JP3268049B2 - Quartz glass material and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz glass material and a method for producing the same, and more particularly, to a quartz glass material suitable for semiconductor production.
The present invention relates to a quartz glass material having high purity, high viscosity and excellent mechanical strength, and a method for producing the same.

[0002]

2. Description of the Related Art Quartz glass has excellent heat resistance, thermal shock resistance, chemical resistance, and high mechanical strength, and is used as a member for various applications. In the semiconductor manufacturing process, many quartz glasses are used as materials or members. A typical example of a quartz glass member used in a semiconductor manufacturing process is a crucible for pulling a silicon (Si) single crystal. Conventionally, most of these Si single crystal pulling crucibles are produced by melting natural raw materials. In the above-mentioned Si single crystal pulling, the quartz glass crucible is placed under a high temperature of 1400 ° C. or more for a long time, and although it has excellent heat resistance, viscous flow (deformation) is generated by heating, and the Si melt in the crucible is heated. Convection is disturbed,
This is a problem in the production of Si single crystals.

[0003] The main factors that lower the viscosity of quartz glass are:
This is the destruction of the Si-O irregular network structure due to the presence of metal impurities and OH groups. Therefore, in order to increase the viscosity of quartz glass, it is only necessary to increase the purity of quartz glass and remove these factors. It is also known that the viscosity can be increased by crystallizing the glass separately from the purification. In order to solve the above problems, various methods for increasing the viscosity of quartz glass have been proposed based on these principles. For example, a method has been proposed in which the content of alkali metals such as Na, K, and Li is suppressed to 0.5 ppm or less, the viscosity of quartz glass is increased, and devitrification is prevented (Japanese Patent Application Laid-Open (JP-A) Sho.
59-23314). In addition, a method of increasing the viscosity by crystallization has been proposed separately from the above-described purification. For example, Japanese Patent Publication Nos. 47-1477 and 47-1883 propose a method in which the outer surface of a quartz glass member is coated with a cristobalite layer and the resultant is baked to increase the viscosity. Further, as a method utilizing crystallization, there has been proposed a method in which a nucleating agent such as Al is applied to the outer surface of a quartz glass member and heat-treated to form a crystal layer in the glass layer (JP-A-1-126238). ).

[0004]

However, the above-mentioned proposed methods still have problems. That is, the method of suppressing the content of the alkali metal can achieve a certain increase in viscosity, but it is difficult to obtain a higher viscosity. In addition, alkali metals such as Na and K have a large diffusing capacity in glass, and even if they are manufactured with a reduced content, they inevitably invade from the external atmosphere and lower their viscosity during prolonged high-temperature treatment. Become. Further, in the method of covering the cristobalite layer, stress is unavoidable at the boundary between the cristobalite layer and the glass layer, and cracks and the like are easily generated. Furthermore, there is a high possibility that semiconductor dust will be generated, and use in a semiconductor manufacturing environment where extremely high cleanliness is required is not preferable. Further, the method of applying a nucleating agent to the outside is not preferable because a residue of the applied nucleating agent may become a source of contaminants in a semiconductor manufacturing process requiring high purity. Further, even if a crystal layer is formed in the glass layer, stress generated between the two layers is still unavoidable, and may be cracked when performing high-temperature treatment for a long time. An object of the present invention is to provide a quartz glass material which is highly viscous and has a small deformation due to heat even when used for a long time at a high temperature in consideration of the problems of the above-mentioned conventional technology.

[0005]

According to the present invention, mainly N
The total content of alkali metals consisting of a, K and Li is 1 p
pm or less, and each metal impurity content is 10 ppm or less.
One or more metal atom components selected from the group consisting of Al, Y and La constituting a nucleating agent for cristobalite crystal growth at a temperature of not less than 30 ° C. are uniformly dispersed in a content of 30 to 200 ppm. A quartz glass material is provided.

Further, the present invention relates to a high-purity quartz raw material powder containing 1 ppm or less of an alkali metal mainly composed of Na, K and Li and containing 10 ppm or less of each metal impurity, from A1, Y and La. A mixed quartz powder obtained by adding and mixing as a nucleating agent at least one of nitrate or sulfate-containing solutions of metal atom components selected from the group consisting of: Provided is a method for manufacturing a quartz glass material, characterized by being formed by: In the present invention, the quartz glass material includes both raw materials for the quartz glass member and products formed on various quartz glass members.

[0007]

The present invention is constructed as described above, and the quartz glass material is heated to 1400 ° C. or more and has a nucleating agent dispersed therein, for example, a metal atom component of A1, Y, La as a nucleus, Cristobalite crystals can be grown in proportion to the nucleating agent concentration and the heat treatment time. That is, the quartz glass material of the present invention has a structural distortion region based on a metal atom component as a nucleating agent therein, and the region grows in crystal at a predetermined temperature, thereby increasing the viscosity. Therefore, a sufficient effect of increasing the viscosity can be obtained by adding a trace amount of metal atom components.

Further, the cristobalite crystal formed in the quartz glass material grows centering on the nucleating agent dispersed and contained therein, so that it is uniformly dispersed in the quartz glass not in a layer but in a dot-like manner. There is no possibility that stress will occur. Furthermore, the metal atoms of the nucleating agent diffuse during melting,
The nucleating agent has a lower mobility in quartz glass than alkali metals such as Na and K, that is, a low diffusivity, and cristobalite crystals are crystallized from the inside to the outside in the inner and outer layers of the quartz glass material. Since it is formed with the change rate changed, the viscosity can be increased without leaving any stress in each part of the quartz glass material. For example, when a quartz glass crucible is formed, a decrease in strength due to cracks or the like due to a difference in the coefficient of thermal expansion can be prevented.

The metal atom component of the nucleating agent of the present invention is, for example, a solution containing A1, Y, and La metal atom components in the form of nitrates or sulfates, generally as an aqueous solution, in a high-purity quartz raw material powder. Since they are added and mixed, they can be uniformly dispersed at the atomic level in the quartz glass material. Therefore, the quartz glass material of the present invention can be obtained as a transparent glass body by melting the high-purity quartz raw material powder in which the nucleating material is homogeneously dispersed. In this case, the nitrate can be added as an alcohol solution in addition to the aqueous solution. Also, most of the crystal parts formed in the quartz glass material of the present invention exist inside the quartz glass material as described above. Therefore, in the quartz glass material of the present invention, for example, in a member used in a semiconductor manufacturing process, a portion exposed in a semiconductor manufacturing process system is covered with ordinary high-purity quartz glass to contaminate a semiconductor product being processed. There is no danger.

Hereinafter, the present invention will be described in more detail. As the high-purity quartz raw material powder of the present invention, the content of alkali metals, particularly Na, K and Li is 1 ppm or less in total, and the content of metal impurities such as Al, Fe, Ca, and Mg is respectively High-purity quartz powder or quartz glass powder having a concentration of 10 ppm or less is used. The above-mentioned high-purity quartz raw material powder can be a commercially available product.Also, natural quartz is crushed and treated with hydrofluoric acid and chlorine gas to reduce alkali metals and other impurity metals to the above-mentioned predetermined amount or less. It can also be used.

The nucleating agent of the present invention contains 3
0 to 200 ppm is dispersed and contained, and when heated to a temperature of 1400 ° C. or more, quartz glass can become a crystal nucleus for cristobalite crystal. As the nucleating agent, generally, a metal compound such as a metal oxide containing a metal atom as a constituent can be exemplified. In this case, the presence of a metal atom component constituting the nucleating agent is indispensable, as long as it is homogeneously dispersed in the quartz glass material as described above,
Usually, it is dispersed in the form of an oxide of the metal atomic component. Examples of the metal atom component include rare earth elements such as A1, Y, and La. Usually, a nucleating agent containing one or more of A1, Y and La as metal atom components is used. In the present invention, when the content of the nucleating agent in the quartz glass material is less than 30 ppm, almost no effect is obtained,
Further, even if the content exceeds 200 ppm, the viscosity of the quartz glass does not increase any more.

The nucleating agent of the present invention is added to and mixed with the above-mentioned high-purity quartz raw material powder, and is dispersed and contained as it is in the quartz glass when the high-purity quartz raw material powder is melted and vitrified. It is generally preferable to add the metal atom component to the high-purity quartz raw material powder as a nitrate or a sulfate and as an aqueous solution of the salt. When added as an aqueous solution, mixing with the high-purity quartz raw material powder can be uniformly and easily performed, and the nucleating agent can be uniformly mixed with the high-purity quartz raw material powder. Therefore, the nucleus forming material can be homogeneously dispersed in the quartz mixed powder and the quartz glass material, which is preferable. Further, the nitrate or sulfate of the metal atom component constituting the nucleating agent is water-soluble, and is preferable because, for example, there is no possibility that an anion remains in quartz glass like a halide. preferable.
This is because nitrates are easily dissolved and easily decomposed into oxides by heating.

In the present invention, the high-purity quartz raw material powder to which the aqueous solution of nitrate or sulfate of the metal atom component has been added as described above is appropriately heated in the air to decompose and remove the acid component, thereby forming nuclei. The constituent metal atom components of the agent are usually
A quartz mixed powder dispersed and contained in the form of an oxide can be obtained, and the quartz mixed powder can be melted and vitrified to contain a nucleating material in a quartz glass material. For example, in the case of nitrate, it can be treated at 800 to 1000 ° C. to remove only nitric acid in the form of nitrogen oxides (NO _x ). If it is a sulfate, it can be treated at 900 to 1200 ° C. to remove only sulfuric acid as sulfur oxide (SO _x ).

[0014] The melting and vitrification of the quartz mixed powder of the present invention is as follows.
Processing can be performed by a known method. For example, usually, after heating to 1600 to 1800 ° C. to melt a quartz mixed powder in which the constituent metal atom components of the nucleating agent are dispersed and dispersed, the mixture is cooled to 1000 ° C. or less at a cooling rate of 2 ° C./min to vitrify. Can be.

In the present invention, a quartz mixed powder obtained by dispersing and containing the constituent metal atoms of the nucleating agent obtained as described above is formed into a final member, and then fused and vitrified into a quartz glass material. You may. Further, a quartz glass material in which a nucleating agent is uniformly dispersed and contained may be powdered and used as a raw material of a final member. Further, the quartz glass material of the present invention may be used, for example, as the center of a quartz glass member such as a quartz glass tube or a quartz glass crucible, and the outer peripheral portion may be covered with ordinary high-purity quartz glass. The quartz glass material thus obtained increases the viscosity of the central portion and does not deform even during high-temperature processing, and thus is preferable as a high-temperature operating member. In addition, the metal atom component of the nucleating agent contained in the quartz glass material of the present invention disposed at the center does not scatter as an impurity to the outside, and can be suitably used particularly as a quartz glass member in a semiconductor manufacturing process. it can.

[0016]

EXAMPLES The present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples. Example 1 A natural crystal was crushed, washed with hydrofluoric acid, and further treated with chlorine gas to reduce the total content of Na, K, and Li to 1 ppm or less.
Al content is 5ppm and total impurity content is 10ppm
A high-purity quartz raw material powder having the following composition was obtained. To 100 g of the high-purity quartz raw material powder obtained above, an aqueous solution of Al (NO ₃ ) ₃ having an Al ion concentration of 500 ppm was impregnated and mixed with 10 cc of the raw material powder so that the amount of Al added to the raw material powder was 50 ppm. . Next, the high-purity quartz raw material powder impregnated and mixed with an aqueous solution of Al (NO ₃ ) ₃ is treated at 800 to 1000 ° C. in the air to remove nitric acid in the form of NO _X , thereby forming an Al component serving as a nucleating agent. Was obtained in a dispersed manner. This mixed quartz powder was melted and vitrified to obtain a transparent quartz glass material.

A part of the obtained transparent quartz glass material is collected as a sample, heated at 1470 ° C. for 0 to 5 hours in increments of 1 hour, heated and crystal-grown, and the crystal growth state is different. Glass material was created. The viscosity (poise) at 1420 ° C. of each of the obtained quartz glass materials on which the crystals were grown was measured by a beam bending method. Table 1 shows the measurement results.

[0018]

[Table 1]

The ratio η / r of the viscosity value η of the quartz glass materials having different heating times, that is, different crystal growth states, to the viscosity value η ₀ of the quartz glass material not subjected to the heat treatment (holding for 0 hours). FIG. 1 shows the relationship between η ₀ and the heat treatment time (retention time at 1470 ° C.).

Examples 2 to 6 Transparent quartz glass was obtained in the same manner as in Example 1 except that the solution of the nucleating material to be added and the concentration thereof were changed. The obtained transparent quartz glass material was heat-treated at 1470 ° C. for a different holding time in the same manner as in Example 1. The viscosity of each heat-treated quartz glass material was measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 A transparent quartz glass was obtained in the same manner as in Example 1 except that the high-purity quartz raw material powder obtained in Example 1 was melted without adding Al and used as it was. A sample was taken from the obtained transparent quartz glass without a nucleating material in the same manner as in Example 1, and similarly heated at 1470 ° C. for 1 to 5 hours and held for 1 hour. The viscosity of the heat-treated quartz glass at 1420 ° C. was measured in the same manner as in Example 1. FIG. 1 shows the change over time in the obtained viscosity.

As is clear from FIG. 1 of the above Examples and Comparative Examples, the viscosity of the quartz glass material of the present invention prepared by adding Al increases as the heat treatment time increases, and 1470.
It can be seen that the viscosity of the quartz glass material kept at 5 ° C. for 5 hours is about 10,000 times the viscosity of the quartz glass that is not heat-treated. In addition, also in the case of a normal high-purity quartz glass material to which Al is not added as a nucleus forming material, cristobalite is generated when heat-treated, and the viscosity is slightly increased. However, when the quartz glass materials subjected to the heat treatment for 5 hours are compared, it can be seen that the viscosity of the quartz glass material containing the nucleating material is about 2,000 times higher than that of the quartz glass material not containing the nucleating material. That is, even when used under high temperature,
The viscosity increases with time, and sufficient strength can be provided.

Example 7 Using the quartz mixed powder obtained in Example 1, a quartz glass tube having a structure as shown in a vertical sectional view of FIG. 2 was prepared. That is, FIG.
In, the outer diameter is 9 mm, the inner diameter is 5 mm, and the length is 200 mm
The inner ring portion 2 and the outer ring portion 4 of the circular tube 1 are formed using the high-purity quartz raw material powder used in Example 1, and the inner ring portion 3 (hatched portion) inside the outer ring portion 4 is formed in Example. A transparent quartz glass tube was formed by forming, melting, and vitrifying the quartz mixed powder obtained in 1 above. In addition, after melting and vitrification, the outer ring portion 4 is 1 mm,
The middle ring part 3 was formed so as to have a thickness of 500 to 1000 μm. The obtained quartz glass tube was placed on a 150 mm span and heat-treated at 1450 ° C. for 5 hours, but almost no deformation was observed.

Comparative Example 2 A quartz glass tube was produced in the same manner as in Example 7, except that the powder was formed using only the high-purity quartz raw material powder. The obtained quartz glass tube was placed on a 150 mm span in the same manner as in Example 2, and was heated at 1450 ° C. for 5 hours. As a result, the amount of deformation (bending) was 1500 μm.

[0025]

The quartz glass material of the present invention has 1
The metal atom component that is the nucleus for crystal growth in high-temperature treatment at 400 ° C or higher is homogeneously dispersed and present, and the crystal grows and increases in viscosity even when used in a high temperature range, so that stress occurs inside. In addition, it has an advantageous property that heat deformation is extremely small and mechanical strength is large. In particular, when a quartz glass crucible for pulling a Si single crystal in semiconductor production using the quartz glass material of the present invention is formed, thermal deformation of the quartz glass crucible is extremely small without causing stress inside the crucible, and No adverse effects. In addition, crystal growth proceeds inside the quartz glass material, and the exposed surface with the outside is coated and melted with ordinary high-purity quartz glass for use, so that the metal atom component added as a nucleating agent in the present invention becomes an external impurity. Scattered and diffused, and there is no danger of generating dust, particularly as a contamination source in a semiconductor manufacturing environment.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a heat treatment time and a viscosity value η in a quartz glass material of one embodiment of the present invention and a conventional high-purity quartz glass.

FIG. 2 is a vertical sectional view of a quartz glass tube according to an embodiment of the present invention.

[Explanation of symbols]

 1 quartz glass tube 2 inner ring 3 middle ring 4 outer ring

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-59-129421 (JP, A) JP-A-3-208835 (JP, A) JP-A-2-229735 (JP, A) JP-A 64-64 82526 (JP, A) JP-A-63-215600 (JP, A) JP-A-6-191888 (JP, A) JP-A-61-101430 (JP, A) JP-A-1-126238 (JP, A) US Patent 5053359 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03C 1/00-14/00 WPI / L (QUESTEL)

Claims (4)

(57) [Claims] 1. A high-purity quartz raw material powder having a total content of alkali metals mainly composed of Na, K and Li of 1 ppm or less, and other metal impurities of 10 ppm or less, respectively. One or more metal atom components selected from the group consisting of Al, Y and La constituting a nucleating agent for cristobalite crystal growth are 30 to
A quartz glass material which is homogeneously dispersed at a content of 200 ppm . 2. A comprising a coating layer formed from a high-purity silica glass material to the peripheral surface claim 1 silica glass material according. 3. A high-purity quartz raw material powder containing 1 ppm or less of an alkali metal mainly consisting of Na, K and Li and having a content of each metal impurity of 10 ppm or less, Al, Y
And at least one of a nitrate or sulfate-containing solution of a metal atom component selected from the group consisting of La and La as a nucleating agent, followed by heat treatment to remove the acid component. A method for producing a quartz glass material, characterized by being formed by vitrification. 4. The method of producing a quartz glass material according to claim 3 , wherein said mixed quartz powder contains 30 to 200 ppm of said metal atom component.