JPS6341879B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high dissociation pressure compound semiconductor single crystal pulling apparatus most suitable for producing high resistance substrates for ICs and highly doped materials for lasers.

Prior Art In the production of single crystals of high dissociation pressure compounds, control of the stoichiometry of the crystals is important. If there is a stoichiometric deviation in the raw material melt, point defects are introduced into the crystal, and the point defects condense and become dislocations. It is known that these lattice defects greatly affect device performance. In order to optimally control stoichiometry, it is effective not only to cover the raw material melt with an atmosphere of high dissociation pressure components at the optimum pressure during crystal growth, but also to heat treat the crystal wafer in such an atmosphere. it is conceivable that. For equipment used for this purpose, sealing high dissociation pressure components at high temperatures is an important technology. The following describes a GaAs pulling method as an example.

The pulling method is known as a method for growing GaAs single crystals, and because it is possible to grow crystals with <100> orientation, it is considered the most suitable method for manufacturing high-resistance substrates for ICs.

Generally, in order to avoid scattering of arsenic, which is a high dissociation pressure component, the LEC method is carried out in which the top of the GaAs melt in the crucible is sealed with B ₂ O ₃ liquid.
With this method, it is difficult to reduce and control the defect density. In other words, it is impossible to strictly control the stoichiometry beyond the elemental distribution of the raw material, a large amount of point defects derived from non-stoichiometry are introduced into the crystal, and in order to prevent arsenic from scattering from the crystal surface, The inability to reduce the temperature gradient directly above the solid-liquid interface also causes an increase in dislocation density due to thermal strain during solidification.

In order to improve these shortcomings of the LEC method,
It is necessary to pull the crystal under controlled arsenic pressure. He was the first to develop and apply for a patent on a pulling device that enabled such pulling and the growth of large-diameter crystals (patent application filed in 1983).
157883).

Specifically, as shown in Fig. 3, the arsenic gas sealed container can be divided into an upper container 1 and a lower container 2, and a liquid seal holding part 3 is provided at the joint, and a liquid B ₂ O ₃ and immersing the lower end of the upper container 1 therein, the arsenic gas is sealed inside the container. Then, while rotating the crucible 4, the crystal 6 is pulled up by the pulling shaft 5.

The arsenic pressure in the sealed vessel is controlled by controlling the temperature of the arsenic pressure control furnace 10 to condense arsenic there, and to maintain the temperature of any other part of the sealed vessel higher than this.

Since this device is split-type, the container can be used repeatedly, but the problem lies in the sealing at the split points. In other words, the container is sealed by immersing the lower end of the upper container in the liquid B ₂ O ₃ held in the liquid seal holding part 3, but this structure of the seal does not allow for pressure differences between the inside and outside of the container. At this time, the B ₂ O ₃ liquid overflows and arsenic is lost, so careful attention must be paid to the balance of pressure inside and outside the container. This is especially a problem when the internal arsenic pressure changes drastically during the temperature rise leading to the melting of the raw material and during the temperature drop after completion of lifting, and it is necessary to change the pressure slowly enough to always maintain a balance between the pressure inside and outside the container. In particular, if the imbalance between the internal and external pressures of the container is large during temperature rise, the stoichiometry control of the crystal will lead to a fatal failure. Therefore, in order to improve operability, it is essential to improve the seals at the dividing points of the sealed container.

Means for Solving the Problems The present invention provides an apparatus for manufacturing a high dissociation pressure compound semiconductor single crystal by a pulling method while controlling the pressure of a high dissociation pressure component gas sealed in a container, in which the container can be divided. A high dissociation pressure compound semiconductor single crystal processing apparatus is characterized in that a solid or liquid sealing material is applied to the joint portion of the divided portion, and a stress applying mechanism to the joint portion is provided.

In the above, the number of divisions of the container is not limited to one, but may be two or more.

The sealing material used is a solid sealing material such as expanded graphite, or a liquid sealing material such as B ₂ O ₃ or Ga. However, Ga reacts with high dissociation pressure component gas at high temperatures to form compounds (in the case of As gas,
B ₂ O ₃ is better for repeated use of seals because it forms a skin of GaAs).

A solid sealing material has the advantage of simplifying the structure of the sealing part, being compatible with surrounding materials, and is easy to maintain.

It is also possible to combine solid and liquid sealants to seal with a solid seal immersed in a sealing liquid. In this case, the sealing becomes more complete and at the same time contamination with impurity elements from the solid sealing material can be prevented.

This joint is equipped with a mechanism that constantly applies stress. For example, there is a means for elastically supporting the lower container using a spring.

In this case, the purpose can be achieved by adjusting the strength of the spring appropriately, detecting the position of the movable part of the container, and applying appropriate pressure. Another method would be to insert a load cell in place of the spring and apply stress while automatically controlling the joint so that a constant force is applied to the joint.

The container is equipped with an optical window for internal observation, if necessary, to constantly observe the state of crystal growth.

Further, the material constituting the container is selected from one or more of the following (A) to (D).

(A) Ceramics (silicon carbide, silicon nitride, sialon, boron nitride, aluminum nitride, alumina, zirconia, titanium carbide, titanium nitride) (B) Gas-impermeable carbon (C) Heat-resistant metal materials (molybdenum, molybdenum alloys, tungsten) , tungsten alloy) (D) Carbon or heat-resistant metal material [stainless steel, nickel-based alloy, cobalt-based alloy, in addition to those listed in (C)] whose surface is coated with the ceramics listed in (A) Selection of these materials was done as follows. In other words, 600 to 1250℃ in an arsenic atmosphere of 1 atm.
The test pieces of each material were kept for about 20 hours and then slowly cooled.
When this method is used, heat-resistant steel (K-63), cobalt-based alloy (HS25), and nickel-based alloy (Hastelloy), which are commonly used as container materials, are easily exposed to arsenic atmosphere as they are. However, as a result of many tests and studies, the above material was found to be suitable. Similarly, we investigated the phosphorus atmosphere, which is another high dissociation pressure component, and found that the above materials could be used.

Function: The stress applying device allows the upper and lower containers to be brought into close contact with each other under an appropriate stress, and to ensure that the contact is uniformly applied over the entire contact surface. Furthermore, after the contact surfaces are in close contact with each other, the stress applied to the container can be kept within a sufficiently safe range by selecting a spring coefficient or by automatic control using a load cell against thermal expansion of the container due to an increase in container temperature.

Even when a liquid seal is used, the joints are in close contact with each other so that even if a pressure difference occurs between the inside and outside of the container, the sealing liquid will not suddenly overflow.

Example An example will be described based on the drawings. Figure 1 shows an example in which the divided parts of a sealed container in a lifting device are sealed with a liquid seal. A seal holding part 3 is provided, into which liquid B ₂ O ₃ 7 is placed and the lower end of the upper container 1 is immersed. At this time, the lower container 2 is elastically supported by the spring 8. A coil spring was used as the spring 8, and a stress of 20 to 30 kg/cm ² was applied to the contact portion. This spring 8 ensures that the upper and lower containers are brought into close contact while applying appropriate stress, and also facilitates that the contact is made uniformly over the entire contact surface. Furthermore, by selecting a spring coefficient, the stress applied to the container wall can be kept within a sufficiently safe range even against thermal expansion of the container due to an increase in the container temperature after the contact surfaces are brought into close contact.

In the drawing, reference numeral 9 denotes an optical window, which is made of quartz rod, and whose tip is kept at 850°C so that the state during crystal pulling can be observed from the outside. 10 is an arsenic pressure controlled furnace, and 11 is a heater.

To use such an apparatus, a crucible made of PBN was used, 1 kg of Ga + As was charged, and after direct synthesis in a sealed container, a GaAs single crystal was grown while keeping the arsenic pressure constant. The container was not damaged and the optical window was not fogged. Furthermore, the loss of arsenic before and after the pulling operation was less than 1%.

Figure 2 shows an example of using a solid seal 12 to seal the joint of a sealed container in a lifting device. Expanded graphite was selected as the sealing material, which is elastic at high temperatures and has sufficient adhesion to seal gas. It is something. For this seal as well, the lower container 2 was elastically supported via a spring of the above-mentioned strength, and an appropriate stress was constantly and uniformly applied to the solid seal 12 to avoid damage to the container due to thermal expansion. Further, in order to effectively apply the stress applied to the container to the sealing surface, it is desirable to reduce the contact area, and for this purpose, the lower end of the upper container is curved.

In each of the above specific examples, as a representative of high dissociation pressure compounds,
Although GaAs has been described as an example, the invention is not limited to GaAs, and can also be applied to other high dissociation pressure compounds, such as InAs, which is an As compound, and InP, which is a P compound.

Effects of the invention The sealed container in the atmosphere of a high dissociation pressure component can be divided to facilitate the extraction of crystals produced by pulling, and the solid or liquid seals at the joints are tightly sealed to improve operability when balancing the pressure inside and outside the container. I raised it. The apparatus of the present invention is made of a material that has sufficient strength at high temperatures for growing single crystals and can withstand an atmosphere of high dissociation pressure components, making it possible to use it repeatedly. As a result, a homogeneous, high quality, high dissociation pressure compound semiconductor single crystal can always be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG.
The figure shows a cross-sectional view of a modified example of the joint, and FIG. 3 shows a cross-sectional view of a previous example. DESCRIPTION OF SYMBOLS 1... Upper container, 2... Lower container, 3... Liquid seal holding part, 4... Rotating crucible, 5... Pulling shaft, 6...
Crystal, 7...Liquid B ₂ O ₃ , 8... Spring, 9... Optical window,
DESCRIPTION OF SYMBOLS 10... Arsenic pressure control furnace, 11... Heater, 12... Solid seal, 13... Container drive shaft, 14... Crucible rotation lower shaft, 15... Rotating seal.

Claims (1)

[Scope of Claims] 1. In an apparatus for manufacturing a high dissociation pressure compound semiconductor single crystal by a pulling method while controlling the pressure of a high dissociation pressure component gas sealed in a container, the container is configured to be splittable, and the splitting method is performed. A high dissociation pressure compound semiconductor single crystal pulling apparatus, characterized in that a solid or liquid sealing material is applied to a joint at a location, and a stress applying mechanism is provided to the joint. 2. The high dissociation pressure compound semiconductor single crystal pulling apparatus according to claim 1, wherein the material constituting the container is composed of one or more of the following materials (A) to (D). (A) Ceramics (silicon carbide, silicon nitride, sialon, boron nitride, aluminum nitride, alumina, zirconia, titanium carbide, titanium nitride) (B) Gas-impermeable carbon (C) Heat-resistant metal materials (molybdenum, molybdenum alloys, tungsten) , tungsten alloy) (D) Carbon or heat-resistant metal material [stainless steel, nickel-based alloy, cobalt-based alloy, in addition to those listed in (c)] whose surface is coated with the ceramics described in (A).