JPS61210616A - Formation of semiconductor thin film - Google Patents

Abstract

PURPOSE:To prevent the generation of thermal deformation by epitaxially growing a semiconductor thin film by heating a compound semiconductor substrate to be grown through a compound semiconductor substrate made of the same material. CONSTITUTION:When a compound semiconductor substrate 2 which has a thermal decomposition prevention layer on the back surface and is made of the same material with a compound semiconductor substrate to be grown is heated from the back surface, the thermal decomposition of materials constituting a substrate from the back surface of the substrate 1 is restrained by the vapor pressure of the materials constituting the substrate escaped from the front surface of the substrate 2 which is heated directly by the heat conduction or the heat radiation from the front surface of the substrate 2 at a higher temperature than the temperature of the compound semiconductor substrate 1 to be grown and the flat back surface of the substrate 1 is maintained after the growth. Since the thermal decomposition prevention layer exists on the back surface of the substrate 2, the evaporation of component materials from the back surface of the compound substrate 2 is prevented. The generation of the thermal deformation of the substrate 1 is also prevented since the thermal decomposition prevention layer is not provided on the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for forming a semiconductor thin film, in which a semiconductor thin film is epitaxially grown while heating a compound semiconductor substrate to be grown, using the MBE method (molecular beam epitaxial method) or the like.

<Prior art> In recent years, the MBE method has been used for ultra-high frequency semiconductors because it has advantages such as excellent controllability of grown semiconductor thin films and impurity doping, and the ability to obtain steep and flat heterointerfaces. It is attracting attention as a method for manufacturing optoelectronic devices such as devices or semiconductor lasers.

Conventionally, in the MBE method, a jig (hereinafter referred to as a susceptor) made of a high-melting point metal such as molybdenum (MO) is used to hold the semiconductor substrate to be grown in a growth chamber and heat it to a desired temperature. Soldering is performed using a low melting point metal (hereinafter referred to as solder) such as (In). The method used to heat a semiconductor substrate during crystal growth is to first heat the susceptor with a tantalum heater installed behind the susceptor, and then heat the semiconductor substrate by heat conduction through the molten solder. Such a method of heating a semiconductor substrate requires a step of removing solder deposited on the back surface of the semiconductor substrate after epitaxial growth. Normally, the solder described in "2" can be removed by etching with hot hydrochloric acid, etc. However, since the solder causes a chemical reaction with the back surface of the semiconductor substrate when heated, even after the solder is removed, there will be unevenness and unevenness on the back surface of the semiconductor substrate. Roughness occurs.

This unevenness on the back surface of the semiconductor substrate is a serious problem in the production of devices using MBE-grown semiconductor substrates, as it makes the semiconductor substrate easy to break during subsequent photolithography and other processes, and also makes microfabrication difficult. there were.

In recent years, in order to solve such problems, a so-called solder-free substrate heating method has been proposed in which a solder such as In is not used between the susceptor and the back surface of the semiconductor substrate.

The first method is to fix the semiconductor substrate to a susceptor that has a through hole that is the same size or smaller than the semiconductor substrate, and directly heat the semiconductor substrate through the through hole by heat radiation from a heater. There is. However, with this method, it is difficult to keep the temperature distribution within the plane of the semiconductor substrate below ±30°C, and although there is no problem when the semiconductor paper board is grown at a temperature of about 600°C,
For example, when using a compound semiconductor substrate such as gallium arsenide (GaAs),
When heated above ℃, the constituent materials of the compound semiconductor substrate are
It evaporates violently from the back side of the compound semiconductor substrate, causing unevenness or surface roughness on the back side of the compound semiconductor substrate.

In addition, as a second method, the back surface of the compound semiconductor substrate to be grown is directly brought into close contact with a susceptor made of a material such as Mo,
There is a method in which the susceptor is heated by a heater behind the susceptor, and the compound semiconductor substrate to be grown is heated by thermal conduction or thermal radiation from the susceptor. However, this second
In this method, the degree of adhesion between the compound semiconductor substrate and the susceptor is poor, and the temperature at the center of the compound semiconductor substrate decreases.
Furthermore, when a compound semiconductor substrate is grown at a temperature of 700° C. or higher, roughness and unevenness are observed on the back surface due to thermal decomposition.

In addition, as a third method, M
There is a method in which a high-melting point metal such as O is vapor-deposited in advance by sputtering or the like, and the back surface of the compound semiconductor substrate is directly heated by thermal radiation from a heater using the first method described above.

However, although this third method suppresses thermal decomposition on the back surface of the compound semiconductor substrate, it requires an additional step of vapor depositing a high melting point metal on the back surface of the compound semiconductor substrate before MBE growth, and also requires cleaning of the surface of the compound semiconductor substrate. This results in an increase in surface defects after growth. Furthermore, thermal distortion during growth occurs due to the difference in coefficient of thermal expansion between the high melting point metal on the back surface and the GaAs substrate, making it impractical.

<Objective of the Invention> Therefore, an object of the present invention is to apply MBE to a compound semiconductor substrate to be grown, such as GaAs, which contains a component that is released by heating.
In a method for epitaxially growing a semiconductor thin film by a method, the compound semiconductor substrate to be grown is heated to a relatively high temperature without complicating the pretreatment process of the compound semiconductor substrate to be grown before the epitaxial growth of the compound semiconductor substrate to be grown. However, it is possible to suppress the evaporation of substrate constituent materials from the back surface of the compound semiconductor substrate to be grown, maintain the flatness of the back surface of the compound semiconductor substrate, and prevent thermal distortion from occurring due to thermal history during epitaxial growth. That's true.

<Structure and operation of the invention> In order to achieve the above object, the present invention includes mounting a compound semiconductor substrate made of the same material as the compound semiconductor substrate to be grown and having a thermal decomposition prevention layer on the back surface on a susceptor, and The method is characterized in that a compound semiconductor substrate to be grown (2) is brought into close contact with the surface of the compound semiconductor substrate, and the compound semiconductor substrate to be grown is heated via the compound semiconductor substrate to epitaxially grow a semiconductor thin film.

When the compound semiconductor substrate having a thermal decomposition prevention layer on the back side is heated from the back side, it is immediately heated to a higher temperature than the compound semiconductor substrate to be grown due to thermal conduction or thermal radiation from the surface of the compound semiconductor substrate. The vapor pressure of the substrate constituents that separate from the surface of the compound semiconductor substrate suppresses thermal decomposition of the substrate constituents from the backside of the compound semiconductor substrate to be grown, and the flat backside of the compound semiconductor substrate to be grown is maintained even after growth. be done. Furthermore, since the thermal decomposition prevention layer exists on the back surface of the compound semiconductor substrate, evaporation of the constituent materials of the compound semiconductor substrate from the back surface is prevented.

Furthermore, since the compound semiconductor substrate to be grown itself is not provided with a thermal decomposition prevention layer, the occurrence of thermal strain in the compound semiconductor substrate to be grown itself is prevented.

<Example> Hereinafter, the present invention will be explained in detail with reference to an illustrated example in which a semiconductor thin film is grown by MBE.

In FIG. 1, ■ is a GaAs substrate to be grown with a diameter of 2'', which is an example of a compound semiconductor substrate to be grown, and 2 is the above-mentioned G to be grown.
It is a GaAs substrate with a diameter of 2'', which is a compound semiconductor substrate made of the same constituent material as the aAs substrate 1, and a silicon nitride (SiN) layer as an example of a thermal decomposition prevention layer is formed on the back surface 2a of the GaAs substrate 2 by RF sputtering. (High frequency sputtering method).

The GaAs substrate 1 to be grown and the GaAs substrate 2 are stacked and fitted into the stepped hole 3c of the flantz portion 3b of the Mo susceptor 3, which has a through hole 3a slightly smaller than the GaAs substrate 1 to be grown. It matches. Then, the outer periphery of the GaAs substrate 1 to be grown is held down with the stopper 4, and the stopper 4 is attached to the flange portion 3C with the wire 5 (J).
1. The GaAs substrate 1 to be grown and the GaAs substrate 2 are mounted on a susceptor 3. - The back surface 2a of the GaAs substrate 2 having the SiN layer is provided with a through hole 3a, and the GaAs substrate 2 is directly heated by heat radiation by the heater 6 disposed in the through hole 3a. I'm trying to heat it up.

” When the GaAs substrate 2 is heated by the heater 6,
The GaAs substrate 1 to be grown is uniformly heated to, for example, 700° C. by thermal radiation or conduction from the surface of the GaAs substrate 2 . The surface of the heated GaAs substrate to be grown is irradiated with molecular beams 7 of Ga and As, and a semiconductor thin film (not shown) is epitaxially grown.

At this time, on the back surface of the GaAs substrate 1 to be grown, the constituent material (Ga) is grown at a predetermined vapor pressure corresponding to its temperature.

However, due to the vapor pressure of the Ga and As released from the surface of the GaAs substrate 2, which is directly heated to a higher temperature than the GaAs substrate 1 to be grown, the GaAs to be grown is evaporated.
Evaporation of Ga and As from the back surface of the s-substrate 1 is suppressed, and therefore the flatness of the back surface of the GaAs substrate 1 to be grown is ensured even after growth.

In addition, although the back surface 2a of the GaAs substrate 2 is directly heated by the heater 6, the SiN layer
evaporation is suppressed. Therefore, the GaAs substrate 2 is
It could also be used when growing a CaAs substrate 1 to be grown over a long period of time or over multiple times.

In addition, since no thermal decomposition prevention layer made of a different material such as MO is provided on the back surface of the GaAs substrate 1 to be grown, and the GaAs substrate 2 made of the same constituent material is in close contact with it, the thermal history during growth No thermal distortion etc. will occur.

In the first embodiment, a GaAs substrate was used as the compound semiconductor substrate, but an InP substrate or the like may also be used.

In addition, although a SiN layer was used as the thermal decomposition prevention layer,
An O2 layer, a BN layer, etc. may also be used.

<Effects of the Invention> As is clear from the above, according to the present invention, in MBE growth etc., without complicating the substrate pretreatment process,
Even at a relatively high substrate temperature, the flatness of the compound semiconductor substrate to be grown can be maintained, and thermal distortion due to thermal history during growth can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an apparatus used in an embodiment of the present invention. 1. GaAs substrate to be grown, 2-GaAs substrate, 3 susceptor.

Claims (1)

[Claims] (1) In a semiconductor thin film forming method in which a semiconductor thin film is epitaxially grown on the surface of a compound semiconductor substrate to be grown while maintaining the compound semiconductor substrate to be grown which has been prepared in advance heated to a desired temperature, the compound semiconductor substrate to be grown is A compound semiconductor substrate made of the same kind of material and having a thermal decomposition prevention layer on the back surface is mounted on a susceptor, and the compound semiconductor substrate to be grown is brought into close contact with the surface of the compound semiconductor substrate, and the compound semiconductor substrate to be grown is A method for forming a semiconductor thin film, comprising epitaxially growing a semiconductor thin film by heating through the compound semiconductor substrate.