JPH03145720A - Compound semiconductor growth method and silicon substrate to be used thereon - Google Patents

Abstract

PURPOSE:To reduce the autodoping of silicon from a silicon substrate to compound semiconductor generating when the compound semiconductor is being grown by a method wherein a protective film is provided on the prescribed region of a silicon substrate other than the region where the compound semiconductor will be grown. CONSTITUTION:A silicon oxide film 23 of 100Angstrom or more in thickness, 4700Angstrom for example, is formed on the whole surface of a silicon substrate 21 as a protective film 23. Then, a material showing resistive property against a silicon oxide film removing means, such as a resist 25 for example, is formed on the prescribed region other than the region where a compound semiconductor will be grown such as a rear surface 21b for example. Then, the part exposed from the resist 25 on the protective film 23 is removed by a well known oxide film removing method, and the main surface 21a of the silicon substrate 21 is exposed. Subsequently, a GaAs layer 27 is grown on the silicon substrate 21 as a compound semiconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for growing a compound semiconductor on a silicon (Si) substrate and a silicon substrate used in the method.

(Prior art) If it is possible to grow a compound semiconductor such as GaAs on a silicon substrate, it will not only be possible to obtain a compound semiconductor substrate with an unprecedented large area, but also to develop the characteristics of silicon and the characteristics of compound semiconductors. It is expected that a useful semiconductor device that takes advantage of this can be obtained. Therefore, research has been actively conducted to grow compound semiconductors on silicon substrates.

For example, in the literature "Heteroepitaxy of GaAs/Si by rMOCVD": 15th Thin Film and Surface Physics Seminar (19B?) pp. 181-193), there is a method for growing single-domain GaAs7a on a silicon substrate. Two typical growth methods are disclosed.

One method is to first heat-treat the silicon substrate at a high temperature of 850"C or higher in order to clean the surface of the silicon substrate, then grow a GaAs vanoa layer on the silicon substrate at a low temperature, and then heat it at a high temperature to form the desired layer. This is a so-called two-step growth method in which a GaAs layer of 200 nm is grown.

The other method is to first form a strained superlattice on a silicon substrate and then use GaAs%
It's a way to grow.

In addition, in order to reduce Takada dislocations that occur in the compound semiconductor layer during growth, a so-called heat treatment method is used in which the growth of the compound semiconductor layer is temporarily interrupted during the growth method described above and annealing is performed at high temperatures. There was also.

In any of these methods, as shown in the cross-sectional view in FIG. Then, as shown in Figure 3 (B),
The compound semiconductor 13 has been grown on, for example, the main surface 11a of the substrate 11 as a region on which the compound semiconductor is grown, by a two-step growth method or a method using a strained superlattice buffer layer.

(Problem to be solved by the invention) However, since the conventional method includes a step of heat-treating the silicon substrate at high temperature, silicon auto-dopes from the silicon substrate into the compound semiconductor growth layer. As a result, there was a problem in that the quality of the compound semiconductor obtained on the silicon substrate was degraded.

For example, when an undoped GaAs layer is grown on a silicon substrate by the two-step growth method described above, the resulting layer has an electron concentration of 1xlO16crrr3.
This resulted in an n-type GaAs layer. The electron concentration of the GaAs layer obtained when an undoped GaAs layer is grown on a GaAs substrate is usually lX1014 cm-
Considering that it is less than 3, it can be seen how high the electron concentration of GaAs grown on a silicon substrate is.

Furthermore, when the heat treatment method described above is used to reduce the number of dislocations in the compound semiconductor layer, the electron concentration in the GaAs layer is as follows:
In the heat-treated part, the thickness was on the order of 10 cm-3.

P like this. In order to solve this problem, the inventor of this application has conducted various studies and found that it is difficult to prevent silicon autodoping from the compound semiconductor growth region of the silicon substrate to the compound semiconductor growth layer. It was concluded that the quality of compound semiconductor growth layers could be improved by preventing silicon autodoping from regions other than the growth region.

This invention was made with attention to such a conclusion, and therefore, the purpose of this invention is to improve the growth of silicon from a silicon substrate to a compound semiconductor during the process of growing a compound semiconductor on a silicon substrate. The present invention provides a method for reducing autodoping compared to conventional methods, and a silicon substrate for use in this method.

(Means for Solving the Problem) In order to achieve this object, according to the first invention of this application, when growing a compound semiconductor on a silicon substrate, the area of the silicon substrate other than the area where the compound semiconductor is grown is The present invention is characterized in that a protective film is provided in a predetermined region to prevent autodoping of silicon from this region to the compound semiconductor, and a compound semiconductor is grown on the silicon substrate with this protective film.

Further, according to the second invention of this application, in a silicon substrate on which a compound semiconductor is grown, autodoping of silicon from this region to the compound semiconductor layer is performed in a predetermined region other than the region where the compound semiconductor is grown. It is characterized by comprising a protective film that prevents

In carrying out the above-mentioned first and second inventions, it is preferable to use a silicon oxide film as the above-mentioned protective film. In addition,
The silicon oxide film used here as a protective film is different from the natural oxide film that is normally formed on silicon substrates, and is designed so that it will not be removed by the cleaning process of the silicon substrate that is performed before the growth of compound semiconductors. It means a film with a thickness of Considering that the thickness of the general natural oxide film is said to be several tens of layers at most, the thickness of the silicon oxide film as the protective film in this invention is, for example, 1.
The thickness is preferably 00 Å or more, preferably several 100 Å or more.

Moreover, the silicon substrate referred to in the first and second inventions also includes those having an epitaxial silicon layer on the silicon substrate.

(Function) According to the configurations of the first and second inventions of this application, during the compound semiconductor growth process, the area other than the area on the silicon substrate where the compound semiconductor is grown (growth area) due to the effect of the protective film. Since autodoping of silicon into the compound semiconductor growth layer can be prevented, the quality of the compound semiconductor growth layer can be improved, as is clear from the experimental results described later.

(Example) Hereinafter, an example of the compound semiconductor growth method of the present invention and an example of a silicon substrate used therein will be described with reference to the drawings. Note that the drawings used in the following description schematically show the dimensions, shapes, and arrangement relationships of each component to the extent that the present invention can be understood.

First, an embodiment of the method for growing a compound semiconductor, which is the first invention, will be explained. FIGS. 1A to 1E are process diagrams for explaining the process, and each figure shows a cross-sectional view of the sample at one of the main steps in the process.

First, a protective film is provided in a predetermined region of the silicon substrate other than the region where the compound semiconductor is grown (hereinafter referred to as a growth region) to prevent autodoping of silicon from this region to the compound semiconductor layer. .

First, a silicon substrate 21 is prepared (Fig. 1(A)
).

Next, this silicon substrate 21 is oxidized by, for example, a thermal oxidation method to form a silicon oxide film 23 and a protective film 2 on the entire surface of the silicon substrate 21 to a thickness of 100 Å or more.
3 (FIG. 1(B)).

Next, in this embodiment, a predetermined region of the silicon substrate 21 other than the region where the compound semiconductor is to be grown (growth region) is defined as the back surface 21b of the silicon substrate 21, and this back surface 2Ib
A resist 25, for example, is formed on the silicon oxide film removing means (for example, fluorine M), which is resistant to I (the first
Figure (C)).

Next, the resist 25 of the protective film (silicon oxide film) 23 is
The exposed portion is removed by a known silicon oxide film removing means to expose the main surface 21a of the silicon substrate 21 (FIG. 1(D)).

Next, Ga is added to this silicon substrate 21 as a compound semiconductor.
An As layer 27 is grown. In this case, any conventional growth method may be used. The structure obtained by this growth is shown in FIG. 1(E).

Next, characteristics representing the quality of the GaAs layer 27 grown as described above were measured. In preparing the sample for this measurement, the GaAs layer was grown using the two-step growth method described above, and in order to make the GaAs layer 27 semi-insulating, it was doped with vanadium (V) t. I did it while doing so. The growth was then stopped when the thickness of the GaAs layer 27 reached 2 um.

The measurements were carried out as follows.

A portion of the protective film on the back surface 21b of the silicon substrate 21 is removed to expose a portion of the back surface 21b. Ohmic electrodes are formed on this exposed surface and on the surface of the GaAs layer 27, respectively. Next, a voltage was applied between these ohmic electrodes and this voltage was gradually increased, and the voltage when the current flowing between the ohmic electrodes reached 10 uA (hereinafter abbreviated as withstand voltage) was determined. As a result, the breakdown voltage was approximately 40V.

On the other hand, a sample of a comparative example was obtained by growing GaAs on a silicon substrate by the same procedure as in the example (i.e., by the conventional two-step growth method) except that a protective film for preventing autodoping was not provided. When the withstand voltage of this sample was measured, it was found to be several volts, which was much lower than that of the example.

From the above experimental results, it can be seen that the quality of the GaAs layer formed on a silicon substrate according to the growth method of the present invention is improved over that of the GaAs layer formed on a silicon substrate using the conventional growth method.

〉≦v) Base layer [ΣTomo Yodo Next, an embodiment of the silicon substrate, which is the second invention, will be described.

First Example> As a first example, an example of a silicon substrate is shown in which a compound semiconductor growth region is the main surface of the silicon substrate and a predetermined region other than the growth region is the back surface. The silicon substrate of this first embodiment corresponds to the silicon substrate shown in FIG. 1(D).

<Second Example> FIG. 2(c) is a cross-sectional view schematically showing the structure of a silicon substrate 21 of a second example. The silicon substrate 21 of the second embodiment is an example in which a compound semiconductor growth region is the main surface 21a of the silicon substrate, and predetermined regions other than the growth region are the back surface 21b and side surfaces 21c. Therefore, the protective film 23 is formed on the back surface 21b and the side surface 21C of the silicon substrate 21.
It is formed.

<Third Example> FIG. 2(8) is a cross-sectional view schematically showing the structure of a silicon substrate of a third example. In the silicon substrate 21 of the third embodiment, a region on which a compound semiconductor is grown is a part 21aa of the main surface of the silicon substrate, and a predetermined region other than the region to be grown is a region other than the part 21aa on the main surface of the entire surface. This is an example. Therefore, the protective film 23 is formed on the entire surface of the silicon substrate 21 excluding a portion 21aa of the main surface.

In the above, examples of the compound semiconductor growth method of this application and the silicon substrate used therein have been described, but the present invention is not limited to the above-mentioned examples only, and can be applied to various methods as described below. changes or transformations may be made.

In an embodiment of the invention of the growth method described above, a compound semiconductor! G
Although aAs is used, the present invention can also be applied to the growth of other compound semiconductors than GaAs.

Further, in each of the above-mentioned embodiments, an example has been described in which the protective film for preventing silicon autodoping is made of a silicon oxide film, but this protective film may be made of other materials. Such a material may include, for example, a silicon nitride film.

(Effects of the Invention) As is clear from the above description, according to the method of growing a compound semiconductor of this application and the silicon substrate used therein, the region of the silicon substrate where the compound semiconductor is grown (
Since autodoping of silicon into the compound semiconductor growth layer from a region other than the region to be grown can be prevented, the quality of the compound semiconductor growth layer can be improved.

[Brief explanation of the drawing]

FIGS. 1(A) to (E) are process diagrams showing an example of a method for growing a compound semiconductor; FIGS. 2(A) and (B) are views for explaining an example of a silicon substrate; Figures (A) and CB) are diagrams for explaining the conventional technology. 21...Silicon substrate, 21a...Main surface 21b
...back side, 21c...side surface 21aa...
- Part of main surface 23...Protective film for autodoping opening 25...Resist, 27...GaAs layer.

Claims (2)

[Claims] (1) When growing a compound semiconductor on a silicon substrate, a protective film is provided in a predetermined region of the silicon substrate other than the region where the compound semiconductor is grown to prevent autodoping of silicon from the region to the compound semiconductor, A method for growing a compound semiconductor, comprising growing a compound semiconductor on the silicon substrate with a protective film. (2) In a silicon substrate on which a compound semiconductor is grown, a protective film is provided in a predetermined region other than the region on which the compound semiconductor is grown to prevent autodoping of silicon from the region to the compound semiconductor. silicon substrate.