JPH0226887A - Liquid phase epitaxial growth method - Google Patents

Abstract

PURPOSE:To shorten the time required for a growth stage and to improve productivity by removing impurities such as oxygen and moisture adsorbed in a growth system including a boat for growth by first heat treatment at a low temp. and by carrying out a second heat treatment at a high temp. CONSTITUTION:In a liq. phase epitaxial growth stage with a metal having >=80 deg.C m.p. as a solvent, a boat, a solute, a crystal substrate and the solvent metal are used in a growth system. They are subjected to a first heat treatment at >=80 deg.C to the m.p. of the solvent metal in a flow of an inert gas or gaseous hydrogen to remove impurities adsorbed in the growth system. Melting or baking is then carried out by a second heat treatment at the m.p. of the solvent metal or above.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid phase epitaxial growth method used for compound semiconductor crystal growth and the like.

[Conventional technology]

The liquid phase epitaxial growth method is particularly the simplest method among methods for growing epitaxial crystals of compound semiconductors, and can obtain high-quality crystals in a small area.

This method basically involves dissolving a solute in a solvent of a low-melting point metal such as In or Ga at a predetermined temperature, reaching near saturation and holding for a certain period of time, and then slowly cooling this melt to reduce the solubility. , the excess solute corresponding to the width of the temperature drop is precipitated as crystals on a substrate such as InP XGaAs,
This method is used to obtain epitaxial crystals such as InP and InGaAsP.

Properties of epitaxial crystals obtained by this method,
In other words, the impurity concentration, electrical properties such as mobility, and crystallinity are determined not only by the high purity of the raw materials such as the solvent but also by the high purity of InP.
,, It is known that it greatly depends on the presence of solutes such as GaAs and impurities such as oxygen and moisture adsorbed on the boat used for growth.

In order to highly purify raw materials or remove these impurities, growth boats containing solutes and growth melt are usually exposed to inert gas such as argon, nitrogen, or hydrogen gas for an extremely long period of time. It is necessary to perform high-temperature heat treatment inside.

For example, when growing an InP crystal on an InP substrate by liquid phase epitaxy, in order to make the carrier concentration of the crystal about 5 x 10'6 atoms cm-', the In melt is heated at 700° in advance. Baking heat treatment is performed at C for about 10 hours while flowing hydrogen gas (Special Publication No. 61-123)
(See Publication No. 69). After this baking is completed and cooled, the raw material is placed in a predetermined boat, heated again in the apparatus, and kept at high temperature for a certain period of time before epitaxial growth is performed.

[Problem to be solved by the invention]

As described above, the conventional method has disadvantages in that it requires high-temperature heat treatment over a long period of time, resulting in poor productivity and consuming a large amount of electricity and high-purity gas.

In addition, when performing epitaxial growth using these raw materials after baking the raw materials, the amount of impurities such as oxygen and moisture adsorbed to the growth boat or solvent varies depending on the handling when loading the raw materials into the growth equipment. Even if high-temperature heat treatment is performed for a predetermined period of time, crystals with the desired impurity concentration may not be obtained, and reproducibility may be poor.

In addition to this, if the temperature starts to rise to a high temperature before the impurities such as oxygen and moisture adsorbed on the growth boat are sufficiently removed, these impurities will locally gather at a high concentration during this temperature rise. , these molecules mix into the growing melt.

This has the disadvantage that the growth melt is contaminated and a longer heat treatment is required to remove these impurity molecules.

The present invention aims to solve the above-mentioned problems in a liquid phase epitaxial growth method.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a liquid phase epitaxial growth method using a metal with a melting point of 80° C. or higher as a solvent, in which the boat, solute, crystal substrate, and solvent metal used in the growth step are replaced with an inert gas or hydrogen gas. The first step is performed in a gas stream at a temperature of 80"C or higher and lower than the melting point of the solvent metal.
This is followed by a second heat treatment at a temperature equal to or higher than the melting point of the solvent metal for melting or baking.

It is desirable that this first heat treatment is performed until the impurity gas concentration is sufficiently reduced, and after detecting the decrease in the impurity gas concentration, the temperature is raised as it is and the second heat treatment is performed. Further, the lower limit of the first heat treatment temperature is preferably 100'C or higher, which is the boiling point of water.

Here, the second heat treatment includes baking, but also includes setting the temperature to a predetermined temperature for liquid phase epitaxial growth and holding it for a predetermined time until slow cooling is started.

[For production]

According to the liquid phase epitaxial growth method according to the present invention, since impurities such as oxygen and moisture adsorbed in the growth system such as a growth boat can be sufficiently removed by the first heat treatment, the second heat treatment performed subsequently The reproducibility of the effect is improved, and the time for the second heat treatment can also be shortened.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

In this example, InPO liquid phase epitaxial growth is taken as an example, and In as a growth solvent, InP as a solute, and an InP substrate as a crystal substrate are placed in predetermined positions in a graphite boat for growth 1 shown in FIG. 1 is placed in a quartz reaction tube 2. Next, the inside of this tube is evacuated to a pressure of 10-5 Pa or less, and then hydrogen is replaced and hydrogen is caused to flow at a rate of 26/min. The melting point of In is approximately 1
Since the temperature is 55°C, the graphite boat 1 for growth is heated to 130°C as the first heat treatment as shown in the temperature program shown in Fig. 2 using the heating furnace 3 shown in Fig. 1, and the oxygen concentration as described below is o. Hold for about 1 hour until o5ppm or less. After that, a second heat treatment at 685°C
Raise the temperature to 1-2 hours. Thereafter, slow cooling is started at a cooling rate of 0.45° C./min, and InP is epitaxially grown on the crystal substrate within a predetermined temperature range.

Among the impurities, it is possible to know whether oxygen in particular has been removed from the growth system by monitoring the oxygen concentration in the hydrogen gas flowing through the reaction tube and coming out. According to the results of this monitor, the oxygen concentration in the hydrogen gas does not increase even if the temperature is further increased after the first heat treatment is performed at a low temperature (130°C) for one hour. It was found that oxygen could be sufficiently removed from the growth system such as commercial boards.

In order to confirm the effect of the first heat treatment according to the present invention, a case where liquid phase epitaxial growth was performed without performing this first heat treatment under the same conditions as the temperature program shown in FIG. 2, and a case where the temperature program shown in FIG. The carrier mobility was measured at an absolute temperature of 300° for each InP crystal obtained when the first heat treatment was performed according to the program and liquid phase epitaxial growth was performed. According to the results, the former case was approximately 3000 c+a/Volt·sec, while the latter method according to the present invention was approximately 4500 cd/sec.
It was Volt/second. As a result, it was found that the impurity concentration was considerably reduced, and it was concluded that the first heat treatment in the present invention has an extremely large effect.

In this example, when performing liquid phase epitaxial growth, the first heat treatment was performed at a low temperature and the above-mentioned effect was obtained. If heat treatment is performed at a low temperature, a similar effect of removing impurities can be obtained, and the baking time at a high temperature can be shortened.

〔Effect of the invention〕

Since the present invention has the above-described configuration, purification of the growth melt or the growth raw material in the liquid phase epitaxial growth method can be performed in a certain short time by performing the first heat treatment at a low temperature. , the resulting epitaxial crystal has certain excellent properties.

Since epitaxial growth can be performed in a short time and the crystal substrate is not exposed to high temperatures for a long period of time, adverse effects on the crystal substrate can be reduced.

The time required for the liquid phase epitaxial growth process for obtaining high-purity epitaxial crystals can be greatly shortened and productivity can be improved. In addition, it is economically advantageous because it consumes less electricity and less high-purity gas.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus used for liquid phase epitaxial growth in this example, and FIG. 2 is a temperature program diagram for the liquid phase epitaxial growth process in this example. In addition, in the symbols used in the drawings, 1-・=-----111-----Growth graphite port 2--・-----1・----1--------Quartz reaction tube 3--111-----Heating furnace.

Claims (1)

[Claims] In a liquid phase epitaxial growth method using a metal with a melting point of 80° C. or higher as a solvent, a boat, a solute, a crystal substrate, and a solvent metal used in the growth step are grown in an inert gas or hydrogen gas stream for 80° C. ℃
Liquid phase epitaxial growth characterized by performing a first heat treatment at a temperature above and below the melting point of the solvent metal, and subsequently performing a second heat treatment at a temperature above the melting point of the solvent metal for melting or baking. Method.