JPH05294783A - Silicon single crystal producing device - Google Patents

Abstract

PURPOSE:To stably pull up a silicon single crystal at a low speed and to decrease the oxygen concn. in the single crystal in the production of the single crystal by moderating the temp. gradient and lowering the temp. of the wall of a crucible. CONSTITUTION:A conical heat shield is set to disturb the radiation of heat from a silicon single crystal 5 to the wall 13 of a chamber and fixed to a silicon single crystal lifting shaft, and a cylindrical heat shielding wall consisting of a heat reflecting plate 17, a heat shielding plate 16 and a support 15 is erected on the upper edge of a crucible 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a silicon single crystal which relaxes a temperature gradient in a silicon single crystal produced by the CZ method and enables stable low speed pulling.

[0002]

2. Description of the Related Art CZ is commonly used in the production of silicon single crystals.
(Czochralski) method is used. In the CZ method, a raw material for a single crystal is put into a quartz crucible installed in a chamber, this is heated and melted by a heater, and then a seed crystal is immersed in this melt and pulled upward while being rotated. Grow a single crystal at the bottom.

In recent years, as the density of LSIs has increased, the quality required for semiconductor crystals, especially silicon single crystals, has become severe. For example, further reduction of minute defects, SiO fine particles, and the like taken into the single crystal during pulling is applicable. This is because, during the subsequent manufacturing of the silicon wafer, it causes a problem such as deterioration of quality such as resistance of the thermal oxide film.

Therefore, a technique for gradually pulling up a silicon single crystal (Japanese Patent Laid-Open No. 57-71894) and a technique for preventing the above-mentioned adverse effects by reducing the pulling speed to a low speed of 0.3 to 1.5 mm / min (special feature: (Kaihei 3-275586), there is known a technique (Japanese Patent Laid-Open No. 3-271198) in which a protective cover is installed on the neck portion in order to prevent SiO fine particles deposited on the upper part of the apparatus after evaporation from falling.

Further, in addition to the heat shield, a technique for preventing the generation of SiO fine particles by installing a heat shield on the upper part of the crucible and circulating an atmospheric gas under reduced pressure (Japanese Patent Laid-Open No. 57-40119), A technique of installing a partition member in the crucible (Japanese Patent Laid-Open No. 3-271187) is known. Further, a technology for stabilizing the quality by installing a cooling mechanism for heating at a temperature lower than the crucible wall temperature above the crucible to control the thermal history of the single crystal (JP-A-57-20539).
No. 7), a technique of installing a lid directly above the crucible as a heat shield (Japanese Unexamined Patent Publication No. 55-113693), and a technique of installing partition walls as a heat shield in order to prevent falling of SiO fine particles and promote discharge. JP-A-57-123890), a technique for installing a gas guide jig (JP-A-59-14149).
No. 4) is known.

[0006]

Problems to be Solved by the Invention JP-A-57-7189
In the technique described in Japanese Patent No. 4, the crucible has a short service life,
In addition, there are problems such as contamination of the melt due to the components of the film. In the technique disclosed in Japanese Patent Laid-Open No. 3-275586, there is no improvement in the device, and thus there is a problem in stabilizing pulling. JP-A-3-271198 and JP-A-3-271187
Although the technique described in Japanese Patent Laid-Open Publication No. 2004-126242 suppresses the mixing of SiO fine particles by dropping, it has a problem such as precipitation of polycrystals. Japanese Patent Publication 57-
According to the techniques disclosed in Japanese Patent No. 40119 and Japanese Patent Laid-Open No. 55-113693, since Si is installed directly above the crucible, Si is used.
Adhesion and precipitation of O fine particles cannot be avoided. JP-A-57-
The technique disclosed in Japanese Patent No. 205397 has a problem in that the crystal is severely deformed due to the increase in the crystal growth rate due to the heating during pulling. JP-A-57-12389
According to the techniques described in JP-A No. 0 and JP-A-59-141494, mixing of SiO ₂ particles by dropping is suppressed,
Insulation effect is insufficient, so there is a problem in stable pulling.

An object of the present invention is to provide a manufacturing technique which solves the above problems, relaxes the temperature gradient in a silicon single crystal, and enables stable low-speed pulling.

[0008]

The present invention comprises the following technical means as an apparatus for producing a silicon single crystal that solves the above problems. (A) An umbrella-shaped heat shield is provided on the pulling shaft of the silicon single crystal of the CZ method manufacturing apparatus. (B) A cylindrical heat-shielding wall, which is composed of a heat-reflecting plate, a heat-shielding plate, and a support material and surrounds the pulled crystal, is provided upright on the upper edge of the crucible.

[0009]

The crystal growth is extremely sensitive to temperature. For example, when the temperature rises, it is likely to be polycrystallized, and when the temperature falls, the crystal is severely deformed due to the increase in growth rate. Therefore, when the silicon single crystal is pulled up by the CZ method, the temperature gradient (temperature distribution) in the single crystal has an important meaning.

The inventors of the present invention can reduce the temperature gradient in the silicon single crystal by providing an umbrella-shaped heat shield covering the upper part of the single crystal and a cylindrical heat shield wall standing on the upper edge of the crucible. The present invention has been completed by finding that it is extremely effective. The umbrella-shaped heat shield is composed of a heat shield plate and a heat insulating material mounting tool for attaching the heat shield plate to the pulling shaft of the silicon crystal. Since the heat shield plate has a low emissivity and covers the upper end surface of the single crystal, cooling from the upper end surface of the single crystal to the chamber wall cooled by water is suppressed. Further, since this heat shield plate is attached to the pull-up shaft via the heat insulating material, cooling due to heat conduction from the heat shield plate to the pull-up shaft is suppressed, and the heat shield plate is kept at a high temperature. Therefore, due to the heat retaining effect, it is possible to suppress the cooling due to the radiation from the upper end surface of the single crystal to the heat shield plate. From the above, since the heat dissipation from the single crystal upward is suppressed, the single crystal is kept warm,
The temperature gradient in the single crystal is relaxed.

Next, as a cylindrical heat shield wall, a heat reflection plate surrounding the periphery of the single crystal reflects radiation from the melt surface and the single crystal surface toward the single crystal side surface. The cooling of the single crystal is suppressed and the single crystal is kept warm. Further, the heat reflection plate surrounding the single crystal is kept warm by the heat from the melt surface through the heat shield plate that absorbs the radiant heat from the melt surface, so that the single crystal side face to the heat reflection plate Cooling due to radiation is suppressed.

Since the heat shield wall composed of the heat reflection plate and the heat shield plate is installed on the support member at the upper end of the crucible wall, it is always above the upper end of the crucible wall, and is radiated by the heat radiated from the crucible wall surface to the single crystal. It is possible to effectively suppress the cooling of the single crystal above the upper end of the crucible wall due to heat radiation from the single crystal to the water-cooled chamber wall without impeding the heat retaining effect.

By providing the umbrella-shaped heat shield and the cylindrical heat shield wall, not only the cooling due to the radiation from both the upper and side surfaces of the single crystal is suppressed but also the single crystal is effectively kept warm. Thereby, the temperature gradient in the single crystal can be relaxed. Recently, in order to satisfy the quality of a silicon single crystal, it has been required to slow down the pulling speed despite the decrease in productivity. Generally, the following equation is known as a relational expression between the temperature gradient in the single crystal and the pulling rate.

[0014] V = (1 / ρH) × (Ks × (dTs / dZ) -K L × (dT L / dZ)) However, V: pulling speed [rho: Single crystal density H: latent heat of solidification Ks: Single the thermal conductivity of the crystal K _L: thermal conductivity of the melt Ts: single crystal temperature T _L: temperature of the melt Z: in pulling axis direction distance above equation, to the pulling speed to a low speed, the It is necessary to reduce the first term on the right side and increase the second term. Specifically, the relaxation of the temperature gradient in the single crystal corresponds to the sharpening of the temperature gradient in the melt, but the conventional operating conditions can control only the temperature gradient in the melt. Raising the heater temperature in order to make this temperature gradient steep causes the following problems, which is not preferable.

(1) Natural convection is strong, temperature fluctuations are severe, and crystal growth is not stable. (2) Since the temperature around the crucible is increased, the penetration of oxygen, impurities, etc. from the crucible wall into the melt becomes large, and the quality of the single crystal cannot be controlled. (3) The power consumption of the heater is large, the parts in the chamber are heavily worn, and the overall cost is increased.

According to the present invention, since the temperature gradient in the silicon single crystal is relaxed by the installation of the umbrella-shaped heat shield and the cylindrical heat shield wall, the first term on the right side of the above equation is reduced particularly. The pulling speed can be reduced due to the effect.

[0017]

1 is a schematic sectional view of the inside of a chamber showing an embodiment of the present invention. 45 kg of raw material silicon was charged into a quartz crucible 7 having a diameter of 16 inches and melted to obtain a silicon melt 6
A single crystal 5 having a diameter of 6 inches was pulled from the. At this time,
As an umbrella-shaped heat shield, a molybdenum conical shape (bottom: diameter 7 inches, vertical cross-section apex angle: between a pull-up shaft 1 and a crystal holder 4 with a porous alumina heat insulating material 2 interposed therebetween. 100
The heat shield plate 3 of (°) was used. The material of the heat insulating material 2 is not limited to this, and any material having heat resistance and low thermal conductivity may be used. The material, shape, and size of the heat shield plate 3 are not limited to those described above, and a material having heat resistance and low emissivity is used so that the inert gas flow from the upper portion is not disturbed and the single crystal 5 Any material having an outer diameter larger than the diameter may be used. Normally, tantalum can be used as the material in addition to molybdenum.

Further, as a cylindrical heat shield wall, a support member composed of the ring 14 and the support base 15 shown in FIG. 2 is installed in the chamber, and the heat shield plate 16 and the heat shield plate shown in FIG. A heat insulating material composed of the reflector 17 was installed. Ring 14
Match the shape to the top of the carbon crucible 8
No. 5 was installed by adjusting the upper end of the center of the crucible so that the lower end of the heat reflection plate 17 fits the upper end of the quartz crucible 7. Although molybdenum was used as the material of both the ring 14 and the support 15, another material may be used as long as it has heat resistance capable of maintaining its shape.

The heat shield plate 16 has an outer diameter of 14 inches and a thickness of 5
Although it is made of graphite of mm, it is installed with a groove so that the gas such as SiO from the quartz crucible wall and the surface of the melt flows sufficiently, and the material should have high emissivity and high thermal conductivity. Good. The heat reflection plate 17 is a molybdenum cylinder having an inner diameter of 12 inches, a thickness of 2 mm, and a height of 200 mm, and is installed on the heat shield plate 16. This is located between the quartz crucible 7 and the chamber 13. Any material may be used as long as it is high enough to enter and has a low emissivity, and tantalum can be used as a normal material in addition to molybdenum. It is preferable that the inner diameter is larger than 8 inches with respect to 6 inches of the single crystal because the heat retention of the single crystal is good.

FIG. 4 shows the results of comparison of the temperature of the single crystal pulled up with the above-mentioned umbrella-shaped heat shield and cylindrical heat shield wall with those of the prior art. For example, when the crystal length is 300 mm, the temperature difference between the upper and lower ends of the crystal is conventionally about 750 ° C., but in the embodiment, the upper and lower temperature difference is about 500 ° C., which is about 250 ° C. According to the present invention, the temperature gradient in the single crystal is relaxed.

Further, according to the present invention, the pulling speed is set to the low speed of the target value of 20 mm / hr while controlling the diameter of the single crystal. FIG. 5 shows the result of comparison of the fluctuation range of the pulling speed at this time with that of the conventional technique. According to the present invention, the fluctuation range of the velocity is reduced particularly in the first half of the crystal growth, and the slow pulling can be stabilized. Furthermore, according to the present invention, the temperature of the crucible wall can be lowered by about 10 ° C. by the heat retaining effect of the umbrella-shaped heat shield and the cylindrical heat shield wall, and the melting of oxygen from the crucible wall into the melt can be achieved. Since it was suppressed, the oxygen concentration of the single crystal in the slow pulling could be reduced by about 2.5 ppma.

[0022]

According to the present invention, an umbrella-shaped heat shield is provided on the pulling shaft, and a cylindrical heat shield wall composed of a heat reflection plate, a heat shield plate and a supporting member is installed above the crucible. Due to
The temperature gradient in the silicon single crystal was relaxed, and stable low-speed pulling became possible. Further, the temperature of the crucible wall can be lowered by the heat retaining effect of the umbrella-shaped heat shield and the cylindrical heat shield wall, and the oxygen concentration of the single crystal can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of the inside of a chamber showing an embodiment of the present invention.

FIG. 2 is a top view and a vertical cross-sectional view showing an example of a support material of the present invention.

FIG. 3 is a top view and a vertical sectional view showing an example of a heat shield plate and a heat reflector plate of the present invention.

FIG. 4 is a diagram comparing the temperature of a single crystal pulled according to an example of the present invention with that of a conventional technique.

FIG. 5 is a diagram comparing the fluctuation range of the pulling speed when the pulling speed is set to a low speed of a target value of 20 mm / hr while controlling the diameter of the single crystal according to an example of the present invention, in comparison with the related art. ..

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pull-up shaft 2 Heat insulating material 3 Heat shielding plate 4 Crystal holder 5 Silicon single crystal 6 Silicon melt 7 Quarts crucible 8 Carbon crucible 9 Heater 10 Heat insulating material 11 Heat insulating material 13 Chamber 14 Ring 15 Support stand 16 Heat shielding plate 17 Heat reflection plate Board

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Murakami 1 Kawasaki-cho, Chuo-ku, Chiba City Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Yasuyuki Seki 1 Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Co., Ltd. Research headquarters

Claims (1)

[Claims] 1. A crucible having a cylindrical heat-shielding wall surrounding a pull-up crystal, which comprises an umbrella-shaped heat shield mounted on a pull-up shaft of a silicon single crystal and which comprises a heat-reflecting plate, a heat-shielding plate and a supporting material. An apparatus for producing a silicon single crystal, which is erected on the upper edge.