JPS58145690A - Production of compound semiconductor - Google Patents

Abstract

PURPOSE:In the production of single crystals of compound semiconductor containing volatile components by the liquid capsule method, the polycrystals as a raw material is previously treated with hydrofluoric acid to prevent the formation of polycrystals and increase the yield. CONSTITUTION:Polycrystals as a raw material, such as GaP polycrystals, are dipped in hydrofluoric acid at room temperature for about 24hr and treated with aqua regia under boiling or may be boiled in a combination of hydrofluoric acid and aqua regia. Then, the resultant polycrystals (3) of, e.g., GaP, as a raw material, and B2O3 (4) as the liquid capsule are placed in a quartz crucible (2) in the pressure vessel (1) and melted by heating with heater (5) to cover the surface of GaP melt with B2O3 melt. Further, the vessel (1) is pressurized with a nitrogen gas up to about 70 atmospheric pressure. Then, a seed crystal (6) is dipped through the layer of B2O3 in the melt of GaP (3) and pulled up while rotating to form the single crystal (7).

Description

[Detailed description of the invention] Technical field to which the invention belongs This invention relates to improvements in methods for manufacturing compound semiconductors.

Prior art and its problems Compound semiconductor single crystals containing volatile components are generally produced by the liquid encapsulation method (LEC method).

Here, the production of GaP single crystal will be described as a typical example.

The figure is an explanatory diagram of a GaP single crystal growth apparatus using the LEC method.
P (3) and liquid capsule B203 (4) are heated and melted by a carbon heater (5), and GaP
The liquid surface of (3) is covered with B 203 (4). The inside of the pressure vessel (1) is filled in advance with N2 gas by vacuum displacement, and as the temperature rises, the pressure is increased and maintained at about 70 atmospheres during melting to prevent decomposition and evaporation of GaP. In this state, the yuzu crystal (6) is immersed in the GaP melt through the B 203 (4) layer and gradually pulled up while rotating to create a GaP single crystal (7).

GaP polycrystals as a raw material are generally synthesized directly in a dedicated high-pressure vessel by reacting Ga and P without controlling the vapor pressure of P, and are quite expensive. In addition, GaP polycrystals recovered must be reused as raw materials due to generation of twins, polycrystalization, and production discontinuation due to equipment trouble during single crystal production by the LEC method. The head and tail parts of other GaP single crystals produced will also be collected and reused.

Conventionally, these were appropriately ground (about 10 to 50 ψ), boiled in aqua regia (1 volume of nitric acid, 3 volumes of hydrochloric acid) for about 10 minutes, washed with pure water, dried, and charged into a quartz crucible.

Thereafter, a GaP single crystal is pulled using the LEC method. In this case, when a seed crystal is attached to the melt surface, the temperature is gradually lowered, and the seed crystal is pulled up to initiate head growth, polycrystals are often observed to form on the melt surface. If this is pulled up as it is, only a polycrystalline ingot can be obtained, so the temperature is raised, the polycrystalline part is melted back, the seed crystals are separated from the liquid surface, and after the temperature stabilizes, the seed crystals are attached to the liquid surface again. (seeding). It is thought that some kind of impurity in the raw material is involved in the generation of such polycrystals, but it is not clear. However, if the seeding process is repeated several times, polycrystals may no longer occur. This is considered to be because impurities that form the core of polycrystals gradually diffuse into B2O3.

Since B2O3 has a gettering effect of absorbing metal oxides, there is a possibility that the impurity is some kind of oxide. Even if polycrystals do not occur in the early stages of growth, when the pulling process is completed and the crystals are removed from the high-pressure vessel, polycrystals have formed from the middle of the ingot, and Ga
This reduces the yield of P single crystal production. It is also true that there are impurities in the GaP raw material that are a factor in the generation of polycrystals, which means that even if polycrystals do not form, trace amounts of impurities are mixed into the GaP single crystal, leading to a decrease in quality. 7 Good. Other possible impurities include S that comes into contact with the 1JaP raw material during the production process.
There are i02 and B2O3. Quartz (5i02) is a GaP polycrystal that is solidified after melting in a quartz crucible.
Strongly adheres to the surface. It was also found that B2O3 was sometimes mixed not only on the surface but also in the pores inside the crystal mass. Although it is difficult to determine the impurities that cause the generation of polycrystals, from the possible impurities in the GaP raw material crystals, it is assumed that pretreatment with hydrofluoric acid is more effective in preventing the generation of polycrystals.

It is thought that these impurities are not sufficiently removed in conventional aqua regia treatment, leading to the frequent occurrence of polycrystals.

OBJECTS OF THE INVENTION An object of the present invention is to provide a method for preventing the generation of polycrystals and significantly improving the yield of compound semiconductor single crystal production.

Summary of the Invention It is believed that some impurity in the raw material GaP polycrystal is involved in the generation of polycrystals, and the expected impurities include 8 i02, B2O3, and other metal oxides. I tried pretreatment with acid. Specifically, a step of immersing the raw material GaP polycrystal in hydrofluoric acid at room temperature for about 24 hours was added before the conventional boiling treatment with aqua regia.

In addition, in order to complete this treatment in one step, the objective could also be achieved by boiling in a solution of aqua regia decahydrofluoric acid (1 volume of nitric acid, 1 volume of hydrofluoric acid, 1 volume of decafluoric acid).

Effects of the Invention By etching the GaP raw material crystal in advance with hydrofluoric acid or a solution containing hydrofluoric acid, for example, a solution of hydrofluoric acid added to aqua regia, impurities that cause polycrystal formation in the production of GaP single crystals can be removed. As a result, polycrystalization could be prevented and the yield could be significantly improved.

Embodiments of the Invention An example will be shown in comparison with a conventional treatment method using aqua regia. The treatment methods were boiling with aqueous aqua regia, solution C (1 volume of nitric acid, 1 volume of hydrofluoric acid, 1 volume of hydrofluoric acid) prepared by adding hydrofluoric acid to aqua regia, and immersion in hydrofluoric acid for 24 hours at room temperature. After that, we compared the experimental results when the samples were boiled in aqua regia. At this time, it has also become clear that it is better to crush the raw material GaP crystal into smaller pieces than before. In conventional aqua regia treatment, 4 to 5 out of 10 pulled crystals become polycrystalline (single rate 5/10 to 6/10) The number of times polycrystals that were visible on the melt surface during head growth was 16. ~23 times, which is very high. The raw material crystal is about 5 to 50 ψ rather than about 10 to 50 ψ.
The occurrence of polycrystals decreased when the grain size was made finer to about 10ψ. Since GaP is hard, making it even finer would result in contamination and increase the number of steps, which is considered undesirable. When hydrofluoric acid was used for the aqua regia treatment described above, the occurrence of polycrystals on the melt surface was drastically reduced to 1 to 3 times in 5 pulling experiments, and the number of pulled crystals was 10 times.
None of the samples were polycrystalline. These results are summarized in Table 1.

The following is a blank space: Table 1 In addition to GaP, the present invention also applies to
This method is also effective for compound semiconductors such as A-V.

[Brief explanation of the drawing]

The drawing is a cross-sectional view of an apparatus for explaining GaP single crystal growth by the LEC method. □ ■...High pressure vessel 2...Quartz crucible 3-Ga
P-fusion Q 4. ,,]32o35... Carbon heater 6... Seed crystal 7... Pulled crystal

Claims (1)

[Claims] 1. A method for producing a compound semiconductor, which comprises surface-treating a compound semiconductor crystal used as a raw material in advance with hydrofluoric acid or a solution containing hydrofluoric acid when producing a compound semiconductor single crystal.