JP2700145B2 - Method for manufacturing compound semiconductor single crystal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a compound semiconductor crystal by a liquid-sealed chiroporous method (hereinafter, referred to as LEK method).

[Prior Art] Generally, III-V and II-VI of GaP, GaAs, InP, CdTe, etc.
Since a group _III compound semiconductor has a high vapor pressure near the melting point, a single crystal is grown by a liquid sealing method in which a raw material melt is covered with a liquid sealing agent layer made of B ₂ O ₃ or the like. Current,
As the liquid sealing method, a liquid sealing Czochralski method (LEC method), a LEK method, and the like are known. The LEC method is a method in which the seed crystal is pulled up as the crystal grows.The crystal orientation can be controlled by seeding, and high-purity crystals can be easily obtained. In addition, it is difficult to obtain a straight body, and the temperature distribution in the melt during crystal growth is large, so that the thermal stress applied to the crystal increases and the dislocation density increases.

On the other hand, in the LEK method, the seed crystal is grown in a water-resistant crucible without rotating the seed crystal, but rotating the seed crystal. Therefore, the diameter of the grown crystal depends on the inner diameter of the crucible. As a result, the diameter can be easily controlled, and the temperature gradient in the melt during crystal growth is several degrees Celsius / cm, which is an order of magnitude smaller than the LEC method. have.

Conventionally, such an LEK method has been performed, for example, as shown in FIGS. 5 (a) and 5 (b).

The crystal growth apparatus in FIGS. 5 (a) and 5 (b)
A cylindrical heater 2 in a closed high-pressure vessel 1 is provided, and a crucible 3 is provided at the center of the heater 2. The crucible 3 is rotatably supported by a support shaft 4 fixed to a lower end thereof. The crucible 3 contains a raw material melt 5 such as GaAs, and the upper surface of the raw material melt 5 has a liquid sealant layer 6 made of B ₂ O ₃ or the like.
Covered with.

On the other hand, from above the crucible 3, a crystal pulling shaft 7 is suspended vertically and rotatably in the high-pressure vessel 1. The crystal pulling shaft 7 holds a seed crystal, and the raw material melt 5 in the crucible 3. Can be brought into contact with the surface. Further, a gas introduction pipe 8 for introducing a high-pressure inert gas is connected to an upper portion of the side wall of the high-pressure vessel 1 so that the pressure inside the high-pressure vessel 1 can be set to a predetermined pressure. .

The conventional LEK method uses such a crystal growth apparatus,
First, as shown in FIG. 5 (a), the seed crystal is immersed in the raw material melt 5 by the crystal pulling shaft 7, and the crucible 3 and the pulling shaft 7 are rotated to grow a single crystal without pulling. After the growth of the crystal 9, as shown in FIG. 5 (b), the crystal 9 is pulled up into a high-pressure inert gas 10 above the liquid sealant layer 6 and cooled to separate it from the raw material melt 5. I was

[Problems to be Solved by the Invention] However, in the above-mentioned conventional LEK method, the liquid crystal is cooled in the high-pressure inert gas 10 filled with the high-pressure inert gas, so that the convection of the gas causes the vicinity of the melting point. Since the crystal was cooled rapidly at this temperature, the thermal stress in the crystal increased, and dislocations occurred. Thus, for example, G,
Jacob, "A NOVEL CRYSTAL GROWTH METHOD FOR G
aAs: THE LIQUID ENCAPSULATED KYROPOULOS METHO
D ", J. Cryst Growth 58 (1985) 455, when crystal 9 is cut perpendicular to the growth axis to form a circular wafer, as shown in FIG. Is 2 × 10 ^{3 to} 3 × 10 ³ / cm ² , which is 1 compared to the LEC method.
It is reduced by about an order of magnitude, but 5 × 10 ⁴ pieces / cm
Dislocations having a density of ² occurred, and the in-plane distribution of the wafer was extremely non-uniform.

The present invention has been made in view of such problems, and it is an object of the present invention to provide a method for manufacturing a compound semiconductor single crystal that can reduce the dislocation density in a crystal and make the distribution in a wafer plane uniform. Is what you do.

[Means for Solving the Problems] In order to solve the above problems, the present inventors have considered that if the crystal is cooled in a crucible, it is possible to prevent a rapid temperature change accompanying pulling, and the LEK method After completion of the crystal growth, the crystal was pulled up into a high-pressure inert gas and cooled in a crucible.

On the other hand, the conventional method of raising the pressure to a high-pressure inert gas after the completion of crystal growth is to separate the crystal from the raw material melt and to prevent cracks from entering the crystal due to the stress due to the difference in thermal expansion coefficient between the crystal and the sealant. To do that.

The inventors thought that such cracks could be reduced by optimizing the cooling profile, and after cooling the crystal, cooled at various rates and repeated the experiment. as a result,
As shown in FIG. 1, the cooling rate was 5 ° C.
/ min or less that the occurrence rate of cracks in the crystal can be reduced, and when cooling the crystal in the crucible, since the raw material melt is all solidified, the temperature distribution in the raw material melt is the lowest on the surface, It has been found that it is desirable that the temperature rises toward the bottom of the crucible. This is because when the maximum temperature is reached at the center of the melt, solidification starts from the bottom of the crucible during crystal growth, twins are easily generated, and a single crystal part due to solidification from the top and a polycrystal due to solidification from the bottom This is because there is a possibility that the dislocation density of the single crystal may increase due to the collision of the parts and the generation of stress at the boundary.

However, if the crystal is cooled at a temperature of 5 ° C./cm or less in the crucible as it is after the crystal growth, the occurrence of cracks can be prevented, but the dislocation density in the crystal becomes as shown in FIG. 2, and the crystal obtained by the conventional method is obtained. It was found that the average dislocation density was lower than that in FIG. 7 showing the dislocation density in the middle, but the uniformity was not so much improved. Therefore, the present inventors have conducted further experiments. As a result, there is a clear relationship between the crystal shape and the uniformity of the dislocation density as shown in FIG. 3, and a crystal (1 kg) of the same weight is grown. In this case, it has been found that a crystal having a substantially uniform dislocation density can be obtained by setting the ratio L / D of the height L and the diameter D of the crystal to 0.8 or more.

The present invention has been made based on the above findings, and covers a raw material melt in a crucible arranged in a high-pressure container with a liquid sealant layer, makes the inside of the high-pressure container a high-pressure inert gas atmosphere, and seeds the raw material melt. In a method for producing a compound semiconductor single crystal in which a single crystal is grown by immersing the crystal, the height of the single crystal is L, and the diameter is D, where L / D is 0.8 or more, The present invention proposes that the single crystal is not pulled up after completion of the growth, and is cooled to room temperature at a cooling rate of 5 ° C./min or less under the liquid sealant layer in the crucible as it is.

[Action] According to the method for producing a compound semiconductor single crystal as described above, the crystal is cooled in a crucible having no temperature change after the crystal growth, and the cooling rate is set to 5 ° C./min or less. The difference in the coefficient of thermal expansion with the stopper is reduced, and thermal stress is less likely to occur, thereby preventing the occurrence of cracks and making the L / D 0.8 or more, so that the crystal diameter becomes relatively small, The temperature difference between the central part and the outer peripheral part can be reduced, thereby reducing the dislocation density,
In addition, the uniformity of the distribution within the wafer surface can be improved.

Example (First Example) The crystal growth apparatus has the same configuration as the conventional one (FIG. 5 (a)).
Reference) was used.

First, 1.1 kg of GaAs polycrystal, B ₂ O ₃
Is weighed so as to have a thickness of 25 mm and placed in a crucible 3 made of pBN having an inner diameter of 60 mm.
The temperature was raised to ℃ or more, and GaAs and B ₂ O ₃ were melted. At this time, an inert gas such as, for example, an argon gas was introduced from the gas introduction pipe 8 to prevent the volatilization of As, and the inside of the high-pressure vessel 1 was set to 30 atm.

Next, after adjusting the surface temperature of the GaAs melt to a temperature slightly higher than the melting point of GaAs, the crystal pulling shaft 7 is lowered,
Seed the (100) face seed crystal into the raw material melt 5 and add
While cooling at a rate of 1 ° C./hr, a crystal was grown for 30 hours. At this time, the crystal pulling shaft 7 was rotated at 5 rpm, and the crucible 3 was rotated at 5 rpm in the opposite direction.

Approximately 30 hours later, when the crystal has almost grown to the bottom of the crucible, terminate the growth, stop the rotation of the crystal and the crucible,
Without pulling the crystal 9, the crystal was cooled to room temperature at a rate of 5 ° C./min under the liquid sealant layer 6 in the crucible. The crystals obtained in this way are flat-topped, 60 mm in diameter and length
The single crystal was 75 mm and weighed about 1.1 kg.

The crystal thus obtained was cut 1 cm below the seeding position to form a (100) plane circular wafer, and the dislocation density was measured. The result is shown in FIG. As can be seen from FIG. 4, the dislocation density of the wafer was 2 × 10 ^{3 to} 3 × 10 ³ / cm ² , and the uniformity of the in-plane distribution was good.

(Second Example) InP single crystals were grown using an apparatus as shown in FIG.

In the crystal growth apparatus shown in FIG. 6, a heat shield plate 14 that covers the liquid sealant layer 6 at a distance of 2 to 3 mm from the upper surface of the liquid sealant layer 6 (the interface with the high-pressure inert gas 10) is provided so as to be able to move up and down. Have been. The heat shield plate 14 is made of high-purity quartz, has a flange portion 14a on the periphery, and has a hole 14b formed at the center with a diameter sufficient for a seed crystal to be inserted.

The reason why the shielding plate 14 covers the upper part of the liquid sealant layer 6 is that twins are easily generated in InP due to fluctuations in the temperature of the raw material melt due to gas convection without the shielding plate. With the above equipment, the argon pressure inside the furnace was set to 50 atm and the inside of the furnace was
InP crystals were grown under the same conditions and under the same conditions as in the first embodiment except that the temperature was raised to 1100 ° C. or higher. The obtained InP crystals were single crystals having a diameter of 60 mm, a length of 70 mm, and a weight of about 1 kg. there were.

A wafer was cut out of the crystal obtained in this example in the same manner as in the first example, and the dislocation density was measured. As a result, the dislocation density was as low as 1 × 10 ³ to 2 × 10 ³ / cm ^-2 ,
In addition, the wafer in-plane uniformity was excellent. In the present embodiment, the provision of the heat shield plate 14 enables the high-pressure inert gas 10
Temperature fluctuations in the raw material melt 5 due to convection inside are reduced,
The quality of the crystal is improved.

The material of the heat shield plate 14 used in the present embodiment is not limited to high-purity quartz, but may be a high-purity heat-resistant material such as BN (boron nitride) or graphite.

In the above two examples, in both cases, after the crystal growth, the crystal is de-cooled in the liquid sealant having a large viscosity and a large specific heat as compared with the inert gas. Convection, such as when cooling, is less likely to occur in the liquid sealant. Therefore, rapid and uneven cooling is prevented as compared with cooling in gas. Furthermore, since cooling is performed under the liquid sealant, volatilization of As, P, and the like from the crystal can be prevented.

In each of the above embodiments, GaAs single crystal and In
Although the growth of the P single crystal has been described, the present invention is not limited to such examples, but includes GaP, CdTe, and the like.
The present invention is applicable to the growth of II-V and II-VI compound semiconductor single crystals.

Further, the crucible does not need to have a perfect cylindrical shape as shown in FIGS. 5 and 6, and it is easier to take out a crystal by making a crucible.

[Effects of the Invention] As described above, according to the method for producing a compound semiconductor single crystal of the present invention, the raw material melt in the crucible arranged in the high-pressure container is covered with the liquid sealant layer, and the high-pressure container is pressurized. In a method for producing a compound semiconductor single crystal in which an inert gas atmosphere is used and a seed crystal is immersed in a raw material melt to grow a single crystal, when the height of the single crystal is L and the diameter is D, Since the crystal was grown so that D became 0.8 or more, and the single crystal was not pulled up after the growth was completed, it was cooled down to room temperature at a cooling rate of 5 ° C./min or less under the liquid sealant layer in the crucible as it was, After the crystal growth, the crystal is cooled in the crucible where the temperature does not change and the cooling rate is slow, so that the difference in the coefficient of thermal expansion from the liquid sealant is relaxed, and thermal stress is less likely to occur, thereby causing cracks. Generation can be prevented and L / D is 0.8
As described above, the diameter of the crystal becomes relatively large, and the temperature difference between the central part and the outer peripheral part can be reduced, thereby reducing the dislocation density and improving the uniformity of the in-plane distribution of the wafer. There is an effect that can be.

[Brief description of the drawings]

FIGS. 1 (a), (b), (c), (d) and (e) respectively show the relationship between the cooling rate and the state of crack generation when a crystal grown by the LEK method is cooled in a crucible. FIG. 2 is a first structural means of the present invention (5 ° C./min in a crucible)
FIG. 3 is a graph showing the distribution of dislocation density in the wafer plane of a crystal obtained by applying only the following cooling (cooling at the following speed). FIG. 3 shows the size (ratio of height to diameter) of the grown crystal and the maximum dislocation density of the wafer. FIG. 4 is a graph showing the relationship between the ratio of the maximum value to the minimum value, FIG. 4 is a graph showing the distribution of the in-plane dislocation density of the crystal obtained by the first embodiment of the present invention, and FIGS. b) is a longitudinal sectional view showing the state of the crystal during the crystal growth process and the crystal cooling process in the conventional LEK method, respectively. FIG. 6 is a longitudinal sectional view showing the crystal growth apparatus used in the second embodiment of the present invention. FIG. 7 is a graph showing the distribution of in-plane dislocation density of a crystal obtained by a conventional method. 1 ... high pressure vessel, 3 ... crucible, 5 ... raw material melt, 6 ...
... Liquid sealant layer, 7 ... Crystal pulling shaft, 8 ... Gas introduction tube, 9 ... Growth crystal, 14 ... Heat shield plate.

Continuation of the front page (72) Inventor Osamu Oda 3-17-35 Nishinaminami, Toda City, Saitama Prefecture Inside Japan Mining Co., Ltd. (56) References JP-A-60-90897 (JP, A) JP-A-1- 145395 (JP, A)

Claims (2)

(57) [Claims] A raw material melt in a crucible placed in a high-pressure vessel is covered with a liquid sealant layer, the inside of the high-pressure vessel is set to a high-pressure inert gas atmosphere, and a seed crystal is immersed in the raw material melt to form a single crystal. In the method for producing a compound semiconductor single crystal to be grown, the shape of the single crystal to be grown is determined by adjusting the ratio L / D of the height L to the diameter D.
0.8 or more, 5 ℃ / below the liquid sealant layer in the crucible
A method for producing a compound semiconductor single crystal, characterized in that cooling is performed at a rate of not more than one minute. 2. A method for producing a compound semiconductor single crystal according to claim 1, wherein the furnace temperature is controlled so that the temperature of the raw material melt becomes higher toward the bottom of the crucible. .