JPH0940434A - High purity quartz glass and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high purity quartz glass suppressible in impurities such as alkali metals and halogen elements and the concentration of contained OH groups at a low concentration. SOLUTION: This quartz glass is obtained by compacting noncrystalline silica powder and sintering it, and the content of each impurity of Na, K, Fe, Ti, Al, Ca, Li and halogen elements such as F and Cl is <=1ppm and also the concentration of the contained OH groups is <=5ppm. In this production method of the quartz glass produced by forming noncrystalline silica powder and sintering it, the powder having average particle diameter of 0.5-10μm and the content of each impurity of Na, K, Fe, Ti, Al, Ca and Li and halogen elements such as F and Cl of <=1ppm is used as the silica powder. The powder is compacted into an objective shape and in the process where the compact is sintered, the compact is subjected to dehydration process at the temp. range of 1100-1600 deg.C in such a state that the compact has opened pores, and then is melted and is vitrified to produce the objective quartz glass.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to quartz glass, and more particularly to high-purity quartz glass obtained by melting after sintering and a method for producing the same, and more specifically, it has a high purity of impurities such as alkali of 1 ppm or less. And the concentration of contained OH groups is 5
TECHNICAL FIELD The present invention relates to high-purity quartz glass which is less than or equal to ppm and is useful in the field of semiconductor manufacturing, glass substrates, and the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art As a conventional method for producing quartz glass,
A method of melting a natural raw material such as crystal powder or silica sand in an electric furnace or a method of melting with an oxyhydrogen flame is known. Opaque quartz glass is manufactured by a method in which a foaming agent such as calcium carbonate is added to the above natural raw material and melted. However, since natural products are used as raw materials,
Although the concentration of contained OH groups is low, it contains impurities such as alkali, and therefore, there is a problem when used in the field of semiconductor manufacturing. Although the above-mentioned purification treatment of the natural quartz powder has been carried out, it has not been achieved by this method until now that all impurities that affect the purification are suppressed to 1 ppm or less.

As a countermeasure for this, quartz glass by a VAD method for sintering a deposit of synthetic amorphous silica powder or a sol-gel method for sintering an amorphous silica powder obtained by hydrolysis of silicic acid alkoxide has been studied. Has been done.
However, when synthetic amorphous silica powder is used, high purification is possible, but the problem is that the content of OH groups is high and the heat resistance is inferior to that of quartz glass using natural quartz material. Not resolved. Further, a method of dehydrating with a dehydrating agent such as Cl or F has been considered, but there is a problem that the halogen element remains as an impurity.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has the same high purity as when the above-mentioned synthetic silica is used as a raw material, that is, an alkali metal, a halogen element, or the like. 1p each of the impurities
The purpose of the present invention is to provide a high-purity quartz glass which can be suppressed to pm or less and has an OH group concentration of 5 ppm or less without dehydration treatment with a dehydrating agent or the like.

[0005]

In order to solve such a problem, the inventor of the present invention has made extensive studies, and as a result, completed the present invention.

That is, the present invention provides a method for producing quartz glass by molding and sintering amorphous silica powder,
The silica powder has an average particle size of 0.5 to 10 μm, and contains Na, K, Fe, Ti, Al, Ca, Li and F,
A powder having an impurity content of halogen element such as Cl of 1 ppm or less is used, the powder is molded into a desired shape, and the molded body has open pores in the process of sintering 1100. The present invention relates to a method for producing high-purity quartz glass, which comprises performing dehydration treatment at a temperature rising rate within a temperature range of ˜1600 ° C. at 100 ° C./h or less, and then melting and vitrifying. Further, the quartz glass obtained in this manner has an impurity content of 1 pp of halogen elements such as Na, K, Fe, Ti, Al, Ca, Li, F, and Cl.
m or less and the content of OH group concentration is 5 ppm or less.

Further, the present invention will be described in detail.

The amorphous silica powder used in the present invention includes Na, K, Fe, Ti, Al, Ca, Li, F, and C.
If the content of each impurity of halogen element such as 1 is 1 ppm or less, the method for producing the powder is not particularly limited. For example,
Method using silicic acid from which sodium is removed from sodium silicate, method of thermally hydrolyzing silicon tetrachloride, method of firing silica obtained by hydrolyzing silicon alkoxide under hydrochloric acid or ammonia catalyst And purifying silica obtained by reacting an aqueous solution of an alkali metal silicic acid with an acid,
Amorphous silica powder is produced by a method such as firing.
By using such a raw material, the treatment for removing impurities can be omitted. Further, it is essential that the average particle diameter of the silica powder is within the range of 0.5 to 10 μm. The reason for defining the average particle size here is from the viewpoint of whether powder molding is possible, and powder molding is impossible with an average particle size outside this range. Incidentally, the average particle size referred to here is an average value of the size of the primary particles,
It is not intended for secondary particles produced by natural agglomeration or granulation operations. As a measuring method, for example, there is a method of dispersing the powder in a solvent by ultrasonic waves or the like and measuring the particle size from light scattering.

The molding method is not particularly limited, but it is necessary to select a method in which impurities are not mixed in the molding process. For example, a casting method can be used as one of the molding methods, but it is preferable to use a resin as the material of the mold. If plaster is used as the material of the mold, calcium will be mixed as an impurity. Further, in order to facilitate the molding, it is possible to add an auxiliary agent such as a binder, but it is necessary to select one having an impurity content of 1 ppm or less.

In sintering, the compact has open pores 11
The temperature rising rate within the temperature range of 00 to 1600 ° C is 150 ° C /
It is essential to sinter at h or less. The OH groups are desorbed by heating at a temperature of 1100 ° C. or higher when the pores of the molded body are open pores. Here, if the temperature is lower than 1100 ° C., the temperature is too low and the elimination of OH groups hardly occurs. When the temperature is higher than 1600 ° C, closed pores are formed and OH group elimination does not occur. Similarly, when the temperature rising rate is higher than 150 ° C./h, the closed pores are formed before the OH group is eliminated, and the elimination does not occur. However, before reaching 1600 ° C, O
When the elimination of the H group is completed, the temperature rising rate after that temperature may be higher than 150 ° C./h. Also, 11
It is also possible to maintain the temperature within the temperature range of 00 to 1600 ° C., and depending on the molded product, most of the OH groups may be eliminated by maintaining the temperature around 1300 to 1450 ° C. for several hours. In such a case, the temperature rising rate after that temperature may be higher than 150 ° C./h.

Here, when the molded product has open pores, it is in a vacuum atmosphere, and when it has closed pores, it becomes transparent glass when gas is introduced. Further, when the atmosphere of the molded product is in the state of open pores and the atmosphere is nitrogen gas or argon gas atmosphere, it becomes opaque glass. The temperature at which the closed pores are formed depends on the particle size,
It is related to the density of the molded body, the heating rate, etc. For example, if the particle size is small or the density of the molded body is high, closed pores are formed at a low temperature.

Before the glass is melted, an amorphous substance may be crystallized into a crystalline substance. This has an effect on the glass whether it is an amorphous substance or a crystalline substance. Do not give.

175 of these amorphous or crystalline materials
Vitrification is performed at a temperature of 0 ° C. or higher, preferably 1770 to 1850 ° C. For complete melting, it is preferable to hold at the above temperature for a predetermined time, but the holding temperature differs depending on the temperature and the shape of the molded body, and if it is a temperature that melts instantly, it is not necessary to hold at that temperature. .

[0014]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Example 1 500 g of amorphous silica powder having the purity shown in Table 1 and having an average particle size of 1 μm was dispersed in 500 g of pure water to obtain a slurry. After sufficiently defoaming this slurry, the slurry is poured into a porous casting mold made of epoxy resin having a space of φ150 mm × 10 mm so as not to entrap bubbles. Here, if defoaming is insufficient, large bubbles will be formed in the glass. The formed body is thoroughly dried and then placed in an electric furnace for 1 hour.
The temperature was raised in the temperature range of 100 to 1600 ° C. at a heating rate of 60 ° C./h. In order to make the glass of the present example transparent glass, a vacuum atmosphere (2 × 10 ⁻³ torr) was used up to 1600 ° C.
Then, the mixture was sintered in r), and then nitrogen gas was introduced to a pressure of 1.2 kg / cm ² and heated at 1800 ° C. for 15 minutes to melt. Here, the temperature was raised up to 1100 ° C. and 300 ° C./h in the temperature range of 1600 ° C. or higher. Carbon was used as the firing setter.

[0016]

[Table 1]

The obtained glass had the purities shown in Table 2 and the concentration of contained OH groups was 2 ppm. Further, there were no bubbles of 50 μm or more in the glass, and there were very few bubbles smaller than 50 μm, and it was possible to obtain a glass having high transparency.

[0018]

[Table 2]

The impurities were analyzed by ICP emission spectroscopy and ICP gravimetric analysis. Contained OH group concentration is FT
-Using an IR device, the wavelength of the IR transmitted light of the sample is 37
It was quantified by the OH group absorption spectrum of 00 Kaiser.

Example 2 Amorphous silica powder having a purity shown in Table 1 and having an average particle size of 5 μm was used at a pressure of 500 k using a φ70 mm metal press die.
It was molded at a pressure of g / cm ² . The obtained molded body has a temperature range of 1100-1600 ° C. in the electric furnace of 100 ° C. /
The temperature was raised at a heating rate of h. The glass of this example was sintered in a nitrogen atmosphere to make it opaque, and the temperature was 1800 ° C.
It was heated for 15 minutes to melt. Here, the temperature was raised to 1100 ° C. at 300 ° C./h above 1600 ° C. Carbon was used as the firing setter. The obtained glass is
It had the purity shown in Table 2 and contained OH group concentration of 3 ppm. Further, the glass was opaque glass having closed cells with an average diameter of 20 to 40 μm.

Comparative Example 1 Using the same starting materials as in Example 1, a molded body was prepared in the same manner. The formed body is 1100-1 in the electric furnace.
Within the temperature range of 600 ° C., the temperature was raised at a heating rate of 600 ° C./h. Other than that, glass was prepared under the same atmosphere and melting conditions. The obtained glass had the same purity and transparency as those of Example 1, but had a contained OH group concentration of 68 pp.
m.

Comparative Example 2 Using the same starting materials as in Example 1, a molded body was prepared in the same manner. The formed body was heated in an electric furnace in a vacuum atmosphere up to 1000 ° C at 300 ° C / h, and the temperature was raised to 3 ° C.
After holding for 1 hour, the temperature was raised to 1650 ° C. at 300 ° C./h and kept at that temperature for another 3 hours. After that, 1.2 kg
Nitrogen gas is introduced up to a pressure of / cm ^{2 and} the temperature is 15 ° C. at 1800 ° C.
It was heated and melted for a minute.

The obtained glass had the same purity as in Example 1,
Although it had transparency, the contained OH group concentration was 20 ppm.

[0024]

As described in detail above, if the production method of the present invention is used, the content of O is eliminated even if the dehydration treatment is not performed with a dehydrating agent or the like.
High-purity quartz glass having an H group concentration of 5 ppm or less can be constantly produced, and the production is inexpensive. Further, the quartz glass obtained by the method of the present invention is a quartz glass having high purity and excellent high temperature viscous properties, and in the transparent glass, there are no bubbles of 50 μm or more,
The number of bubbles smaller than m is also very small, and the opaque glass is a glass in which closed cells having an average diameter of 20 to 40 μm are uniformly distributed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Tsukuma 1-18-7 Fujisaki, Tsuchiura City, Ibaraki Prefecture (72) Inventor Masayuki Kudo 447-22 Tsukisato, Edozaki-cho, Inashiki-gun, Ibaraki Prefecture (72) Inventor Sudo 2-7 Tokamachi, Yamagata City, Yamagata Prefecture 4-7 (72) Inventor Yoshikazu Kikuchi 43-7 Tsuruta, Sagae City, Sagae City, Yamagata Prefecture

Claims (3)

[Claims] 1. A quartz glass obtained by molding and sintering amorphous silica powder, which comprises Na, K, Fe, Ti and A.
The content of each impurity of halogen elements such as 1, Ca, Li, F, and Cl is 1 ppm or less, and the concentration of contained OH group is 5 p.
High-purity quartz glass of pm or less. 2. A method for producing a quartz glass by molding an amorphous silica powder and sintering the silica powder, wherein the silica powder has an average particle size of 0.5 to 10 μm, and Na, K, F.
e, Ti, Al, Ca, Li, F, Cl, etc., each of which has a content of impurities of 1 ppm or less of a halogen element is used, and the powder is molded into a desired shape, and then the molded body is sintered. 1100-1 which is a state in which the molded body has open pores
The method for producing high-purity quartz glass according to claim 1, which comprises performing dehydration treatment within a temperature range of 600 ° C. and then melting and vitrifying. 3. In the dehydration treatment within the temperature range of 1100 to 1600 ° C. according to claim 2, the heating rate is 150 ° C. /
The method for producing the high-purity quartz glass according to claim 2, wherein the h is equal to or less than h.