JPS6158230A - Crystal growth method - Google Patents

Abstract

PURPOSE:To prevent the generation of spits by adding a simple process by a method wherein, after a reactive deposit is grown on the surface of a crystal substrate, the reactive deposit is grown on the surface of a crystal substrate, the reactive deposit is evaporated by applying heat in a vacuum atmosphere, and then crystal is grown by performing a molecular beam epitaxial growth method. CONSTITUTION:A semiinsulative GaAs substrate is exposed to an oxidizing atmosphere. The C on the substrate surface is converted to CO2, a Ga single unit is converted to Ga2O, and an As single unit is converted to AsO3 respectively by the above-mentioned heat treatment. Then, said substrate is heated up in a vacuum atmosphere. The GaO2 and the AsO3 are sublimated by the above-mentioned heat treatment. A GaAs crystal layer is grown on the substrate, the surface of which is cleaned by the above-mentioned procedure, by performing a molecular beam epitaxial growth method (MBE). According to this method, the single unit substance located on the substrate surface, which is the cause of crystal defect generating in the crystal layer grown when the MBE is performed, is converted to a reactive deposit which can be aublimated easily and it is removed in the heat treatment which will be performed subsequently, thereby enabling to have a very clean surface of the substrate. Accord ingly, an excellent crystal layer, having few crystal defects, can be obtained on the above- mentioned substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to molecular beam epitaxial growth (molecular beam epitaxial growth).
This invention relates to improvements in a crystal growth method called the ar beam epitaxy (MBE) method.

[Conventional technology]

In recent years, techniques for growing and growing compound semiconductor crystal layers by applying the MBE method have come into widespread use.

The reason for this is that it is useful for growing extremely thin, high-quality compound semiconductor crystal layers.

Conventionally, when implementing the MBE method, as a pretreatment to grow a high-quality crystal layer, the surface of the crystal substrate is washed with organic liquid, and then the substrate is wet-etched.
The method is to wash it with pure water, dry it, place it in an MBE growth apparatus, and heat it up. When etching the substrate, if the substrate is a GaAs-based substrate, a mixed solution of H2SO and +H2O2 is used as the etching solution.

[Problem that the invention seeks to solve]

Although it is said that the MBE method can grow high-quality crystals, the occurrence of some crystal defects cannot be avoided.

In other words, although the cause has not been confirmed, in the case of GaAs-based substrates, carbon (C) remaining on the surface or the presence of Ga alone is called spit when the MBE method is applied to grow a crystal layer. It is thought to induce crystal defects. The presence of carbon is caused by organic substances (for example, wax) used when processing the substrate or residues from cleaning with an organic liquid.

The present invention makes it possible to suppress the generation of spits by adding a very simple process when growing crystals by molecular beam epitaxial growth.

[Means for solving problems]

In the crystal growth method of the present invention, a crystal substrate is exposed to an active gas atmosphere to generate a reactive deposit on the surface of the crystal substrate, the reactive deposit is evaporated by heating in a high vacuum, and then the reactive deposit is evaporated by heating in a high vacuum. , a crystal is grown on the surface of the crystal substrate using a molecular beam epitaxial growth method.

[Effect]

As mentioned above, the crystal defects called spits that occur when crystals are grown on GaAs-based crystal substrates by applying the MBE method are believed to be carbon remaining on the surface, and those that are caused by Ga alone. Although the theory that it is Ga alone seems to be a strong force, according to the inventor's experiments, it has been found that the influence of carbon is also quite large.

According to the above means, carbon on the substrate surface reacts with the active gas and becomes gasified, and Ga alone also reacts with the active gas to form a deposit that easily sublimes.This deposit is easily evaporated by heat treatment, so that the substrate The surface can be kept in a clean state without the presence of carbon or Ga alone, and therefore the crystal layer grown thereon has extremely few defects.

- [Example] (1) A semi-insulating GaAs substrate is cleaned with an organic liquid.

[Slight etching is applied to the substrate surface using a 21 Hz SO4+H20z mixture.

(3) Wash the substrate with pure water.

(4) Expose the substrate to an oxidizing atmosphere (active gas atmosphere).

Due to this oxidation treatment, the carbon on the substrate surface becomes COz,
The caB body changes to Ga2O, and the As body changes to As03.

(5) Place the substrate in an MBE growth apparatus for 500
C) Heat treatment at a higher temperature.

Usually, G a 20 is at a temperature of ~500 ('C), and AS03 is at a temperature of 135 ("II:) (7). Note that Co2 is a gas, so it is already vaporized.

(6) A normal MBE method is applied to grow a GaAs crystal layer on the substrate whose surface has been cleaned through the above steps.

The crystal defects in the GaAs crystal layer thus obtained were about 1/10 of that in the GaAs crystal layer grown by the conventional technique. In the above example, the substrate was exposed to an oxidizing atmosphere, but this atmosphere can also be replaced by a hydrogen atmosphere, and if only an oxidizing atmosphere is used, the oxide layer will be thick. On the other hand, if there is a risk that the crystallinity may deteriorate, it is better to mix an appropriate amount of argon (Ar) gas into the active gas and use the sputtering effect together.

The figure is a diagram showing data when a substrate surface is processed according to the present invention, with the number of spits plotted on the vertical axis and the processing time (in minutes) plotted on the horizontal axis.

Here, a parallel plate type dry etching device is used.
13. Experiments were conducted by generating plasma at a frequency of 56 MHz. The diameter of the sample wafer is approximately 5 (am) (2 (inches)), and the Δ mark is H.
2 ion, X marks represent Ar ions, and O marks represent 02 ions.

〔Effect of the invention〕

The crystal growth method of the present invention involves exposing a crystal substrate to an active gas atmosphere to generate a reactive deposit on the surface of the crystal substrate, then evaporating the reactive deposit by heating in a high vacuum, and then , a crystal is grown on the surface of the crystal substrate using a molecular beam epitaxial growth method.

In this way, the single substance on the substrate surface that causes crystal defects that occur in the crystal layer grown by applying the MBE method becomes a reaction deposit that easily sublimes, and is removed during the subsequent heat treatment process. Since the carbon is gasified and diffused, the surface of the substrate becomes extremely clean. Therefore, the crystal layer grown thereon can be of good quality with few crystal defects.

[Brief explanation of drawings]

The figure is a diagram showing the relationship between the number of spits and the processing time.

Claims (1)

[Claims] A crystal substrate is exposed to an active gas atmosphere to generate a reactive deposit on the surface of the crystal substrate, then the reactive deposit is evaporated by heating in a high vacuum, and then the reactive deposit is evaporated by molecular beam epitaxial growth. A crystal growth method comprising the step of growing a crystal on the surface of a crystal substrate.