JPH0339039B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for producing single crystals of high dissociation pressure compounds, such as gallium arsenide substrates (GaAs substrates), for ultrahigh speed ICs and lasers.

Conventional technology As a method for producing high dissociation pressure compounds such as GaAs substrates for ultra-high-speed ICs and lasers, the Czyochralski (CZ) method can easily produce round ingots with <100> orientation compared to the horizontal Bridgeman (HB) method. It has the characteristic of being able to obtain, and is regarded as important. but,
This CZ method leaves unresolved problems in terms of optimization and controllability of crystal growth conditions for reducing and uniformizing the lattice defect density in products.

One of these issues is optimizing the pressure of arsenic, which is a high dissociation pressure component, and the other is optimizing the thermal environment during growth.

To explain the first problem, conventionally, the mainstream was the liquid encapsulation Czyochralski (LEC) method, which prevents arsenic from scattering by sealing the surface of the GaAs melt with boron oxide. Since it is not possible to make adjustments beyond the element distribution, more precise control of stoichiometry is required to further reduce the lattice defect density. for that purpose,
During crystal growth, it is necessary to always cover the melt surface with a constant optimum arsenic pressure and control the stoichiometry of the melt.

For this purpose, it is necessary to seal the arsenic atmosphere in a container made of a material that is stable at the high temperatures used for crystal growth, and this sealed container must also have an arsenic pressure control section to accurately control the arsenic pressure. ,
It is necessary to have functions such as being able to seal in arsenic gas against rotation of the vertical axis, being able to be easily and repeatedly cut off to take out the crystal, and being able to optically observe the crystal during growth.

As a crystal growth device that satisfies these conditions,
The present inventors have previously proposed an apparatus for growing an arsenic compound single crystal (Japanese Patent Application No. 157883/1983).

For the second problem, optimizing the thermal conditions during growth, it is important to control the temperature and temperature gradient at the growth interface.
The temperature at the growth interface needs to be constant for precise control of stoichiometry, and the temperature gradient determines the growth rate, but thermal strain during solidification causes lattice defects. A constant defect density is necessary for crystal growth with uniform defect density.

Furthermore, lowering the temperature gradient at the solid-liquid interface has a great effect on lowering the dislocation density, but on the other hand, the range of appropriate melt temperature and pulling rate for crystal growth becomes narrower, and the precision of melt temperature cannot be adjusted. Without proper control, single crystal growth is impossible.

Conventionally, control of thermal conditions has been a blind spot in the CZ method. Conventionally, in order to compensate for the latent heat of solidification and maintain the solid-liquid interface and temperature constant under conditions where the melt surface position decreases with crystal growth,
It has been practiced to gradually change the temperature of the heater according to an empirically determined program.

Problems to be Solved by the Invention However, the above method does not guarantee that the thermal environment at the solid-liquid interface remains constant, and is not sufficient to improve the quality of crystals.

It is effective to keep the melt surface position constant in order to control the thermal environment at the solid-liquid interface, but this alone may cause changes in the melt volume, crystal growth and the accompanying release of latent heat, and the crucible edge position. Due to changes, etc., the melt surface temperature cannot be kept constant.

For this reason, it is necessary to directly detect and control the temperature of the melt surface. The first possible way to do this is to use a thermocouple, but inserting a thermocouple directly into the melt will cause unnecessary disturbance to the movement of the melt as the crucible rotates, resulting in uniform crystal growth. give the factors. Moreover, it is difficult to read the temperature in areas with strong temperature gradients, and it is also difficult to operate.

Means for Solving the Problems This invention attempts to solve the difficulty in precisely controlling the thermal environment of the CZ method, and its configuration is to seal the high dissociation pressure component gas and control the pressure. In a method for pulling a single crystal of a high dissociation pressure compound, the inner container for sealing the high dissociation pressure component gas is constructed so that it can be divided and the divided portion can be fixed with good sealing, and the upper part of the inner container and the inner container are separated. At the bottom, rotary seals with liquid sealing material are provided for bearing parts that enable rotation and vertical movement of the upper and lower rotating shafts, and a translucent material is bonded to the upper part of the inner container with good adhesion. This is a method for growing single crystals of high dissociation pressure compounds, which is characterized by optically detecting the temperature of the melt surface through an optical window, and controlling the heating source based on the results.

In the method described in Japanese Patent Application No. 58-157883, the arsenic compound single crystal is grown in a container that seals arsenic gas, so there is no need to seal with boron oxide, which was required in the past, and it is not necessary to use a sealed container. The melt surface can be directly observed using a penetrating optical window such as a quartz rod, quartz pipe, or glass fiber. This optical window may be made of other light-transmitting material, such as sapphire, or may have a plate-like shape in the inner container. The joint with the inner container must be able to seal the arsenic atmosphere sufficiently well, and examples of joints used for this purpose include the use of a taper joint and a solid gasket such as expanded graphite. Through such an optical window, the temperature of the melt surface can be measured using an infrared radiation thermometer. At this time, the above optical window
When condensation of Ga ₂ O ₃ , GaAs, As, etc. occurs, light absorption occurs and significantly impedes measurement, but this can be avoided by the following method.

(1) Set the temperature at the tip of the optical window to 610 to 950℃ or 1080℃.
Keep at a temperature of ~1200°C.

(2) Does not use quartz as the arsenic atmosphere sealed container or crucible material, reduces residual oxygen, and reduces Ga ₂ O ₃
To suppress reactions caused by oxygen that cause condensation of GaAs and GaAs.

(3) By setting the wavelength of the infrared radiation thermometer used to be around 1 μm and using a dual-wavelength type, constant temperature support can be obtained even when cloudy weather occurs. Arsenic gas and quartz do not absorb light in this wavelength range, and are suitable for the purpose of this invention.

Embodiments of the present invention will be specifically described with reference to the drawings. FIG. 1 is a sectional view showing an outline of an apparatus suitable for carrying out the present invention. Outer chamber 15 with inert gas inlet pipe 13 and exhaust pipe 14
an inner chamber 10 with an inner chamber lid 9 therein;
A heater 5 and a main heater 6 are provided to surround the chamber. Inner chamber 1
0 contains outer chamber 15 and inner chamber 1.
There is a crucible 11 made of PBN supported by a rotating shaft that penetrates the wall of the crucible and can move up and down and rotate. It passes through the outer chamber 15 and the inner chamber lid 9 and can move up and down and rotate. A seal 7 is provided at a location where the rotating shaft passes through the inner chamber 10 and the inner chamber lid 9, and the inner chamber lid 9 is provided with an arsenic pressure controlled furnace 4.

A quartz rod 1 is provided as an optical window passing through the outer chamber 15 and the inner chamber lid 9. A taper joint 17 was used to join the inner chamber lid. A thermometer with a diameter of 1 μm is used to detect the temperature of the melt surface in the crucible 11 through this.
A dual-wavelength infrared radiation pyrometer 2 using a wavelength of 0.85 μm is adopted.

Using the analog signal obtained from this dual-wavelength infrared radiation pyrometer 2 and the power of the thermocouple 8 in contact with the main heater 6 for heating the crucible, the output of the heater is controlled in a cascade manner by the cascade temperature controller 3. do. In addition, in order to maintain the melt level in the crucible 11 at a constant height while the single crystal 12 is being pulled, a drop in the liquid level is detected based on a signal from a gravimetric automatic diameter control sensor connected to the pulling rotation shaft. is determined by a computer and automatically corrected.

In the above embodiment, the optical window 1 is joined by a tapered joint 17, but as shown in FIG. This may also be carried out by compressing the mixture by means of. Such a lowering mechanism may be provided at a penetration point of the outer chamber 15.

Example A total of 800 gr of Ga and As was loaded into the crucible 11,
After directly synthesizing GaAs in an arsenic gas sealed container,
GaAs single crystal was pulled. During this time, the tip of the quartz rod 1 for optical windows was always kept at about 850°C.
No clouding occurred. The indication from the dual-wavelength radiation pyrometer 2 reflected fluctuations in the temperature of the liquid surface, and showed fluctuations of approximately ±5°C at the peak value, but after the start of lifting,
The average temperature after entering the straight body was maintained at ±1°C. As a result, uniform crystals (diameter 4.5 cmφ, length 7 cm) with an EPD of 2000 cm ^-3 or less were obtained from the front part to the back part at a center area of about 2.5 cmφ.

Although the present invention has been explained using GaAs as an example, it is not limited to GaAs, and can also be applied to high dissociation pressure compounds such as InAs.

Effects As explained above, according to the present invention, it is possible to produce a high dissociation pressure compound single crystal in which the longitudinal uniformity of the dislocation distribution is greatly improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of an apparatus suitable for carrying out the present invention, and FIG. 2 is a detailed view of another embodiment of the joint portion of the optical window with the inner container. 1... Quartz rod, 2... Two-wave infrared radiation pyrometer, 3... Cascade temperature controller, 4... Arsenic pressure control furnace, 5... Heater, 6... Main heater,
7... Rotating seal, 8... Thermocouple, 9... Inner chamber lid, 10... Inner chamber, 11... Crucible, 12... Single crystal, 13... Inert gas introduction pipe, 14... Exhaust pipe , 15...outer chamber, 1
6... Pulling shaft, 17... Taper joint,
18...solid gasket, 19...screw.

Claims (1)

[Claims] 1. A method for pulling a single crystal of a high dissociation pressure compound while sealing a high dissociation pressure component gas and controlling the pressure, in which the inner container for sealing the high dissociation pressure component gas is divisible, and The divided parts are configured to be fixed with good sealing performance, and the upper and lower parts of the inner container each have a liquid sealing material for a bearing part that enables the rotation and vertical movement of the upper and lower rotating shafts. A rotary seal is provided, and the temperature of the melt surface is optically detected through an optical window made of a translucent material bonded to the upper part of the inner container with good adhesion, and the heating source is controlled based on the results. A method for growing single crystals of high dissociation pressure compounds. 2. The high dissociation pressure compound single crystal growth method according to claim 1, wherein the optical window is joined to the inner container with a tapered joint. 3. The high dissociation pressure compound single crystal growth method according to claim 1, wherein the optical window is joined to the inner container using a solid gasket.