JPH05213693A - Formation of crystalline layer of compound semiconductor - Google Patents

Abstract

PURPOSE:To form a crystalline layer of a compd. semiconductor nearly free from dislocation and residual stress on a porous silicon substrate. CONSTITUTION:When the surface of a silicon substrate is made porous and compd. semiconductor crystals are grown on the substrate to form a crystalline layer of the compd. semiconductor, the substrate is heated at a relatively low temp. of <=500 deg.C in a vacuum of <=10<-1>Torr before introducing gaseous starting materials for the crystal growth and carrier gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a crystal layer of a compound semiconductor on a porous silicon substrate.

[0002]

2. Description of the Related Art Many attempts have been made to grow a compound semiconductor such as GaAs on a silicon substrate from the viewpoint of cost reduction and hybridization. However, due to the difference in physical properties between the compound semiconductor and silicon (lattice mismatch, difference in thermal expansion coefficient, problem of growing polar substance on non-polar substance, etc.), it is different from normal growth method. A method is needed. For example, methods such as two-step growth, thermal cycle annealing, and strained superlattice have been used to grow a single crystal thin film of a compound semiconductor, which is a different material, on a silicon substrate.

[0003]

However, the above-mentioned silico
The method using a silicon substrate is a method of forming a compound semiconductor on a single crystal substrate.
It is said that the crystallinity of the grown thin film is inferior to the case of lengthening
There was a problem. That is, it is caused by the difference in the above physical properties.
Problems such as dislocation, residual stress, warpage, etc. are not completely solved,
Taking the dislocation density as an example, the GaAs substrate obtained by the LEC method
Dislocation density is 10^Fourcm^-2Whereas the degree is silicon
The GaAs crystal thin film grown on the substrate is 10 ⁶cm^-2And
It shows a fairly high value. Therefore, the present invention is
The points are eliminated, and there are few dislocations and residual stresses on the silicon substrate.
An attempt to provide a method for forming a crystalline layer of a compound semiconductor
It is something.

[0004]

The present invention provides a method for forming a crystal layer of a compound semiconductor, which comprises a porosification step for making the surface of a silicon substrate porous and a compound semiconductor crystal growth step. A method for forming a crystal layer of a compound semiconductor, which comprises heating in a vacuum of 10 ^-1 Torr or less at a relatively low temperature of 500 ° C. or less before introducing a source gas or a carrier gas in a crystal growth step. . As a method of making the surface of the silicon substrate porous, a method of making it porous by an anodization method in a hydrofluoric acid solution is preferable. The thickness of the porous layer is not particularly limited, but may be, for example, 0. It can be formed with a thickness of several μm to several hundred μm. The pore size of the porous material is, for example, 20 to 3
The size is about 00Å.

As a compound semiconductor grown on a silicon substrate, for example, a binary III-V group compound semiconductor such as GaAs, GaP, InP, or AlGaAs or AlGa.
P, InAlAs, InAlP, GaAsP, GaIn
Ternary III-V group compound semiconductors such as P, and Zn
It is selected from II-VI group compound semiconductors such as S and ZnSe. Further, these compound semiconductors can be stacked.

[0006]

When the compound semiconductor is grown on the porous silicon substrate, the strain due to the lattice mismatch can be relaxed and grown, so that the introduction of misfit dislocations can be prevented. Further, the porous silicon has flexibility that Young's modulus is about 1/10 of that of ordinary silicon, and the contact area between the thin film and the substrate can be reduced. Therefore, even in a combination such as a III-V group compound semiconductor and silicon, which have greatly different thermal expansion coefficients, the strain between the two substances can be absorbed by the porous portion, and the dislocation or residual of the compound semiconductor layer can be absorbed. The stress can be significantly reduced.

Conventionally, a silicon substrate was made porous in a hydrofluoric acid solution by an anodization method, dried by nitrogen blowing, and put into a growth furnace to start the growth of a compound semiconductor single crystal. According to this method, the crystallinity of the grown compound semiconductor thin film was poor, and good reproducibility could not be obtained. The present inventors investigated the cause and found that the pore diameter of the porous portion is as small as 20 to 300 Å, so that water or hydrofluoric acid that has entered the pores during the porosification step is sufficiently dried by nitrogen blow drying. It was found that the crystallinity deteriorates because it cannot be removed and is leached and adhered to the substrate surface in the compound semiconductor growth step.

By heating the silicon substrate at 800 to 1000 ° C. in hydrogen and arsine before crystal growth, the surface of the silicon plateau is cleaned not in the holes,
Moreover, a thermal cleaning method has been proposed in which the properties of the grown compound semiconductor crystal are improved by rearrangement of atoms, but sufficient crystallinity cannot be obtained due to high heating temperature, and reproducibility is also poor. It was

Therefore, in the present invention, when a compound semiconductor is grown using a porous silicon substrate, 10 ^-1 T is introduced before introducing a source gas or a carrier gas such as hydrogen.
By heating at a relatively low temperature of 500 ° C. or lower in a vacuum of or or lower, it is possible to sufficiently remove water and hydrofluoric acid that have entered the pores in the porosification step, and to grow the compound semiconductor to be grown thereafter. The thin film had improved crystallinity and good reproducibility. Since porous silicon is vulnerable to heat and its structure is apt to change, and its crystallinity deteriorates at a high temperature of more than 500 ° C.
It was decided to heat at a relatively low temperature of 00 ° C. or less.

[0010]

Example An GaAs thin film was grown on a substrate whose surface was made porous by anodizing in a hydrofluoric acid solution according to the growth profile shown in FIG. First,
After setting the porous substrate in the growth furnace,
The temperature was raised to 400 ° C while exhausted to 0 ^-6 Torr vacuum.
Stabilized for 30 minutes and held. After that, hydrogen and arsine gas were introduced into the furnace and the temperature was raised to 420 ° C, and the temperature was stabilized to grow the GaAs thin film to a thickness of 150Å. Then, the temperature was raised to 550 ° C and stabilized to this temperature. GaAs thin film is grown to a thickness of 2.5 μm, and the temperature is raised to 650 ° C. and stabilized at this temperature.
The thin film was grown to a thickness of 2.5 μm.

Comparative Example A GaAs thin film was grown on a substrate whose surface was made porous by anodizing the surface of a silicon substrate in a hydrofluoric acid solution according to the growth profile shown in FIG. First, after setting the porous substrate in the growth furnace, hydrogen and arsine gas were introduced into the furnace and the temperature was changed to 420 ° C.
The temperature of the GaAs thin film is raised to 150 ° C and stabilized at this temperature.
It is grown to a thickness of Å, then heated to 550 ° C, stabilized to this temperature to grow a GaAs thin film to a thickness of 2.5 μm, further heated to 650 ° C, stabilized to this temperature and made to GaAs. The thin film was grown to a thickness of 2.5 μm.

(Comparison evaluation) When the grown GaAs thin films were compared with each other by the half-value width of the peak due to the GaAs thin films by the two-crystal X-ray diffraction method, the GaAs thin film obtained in the comparative example had a large half value width of 250 seconds. On the other hand, the GaAs thin film obtained with the half width of the example shows a significantly small half width of 160 seconds, which means that the crystallinity is improved.

[0013]

According to the present invention, by adopting the above-mentioned structure, dislocations having a small full width at half maximum can be formed on the porous silicon substrate.
It has become possible to grow a compound semiconductor thin film with little residual stress.

[Brief description of drawings]

FIG. 1 is a diagram showing a growth temperature profile adopted in an example of the present invention.

FIG. 2 is a diagram showing a growth temperature profile adopted in Comparative Example 2.

Claims (1)

[Claims] 1. A porosity for making the surface of a silicon substrate porous.
Having a qualification step and a compound semiconductor crystal growth step
In a method for forming a crystalline layer of a compound semiconductor,
Introduce source gas and carrier gas in the conductor crystal growth process
10 before ^-1In vacuum below Torr, below 500 ° C
Of compound semiconductors characterized by heating at a relatively low temperature
Method for forming crystal layer.