JPH0566913B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to single crystal growth technology, and in particular to the structure of a susceptor that holds a pBN (pyrolyte boron nitride) crucible used in a single crystal growth apparatus using a pulling method. Concerning techniques that can be used effectively.

[Prior art] As a method for growing semiconductor single crystals, raw materials are placed in a crucible, heated and melted, a seed crystal is brought into contact with the surface of the melt, and the crystal is grown by pulling it while rotating. There is a law.
In addition, in the growth of compound semiconductor single crystals such as GaAs, in order to prevent the dissociation of As, which has a high vapor pressure,
A liquid encapsulation Czyochralski method (hereinafter referred to as LEC method) using a sealant such as B ₂ O ₃ is utilized.

Figure 2 shows a typical configuration example of a single crystal growth apparatus using the LEC method.

This device has a heater 2 inside a high pressure resistant container 1.
Insulating materials 3a and 3b are provided to surround this, and a crucible 5 held by a susceptor 4 is placed in the center of the heater 2. The crucible 5 is heated by the heater 2, and the heat insulating material 3a,
3b and the susceptor 4, the internal raw material is melted. With the surface of the raw material melt 6 sealed with a sealant, the seed crystal 8 at the lower end of the pulling shaft 7 is brought into contact with the surface of the melt 6 and gradually pulled up while rotating. , a crystal body 9 is grown. Note that the susceptor 4 is also rotated by the rotating shaft 10.

Conventionally, quartz, pBN, aluminum nitride, or the like has been used as the material for the crucible 5 used in the above-mentioned crystal growth apparatus. Of these, from the perspective of preventing impurities from entering the raw material melt,
A pBN crucible is best.

[Problems to be Solved by the Invention] However, since the pBN crucible is formed by a lamination method using a gas phase reaction, it has anisotropy in terms of thermal conductivity. That is, the thermal conductivity in the layer direction (direction parallel to the wall surface) is much higher than that in the thickness direction. In terms of specific numbers, the thermal conductivity in the thickness direction is approximately 0.007 cal/cm・
sec・℃, while the thermal conductivity in the layer direction reaches approximately 0.15 cal/cm・sec・℃.

It was found that in such a pBN crucible, due to its heat conduction anisotropy, the temperature in the center becomes higher, as shown in Figure 3, which shows the temperature distribution along the radial direction of the crucible. This is because when a pBN crucible is heated from the outside, the heat applied to the side wall is transmitted downward, increasing the temperature of the bottom wall of the crucible, and the raw material inside the crucible is heated not only from the side wall but also from the bottom wall. It is thought that this is because the raw material melt is heated quite strongly, causing convection in the raw material melt, and as a result, the temperature at the center of the melt becomes high. The above tendency is remarkable when not only the crucible but also the susceptor supporting it are made of pBN like the crucible.

If the crystal is pulled from the melt surface while the temperature at the center is high as described above, the grown crystal tends to become polycrystalline and the yield decreases.

This invention was made in view of the above-mentioned problems, and its purpose is to suppress polycrystallization and grow semiconductor single crystals with a high single crystallization rate, thereby increasing the yield. The aim is to improve.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a susceptor that holds a crucible by making the bottom wall thinner than the side walls, providing a slit from the wall surface to the bottom surface, and making the bottom wall thinner than the side wall. Means for reducing the amount of heat transmitted from the side wall of the susceptor to the bottom wall is provided, such as providing a heat shield plate on the periphery to block radiant heat from the heater.

[Operation] According to the above-mentioned means, the amount of heat transmitted from the side wall of the susceptor holding the crucible to the bottom wall is reduced, and the heat inside the crucible heated through the susceptor is mainly transmitted through the side wall, and the amount of heat transmitted from the side wall to the bottom wall is reduced. As the amount of heating from the crucible becomes relatively small, the temperature of the raw material melt in the crucible becomes lower towards the center, thereby achieving the above-mentioned purpose of improving the single crystallization rate of the growing crystal. can be achieved.

[Embodiment] FIGS. 1A and 1B show an embodiment of a susceptor applied to the present invention.

The susceptor 4 of this embodiment has a cylindrical shape with a bottom corresponding to the outer shape of the crucible supported by the susceptor 4, and the bottom wall 4a is formed to be thinner than the side wall 4b. Further, a heat shield plate 4c that protrudes downward is provided on the periphery of the bottom wall 4a. The heat shield plate 4c may be formed integrally with the susceptor main body, or may be formed separately and adhered to the bottom wall periphery of the susceptor 4.

Furthermore, the susceptor 4 of the above embodiment has a side wall 4.
A plurality of slits 4d (three in the drawing) are formed from the upper end of b to part of the bottom wall. The material of the susceptor 4 is graphite, boron nitride,
It is best to use heat-resistant and strong materials such as pBN, aluminum nitride, and quartz.

When the crucible is held by the susceptor 4 having the above-described structure and heated by placing a crystal growth device as shown in FIG. Since the slit 4d is formed in the side wall 4b, the amount of heat transmitted from the side wall 4b to the bottom wall 4a is reduced. Further, since the heat shield plate 4c is suspended from the periphery of the bottom wall 4a, the radiant heat radiated from the heater 2 toward the bottom wall of the susceptor 4 is blocked by the heat shield plate 4c, and the susceptor bottom due to the radiant heat is blocked by the heat shield plate 4c. The temperature rise of the wall is suppressed.

Furthermore, since the bottom wall 4a of the susceptor 4 is thin, the cross-sectional area for heat conduction is reduced, making it difficult for heat to be transmitted from the periphery toward the center.

As a result, the temperature of the bottom wall of the crucible 5 held by the susceptor 4 is suppressed lower than that of the side wall, and convection is generated in the center of the raw material melt 6 in the crucible 5 from bottom to top. The temperature at the center of the melt becomes the lowest.

By the way, a GaAs polycrystal is charged in a pBN crucible, held by a susceptor 4 as shown in Fig. 1, set in the apparatus shown in Fig. 2, and heated by a heater 2.
After heating to a temperature above the melting point of GaAs, we inserted a thermocouple into the raw material melt and measured the temperature distribution in the diametrical direction of the crucible. As shown in Figure 4, the temperature gradually increased toward the center of the melt. It was found that a temperature distribution that decreases in temperature can be obtained.

Furthermore, as a result of crystal growth under such conditions, the rate of single crystallization was higher than when a susceptor to which the present invention was not applied was used.
Moreover, because a pBN crucible was used, high-quality GaAs single crystals were naturally obtained with less contamination of impurities inside the crystal.

In the above embodiment, the bottom wall 4a of the susceptor 4 that holds the crucible 5 is made thinner than the side wall 4b, and the side wall 4b and a part of the bottom wall 4a are provided with slits 4d.
A heat shield plate 4c is provided on the periphery of the bottom wall to reduce the amount of heat transferred to the center of the bottom wall.
These three means can be used independently or in combination.
Two of these may be applied in combination.

Furthermore, in the embodiment described above, the slit 4d for reducing the cross-sectional area of heat conduction is formed in the vertical direction over a part of the side wall and bottom wall 4a of the susceptor 4, but the slit 4d in the embodiment is formed in the lower part of the side wall 4b. The slit may be formed in a direction perpendicular to 4d, or the slit may be formed only on the side wall of the susceptor. However, as in the embodiment, the easiest method for processing is to form it vertically from the upper end. Furthermore, instead of a slit that completely penetrates the wall surface, a groove that reduces the cross-sectional area may be formed.

[Effects of the Invention] As explained above, the present invention provides a single-crystal device using the pulling method by making the bottom wall of the susceptor that holds the crucible thinner than the side wall, or by forming a slit from the wall surface to the bottom surface of the susceptor. Since a heat shield plate is provided on the periphery of the bottom wall of the susceptor, the amount of heating from the side of the bottom wall of the crucible is reduced, and thereby the temperature of the raw material melt in the crucible is lower than that at the center. This has the effect of improving the single crystallization rate of the grown crystal.

Note that the present invention is not limited to pBN crucibles,
It can be used in a crystal growth device that uses a crucible with heat conduction anisotropy.

[Brief explanation of drawings]

1A and 1B are a perspective view and a sectional view showing an embodiment of a susceptor of a single crystal growth apparatus to which the present invention is applied, and FIG. 2 is an example of the configuration of a single crystal growth apparatus to which the present invention is applied. FIG. 3 is a graph showing the temperature distribution inside the crucible in a conventional single crystal growth apparatus, and FIG. 4 is a graph showing the temperature distribution inside the crucible in the single crystal growth apparatus to which the present invention is applied. . 2... Heater, 4... Susceptor, 4a... Bottom wall, 4b... Side wall, 4c... Heat shield plate, 4d... Slit, 5... Crucible, 6... Raw material melt.

Claims (1)

[Claims] 1. Putting raw materials in a crucible and heating them with a heater,
A single crystal growth apparatus for growing a single crystal by melting the raw material melt and gradually pulling it up by bringing a seed crystal into contact with the surface of the raw material melt, comprising means for reducing the amount of heat transferred to the bottom of the crucible. A single crystal growth device featuring: 2. The single crystal growth apparatus according to claim 1, wherein the means for reducing the amount of heat transfer comprises making the thickness of the bottom wall of the susceptor that holds the crucible thinner than the thickness of the side wall. 3. The single crystal growth apparatus according to claim 1, wherein the heat transfer amount reducing means comprises forming a slit in the susceptor that holds the crucible to reduce the heat conduction area in the vertical direction. 4. The single crystal growth apparatus according to claim 1, wherein the heat transfer amount reducing means is provided with a heat shield plate projecting downward on the periphery of the bottom wall of the susceptor that holds the crucible.