JPH0699221B2 - Compound semiconductor crystal growth device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a compound semiconductor crystal growing apparatus for growing a compound semiconductor crystal such as a GaAs crystal using an airtight container, and in particular, providing a pressure buffer space to provide airtightness. The present invention relates to a device in which the inflow of impurities into a container is suppressed.

[Prior Art] A compound semiconductor crystal, for example, a GaAs crystal, has excellent properties not found in other materials, such as light emission characteristics, magnetoelectric conversion characteristics, and high electron speed, and is a material of extremely high industrial value. .
A large number of methods have been proposed for the crystal growth method, and some methods have been used for industrial production. Among them, the most widely used method is to float an inert liquid such as B ₂ and ₃ on a GaAs melt, prevent the dissociation of As from the solution, and rotate the seed crystal in contact with the melt as a nucleus. It is a liquid sealing pulling method (LEC method) that pulls up while. This method has a feature that a single crystal can be obtained relatively easily, has a high industrial productivity, and has been put to practical use in applications such as semi-insulating GaAs crystal for LSI.

By the way, when an inert liquid of B ₂ O ₃ is floated on the GaAs melt,
The temperature gradient in this portion becomes large, and the crystal is subjected to thermal strain. Since GaAs crystals are inherently brittle and weak against thermal strain, the thermal strain applied to the crystals during manufacturing may cause crystal defects called dislocations or, in extreme cases, cracks in the crystals. In order to improve these, it is effective to make the temperature distribution of the entire crystal uniform and reduce the thermal strain. However, in this case, since the temperature of the entire crystal rises, As is dissociated from the crystal surface during pulling, Ga is precipitated on the crystal surface, and a new source of dislocations is generated.

Therefore, in order to solve these problems, the LEC method was improved by covering the crucible with an airtight container made of a quartz container or the like, and the gap between the pulling shaft and the airtight container was covered with a B ₂ O ₃ liquid sealant. It has been proposed to prevent the dissociation of As from the surface of the GaAs melt by closing the inside of the container with an As atmosphere in an airtight container (JP-B-61-1397). It is called the double melt seal pull-up method and is the most suitable method for growing GaAs crystals in an environment with small thermal strain.

Another method for reducing thermal strain is called the vertical Bridgman method. A GaAs raw material is put into a vertically long crucible to make a GaAs solution, and the GaAs crystal is manufactured by solidifying from the bottom of the crucible provided with a seed crystal. In this method, since it is necessary to prevent the dissociation of As from the melt, the whole crucible is covered with an airtight container, and the As placed in the crucible is heated and gasified to create an As atmosphere (WAGault et al. J.
Crystal Growth 74, P491 (1986)). Compared to the LEC method, it is easier to soak the entire crucible and a crystal with less dislocations can be obtained.

Any of the methods described above can produce a crystal with a small thermal strain. However, since the growth is basically in an airtight container, it is necessary to balance the pressure inside and outside the container, and if the pressure balance is not good, the container may explode. Therefore, pores for pressure balance may be provided (see Japanese Patent Laid-Open No. HEI-1
-37497), a buffer passage for preventing the diffusion of As, which is a volatile component, out of the container is provided by further developing it (Japanese Patent Application No. 01-272542) to provide a diffusion barrier for As. It has been devised to do so. As a result, it is possible to prevent As from being dissociated from the GaAs melt even if the container is not a completely airtight container, so that it is possible to grow a good quality crystal with small thermal strain in a simple and highly operable device.

[Problems to be Solved by the Invention] However, even with these methods in which the thermal strain is small and the dissociation of As can be prevented, the gas outside the container flows in as the pressure inside and outside the container fluctuates. Therefore, even if impurity contamination is prevented at the stage of accommodating the melt raw material, there is a possibility that a gas containing impurities (for example, Si or the like) outside the container may flow in during growth to contaminate the grown crystal. High purity is required for compound semiconductors such as GaAs, and even when impurities are added,
Since a limited element is added at a limited concentration, the accidental inclusion of impurities as described above is the most undesirable phenomenon and is a serious problem.

An object of the present invention is to provide a buffer space for preventing the inflow of an impurity gas from the outside when growing a compound semiconductor crystal in a growing device having a pore or a pressure buffer passage in an airtight container, thereby providing the above-mentioned structure. It is an object of the present invention to provide a compound semiconductor crystal growing device capable of growing a high-purity compound semiconductor crystal by solving the drawbacks of the conventional techniques.

[Means for Solving the Problems] The present invention covers the entire crucible in which the compound semiconductor melt is collected with a highly airtight container, and the inside of this airtight container has a high vapor pressure among the compound elements constituting the melt. The present invention is applied to a compound semiconductor crystal growing apparatus in which an atmosphere containing the other element gas is provided and a pressure buffer passage having a narrowed passage for communicating the inside and the outside of the container is provided in an airtight container.

Then, in addition to the spatially narrowed pressure buffer passage, a spatially widened pressure buffer space is provided. This pressure buffer space is provided at either or both of the inlet and outlet of the pressure buffer passage.
Is the volume of the air-tight container almost equal to the volume of the space filled with gas?
It is composed of a pressure buffer container having a volume larger than that.

The pressure buffer passage includes pores and a pressure buffer passage, and the pressure buffer passage further includes a thin tube and a labyrinth structure.

The pressure buffer container is constituted by a container having an appropriate gas inlet / outlet for letting out gas entering from the pressure buffer passage or allowing gas to enter the container, and this is attached to the pressure buffer passage provided in the airtight container. The mounting position is inside the airtight container,
It may be external to the airtight container, and attached to the gas inlet / outlet portion of the pores or buffer passage. The volume of the pressure buffer container is preferably as large as possible. As a rough guide, if the volume of the space filled with the gas in the airtight container is approximately the same, the pollution phenomenon due to the inflow and outflow of gas can be effectively mitigated.

As a material of the container forming the buffer space, a high-purity material that is stable at high temperature and does not become a new impurity contamination source to a desired semiconductor crystal is preferable. Like the material of the airtight container or the crucible, for example, a pyrolytic BN (PBN),
Quartz, alumina, boron nitride, silicon nitride, silicon carbide and the like are preferable.

[Operation] When the pressure buffer passage is equipped with a pressure buffer container having a volume approximately equal to or larger than the volume of the space filled with the gas in the airtight container, the pressure outside the airtight container will be affected by the pressure fluctuation inside and outside the airtight container. Even if the gas is about to flow in, the pressure spreadability of the gas is high due to the spatial expansion, and the fluidity of the gas is suppressed to a low level. Therefore, the flow of the gas outside it stops inside the pressure buffer container and does not touch the melt. You can

Therefore, if impurity contamination is prevented at the stage of containing the melt raw material, the gas containing impurities outside the container does not flow during growth, and the grown crystal is not contaminated.

Example An example of the present invention applied to the growth of a GaAs single crystal will be described below with reference to the drawings.

Example 1 A melt seal pulling apparatus as shown in FIG. 1 was used. As
An airtight container 2 is placed around the crucible 1 to create a gas atmosphere.
The airtight container 2 is further covered with a high pressure container 7 filled with an inert gas.

The airtight container 2 is made of pBN, and the crucible 1 also made of pBN is placed on the lower part of the airtight container 2, and the rotary shaft 9 for rotating the airtight container 2 is attached to the bottom of the crucible 1. The upper part of the airtight container 2 is open for inserting the pulling shaft 3 and the like into the airtight container 2.
The B ₂ O ₃ liquid sealant 4 is poured into the opening into which the pulling shaft 3 is inserted, so that the opening is closed. By sealing the airtight container 2 in this manner, the inside of the airtight container 2 is closed.
The As atmosphere is configured to prevent As dissociation from the surface of the GaAs melt 5 accumulated in the crucible 1. Also, Ga
Heater 8 for giving a growth temperature for growing As crystal 6
Are provided on the outer periphery of the airtight container 2.

A diameter is reduced between the upper part and the lower part of the airtight container 2, and the As gas in the airtight container 2 is prevented from leaking as much as possible while balancing the pressure inside and outside the airtight container 2 at the reduced diameter part. A labyrinth structure 10 is provided.

B ₂ between the pulling shaft 3 and the airtight container 2 for airtightness of the airtight container _2.
O ₃ liquid sealant 4 was put in to form a melt seal. The airtight container 2 is provided with a labyrinth structure 10 as a buffer passage for preventing diffusion of As. The labyrinth structure 10 prevents the As gas in the airtight container 2 from leaking to the extent possible while balancing the pressure inside and outside the airtight container 2. The labyrinth structure 10 is composed of a mouthpiece-shaped opening provided in the airtight container 2 and a cap that closes the mouthpiece-shaped opening, thereby forming a meandering passage.

Further, as a buffer space, a pressure buffer container 12 made of pBN and having a volume substantially equal to the volume of the airtight container 2 was continuously provided outside the labyrinth structure 10. This pressure buffer container 12 has a gas inlet / outlet hole 13, and the cross section of this hole 13 is made as small as possible in comparison with the container cross section.

In this way, the airtight container 2 made of pBN is placed in the pressure vessel 7, and the GaAs melt 5 is placed in the crucible 1 made of pBN which is also placed therein, and the GaAs seed crystal 1 is brought into contact with the melt from above. The GaAs crystal was grown by pulling it while rotating. Specifically, a crystal having a diameter of 110 mm and a length of 260 mm was grown from Ga6800 g and As7450 g. Lifting speed 10mm / h
Then, a crystal having a <100> orientation was produced. The crystals obtained are 10 ⁷
It showed a high resistance on the order of Ω · cm and the impurity concentration was below the detection limit of 5 × 10 ¹⁴ cm ⁻³ or less. The reproducibility of quality was good.

Example 2 As shown in FIG. 2, a vertical Bridgman device was used.
Even in the case of using a vertical Bridgman apparatus, in order to create an As gas atmosphere, the entire crucible 21 made of pBN is covered with an airtight container 22 made of pBN to prevent the dissociation of As from the GaAs melt 25. The As placed inside is heated and gasified to create an As atmosphere. The airtight container 22 is further covered with the pressure container 27. A heater 28 is provided on the outer periphery of the airtight container 22 to uniformly heat the entire crucible 21 having a long length inside the airtight container 22.

At the bottom of the long crucible 21 stored in the airtight container 22, Ga
An As seed crystal 31 is placed. GaAs on this GaAs seed crystal 31
The melt 25 is put and solidified from the bottom of the crucible to obtain a GaAs crystal 26.

A labyrinth structure 30 for pressure balance is provided on the top of the airtight container 22 as described above, and a pressure buffer container 32 constituting a buffer space made of pBN is provided outside the labyrinth structure 30, and thus made of pBN in the pressure container 27. A pBN airtight container 22 containing a crucible 21 was placed, and a GaAs seed crystal 31 was placed in the lower part of the crucible to accommodate the GaAs.
The melt 25 is solidified from below. Specifically, Ga6800 g and As7450 g were put into the crucible 21 and reacted, and then gradually cooled to grow a crystal from below to obtain about 14250 g of a crystal having a diameter of 110 mm. The specific resistance was as high as 10 ⁷ Ω · cm, and the impurity concentration was 5 × 10 ¹⁴ cm ⁻³ or less. Good high-purity crystals were obtained.

Comparative Example 1 Crystals were produced by removing the pressure buffer container 22 with the vertical Bridgman apparatus shown in FIG. The other conditions are the same as in Example 2. The results are compared and shown in the table below.

While high-purity crystals were obtained in Examples 1 and 2, Si contamination was observed in Comparative Examples. It is considered that this is because the pollutant gas generated from the member outside the airtight container entered the airtight container by the reverse diffusion during the growth.

As described above, according to the present embodiment, by providing a pressure buffer container in addition to the pressure buffer passage, while balancing the pressure inside and outside the airtight container, by further enhancing the buffer property of gas,
Since leakage of elemental gas in the airtight container is minimized and GaAs containing impurities is prevented from flowing into the airtight container from outside the airtight container, the desired elemental gas atmosphere can be maintained with good reproducibility and stability. it can. Therefore, it becomes easy to control the composition of the grown crystal, and unlike the conventional case, it is possible to stably and safely grow the compound semiconductor crystal in an environment with a small thermal strain without accidentally mixing impurities. . This can sufficiently meet the ever-increasing demand for high purity in the field of semiconductors.

Further, since a high quality crystal can be stably grown with a simple structure in which a pressure buffer container is added to the already proposed apparatus, it is excellent in economic efficiency.

Although the pressure buffer container is provided outside the passage of the labyrinth structure in the first and second embodiments, it may be provided inside the passage, that is, in the middle thereof as described above. The pressure buffer container may be divided into a plurality of spaces so that they communicate with each other, instead of forming a single space.

Further, the present invention can be similarly applied to other compound semiconductors other than GaAs dealt with in the above embodiments, such as InAs, InP and GaP.

[Effects of the Invention] According to the present invention, by interposing a buffer space, it is possible to effectively prevent impurities from entering from the outside, so that a high-purity crystal can be obtained, and a compound semiconductor crystal of stable quality can be obtained. Can be obtained with good reproducibility.

[Brief description of drawings]

FIG. 1 is a block diagram of a lifting device according to a first embodiment of the present invention,
FIG. 2 is a block diagram of a vertical Bridgman device according to the second embodiment. 2, 22 ... Airtight container (made of pBN), 5, 25 ... GaAs melt, 6, 2
6 ... GaAs crystal, 2, 27 ... Pressure vessel, 8, 28 ... Heater, 1
0, 30 ... Labyrinth structure (pBN), 11, 31 ... GaAs seed crystal, 12, 32 ... Pressure buffer container (pBN).

Claims (1)

[Claims] 1. An atmosphere in which the whole crucible containing a compound semiconductor melt is covered with a highly airtight container, and the airtight container contains an element gas having a higher vapor pressure of the compound elements constituting the melt. And, in the growing device for a compound semiconductor crystal provided with a pressure buffer passage narrowing a flow path communicating between the inside and the outside of the airtight container, at least one of the inlet and outlet of the pressure buffer passage is filled with gas in the airtight container An apparatus for growing a compound semiconductor crystal, comprising a pressure buffer container having a volume substantially equal to or larger than the volume of space.