heat treatment. As the strain increased, the electrodes became brittle. The ohmic electrode for InP using tungsten as the second metal film, which is an embodiment of the present invention, can be heat-treated at 450°C or higher.
Unlike the conventional structure, it was thermally stable and no change in device characteristics was observed even during various temperature raising processes after electrode formation.

The effect of increasing thermal stability as described above can be obtained by covering the first metal film and performing heat treatment on the semiconductor substrate.
It can also be obtained by depositing the second metal film after an alloying reaction between the semiconductor substrate and the first metal film. Figure 4 shows the relationship between InP and InP, which was formed by depositing an Au-Zn alloy containing 3% by weight of Zn on an InP substrate 41 to a thickness of 0.15 μm and then heat-treating it at 430°C for 1 minute in a non-oxidizing atmosphere. A tungsten film 43 with a thickness of 0.15 μm is formed on the reaction layer 42.
It is coated to a thickness of .

The electrode manufactured in this way also had high thermal stability even during the temperature rising process after electrode formation, and there were few changes in device characteristics. The reason for this is that the tungsten film captures phosphorus generated during the temperature rising process, suppressing the decomposition of InP and preventing the promotion of electrode reactions.

As described above, as an example of the present invention, InP is applied to a semiconductor substrate.
However, it is also applicable to other semiconductor materials in which group V elements are easily dissociated, such as InGaAsP mixed crystal, InAs, etc. The second metal film material group (W, Mo, Ta, Hf) described in the present invention forms a compound that is difficult to dissociate with arsenic (As), so it is not suitable for compound semiconductors containing arsenic (As) as a group V element. It is also effective. In addition to materials containing gold such as gold-germanium alloy and gold-tin alloy, materials containing indium such as indium, indium-tellurium alloy, and indium-tin alloy can be used as the first metal film material, and silver- Tin alloy, indium-tin
The effects described in the present invention can also be obtained by depositing the second metal film on a material containing silver such as a silver alloy.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the structure of a conventional ohmic electrode, Fig. 1a shows the structure of an electrode heat-treated at 415°C to 440°C in a non-oxidizing atmosphere, and Fig. 1b shows the structure of the electrode.
The structure of an electrode heat-treated at 450°C or higher is shown. In the figure, 11 is an InP substrate, 12 is a reaction layer made of Au-In formed by heat treatment at 415°C to 440°C, and 13 is at 450°C.
The reactants formed by the above heat treatment are shown. FIG. 2 is a sectional view showing the structure of an electrode obtained by the manufacturing method of the present invention. FIG. 2a shows the electrode structure immediately after deposition, and FIG. 2b shows the structure of the electrode after heat treatment at 490°C. In the figure, 21 is an InP substrate, 22 is a first metal film made of an Au-Zn alloy, 23 is a second metal film made of W, and 24 is a reaction layer formed by heat treatment at 490°C. FIG. 3 shows the results of measuring the depth distribution of elements in the electrode of FIG. 2b by Auger electron spectroscopy. FIG. 4 is a cross-sectional view showing the structure of an ohmic electrode according to an embodiment of the present invention.
4 is an InP substrate, 42 is a reaction layer of InP and a first metal film made of an Au-Zn alloy, and 43 is a tungsten film.

Claims (1)

[Claims] A first metal film containing gold, silver, or indium as a main component is deposited on the surface of a - group compound semiconductor containing indium as a group 1 element and phosphorus or arsenic as a group V element, and further comprising: depositing a first metal film mainly composed of gold, silver, or indium; A second metal film containing one or more elements selected from the element group consisting of tungsten, molybdenum, tantalum, and hafnium and having a thickness of 0.5 to 2 times that of the first metal film is deposited thereon. A method for producing an ohmic electrode, which is then subjected to heat treatment at a temperature of 450°C or higher.