JPH0355437B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for growing crystals of compound semiconductors, and in particular to a compound semiconductor method for epitaxially growing a - group compound semiconductor such as GaAs on a Si substrate with a plane orientation of (100). This invention relates to a method for growing crystals.

[Conventional technology]

If we can grow a compound semiconductor such as GaAs on a Si substrate and obtain a high-quality crystal, for example, a crystal with the same quality as a crystal grown on a GaAs substrate,
It is possible to develop new devices that have the advantages of both Si semiconductors and compound semiconductors. for example,
Hybridization will become possible in a new and broader sense, such as the creation of compound semiconductor light-emitting devices on SiLSI.

There are two problems in terms of crystal growth technology when growing a - group compound semiconductor crystal on a Si substrate. That is, (1) the deviation of the lattice constant is extremely large. For example, in the case of GaAs, it is 4% or more. (2) Unlike Si, GaAs is a binary semiconductor and has polarity.

Due to these problems, the conventional method uses Si substrates and GaAs substrates.
First, a buffer layer is grown between the crystals. For the buffer layer, for example, a unitary semiconductor Ge with a small difference in lattice constant from GaAs may be used, or a layer grown at a low temperature may be used.
A GaAs layer is also used.

Among these conventional methods, a method using a low temperature grown GaAs buffer layer is shown in FIG. This method is
Japanese Journal of Applied Physics, 24(6),
June (1985), p. 391.

[Problem that the invention seeks to solve]

However, even when these buffer layers are used, the following problems occur. That is, (1) the buffer layer growth conditions are not completely understood, so the quality of the buffer layer varies, the quality of the GaAs crystal grown on it varies, and the reproducibility of crystal growth deteriorates. Furthermore, there are also problems with (2) stability (change over time) of the grown layer, such as reduced reliability due to the presence of the buffer layer. Furthermore, as a matter of course, (3) compared to GaAs growth on a GaAs substrate,
It requires a complicated process.

The present invention is intended to solve the problems included in the conventional method used to grow crystals of compound semiconductors such as GaAs on Si substrates, that is, the method using a low-temperature growth buffer layer. An object of the present invention is to provide a method for growing compound semiconductor crystals that improves reproducibility and stability of the grown layer and simplifies the process.

[Means for solving problems]

That is, the compound semiconductor crystal growth method of the present invention is a method for growing crystals of - group compound semiconductors on a Si substrate by molecular beam epitaxial growth method, which includes: (a) growing a Si substrate cleaned by a chemical treatment;
A first step of performing heat treatment at a temperature of 1000°C or more for 30 minutes or more under an ultra-high vacuum of 10 ^-10 Torr or less, and then cooling the Si substrate once to a temperature of 600°C or less; (b) in a vacuum; (c) a second step of heating the Si substrate to a temperature within a range of 600 to 750°C while irradiating the Si substrate with a molecular beam of a group V element; and a third step of simultaneously irradiating the Si substrate heated to a temperature within the above range to epitaxially grow group and group compound semiconductors on the Si substrate.

In the method of the present invention, unlike the conventional method, sufficient consideration is given to the heat treatment process after cleaning the Si substrate and before GaAs crystal growth, and the optimum conditions are found. It has become a process that does not require This method is
The process consists of a cleaning process for the Si substrate, a heat treatment process, and a crystal growth process using the molecular beam epitaxial growth method under the same conditions as those used for crystal growth on a normal GaAs substrate. This eliminates the need for a buffer layer growth process and allows the resulting structure to have no buffer layer.
The above three problems associated with the conventional method due to the buffer layer can be improved.

The basic components of the compound semiconductor crystal growth method according to the present invention include first a cleaning process of a Si substrate with a plane orientation of (100), then an ultra-high vacuum (vacuum degree
10 ^-10 Torr or less), followed by a crystal growth process using molecular beam epitaxial growth of GaAs or other compound semiconductors on a Si substrate.

The cleaning process for Si substrates consists of a conventional degreasing process using an organic solvent, followed by a process of repeating surface treatment using a chemical etchant several times to form a clean surface. At the final stage of this process, the Si surface is thin.
It will be covered with a SiO ₂ film. This SiO ₂ film serves to protect the substrate surface during substrate transfer between the cleaning process and the next heat treatment process. Next, this Si substrate is inserted into a chamber under ultra-high vacuum. Here comes the heat treatment step. In this process, Si
The temperature of the substrate is raised to remove the SiO ₂ and SiC films on the surface (800°C to 900°C), and then the temperature is further raised (1000°C to 1050°C) to change the crystal morphology of the Si surface to GaAs.
Change it into a form that is convenient for growth. How the Si surface changes after heat treatment at this high temperature (1000°C to 1050°C) for 30 minutes is shown below using Figure 3. first,
The Si surface, which has been cleaned after removing the SiO ₂ film, is Si
Steps (unevenness) occur in the arrangement of atoms in units of one atomic layer. This is even higher temperature (1000-1050℃)
When heat treatment is performed, it is thought that a step of two atomic layers will occur in the atomic arrangement on the Si surface due to the high temperature heat treatment, and if this happens, the atomic arrangement will change in the growth direction in the crystal growth of - group compound semiconductors, which are binary crystals. The consistency of the crystals becomes better and single crystal growth becomes possible. If the step remains one atomic layer, a grain boundary will occur at the step and it will not become a perfect single crystal. The final crystal growth step is carried out under the same conditions as for crystal growth on a normal GaAs substrate (substrate temperature 600°C to 700°C, group element/group element molecular beam flux ratio 1 to 5, growth rate 0.5 to 2 μm/
hr) by molecular beam epitaxial growth.

The embodiments of the present invention will be mainly described using GaAs as a compound semiconductor, but in addition to this, Al _x Ga _(1-x) As
The crystal growth method of the present invention can also be applied to (0<x≦1) or other - group compound semiconductors. Also, regarding conductivity,
Although Si-doped n-type will be described, other dopant materials and P-type can be similarly applied. By the way, if the crystal material is different, Si
Although the heat treatment process for the substrate may be the same, it must be noted that the growth conditions in the crystal growth process differ depending on the material. In this case as well, the growth conditions may be the same as the conventional conditions.

Further, in the embodiment, an example in which the Si substrate has a (100) plane will be described, but the present invention can also be applied to other planes such as (111) and (110).

〔Example〕

The invention will be explained in more detail in the following examples. Note that the present invention is not limited to the following examples.

Examples of the crystal growth method according to the present invention are shown below.
The basic configuration is shown in FIG. 1 and consists of a cleaning process, a heat treatment process, and a crystal growth process.

First, in the cleaning process, the plane orientation for crystal growth (100) is
A Si substrate (for example, n-type, ρ = 2 to 3 Ω·cm, 2 inches φ) is degreased and cleaned for about 15 minutes by applying ultrasonic waves using an organic solvent such as trichlene, acetone, isopropyl alcohol, etc. Next, it is treated with a scientific etchant. Here, first, the Si substrate is soaked in an etchant (H ₂ SO ₄ :H ₂ O ₂ =4:1) for about 5 minutes to form a thin SiO ₂ film on the surface. Then that
Etch the SiO ₂ film with 5% HF solution. After performing this process several times, the Si substrate was heated to H ₂ SO ₄ :H ₂ O ₂ =4:
1. Soak in solution for about 10 minutes to form a thin SiO ₂ film on the surface. This film is applied to prevent the surface of the substrate from being contaminated during the transportation stage before it is placed into the vacuum chamber.

Next, the Si substrate that has undergone the cleaning process is placed in a preparation chamber of a molecular beam epitaxial growth apparatus and subjected to heat treatment. The processing conditions are 900°C to 1050°C for 30 minutes under ultra-high vacuum (vacuum level 10 ^-10 Torr or less).

This example was carried out under four conditions in which the temperature was varied by 50° C. within the above temperature range in order to find the optimum processing temperature. Thereafter, the substrate temperature is lowered to 300°C and the substrate is transferred to a growth chamber under ultra-high vacuum to begin the crystal growth process.

This process uses molecular beam epitaxial growth. First, the temperature of the As source is increased, and As ₄ ,
While applying a molecular beam such as As ₂ to the Si substrate, the substrate temperature is adjusted.
Raise to 600℃ (growth temperature). At this temperature, group element/group element flux ratio 3, growth rate
n-GaAs while doping with Si under the condition of 1 μm/hr.
The layer was crystal grown to approximately 2 μm. Grown n-GaAs
To evaluate the crystallinity of the layer, the surface morphology was observed using an interference microscope, and the mobility and electron concentration were measured using Hall measurement and CV measurement.

The observation results of surface morphology are shown in FIGS. 4 to 7. The surface morphology showed significant differences depending on the heat treatment temperature, with treatment temperatures of 900℃ (Figure 4) and 950℃.
(Fig. 5), a unique boundary morphology is observed when grains grow. On the other hand, 1000℃
At 1050°C (Fig. 6) and 1050°C (Fig. 7), the surface condition became uniform and no morphology was observed, indicating that a good single crystal was obtained. Next, the Hall measurement results are shown in FIG. At heat treatment temperatures of 900°C and 950°C, the electron hole mobility becomes extremely low.
On the other hand, at 1000℃ and 1050℃, it is 2000 (cm ² /V.
S) or higher. As far as hole mobility is concerned, heat treatment at 1000°C appears to yield better results than at 1050°C. Since hole measurements can only obtain information averaged in the depth direction, we used the CV measurement method to determine the electron concentration distribution in the depth direction. Heat treatment temperature 950℃,
The results at 1000°C are shown in Figure 9. Both results show that as the distance from the Si substrate interface increases, the GaAs crystallinity improves, and the activation rate of doped Si improves, leading to an increase in electron concentration.

The rate of increase is more remarkable when the heat treatment temperature is 1000°C, and if the layer is grown to a thickness of about 2 μm, the n-
A value approximately equal to the electron concentration of the GaAs layer was obtained.

From the above three evaluation results, it is determined that the optimum temperature range of the heat treatment temperature in this example is 1000 to 1050°C. It was also found that a layer with good crystallinity sufficient for device fabrication can be obtained from a layer with crystal growth of 2 μm or more from the Si substrate interface.

〔Effect of the invention〕

As described above, the compound semiconductor crystal growth method of the present invention heat-treats a Si substrate under predetermined conditions, and then irradiates the Si substrate with a molecular beam of a group element while
The Si substrate is heated to a predetermined temperature, and then molecular beams of group and group elements are simultaneously irradiated onto the Si substrate to epitaxially grow the − group compound semiconductor on the Si substrate. By choosing appropriately, GaAs crystals can be grown without buffer layer growth. Furthermore, in this method, compared to the conventional crystal growth method in which growth of a buffer layer is interposed, the step of forming a buffer layer can be omitted, thereby improving the reproducibility of the crystal growth process compared to the conventional method. In addition, it is possible to suppress the occurrence of deterioration over time due to a buffer layer that may occur after growth.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the compound semiconductor crystal growth method of the present invention, FIG. 2 is an explanatory diagram of the conventional compound semiconductor crystal growth method, and FIG. 3 is an explanatory diagram of the crystal surface morphology in the heat treatment step in the method of the present invention. Figures 4 to 7 are explanatory diagrams showing variations at heat treatment temperatures of 900°C, 950°C, 1000°C and
Micrograph showing the structure (surface morphology) of n-GaAs crystal when grown at 1050℃, No. 8
The figure shows heat treatment temperature and n-
Figure 9 is a graph showing the relationship between the hole mobility of GaAs crystal and the n-GaAs obtained by the method of the present invention.
3 is a graph showing the depth distribution of electron concentration in FIG.

Claims (1)

[Claims] A method for growing crystals of a 1-group compound semiconductor on a Si substrate by molecular beam epitaxial growth, which includes: (a) a Si substrate cleaned by a chemical treatment;
A first step of performing heat treatment at a temperature of 1000°C or more for 30 minutes or more under an ultra-high vacuum of 10 ^-10 Torr or less, and then cooling the Si substrate once to a temperature of 600°C or less; (b) in a vacuum; (c) a second step of heating the Si substrate to a temperature within a range of 600 to 750°C while irradiating the Si substrate with a molecular beam of a group V element; a third step of epitaxially growing a - group compound semiconductor on the Si substrate by simultaneously irradiating the Si substrate heated to a temperature within the above range. How to grow. 2. The compound semiconductor crystal growth method according to claim 1, wherein the Si substrate has a (100) plane orientation, and the first step heat treatment is performed at 1000 to 1050°C. Group 3 element is Ga and/or Al,
Claim 1, wherein the group element is As, and GaAs and/or Al _x Ga _(1-x) As (0<x≦1) are epitaxially grown on a Si substrate. Compound semiconductor crystal growth method. Flux ratio of group element to group 4 element is 1 to 5, and epitaxial growth rate is 0.5 to 2μ
4. The method for growing compound semiconductor crystals according to claim 3, wherein the growth rate is m/hr. 5. The compound semiconductor crystal growth method according to claim 1, wherein the first step and the second and third steps are performed in different vacuum chambers.