JP2006232570A - METHOD FOR PRODUCING GaAs SINGLE CRYSTAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the assembly of dislocations causing crystal defects and the polycrystallization by making the shape of the solid-liquid interface stable and flat without lowering the crystal growth speed when the shoulder part of a crystal being pulled is formed. <P>SOLUTION: The periphery of a seed crystal in a crucible is covered with an umbrella-like heat insulation cover having a flat top part. Thereby, the temperature change in the vicinity of the shoulder part in the pulling direction of the crystal can be suppressed small when the shoulder part is formed, and the temperature change in the vicinity of the shoulder part in the direction perpendicular to the pulling direction of the crystal can be also suppressed small. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, a raw material melt of GaAs is put in a crucible in a pressure vessel, and the surface thereof is covered with a liquid sealant, and a seed crystal is brought into contact with the melt and pulled upward while being slowly rotated. The present invention relates to an improvement in a method for producing a GaAs single crystal called a so-called LEC method (Liquid Encapsulated Czochralski) in which a liquid is gradually solidified from the seed crystal to grow a crystal.

In the method for producing a GaAs single crystal by the LEC method, As in the GaAs raw material melt has a high vapor pressure in the vicinity of the melting point, and therefore has a property of being easily dissociated from the raw material melt. In order to prevent this As dissociation, the surface of the raw material melt is generally covered with a liquid sealant such as B ₂ O ₃ , and an inert gas such as Ar is further introduced to introduce the raw material melt. Is pressed to prevent decomposition and evaporation of As from the raw material melt.

An example of a method for producing a GaAs single crystal by the LEC method is shown in FIG. That is, a crucible 1 ′ containing polycrystalline GaAs as a raw material and B ₂ O ₃ 3 ′ as a liquid sealant is placed in a pressure vessel (not shown) constituting a pulling furnace, and the temperature is increased. The crystal GaAs is changed to a GaAs melt 4 ′, and the surface of the GaAs melt 4 ′ is covered with a liquid sealant 3 ′. Then, the GaAs seed crystal 5 ′ fixed to the lower end of the pulling shaft 6 ′ is brought into contact with the GaAs melt 4 ′, and the pulling shaft 6 ′ is pulled upward while being slowly rotated, so that the seed crystal 5 ′ is pulled up. As a starting point, the GaAs melt 4 ′ is gradually solidified and crystal growth is performed to produce a GaAs single crystal 2 ′.

  In the LEC method, the temperature gradient in the pressure vessel tends to follow the crystal growth direction and the crystal growth proceeds faster than the other crystal growth methods in boats or encapsulated. Therefore, there is a feature that the crystal growth rate can be increased if the pulling rate of the crystal from the melt is changed. However, when pulling, the large temperature gradient in the crystal growth direction means that the crystal growth rate can be increased, but on the other hand, the biggest problem in producing a single crystal is that polycrystallization is likely to occur. There is. Here, whether or not polycrystallization occurs depends largely on the solid-liquid interface shape between the crystal solidified portion and the melt portion following the seed crystal 5 '. FIG. 6 schematically shows a solid-liquid interface shape at the time of forming the shoulder portion of the pulled crystal after seeding. According to this, the solid-liquid interface shape exhibits a concave shape in the crystal growth direction (melt side), and in this case, the dislocations propagate in the crystal growth direction perpendicularly from the solid-liquid interface. Aggregation is likely to occur, and the pulled crystal 2 ′ is likely to be polycrystallized.

In addition, the presence of the liquid sealant 3 ′ made of B ₂ O ₃ 3 ′ and its layer thickness affect the temperature distribution in the pressure vessel, and in particular, the outer diameter of the pulled crystal is increased soon after the start of crystal growth. In the shoulder formation process that gradually increases to the target straight body size, the crystal 2 ′ head comes out from the upper part of B ₂ O ₃ 3 ′ as the crystal growth proceeds. Then, on the melt 4 ′ side, the heat radiation from the head of the crystal 2 ′ proceeds rapidly, and the growth rate of the crystal 2 ′ increases. For this reason, the solid-liquid interface shape changes, for example, as shown in FIG. 6, and the state of crystal growth tends to become unstable. That is, in the case of the LEC method, in order to ensure the crystal growth in the pulling direction, the temperature gradient is large and the temperature fluctuation is large, and the solid-liquid interface shape at the time of shoulder formation due to the presence of the liquid sealant There is an essential problem that the change in shape tends to be concave and the dislocations are likely to be aggregated and polycrystallized easily.

For such a problem, for example, (1) as a means for controlling the cooling rate of the crystal, a method of providing a heat shield around the crystal has been proposed (see Patent Document 1).
Similarly, (2) as a means for controlling the cooling rate of the crystal, there has been proposed a method in which a chuck for connecting the seed crystal is provided with an umbrella-shaped reflecting plate facing the bottom of the crucible (Patent Literature). 2).
Japanese Patent Publication No.51-47153 JP-A-5-221786

  However, in the case of the method (1), there is a problem that the heat insulating effect by the heat shield is low in the vicinity of the solid-liquid interface and the cooling rate in the vicinity of the solid-liquid interface is slowed, and the crystal growth rate is lowered. In the case of the method (2), the shape of the umbrella-shaped reflecting plate concentrates the heat reflection effect on the axis of the pulling crystal, has little effect of improving the temperature gradient in the vicinity of the shoulder, and the solid-liquid interface shape. Therefore, there is a problem that dislocation aggregation and polycrystallization can occur.

  Therefore, the present invention provides a set of dislocations and polycrystals that cause crystal defects by stabilizing and flattening the solid-liquid interface shape during the formation of the shoulder portion of the pulled crystal without reducing the crystal growth rate. An object of the present invention is to provide a method for producing a GaAs single crystal that can prevent the formation of the GaAs.

In the method for producing a GaAs single crystal according to the first aspect of the present invention, a raw material melt of GaAs is put in a crucible in a pressure vessel, the surface is covered with a liquid sealant, and a seed crystal is brought into contact with the melt and slowly. In the method of manufacturing a GaAs single crystal in which the melt is gradually solidified from the seed crystal while being rotated, and the crystal is grown, the umbrella around the seed crystal in the crucible is flattened at the top. It is characterized by being surrounded by a heat insulating cover.
By using the umbrella-shaped heat insulating cover having a flat top as described above, the temperature change in the vicinity of the shoulder in the pulling direction of the crystal can be suppressed at the time of forming the shoulder, and the direction perpendicular to the pulling direction of the crystal. The temperature change in the vicinity of the shoulder at can be suppressed to a small level.

According to a second aspect of the present invention, there is provided a method for producing a GaAs single crystal, wherein at least when the shoulder portion of the pulled crystal is formed, a part of the heat insulating cover is immersed in a liquid sealant.
Thus, by immersing a part (lower part) of the heat retaining cover in the liquid sealant, the temperature change in the vicinity of the shoulder can be reliably suppressed to be small when the shoulder is formed.

In the method for producing a GaAs single crystal according to a third aspect of the present invention, the heat insulating cover has a height equal to or greater than a layer thickness of the liquid sealant, and a diameter of the bottom portion of the straight body portion of the pulled crystal. It is 5 to 2.0 times.
The preferable height of the heat insulating cover is about 1 to 3 times, preferably about 1 to 2 times the layer thickness of the liquid sealant, and if the height is less than the layer thickness of the liquid sealant, The effect of suppressing the temperature change near the shoulder when forming the part is small, and if the height exceeds three times that of the liquid sealant, the temperature change near the shoulder particularly in the direction perpendicular to the crystal pulling direction is reduced. It cannot be kept small.

  According to a fourth aspect of the present invention, there is provided the method for producing a GaAs single crystal, wherein the heat insulating cover is made of PBN (pyrolytic boron nitride).

  According to the present invention, the periphery of the seed crystal in the crucible is surrounded by an umbrella-shaped heat insulating cover with a flat top, and the solid-liquid interface shape is stabilized and flattened when forming the shoulder of the pulled crystal. As a result, it is possible to obtain a GaAs single crystal in which dislocation aggregation is suppressed and polycrystallization is prevented. Moreover, the above effect can be achieved without reducing the crystal growth rate by removing the heat insulating cover or making the movement adjustable together with the crystal growth.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows a state in which a GaAs melt 4 and B ₂ O ₃ 3 as a liquid sealant are accommodated in a crucible 1 of a pressure vessel (not shown). In this state, after covering the periphery of the seed crystal 5 connected to the lower end of the pulling shaft with the heat insulating cover 7, the seed crystal 5 is immersed in the GaAs melt 4. At this time, the heat insulating cover 7 is also lowered simultaneously, and crystals are grown while the heat insulating cover 7 is immersed in B ₂ O ₃ 3. FIG. 2 represents the initial stage of crystal growth. The growing crystal 2 is not pulled up on B ₂ O ₃ 3, and the heat insulating cover 7 is also immersed in B ₂ O ₃ 3. Then, as shown in FIG. 3, when the crystal growth proceeds and the shoulder portion including the head of the crystal comes out of B ₂ O ₃ 3, the heat insulating cover 7 is moved upward so that the inside of B ₂ O ₃ 3 is moved out. Is issued.

The heat insulating cover 7 prevents the crystal 2 from abruptly dissipating heat when the crystal 2 grows above the B ₂ O ₃ 3. However, when the shoulder portion of the crystal 2 is exposed from the B ₂ O ₃ 3 and the straight body reaches the target outer diameter and starts to grow stably, the effect of preventing rapid heat dissipation is cooled with the heat insulating cover 7 installed. It becomes an obstacle. In this state, if the cooling is insufficient, the growth interface becomes concave and dislocations are aggregated, causing crystal defects. Therefore, when the growth of the shoulder portion of the crystal 2 is finished, the heat insulating cover 7 needs to be removed or moved to a place where the influence is small.

Further, the purpose of the heat insulating cover 7 is to prevent the rapid heat dispersion in the region of the crystal 2 covered thereby and to maintain the heat, so that the optimum size according to the size of the shoulder portion of the crystal 2 is set. It is necessary to select. FIG. 4 schematically shows the size and shape of the heat insulating cover. If the heat insulating cover 7 is too small with respect to the size of the shoulder portion of the crystal 2, the heat passes through the periphery of the heat insulating cover 7 and convects, so that the heat insulating effect cannot be obtained. Accordingly, it is optimal that the heat insulating cover 7 has a height equal to or greater than the layer thickness of B ₂ O ₃ 3 and a size (= diameter of the bottom side) of 1.5 to 2.0 times the straight body portion of the crystal. Moreover, in order to make the heat retention effect balanced, it is necessary to make it the umbrella shape which made the top part flat.

[Example 1]
In the above method, 10 GaAs single crystals having a diameter of 100 mm and a length of 300 mm were pulled up. At this time, an umbrella-shaped heat insulating cover made of a thin plate having a thickness of 3 mm made of PBN and having a flat top was installed on the pulling shaft. The charge amount of GaAs is 20 kg, the atmospheric gas, the pressure is Ar 20 kg / cm ² , and the pulling speed is 8 mm / h.

[Comparative Example 1]
On the other hand, the following comparative example was implemented. Ten GaAs single crystals having a diameter of 100 mm and a length of 300 mm were pulled up. At this time, no heat insulation cover was installed on the pulling shaft. The charge amount of GaAs was 20 kg, the atmospheric gas, the pressure was Ar 20 kg / cm ² , and the pulling rate was 8 mm / h.

Table 1 shows the growth results of the crystals grown by the methods of Example 1 and Comparative Example 1, respectively. As a result, it can be seen that the single crystal can be grown with a higher yield by covering the seed crystal with the heat insulating cover than when covering the seed crystal with the heat insulating cover when forming the shoulder portion.

It is a schematic diagram of the GaAs single crystal growth method which shows embodiment of this invention. In the manufacturing method of the GaAs single crystal is a schematic diagram showing a state in which the crystal shoulder does not protrude from the B ₂ O ₃ layer in. In the manufacturing method of the GaAs single crystal is a schematic view showing a state where the crystal shoulders protruding from B ₂ O ₃ layer in. It is the schematic diagram which looked at the optimal relationship between the dimension and shape of a heat insulating cover. It is a schematic diagram which shows the manufacturing method of the conventional GaAs single crystal. It is a schematic diagram which shows the state at the time of the shoulder part formation of the crystal | crystallization in the manufacturing method of the conventional GaAs single crystal.

Explanation of symbols

1 crucible 2 crystal 3 B ₂ O ₃ (liquid sealant)
4 GaAs melt 5 Seed crystal 6 Pull-up shaft 7 Thermal insulation cover

Claims (4)

  The raw material melt of GaAs is put into a crucible in a pressure vessel, the surface is covered with a liquid sealant, the seed crystal is brought into contact with the melt and pulled upward while rotating, and the melt is pulled from the seed crystal. A method for producing a GaAs single crystal, wherein the seed crystal in the crucible is surrounded by an umbrella-shaped heat insulation cover having a flat top portion in a method for producing a GaAs single crystal that is gradually solidified and grown. Method.   2. The method for producing a GaAs single crystal according to claim 1, wherein a part of the heat insulating cover is immersed in a liquid sealant at least when the shoulder portion of the pulled crystal is formed.   The heat insulation cover has a height equal to or greater than a layer thickness of the liquid sealant, and a diameter of a bottom portion of the heat insulation cover is 1.5 to 2.0 times that of a straight body portion of the pulled crystal. Item 3. A method for producing a GaAs single crystal according to Item 1 or 2.   The method for producing a GaAs single crystal according to any one of claims 1 to 3, wherein the heat insulating cover is made of PBN (pyrolytic boron nitride).

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