JP2617147B2 - Method for producing high-density high-purity glassy carbon material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a glassy carbon material having high density and high purity.

[0002]

2. Description of the Related Art A glassy carbon material is a heterogeneous carbon material having a vitreous structure, and is widely used in various fields in various fields by utilizing its properties. Particularly recently, it has been revealed that the homogeneous and dense non-polluting material structure is suitable as an electrode for plasma etching of silicon wafers or a member for ion implantation equipment, and these semiconductors have already entered the practical stage. Very high material purity is required for glassy carbon members used in the field.

[0003] Usually, a glassy carbon material is produced by a method in which an initial condensate of a phenol resin or a furfuryl alcohol resin is used as a raw material, a curing agent is added to the raw material, and the mixture is molded and cured, and then calcined and carbonized. At this stage of production, impurities may be mixed in from the raw material resin, the curing agent, the atmospheric gas during calcining and the like, and the purity of the product may be reduced.

[0004] However, it is extremely difficult to purify the impurities mixed into the glassy carbon structure due to the above-mentioned reasons in post-treatment. In other words, as an effective means for purifying general carbon materials, a method of deashing with a halogen-based gas in a high temperature range of 2000 ° C. or higher is known, but glassy carbon materials are different from general carbon materials. On the contrary, since it has a very dense closed tissue, the dispersion of the demineralized gas into the tissue is hindered, and the diffusion and removal of impurities do not proceed smoothly. In addition, it is almost impossible to remove the sulfur component from the commonly used p-toluenesulfonic acid hardener by this type of demineralization treatment.

[0005] In order to cope with such a situation, the present inventors use a phenol resin having a molecular weight of 100 or more, a viscosity of 1 to 100 poise, a gel time of 5 to 60 minutes and an ash content of less than 5 ppm as a raw material, A method for producing a high-purity glassy carbon material, which is formed without addition and heat-cured and then calcined in a high-purity non-oxidizing gas atmosphere, has been developed, and has already been proposed as Japanese Patent Application No. 3-39111.

[0006]

According to the above method,
The process uses a high-purity phenol resin of specific properties that can be smoothly cured by heating without the addition of a curing agent, and calcinates and carbonizes it in a high-purity environment. Has purity. But,
There are still issues to be improved, such as the presence of a lot with a low texture density in the product or the production of cracks in the material structure when manufacturing a plate with a thickness of 2 mm or more, reducing the product yield. I was

According to the present invention, as a result of repeated studies and researches on the properties of the raw material phenolic resin and the mechanism of conversion to the glassy carbon structure, a range of properties of the raw material resin suitable for solving the above problems was found. It has been developed.
Accordingly, an object of the present invention is to provide a production method for stably obtaining a high-density, high-purity glassy carbon material with good product yield even if the thickness is 2 mm or more.

[0008]

In order to achieve the above object, a method for producing a high-density and high-purity glassy carbon material according to the present invention comprises a nonvolatile matter of 50 to 80% and an average molecular weight of 100 to 140.
A liquid phenol resin having a viscosity of 1 to 20 poise, a gel time of 15 to 45 minutes, and an ash content of less than 5 ppm is used as a raw material,
It is characterized in that after heating and hardening, it is subjected to a calcination treatment in a high-purity non-oxidizing gas atmosphere.

The numerical values of the property characteristics in the above constitution are as follows: the molecular weight is based on the freezing point depression method using a dioxane solvent, and the nonvolatile content, the viscosity and the gelation time are based on JIS K6909-1977.
"Liquid phenolic resin test method", ash content is JIS
M8812-1976 These are the values measured by the "ash content determination method".

[0010] Among the raw material characteristics specified in the present invention, the range of 50 to 80% of non-volatile content is a necessary condition for increasing the density of the obtained glassy carbon structure, and if this content is less than 50%. Non-volatile components are more likely to remain inside, causing pores. If it exceeds 80%, gelation time will be faster than 15 minutes, and pores will also occur, all of which will reduce the density of the tissue. Becomes

The use of a phenolic resin having an average molecular weight of 100 to 140 is a requirement for obtaining a glassy carbon material having a high density and a high tissue strength. If the average molecular weight is less than 100, the crosslinked structure after curing becomes weak. It does not convert to high-strength carbides. If it exceeds 140, the viscosity increases to more than 20 poise and the number of pores increases.

The viscosity is set in the range of 1 to 20 poise,
If it is less than 1 poise, the strength of the structure after carbonization is reduced. If it exceeds 20 poise, it is difficult to remove bubbles before curing, and pores occur frequently. In addition, the use of a property resin having a gelation time in the range of 15 to 45 minutes is such that, for a phenol resin of less than 15 minutes, gelation proceeds during the defoaming treatment and pores remain, and on the other hand, over 45 minutes During the gelation time, wrinkles occur in the tissue during curing.

The use of a phenol resin having an ash content of less than 5 ppm is an important requirement for producing a high-purity glassy carbon material. So that high purity characteristics cannot be imparted.

The thermosetting liquid phenol resin raw material used in the present invention is produced by a method in which a highly pure phenol and formalin are subjected to a condensation reaction in a clean container in the presence of an alkali catalyst. At this time, both phenol and formalin have an ash content of less than 5 ppm, and use ammonia as an alkaline catalyst which evaporates and disappears during calcining and carbonization.
Urea base materials such as methylamine and diphenylamine are applied, and the molar ratio of formalin to phenol (F
/ P) 1.0-1.5, pH 4-6, temperature 75-98 ° C, time 1-5
By adjusting the reaction conditions to time, a phenol resin having the above-mentioned properties can be synthesized.

The phenolic resin raw material is molded and heat-cured without adding any curing agent. In this case, since the raw material is in a liquid state, molding is performed by a cast molding method or a multiple molding (overcoating) method. However, in order to form into a shape such as a crucible or a pipe using a molding method or an extrusion molding method, a powdery phenol resin having an ash content of less than 5 ppm is blended with the above-mentioned liquid phenol resin as a raw material. Subjecting the kneaded material to a molding step is an effective process. In this case, as the powdery phenol resin to be blended in this case, one obtained by hardening and pulverizing the above-mentioned liquid phenol resin is suitably used. The curing process is performed in a temperature range of 150 to 250 ° C.

The cured molded body is then transferred to a heating furnace maintained in a high-purity non-oxidizing gas atmosphere and calcined in a temperature range of 800 ° C. or more. As the non-oxidizing gas blown into the heating furnace, hydrogen having at least an impurity content of less than 10 ppm,
Argon, nitrogen and the like are used. The material after calcining may be used in a non-oxidizing gas atmosphere
Graphitization treatment is performed at a temperature of 00 ° C. or higher. The calcined carbonization and / or graphitization may be carried out at normal pressure, but when carried out under reduced pressure, the evaporation of impurities is promoted, so that a better purification result is brought. In addition, in order to remove impurities based on external contamination, a demineralization treatment using a halogen-based gas can be performed as a post-treatment. Through these steps, a high-density and high-purity glassy carbon material is manufactured.

[0017]

According to the present invention, a thermosetting phenolic resin liquid having the property characteristics of converting into a high-purity and high-density vitreous carbonized structure is selectively used as a raw material, and a hardening agent serving as an impurity mixing source is not added. The calcined carbonization is performed in a non-polluting heating environment. This material selection and non-contamination process effectively reduce the occurrence of low-density tissue lots and the inclusion of impurities, so that even for thick products with a thickness of 2 mm or more, product yield is always high and high-density and high-purity It is possible to produce a glassy carbon material having the following.

[0018]

Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1 to 5, Comparative Examples 1 to 5 Phenol, formalin and ammonia having an impurity content of 1 ppm or less were placed in a three-necked flask, and subjected to addition condensation reaction and dehydration concentration under different conditions. A phenol resin precondensate (liquid resin) having the properties shown was prepared.

[0020]

[Table 1]

Each phenolic resin liquid shown in Table 1 is used as a raw material, poured into a quartz vat (100 mm long, 50 mm high), placed in a vacuum desiccator, and evacuated at 10 torr for 1 hour to remove air bubbles remaining in the resin liquid. Removed. Then, it was transferred to an electric drier in an atmosphere from which dust was completely removed, and heat-cured at 180 ° C. for 1 hour to obtain a molded plate having a length and width of 90 mm and a thickness of about 5 mm. This molded plate was sandwiched between high-purity graphite plates (G347SS, manufactured by Tokai Carbon Co., Ltd.) having impurities of less than 5 ppm, and similarly high-purity graphite heaters (G151ASS, manufactured by Tokai Carbon Co., Ltd.)
Is set in a packingless heating furnace (TP150, manufactured by Tokai High Heat Industry Co., Ltd.), and the atmosphere in the furnace is adjusted to 10 impurities.
10 ° C / hr while maintaining with high purity argon gas of less than ppm
At a heating rate of 2000 ° C. to perform a carbonization treatment to produce a plate-like glassy carbon material having a length and width of 70 mm and a thickness of about 4 mm. The product yield, physical properties, purity properties and the like of each of the glassy carbon materials thus manufactured were measured, and the results are shown in Table 2.

[0022]

[Table 2]

From the results shown in Table 1, it can be seen that Examples 1 to 5 have a wall thickness of 2 mm or more, a high yield of 80% or more in product yield, a bulk density of 1.51 or more, and an ash and sulfur content of 10 pp.
It is understood that a high-density and high-purity glassy carbon material of less than m 2 can be obtained. On the other hand, it is recognized that in each of the comparative examples that do not satisfy the raw material characteristic requirements of the present invention, the product yield is extremely reduced, and the density and purity are also inferior.

[0024]

As described above, according to the present invention, a liquid phenol resin having specific properties is used as a raw material and subjected to molding, hardening, and calcining in a non-contaminating heat treatment step, thereby achieving high density and high purity. It is possible to produce a glassy carbon material having a good product yield. Therefore, it is extremely useful as a manufacturing technique of a member for a semiconductor field requiring high purity and high material properties.

Claims (1)

(57) [Claims] 1. A non-volatile content of 50 to 80% and an average molecular weight of 100 to 14.
0, viscosity 1-20 poise, gel time 15-45 minutes, ash content less than 5 ppm
A method for producing a high-density and high-purity glassy carbon material, comprising heating and curing and then performing a calcination treatment in a high-purity non-oxidizing gas atmosphere.