JP3408917B2 - High purity quartz glass and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to quartz glass used in the semiconductor industry and optical communication fields and a method for producing the same, and in particular, quartz glass containing a small amount of zirconium element,
For example, the present invention relates to a quartz glass crucible for pulling a silicon single crystal and a method for manufacturing the same.

[0002]

[Related Art] Conventionally, when high-purity quartz glass is required in the production of fused silica by using natural quartz as a raw material to melt and vitrify it, heating the raw material with increased purity through various unit purification means. It was manufactured by melting.

The main unit refining means are crushing, classification, flotation, magnetic separation, etching, high temperature heating, heat treatment in a halogen-containing atmosphere, electrolysis refining and the like.

[0004]

However, there are some elements that cannot be removed even if the contamination at the time of heating and melting is prevented as much as possible using the highly purified raw material. And, some of them are elements that impair their performance when used for the semiconductor industry or for optics. Recent advances in semiconductor engineering and optical technology
Even if the content was at a level that was acceptable in the past, it has reached the point where it is not acceptable because it is a harmful amount.

[0007] In particular, although it has been understood that the zirconium element is contained in natural quartz glass in an amount of about 1 ppm, it is desired to further reduce it, preferably to 0.8 ppm or less. In the present specification, the concentration indication in ppm means weight ppm indicating weight concentration.

However, by utilizing the conventional refining techniques as described above, the zirconium element content is 0.2 ppm.
Even if a high-purity silica powder as analyzed below is produced, the silica glass obtained by melting the silica powder has a disadvantage that it contains about 1 ppm of zirconium element.

When the quartz glass crucible for pulling a single crystal having a zirconium element content of about 1 ppm produced as described above is used, the zirconium element content is 0.2 ppm.
It was not possible to obtain a high-quality silicon single crystal as when using the following synthetic quartz glass crucible.

The present invention has been made in view of the above circumstances, and provides a high-purity quartz glass which is manufactured from natural quartz with a high purity, particularly, a low amount of zirconium (Zr) and at a low cost, and a method for producing the same. With the goal.

[0009]

In order to achieve the above object, a method for producing high-purity quartz glass according to the present invention is a method for producing natural quartz glass by heating and melting crystalline natural quartz. In purifying a natural quartz raw material by sequentially combining one or more unit purification means,
After carrying out a predetermined unit purification means, a part of the quartz raw material is extracted for analysis and decomposed with hydrofluoric acid or a mixed acid of hydrofluoric acid and other inorganic acid, and then the decomposed solution is left as it is. Alternatively, after further adding another inorganic acid, the mixture is evaporated to dryness, an alkali metal salt or hydroxide is added to the residue and the mixture is heated and melted, and then the alkali metal salt or hydroxide is added to an inorganic acid aqueous solution or pure water. Dissolved in the solution and quantitatively analyzing the impurities in the solution to determine the content of impurities in the crystalline natural quartz. The purified crystalline natural quartz whose content is below a specified value is melted by heating. It is characterized by producing high-purity quartz glass by.

The following method is generally used as a means for refining a raw material for natural quartz. First, a natural quartz raw material is pulverized into a powder, which is then washed or subjected to flotation, magnetic separation, etching with hydrofluoric acid or the like to obtain a high-purity quartz powder. In these treatments, the method described in JP-A-52-121017 (flotation) or JP-B-38-21986 is used.
The method described in Japanese Patent Publication (acid cleaning) can be applied.

In general, quartz powder having a zirconium element content of about 1 to 2 ppm can be obtained from a rough stone containing a few percent zirconium element by such a method. In addition,
Quartz powder is crystallographically the same as quartz powder and is not distinguished herein.

Next, in order to further reduce the alkali element, the iron element or the copper element, heat treatment is performed at about 1000 ° C. in a halogen element-containing atmosphere. This treatment is known as a general means for removing impurities (JP-A-48-69).
794). By this treatment, a refined raw material having an alkali element of 0.2 ppm or less and a copper element of 0.1 ppm or less can be obtained. At this time, when evaluated by an ordinary quartz glass analysis method, zirconium element is also 0.2 ppm at the same time.
It appears to have been purified below.

As a usual method for analyzing quartz glass, hydrofluoric acid is used to decompose and make a solution, and this solution is directly analyzed by a flameless atomic absorption spectrophotometer, or evaporated to dryness, and then recovered with dilute nitric acid. ICP-AES (plasma emission method)
And ICP-MS (plasma mass spectrometry). Further, an improved method such as that disclosed in Japanese Patent Laid-Open No. 7-72056, in which decomposition and evaporation to dryness are simultaneously performed with hydrogen fluoride gas, has also begun to be used.

However, in the analytical method used in the method of the present invention, the residue is recovered with a molten alkali compound after evaporation to dryness. This alkaline compound is further made into an aqueous solution, and this solution is quantitatively analyzed by a usual separation / analysis means.

In this way, it was found that in the conventional analysis method, about 1 ppm of zirconium element may be analyzed even from the quartz powder which appeared to be purified to 0.2 ppm or less.

According to a method such as neutron activation analysis, the total amount of zirconium element can be analyzed regardless of the existing form. Although it seems to be sufficiently purified by the analysis method of decomposing it with ordinary hydrofluoric acid and analyzing the decomposing solution by ICP-AES (plasma emission method), etc. In this case, it can be seen that the zirconium element content is purified to 0.8 ppm or less, further to about 0.3 ppm.

According to the conventional analysis method, it seems that the zirconium element content of the raw material quartz powder and the analysis value of the zirconium element content in the produced quartz glass have no relation to each other. Only when the analysis method of the present invention was adopted, the zirconium content in the raw material quartz powder and the zirconium content in the obtained silica glass could be reported to be the same.

For example, in the case where analysis and selection are carried out by the conventional method, in order to produce a quartz glass having a zirconium content of 0.8 ppm or less, quartz glass having a zirconium content of 0.8 ppm or less is selectively used. Even if it was produced, about 30% of the cases produced a rejected product exceeding 0.8 ppm.

On the other hand, when analysis and selection were carried out by the method of the present invention, no rejection was found. It has also become possible to control contamination in the melting process so that the zirconium content of the quartz glass is equal to the zirconium content of the raw material.

The present inventors have found that, in particular, zirconium (Zr)
As a result of earnest research to obtain a quartz glass crucible having a small element content, the following findings have been obtained. Zirconium (Zr) can be reduced by flotation or washing with hydrofluoric acid, but the practical limit is about 1 to 2 ppm. When this substance and fused silica glass were analyzed by a conventional method, the zirconium (Zr) content of the raw quartz powder and the zirconium (Zr
r) Content is consistent.

The heat treatment in an atmosphere containing a halogen element can further reduce the zirconium (Zr) element content. Although the true total content can be reduced, analysis by conventional methods appears to purify more rapidly than it actually is. That is, zirconium (Zr) in the raw material crystal powder is analyzed to 0.2 ppm or less by heating once in a halogen atmosphere, but the zirconium (Zr) content in the quartz glass obtained by melting the powder is 1. It often happens that it is analyzed as 0 ppm.

When the heat treatment is performed in an atmosphere containing a halogen element, the total amount of zirconium (Zr) contained in the quartz powder cannot be actually known by the conventional analysis method. Zirconium (Z that is actually contained in the quartz powder only by the analysis method of the present invention using the molten alkali compound is
The total amount of r) can be known. On the other hand, the zirconium (Zr) content in the fused vitrified quartz glass can be correctly known by the conventional analysis method or the analysis method employed in the method of the present invention.

The rate at which the zirconium (Zr) element is reduced by heating in a halogen atmosphere is not constant, depending on the history and origin of the raw material. Only by analyzing and grasping and selecting the zirconium (Zr) content after heating in a halogen atmosphere, a quartz powder raw material having a low zirconium (Zr) content can be stably used, resulting in a good yield and a low yield. Quartz glass having a zirconium (Zr) content can be manufactured.

According to the research conducted by the present inventors, another means for knowing the total amount of zirconium contained is the neutron activation analysis as in the method for analyzing elemental zirconium employed in the present invention. This method is expensive because it requires a large-scale facility as a neutron source, and therefore, there are few facilities available in the world, so rapid analysis cannot be performed. It is difficult to use as an analysis method for monitoring the quality by incorporating it into the production line.

The analytical method used in the method of the present invention is described in detail below. First, crystal powder is heated with hydrofluoric acid in a pressurized acid decomposition container to 100 ° C. or higher to form a decomposition solution. Instead of this hydrofluoric acid, a mixed acid of hydrofluoric acid and another inorganic acid can be used. Examples of the other inorganic acid mentioned here include nitric acid and sulfuric acid.

Next, when the solution containing silicon fluoride as a main component is heated in an open state, the volatile silicon fluoride is volatilized and dissipated, and the silicon component is lost and the residual impurities are contained. Only things remain. In analytical chemistry, the operation "drying" does not necessarily mean "solidifying". If it is dried until it becomes a solid, it may not be possible to recover it with a dilute acid in a later step.

The purpose of this evaporation-drying treatment is to volatilize and dissipate the volatile substances completely, and therefore, a small amount of sulfuric acid is added as a non-volatile acid, and then heating operation is performed until sulfuric acid white smoke appears. We call it "dryness". In particular, it is sometimes called “white smoke dryness”. In the case of the present invention, the main components such as silicon and fluorine can be completely removed by adding sulfuric acid to dryness in white smoke. As the acid to be added when the white smoke is dried, not only sulfuric acid but also nitric acid or perchloric acid may be used.

In the present invention, after evaporation to dryness, the residue is alkali-melted. The operation of alkali melting is performed by heating and melting a compound such as an alkali metal salt that is not an aqueous solution,
This is an operation of dissolving a target substance in a liquid having a strong dissolving power of several hundreds of degrees Celsius or more.

For example, specifically, borax or its anhydrous salt sodium tetraborate as an alkali metal salt is heated to 800 ° C. or higher in a platinum container and melted. Sodium tetraborate without water of crystallization is more convenient because a high-purity reagent is easily available, and no scattering occurs when water of crystallization is released. Other alkaline compounds such as NaCl,
Similarly, NaOH or the like can be used. A container made of platinum can be preferably used as the alkali melting container.

When the molten salt is cooled to room temperature, it becomes a solid alkali salt. This product can be easily dissolved in a dilute aqueous solution of acid, for example, dilute hydrochloric acid or dilute nitric acid. It is preferable to heat to a degree that does not boil to aid dissolution.

The aqueous solution obtained above is brought to a constant volume by a usual method, and the concentration of dissolved impurities is measured. When analyzing zirconium (Zr) which is a particularly important element in the method of the present invention, ICP-AES (plasma emission method) can be preferably used.

As a refining means preferably used in the method of the present invention, heating the crystalline natural quartz raw material in an atmosphere containing a halogen element can be mentioned. Further, zirconium element can be cited as an impurity measurement target in the present invention, and by setting the content of this zirconium element to a predetermined value, preferably 0.8 ppm or less, high-purity quartz glass, for example, silicon single crystal A quartz glass crucible for pulling up can be obtained.

The high-purity quartz glass of the present invention, for example, a quartz glass crucible for pulling a silicon single crystal, may be manufactured by a conventional method. For example, the quartz raw material powder is placed in a heat-resistant mold rotating about a vertical axis. It can be manufactured by filling and heating and melting from the inside.

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by these examples.

Example 1 Natural quartz powder for producing quartz glass, which was beneficiated and refined from a pegmatite deposit, was passed through 1 while passing chlorine and hydrogen chloride gas.
Continuous heat treatment is carried out in a rotary kiln with a residence time of 1 hour at 150 ° C.

Samples for analysis were collected from each of the processed quartz powders for 10 lots, 5 g of which was placed in a closed container together with 25 ml of 50% hydrofluoric acid, and heated at 160 ° C. for 4 hours and pressurized. Acid decomposes. After cooling, the decomposition solution was transferred to a platinum dish, taking care not to lose invisible unmelted Zr-containing particles, and 2 to 3 drops of sulfuric acid was added to dry the mixture until white sulfuric acid smoke appeared.

Anhydrous sodium borate (Na ₂ B ₄ O ₇ ) 2
Add gram and heat to above 800 ° C. to melt the residue after drying to dryness. The cooled melt is dissolved in dilute hydrochloric acid, and the purified solution is adjusted to a volume of 50 ml with pure water. The zirconium (Zr) element content of this aqueous solution is analyzed and measured by ICP-AES (plasma emission method).

A lot of quartz powder raw material having a zirconium (Zr) content of 0.5 to 0.7 ppm is selected, and the quartz raw material powder is filled in a heat-resistant mold rotating about a vertical axis, Twenty crucibles for pulling a silicon single crystal were melt-molded by heating and melting from the inside.

The zirconium (Zr) content of the obtained crucible was measured.
It had a zirconium (Zr) content in the range of 5 to 0.7 ppm.

Comparative Example 1 In the same manner as in Example 1, natural quartz powder for producing quartz glass, which was beneficiated and refined from a pegmatite deposit, was passed through a rotary kiln having a residence time of 1 hour at 1150 ° C. while passing chlorine and hydrogen chloride gas. Then, the continuous heat treatment was performed.

The zirconium (Zr) element content in the quartz powder after the treatment was measured by a conventional analysis method. That is, 5 g of the treated quartz powder is placed in a closed container together with 25 ml of 50% hydrofluoric acid, and heated at 160 ° C. for 4 hours to undergo acid decomposition under pressure. After cooling, transfer the decomposition solution to a platinum dish,
Add 2-3 drops of sulfuric acid and dry to white smoke of sulfuric acid. The residue is recovered with dilute hydrochloric acid, the volume of the purified solution is adjusted to 50 ml with pure water, and the zirconium (Zr) element content of this aqueous solution is analyzed and measured by ICP-AES (plasma emission method).

The analytical values of zirconium (Zr) observed in all lots were 0.2 ppm or less, which is the lower limit of quantification in the analysis. Using this quartz powder raw material,
The quartz raw material powder was filled in a heat-resistant mold rotating around a vertical axis, and heat-melted from the inside to melt-mold 20 crucibles for pulling a silicon single crystal.

The zirconium (Zr) content of the obtained crucible was measured. As a result, 14 crucibles having a Zr content in the range of 0.5 to 0.8 ppm were obtained,
There were 6 crucibles with a Zr content in the range 0.9 to 1.2 ppm. Example 2 A silicon single crystal having a nominal diameter of 8 inches was pulled using the crucibles having different zirconium (Zr) contents prepared in Example 1 above. When the Zr content was 0.5 to 0.8 ppm, three single crystals could be continuously pulled up.

Comparative Example 2 A silicon single crystal was pulled in the same manner as in Example 2 using the crucibles having different zirconium (Zr) contents prepared in Comparative Example 1 above. Zr content from 0.9ppm to 1.2pp
When the crucible of m was used, the first single crystal could be pulled normally, but grain boundaries were introduced into the crystal during pulling of the second, and pulling was interrupted. In this state again, we tried to pull up the single crystal, but the seeding did not go well, and the remaining silicon melt had to be discarded.

According to the method for producing quartz glass of the present invention,
Even if a heat treatment in a halogen gas atmosphere is used in combination in the refining process of the raw material crystal powder, the zirconium (Zr) content can be correctly, easily and inexpensively analyzed at the stage of the raw material powder. A crucible of high purity can be efficiently manufactured.

When the crucible having a zirconium content of 0.8 ppm or less produced in this manner is used, a plurality of large diameter single crystals having a nominal diameter of 8 inches can be continuously pulled up.

[0046]

As described above, according to the present invention, high purity, particularly zirconium (Zr), is obtained by using natural quartz as a raw material.
The great effect that quartz glass can be manufactured at low cost and at low cost is achieved.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyotaka Maekawa 2-5-5 Kitafu, Takefu-shi, Fukui Prefecture Fukui Environmental Analysis Center (72) Inventor Tadazaji Tsuji 2-chome Kitafu, Takefu-shi, Fukui Fukui Environmental Analysis Center Co., Ltd. (72) Inventor Manabu Saito 2-15, Kitafu, Takefu City, Fukui Prefecture Fukui Environmental Analysis Center (56) Reference JP-A-7-72056 (JP, A) Kaihei 4-108683 (JP, A) JP 48-69794 (JP, A) JP 5-273132 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C03B 20 / 00 C01B 33/18 C03C 3/06 G01N 1/28

Claims (5)

(57) [Claims] 1. In a method for producing natural quartz glass, which is produced by heating and melting crystalline natural quartz, the crystalline natural quartz raw material is purified by sequentially performing a combination of one or more unit refining means. After carrying out the unit refining means of, a part of the quartz raw material is extracted for analysis and decomposed with hydrofluoric acid or a mixed acid of hydrofluoric acid and other inorganic acid, and then the decomposed solution as it is or After further adding another inorganic acid, evaporate to dryness, add an alkali metal salt or hydroxide to the residue and heat and melt, and then add the alkali metal salt or hydroxide with an inorganic acid aqueous solution or pure water. By dissolving and quantitatively analyzing the impurities in the solution, the content of impurities in the crystalline natural quartz is obtained, and the purified crystalline natural quartz whose content of impurities is equal to or less than a predetermined value is heated and melted. A method for producing high-purity quartz glass, which comprises producing high-purity quartz glass by melting. 2. The predetermined unit refining means is to heat the crystalline natural quartz raw material in a halogen element-containing atmosphere, and the impurity to be analyzed in the crystalline natural quartz is zirconium element. The method for producing high-purity quartz glass according to claim 1. 3. The method for producing high-purity quartz glass according to claim 2, wherein the zirconium element content in the purified crystalline natural quartz is 0.8 ppm or less. 4. The content of zirconium element is 0.8 pp.
A purified crystalline natural quartz having a size of m or less is used as a raw material.
A high-purity quartz glass produced by the production method described above and having a zirconium element content of 0.8 ppm or less. 5. The high-purity quartz glass according to claim 4, which is produced by heating and melting from inside the purified crystalline natural quartz powder filled in a mold rotating about a vertical axis. A quartz glass crucible for pulling a silicon single crystal.