JPH0717389B2 - Method for producing synthetic quartz glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a method for producing synthetic quartz glass, particularly for semiconductors such as process tubes, boats, and cantilevers because of its high purity, high viscosity, and low gas emission. The present invention relates to a synthetic quartz glass manufacturing method suitable for a heat-resistant jig.

[Prior Art] For the production of quartz glass, use natural quartz powder under reduced pressure.
Well known is the method of melting at temperatures around 000 ° C,
For this, crystal powder was placed in a graphite crucible lined with silicon carbide, melted at 2,000 ° C under a reduced pressure of 10 ^-2 to 10 ^-4 Torr, the reduced pressure was released during cooling, and pressure was applied by carbon dioxide gas. The method of making bubbles so small that they cannot be seen with the naked eye is called the Herberger method. And the quartz glass made by this method has extremely low OH group content,
Since it contains a —Si—Si— bond, it has high viscosity and slow diffusion of impurities. Therefore, it is widely used in semiconductor diffusion members, lamps and the like.

For the production of this quartz glass, fumed silica is molded using a binder, sintered at 1,300-1,500 ° C under reduced pressure, and continuously piped, a flame hydrolysis method for silicon tetrachloride. It is also known that the fine powder silica soot produced in step 1 is attached to a target, and the porous chamber glass member obtained by growing is sintered under reduced pressure. Further, silica sol obtained by hydrolyzing alkoxysilane is colloidal silica. A sol-gel method is also known in which the materials are mixed, molded, and then sintered under reduced pressure.

[Problems to be solved by the invention] However, the purity of the quartz glass obtained by the method of melting the natural quartz in vacuum is poor, for example, Al is 20 ppm and Fe is 1 pp.
Since m, Na, K, Li, and Ca are 1 to 2 ppm, if they are used as a semiconductor diffusion furnace member, the silicon wafer will be contaminated by the diffusion of impurities, which poses a major problem in improving the integration of silicon devices. It has the disadvantage of giving, and the method of using fuming silica is cheap, but this also
Al, Fe are 500 ppb, Na, K, Li, Ca are 2 to 300 ppb, and the purity is not so good and the viscosity is not high.

Further, the soot method by flame hydrolysis of silicon tetrachloride described above has a disadvantage that the amount of oxyhydrogen used is large compared to the weight of the product and it is disadvantageous in terms of cost, and mass production and enlargement are difficult. . The sol-gel method of mixing and molding silica sol and colloidal silica is broken when the drying, calcination, and sintering speeds are high, and this tendency is strong especially for large products, mass production at high cost, large size However, in order to further increase the purity, not only the selection of reagents and tools but also the disadvantage of drying, calcination and sintering in a clean room is disadvantageous.

[Means for Solving the Problems] The present invention relates to a method for producing synthetic quartz glass, which solves the above disadvantages and drawbacks, in which methyl silicate is added in the presence of water in the presence of water at 40-50%. Hydrolyzed in a system consisting of water at ℃, polycondensed to a particle size of 400-1,0
After producing 00nm silica particles, solid-liquid separation, dehydration, and drying to powder, heat this in an oxidizing atmosphere to decarburize it, then pack it in a heat-resistant case and store at 10 ^-2 to 10 ^-4 Torr. It is characterized in that it is sintered at 1,500 to 1,700 ° C under reduced pressure and then heated to 1,800 to 2,200 ° C under normal pressure or pressure.

That is, as a result of various studies on the method for obtaining synthetic silica glass having high purity, high viscosity, bubble-free and good transparency, the present inventors have found that alkoxysilane, which is a starting material in the sol-gel method, has low viscosity. It is not necessary to dilute it with a solvent such as alcohol, and it is specified as methyl silicate that can be added as it is.After sufficiently purifying it, hydrolysis with a system consisting of water at 40-50 ° C in the presence of ammonia water without the addition of alcohol is carried out. When is decomposed, particle size solid-liquid separation can be easily large, spherical silica can be easily obtained with a three-dimensional matrix structure larger pore size, which is packed into the heat-resistant container such as carbon case with the powder, 10 ^{- 2-10 -4} sintered under a reduced pressure of torr, then 1,800 ° C. transparent by heating at a higher temperature than at a high purity, high viscosity, yet very slow synthetic quartz diffusion rate of the impurity It found that it is possible to obtain a lath, this sintering conditions, and completed the present invention by studying on heat treatment conditions of the posterior.

This will be described in more detail below.

[Operation] The method for producing synthetic quartz glass of the present invention is performed by adding methyl silicate in the presence of ammonia water in the presence of ammonia water without adding alcohol.
The silica particles are hydrolyzed at 50 ° C. in a system consisting of water, and then silica particles are decarburized, sintered, and heat-treated to obtain quartz glass.

The starting material in the method of the present invention has a low viscosity, does not require alcohol dilution, and is highly reactive, and easily reacts even when added to a system consisting of water without a solvent such as alcohol in the presence of aqueous ammonia. Methyl silicate is selected because it produces large spherical silica with a particle size of 400 to 1,000 nm, and because it is a system consisting mostly of water, it can be easily separated, but this methyl silicate is Since the target synthetic quartz glass is of high purity, it must be supplied in advance as being sufficiently purified by distillation or the like.

This methyl silicate is hydrolyzed to form a silica sol. When this hydrolysis is carried out in the presence of a known acid catalyst such as hydrochloric acid, the silica obtained has a small particle size, and therefore in the presence of an ammonia catalyst. You need to do it in. Therefore, if this methyl silicate is hydrolyzed in the presence of aqueous ammonia at 40-50 ° C in a system consisting of water without the addition of alcohol, the resulting silica will have a particle size of 40
It becomes a large sphere with a size of 0 to 1,000 nm, which has a very regular three-dimensional matrix structure with large pores on its surface.

If the hydrolysis reaction in this water system is less than 40 ° C, the particle size of silica will be less than 400 nm, and if it exceeds 50 ° C, it will become a large lump, so it is necessary to perform it at 40-50 ° C. The silica thus obtained is subjected to solid-liquid separation more easily than silica by using a filter press to obtain silica.

The silica powder obtained by drying the silica thus obtained is then packed in a carbon case and sintered under reduced pressure, but when the reduced pressure exceeds 10 ^-2 Torr, defoaming is sufficient. Less than 10 ^-2 Torr, preferably
It should be 10 ^-2 to 10 ^-4 torr. Also, if the sintering temperature is less than 1,500 ° C, sufficient sintering cannot be performed,
Therefore, the heating in the next stage makes it opaque in appearance, and when the temperature is higher than 1,700 ° C, the bubbles contained in the silica particles grow and grow, and the bubbles remain until the end. It must be in the range of 1,500 to 1,700 ° C.

Silica is made into synthetic glass by this sintering, but in the method of the present invention, the silica glass thus obtained is
Heat to 800-2,200 ℃. That is, the quartz glass as a sintered product thus obtained is taken out of the furnace and then heated again. The heating temperature is 1,800.
If the temperature is set to ~ 2,200 ° C, the viscosity of the quartz glass becomes low and the bubbles generated in the pressure reduction sintering in the previous stage are easily collapsed due to the pressure difference, which gives the advantage that there is no visible bubble. Then, SiO vapor is violently generated, so this is preferably in the range of 1,800 to 2,000 ° C. It should be noted that this heating may be performed at normal pressure, but this may be performed under pressure at 1 to 10 atm, and if pressure is applied, the bubbles will collapse more and more and it will not be visible at all. To be

[Examples] Next, examples and comparative examples of the present invention will be described.

Example 1 1 m ³ of glass-lined reactor 20 wt% of aqueous NH ₄ OH 300
1 liter was added, and 265 liters of sufficiently purified methyl silicate was added dropwise to the mixture to cause a hydrolysis reaction at 40 to 50 ° C. The reaction solution was subjected to solid-liquid separation with a filter press to prepare 135 kg of silica powder.

Then, put this silica in a quartz container, heat-treat it at 800 ° C for 20 hours in the presence of clean air to dehydrate it, and decarburize it. As a result, the silica powder weighed 95 kg.
It is packed in a carbon case with a volume of 1,000 liters of 300 mmφ × inner diameter 280 mmφ and decompressed at 10 ^-3 torr at a heating rate of 50 ° C / hour for 1,60
When the temperature was raised to 0 ° C., sintering was performed for 2 hours, the temperature was lowered, and the product was taken out to obtain a quartz ingot having an outer diameter of 278 mmφ and a volume of 75 l.

Next, this ingot was placed under an argon gas atmosphere for 2,000
When heat-treated at ℃ for 1 hour, the diameter is 470mmφ and the volume is 2
A transparent ingot (44 kg) of 5 liters was obtained, and the amount of impurities (chemical analysis value), viscosity, and diffusion rate of impurities (diffusion coefficient of Na ⁺ ions) were examined, and the results shown in Table 1 were obtained. Was given.

However, for comparison, quartz produced by melting natural quartz powder at 2,000 ° C. under a reduced pressure of 10 ⁻³ Torr (Comparative Example 1) and fuming silica were molded into a columnar shape using polyvinyl alcohol, Quartz made by sintering at 1,500 ° C. under a reduced pressure of ⁻³ Torr (Comparative Example 2), silica sol obtained by hydrolyzing tetraethyl silicate in the presence of hydrochloric acid was mixed with colloidal silica, and then molded. -1,800 ° C under reduced pressure of ^-1 Torr
When the chemical analysis value, the viscosity, and the diffusion rate of impurities were examined for the quartz (Comparative Example 3) obtained by sintering at.
The results as shown in the table were obtained, and it was confirmed that the quartz obtained by the method of the present invention has excellent physical properties.

Example 2 The opaque quartz ingot obtained in Example 1 was subjected to circular polishing to make a 250 mmφ × 70 l ingot, and the center of which was 50 mm.
Drill a φ hole and stretch in an electric furnace at 1,950 ° C to obtain an outer diameter of 70 m.
A pipe with a diameter of 60 mm and an inner diameter of 60 mm was made, and for the above opaque ingot, this was made into a 100 mmφ × 70 l ingot by circular grinding and then 10 mm using an oxyhydrogen flame burner.
A φ Muku rod was prototyped.

Next, when the physical properties of the quartz pipe and the rod thus produced were examined, they showed the same characteristics as in Table 1 of Example 1.

[Effects of the Invention] As described above, the method for producing the synthetic quartz glass of the present invention is as follows.
Methyl silicate is hydrolyzed in the system consisting of water at 40-50 ° C in the presence of aqueous ammonia without the addition of alcohol,
The silica powder obtained by polycondensation is heated in an oxidizing atmosphere to decarburize it, put it in a heat-resistant container, sinter it under a reduced pressure of 10 ^-2 to 10 ^-4 Torr at 1,500 to 1,700 ° C, and then 1,800 to It is heated to 2,200 ° C. According to this, it is possible to obtain synthetic quartz glass with high purity, high viscosity, bubble-free, good transparency, and extremely slow diffusion rate of impurities. The advantage is that synthetic quartz glass, which is useful as a heat-resistant jig for semiconductors such as cantilevers and as a sealing tube material such as halogen lamps and infrared heaters, can be easily and inexpensively obtained.

Claims (1)

[Claims] 1. Methyl silicate is hydrolyzed in the presence of aqueous ammonia at 40 to 50 ° C. in a system consisting of water without addition of alcohol and polycondensed to produce silica particles having a particle size of 400 to 1,000 nm. , Solid-liquid separation, dehydration, drying to powder, heating in an oxidizing atmosphere to decarburize, packing in a heat-resistant case, and 1,500 to 1,7 under a reduced pressure of 10 ^-2 torr or less.
Sinter at 00 ℃, and then under normal pressure or pressure, 1,800-2,2
A method for producing synthetic quartz glass, which comprises heating to 00 ° C.