JPH09106949A - Compound semiconductor substrate and manufacturing method thereof - Google Patents

Abstract

(57) Abstract: The surface of the compound semiconductor thin film 12 is not flat,
In addition, device characteristics such as HEMT are deteriorated due to poor crystallinity. SOLUTION: A compound semiconductor substrate 10 in which compound semiconductor thin films 20 having different lattice constants are formed on a Si substrate 11
On the first compound semiconductor thin film 12a, the compound semiconductor thin film 20 is formed at the first crystal growth temperature and heat-treated at a temperature not lower than the second crystal growth temperature and not higher than 650 ° C. And a second compound semiconductor thin film 14 formed on the metal thin film 13a at the second crystal growth temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor substrate and a method for manufacturing the same, and more particularly to a compound semiconductor substrate used for, for example, an optical or high-speed electronic device and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a compound semiconductor thin film, which is different from the compound semiconductor thin film, is epitaxially grown on a substrate, and the manufacture of the compound semiconductor thin film and a compound semiconductor substrate capable of utilizing respective advantages of the substrate have been studied. For example, by epitaxially growing a GaAs thin film on a silicon (hereinafter referred to as Si) substrate, a compound semiconductor substrate (GaAs / Si) having both the mechanical strength of the Si substrate and the high-speed response of GaAs is manufactured. Cage,
The compound semiconductor substrate obtained by such a method is
It is applied to electronic devices and optical devices.

However, the compound semiconductor substrate (G
Since Si and GaAs in (aAs / Si) have different lattice constants, it was difficult to directly epitaxially grow the GaAs layer on the Si substrate. In order to deal with this problem, a two-step growth method has been proposed (Akiyama et al: Japanese Journal of Applied Phy.
sics Vol.23 (1984), No.11, L843 ~ L845). First, at a relatively low temperature (first crystal growth temperature) of about 400 to 500 [deg.] C., a first compound semiconductor thin film of GaAs or the like having an amorphous state of about 5 to 20 nm is grown on a Si substrate. Next, the temperature is raised to a relatively high temperature (second crystal growth temperature) of about 600 to 750 ° C. to single crystallize the first compound semiconductor thin film by solid phase growth, and a second crystal of GaAs or the like is formed thereon. Is a method of epitaxially growing the compound semiconductor thin film of (3) by a desired thickness.

[0004]

In the method of manufacturing a compound semiconductor substrate by the above two-step growth method, a compound semiconductor thin film can be epitaxially grown on a Si substrate. However, as shown in FIG. 3, when the first compound semiconductor thin film 12 close to the amorphous state is grown on the Si substrate 11 (FIG. 3A), the first compound semiconductor thin film 12 is formed near the interface between these. Strain energy based on the difference in lattice constant between the Si substrate 11 and the Si substrate 11 is easily generated. Further, when the temperature is raised from the first crystal growth temperature to the second crystal growth temperature, the first compound semiconductor thin film 12 aggregates due to the effect of heat to form island crystals 12b (FIG. 3B). Although not shown, when the second compound semiconductor thin film is further epitaxially grown on the island-shaped crystals 12b, the islands become large and dislocations occur near the meeting points when the islands meet with each other, and the surface of these island-shaped crystals 12b grows. The surface roughness occurs on the surface of the second compound semiconductor thin film, reflecting the uneven shape of the above. With such a compound semiconductor substrate, a high electron mobility transistor (HEM
When an electronic device such as T: High Electron Mobility Transistor) is formed, there is a problem that the mobility of the two-dimensional electron gas at the interface of the active layer is likely to be lowered and the characteristics of the device are deteriorated.

The present invention has been made in view of these problems, and a compound semiconductor thin film having a flat surface and excellent crystallinity was epitaxially grown on a Si substrate without forming island crystals. An object is to provide a compound semiconductor substrate and a method for manufacturing the same.

[0006]

Means for Solving the Problems and Effects Thereof In order to improve the flatness of the Si substrate that determines device characteristics such as HEMT, the first compound semiconductor thin film is aggregated by the heat treatment to form islands. It should be suppressed.

Generally, at the time of the island formation, the relationship between the surface energy of the first compound semiconductor thin film and the Si substrate and the interface energy between the first compound semiconductor thin film and the Si substrate is as follows: The shape is determined so that the surface energy of the first compound semiconductor thin film is minimized. Therefore, if the surface energy of the first compound semiconductor thin film can be lowered, the island formation can be suppressed.

The present inventors suppress the formation of islands of the first compound semiconductor thin film by forming a metal thin film of 1 to 2 atomic layers after forming the first compound semiconductor thin film and then performing heat treatment. The inventors have found what can be done and have completed the present invention.

That is, in order to achieve the above object, the compound semiconductor substrate according to the present invention is a compound semiconductor substrate in which a compound semiconductor thin film is formed on a Si substrate, wherein the compound semiconductor thin film is at a first crystal growth temperature. A first compound semiconductor thin film formed and heat-treated at a temperature not lower than a second crystal growth temperature and not higher than 650 ° C .; a metal thin film having 1 to 2 atomic layers formed on the first compound semiconductor thin film; It is characterized by comprising a second compound semiconductor thin film formed on the metal thin film at the second crystal growth temperature.

According to the above compound semiconductor substrate, the compound semiconductor thin film having a flat surface and excellent crystallinity is epitaxially grown on the Si substrate, and device characteristics such as HEMT can be improved.

When the metal thin film becomes thick, island formation occurs during heat treatment. On the other hand, if it is too thin, there is no effect of forming a metal thin film. The metal thin film is preferably 1 to 2 atomic layers, and most preferably formed to be 1 atomic layer.

The method of manufacturing a compound semiconductor substrate according to the present invention is the method of manufacturing a compound semiconductor substrate in which a compound semiconductor thin film is formed on a Si substrate, wherein the first compound semiconductor thin film is formed at a first crystal growth temperature. A step of forming, a step of forming a metal thin film of 1 to 2 atomic layers on the first compound semiconductor thin film, and a step of performing heat treatment by raising the temperature to a temperature of not lower than a second crystal growth temperature and not higher than 650 ° C. And a step of forming a second compound semiconductor thin film at the second crystal growth temperature.

According to the above method of manufacturing a compound semiconductor substrate, the first compound semiconductor thin film is formed, and then the metal thin film is formed by one or two atomic layers to reduce the surface energy of the first compound semiconductor thin film. Since the island formation of the first compound semiconductor thin film during the heat treatment can be suppressed, the compound semiconductor substrate having excellent surface flatness and crystallinity of the compound semiconductor thin film can be formed. This heat treatment temperature is 650 ° C
If it exceeds, the island formation occurs, so this temperature is set to the second crystal growth temperature or more and 650 ° C. or less.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a compound semiconductor substrate and a method of manufacturing the same according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing the structure of a compound semiconductor substrate (GaAs / Si) according to the embodiment when GaAs is used for the compound semiconductor thin film and In is used for the metal thin film. )-(C) are schematic partial cross-sectional views showing a part of the steps in manufacturing the compound semiconductor substrate. Note that components having the same functions as those of the conventional example are denoted by the same reference numerals.

A first compound semiconductor thin film 12a is formed on the Si substrate 11, and the first compound semiconductor thin film 12a is formed.
A metal thin film 13a is formed on the above, and a second compound semiconductor thin film 14 is further formed thereon.
These first compound semiconductor thin film 12a and metal thin film 13a
The compound semiconductor thin film 20 is composed of the second compound semiconductor thin film 14 and the second compound semiconductor thin film 14.

In manufacturing the compound semiconductor substrate 10 having the above structure, the surface of the Si substrate 11 is first cleaned using a hydrofluoric acid-based etchant to remove the natural oxide film (not shown) on the Si substrate 11. After that, it is immersed in a mixed aqueous solution of aqueous ammonia, hydrogen peroxide and pure water to form a thin oxide film as a surface protective film. Next, after placing this in an ultra-high vacuum chamber (not shown), the inside of the chamber is heated to raise the Si substrate 11 to a predetermined substrate temperature to remove the oxide film and form a clean surface. To do. Next, Si
The substrate 11 is cooled to a predetermined substrate temperature, the Ga cell and the As cell of an epitaxial growth apparatus (not shown) are opened, and a predetermined growth rate, a partial pressure ratio of Ga to a predetermined As (Ga to a vapor pressure of As). The first compound semiconductor thin film (before heat treatment) 12 is epitaxially grown to a predetermined thickness at a vapor pressure ratio) (FIG. 2A). Then, the G
The a cell and the As cell are closed, the In cell is opened with the substrate temperature at the time of the temperature decrease, and a metal thin film (before heat treatment) 13 is formed on the first compound semiconductor thin film (before heat treatment) 12 in an amount of 1 to 2 atomic layers. (FIG. 2B). Next, after opening the As cell and heating the substrate to a predetermined substrate temperature while irradiating with As flux, heat treatment is performed for 5 to 10 minutes (see FIG. 2).
(C)) While maintaining the substrate temperature, the Ga cell is opened, and the second compound semiconductor thin film 14 is grown to a predetermined thickness at a predetermined growth rate and a predetermined partial pressure ratio of Ga to As.

Although the molecular beam epitaxy (MBE) method is used as the growth method in the present embodiment, the growth method is not limited to this, and as another embodiment, a metal organic chemical vapor deposition (MOCVD) method is used. But it is possible. In this case, the raw materials are trimethylgallium (TMG) and arsine (As
H ₃ ) and trimethylindium (TMI) are used.

Further, in this embodiment, GaAs is used as a raw material for the compound semiconductor thin film 20, but the present invention is not limited to this, and InP and Ga may be used as another embodiment.
It is also possible to grow a compound semiconductor thin film such as P or InAs.

In addition, although In is used as a raw material for the metal thin film 13a in the present embodiment, the present invention is not limited to this. In another form, elements other than the elements used for the first and second compound semiconductors are used. Any metal element that can form a mixed crystal with these compound semiconductors or can serve as an n-type or p-type dopant can be used, and Sn, Sb, Bi, or the like can also be used.

[0021]

【Example】

Thin film forming method: Molecular beam epitaxy Raw material: Solid Ga, As, In Si substrate 11: Si substrate having (001) plane orientation and tilted by 2 ° in [110] direction When removing oxide film on Si substrate 11 surface Substrate temperature: 900 ° C. Substrate temperature during cooling: 400 ° C. Film thickness of first compound semiconductor thin film 12a: 0.1 μm Growth rate of first compound semiconductor thin film (before heat treatment) 12:
0.3 μm / h As during growth of first compound semiconductor thin film (before heat treatment) 12
Ratio of Ga to Ga: 10 Substrate temperature during heating: 600 ° C. Heat treatment time: 10 minutes Thickness of second compound semiconductor thin film 14: 3 μm Growth rate of second compound semiconductor thin film 14: 1.0 μm /
h G for As during the growth of the second compound semiconductor thin film 14
Partial pressure ratio of a: 20 Hereinafter, the results of investigating the flatness and crystallinity of the compound semiconductor thin film 20 grown by the manufacturing method according to the example will be described.

The second compound semiconductor thin film 14 has a flatness.
The surface roughness of is measured by an atomic force microscope (AFM),
Table 1 shows the results of evaluation based on the standard deviation of the heights of the convex portions on the reference virtual plane. As a comparative example, Table 1 also shows the results of evaluation using a compound semiconductor thin film formed by the conventional two-step growth method.

[0023]

[Table 1]

As is clear from Table 1, the flatness of the compound semiconductor thin film 20 of the example is 3.0 to 6.0 nm as compared with the flatness of the compound semiconductor thin film of the comparative example of 5.0 to 6.0 nm.
The thickness is 3.5 nm, and the first compound semiconductor thin film 12
The surfaces of a and the second compound semiconductor thin film 14 are flattened.

Next, the compound semiconductor thin film 20 is crystallized.
Table 2 shows the results of evaluation of the crystallinity of the above by the half width of the X-ray 2 crystal diffraction peak. The comparative example is the same as that used in the investigation of the flatness.

[0026]

[Table 2]

As is clear from Table 2, the compound semiconductor thin film 20 according to the example has excellent crystallinity as compared with the comparative example, and the first compound semiconductor thin film 12a and the second compound semiconductor thin film
The dislocation density in the compound semiconductor thin film 14 is decreased.

As is clear from the above results, according to the compound semiconductor substrate 10 of the example, the compound semiconductor thin film 2
0 is formed at the first crystal growth temperature and is heat-treated at a temperature not lower than the second crystal growth temperature and not higher than 650 ° C., and 1 is formed on the first compound semiconductor thin film 12a. ˜2 atomic layer metal thin film 13a and a second thin film formed on the metal thin film 13a at the second crystal growth temperature
Since the compound semiconductor thin film 14 is composed of the compound semiconductor thin film 14, the compound semiconductor thin film 20 has a flat surface and excellent crystallinity, so that device characteristics such as HEMT can be improved.

Further, the compound semiconductor substrate 10 according to the embodiment.
According to the manufacturing method of 1., the step of forming the first compound semiconductor thin film (before heat treatment) 12 at the first crystal growth temperature;
Forming 1 to 2 atomic layers of a metal thin film (before heat treatment) 13 on the compound semiconductor thin film (before heat treatment) 12 and performing heat treatment by raising the temperature to a temperature not lower than the second crystal growth temperature and not higher than 650 ° C. And the step of forming the second compound semiconductor thin film 14 at the second crystal growth temperature,
Since the surface energy of the first compound semiconductor thin film (before heat treatment) 12 can be lowered and the islanding of the first compound semiconductor thin film (before heat treatment) 12 at the time of heat treatment can be suppressed, the surface flatness of the compound semiconductor thin film 20. Also, the compound semiconductor substrate 10 having excellent crystallinity can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a compound semiconductor substrate according to an embodiment of the present invention.

FIG. 2 is a schematic partial cross-sectional view showing a part of the manufacturing process of the compound semiconductor substrate according to the embodiment in the order of processes.

FIG. 3 is a schematic partial cross-sectional view showing, in the order of steps, part of a conventional method of manufacturing a compound semiconductor substrate by a two-step growth method.

[Explanation of symbols]

 11 Si substrate 12a First compound semiconductor thin film 13a Metal thin film 14 Second compound semiconductor thin film 20 Compound semiconductor thin film

Claims (2)

[Claims] 1. A compound semiconductor substrate having a compound semiconductor thin film formed on a Si substrate, wherein the compound semiconductor thin film is formed at a first crystal growth temperature and at a temperature of not lower than a second crystal growth temperature and not higher than 650 ° C. Formed on the first compound semiconductor thin film, a metal thin film of 1 to 2 atomic layers formed on the first compound semiconductor thin film, and formed on the metal thin film at the second crystal growth temperature. A compound semiconductor substrate comprising a second compound semiconductor thin film. 2. A method of manufacturing a compound semiconductor substrate for forming a compound semiconductor thin film on a Si substrate, the method comprising forming a first compound semiconductor thin film at a first crystal growth temperature,
Forming a metal thin film of 1 to 2 atomic layers on the first compound semiconductor thin film; performing a heat treatment by raising the temperature to a second crystal growth temperature or more and 650 ° C. or less;
And a step of forming a second compound semiconductor thin film at a crystal growth temperature.