JPH0617236A - Vessel for molten metal - Google Patents

Abstract

PURPOSE:To lessen the wettability to and reactivity metal and to prevent the generation of carbon dust by forming an amorphous carbon film on the surface of an isotropic graphite base material having a prescribed bulk density, average pore radius anisotropic ratio and inorg. impurities. CONSTITUTION:This vessel for molten metal is formed by coating the amorphous carbon film on the surface of the isotropic graphite base material. The vessel is used as a crucible for pulling up a silicon single crystal or as a crucible or boat for vapor deposition of gold, zinc, nickel, aluminum, silicon or the alloys thereof. The above-mentioned isotropic graphite base material has 1.7 to 1.9g/cm<3> bulk density, 0.2 to 2mum average pore radius, <=1.05 anisotropic ratio and <=5ppm inorg. impurities. The amorphous carbon film is obtd. by impregnating the base material with an org. solvent of a polyamide resin (more particularly an arom. polyimide resin).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphite container for molten metal, which is preferably used in a crucible for pulling a semiconductor single crystal, a crucible for melting a metal, a crucible for vapor deposition of metal, a boat, and the like.

[0002]

2. Description of the Related Art Materials used in contact with and treating molten metal are excellent in heat resistance, high thermal conductivity, low wettability with molten metal, thermal shock resistance and mechanical strength. It is an indispensable condition, and depending on the case, it is required to have good electrical conductivity, oxidation resistance and impermeability.

From these requirements, heat-resistant alloys and ceramic materials have been conventionally used as materials satisfying the above requirements. However, recently, many graphite materials are lightweight and excellent in the above requirements. It is being used.

In particular, isotropic graphite materials, which are easy to machine and have uniform electrical and physical properties, are very often used. As is well known, graphite materials are not particularly softened or deformed even at high temperatures, and are particularly excellent in that they have a low vapor pressure, and have low wettability with metals and self-lubricity. However, it does not pollute the molten metal and graphite itself has strong corrosion resistance, and has been used as a container material for molten metal.

[0005]

However, not only materials for producing new materials resulting from recent technological advances, new alloys due to diversifying needs, and materials for producing ultra-high purity metals due to high performance requirements, but also Further improvements have also been demanded for crucibles for pulling single crystals, crucibles for melting metals, crucibles for vapor deposition of metals, and boats.

The items that have been improved are listed below. Ultra-high purity, that is, the amount of inorganic impurities contained in the carbon material is extremely low and substantially zero.

To develop a carbon material having very low affinity, wettability and reactivity with new metals and new alloys. For example, develop carbon materials for processing copper alloys, titanium alloys (which produce metal carbide), and aluminum that contain iron, nickel, chromium, beryllium, silicon, etc.

Being impermeable. The isotropic graphite material is formed by molding and firing fine carbon particles, and generally has very fine pores. Therefore, highly penetrable aluminum or the like is transmitted through the pores and further reacts with graphite to form aluminum carbide. Prevent this by making it impermeable.

Prevention of generation of coal dust. The carbon material is formed by molding and firing fine carbon particles, and even after a high temperature treatment of 2000 ° C. or more, a small amount of coal dust may get mixed into the molten metal, and this should be prevented.

As described above, in various respects, there is a demand for a solution as a carbon material for treating molten metal.

[0011]

[Problems to be Solved by the Invention] The above problem is a graphite material having a bulk density of the graphite base material of 1.7 to 1.9 g / cm ³ and an average pore radius of 0.2 to 2.0 μm. Moreover, the anisotropic ratio is less than 1.05 and the total amount of inorganic impurities other than carbon is 5 ppm.
Selectively use the following isotropic graphite materials.

Forming an amorphous carbon film on the surface of the above graphite material. It has been found that all the above problems can be solved by the synergistic effect with the above, and the present invention has been completed here.

[0013]

First, the isotropic graphite material as the base material will be described. The isotropic graphite material mentioned here is different from general natural graphite material, and the mechanical, physical and chemical properties of the graphite material are substantially uniform in all directions of the X, Y and Z axes. In other words, the graphite material has an anisotropic ratio of 1.05 or less.

Therefore, the isotropic graphite base material used in the present invention is, in principle, an artificial synthetic material, and the manufacturing method is not particularly limited as long as the anisotropic ratio is within the predetermined range.
For example, as shown in Japanese Examined Patent Publication No. 1-16789, finely pulverized carbon powder is mixed with a binder, molded and fired, and then fired at a high temperature to be graphitized. Since the powder is solidified in this way, it has fine pores,
The bulk specific gravity and the pore radius can be controlled by appropriately selecting the raw materials and the production conditions.

The presence of such pores is closely related to the permeability and the bonding strength of the coating layer to the base material after solidification when the graphite base material is impregnated or coated with the polymer substance in a later step. Have a relationship. That is, a polymer substance generally has a high viscosity, and if the pore size is too small, the polymer substance solution has poor penetrability into the graphite substrate, and only surface coating is performed, and the graphite substrate and the amorphous carbon film are Has a small anchoring effect and weakens the bonding strength between the surface of the base material and the coating layer and causes peeling.

On the contrary, if the pore size is too large,
The polymer solution permeates into the pores of the base material and does not cover the surface, so that the surface of the target carbon material becomes rough and the strength of the base material also decreases. As a result of repeating experiments on this point under various conditions, the pore radius of the graphite base material was 0.2.
.About.2.0 .mu.m, especially 0.7 to 1.8 .mu.m has been found to be suitable.

The pore radius of such a graphite base material can be measured by a mercury porosimetry method, for example, using an apparatus manufactured by Carlo Erba Co. An example of the measurement result is shown in FIG. The horizontal axis in FIG. 1 represents the pore radius, the vertical axis represents the cumulative volume of the pores as A, and B is the differential value of A, showing the distribution state of the pore radii. From this, it is understood that the pore radius is controlled within a very narrow range.

Further, the bulk specific gravity is related to the degree of graphitization of the graphite base material, but is also an index of the cumulative total amount of the pore space, and together with the size of the pores, the permeability of the polymer substance is high. Will be the factor that governs.

By repeating various experiments, the isotropic graphite base material used in the present invention has a pore radius of 0.2 to 2.0.
The specific gravity is from 0.7 to 1.8 μm, and the bulk specific gravity is from 1.7 to 1.9 g / cm ³ . If the pore radius is smaller than 0.2 μm, the resin liquid permeability is poor, and conversely 2.
If it is more than 0 μm, the effect of filling the pores by the resin for sealing is weakened. This point is also shown in Table 4 below. Table 4 shows the results of comparing the characteristics of the base material and the properties of the obtained crucibles for Examples 6 to 8 and Comparative Examples 4 to 6.

Next, the isotropic graphite base material having such properties is preferably subjected to a purification treatment depending on its use. This is because, for example, a high-precision special-purpose alloy or the like causes the molten metal to be contaminated by leaching, volatilization, diffusion, and the like of inorganic impurities that are present in a trace amount in the graphite base material or the polymer substance.

As a method for purifying a graphite base material for such a purpose, for example, the method of Japanese Patent Application No. 61-224131 can be applied. According to this method, the total amount of the inorganic impurity elements excluding the carbon component in the graphite base material is 2 ppm or less,
It can be highly purified to a level substantially close to zero.

As described above, the optimum range of the physical properties of the graphite base material, particularly the pore radius and the bulk specific gravity, is specified, and this is ultra-highly purified according to the application, so that the amorphous carbon film in the next step can be obtained. It can be formed firmly and completely.

It is known per se to coat and impregnate a surface of a graphite substrate with a polymer substance and then to bake it. For example:

Japanese Patent Publication No. 46-21093 discloses a method of impregnating a mold with a formaldehyde resin, Japanese Patent Publication No. 46-26.
No. 087 is a method of impregnating a carbon material for machinery with a polyamide-imide resin, and Japanese Patent Publication No. 52-39684 is heat-treated with a glassy carbon precursor and mixed with an organic solvent, and the slurry is applied to a substrate to form a glassy carbon. Is described. Japanese Patent Publication No. 2-7915 discloses that an organic polymer is dissolved in an aliphatic solvent and coated on a carbon material.
No. 2887 describes that the pores of a carbon substrate are impregnated with a phenol resin or a furan resin and the surface is coated with a glassy carbon coating.

To summarize these, synthetic polymer substances such as phenol resin, furan resin, vinyl chloride resin, furfuryl alcohol resin, polyimide resin, polyamideimide resin, etc., which are appropriately diluted with a solvent, or these The synthetic polymer substance is preliminarily caramelized in a separate container, and further diluted with a suitable solvent. The graphite substrate is impregnated, coated, sprayed, dipped and treated by such means.

It is also known that these polymer substances are not simply impregnated and coated, but further impregnated and coated and then carbonized at a temperature of several hundreds of degrees Celsius. Such a synthetic polymer material, when carbonized at a high temperature, produces so-called non-graphitizable carbon, that is, carbon also called amorphous carbon or glassy carbon, which is difficult to graphitize (crystallize). This carbon has advantages that it has a smooth surface, is hard, is impermeable to gas and liquid, has no dust from the surface, and has low sliding resistance. However, on the other hand, the workability is poor, the mechanical strength is low,
It is also known that it is easily cracked, peels off from the graphite base material, and causes cracks and the like.

In the present invention, a graphite base material having the specific bulk specific gravity and pore radius as described above is particularly selected, and a polymeric substance is used as a raw material to form amorphous carbon on the surface of the graphite base material. As a result, all the drawbacks of the conventional method can be compensated. In particular, a polyimide-based resin and / or a polyamide-imide-based resin having a high film-forming property as the polymer substance is preferable, and a polyamide-imide resin is particularly preferably used.

According to the research conducted by the present inventors, a polyamide-imide resin is dissolved in a solvent and impregnated or applied on the surface of a graphite base material, which is cured and carbonized, and then graphitized if necessary. (Hereinafter, this operation is abbreviated as "pie coat treatment".) It is clear that the carbon / carbon composite material having the obtained carbon coating has a significantly improved dropout of particles and hardly produces dust as shown in Example 1. Became.

As the polymer substance used in the present invention,
Penetrates deep into the pores of the carbon substrate to be coated,
It is necessary to prevent the base material from peeling off from the surface layer by the anchor effect and to increase the mechanical strength. Therefore, it is necessary to lower the viscosity of the polymer solution to improve the permeability, but in such a case, the method for lowering the viscosity is

(1) A method of diluting with a large amount of solvent (2) A method of using a high molecular weight substance having a small molecular weight (in other words, a substance close to an oligomer state).

However, as a result of experiments under various conditions, (1)
In the case of the method of (1), after the solvent is removed by evaporation, only a very small amount of the polymer substance remains, and the polymer layer itself has many holes through which the solvent has escaped and becomes rough, so the strength is low and the coating effect Has the drawback of being substantially low.

In the case of the method (2), if the molecular weight is too small, it is thermally unstable and decomposes at a slight temperature rise.
Evaporation reduces the coating effect. In addition, it was found that a polymer material having excellent heat resistance is desirable.

The inventors of the present invention first specified a graphite base material as a base material, and further changed the kind and molecular weight of the polymer substance used in combination with this, the concentration in the solvent, and the like to determine the most impregnation condition. The inventors have found good conditions and completed the present invention.

As a result of various tests, it was found that a polyamide-imide resin, particularly an aromatic polyamide-imide resin, was most suitable as the polymer substance used in the present invention. Its structural formula is as follows.

[0035]

[Chemical 1]

However, in the formula, n is 1 to 1000, preferably 1
It is an integer of 0 to 100, and R is a hydrocarbon group, preferably an alkyl group, and particularly preferably a lower alkyl group.

This resin is known as a heat resistant resin like the polyimide resin and the polybenzimidazole resin. This resin is generally convenient because it can form a film that is elastic even though it is hard and has good adhesiveness with the graphite base material, and that once the surface layer is formed, it does not easily separate from the base material due to the anchor effect or the like. is there.

As the molecular weight of the polyamide-imide resin,
In the above formula, n is preferably about 10 to 100, and when n is 1000 to 10000, it is difficult to dissolve in a solvent, the viscosity of the solution increases, and the penetrability into the graphite base material deteriorates. When n is less than 10, the surface layer hardness when carbonized and baked is low, and the covering effect is small.

As a solvent for dissolving the polyamide-imide resin, dimethylacetamide, dimethylformamide, dimethylsulfoxide and N-methyl-2-pyrrolidone are preferably used.

The concentration of the polyamide-imide resin in the solvent varies depending on the solvent, but in order to maintain the viscosity suitable for spraying for surface treatment and coating, the resin component (solid content) should be adjusted. The concentration is 10 to 50 by weight.
%, Preferably about 20 to 35%. If the amount of the resin component is too small, the viscosity is low and the permeability is good, but the coating layer after volatilizing the solvent has a low mechanical strength and a low degree of impermeability.

On the other hand, if the amount of the resin component is too large, white turbidity occurs and the stock solution of the preparation is poor in storage property.

There is a correlation between the molecular weight of the resin and the resin concentration in the solvent, and in order to maintain good workability, the molecular weight and the solution concentration are limited as described above.

Although the most preferable polyamide-imide resin of the polymer substance used in the present invention has been described above, it is also possible to use phenol resin, furan resin, vinyl chloride resin, furfuryl alcohol resin, polyimide resin and the like. You can However, as already mentioned, the polyimide resin and the polyamide-imide resin are preferable,
In particular, the polyamide-imide resin has a particularly good affinity for the above specific graphite base material, can form an extremely excellent coating film, and when blended in the above-mentioned molecular weight and solution concentration, the permeability is also good, and when carbonized, it becomes fine.・ Since the pores are filled, there is no leakage of molten metal, and the surface affinity with the metal is low,
The conditions required for a molten metal container, for example, a crucible for pulling a silicon single crystal, a crucible for melting a metal, a crucible for vapor deposition of a metal, and a boat are extremely well satisfied.

The mode of the method of the present invention will be described below in the order of the manufacturing steps. First, a graphite base material is coated or dipped with an organic solvent solution of a polymeric substance, particularly an aromatic polyamide-imide resin, to impregnate the solution or a part thereof. The raw graphite base material used at this time is an isotropic graphite base material having the above-described pore radius and bulk specific gravity. Further, a graphite / graphite composite material or the like can be used as the graphite base material.

The above-mentioned graphite base material is coated or impregnated with an organic solvent solution of the above-mentioned polymer substance. As these methods, any method such as brush painting, spray spraying, dipping and the like can be adopted. The coating amount of the polymer substance is usually 1 to 20 μm as the thickness of the coating layer.
m, preferably about 5 to 10 μm. It is not necessary to make it too thick, and if the film thickness is too thick, it is rather harmful due to cracks and the like. On the contrary, if it is too thin, the uncoated portion remains and the coating effect tends to be uneven.

The thickness of such an amorphous carbon layer depends on the SEM.
It can be measured by a (scanning electron microscope), the relationship between the coating conditions and the surface layer thickness is optimized by using SEM, and the thickness is controlled to be 5 to 10 μm. Thereafter, the coating was performed empirically under the conditions. . FIG. 2 is a simulated view of an SEM photograph of a sample coated to about 40 μm, where 1 is a substrate not coated and 2 is coated.

In the present invention, after impregnating and coating with a polymer substance, heating at 300 to 400 ° C. to volatilize and remove the solvent and cure the polymer substance, and then baking in a non-oxidizing atmosphere. To carbonize or further graphitize the polymer coating.

The graphite-based carbon composite material coated with amorphous carbon, which is obtained by such a method, is a carbonaceous or graphite coating of a carbonized resin of a high molecular substance aromatic polyamide-imide resin. Is strongly formed,
It has the characteristics that it does not cause particle separation or dust, and has high mechanical strength.

Further, the portion that comes into contact with the liquid metal is required to have low wettability and low chemical reactivity. As described in detail above, the carbon composite material according to the present invention uses (I) an isotropic graphite base material in which the bulk density and the pore radius are specially limited, whereby the polymer substance permeates and solidifies. Due to the anchor effect that occurs when doing, mechanical strength and peeling resistance are enhanced,
(B) In particular, by using a polyamide-imide resin, which is preferable as a polymer substance and having a good film-forming property, and the thickness of the amorphous carbon layer coated on the surface is limited to 5 to 10 μm, no cracking occurs, It is possible to form a hard amorphous carbon with a smooth surface, and for the first time, due to the combined effect (synergistic effect) of (a) and (b), a crucible for pulling a silicon single crystal, a crucible for melting a metal, a crucible for metal deposition and a boat. The material suitable as is completed.

[0050]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples.

[0051]

Examples 1 to 3 and

[Comparative Examples 1 to 3] Isotropic graphite (trade name: "IG-11" manufactured by Toyo Tanso Co., Ltd., anisotropic ratio 1.03, bulk density 1.77 g / c)
m ^3, the pore pore radius 1.7 [mu] m) the crucible (outer diameter 250m
m, inner diameter of 200 mm, height of 300 mm), and then 10-100 mer of N-methyl-2 polyamide-imide resin
A 30% solution of pyrrolidone was applied by a spray method and N ₂
Baked at 1000 ° C. As a result of cutting and observing the separately prepared sample, the thickness of the layer coated with amorphous carbon is about 1
It was about 0 μm.

Metal crucible (Example 1) 5 was added to the crucible.
When 0 kg was filled and melted by induction heating in a vacuum melting furnace, the graphite crucible life was as shown in Table 1 compared to the conventional graphite crucible life. Next, by changing the kind of metal, zinc (Example 2) and gold (Example 3) were also dissolved in the same manner as nickel. The results are also shown in Table 1.

Further, the crucible processed before applying the polyamide-imide resin in the above was also treated in the same manner. The results are also shown in Table 1.

[0054]

[Table 1]

As described above, it is understood that the life of the graphite crucible of the present invention is longer than that of the conventional crucible for any metal.

[0056]

Example 4 and

[Comparative Example 4] An isotropic graphite base material having a bulk density of 1.90 g / cm ³ manufactured by Toyo Tanso Co., Ltd. "VD-30 Anisotropic ratio 1.05, pore-pore radius 1.5 μm" A vacuum evaporation crucible (Comparative Example 4) was placed under reduced pressure (10 torr) for 1 hour, and then under pressure (7 kgf / cm ² ) for 1 hour, 10- to 100-mer N-methyl-2pyrrolidone of polyamideimide resin.
% Solution was impregnated and further heat-treated at 1000 ° C. under N ₂ atmosphere.

Using both crucibles, 1450 ° C. 10 ⁻⁴
Al was vapor-deposited under a vacuum of torr. The results are shown in Table 2.

[0058]

[Table 2]

As is apparent from Table 2 above, the crucible of the present invention is remarkably superior to the conventional one.

[0060]

Example 5 and

[Comparative Example 5] High-purity isotropic graphite (trade name: Toyo Tanso Co., Ltd.)
Ltd. "IG-710" bulk density 1.83 g / cm ^3, anisotropic ratio 1.0
2. Pore pore radius 1.8μm) crucible (outer diameter 445m
m, inner diameter 405 mm, height 300 mm), and then subjected to "pie coat treatment" and further purification treatment.

A quartz crucible filled with 35 kg of polysilicon was placed in these and the silicon single crystal was pulled up by the CZ method for 5 minutes. The graphite crucible life was as shown in Table 3 as compared with the life of the conventional graphite crucible. It was

[0062]

[Table 3]

As described above, the crucible life of the embodiment is about 1.5 times that of the conventional product. The "pie coat treatment" is the same as in Examples 1, 2 and 3.

[0064]

Examples 6 to 8 and Comparative Examples 6 to 8 Table 4 shows the characteristics of the base material before the "pie coat" process and the samples (boats for molten metal) obtained by the "pie coat" process. The result of having compared with a property is shown.

In the table, various carbon materials (all manufactured by Toyo Tanso Co., Ltd.) having different bulk densities (g / cm ³ ), average pore radii (μm) and anisotropic ratios are shown in metal melting boats ( Length 50, width 10,
35m long, 7 wide, 7m deep with a base material of 10m / m in height
(a boat-shaped member provided with a concave portion of m) was subjected to a "pie coat treatment" in the same manner as in Example 1, and then the sample was subjected to high-purity treatment under reduced pressure with a halogen-containing gas. Therefore, the amounts of impurities in Table 4 are those obtained by performing the high purification treatment after the pie coat treatment.

However, with respect to Example 8, no particular purification treatment was performed. More specifically, the bulk density is 1.7 to 1.9.
Substrates with g / cm ³ and average pore radii of 0.2 to 2.0 μm and anisotropic ratios of 1.05 or less were brought into contact with halogen-containing gas under reduced pressure to obtain a high-purity container. 99.99%
An aluminum piece (manufactured by Sumitomo Chemical Co., Ltd.) was placed in a quartz tube under reduced pressure at 1000 ° C. for 1 hour to be heated and melted.

[0067]

[Table 4]

This operation was repeated 5 times, but especially in Examples 6 and 7, there was no significant change in the container and no cracks occurred.

However, in the case of using the base material from which the high-purity treatment was omitted (Example 8), the total amount of inorganic impurities in the base material was 10 ppm, and the purity of the aluminum lump taken out by cooling was 99.96%. It was falling. However, there was no significant change in the container and no cracks occurred.

When a substrate having an anisotropic ratio of 1.18 was used (Comparative Example 6), the amorphous carbon layer was peeled off from the graphite substrate and the average pore radius was 2.6 μm. In the case of using the base material (Comparative Example 7), after the "pie coat treatment",
However, fine pores remained, and a slight amount of aluminum exudation was observed at the bottom of the container.

The bulk density is indirectly related to the average pore radius, but is also a physical property related to the total amount of pores in the carbonaceous material, which is one index showing the physical properties of the carbonaceous material. In the case of a container using a base material of 0.62 g / cm ³ (Comparative Example 8), due to the difference in the coefficient of thermal expansion between aluminum that has penetrated into the carbon material and the carbon material that constitutes the base material, melting and cooling Repeated three times, cracks occurred in the container.

[0072]

[Brief description of drawings]

[0073]

[Figure 1]

It is a graph showing the relationship between the cumulative pore volume of the graphite base material and the pore radius.

Claims (3)

[Claims] 1. A bulk density of 1.7 to 1.9 g / cm ³ , an average pore radius of 0.2 to 2.0 μm, an anisotropic ratio of 1.05 or less, and, if necessary, an inorganic impurity other than carbon. A container for molten metal, in which an amorphous carbon coating is formed on the surface of an isotropic graphite base material having a total sum of 5 ppm or less. 2. The container according to claim 1, wherein the amorphous carbon coating film is obtained from a polyamideimide resin. 3. The container according to claim 1, wherein the molten metal container is a crucible for pulling a silicon single crystal, a crucible for vapor deposition of at least one metal of gold, zinc, nickel, aluminum or silicon or an alloy thereof, or a boat. .