JP2608448B2 - Processing method of GaAs substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for treating a GaAs substrate, which is suitable as a pretreatment for epitaxially growing a compound semiconductor layer on the substrate, by reducing the amount of carbon impurities on the surface of the GaAs substrate. In order to make it possible to epitaxially grow a high-quality compound semiconductor layer thereon, and to obtain good electrical characteristics when a semiconductor device is manufactured using the GaAs substrate, a GaAs substrate is used. A step of immersing in pure water at the final stage of the wet treatment, and then stopping the flow of pure water to stop the GaAs
Leaving the substrate in pure water of still water to form an oxide film on the surface.

[Industrial applications]

The present invention relates to a method for processing a GaAs substrate, which is suitable for performing as a pretreatment when a compound semiconductor layer is epitaxially grown on a substrate.

[Conventional technology]

At present, for example, high electron mobility transistors (high ele
When manufacturing ultra-high-speed compound semiconductor devices such as ctron mobility transistors (HEMT) or optical semiconductor devices, for example, molecular beam epitaxial growth (molecula)
r beam epitaxy (MBE) method and metal organic chemical vapor deposition (meta
A GaAs layer or an AlGaAs layer is epitaxially grown on a GaAs substrate by applying a method such as lorganic chemical vapor deposition (MOCVD).

At this time, it is important to sufficiently remove contaminants adhering to the surface of the GaAs substrate. Without such a method, a high-quality epitaxially grown compound semiconductor layer cannot be obtained.

Conventionally, the GsAa substrate is generally degreased and cleaned → mildly etched → washed with water → heated to 600 to 650 ° C while irradiating the As beam in a vacuum, that is, so-called thermal cleaning. is there.

[Problems to be solved by the invention]

When the above-described thermal cleaning is performed, the oxide film on the surface of the GaAs substrate is removed, but impurities mainly composed of carbon cannot be completely removed. Therefore, the interface between the epitaxially grown compound semiconductor layer and the GaAs substrate is removed. A depletion layer is generated, and the electrical characteristics deteriorate.

The present invention reduces the amount of carbon impurities on the surface of a GaAs substrate so that a high-quality compound semiconductor layer can be epitaxially grown thereon, and has good electrical characteristics when a semiconductor device is manufactured. I do.

[Means for solving the problem]

The present invention utilizes the characteristics of GaAs with respect to pure water.

That is, since GaAs has polarity, it exhibits the following characteristics with respect to pure water.

(1) Etched in running water. In this case, the etching rate is about 1 to 1.5 [Å / min].

(2) A Ga oxide film is formed on the surface in still water. For this reason, the GaAs substrate is immersed in running pure water at the final stage of normal substrate processing (wet processing),
After passing [minutes] to 1 [hour], stop the flow of pure water,
A Ga oxide film having a thickness of, for example, 50 [Å] is intentionally formed on the surface.

The “wet treatment” generally refers to degreasing of organic substances with acetone, trichloroethylene, ethyl alcohol, or the like, or metal impurities or polishing with an acid or alkaline aqueous solution such as sulfuric acid, hydrogen peroxide, hydrochloric acid, or ammonia. It refers to a process including etching for removing a damaged layer.

When the above treatment is performed, since the purity of pure water is extremely high, impurities such as carbon hardly exist at the oxide film / substrate interface or in the oxide film.

The GaAs substrate that has been subjected to this processing is transported through the atmosphere into the vacuum of an epitaxial growth apparatus such as an MBE apparatus.
Therefore, carbon impurities may be deposited on the surface of the Ga oxide film in the process, but since the Ga oxide film is thicker than the natural oxide film, a process of sublimating the Ga oxide film in the vacuum, That is, it can be easily removed in the process of thermal cleaning.

From the above, in the method for processing a GaAs substrate according to the present invention, the step of immersing the GaAs substrate in running pure water at the final stage of the wet processing, and then stopping the flow of pure water. A step of leaving the GaAs substrate in still water of pure water to form an oxide film on the surface.

[Action]

By taking the above measures, the residual carbon impurities on the surface of the GaAs substrate are drastically reduced. Therefore, when a compound semiconductor layer is epitaxially grown thereon, problems such as expansion of a depletion layer from the interface are solved, and electrical characteristics are reduced. Can manufacture a good semiconductor device, and the technology required for performing such a process is an extremely simple means that is not called a technology in the semiconductor field. Therefore, the implementation is easy.

〔Example〕

FIG. 1 is a diagram showing an Auger spectrum of a GaAs substrate processed according to an embodiment of the present invention;
FIG. 2 and FIG. 3 are diagrams showing Auger spectra of a GaAs substrate subjected to a process for comparison with one embodiment of the present invention.

As an example of the present invention which obtained the results shown in FIG. 1, as an example, a normal wet-processed GaAs substrate was immersed in running pure water for about 60 minutes, and then immersed in the still water for 10 minutes. time〕
The pure water is referred to as one of> 18 [MΩ].

As an example of an experiment which obtained the results shown in FIG. 2, a GaAs substrate subjected to a normal wet treatment was immersed in running pure water for 10 hours.

An example of an experiment that obtained the results shown in FIG. 3 relates to a GaAs substrate that has been subjected to ordinary wet processing.

In each figure, C _C is the carbon concentration, C _O is the oxygen concentration, and C _Ga is G
The a concentration and C _As indicate the As concentration, respectively.

In the experimental example shown in FIG. 3, that is, the experimental example according to the prior art, the amount of carbon is very large, and it is extremely difficult to remove it. Also, in the experimental example shown in FIG. 2, that is, in the experimental example in which the sample was immersed in running water for 10 hours, oxygen and carbon adhered to the surface. And it is difficult to remove it.

In accordance with one embodiment of the present invention as seen in FIG.
The formation of a Ga oxide film on the surface of the GaAs substrate was observed, and the amount of carbon was remarkably small, because carbon hardly adhered to the surface of the Ga oxide film. When the GaAs substrate subjected to such treatment is heated in vacuum to sublimate the Ga oxide film, the fact that carbon impurities are present only on the surface and that the Ga oxide film is sufficiently thick are combined. , GaAs just before compound semiconductor layer growth
It is possible to significantly reduce the amount of residual carbon impurities on the substrate surface.

〔The invention's effect〕

In the method for treating a GaAs substrate according to the present invention, a step of immersing the GaAs substrate in running pure water at the final stage of the wet processing, and stopping the flow of the pure water to bring the GaAs substrate into pure water. Standing in still water to form an oxide film on the surface.

By taking the above measures, the residual carbon impurities on the surface of the GaAs substrate are drastically reduced. Therefore, when a compound semiconductor layer is epitaxially grown thereon, problems such as expansion of a depletion layer from the interface are solved, and electrical characteristics are reduced. Can manufacture a good semiconductor device, and the technology required for performing such a process is an extremely simple means that is not called a technology in the semiconductor field. Therefore, the implementation is easy.

[Brief description of the drawings]

FIG. 1 is a diagram showing an Auger spectrum of a GaAs substrate processed according to one embodiment of the present invention, and FIGS. 2 and 3 are diagrams of a GaAs substrate subjected to processing for comparison with the one embodiment of the present invention. FIG. 3 is a diagram illustrating an Auger spectrum. In the figure, C _C indicates the carbon concentration, C _O indicates the oxygen concentration, C _Ga indicates the Ga concentration, and C _As indicates the As concentration.

Claims (1)

(57) [Claims] A step of immersing the GaAs substrate in running pure water at the final stage of wet processing; and stopping the flow of pure water, leaving the GaAs substrate in still water of pure water, Forming an oxide film. A method for processing a GaAs substrate, comprising: