JPH05345620A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To produce a quartz glass material, e.g. a large-sized tool material for a semiconductor process in high purity for a short time. CONSTITUTION:Crystalline or amorphous silica having >=1 to <=500mum average grain diameter is mixed with 'a mixture composed of a silicic acid ester, water regulated to pH<=3 and a water-soluble organic solvent having >=120 deg.C boiling point' in 300-100 pts.wt. total amount thereof and the resultant mixture is gelatinized in a mold, released from the mold and then thermally sintered at 1400-1850 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing silica glass used in, for example, a semiconductor process.

[0002]

2. Description of the Related Art Generally, a quartz glass tool material used in a semiconductor process or the like is manufactured as follows.

(1) A material having a simple shape such as a pipe or a plate is made.

(2) A material is welded or machined to obtain a target shape.

However, in a tool material having a relatively simple shape,
A direct molding method has also been put into practical use. For example, a single crystal pulling crucible is directly processed into a crucible by arc melting raw material powder.

In recent years, the sol-gel method has attracted attention and has been developed as a method for producing quartz glass by direct molding. In the sol-gel method, the drying process and the firing process are very difficult. These steps have the disadvantages of being time-consuming and having a poor yield. Various improvements have been proposed to eliminate such drawbacks.

[0007]

In the general manufacturing method described above, it takes a long time for processing, requires skill, and is wasteful in terms of materials.

Further, in the production by the above-mentioned direct molding method, there is a problem that a large amount of impurities are likely to be mixed.

Further, in the sol-gel method described above, a simple shape is mainly used, and it is difficult to apply it to a large-sized and complicated-shaped tool material.

The present invention provides a method for producing quartz glass, which is capable of producing highly purified and complicated materials such as large-scale semiconductor process tool materials in a short time with a high material yield and a high purity. The purpose is to

[0011]

The present invention has an average particle size of 1 μm.
m or more and 500 μm or less of crystalline or amorphous silica is mixed with a first mixture consisting of a silicate ester, water adjusted to pH 3 or less, and an organic solvent soluble in water and having a boiling point of 120 ° C. or more to form a second mixture. The gist is a method for producing quartz glass, which is characterized in that the second mixture is gelled in a mold, released from the mold, and then heated.

EXAMPLES In the method for producing quartz glass of the present invention, crystalline or amorphous silica having an average particle size of 1 μm or more and 500 μm or less, preferably 10 μm or more and 100 μm or less is used as a starting material.

If the average particle size is less than 1 μm, the pore size of the molded product will be small, and bubbles will be less likely to escape during calcination, which is unsuitable. On the other hand, if the average particle size is larger than 500 μm, the average pore size becomes large and it becomes difficult to pour the slurry into the mold.

As a binder, first, a silicate ester, pH 3
A first mixture composed of water and an organic solvent having a boiling point of 120 ° C. or higher, which is soluble in water, is prepared to prepare a silica powder 100.
A total of 30 to 100 parts by weight of the first mixture is mixed with parts by weight to form a second mixture, which is made into a slurry. This second mixture is also called a mixed dispersion medium or dispersion medium.

Further, since the silicate ester and water are not directly mixed (becomes a homogeneous solution after hydrolysis), a solvent for mixing them, for example, alcohol may be added appropriately.

The amount of the second mixture (mixing dispersion medium) added to 100 parts by weight of the above-mentioned silica powder is preferably 30 to 100 parts by weight. When the amount of the second mixture (mixing dispersion medium) is less than 30 parts by weight, mixing becomes difficult, and when it exceeds 100 parts by weight, the density of the molded body tends to be low.

The silicate ester is not particularly limited, but easily available ones such as ethyl silicate and methyl silicate are preferable. The addition amount of the silicate ester depends on the particle size of the silica particles, and when using fine particles, it is better to increase the addition amount.

Water is added to adjust the pH to 3 or less with an acid in order to hydrolyze the silicate ester. The acid at this time is also not particularly limited, but acids such as hydrochloric acid, nitric acid, and acetic acid that volatilize during heating and do not easily remain are preferable.

The amount of water added is preferably not less than 30 times the hydrolysis equivalent of the silicate ester (not more than the hydrolysis equivalent). If the amount of water is less than the hydrolysis equivalent of silicate ester, the hydrolysis does not proceed sufficiently, and if it is more than 30 times, gelation becomes slow,
In addition, the strength of the gel decreases, making it difficult to handle.

The organic solvent is soluble in water and is present in the molded body even after evaporation of water or the hydrolysis product of ethyl silicate, alcohol, so that liquid evaporation during temperature rise can be prevented. It has a role of preventing accompanying cracks. Since the boiling point of the alcohol produced from commonly available silicate ester is lower than the boiling point of water, the boiling point of the organic solvent used may be higher than 100 ° C. (1 atm), but the boiling point of water is preferably low. An organic solvent having a boiling point of 120 ° C. or higher is suitable. You may use 2 or more types of organic solvents.

Although an example in which everything is mixed at the time of hydrolysis has been described, it is sufficient to mix everything before the hydrolyzed silicate ester gels, and the mixing procedure is not particularly limited.

Further, the gelation time can be shortened by adjusting the pH of the slurry after hydrolysis to 3.5 to 5.5. When the pH of the slurry is less than 3.5, the gelation time is long and not practical. PH of slurry
The higher the, the faster the gel time. At pH = 3.5 (20 ° C.), it is about 30 hours (h), which is a practical range, although it depends on the composition. On the other hand, when the pH is higher than 5.5, the gelation time becomes very short,
Work becomes difficult.

The base aqueous solution used for adjusting the pH is preferably a base that volatilizes during heating and does not easily remain, an organic base such as ammonia is suitable, and NaOH, KOH and the like are not suitable.

The thus-prepared slurry is poured into a mold and allowed to stand in a sealed state to gel in the mold. The gelation time depends on the pH of the slurry.

Since the gel shrinks with time, it is preferable to release it after gelling. It is preferable to release only the mold parts that are at least in the contraction direction.

Further, the strength of the gel immediately after gelation is weak, and therefore, in order to exert the strength, at least 3 gels are required in the closed state.
It is preferable to stand or hold for a time. However,
There is no problem in exposing to the release atmosphere in a short time at the time of releasing the mold, but this time is preferably as short as possible. Further, by increasing the temperature at this time, the strength development time can be shortened. At this time, it is preferable to prevent volatilization from the molded body, and it is preferable to place it in a pressure resistant container that can withstand the vapor pressure at that temperature.

In the state of the molded body, it is possible to easily perform processing such as drilling and diameter matching by using a cutting tool made of quartz glass.
More preferably, two or more parts can be combined into one molded body.

The compact thus obtained by combining a plurality of parts is heat-sintered to form a quartz glass product. At this time, the drying step of the molded body is not particularly required, and the molding step is sent to the heating step. This is a significant difference from the usual sol-gel method, which requires a long drying time.

The heating temperature varies depending on the particle size of the silica powder, but a transparent body can be obtained at 1400 ° C to 1850 ° C.
Although it depends on the particle size, a porous body can be obtained by keeping the heating temperature lower than the temperature at which a transparent body is obtained.

The heating rate is relatively low up to the boiling point of the organic solvent mixed during slurry preparation, that is, 200 ° C. /
h or less, preferably 100 ° C./h is suitable, and thereafter, 1000 ° C./h or less, preferably 600 ° C./h or less is suitable. When the temperature is raised at a rate higher than 1000 ° C./h, the molded body is cracked due to the rapid volatilization of the solvent, and the fired body is swollen due to the rapid closed pores, which is not suitable.

Also, the above-mentioned clearing temperature of 1400 ° C.
˜1850 ° C., but depending on the particle size, calcination is performed at 1200 ° C. to 1600 ° C., then
A method of heating to a clearing temperature of 1400 ° C to 1850 ° C can also be used.

In calcination, deformation can be prevented and high purity can be maintained by using coarse crystalline silica powder as a filling powder.

Further, even in this calcination state, the processing such as drilling and diameter matching can be easily performed by the cutting tool made of quartz glass. Furthermore, two or more parts can be combined into one calcined body. Further, after calcination, it is possible to combine two or more molded bodies into one molded body and then heat and sinter.

Further, in the main firing after the calcination, a low OH quartz glass product can be obtained by reducing the pressure of the atmosphere. By performing the firing treatment in a Cl ₂ -containing atmosphere, it is possible to obtain a quartz glass product containing very few metal impurities.

Hereinafter, preferred examples and comparative examples of the present invention will be described.

Example 1 25 parts by weight of ethyl silicate, 20 parts by weight of 0.01N hydrochloric acid and 5 parts by weight of ethylene glycol were added to 100 parts by weight of quartz powder having an average particle size of 30 μm, and the mixture was stirred for 1 hour to form a slurry.

On the other hand, the mold shown in FIG. 1 was used. This type is
It consists of an outer mold 1 and inner molds 2, 3. The above-mentioned slurry was poured into the gap 4 of the mold having this shape, sealed and held.

The slurry gelled after 5 days, so the molded body was released from the mold, sealed and held for 10 hours.

Then, it was placed in an electric furnace and heated up to 400 ° C. at a heating rate of 100 ° C./h, thereafter heated at a heating rate of 600 ° C./h and heated at 1850 ° C. for 30 minutes. .. Then, transparent quartz glass was obtained.

Example 2 Under the same conditions as in Example 1, trial production was carried out while changing the raw material particle size. The results are shown in Table 1. The yield indicated the ratio of the number of non-defective products among 20 products. Table 1 shows the effect of raw material particle size.

As is clear from Table 1, in the examples of the present invention, the yield was good in both the molding step and the firing step. However, in the comparative example having an average particle size of more than 500 μm, the moldability was poor and the yield of the molding process was 0%, which was not suitable. Further, in Comparative Examples smaller than 1 μm, bubbles were generated or cracks were generated during firing, and the yield in the firing process was low or 0%, which was not suitable.

[0042]

[Table 1] Example 3 Under the same conditions as in Example 1, only an organic solvent to be added was changed and a trial production was performed. The results are shown in Table 2. Yield is 20
The number of non-defective products in each product is shown. Table 2 shows the effect of the added organic solvent.

As shown in Table 2, in all the examples of the present invention, the firing yield was good, but the comparative examples of 1-propanol in which the boiling point of the organic solvent was 120 ° C. or less, and 1-propanol
In the comparative example of butanol, cracking occurred during firing, the firing yield was poor, and it was not suitable.

[0044]

[Table 2] Example 4 Under the same conditions as in Example 1, the amount of the dispersion medium to be added to the quartz powder was changed and trial production was performed. The results are shown in Table 3. The composition ratio of the dispersion medium to be added is 25: 2 by weight ratio of ethyl silicate: 0.01N hydrochloric acid: ethylene glycol.
It was set to 0: 5. The yield indicated the ratio of the number of non-defective products among 20 products. Table 3 shows the effect of the ratio of the dispersion medium added.

With such a composition ratio, silica 10
When the dispersion medium is 30 to 100 parts by weight with respect to 0 parts by weight, molding is difficult when the dispersion medium is lower than 30 parts by weight, and the molding yield is 0%. On the other hand, when the amount was more than 100 parts by weight, the powder ratio was low, the molded body was difficult to handle, cracking occurred during firing, and the firing yield was 0%, so that a good product could not be obtained.

[0046]

[Table 3] Example 5 Under the same conditions as in Example 1, trial production was carried out by changing the time period for keeping the molded body in a sealed state after releasing from the mold. The results are shown in Table 4. The yield indicated the ratio of the number of non-defective products among 20 products. Table 4
Indicates the effect of holding time after gelling (at 25 ° C.).

Under these conditions, the holding time is preferably 3 hours or longer, and when the holding time is shorter than 3 hours, cracks are likely to occur during firing and the firing yield is poor.

[0048]

[Table 4] Here, the holding time is the time obtained by subtracting the gelling time from the time when the molded body is exposed to the release atmosphere. The gelation time is the time when the slurry stopped flowing even when tilted.
The holding time in Example 1 is 5 hours (h).

Example 6 25 parts by weight of ethyl silicate, 20 parts by weight of 0.01N hydrochloric acid and 5 parts by weight of ethylene glycol were added to 100 parts by weight of silica glass powder having an average particle size of 30 μm, and the mixture was stirred for 1 hour to form a slurry.

On the other hand, using a mold having a shape as shown in FIG. 1, the slurry was poured into the gap 4, sealed, and held.

The gel was gelated after 5 days, so the molded product was released from the mold, sealed and held for 10 hours.

Then, the molded body is put in an electric furnace and heated to 400 ° C.
Then, the temperature was raised at a temperature rising rate of 100 ° C./h, and thereafter, the temperature was raised at a temperature rising rate of 600 ° C./h and heated at 1850 ° C. for 30 minutes to obtain transparent quartz glass.

[0053]Example 7  A molded body was produced in the same manner as in Example 6. This molded body
A through hole having a diameter of 25 mm was drilled from the side surface of the. This
An outer diameter of 25 mm and an inner diameter of 20 m manufactured by the same method.
A tubular molded body of m and 200 mm in length was fitted.

Then, the molded body is put in an electric furnace and the
The temperature was raised to 0 ° C. at a temperature rising rate of 100 ° C./h, and thereafter, the temperature was raised at a temperature rising rate of 600 ° C./h and heated at 1850 ° C. for 30 minutes. Then, transparent quartz glass was obtained.

Example 8 A calcined body was prepared in the same manner as in Example 6. The side surface of this calcined body was penetrated with a drill to form a through hole having a diameter of 25 mm. An outer diameter of 25 mm and an inner diameter of 2 manufactured by the same method
A tubular calcined body having a length of 0 mm and a length of 200 mm was fitted.

After that, the molded body is put in an electric furnace, and
Heated at 50 ° C. for 30 minutes. Then, transparent quartz glass was obtained.

Example 9 To 100 parts by weight of quartz powder having an average particle size of 30 μm, 25 parts by weight of ethyl silicate, 20 parts by weight of 0.01N hydrochloric acid and 5 parts by weight of ethylene glycol were added and stirred for 1 hour. Then 1
% Ammonia water was added to adjust the pH to 4.2 to make a slurry.

On the other hand, using a mold having a shape as shown in FIG. 1, the slurry was poured into the gap 4, sealed, and held.

The gel was gelated after 5 hours, so the molded product was released from the mold, sealed and held for 10 hours.

Then, the molded body is put into an electric furnace and heated to 400 ° C.
Up to 100 ° C / h and then 600
The temperature was raised at .degree. C./h and heated at 1850.degree. C. for 30 minutes. Then, transparent quartz glass was obtained.

Example 10 A molded body was produced in the same manner as in Example 7.

The molded body is placed in an electric furnace and the temperature is set to 1400 in the atmosphere.
It was calcined at 4 ° C. for 4 hours (heating time 4 hours). The calcined body is placed in a vacuum firing furnace and is placed in an atmosphere of N ₂ 0.5 torr for 18
Heated at 50 ° C. for 30 minutes. Then, transparent quartz glass was obtained.

Example 11 A molded body was produced in the same manner as in Example 7.

The molded body is placed in an electric furnace and the temperature is set to 1400 in the atmosphere.
Calcination was performed for 4 hours (temperature rising time 4 hours). The calcined body is put in a vacuum furnace and kept at 1400 ° C. for 1 hour with 5% Cl ₂ /95% He.
After performing the treatment of, in an atmosphere of N ₂ 0.5 torr,
Heated at 1850 ° C. for 30 minutes. Then, transparent quartz glass was obtained.

The present invention is not limited to the above embodiment.

[0066]

According to the method of the present invention, quartz glass such as a large-scale semiconductor process tool material can be manufactured with high purity in a very short time. Therefore, the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a mold for molding a slurry used in manufacturing the quartz glass of the present invention.

[Explanation of symbols]

 1 Outer mold 2 Inner mold 3 Inner mold 4 Gap ◆

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Takahashi No. 30 Soya, Hadano City, Kanagawa Prefecture Toshiba Ceramics Co., Ltd.

Claims (1)

[Claims] 1. A first mixture comprising crystalline or amorphous silica having an average particle size of 1 μm or more and 500 μm or less, silicate ester, water adjusted to pH 3 or less, and an organic solvent soluble in water and having a boiling point of 120 ° C. or more. To form a second mixture, which is then gelled in the mold and demolded,
A method for producing quartz glass, which comprises heating.