JP3040310B2 - Manufacturing method of synthetic quartz glass - Google Patents

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 synthetic quartz glass, and more particularly to a method for producing synthetic quartz glass in which ammonia and alcohol are recovered and reused in a method for producing synthetic quartz glass by a sol-gel method. is there.

[0002]

2. Description of the Related Art In recent years, semiconductor materials, particularly crucibles for pulling silicon single crystals, heat-resistant semiconductor jigs, etc., are required to have high purity and high heat resistance at high temperatures. The use of synthetic quartz glass powder instead of natural quartz glass powder is being studied, and the use of this synthetic quartz glass powder as a high-purity filler for resin compositions for semiconductor encapsulation is also being considered. If the agent contains a small amount of uranium, thorium or the like, a soft error is caused by the α-ray emitted from the agent, so that it is required that the content of uranium and thorium be extremely small.

The method for producing the synthetic quartz glass is as follows: 1) Flame hydrolysis of silicon tetrachloride or the like in an oxyhydrogen flame to form silica fine particles, which are deposited on a heat-resistant carrier and melted at the same time as synthetic quartz. A method of forming a glass, or 2) forming a porous glass base material from the silica fine particles,
A method of fusing it to form a synthetic quartz glass, 3) a method of using a plasma flame in place of the oxyhydrogen flame, and the like are known. 4) Alkoxysilane is dissolved in an alcohol solvent in the presence of an acidic catalyst. A so-called sol-gel method is also known, in which a silica sol is synthesized by hydrolysis, dried into a gel, dried, calcined, and sintered to obtain a synthetic quartz glass.

[0004]

However, this 1),
Synthetic quartz glass produced by the method 2) has disadvantages of low viscosity at high temperature and foaming at high temperature in a vacuum because a few hundred ppm of hydroxyl groups (OH groups) remain in the glass. The method 3) has disadvantages of high cost and difficulty in mass production, and the sol-gel method 4) can relatively easily obtain a high-purity product.
The groups tend to remain, and it takes a long time to obtain the final glass product, and it is difficult to obtain a high-temperature viscous material.The carbon content generated by the decomposition of the alkyl group in the alkoxysilane is contained in the glass. When this is used as a crucible for pulling a silicon single crystal and a jig for diffusion, there is a disadvantage that many bubbles and black spot impurities are generated.

Therefore, the present inventors have conducted research on a method for producing synthetic quartz glass having a high viscosity at a high temperature by a sol-gel method, in which tetramethoxysilane (TMOS) is added to an aqueous solution containing 20 to 5% by weight of ammonia. It is hydrolyzed below to synthesize primary silica fine particles, calcined, sintered,
A method of melting after pulverization has been proposed (JP-A-2-80329)
No., Japanese Patent Publication No. 5-67575, JP-A-3-5329)
According to these, since residual OH groups and Cl groups can be removed, they can be used for a crucible for pulling a silicon single crystal, a heat-resistant semiconductor jig, and the like. It has been confirmed that it can be applied,
Since this tetramethoxysilane is generally synthesized by the reaction of chlorosilane and alcohol, it contains a small amount of chlorine.Therefore, a small amount of chlorine is contained in the silica gel at the time of hydrolysis, and this causes foaming of the glass or hydrolysis. There is a problem that the alcohol-water-ammonia solution after decomposition is discarded.

As for the method for producing synthetic quartz glass by the sol-gel method, it has been proposed that heated alcohol is brought into contact with the gel to recover the alcohol contained in the gel (Japanese Patent Publication No. Hei 6 (1994)). -643), but
Since this method uses acetic acid as a catalyst and does not use ammonia, it does not describe a method of using the recovered alcohol, but a method of recovering an alcohol-water-ammonia solution.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a synthetic quartz glass which solves such disadvantages, disadvantages and problems in the conventional method, which comprises converting an alkoxysilane into ammonia and / or aqueous ammonia. The silica sol suspension is continuously hydrolyzed and polycondensed under the conditions to obtain a silica sol suspension, which is separated into solid and liquid. Then, the silica is dried, calcined, and sintered to obtain a synthetic quartz glass by a sol-gel method. In the method for producing quartz glass, a step of separating an alcohol-water-ammonia solution from silica fine particles from a cloudy liquid after solid-liquid separation, a step of separating and recovering an alcohol-water-ammonia vapor into ammonia and a water-alcohol solution, Ammonia is introduced into the hydrolysis-condensation polymerizer again, followed by distillation of high-purity alcohol from the water-alcohol solution That step, in which the alcohol distilled reacted with metallic silicon, characterized in that it consists of a step of obtaining alkoxysilane.

That is, the present inventors continuously hydrolyze and polycondensate alkoxysilane in the presence of ammonia and / or aqueous ammonia, subject the resulting silica sol suspension to solid-liquid separation, and then convert the silica Various studies were conducted on the method of recovering and reusing ammonia and alcohol in the synthetic quartz glass manufacturing method by the sol-gel method of drying, calcining and sintering. First, the silica sol suspension was separated by solid-liquid separation. Silica fine particles and an alcohol-water-ammonia-based solution are separated and recovered from the obtained cloudy liquid, and the silica fine particles are made into synthetic quartz glass based on a conventional method.
The alcohol-water-ammonia solution is vaporized and separated and recovered as ammonia and a water-alcohol solution. If ammonia is introduced again into the hydrolysis-condensation polymerization apparatus, the ammonia is directly recycled to the alkoxysilane hydrolysis step. Found that it can be used. In addition, the alcohol-water solution separated and recovered here is distilled to recover high-purity alcohol, and the alcohol is reacted with silicon metal to form alkoxysilane. The present invention has been completed by confirming that it can be advantageously obtained.
This is described in more detail below.

[0009]

According to the method for producing synthetic quartz glass of the present invention, alkoxysilane is continuously hydrolyzed and polycondensed in an aqueous solution containing ammonia and / or ammonia and alcohol to form a silica sol suspension, which is solid-liquid. In a method for producing synthetic quartz glass by a sol-gel method of separating, drying, calcining and sintering the obtained silica, silica fine particles and an alcohol-water-ammonia system are obtained by simple evaporation from a cloudy liquid after solid-liquid separation. A step of separating the solution, a step of separating ammonia obtained by separating the ammonia and the water-alcohol solution from the alcohol-water-ammonia-based vapor, and a step of circulating the ammonia again into the hydrolysis-condensation polymerization apparatus, and Recovering as pure alcohol,
Reacting the alcohol with silicon metal to form an alkoxysilane, and circulating the alkoxysilane as a starting material, whereby ammonia and alcohol are recovered as active ingredients,
The advantage of being able to be reused is that the production of this synthetic quartz glass can be advantageously carried out.

[0010] The alkoxysilane used in the present invention is preferably tetraalkoxysilane because of its high cost and high reaction rate. Synthetic quartz glass obtained by using tetraethoxysilane is preferred. Is higher in the amount of OH groups than when tetramethoxysilane is used, and disadvantageously lower in high-temperature viscosity. Therefore, tetramethoxysilane is preferably used. The hydrolysis of the alkoxysilane is carried out in the presence of ammonia. The ammonia may be high-purity 28% aqueous ammonia, which may be a mixed solution of aqueous ammonia and alcohol. From the viewpoint of maintaining a high reaction rate and separating and collecting waste liquid.

However, when the alkoxysilane is hydrolyzed, the alkoxysilane and ammonia are simultaneously dropped into the reactor. If the concentration of the dropped ammonia is 20% or less, the reaction at the time of hydrolysis may occur. Gelation is promoted in the vessel, continuous operation is often impossible, and even if continuous operation can be performed, black spot impurities are generated at the time of calcining silica, or it becomes gray calcined powder, Because it becomes a glass with low foaming and high temperature viscosity,
This is preferably at least 20%.

The particle size of the silica fine particles in the silica sol suspension obtained by this hydrolysis and condensation polymerization is controlled by the weight ratio of alkoxysilane, ammonia, methanol and water, the reaction temperature, the stirring speed and the supply speed. In order to produce a silica powder having a low OH group content and excellent handling properties in subsequent operations, the average particle size (including primary particles and their aggregated particles) should be 200 to 5,000 nm. Good. The silica particle slurry thus obtained is separated by an existing solid-liquid separation operation,
As the solid-liquid separator, a centrifuge, a filter press, and a pressure / vacuum filter are suitable.

[0013] In the production of synthetic quartz glass from the silica fine particles separated in a solid-liquid manner in this way, this product is used for removing organic substances, moisture and the like remaining therein.
Dried and calcined in air or oxygen. This calcining
At 1,000 ° C or lower, organic substances are not completely oxidized and remain as black spots, or OH groups remain in the glass due to incomplete closure, and remain in pores until the next step of sintering vitrification. Impurities may be mixed in, and if the temperature is higher than 1,300 ° C, melting may start and cannot be recovered as spherical silica fine particles, or bubbles trapped by fusion may be generated as bubbles after sintering, this is
It needs to be performed at about 1,000 to 1,300 ° C. After the completion of the calcination, the material is sintered in a vacuum or helium gas at about 1,500 to 1,900 ° C. to be made into a transparent vitreous glass to obtain a synthetic quartz glass ingot.

The synthetic quartz glass ingot thus obtained is treated with 10 to 20% by weight of hydrofluoric acid for 1 to 5 minutes, and then washed and dried in order to remove foreign substances adhering to the surface during the sintering step. High-purity silica glass powder is obtained through pulverization, classification, magnetic separation, flotation, hydrochloric acid treatment, hydrofluoric acid treatment, and heat treatment, and the particle size distribution is adjusted according to various uses.

In this pulverization, the glass ingot is first made into granules of about 5 to 2 mm by a coarse pulverizer such as a jaw crusher or a hammer crusher, and then pulverized by a medium pulverizer such as a disk mill, a cone mill, a tube mill, and a roll mill. It is industrially preferable to carry out closed circuit pulverization in combination with the step. This pulverization is preferably carried out using an iron-based medium, since iron mixed into the target quartz glass powder by abrasion at the time of pulverization is easily removed by a subsequent magnetic separation process. This may be performed using, for example, a lining, a ball mill or a rod mill in which the balls are iron-based, a jaw crusher, a disc mill, a roller mill, or the like, in which the teeth, crushing plates, and drums are made of iron-based. Also, the classification is preferably performed by using an iron-based sieve or a classifier.

In this classifying step, the synthetic quartz glass powder is preferably sieved to a particle size distribution of 500 to 150 μm, but the sieved product is again classified by a medium pulverizer.
The under-sieved product is recovered and then purified by a refining method that combines magnetic separation, flotation, and acid treatment.
It is desirable to circulate this again as a synthetic quartz glass ingot. In order to obtain industrially sufficiently purified high-purity silica glass powder, 10-35% by weight hydrochloric acid was added to remove fine iron powder adhering to the ingot pulverized powder after magnetic separation. Acid treatment with an aqueous solution, then transfer it to a flotation tank while it is acidic, add pine oil, perform foam continuous flotation to remove rubber and other organic substances that cause bubbles during crucible formation, and then dehydrate and dry. After that, in order to completely remove organic substances such as pine oil, final calcination may be performed at a temperature of 800 to 1,300 ° C. However, when hydrofluoric acid washing of 2 to 10% by weight is performed as a pretreatment of the final calcination, Coloring and the like after calcination can be prevented, and dirt on the particle surface can be removed and the purity can be improved.

According to the present invention, there is provided a method for producing a high-purity synthetic quartz glass by the above-mentioned sol-gel method, wherein a continuously produced silica sol suspension is obtained by continuously hydrolyzing and polycondensing alkoxysilane in the presence of ammonia. Ammonia is recovered from the alcohol-water-ammonia-based suspension solution produced at the time of solid-liquid separation and circulated to the hydrolysis step, and high-purity alcohol is recovered and separated from the alcohol-water-based solution from which ammonia has been separated by distillation. , An alkoxysilane synthesis raw material.

The alcohol-water-ammonia-based suspension separated from the silica sol suspension contains a small amount of silica fine particles and is cloudy, so that the silica fine particles are first separated by simple evaporation. This single evaporation may be a batch type or a continuous type, but is preferably a continuous type in order to stabilize the amount of ammonia gas generated. The alcohol-water-ammonia-based vapor from which the silica fine particles have been separated may be once liquefied by an aggregator and introduced into the ammonia separation tower by a pump, or may be introduced into the ammonia separation tower without agglomeration. In order to reduce the ammonia concentration in the reboiler, it is preferable to introduce the ammonia into the ammonia separation tower without agglomeration. It is good to introduce near.

The temperature of the condenser of the ammonia separation tower may be 0 to 30 ° C., which is a temperature at which alcoholic water can be condensed. If the temperature is lowered, the ammonia concentration of the reflux liquid increases, and the ammonia concentration of the separation tower is increased. Is 1,00
The concentration of ammonia is preferably not more than 200 ppm, more preferably not more than 50 ppm, since it becomes 0 ppm or more, and thereafter it becomes difficult to recover high-purity alcohol. In this manner, high-concentration ammonia vapor is obtained from the top of the ammonia separation tower except for the partial pressure of methanol, and an alcohol aqueous solution having an ammonia concentration of 50 ppm or less is obtained from the kettle.
The ammonia vapor obtained from the top of the ammonia separation tower may be introduced as it is or in ultrapure water to be introduced into a hydrolysis-condensation polymerization reactor as ammonia water. Industrial advantage of being able to

From the alcohol-water solution from which ammonia has been separated, high-purity alcohol is recovered by a known method such as distillation. In order to react this alcohol with silicon metal to form alkoxysilane, a reaction catalyst is used. 1,000 ppm or less of water and 1,000 p of water to prevent deactivation
pm or less, preferably ammonia 500 ppm or less, moisture 500 ppm
It is necessary to: This alkoxysilane can be used as a starting material, and since it is synthesized in a system substantially free of chlorine, there is no black spot impurities during calcination, no foaming during sintering, and high heat-resistant synthetic quartz The advantage is that it gives glass.

As described above, according to the present invention, ammonia and alcohol can be recovered from the alcohol-water-ammonia liquid after solid-liquid separation by a simple apparatus in a closed circuit that does not leave the system. Has the advantage of only requiring replenishment at the time of use,
This may be performed, for example, by the system shown in FIG. FIG. 1 shows a system diagram of the entire reaction system of the synthetic quartz glass production method according to the present invention, which is started by the hydrolysis-condensation polymerization of alkoxysilane with ammonia, and the silica sol suspension produced thereby is It is separated into fine silica particles and an alcohol-water-ammonia solution by solid-liquid separation. These silica fine particles are dried, calcined, and sintered to obtain the target synthetic quartz glass. The alcohol-water-ammonia solution separates ammonia by simple distillation. This ammonia gas is circulated to the hydrolysis polycondenser as it is or as ammonia water dissolved in water.Alcohol is produced from the alcohol-aqueous solution by distillation, and the alcohol is converted into alkoxysilane by reaction with silicon metal. This is circulated as the starting material.

[0022]

Next, examples of the present invention will be described. Example Into a 5 liter reactor made of Teflon lining, 1.0 liter of 28% aqueous ammonia with high purity of semiconductor grade [manufactured by Showa Denko KK] was converted into 20% aqueous ammonia with ultrapure water, and tetramethoxysilane was added thereto. 26.5 liters / hour
When 20% ammonia water and 17.20 liters / hour were simultaneously dropped and reacted in a closed system at 40 to 50 ° C., a silica sol having a silica concentration of about 23% by weight was continuously obtained at 42.60 kg / hour. This was subjected to solid-liquid separation using a centrifuge (manufactured by Kokusai Centrifuge Co., Ltd.) to obtain 12.1 kg / h of a wet gel and 30.5 kg / h of a cloudy methanol-water-ammonia system solution.

When this series of reaction-solid-liquid separation operations was performed continuously for 5 hours, about 150 kg of turbid methanol-
A water-ammonia solution was obtained. The composition was examined by gas chromatography (column: Polapack®). As a result, the ammonia concentration was 10.2% by weight, water was 25.5% by weight, and methanol was 64.3% by weight. Therefore, this methanol
The water-ammonia suspension was charged into a 20-liter glass simple evaporator and subjected to simple distillation.
23.3: When a 76.7% by weight solution was charged and completely refluxed, and the evaporated gas was introduced into the top of the ammonia separation tower, it was found that 97% by weight of ammonia gas was generated at about 3.0 kg / h from the top. The total yield of ammonia was found to be 80% by gas chromatography analysis. In this case, an alcohol aqueous solution having an ammonia concentration of 31 ppm was recovered from the column.

When this alcohol aqueous solution was introduced into an alcohol distillation column, an ammonia concentration of 15
0 ppm, water 300 ppm methanol is recovered at about 19 kg / hour,
The overall methanol yield was about 80% by weight. Next, 10 kg of tetramethoxysilane, 5 kg of silicon metal powder (D _p = 15 μm), and 250 g of sodium methylate were charged into a 20-liter glass-lined reactor equipped with a condenser, and heated to reflux. Methanol =
When 28.4 kg / h of a 1: 4 (molar ratio) mixture was fed, the reaction reached an equilibrium at about 100 ° C. and about 29.5 kg / h of condensate flowed out.
% Of methanol, about 13% by weight of methanol. Then, methanol was separated and recovered by a stripper, circulated to the reactor, and tetramethoxysilane was introduced into the distillation column reboiler.
The yield was 98.5%.

Next, the ammonia gas generated from the above-mentioned ammonia separation tower is circulated to the above-mentioned Teflon-lined hydrolysis reactor through a capillary tube, and the above-mentioned 17.20 liter / hour of 20% by weight of ammonia water is converted into 4% by weight of ammonia. Water was changed to 17.20 liters / hour, and 24.6 liters / hour of tetramethoxysilane obtained above was added thereto. The continuous reaction was continued for 5 hours. As a result, a wet gel of 11.3 kg / hour was obtained. When the wet gel obtained above was dried, calcined and sintered vitrified,
Synthetic quartz glass having an OH group content of 1 ppm or less and a logarithm of viscosity at 1,400 ° C. of 10.70 and 10.74 was obtained.

[0026]

The present invention relates to a method for producing synthetic quartz glass, which comprises continuously hydrolyzing and polycondensing alkoxysilane in the presence of ammonia and / or aqueous ammonia, as described above, to obtain a silica sol suspension. In a method for producing a synthetic quartz glass by a sol-gel method, a liquid is made, the solid-liquid separation is performed, the silica fine particles are dried, calcined, and sintered to obtain a synthetic quartz glass.
Ammonia is recovered from the ammonia-based solution and circulated again to the hydrolysis-condensation polymerization device, and alcohol is recovered from the alcohol-water system, reacted with silicon metal and circulated as alkoxysilane. According to this, ammonia and alcohol can be recovered in a closed circuit without leaving the system, and a synthetic quartz glass substantially free of chlorine can be obtained.
There is no black spot impurities during calcination, no foaming during sintering, and since this is a sol-gel method, it is possible to easily obtain synthetic quartz glass with high purity and extremely low content of radioactive elements. Advantages are given.

[Brief description of the drawings]

FIG. 1 shows a system diagram of the entire reaction system of the method for producing synthetic quartz glass according to the present invention.

Of the front page Continued (72) inventor Michitaka Furusawa Niigata Prefecture medium kubiki County kubiki village Oaza west Fukushima 28 address of 1 Shin-Etsu Chemical Co., Ltd. synthesis technology in the Laboratory (58) investigated the field (Int.Cl. ^7, DB name) C03B 8/02 C03B 19/12 C03B 20/00

Claims (4)

(57) [Claims] 1. An alkoxysilane comprising ammonia and / or
Alternatively, a silica sol suspension is obtained by continuous hydrolysis and polycondensation in the presence of aqueous ammonia, which is subjected to solid-liquid separation, and then the silica fine particles are dried, calcined, and sintered to form a synthetic quartz glass sol. In the method for producing synthetic quartz glass by the gelation method, alcohol-water-
A step of separating the ammonia-based solution from the silica fine particles, a step of separating and recovering the alcohol-water-ammonia-based vapor into ammonia and a water-alcohol solution, and an ammonia circulation step of introducing the recovered ammonia into the hydrolysis-condensation polymerization device again, A step of distilling high-purity alcohol from a water-alcohol-based solution, and a step of reacting the distilled alcohol with silicon metal to obtain an alkoxysilane, wherein the alkoxysilane is circulated as a starting material. A method for producing quartz glass. 2. The method for producing synthetic quartz glass according to claim 1, wherein the alkoxysilane is tetramethoxysilane. 3. The method for producing synthetic quartz glass according to claim 1, wherein the temperature of the step of separating and recovering the alcohol-water-ammonia-based vapor into ammonia and a water-alcohol solution is 0 to 30 ° C. 4. The method for producing synthetic quartz glass according to claim 1, wherein the high-purity alcohol recovered by distillation from the water-alcohol solution has an ammonia content of 1,000 ppm or less and a water content of 1,000 ppm or less.