JPH07277877A - Crucible for pulling up silicon single crystal - Google Patents

Abstract

PURPOSE:To obtain a carbon crucible with which a high-purity silicon single crystal is obtainable without contaminating a silicon single crystal pulling up device by producing this carbon crucible from specific glassy carbon. CONSTITUTION:An initial condensate of a phenolic resin is prepd. by bringing a thermosetting resin, for example, refined phenol and formalin into addition condensation reaction. Furfuryl alcohol is mixed at a ratio of 30wt.% with this initial condensate to prepare a resin compsn. having a viscosity of 40 poise and resin-component 55% as a raw material resin. An outside blind cylindrical vessel having a large bore and height and an inside blind cylindrical vessel of a small bore and height are formed by using polypropylene as a molding flask for molding the crucible. Both are fixed by aligning their centers and heights to form double blind cylindrical vessels. The raw material resin is injected into the space thereof. The raw material resin is then subjected to a deaeration treatment for three hours at 70 deg.C under a reduced pressure and is then subjected to precuring about a whole day and night. The cured resin molding is put into an electric furnace and is baked at 2000 deg.C (>=800 deg.C) in a non-oxidizing gaseous (Ar) atmosphere, by which the crucible consisting of the glassy carbon blank is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon crucible used for a silicon single crystal pulling apparatus for semiconductors by the Czochralski method (hereinafter referred to as CZ method).

[0002]

2. Description of the Related Art As shown in FIG. 1, a silicon single crystal pulling apparatus using the CZ method is a method in which a silicon polycrystal is put in a high-purity quartz crucible 1 and the quartz crucible 1 is rotated by a rotating shaft 6 while externally rotating. Is heated and melted by a heater 3 from the above, and a silicon single crystal (seed crystal) supported by the tip of the pulling shaft 5 is dipped in the melt 8 of the silicon polycrystal, and then the pulling shaft 5 is slowly pulled up. By cooling, the polycrystal of silicon is converted into the single crystal 9.

Since the quartz crucible 1 is softened at a high temperature and has insufficient strength, the quartz crucible 1 is usually made of a carbon crucible 2
It is used by being reinforced by being installed inside. As the carbon crucible 2, a graphite material having high strength at high temperature and high heat resistance and thermal conductivity is generally used.

However, since graphite fine powder easily separates from the surface of the graphite material, the separated fine powder floats inside the silicon single crystal pulling apparatus and is mixed in the melt of the silicon polycrystal to form the silicon single crystal. There is a problem that deteriorates quality. Further, since impurities such as various metals are present in the graphite material in a small amount, these impurities are volatilized at high temperature to become a pollution source, which leads to deterioration of quality.

The semiconductor is required to have extremely high purity, and various members for manufacturing the semiconductor are also required to have extremely high purity. Therefore, it has been proposed to use an extremely high-purity graphite material having a total ash content of 5 ppm or less, particularly preferably 1 ppm or less, for various members such as a graphite crucible for a silicon single crystal pulling apparatus (JP-A-64). −18986
Issue). However, since the graphite material is obtained by sintering an aggregate of fine particles, it is unavoidable that the fine powder graphite is detached from the surface, leading to the solution of the problem of decreasing the purity of the silicon single crystal. Not in.

Japanese Patent Laid-Open No. 252394/1987 discloses a graphite member in which fine graphite powder does not come off from the surface.
There has been proposed a graphite member for a semiconductor melting device such as a graphite crucible in which the surface of the graphite member is coated with glassy carbon which is a thermal decomposition product of an organic polymer. According to this method, since the surface of the graphite crucible is coated with smooth and dense glassy carbon, it becomes possible to suppress the separation of the fine graphite powder.

[0007]

However, since the graphite crucible is used at a high temperature of 1410 ° C. or higher, which is the melting temperature of silicon, the glass crucible coated by the difference in the coefficient of thermal expansion between the graphite member and the vitreous carbon. There was a problem that carbon was cracked or peeled off, and there was a problem that the graphite crucible was broken.

An object of the present invention is to provide a carbon crucible capable of obtaining a high-purity silicon single crystal without contaminating the inside of the silicon single crystal pulling apparatus.

[0009]

In order to achieve the above object, a carbon crucible for pulling a silicon single crystal according to the present invention has a thermosetting resin molded body which is heated and cured at 800 ° C. in a non-oxidizing atmosphere. It is a structural feature that it is composed of glassy carbon that is calcined and carbonized at the above temperature.

The vitreous carbon material has a glassy and dense structure structure, and is more gas-impermeable, abrasion-resistant, corrosion-resistant, self-lubricating, surface-smooth and more robust than other carbon materials. It is a heterogeneous carbon material that is excellent in terms of its properties and has very few impurities such as metals. Therefore, it is useful in various fields of application that are used at high temperatures and require high purity.

Generally, a glassy carbon material is manufactured by a method of firing and carbonizing a precursor obtained by molding a thermosetting resin having a high carbonization residual ratio such as a furan-based or phenol-based carbon material. Since the calcination carbonization process in this process proceeds in the solid phase, the volatile components that are generated in large amounts by the thermal decomposition of the precursor resin are discharged to the outside of the solid phase, and the process of converting into the carbide while shrinking the volume is followed. In this case, when the precursor resin is in a thick state, the pyrolysis gas remains without being discharged from the solid phase,
This causes material defects such as generation of voids, swelling, and cracking. Therefore, it is difficult to obtain a thick block-shaped glassy carbon material, and the field of use has been limited.

The applicant of the present invention has conducted extensive research on a method for manufacturing a thick block-shaped glassy carbon material, and as a result, the result is 5 mm.
We have developed a technology that can produce thick glassy carbon
The application was filed as Japanese Patent Application No. 4-277952. According to this production method, a phenol resin having a molecular weight of 100 or more and a gelation time of 5 to 60 minutes is mixed with furan or a derivative compound thereof to form a resin composition having a viscosity of 1 to 100 poise and a resin content of 50% by weight or more, By molding and curing the resin composition and then firing and carbonizing in a non-oxidizing atmosphere, it is possible to produce a thick glassy carbon material having a homogeneous and dense structure.

The present invention provides a crucible made of glassy carbon instead of a conventional graphite crucible as a carbon crucible for pulling a silicon single crystal by the CZ method by applying this manufacturing technique.

The thermosetting resin used for producing the glassy carbon of the present invention has a molecular weight of 100 or more and a gelation time of 5 to 5.
A 60 minute phenolic resin is used. Molecular weight 100
If it is less than the above range, the crosslinked structure after curing is weak and a high-strength carbide cannot be obtained. Further, in the case of a normal phenol resin having a gelation time of less than 5 minutes, the progress of curing is too fast and unreacted substances and condensed water remain without being volatilized, resulting in remarkable pore generation. Since the curing time increases with the curing time, there is a risk of contamination during the curing process,
This is because the productivity is further reduced.

Next, furan or its derivative compound is mixed with this phenol resin to prepare a two-component resin composition. The furan-based component is mixed in order to improve the carbonization yield during firing and carbonization, and is usually 40
Carbonization yields of ~ 60% can be improved to 65-75%. As the furan derivative compound, a substance having a furan ring in its chemical structure and compatible with a phenol resin is effective, and for example, furfuryl alcohol, furfural,
Furancarboxylic acid methyl ester and the like can be mentioned. The mixing ratio of these furan-based components is appropriately determined according to the resin properties, but is preferably set within the range of approximately 5 to 50% by weight.

A resin composition prepared by mixing a furan-based component with a phenol resin is adjusted to have a viscosity of 1 to 100 poise and a resin content of 50% or more. If the viscosity is less than 1 poise, the structural strength after carbonization is reduced, and if it exceeds 100 poise, the condensation water does not volatilize smoothly during curing, and many pores occur. Further, if the resin content is less than 50%, a large amount of unreacted components are contained during curing, so that cracks and the like are likely to occur in the carbonization and firing stage.

The thermosetting resin as a raw material is poured into a desired crucible-shaped molding frame, and then the raw material is defoamed under reduced pressure, and then the curing reaction is allowed to proceed slowly at a temperature of about 70 ° C. . After the curing reaction has proceeded to such an extent that the mold can be released from the mold, it is removed from the mold and subjected to a curing treatment at a temperature range of 80 to 300 ° C, preferably 150 to 300 ° C. The heat-cured resin molded product is packed in a heating furnace maintained in a non-oxidizing atmosphere, and subjected to a firing carbonization treatment at a temperature of 800 ° C. or higher, preferably in the temperature range of 1410 ° C. or higher, which is the melting point of silicon, to obtain a glassy carbon. A crucible formed by is obtained.

[0018]

The present invention uses a crucible integrally formed of glassy carbon as a crucible for accommodating a quartz crucible, and therefore has a unique property of glassy carbon, that is, a fine structure and wear resistance. It has excellent properties, corrosion resistance, surface smoothness, etc., and is characterized by having very few impurities and isotropic properties.

Therefore, it is possible to avoid generation of fine powder from the surface due to abrasion and volatilization of impurities from the inside at high temperature. Therefore, contamination in the silicon single crystal pulling apparatus is prevented, and high purity silicon single crystal is prevented. It becomes possible to manufacture crystals.

[0020]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples.

Examples and Comparative Examples Phenol purified by vacuum distillation and formalin were subjected to an addition condensation reaction in the presence of ammonia to prepare a phenol resin initial condensate having a molecular weight of 132 and a gelation time of 14 minutes. Furfuryl alcohol was added to and mixed with the phenol resin initial condensate at a ratio of 30% by weight to prepare a resin composition having a viscosity of 40 poise and a resin content of 55%, which was used as a raw material resin.

As a mold for crucible molding, a polypropylene container having a thickness of 5 mm is used, and a cylindrical container having an inner diameter of 108 mm and a height of 150 mm (bottom cylindrical container having an outer bottom) and an inner diameter of 90 mm are used.
mm and a height of 143 mm, a bottomed cylindrical container (inner bottomed cylindrical container) was prepared. The inner bottomed cylindrical container was inserted into the outer bottomed cylindrical container with the center and height aligned and fixed. In this way, a double-bottomed cylindrical container composed of an outer-bottomed cylindrical container and an inner-bottomed cylindrical container was created, and the raw material resin was injected into the space formed between the bottomed cylindrical containers. . Then, after degassing for 3 hours under a reduced pressure of 10 Torr to remove air bubbles remaining in the resin, 70
It was placed in an oven at 0 ° C. and left for one day to be pre-cured. Then, it was taken out from the mold to obtain a resin molded body having an inner diameter of 94 mm, a thickness of 7 mm, and a height of 110 mm. This resin molding is 1 ℃ /
After the temperature was raised to 250 ° C. at a temperature rising rate, the temperature was maintained for 24 hours for curing treatment. This cured resin molded body was placed in an electric furnace and fired at a temperature of 2000 ° C. in an argon gas atmosphere. In this way, an inner diameter of 78 mm made of glassy carbon,
A crucible having a thickness of 5 mm and a height of 90 mm was produced. Various properties of this glassy carbon were measured and shown in Table 1.

[0023]

[Table 1]

A quartz crucible was placed in this crucible, and a silicon polycrystal was placed therein and heated to a temperature of 1430 ° C. to melt it. The amount of carbon mixed in the silicon melt was measured while changing the number of pulling of the single crystal, and the surface condition of the glassy carbon crucible was observed. The obtained results are shown in Table 2.

[0025]

[Table 2]

Comparative Example The same test as in the example was carried out using a graphite crucible that has been conventionally used, the characteristic values thereof are shown in Table 1, and the detected carbon amount and the observation result of the surface state of the crucible are shown in Table 2. Co-published.

From the results shown in Tables 1 and 2, the crucibles of the Examples had less total ash content as impurities than the Comparative Examples, and the results of the silicon single crystal pulling test showed that the amounts of carbon contained in the melt were not detected. I know there is. Further, the state of the crucible surface was not changed even after 60 pulling tests.
However, in the comparative example, even after 20 pull-up tests, it was found that the fine graphite particles that had separated were mixed in the melt, and the crucible surface condition also deteriorated.

[0028]

As described above, according to the present invention, since the carbon crucible for pulling a silicon single crystal is composed of glassy carbon, the fine carbon powder does not come off.
Further, since glassy carbon is extremely high in purity, it is possible to manufacture high quality silicon single crystals.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an apparatus for pulling a silicon single crystal by a CZ method.

[Explanation of symbols]

 1 Quartz crucible 2 Carbon crucible 3 Heater 4 Heat shield 5 Pulling shaft 6 Rotating shaft 7 Pedestal 8 Silicon melt 9 Silicon single crystal

Claims (1)

[Claims] 1. A crucible for pulling a silicon single crystal, wherein a thermosetting resin molding is made of glassy carbon which is heat-cured and then calcined and carbonized at a temperature of 800 ° C. or higher in a non-oxidizing atmosphere.