JPH10101472A - Graphite crucible for pulling up semiconductor monocrystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a graphite crucible able to suppress its reaction with SiO glass in a catalytic reaction with quartz glass at a local temperature by heating the graphite crucible at a specific temperature in the final process. SOLUTION: This graphite crucible is produced at a temperature of final process in the range of 2200-2000 deg.C, to preferably have degree of graphitization P(1- P) of 0.05-0.35, bulk density of 1.7 or more, and intrinsic electric resistance of 2000-4000μΩ-cm. Regulating the temperature of the graphite member in the final process is advantageous for grasping process condition because troublesome analyses, such as X-ray diffraction, is required, and furthermore can substantially increase frequency of pulling up semiconductor monocrystals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphite crucible for pulling a semiconductor single crystal, and particularly to a graphite crucible for pulling a semiconductor single crystal such as silicon, which has a long life.

[0002]

2. Description of the Related Art In general, semiconductor materials, particularly single crystals of silicon, are mainly produced by a rotational pulling method called a Czochralski method. The Czochralski method is a crystal growing method in which a single crystal is grown by rotating and pulling a seed crystal immersed in a melt.

For example, when manufacturing a silicon single crystal, a high-purity polycrystalline silicon is heated and melted by an external carbon heater in a quartz glass crucible housed in a graphite crucible, and a silicon seed crystal is first added to the melt. And slowly pull it up while rotating.

[0004] This operation is carried out at a temperature of about 1450 ° C across the solid-liquid boundary temperature of silicon of 1413 ° C. Since quartz glass begins to soften at a temperature of 1200 ° C or more, it is supported by a graphite crucible. Prevents deformation due to softening. As described above, during the operation of pulling the silicon single crystal, the quartz glass and the graphite come into contact with each other, and the reaction of SiO ₂ + C → CO ₂ + SiO ₂ consumes the graphite crucible, thereby reducing the wall thickness.

In order to prevent this, for example, Japanese Patent Laid-Open No. 63-1
In 17988, the value of the degree of graphitization (1-P) calculated using the Franklin P value is determined at a temperature of 2500 ° C.
A graphite for producing a semiconductor single crystal, comprising a graphite material having a pore structure having a pore size of 0.6 or less after treatment and having a radius of 1 µm or more and occupying 0.1 cm ³ / g or less. Although a crucible has been proposed, the graphite crucible is replaced about 20 times in a single crystal pulling operation.

[0006]

As described above, conventionally, graphite crucibles have a drawback that the durable life is short, and it has been demanded to extend the durable life. A method for preventing a contact reaction with quartz glass at a high temperature or a reaction with a SiO gas atmosphere has not been established.

Japanese Unexamined Patent Publication (Kokai) No. 63-117988 discloses that if the degree of graphitization (1-P) is 0.6 or less, it is all of the actual artificial graphite materials, and it is impossible to expect a particularly long life. is there. Further, analysis by X-ray diffraction is troublesome to measure, and a simple inspection method has been desired.

[0008]

The present inventor has conducted various studies on the reaction between graphite material and silicon in order to solve such a problem. As a result, the final heat treatment temperature of the graphite material used in a graphite crucible is an important factor. Yes, especially 2000-2200 ° C
It has been found that a heat-treated one obtains a remarkable effect.
At this time, the higher the bulk specific gravity of the graphite material, the smaller the open pore area and the smaller the reaction area, so that a desirable result was obtained.

[0009]

As described above, the present invention is advantageous in grasping the process because it does not require complicated analysis by X-ray diffraction or the like as long as the final heat treatment temperature of the graphite material is regulated. In the graphite crucible for pulling a semiconductor single crystal of the present invention, since the reaction with silicon, SiO gas and the like is suppressed, the number of times of pulling a semiconductor single crystal can be greatly increased. Hereinafter, the present invention will be described.

A carbon material (ungraphitized material) having a bulk specific gravity of 1.5 to 1.8, which has been graphitized by changing the heat treatment temperature, is immersed in molten silicon, and the silicidation reaction is performed by X-ray diffraction. analyzed. The results are shown in Table 1. The bulk specific gravity of the used material is around 1.7.

[0011]

[Table 1]

The best results obtained with the graphite material at this time are those in which the final heat treatment temperature is 2000-2200 ° C., the P value P _(1-P) in X-ray diffraction is 0.05-0.35, The bulk specific gravity was 1.7 to 1.86. Electric resistivity is 2000-
4000 μΩ-cm.

The reaction of a graphite crucible for pulling a silicon single crystal is a reaction with quartz glass (SiO ₂ ) and silicon fused with SiO gas. Considering the reaction mechanism, we believe that the following theory holds.

The reaction with the molten silicon is as shown in Table 1, and the results obtained are as follows: a treatment at 2000 to 2200 ° C. and a semi _- graphite having a degree of graphitization P _(1-P) of 0.1 to 0.3 give good results. I have. From this, SiC which is a reaction product of carbon material and Si is obtained.
The semi-graphitic material having a low degree of graphite crystallinity can suppress the contact reaction.

The difficulty of the reaction depends on the crystal structure of the carbon material.
When the degree of graphitization is low and the proportion of the disordered layer is large, the reaction is suppressed. However, a carbonaceous (ungraphitized) material having a small crystallite is presumed to have a large SiC reaction due to a large contact surface with Si.

The reaction with SiO, which is a gas, is a gas diffusion reaction into the crucible material. A gas having a small average pore diameter and a small porosity has a small gas diffusion. Therefore, a crucible material having a small porosity and a significant bulk ratio is desirable.

Since the reaction with SiO ₂ which is a solid is a contact reaction, a product treated at 2000 to 2200 ° C., which is a semi-graphitic carbon material, is considered to be superior to the reaction with molten silicon. In pulling a single crystal, a high-purity material with little generation of impurities is usually used to prevent contamination. Therefore, the graphite crucible is subjected to a material before processing or a high-purification treatment after processing.

[0018]

EXAMPLES The durability life of graphite crucibles for producing semiconductor single crystals is dominated by the reaction with SiO gas, and a reaction test with SiO according to the present invention was carried out. The test conditions were as follows: the test piece was 4 t × 20 × 50 (unit: mm), the test piece was embedded in SiO powder, the atmosphere was kept at 60 torr in argon gas, at 1550 ° C. for 60 minutes, and the weight loss of the carbon material was measured. Table 2 shows the results.

[0019]

[Table 2]

As shown in Table 2, the weight loss of the product treated at 2000 ° C. was 57% smaller than that of the conventional product treated at 2800 ° C., which was 43% less. From the semi-graphitic material obtained by treating the isotropic carbon material at 2000 ° C based on this result,
When a graphite crucible for producing a semiconductor single crystal having a total ash content of 20 ppm or less after crucible processing and high-purity treatment was used, the number of single crystal pulling times was 30 to 40 times as compared with about 20 times in the past.

The characteristics of this graphite crucible material are graphitization degree P
_(1-P) is 0.05-0.35 and electric resistivity is 2000
４4000 μΩ-cm, bulk specific gravity 1.75 to 1.83,
Total ash was 10-20 ppm.

Claims (2)

[Claims] 1. A graphite crucible for pulling a semiconductor single crystal, wherein the graphite crucible is made of a graphite material having a final processing temperature of 2200 to 2000 ° C. 2. A graphite material having a graphitization degree P _(1-P) of 0.05 to 0.05.
0.35, bulk specific gravity 1.7 or more, electrical resistivity 2000
2. The graphite crucible for pulling up a semiconductor single crystal according to claim 1, which has a thickness of about 4000 [mu] [Omega] -cm.