JPH0140000B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to epitaxial growth on a semiconductor substrate,
Carbon boats used for impurity doping, etc.
The present invention relates to a method for purifying carbon members such as substrate supports.

Epitaxial growth techniques are widely used in the formation of semiconductor devices, especially gallium phosphide (GaP),
This is an indispensable method for forming compound semiconductor devices such as gallium arsenide (GaAs). And - elements doped as impurities in compound semiconductors include S, Te, Si, etc. as donors,
Zn, Mg, Si, etc. are used as acceptors.

Quartz or carbon is usually used for epitaxial growth boat members, but carbon must be used to prevent oxygen and Si contamination. However, generally, a sintered body of amorphous particles is used for carbon parts of boats, and this
They often absorb, adsorb, or chemically react with impurities. Particularly, during epitaxial growth, the carbon boat comes into contact with various impurities as described above and is therefore contaminated during this process. If the carbon boat remains contaminated or its purification treatment is insufficient, the epitaxial layer to be grown next will be contaminated and the characteristics of the semiconductor device will be greatly affected. This effect is particularly large when growing an epitaxial layer with a low impurity concentration.

For example, nitrogen (N)-doped GaP (green) or GaAsP (yellow) has a structure in which an n-type epitaxial layer is formed on an n-type substrate and a p-type layer is further formed.
In light emitting diodes (LEDs), the emission output increases as the donor concentration of the n-type layer decreases, so it is necessary to grow an epitaxial layer with a low donor concentration. However, if the purification process of the carbon boat is insufficient and donor impurities remain, it is impossible to grow a low concentration epitaxial layer and the light emitting output decreases. In addition, if acceptor impurities remain even after removing donor impurities, part of the n-type layer may
A characteristic defect occurs in which the mold is reversed.

In general, among the elements doped into the epitaxial layer, group elements Zn, Mg, etc.
Si etc. are difficult to evaporate and cannot be completely removed from the carbon boat simply by heat treatment.
Group elements S, Te, etc. easily evaporate by themselves, but tend to form compounds with carbon, and cannot be completely removed simply by heat treatment.

The present invention solves the above problems and provides a method for purifying carbon boats to completely remove all impurities and obtain a highly pure epitaxial layer.

The figure shows a schematic diagram of an example of a carbon purification treatment apparatus for carrying out the method of the present invention. First, in the first step, in order to remove group elements such as Zn, Mg, etc. and group elements such as Si, a carbon boat 1 is placed in a quartz furnace tube 2 in a gas atmosphere containing halogen, such as hydrogen chloride.
and keep them at 1000℃ with heater 3.
Heat treat for about 3 hours. In this process, these elements become chlorides and easily evaporate. However, even chloride cannot completely remove what is adsorbed deep inside the carbon boat. Therefore, as a second step, the carbon boat is heat-treated at 1000° C. for about 4 hours in a reduced pressure evacuated by a vacuum pump 4 in order to completely remove the group or group elements that have become chlorides. Due to the reduced pressure, chloride adsorbed deep within the carbon boat can also be evaporated and removed from the carbon boat. Furthermore, as a third step, the carbon boat is heat-treated at 1000° C. for about 5 hours in a reducing atmosphere, such as hydrogen, in order to remove group elements S, Te, etc. Through this step, the group elements forming compounds with carbon also become hydrides and can be evaporated and removed from the carbon boat.

Using the carbon boat purified in this way,
When a GaP (green) LED was formed by liquid-phase epitaxial growth, a device with high light output and excellent device characteristics was obtained. On the other hand, when the first or second step was omitted in order to confirm this effect, a characteristic defect occurred in which part of the n-type layer became a p-type layer. Also, if the third step is omitted,
A high donor concentration layer grew and the luminescence output decreased dramatically.

In this way, the first step in the purification process for carbon boats is
It is necessary to perform the second and third steps successively, and if any one of them is missing, it is impossible to grow a highly pure epitaxial layer. Also, even in epitaxial growth where only one of donor or acceptor impurities is doped, Si from water, quartz, etc.
and other substances are unavoidable. Therefore, the above three steps are necessary, and the heat treatment temperature in each step is preferably 950°C to 1200°C.

As is clear from what has been explained above,
According to the present invention, all impurities adsorbed on the carbon boat can be completely removed, making it possible to grow a highly pure epitaxial layer. According to the method of the present invention, it is possible to produce highly efficient light emitting diodes and other devices having highly pure epitaxial layers.

[Brief explanation of drawings]

The figure is a schematic diagram of a carbon boat purification treatment device. 1... Carbon boat, 2... Quartz reaction tube, 3
...Heater, 4...Vacuum pump.

Claims (1)

[Claims] 1 The first step is heat treatment in a gas atmosphere containing halogen, and the second step is heat treatment in reduced pressure or vacuum.
1. A method for purifying a carbon member, comprising the steps of: and a third step of performing heat treatment in a reducing gas atmosphere.