JPH06101454B2 - Vapor phase etching method for compound semiconductor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a vapor phase etching method for compound semiconductors, and a pretreatment of a substrate used for various epitaxial growth such as liquid phase epitaxial growth, vapor phase epitaxial growth such as MOCVD, and molecular beam epitaxial growth. It is the best one to apply.

[Outline of Invention]

The present invention makes it possible to clean the surface of a compound semiconductor and improve its crystallinity by performing etching by heating to a high temperature in a hydrogen gas atmosphere in a vapor phase etching method for a compound semiconductor.

[Conventional technology]

In the epitaxial growth of compound semiconductors, pretreatment of the substrate used for growth is one of the extremely important factors.
This is because if the cleanliness of the substrate surface is poor or the crystallinity is poor, the epitaxial growth layer is adversely affected as it is, and as a result, the surface of the epitaxial growth layer is clouded or crystal defects are formed.
Particularly, in molecular beam epitaxial growth, a peculiar defect called an oval defect occurs on the surface of the epitaxial growth layer, which is a major obstacle in device fabrication.

One of the causes of this defect is considered to be the oxide of the constituent element of the compound semiconductor, and the number of defects can be reduced to about 200 to 300 cm ^-2 by suppressing the formation of this oxide. At present, it is difficult to reduce the defects below this level. Most of the residual defects are considered to be due to the state of the substrate surface before epitaxial growth. Therefore, in order to prevent the occurrence of defects in the epitaxial growth layer, it is essential to improve the cleanliness and crystallinity of the substrate surface.

By the way, conventionally, the pretreatment of the substrate is performed by simply cleaning it with an organic solvent, removing the substrate surface layer by chemical etching using an acid or alkaline etching solution, or sputtering the substrate surface in a high vacuum. It is done by doing.

However, it cannot be expected that a high degree of surface cleanliness and improvement of crystallinity will be obtained by the above-mentioned cleaning with an organic solvent or chemical etching. Further, in the sputtering method, since ions accelerated at a certain speed are irradiated onto the substrate surface, there is a drawback that damage due to irradiation remains on the substrate crystal surface.

In addition to these methods, a vapor phase etching method using a chlorine-based gas at high temperature is known as a relatively effective method. However, since this chlorine-based gas is corrosive, a molecular beam epitaxial growth apparatus is used. In order to introduce it into the interior, it is necessary to take measures to prevent corrosion, so that there is a drawback that the structure of the apparatus becomes complicated.

Note that JP-A-59-65434 is mentioned as a document in which the prior art related to the present invention is described, and in this document, III
When vapor-phase etching a substrate before vapor-phase growth of a group-V compound semiconductor or during growth in a reaction tube during growth, it is used for growth together with hydrogen chloride for etching in the reaction tube.
A vapor phase etching method for a compound semiconductor is disclosed in which vapors of an alkyl compound of a group III element and a hydrogen compound or an alkyl compound of a group V element are introduced.

[Problems to be solved by the invention]

It is an object of the present invention to provide a vapor phase etching method for a compound semiconductor, in which the above-mentioned drawbacks of the prior art are corrected.

[Means for solving problems]

As a result of intensive studies to correct the above-mentioned drawbacks of the prior art, the present inventors have found that a compound semiconductor such as GaAs is thermally treated at a high temperature of 800 ° C. or higher in a hydrogen atmosphere, for example, a hydrogen stream. The inventors have found that phase etching is possible, and have devised the present invention.

That is, in the vapor phase etching method for a compound semiconductor according to the present invention, the etching is performed by heating to a temperature of 800 ° C. or higher in a hydrogen gas atmosphere.

〔Example〕

An example in which the vapor phase etching method for a compound semiconductor according to the present invention is applied to the etching of a typical compound semiconductor, GaAs, will be described below.

By heat-treating GaAs for 30 minutes in a mixed gas flow of hydrogen (H ₂ ) with a small amount of arsine (AsH ₃ ) [total flow rate is 500 cc / min] (total pressure is 760 Torr), partial pressure of AsH ₃ is 3 Torr] , Vapor phase etching was performed. AsH ₃ is mixed with H ₂ here because in a III-V group compound semiconductor such as GaAs,
Since the vapor pressure of the group V element is higher than that of the group III element, when heat treatment is performed at a high temperature for a long time, the group V element, that is, As, is excessively dissociated and a defect called a heat pit is generated on the surface. This is to prevent it from happening.

Figure 1 shows the temperature dependence of the etching amount of GaAs. As is clear from FIG. 1, when vapor phase etching is performed at a high temperature of 800 ° C. or higher, an etching amount of about 30 Å or higher can be obtained.

Next, the results of evaluating the crystallinity of the GaAs surface after vapor phase etching by laser Raman spectroscopy will be described.

Figure 2A shows the result after vapor phase etching by heat treatment at 800 ℃ for 15 minutes in H ₂ gas flow of 500cc / min.
It is a Raman scattering spectrum of the GaAs surface. For comparison, the flow rate is 800cc in an argon (Ar) flow of 500cc / min.
The Raman scattering spectrum of the GaAs surface after heat treatment at 15 ° C for 15 minutes is shown in Fig. 2B. It is considered that the heat treatment in the Ar stream removed the deposits on the GaAs surface, but etching did not occur.

Comparing Fig. 2A and Fig. 2B, the peak intensity of TO phonons (transverse optical phonons), which is forbidden scattering on the (100) GaAs surface used, is smaller in Fig. 2A than in Fig. 2B, The half-width of the LO phonon (longitudinal optical phonon) peak, which is the scattering peak, is smaller in Fig. 2A than in Fig. 2B. These facts show that the vapor phase etching by the high temperature heat treatment in the H ₂ gas flow not only removed the deposits on the GaAs surface but also improved the crystallinity of the GaAs surface. Further, in this example, the oxide having a low vapor pressure formed on the surface of the substrate due to the reducing action of H ₂ can be effectively removed.

Note that FIG. 2A shows the data when GaAs is vapor-phase etched in a H ₂ stream, but the crystallinity of the surface is further improved by vapor-phase etching in a mixed stream in which AsH ₃ is added to H ₂ . It is easily speculated that it is possible.

Further, the GaAs surface after the vapor phase etching according to the above-mentioned embodiment was a perfect mirror surface.

As described above, according to the above-described embodiment, it is possible to remove the deposits on the GaAs surface and improve the crystallinity of the surface by the vapor phase etching of GaAs. Therefore, if GaAs thus obtained is used as a substrate for epitaxial growth of compound semiconductors, contamination due to autodoping, etc. is reduced, and a higher-purity epitaxial layer can be grown, and surface defects of the substrate are It is possible to reduce defects in the epitaxial layer due to In particular, in molecular beam epitaxial growth, oval defect can be reduced.

Further, in the above-mentioned embodiment, since AsH ₃ is added to the H ₂ gas flow, the stoichiometry of GaAs can be maintained or improved. Therefore, if this GaAs is used as a substrate for epitaxial growth, the substrate It is possible to reduce the defects in the epitaxial layer due to the deviation of the iometry.

Also, when manufacturing GaAs ICs, etc. using the GaAs obtained as described above, due to defects, deposits, etc. present on the substrate surface during ion implantation, and local deviation of stoichiometry of the substrate. The non-uniformity of the ion-implanted layer can be reduced, and therefore the yield of ICs and the like can be improved.

Further, according to the above-described embodiment, since the etching can be performed in the epitaxial growth apparatus, the epitaxial growth can be continuously performed without taking the substrate out of the apparatus after the etching. Therefore, not only can the substrate after etching be prevented from coming into contact with the outside air to cause oxidation and the like, but it is efficient.

Furthermore, since etching can be performed without using a corrosive gas such as HC1, it is not necessary to take corrosion prevention measures in the molecular beam epitaxial growth apparatus, and therefore the apparatus configuration is simple.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made based on the technical idea of the present invention. For example, in the above embodiment, the total flow rate of the mixed air flow of H ₂ and AsH ₃ is 500 cc /
Although the partial pressure of AsH ₃ is 3 Torr, the total flow rate of the mixed airflow and the partial pressure of AsH ₃ are not limited to these values, and can be selected as needed. But,
To obtain a sufficient amount of etching, the partial pressure of H ₂ should be 15
It is preferably about 0 Torr to 760 Torr.

Further, this AsH ₃ can be omitted if necessary. Further, various temperatures can be used as long as the temperature during etching is 800 ° C. or higher. Similarly, the etching time can be selected as required. Furthermore, the etching does not necessarily have to be performed in an air stream, but may be performed in an atmosphere containing at least H ₂ .

Further, in the above-mentioned embodiments, the case where the present invention is applied to the etching of GaAs is explained, but III-V other than GaAs is used.
The present invention can be applied to group compound semiconductors and other various compound semiconductors. Here, in order to prevent excessive dissociation of the constituent elements of the compound semiconductor during etching, H ₂ may be added with a gas containing the constituent elements of the compound semiconductor, if necessary. For example, when etching a III-V group compound semiconductor, a corresponding hydride of a V group element (for example, PH _{3 in} the case of GaP) may be mixed in an H ₂ atmosphere as necessary.

〔The invention's effect〕

According to the vapor phase etching method for a compound semiconductor according to the present invention, the surface of the compound semiconductor can be cleaned and the crystallinity can be improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between temperature and etching depth in a vapor phase etching method according to an embodiment in which the present invention is applied to GaAs, and FIGS. 2A and 2B show etching using a hydrogen flow and an argon flow, respectively. It is a graph which shows the Raman scattering spectrum of the GaAs surface which was performed.

Claims (1)

[Claims] 1. A method for vapor phase etching of a compound semiconductor, characterized in that etching is performed by heating at a temperature of 800 ° C. or higher in a hydrogen gas atmosphere.