JP2855408B2 - Single crystal growth equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for growing a single crystal, and more particularly to an apparatus for growing a compound semiconductor single crystal by a liquid-sealed Czochralski (LEC) method.

[0002]

2. Description of the Related Art Conventionally, as a main method for producing a single crystal of a compound semiconductor such as GaAs or InP, a raw material and a sealant are melted in a crucible, and a seed crystal is brought into contact with the surface of the raw material melt and rotated. There is known an LEC method in which a single crystal is grown by gradually pulling it while making the crystal. In this LEC method, in order to prevent the generation of lineage formed by the accumulation of dislocations, the solid-liquid interface between the raw material melt and the grown crystal has an ideal downward convex shape during crystal growth, that is, the lower end of the grown crystal has It is important to maintain a shape that swells into the raw material melt from the outer periphery to the center. This is because, when an epitaxial film is grown on a wafer cut out of the obtained single crystal for the production of an IC, a semiconductor laser, or the like, in the case of a wafer with lineage, the epitaxial film on the lineage generation position is formed. This is because the film is polycrystallized and it is difficult to obtain a good thin film single crystal.

[0003]

SUMMARY OF THE INVENTION However, LEC
In the growth stage of the straight body by the method, the solid-liquid interface shape tends to shift from a downwardly convex shape to a W-shape such that the middle part between the lower periphery and the center of the grown crystal swells into the raw material melt. In addition, there is a problem that dislocations accumulate at an intermediate position between the crystal center and the outer periphery and lineage is easily generated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a single crystal growth apparatus capable of growing a good compound semiconductor single crystal without lineage by the LEC method. To provide.

[0005]

The inventor of the present invention has found that when the solid-liquid interface shape shifts to a W-shape at the stage of growing the straight body portion, a large amount of heat is radiated from the side surfaces of the grown crystal and the top surface of the sealant. The inventors thought that it would be effective to cover the side surfaces of the crystal with a heat shield to prevent this, and completed the present invention.

That is, in the single crystal growing apparatus according to the present invention, a raw material and a sealant are put into a crucible, heated and melted by a heater, and a seed crystal is brought into contact with the surface of the raw material melt and gradually pulled up. In a single crystal growth apparatus for growing a compound semiconductor single crystal, a heat shield having a cylindrical skirt portion which extends from above the crucible to near the upper surface of the melted sealing agent and covers the side of the grown crystal. with a corresponding
The lower end of the skirt of the heat shield and the seal at the start of crystal growth
The distance from the top surface of the blocking agent is greater than 0 mm and 2 mm or less
The heat capacity of the skirt portion of the heat shield is at room temperature.
In particular, it should be between 30 J / K and 100 J / K.
It is a sign.

[0007] More preferably, the heat shield body
The lower end of the cart part and the upper surface of the sealant at the start of crystal growth
Distance should be 0.5 mm or more and 1.5 mm or less
No. Still more preferably, the skirt of the heat shield
The heat capacity of the part is 40 J / K or more and 80 J / K at room temperature.
It is good to be the following.

[0008]

According to the above-mentioned means, in the single crystal growing apparatus used in the LEC method, a cylindrical skirt portion which hangs down from above the crucible to near the upper surface of the melted sealing agent to cover the side of the grown crystal. with a heat shield having, the heat shield
Above the lower end of the skirt portion and the sealant at the start of crystal growth
The distance to the surface is greater than 0 mm and 2 mm or less,
The heat capacity of the skirt of the shield is 30 J /
Since it is K or more and 100 J / K or less, during crystal growth, radiant heat from the side surface of the grown crystal is absorbed by the heat shield,
The temperature at the outer peripheral portion of the crystal is prevented from lowering. As a result, the shape of the solid-liquid interface is always kept in an ideal downward convex shape, and generation of lineage is prevented. Therefore, the yield of the wafer that can be obtained from the grown single crystal is improved.

Here, the distance between the lower end of the skirt portion of the heat shield and the upper surface of the sealant at the start of crystal growth is greater than 0 mm and 2 mm or less, more preferably 0.5 mm or more and 1.5 mm or less. The following is that if the lower end of the skirt portion of the heat shield is immersed in the sealant, heat convection at the growth interface may be disturbed, while the skirt portion of the heat shield is separated from the sealant. If too long, the effect of suppressing the heat radiation from the upper surface of the sealant becomes small, and the temperature at the outer peripheral portion of the crystal tends to decrease.

[0010]

Further, the heat capacity of the skirt portion of the heat shield is 30 J / K or more and 100 J / K or less at room temperature, and more preferably 40 J / K or more and 80 J / K or less when the heat capacity is too small. This is because the effect of suppressing heat radiation from the crystal side face is reduced, while if the heat capacity is too large, the grown crystal is decomposed, which is not preferable.

[0012]

FIG. 1 shows an embodiment of a single crystal growth apparatus according to the present invention.
This will be described below with reference to FIG. First, a configuration example of a single crystal growth apparatus according to the present invention will be described. FIG.
1 is a cross-sectional view of an example of a single crystal growth apparatus according to the present invention, in which 1 is a high-pressure vessel pressurized by an inert gas or nitrogen gas, and 2 is rotatably supported by a crucible support shaft 3. It was a crucible. In this crucible 2, a polycrystalline raw material of a compound semiconductor and a sealant 4 such as B ₂ O ₃ are stored. In addition, from above the high-pressure vessel 1, a pulling shaft 5 is suspended so as to be rotatable and vertically movable into the crucible 2.

The apparatus for growing a single crystal comprises a crucible 2
Sealant melted by heating from above (liquid sealant)
A heat shield 6 having a cylindrical skirt 6A hanging down to the vicinity of the upper surface of the crystal 4 is provided to cover the side of the growing crystal 7. Thereby, heat radiation from the side surface of the grown crystal 7 and the upper surface of the liquid sealant 4 is suppressed, and a decrease in the temperature of the crystal outer peripheral portion is prevented. Therefore, during the crystal growth, the solid-liquid interface between the grown crystal 7 and the raw material melt 8 is maintained in a downward convex shape.

The heat shield 6 is made of, for example, quartz, graphite, pBN or the like. As shown in FIG. 2, a lower half of the heat shield 6 has a cylindrical skirt 6A along the straight body of the grown crystal 7. doing. The skirt 6A has an inner diameter X
1 is formed to have a size, for example, 1.3 times the diameter of the straight body portion of the grown crystal 7, and the lower part thereof is inserted into the crucible 2. In order to avoid contact with the straight body and effectively suppress heat radiation from the crystal side surface, the skirt 6
The inside diameter X1 of A is preferably 1.1 to 1.6 times the size of the straight body portion, and more preferably 1.2 to 1.4 times the size.

The length H of the skirt portion 6A is such that the distance L between the lower end of the skirt portion 6A and the upper surface of the liquid sealant 4 is 1 mm, for example, and the crystal 7 having a desired growth length after the growth is completed.
Has a length such that the crystal shoulder does not collide with the inner surface of the heat shield 6 when the crystal is separated from the raw material melt 8. In order to effectively suppress heat radiation from the upper surface of the liquid sealant 4 without disturbing thermal convection at the growth interface, the distance L between the skirt portion 6A and the liquid sealant 4 is preferably less than 0 mm. 2 mm or less, more preferably 0.5 mm to 1.5 mm
It is good to be the following.

Further, the heat capacity of the skirt portion 6A is, for example, 48.5 J / K, but preferably 30 J / K in order to effectively suppress heat radiation from the crystal side surface within a range where decomposition of the grown crystal 7 does not occur. / K or more and 100 J / K or less, more preferably 40 J / K or more and 80 J / K or less. In order to obtain such a heat capacity, in this example,
The thickness (X2-X1) of the skirt 6A (where X2 is the outer diameter of the skirt 6A) is 2 mm.

Further, the heat shield 6 has a support leg 6B which stands on the heat insulating material 10 surrounding the heater 9 and supports the heat shield 6 itself outside the skirt 6A.
Above the support leg 6B and the skirt 6A, there is an upper cylindrical portion 6C that covers the pulling shaft 5.

Next, a specific example in which an iron-doped InP single crystal having a diameter of 2 inches is grown using the single crystal growth apparatus having the above configuration will be described. However, the present invention is not limited by the specific example. Not something. First, 1100 g of InP was placed in a crucible 2 made of pBN (pyrolytic boron nitride).
A polycrystalline raw material and 500 g of B ₂ O ₃ and 0.03 wt% of iron as a liquid sealant 4 were placed in the high-pressure vessel 1. Then, the crucible 2 is positioned at the lowermost position in the furnace, the temperature of the furnace is increased by the heater 9, B ₂ O ₃ is softened, and when the polycrystalline raw material is melted, the crucible 2 is raised by the crucible support shaft 3. The crystal growth start position, that is, the position where the distance L between the lower end of the skirt portion 6A and the upper surface of the liquid sealant 4 is 1 mm, for example.

Further, the inside of the high-pressure vessel 1 was set to a high pressure, the seed crystal 11 was brought into contact with the liquid surface of the raw material melt 8, the pulling start temperature was adjusted, and then the pulling shaft 5 was pulled up to start crystal growth. It should be noted that the seed crystal 11 has a (100) orientation plane of In.
A P single crystal was used.

The pulling speed was 10 mm per hour. Then, as to the amount by which the liquid level of the raw material melt 8 becomes lower as the crystal growth proceeds, the ascending speed of the crucible 2 by the crucible supporting shaft 3 is determined based on the mass balance of the grown crystal 7 and the raw material melt 8, and the speed is determined. The crucible 2 was raised. Thus, during crystal growth, the distance L between the lower end of the skirt portion 6A of the heat shield 6 and the upper surface of the liquid sealant 4 is always about 1 mm.
Kept.

The separation of the grown crystal 9 is completed immediately before the crystal shoulder comes into contact with the heat shield 6 by setting the pulling speed to 75 mm / h when the solidification rate reaches 0.7. . After the separation, the crucible 2 was lowered and cooled until the furnace temperature reached room temperature, and then the crystal was taken out.

With respect to the obtained InP single crystal, wafers for evaluation were cut out from the upper, middle, and lower portions, respectively, and were etched at room temperature by an etchant obtained by mixing phosphoric acid and hydrobromic acid at a ratio of 2: 1. The etching was performed for minutes, and the dislocation density (EPD: Etch Pit Density) was evaluated. As a result, it was found that the grown single crystal was free of lineage up to the lower portion, and a high quality single crystal could be grown. In the same manner as in the above specific example, the iron-doped InP single crystal and the tin-doped InP single crystal
When grown individually, high-quality single crystals without any lineage were obtained in the same manner as in the above specific examples, and it was confirmed that they were reproducible.

The heat shield 6 is not limited to that of the above embodiment, but may be a skirt 6A which covers the straight body of the grown crystal 7 and can suppress heat radiation from the crystal side surface or the sealant upper surface.
Needless to say, various modifications can be made as long as they have.

Further, by using the single crystal growth apparatus of the present invention, in the conventional single crystal growth apparatus, the maximum temperature gradient in the vertical direction in the encapsulant during growth was 140 to 200 ° C./cm. Can be reduced to 40 ° C./cm by adjusting the thickness and material of the skirt. And
By setting the temperature to 100 ° C./cm or less, the EPD is 10 ⁴ cm.
^-2 iron-doped InP single crystal is obtained, EPD is 500 cm ^-2 or less of dislocation-free single crystal obtained in the following 50 ° C. / cm. In the above specific example, an InP single crystal was grown, but the present invention relates to other compound semiconductors such as Ga.
The present invention is also applicable to single crystal growth of As, InAs, and GaP.

Further, the dopant is not limited to iron or tin,
Sulfur, zinc, or the like may be used, and an undoped single crystal to which no dopant is added can be grown according to the present invention.

[0026]

According to the single crystal growth apparatus of the present invention,
Put the raw material and sealant in the crucible and heat with a heater,
In a single crystal growth apparatus that grows a compound semiconductor single crystal by melting and gradually bringing a seed crystal into contact with the surface of the raw material melt and pulling it up, from above the crucible to near the upper surface of the melted sealant. A heat shield having a cylindrical skirt that hangs down and covers the side of the grown crystal is provided .
The lower end of the skirt portion of the heat shield and the crystal at the start of crystal growth
The distance from the top surface of the sealant is greater than 0 mm and 2 mm or less.
Below, the heat capacity of the skirt of the heat shield is at room temperature.
Therefore, since the radiant heat from the side surface of the grown crystal is absorbed by the skirt portion of the heat shield during the crystal growth and the temperature of the outer peripheral portion of the crystal is prevented from decreasing, the solid-liquid interface shape is formed. Is always kept in an ideal downward convex shape, and generation of lineage can be prevented. Therefore,
The effect that the yield of the wafer which can be obtained from the grown single crystal is improved is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an example of a single crystal growth apparatus according to the present invention.

FIG. 2 is a sectional view of an example of a heat shield provided in the single crystal growth apparatus according to the present invention.

[Explanation of symbols]

 2 crucible 4 sealant 6 heat shield 7 growing crystal 8 raw material melt 9 heater 11 seed crystal

Claims (3)

(57) [Claims] 1. A single crystal in which a compound semiconductor single crystal is grown by placing a raw material and a sealant in a crucible, heating and melting the raw material with a heater, and bringing a seed crystal into contact with the surface of the raw material melt and gradually pulling it up. in the growth apparatus, said from above the crucible, comprises a heat shield having a tubular skirt portion upper surface suspended to the vicinity of covering the side of the grown crystal of the sealing agent were melted, the skirt portion of the heat shield Bottom and crystal growth
The distance from the top surface of the sealant at the start of formation is larger than 0 mm.
2 mm or less, and the heat of the skirt of the heat shield
Capacity is 30 J / K or more and 100 J / K or less at room temperature
Single crystal growth apparatus, characterized in that it. 2. The distance between the lower end of the skirt portion of the heat shield and the upper surface of the sealant at the start of crystal growth is 0.5 mm.
2. The structure according to claim 1 , wherein the distance is not less than 1.5 mm.
Mounting of the single crystal growth apparatus. 3. The heat capacity of the skirt portion of the heat shield is:
The single crystal growth apparatus according to claim 1 or 2, wherein the temperature is at least 40 J / K and at most 80 J / K at room temperature.