JPH0543383A - Method for pulling up single crystal and apparatus therefor - Google Patents

Abstract

PURPOSE:To keep the surface temperature of a molten liquid to a lowest possible level and to increase the pull-up speed of crystal by suppressing the solidification of molten liquid near the crucible wall in the Czochralski process for pulling up a single crystal. CONSTITUTION:Radiant heat from the surface 52 of molten liquid 16 is reflected with a reflection plate 44 toward the contacting region 46 of a crucible 18 and the molten liquid 16. The reflection plate 44 is suspended by a wire 66 and a lateral beam 64 to allow the radiation of heat from the surface of the crystal 14 to a cylindrical member 42. The surface 52 of the molten liquid 16 is maintained to a level higher than the high-temperature zone of the heater 32 to keep the surface temperature of the molten liquid 16 to a low level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for pulling a single crystal by the Czochralski method and an apparatus therefor.

[0002]

2. Description of the Related Art The pulling of a single crystal by the Czochralski method is carried out by storing a melt in a crucible supported by a susceptor and using a seed wire through a seed chuck. In this case, if the temperature of the melt is lowered or the temperature of the pulled single crystal is lowered, the crystal pulling rate becomes faster.

In the case of pulling a single crystal by the Czochralski method, the temperature distribution on the surface of the melt usually has a solidification temperature immediately below the single crystal, and rises from the crystal edge outward in the radial direction and then decreases. ing. The contact area with the crucible wall is higher than the solidification temperature but relatively low. Therefore, for the purpose of increasing the crystal pulling speed, when the temperature of the melt is lowered to operate, the melt temperature near the crucible wall reaches the solidification temperature, and stable pulling of the single crystal cannot be performed. There was a problem.

There is also an idea that the crystal pulling rate can be increased by cutting off the radiant heat from the crucible or the melt to the single crystal in order to lower the temperature of the single crystal during pulling and increase the crystal pulling rate. It was Based on such an idea, conventionally, some techniques have been proposed in which the radiant heat from the crucible and the melt to the crystal is blocked to increase the pulling rate. For example, as in (1) Japanese Patent Publication No. 57-40119 (US Pat. No. 4,330,362) and (2) Japanese Patent Publication No. 58-1080 (US Pat. No. 4,330,361), the crucible and the melt are formed by a metal radiation screen. There is a method of partially covering or a method of using a radiation screen having a heat-insulating multi-layer structure, as in (3) Japanese Patent Publication No. 2-34040.
(4) Japanese Patent Laid-Open No. 64-72984 (US Patent 495
No. 6153), a method of using a heat resistant heat insulating plate in a donut shape is disclosed.

As described above, these prior arts (1) to (4) shield the radiant heat from the crucible and the melt to the crystal, thereby promoting cooling of the single crystal and increasing the crystal pulling rate. The purpose is to do. However, in reality, these techniques have a problem that the cooling of the single crystal is hindered, and the increase of the pulling speed is hindered. This problem will be described below.

[0006] In pulling a silicon single crystal without using a radiation screen, the single crystal in the region immediately after pulling is 130
Radiation is received from the crucible wall at about 0 ° C and the melt at about 1440 ° C. In this case, as the crystal rises, the single crystal faces the cylindrical material having a temperature of about 500 ° C. and radiates heat. On the other hand, in pulling using a radiation screen, direct radiation from the single crystal crucible wall and melt is blocked,
On the other hand, the single crystal faces a radiation screen (about 1000 ° C.) whose temperature is higher than that of the cylindrical material. Therefore, when the radiation screen is used, the single crystal is prevented from radiating heat by the radiation screen and is rather kept warm. Regarding the radiant heat shielding effect from the crucible wall and the melt, the crystal temperature facing the crucible wall and the melt surface is usually at a level of 1000 ° C. or higher, and the radiant heat shielding effect is slight. After all, the radiant screen has a larger effect of blocking the heat radiation of the single crystal and keeping it warmer than the radiant heat shielding effect from the crucible wall and the melt, and the result is that the temperature of the crystal is rather higher than that without the radiant screen. .. As described above, the related art (1) to
In the case of (4), even if an attempt is made to increase the pulling speed, the crystal is kept warm so that the pulling speed is suppressed, which is not so effective for increasing the speed.

(5) In Japanese Patent Laid-Open No. 55-56098 (US Pat. No. 4,378,269), a donut plate-shaped radiant heat shielding plate for covering the upper portions of a melt, a crucible, a heater, etc. is installed, and cooling is performed thereon. Techniques for arranging cylinders have been proposed.
In this technique, since the surface of the melt is entirely covered by the radiant heat shielding plate, the area where the crystal is growing, that is, the contact area between the melt and the single crystal is kept warm, and the crystal pulling rate is rather slow. There was a problem.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to suppress the solidification of the melt in the vicinity of the crucible wall, to keep the temperature of the melt as low as possible, and to achieve high speed in crystal pulling. .. Another object of the present invention is to lower the temperature of the single crystal and to stably increase the crystal pulling rate so as not to hinder the release of heat from the crystal surface.

[0009]

In order to solve the above-mentioned problems, the present invention aims at the contact area between the crucible and the melt surface,
A method for pulling a single crystal, characterized in that a reflector for reflecting radiant heat from the surface of a melt is suspended by a string to grow a crystal. As a single crystal pulling apparatus by the Czochralski method that can preferably carry out the above method, at a position in the crucible lower than the upper end of the crucible, the reflecting surface in the melt surface and the contact region between the crucible and the melt surface. Is provided with a ring-shaped reflecting plate facing each other, and the reflecting plate is hung by a hanging string from the upper part of the furnace.

[0010]

The operation of the present invention will be described in detail below in comparison with the prior art. FIG. 8 is a vertical sectional view of a conventional single crystal pulling apparatus. In pulling a single crystal by the Czochralski method, the melt 16 is stored in a crucible 18 which is supported by a susceptor 20 and rotates, and a single wire 14 is pulled by a seed wire 10 through a seed chuck 12. The crucible 18 is surrounded by a furnace wall 40, and a heater 32 is provided inside the furnace wall on the outer circumference of the crucible 18 to heat the melt 16. In addition, a heat insulating material 26 prevents downward heat radiation through a support post 28 on a base plate 30 at the bottom of the furnace. The heater 32 is supported by a support 34 and is powered by an electrode 36. The heater 32 has a temperature distribution. FIG. 9 shows the temperature distribution in the vertical direction of the heater. The horizontal axis represents the heater temperature, and the vertical axis represents the vertical position from the upper end of the heater. The temperature distribution of the heater is low at the upper and lower ends and is high at the center. In the present invention,
The temperature distribution in the height direction of the heater is actually measured, and the region in the height direction from the maximum temperature to 90% of the maximum temperature is set as the high temperature zone 76 of the heater.

The approximate temperature of each part of the Czochralski pulling apparatus will be described with reference to FIGS. 2 and 3. FIG. 2 shows the case where the radiation screen is not used, and FIG. 3 shows the case where the radiation screen is used. In FIG. 2, the region immediately after pulling up the single crystal 14 has a wall of the crucible 18 of about 1300 ° C. and 1440 ° C.
Radiant from the surface of the melt 16 of about 50
Heat is radiated to the cylindrical member 42 at about 0 ° C. On the other hand, in FIG. 3 using the radiation screen 58, the single crystal 14 blocks direct radiation from the wall of the crucible 18 and the melt 16, but
On the other hand, it faces the radiant screen 58 having a high temperature of about 1000 ° C., and the heat is prevented from being radiated and kept warm. The boundary between the melt 16 and the single crystal 14 is also kept warm and kept at a high temperature. Therefore, the heat retaining effect is greater than the effect of shielding the radiant heat by providing the radiant screen 58, and the crystal pulling speed does not become faster.

FIG. 1 is a vertical sectional view of an embodiment of the device of the present invention. Conventionally, when an attempt is made to increase the pulling rate of the single crystal 14 by lowering the temperature of the heater 32 to lower the temperature of the melt 16, a region 46 where the crucible 18 and the surface of the melt 16 contact each other.
Reached the freezing point and prevented crystal pulling up. Therefore, in the present invention, by using the reflection plate 44, the radiant heat from the surface 52 of the melt 16 is reflected toward the region 46 where the crucible and the melt surface are in contact with each other, and this region is kept warm. As a result, the temperature of the melt 16 near the crucible 18 can be prevented from reaching the freezing point, and stable operation can be achieved. Moreover, since the temperature of the melt 16 decreases, the radiant heat from the melt surface 52 to the single crystal 14 decreases. Further, in the present invention, the reflector 44 is hung by the string 66 so as not to prevent the crystal from facing the low temperature cylindrical member 42, so that the surface of the single crystal 14 is radiated and radiated to the cylindrical member 42. The cooling of the single crystal 14 is promoted. As a result, the pulling speed can be increased.

In the present invention, the string 66 for suspending the reflecting plate has (a) strength for suspending the reflecting plate and durability against high temperature, and (b) radiation heat dissipation to a single crystal cylindrical member. The shape, the material, and the number of hanging pieces do not matter as long as the condition of not hindering is satisfied. That is, an appropriate number of wires, round bars, square bars, or elongated bars having an arbitrary cross-sectional shape can be used.

As another aspect of the present invention, the surface level of the melt 16 is maintained at a high position outside the high temperature zone 76 of the heater 32, so that the heater 32 is substantially heated.
The amount of heat transfer from the melt is reduced, and the temperature near the surface of the melt is lowered. In the present invention, the reflection plate 44 is used to prevent the melt temperature near the crucible wall from reaching the freezing point. Therefore, by adjusting the relative positional relationship between the melt surface and the heater, the melt surface vicinity is adjusted. It is possible to easily lower the temperature and increase the speed of pulling the single crystal.

The shape of the reflector is such that the radiation on the surface of the melt is effectively reflected on the contact area between the crucible wall and the surface of the melt, and the convection of the gas on the surface of the melt is not hindered. The shape is not limited as long as it does not hinder the heat radiation. For example, in FIG.
The cross section may have a linear shape, a broken line shape, a curved shape, or a combination thereof as shown in FIG. The upper end of the reflector is located inside the crucible with the upper end of the crucible wall as the upper limit, and is suspended from above with a string. This allows the reflector to keep the melt near the wall of the crucible warm, while the strings do not interfere with the radiation of the single-crystal cylindrical material. As a result, it is possible to pull down the single crystal at high speed while lowering the temperature of the melt and promoting cooling of the single crystal.

[0016]

【Example】

Example 1 Using the single crystal pulling apparatus by the Czochralski method of the example of the present invention shown in FIG. 1, 45 kg of polycrystalline silicon was charged into a quartz crucible 18 having a diameter of 16 inches,
A silicon single crystal 14 having a diameter of 6 inches was pulled up.

As described in the description of the prior art, merely by lowering the melt temperature, the melt 16 begins to solidify from the region 46 where the crucible and the melt are in contact. Therefore, the reflector 44 of the present invention
Was placed above the melt in the crucible. The reflector 44 was hung from the upper end of the cylindrical member 42 via the wire 66 and the horizontal beam 64. FIG. 4 shows an inverted conical reflector 44 used in this embodiment.
The shapes of the wire 66 and the horizontal beam 64 are shown. Figure 4 (a)
Is a plan view and FIG. 4B is a view taken along the line AA in FIG. The specifications of the reflector 44 are as follows.

Shape: frustoconical ring shown in FIG. 5 (a) Material: molybdenum, both reflector and suspension device Dimensions: In FIG. 4, a = 300 mm, b = 35 mm, c = 35 mm, d = 5
0 mm, e = 2 mmφ, f = 15 mm, g = 530 m
m, θ = 45 ° Installation position: The distance between the lower end of the reflector 44 and the melt surface is 20
mm At the start of crystal pulling, the upper end of the reflection plate 44 is 55 mm below the upper end of the crucible wall. The reflection plate 44 is a molybdenum frustoconical shell-shaped ring plate having high reflectance and excellent heat resistance. However, the reflector 4
The material of No. 4 is not limited to molybdenum, but any material having heat resistance and high reflectance may be used. By providing the reflection plate 44, the radiant heat from the surface 52 of the melt 16 is melted in the crucible 1.
8 and the melt 16 were reflected toward the area 46 in contact with each other, and the area 46 was locally heated. Reflector 44
Was hung from a cross beam 64 protruding from four positions of the cylindrical member 42 through a wire 66 so that the cooling of the crystal by radiation from the crystal surface to the cylindrical member was not hindered. The shape of the reflection plate 44 is set as shown in FIG. 4 and the angle θ of the reflection plate 44 is set to 45 degrees in order to efficiently reflect the radiant heat to the vicinity of the region 46 where the crucible and the melt are in contact with each other.

The temperature distribution in the vertical direction of the heater of the Czochralski lifting device used in this example was measured. FIG. 9 shows this. When the height position of the temperature corresponding to 90% of the maximum temperature is obtained, 31 m downward from the upper end of the heater
It was m. Therefore, the region below this position was set as the high temperature zone of the heater of this device. When pulling a single crystal of a device without a reflector, a radial direction 120 is measured from the center of the crucible.
When the melt surface temperature at the position of mm was measured, it was 1440
It was ℃.

Using the apparatus of the embodiment, the height position of the melt surface was set to -32 mm with respect to the upper end of the heater, and 120 mm from the center of the crucible in the radial direction from the center of the crucible under the condition that the melt surface was within the high temperature zone region of the heater. The temperature at the position was set to 1435 ° C. and the temperature was raised. For comparison, the conventional apparatus shown in FIG. 2 and the apparatus provided with the conventional radiant screen 58 shown in FIG. 3 were used, and the height position of the melt surface with respect to the upper end of the heater was adjusted to −32 mm in the above-mentioned embodiment. The single crystal was pulled at a normal operating temperature under the same pulling conditions. The shape and dimensions of the radiation screen 58 are as follows.

Shape: with frustoconical rim Cone: upper 380 mmφ, lower 270 mmφ, height 255 m
m The position of the upper end is 165 mm above the upper end of the crucible wall Rim: Outer diameter 510 mmφ FIG. 6 shows the temperature distribution 80 of the radiation screen and the temperature of the crystal with respect to the distance from the melt surface to the upper position on the pulling of the single crystal using the radiation screen. 82, and the measured value of the temperature of the crystal at the same distance from the surface of the melt on the pulling of the single crystal when the radiation screen is not used (FIG. 2) 8
It is a comparison of 4. The temperature 80 of the radiation screen is the temperature of the single crystal 8 on the single crystal pulled without the radiation screen.
It can be seen that it is higher than 4. As a result, the crystal temperature 82 on pulling the single crystal using the radiation screen is also
The temperature is higher than the temperature 84 when the radiation screen is not used. In addition, FIG. 7 shows a crystal temperature 88 of the embodiment compared to a crystal temperature 86 when the radiation screen of FIG. 3 is used.
It shows that was able to be lowered. This is because it does not prevent the heat release from the crystal surface. Further, the temperature 88 of the crystal of the example was lower than the temperature 90 of the crystal in the conventional technique (FIG. 2) not using the radiation screen. Moreover, the temperature of the melt could be lowered without solidifying the melt near the crucible until the completion of crystal pulling.
As shown in FIG. 10, the average value of the pulling speed in the straight body of the crystal is 1.6 times more than that in the case of FIG. 2 in which no radiation screen is used,
It was 1.3 times more than when using the radiation screen of FIG.

[Embodiment 2] Using the reflector of the present invention having the same structure as in Embodiment 1, the height position of the melt surface with respect to the upper end of the heater was set to -6 mm, and 120 m from the center of the crucible in the radial direction.
The temperature at the position of m was 1433 ° C. and the temperature was raised. The result is shown in FIG.
Comparison was made at the normal pulling temperature, the same melt level as in the example, and the same pulling conditions. As shown in FIG. 10, the average value of the pulling speed in the straight body portion of the crystal was 1.06 times that when the radiation screen was used. In the case of FIG. 2 in which the radiation screen was not used under the conditions of Example 2, solidification occurred near the crucible wall of the melt, which hindered pulling of the single crystal.

[0023]

The single crystal pulling method and apparatus according to the present invention enable a single crystal to be pulled at high speed. further,
Since the reflector is small, it is easy to handle and inexpensive to install.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional lifting device.

FIG. 3 is a cross-sectional view of a conventional lifting device when a radiation screen is used.

FIG. 4 is a partial vertical cross-sectional view showing the dimensions of a reflection plate and a horizontal beam in the apparatus of the embodiment.

FIG. 5 is a diagram showing an example of a reflector shape in the present invention.

FIG. 6 is a graph showing the relationship between the measured values of the temperature of the radiation screen and the crystal when the radiation screen is used, and the measured values of the crystal temperature when the radiation screen is not used.

FIG. 7 is a graph showing the relationship between the crystal temperature and the height from the melt surface when a radiation screen is used and when a radiation screen is not used when the device of the present invention is used.

FIG. 8 is a vertical cross-sectional view of an example of a conventional single crystal pulling apparatus.

FIG. 9 is a graph showing the temperature distribution of the heater of the apparatus of the embodiment.

FIG. 10 is a graph showing the effect of the example.

[Explanation of symbols]

10 seed wire 12 seed chuck 14 single crystal 16 melt 18 crucible 20 susceptor 22 pedestal 24 crucible shaft 26 heat insulating material 28 post 30 base plate 32 heater 34 support 36 electrode 38 heat insulating material 40 furnace wall 42 cylindrical material 44 reflective plate 46 Region where crucible and melt surface contact 48 single crystal growth region 52 melt surface 58 radiation screen 64 horizontal beam 66 string (wire) 76 high temperature zone

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Murakami 1 Kawasaki-cho, Chiba City Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Teruyuki Sekine 1 Kawasaki-cho Chiba City Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Kazuhiko Echizenya 1 Kawasaki-cho, Chiba City Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Hironari Hidaka 2-3 2-3 Uchisaiwaicho, Chiyoda-ku, Tokyo Kawasaki Steel Co., Ltd. (72) Inventor Yasuyuki Seki 1 Kawasaki-cho, Chiba City Technical Research Division, Kawasaki Steel Corporation

Claims (3)

[Claims] 1. A method of pulling a single crystal by the Czochralski method, wherein a reflector for reflecting radiant heat from the melt surface toward a contact area between the crucible and the melt surface is hung by a string to pull the single crystal. A method for pulling a single crystal, which comprises: 2. The single crystal pulling method according to claim 1, wherein the level of the melt surface is maintained above the high temperature zone of the heater. 3. A single crystal pulling apparatus by the Czochralski method, at a position in the crucible lower than the upper end of the crucible,
Disposed on the melt surface and the contact area between the melt surface and the crucible is a ring-shaped reflecting plate facing the reflecting surface, and the reflecting plate is hung by a hanging string from the furnace top. Lifting device.