JPS63117988A - Graphite crucible for preparation of semiconductor single crystal - Google Patents

Abstract

PURPOSE:To retard the reaction between a graphite and quartz glass and to obtain a single crystal having high durability inexpensively by using a graphite crucible having low degree of graphitization and a specified pore structure. CONSTITUTION:The graphite crucible is prepd. from a graphite material having <=0.6 (after treating at 2,500 deg.C) degree of graphitization (1-P) and <=0.1cm<3>/g volume of pores having >=1mu pore radius measured by a mercury porosimetric method wherein P is 0-1 calculated by using the formula of Franklin wherein d is a spacing of lattice planes by X-ray diffractometry. Then, a quartz glass crucible is housed in this graphite crucible, and the melt of raw materials are charged to the quartz glass crucible and heated with a carbon heater. A seed crystal, for example, a seed crystal of a silicon, is dipped in the melt and pulled up slowly while rotating the pulling shaft. Thus, a single crystal, for example, a single crystal of a silicon is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a graphite crucible for producing semiconductor single crystals, and particularly to a graphite crucible for a single crystal pulling apparatus used when producing semiconductor single crystals such as silicon.

(Prior Art) In general, semiconductor materials, particularly silicon single crystals, are mainly manufactured by a rotational pulling method called the Czochralski method.

The Czochralski method is a crystal growth method in which a single crystal is produced by pulling a seed crystal immersed in a molten liquid while rotating it. For example, when manufacturing silicon single crystals, high-purity silicon polycrystals are heated and melted in a quartz glass crucible housed in a graphite crucible using an external carbon heater, and silicon seed crystals are first immersed in this melt. Slowly pull up while rotating. This operation is carried out at a temperature close to 1450°C across the solid-liquid boundary temperature of silicon, 1413°C, but since silica glass begins to soften at temperatures above 1200°C, it is supported in a graphite crucible and deformed due to softening. is prevented.

In this way, during the silicon single crystal pulling operation, quartz glass and graphite come into contact, and SiO2+C→Co (91” S10
The graphite crucible is consumed by the reaction (9) and thinning progresses. Particularly recently, graphite crucibles that are divided into two or more parts are often used to prevent cracking of the graphite crucible (for example, see Japanese Patent Application Laid-Open No. 58-95693). Since the contact area of the quartz glass becomes large, wear and thinning of the graphite crucible at the mating ends becomes significant. As a result, a phenomenon occurs in which the internal quartz glass crucible softens and protrudes from the gap between the graphite crucible mating parts, increasing the contact area between graphite and quartz glass and further promoting wear and thinning of the graphite crucible. As the thickness decrease progresses and the gap between the mating parts of the graphite crucible increases, the amount of protrusion of the inner quartz glass crucible increases, leading to a situation where the thinned quartz glass crucible ruptures and the molten silicon inside is scattered. arise.

In order to avoid such a risk, the graphite crucible is replaced after about 10 cycles in a normal silicon single crystal pulling operation.

(Problems to be Solved by the Invention) As described above, conventional graphite crucibles have had a short durability life.

Thus, an object of the present invention is to solve the above-mentioned problems of conventional graphite crucibles used when producing semiconductor single crystals such as silicon by the pulling method, and to reduce consumption and thinning due to reaction with quartz glass. Therefore, it is an object of the present invention to provide a graphite crucible for producing a semiconductor single crystal, which is made of a material with a long durable life.

(Means for Solving the Problems) In order to achieve the above object, the present inventors have conducted various studies on the consumption and thinning of graphite crucibles in semiconductor pulling equipment, and have found that the causes of consumption and thinning of graphite crucibles are as follows. It has been found that the difficulty of a contact reaction with a certain quartz glass is controlled by the degree of graphitization and pore structure of the graphite material used. That is, regarding the degree of graphitization, the reaction with quartz glass can be suppressed by lowering the degree of graphitization of the graphite material.
It has been found that if the value of (1-P) calculated using ranklin's P value is 0.6 or less after treatment at a temperature of 2500°C, the contact reaction between the graphite material and silica glass is significantly suppressed. It is something.

On the other hand, regarding the pore structure, the wear and thinning of the graphite crucible progresses due to the contact reaction with the quartz glass, so by reducing the contact area, the reaction between the graphite material and the quartz glass can be suppressed. It is important to control the pore structure, especially when the volume occupied by pores with a radius of 1 μm or more is
It was discovered that the reaction between the graphite material and quartz glass could be minimized by creating a pore structure with a pore structure of cm'/g or less, and the present invention was completed based on this finding.

Here, in the present invention, the value of graphitization degree (1-P) calculated using Franklin's P value is at a temperature of 250 (l"c
Graphite for manufacturing semiconductor single crystals, characterized in that it is made of a graphite material having a pore structure of 0.6 or less after treatment, and in which the volume occupied by pores with a radius of 1 μm or more is 0.1 cm3/g or less It is a crucible.

That is, the present invention uses a graphite crucible material determined by X-ray diffraction analysis and used as an index of the degree of graphitization, in order to reduce the wear and thinning caused by the reaction with quartz glass of the graphite crucible and extend the durable life of the graphite crucible. The value of (1-P) is 0°6 or less after treatment at a temperature of 2500'C, and the volume occupied by pores with a radius of 1 μm or more measured by mercury porosimetry is 0.1 cm'' /g or less.

Here, Franklin's P value is the value of P calculated from the value of the interplanar spacing (dO02) obtained by X-ray diffraction analysis according to the formula: It takes a value from 0 to 1, and this P value represents the probability that a disordered layer exists in the graphite material, and the value of (1-P) is a measure of the degree of graphitization (
Toshihisa Ishikawa, Michi Nagaoki: New Carbon Industry, Kindai Editorial Company (198
2)). In other words, when the value of (1-P) approaches 1, the proportion of disordered layers in the graphite material decreases, indicating a high degree of graphitization, and conversely, when the value of (1-P) approaches 0, the graphite material The proportion of disordered layers in the material increases, indicating a low degree of graphitization.

(Function) As described above, the present invention provides that although silica glass is in a softened state near 1450°C, which is the temperature at which a contact reaction between graphite material and quartz glass occurs, the reaction between the two is essentially in-phase. In such a reaction system, the difficulty of the reaction depends on the crystal structure of the graphite material, and the lower the degree of graphitization of the graphite material and the higher the proportion of disordered layers, the more the reaction is suppressed. be.

Here, the reason why the pore volume of the graphite material with a radius of 1 μm or more is an important factor in the reaction between the graphite material and silica glass is because of the aforementioned SiO□+C→Co(91+SiO+, n
The silicon monoxide gas generated by the reaction reacts with graphite to generate silicon carbide through 2C+ SiO(g) → Si C+ COf91, and this silicon carbide blocks the pores of the graphite material and reduces the surface area. This is because such a pore clogging effect becomes particularly noticeable in the case of pores with a pore radius smaller than 1 μm. In other words, in order for the pore blocking effect by silicon carbide produced as a result of the side reaction of the reaction between the graphite material and silica glass to work effectively and suppress the reaction between the graphite material and silica glass, the radius of the graphite material must be 1
It is necessary to reduce the volume occupied by pores with a radius of 1 μm or more, and the smaller the pore volume, the more the reaction can be suppressed.
If it is less than g, consumption and thinning due to the reaction of graphite material with quartz glass can be significantly reduced.

Incidentally, as a method for manufacturing the graphite material according to the present invention, there is, for example, a method for manufacturing a carbon material disclosed in JP-A-59-207822.

Examples of the present invention will be described below.

Example I Graphite materials were graphitized at a temperature of 2500°C and had different degrees of graphitization and pore structures as shown in Table 1, each having a width of 1.
Samples of 0+ nm, length 50 mm, and thickness 10 mm were cut out, and a quartz glass sample of the same size was loaded on top of each graphite material sample, set in a horizontal electric furnace, and heated at a temperature of 1450°C and a pressure of 5 torr% static. Flow rate 50
Heat treatment was performed for 20 hours under the condition of Ncc/min. The thickness of the graphite material sample after heat treatment was measured, and the amount of thickness reduction of the graphite material sample due to reaction with quartz glass was determined. The results are shown in Table 1.

As shown in Table 1, the degree of graphitization (I-P) of graphite material
Comparative example test floor 4 in which the value of is over 0.6 and the volume occupied by pores with a radius of 1 μm or more exceeds 0.1 cm'/g
Or, the volume occupied by pores with a radius of 1 μm or more in the graphite material is 0.
．． Degree of graphitization (1-P) of 1 cm3/g or less
Test floor 5, test 11kt of comparative example where the value exceeds 0.6
5, the graphitization degree (1-P) of the graphite material is 0.6.
In the case of Comparative Example Test 11kL6 in which the volume occupied by pores with a radius of 1 μm or more exceeds 0.1 cm37g, the amount of thinning of the graphite material after 20 hours of reaction with quartz glass exceeds 1 mm. There is. On the other hand, in the case of test Thl, 2.3, which is an example of the present invention, the amount of thinning of the graphite material after 20 hours of reaction with quartz glass was 172 or less compared to the comparative example. It can be seen that consumption of graphite material and thinning due to reaction with quartz glass are suppressed.

Example 2 The graphite materials of Test i2 of Example 1 and Test No. 4 of Comparative Example were processed to have an inner diameter of 305 mm and an outer diameter of 330 mm, respectively.
A two-part graphite crucible of m was created, and silicon single crystals were pulled using the conventional method using these graphite crucibles.
The durability life of graphite crucibles was compared. The results are shown in Table 2.

As shown in Table 2, test chamber 7 which is an embodiment of the present invention
In the case of , consumption of graphite material due to reaction with quartz glass,
As a result of suppressing thinning, the durable life of the graphite crucible is more than doubled compared to the case of Test No. 8 of the comparative example.

Table 2 (Effects of the Invention) As explained above, according to the present invention, it is possible to significantly reduce consumption and thinning of graphite material due to reaction with quartz glass, and therefore, it is possible to significantly reduce consumption and thinning of graphite material due to reaction with quartz glass. Since the durable life of the graphite crucible used when manufacturing the crystal can be extended, the effect of reducing the manufacturing cost of single crystals is extremely large.

Claims (1)

[Claims] Degree of graphitization (calculated using Franklin's P value)
1-P) is 0.6 or less after treatment at a temperature of 2500°C, and the volume occupied by pores with a radius of 1 μm or more is 0.1
A graphite crucible for producing a semiconductor single crystal, characterized in that it is made of graphite having a pore structure of cm^3/g or less.