JP3393063B2 - Heat-resistant synthetic silica glass for shielding impurity metal and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an impurity metal element,
In particular, the present invention relates to a heat-resistant synthetic silica glass having an excellent shielding property against Na, K, and Li and a method for producing the same, and more specifically, a jig used for heat treatment of a semiconductor material such as a silicon wafer, that is, a wafer boat, a chamber, and The present invention relates to a heat-resistant synthetic silica glass used for a jig used for heat treatment of a furnace core tube or the like, or an optical material for ultraviolet rays, that is, a lens blank setter, a hearth plate, a furnace tube, and the like, and a manufacturing method thereof.

[0002]

Related Art Conventionally, a high temperature electric furnace used for heat treatment of a semiconductor material such as a silicon wafer or heat treatment of an optical material for ultraviolet rays is generally covered with a refractory material such as alumina, mullite or zirconia. Since these refractory materials are molded using various binders in the manufacturing process, they contain a high concentration of impurities, especially Na.

When heat-treating an object to be heat-treated such as the silicon wafer or the ultraviolet optical material in a high temperature electric furnace, a silica glass jig is interposed between the object to be heat-treated and the refractory material. Since Na contained in the refractory material has a large diffusion coefficient, Na diffuses into a heat-treated object such as a silicon wafer or an optical material for ultraviolet rays using a silica glass jig as a medium and contaminates them. was there.

In order to solve such a problem, the applicant of the present application has found that 2 particles of high-purity zirconium are contained in a silica glass matrix having an OH group content of 10 to 500 wtppm.
Already proposed an impurity metal shielding silica glass that does not cause contamination by impurity metals, especially alkali metal elements or alkaline earth metal elements, by uniformly dispersing 0 to 10,000 wtppm and aluminum oxide fine particles at 20 to 5,000 wtppm. (JP-A-10-017334)
issue).

The above-mentioned proposed silica glass uses silica powder as a main raw material in the manufacturing method. In addition to the limited manufacturing method, zirconium oxide and aluminum oxide are doped in the form of fine particles. However, there are problems that the bubble content is large and that a granular structure remains during vitrification. The remaining granular structure of the silica glass also causes devitrification during heat treatment.

The granular structure referred to here is a problem of the uniformity of silica glass, and the fine particles melted during vitrification retain the particle structure even after vitrification, and the particle diameter is 0.5.
It is the one having a size of μm or more and observed with an optical microscope. A micrograph of an example of the surface shape of silica glass showing a granular structure is shown in FIG.

In addition, it is very difficult to uniformly mix silica powder with zirconium oxide fine particles and aluminum oxide fine particles due to the manufacturing method, and when these two types of fine particles are often agglomerated, a non-uniform glass is obtained. was there.
As a result, the silica glass obtained may have insufficient shielding properties against impurity metals, or may partially cause recrystallization and devitrification.

As described above, the conventional synthetic silica glass is inferior in heat resistance and has a problem of devitrification, and is not suitable as a member for heat treatment at high temperature.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and is suitably used for a jig used for heat treatment of semiconductor materials and heat treatment of optical materials for ultraviolet rays. A heat-resistant synthetic silica glass having a uniform and smooth surface shape, which is excellent in shielding impurity metal elements in heat treatment, particularly Na, K, and Li, has no devitrification, and has no granular structure, and its synthetic silica glass. An object is to provide a method that can be efficiently manufactured.

[0010]

In order to achieve the above object, the heat-resistant synthetic silica glass for shielding impurity metals of the present invention comprises a high purity synthetic silica glass having an OH group content of 10 to 300 wtppm and zirconium of 1 to 100 wtppm. And aluminum of 1 to 100 wtppm are uniformly doped without forming a granular structure. However,
The concentration of the dope solution and the concentration of the dope in the glass actually formed are different, and thus it is necessary to adjust the concentration of the dope solution necessary for doping the glass to a predetermined concentration.

With the above-mentioned structure, it is possible to improve the barrier property against the impurity metal during the heat treatment of the synthetic silica glass. Zr ⁴⁺ is incorporated in the Si—O bond and has an ionic radius larger than that of Si ⁴⁺ , so that it has a function of blocking diffusion of alkali metal ions.

When the above Zr ⁴⁺ is doped and then Al ³⁺ is further doped, the charge balance around the Al ³⁺ ions is disrupted, and a state where compensation for positive charges is required occurs, and impurities are generated during heat treatment in a high temperature electric furnace. It has the function of trapping metal and further reducing the pollution of semiconductor products and the like. Further, by co-doping with zirconium and aluminum, the recrystallization resistance at high temperature becomes high, the heat resistance is high even at a high temperature treatment of 900 ° C to 1300 ° C, the strength is less deteriorated, and the silica glass as a jig is used. It is possible to impart preferable performance.

If the contents of zirconium and aluminum are each less than 1 wtppm, the effect of the present invention cannot be achieved. On the other hand, each of these contents is 100 wtpp
If it exceeds m, there are disadvantages that vitrification during production of silica glass becomes difficult, and recrystallization during heat treatment is likely to occur.

By setting the doping amounts of zirconium and aluminum to 10 to 50 wtppm, the devitrification resistance of the synthetic silica glass during heat treatment can be further improved.

The above synthetic silica glass has 10 to 10 OH groups.
Although it contains 300 wtppm, the viscosity of the synthetic silica glass during heat treatment can be improved, and the impurity metal existing in the heat treatment atmosphere even if the semiconductor product is heated at a high temperature of 900 to 1300 ° C. for a long time. , Especially alkali metal ion-exchanges with OH groups or H ⁺ ions in silica glass and is preferentially taken into silica glass,
Less contamination of semiconductor products.

If the OH group content is less than 10 wtppm, the above effect does not occur, and if it exceeds 300 wtppm, the viscosity of the silica glass decreases (reduction of heat resistance), so that it is fused with a heat-treated object during heat treatment or is deformed. It is not preferable because it will occur.

The temperature condition of the above heat treatment is usually 900-1.
The temperature is in the range of about 300 ° C., which is a general processing temperature condition of a high temperature electric furnace used for heat treatment of semiconductor materials such as silicon wafers and optical materials for ultraviolet rays.

The heat-resistant synthetic silica glass for shielding impurity metals is preferably produced from a silicon compound raw material by a soot remelting method of flame hydrolysis.

The zirconium and aluminum are preferably uniformly doped with a solution containing zirconium ions and aluminum ions.

The Cl group contained in the heat-resistant synthetic silica glass for shielding impurity metals is preferably 1000 wtppm or less. When the Cl group content exceeds 1000 wtppm, the Cl group forms a Si-Cl structure in silica glass,
It is not preferable because it causes reduction of viscosity (reduction of heat resistance).

The content of Li, Na and K of the heat resistant synthetic silica glass for shielding the impurity metals is 50 wtppb.
It is preferable that the content of Fe, Ni, and Cu is 10 wtppb or less.

The diffusion coefficient of Na at 1000 ° C. of the heat-resistant synthetic silica glass for shielding impurity metals is 1 × 10.
It is preferably ⁻¹⁰ cm ² / sec or less.

It is preferable that the heat-resistant synthetic silica glass for shielding impurity metals has a viscosity at 1280 ° C. of 10 ^11.6 poise or more. Viscosity at 1280 ℃ is 1
When it is less than 0 ^11.6 poise, heat resistance is also deteriorated, which is not preferable.

More specifically, the heat-resistant synthetic silica glass of the present invention comprises a soot body of silica glass prepared by subjecting a silicon compound as a raw material to an oxyhydrogen flame hydrolysis method to obtain zirconium and It is preferred that aluminum is uniformly doped into the soot body from a solution each present in the form of ions, and the soot body is vitrified, that is, formed by the soot re-solution method.

In this case, silicon tetrachloride is usually used as the silicon compound.

Further, in the case where the soot body of the silica glass is uniformly doped with zirconium and aluminum in the form of ions, the soot body of the silica glass is zirconium salt such as zirconium dichloride (IV). ) Octahydrate, zirconium dinitrate (IV) dihydrate octahydrate and aluminum salts, for example, aluminum chloride hexahydrate, aluminum nitrate nonahydrate by immersion in an aqueous solution, the aqueous solution if necessary A polar solvent such as alcohol may be added.

The zirconium and the aluminum preferably coexist in silica glass.
The presence of zirconium and aluminum in the above content ranges improves the recrystallization resistance and heat resistance of the silica glass at a high temperature of 900 to 1300 ° C.,
Strength deterioration can also be reduced.

The method for producing a heat-resistant synthetic silica glass for shielding impurity metals of the present invention comprises: (a) a step of producing an amorphous silica base material, that is, a soot body by a flame hydrolysis method using a silicon compound raw material; ) A step of uniformly doping the soot body with zirconium and aluminum by immersing the soot body in a solution of a zirconium compound and an aluminum compound, and (c) a step of drying the soot body uniformly doped with zirconium and aluminum. , (D) a step of vitrifying the dried soot body under a reduced pressure atmosphere.

As described above, by applying the so-called soot remelting method to the production of the heat-resistant synthetic silica glass of the present invention, the heat-resistant synthetic silica glass for shielding impurity metals having a uniform and smooth surface shape without a granular structure. Can be efficiently manufactured.

[0030]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

(Examples 1 to 4) By the CVD method (flame hydrolysis method) in which silicon tetrachloride is hydrolyzed in an oxyhydrogen flame,
After depositing soot-like silica fine particles on a target to prepare an amorphous silica base material (soot), and immersing the soot body in a dope solution in which the Zr concentration and the Al concentration are varied as shown in Table 1 Water was removed by drying at 100 to 200 ° C. under atmospheric pressure.

Thereafter, the dried soot body was subjected to 5 × 10 ^-4 To
By heating in a vacuum heat treatment furnace at 1650 ° C. under reduced pressure of rr, transparent vitrification was performed, and heat-resistant synthetic silica glass for shielding impurity metals was prepared.

With respect to the obtained synthetic silica glass, the impurity concentration, the OH group concentration, the Na diffusion coefficient, the viscosity, the devitrification resistance, and the Na contamination amount shown in Table 1 were measured. Shown in 1.

As is clear from the results shown in Table 1, Example 1
The Zr and Al contents of the synthetic silica glass of Nos. 4 to 4 are both within the range of 1 to 100 wtppm, and L
The content of i, Na and K is 50 wtppb or less, the content of Fe, Cu and Ni is 10 wtppb or less, the content of Cl is suppressed to 30 wtppm or less, and the OH group is 90 or 80 wtppm. Was also adjusted to a good range.

Examples 1 to 1 having such an impurity composition
The diffusion coefficient of Na in the synthetic silica glass of No. 4 shows a low numerical value, and when heat treatment is performed using this synthetic silica glass as a medium, the disadvantage that Na diffuses into the heat-treated object and contaminates it is suppressed. It was also confirmed that the synthetic silica glasses of Examples 1 to 4 did not have reduced viscosity, and therefore did not have reduced heat resistance.

Furthermore, the devitrification resistance of the synthetic silica glasses of Examples 1 to 4 was also good, and the devitrification of the synthetic silica glasses of Examples 2 and 3 was very small. Furthermore, N
It was found that the a contamination amount was also suppressed to an extremely low value.

When a micrograph (magnification of 50) of the synthetic silica glass of Example 3 was taken, it was confirmed that it had a uniform and smooth surface shape as shown in FIG.

[0038]

[Table 1]

Comparative Example 1 A synthetic silica glass was prepared in the same manner as in Examples 1 to 4 except that the soot body was not immersed in the Zr and Al dope solution. Various performances of the obtained synthetic silica glass were measured in the same manner as in Examples 1 to 4 and shown in Table 2.

From the results in Table 2, the contents of Li, Na, K, Fe, Cu and Ni of the synthetic silica glass of Comparative Example 1 are the same as those of Examples 1 to 4, and the content of Cl is 30 wt.
It is suppressed to below ppm and the OH group is 260 wtppm, which is good, but both Zr and Al are 0.05 wtppm.
The following was outside the scope of the present invention.

The diffusion coefficient of Na in the synthetic silica glass of Comparative Example 1 having such an impurity composition was increased as compared with Examples 1 to 4, and the viscosity was also slightly lowered. Further, devitrification of this synthetic silica glass was remarkable, and the amount of Na contamination was also increased.

(Comparative Example 2) A synthetic silica glass was prepared in the same manner as in Examples 1 to 4 except that the soot body was dehydrated in a chlorine atmosphere without immersing it in a Zr and Al dope solution. Example 1 of the obtained synthetic silica glass
Various performances were measured in the same manner as in Nos. 4 to 4, and shown in Table 2.

From the results shown in Table 2, the contents of Li, Na, K, Fe, Cu and Ni of the synthetic silica glass of Comparative Example 2 are the same as those of Examples 1 to 4, but Zr and Al are both 0. In addition to 0.05 wtppm or less, which is outside the scope of the present invention, Cl
The content was as high as 1800 wtppm and the OH group concentration was 1 wtppm or less, which was too low.

Although the diffusion coefficient of Na in the synthetic silica glass of Comparative Example 2 having such an impurity composition is the same as that of Example 1 and the viscosity is slightly lowered,
The devitrification was remarkable and the amount of Na contamination was also increased.

(Comparative Example 3) Al concentration of 400 wtppm and Z
Synthetic silica glass was prepared in the same manner as in Examples 1 to 4 except that the silica glass was immersed in a dope solution having an r concentration of 400 wtppm.
Various performances of the obtained synthetic silica glass were measured in the same manner as in Examples 1 to 4 and shown in Table 2.

From the results shown in Table 2, Li, Na, K, Fe, Cu, Ni, Cl and O of the synthetic silica glass of Comparative Example 3 were obtained.
The H group content was the same as in Examples 1 to 4, but both Zr and Al exceeded 100 wtppm, which was outside the scope of the present invention.

The Na diffusion coefficient of the synthetic silica glass of Comparative Example 3 having such an impurity composition is less than that of Example 1 and the viscosity is slightly lowered, but the devitrification is remarkable and The amount of Na contamination was also increasing.

Comparative Example 4 A synthetic silica glass was prepared from silicon tetrachloride as a raw material by a direct method of oxyhydrogen flame hydrolysis without doping with Zr and Al. Various performances of the obtained synthetic silica glass were measured in the same manner as in Examples 1 to 4 and shown in Table 2.

From the results shown in Table 2, the contents of Li, Na, K, Fe, Cu and Ni of the synthetic silica glass of Comparative Example 4 are the same as those of Examples 1 to 4, and the Cl content is also good at 130. However, both Zr and Al are 0.05 wtppm
In addition to the following and outside the scope of the present invention, the OH group content is also 65
It was as high as 0 wtppm.

The Na diffusion coefficient of the synthetic silica glass of Comparative Example 4 having such an impurity composition was increased as compared with Examples 1 to 4, and the viscosity was also significantly decreased.
Further, devitrification of this synthetic silica glass is remarkable, and Na
The amount of pollution was also increasing.

[0051]

[Table 2]

(Comparative Example 5) Silica glass [trade name: Heralu] made from natural quartz by the oxyhydrogen Bernoulli method
x, Shin-Etsu Quartz Co., Ltd.] was prepared. Various performances of the obtained silica glass were measured in the same manner as in Examples 1 to 4, and shown in Table 3.

From the results of Table 3, Al of the silica glass of Comparative Example 5 is within the definition of the present invention, and the content of Cl and OH groups is good, but the content of Zr is low and Li, Na,
The concentrations of K, Fe, Cu and Ni were all too high.

The Na diffusion coefficient of the silica glass of Comparative Example 5 having such an impurity composition was increased as compared with Examples 1 to 4, and the viscosity was also slightly decreased. Further, although devitrification of this silica glass was slightly recognized, the amount of Na contamination was significantly increased.

(Comparative Example 6) Silica glass [trade name: Heralux- using natural quartz as a raw material by an electric melting method]
E, Shin-Etsu Quartz Co., Ltd.] was prepared. Various performances of the obtained silica glass were measured in the same manner as in Examples 1 to 4, and shown in Table 3.

From the results shown in Table 3, Al of the silica glass of Comparative Example 6 is within the definition of the present invention, the content of Cl and OH groups is good, but the content of Zr is low, and Li, N
The concentrations of a, K, Fe, Cu and Ni were all too high.

The diffusion coefficient of Na in the silica glass of Comparative Example 6 having such an impurity composition was increased as compared with Examples 1 to 4, but the viscosity was not reduced. Also,
Although devitrification of this silica glass was slightly observed, the amount of Na contamination was significantly increased.

Comparative Example 7 A silica powder having a purified OH group content and a particle size of 10 to 200 μm.
m synthetic cristobalite powder with a particle size of 0.1-10 μm
100 wtppm of ZrO _{2 and} 100 wtp of Al ₂ O _{3 in the} range of
After pm was mixed and uniformly mixed in a V-type mixer, the mixture was heated and melted to prepare silica glass. Various performances of the obtained silica glass were measured in the same manner as in Examples 1 to 4, and shown in Table 3.

From the results shown in Table 3, Zr and Al of the silica glass of Comparative Example 7 are within the specifications of the present invention, and the Cl and OH group contents are good, but Li, Na, and
The concentrations of K, Fe, Cu and Ni were all too high.

The diffusion coefficient of Na in the silica glass of Comparative Example 7 having such an impurity composition was the same as that of Examples 1 to 4, and the viscosity was not lowered, but the devitrification was remarkable and the amount of Na contamination was large. Was also increasing. When a micrograph (magnification of 50) of this silica glass was taken, it was found that the silica glass had a surface shape having a granular structure as shown in FIG.

[0061]

[Table 3]

The evaluation items of Examples 1 to 4 and Comparative Examples 1 to 7 were measured or evaluated by the following methods.

(1) Impurity analysis: atomic absorption spectroscopy (2) OH group concentration measurement: infrared absorption spectroscopy [DM Dodd,
DBFraser; Journal of Applied Physics, Vol.37, p.3911
(1966))

(3) Measurement of Na diffusion coefficient: size 20 × 2
A glass sample to be measured having a mirror finish of 0 × 5 mm was prepared, and a saline solution was applied onto the glass sample, dried at 100 ° C., and then heat-treated at 1000 ° C. for 50 hours in the atmosphere, and then subjected to the LMA method (Laser Micro Analysis method) is used to measure the Na diffusion concentration distribution in the depth direction from the surface of the glass sample, and the diffusion coefficient is determined according to Fick's law.

(4) Viscosity measurement: beam bending method (Keiji Kobayashi, Ryosuke Yokota; Journal of Ceramic Industry, Vol. 76, No. 7)
(No. 1968, 218-223)

(5) Devitrification resistance: A glass sample to be measured was heat-treated at 1300 ° C. for 100 hours in a high temperature atmospheric furnace,
The degree of devitrification of the sample after the heat treatment is visually evaluated. The evaluation of visual judgment is as follows. ⊚: Devitrification is extremely small. : Indicates that some devitrification was observed. X: Devitrification is remarkable.

(6) Na contamination amount of glass sample: A glass sample (glass plate) (thickness: 10 mm) to be measured was installed at the bottom of a high temperature atmospheric furnace, and a standard silica glass sample [trade name] was placed at the center of the glass plate. [Heralux-LA, Shin-Etsu Quartz Co., Ltd.], and heat-treated at 1100 ° C. for 1000 hours. After the heat-treatment, a standard silica glass sample was collected and
The amount of contamination was measured.

[0068]

As described above, the heat-resistant synthetic silica glass of the present invention can be used for the impurity metal elements, especially Na, K, in the heat treatment of the semiconductor material and the heat treatment of the optical material for ultraviolet rays.
It has an excellent Li shielding property, has no devitrification, has no granular structure, and has a uniform and smooth surface shape, and has an effect of being suitably used for a jig used for the heat treatment. Further, according to the method of the present invention, the effect that the synthetic silica glass having the above-mentioned excellent performance can be efficiently produced is achieved.

[Brief description of drawings]

FIG. 1 is a micrograph showing a surface shape of a synthetic silica glass prepared in Example 3.

FIG. 2 is a micrograph showing the surface shape of silica glass prepared in Comparative Example 7.

Continuation of the front page (56) Reference JP 10-17334 (JP, A) JP 10-7434 (JP, A) JP 5-294660 (JP, A) JP 3-252320 (JP , A) JP-A-7-196326 (JP, A) JP-A-3-137012 (JP, A) JP-A-3-83833 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) C03B 20/00 C03B 8/04 C03C 3/06

Claims (9)

(57) [Claims] 1. A high-purity synthetic silica glass having an OH group content of 10 to 300 wtppm and zirconium of 1 to 100 wtppm.
And heat-resistant synthetic silica glass for shielding impurity metals, characterized by being uniformly doped with 1 to 100 wtppm of aluminum without forming a granular structure. 2. The heat resistant synthetic silica glass for shielding impurity metals according to claim 1, wherein said zirconium is doped in an amount of 10 to 50 wtppm and said aluminum is doped in an amount of 10 to 50 wtppm. 3. The heat-resistant synthetic silica glass for shielding an impurity metal according to claim 1, which is produced from a silicon compound raw material by a soot remelting method of a flame hydrolysis method. 4. The zirconium and aluminum are uniformly doped with a solution containing zirconium ions and aluminum ions.
The heat-resistant synthetic silica glass for shielding impurity metals according to any one of 3 above. 5. The heat resistant synthetic silica glass for shielding an impurity metal according to claim 1, wherein the Cl group is 1000 wtppm or less. 6. The contents of Li, Na and K are each 5
The heat-resistant synthetic silica glass for shielding an impurity metal according to any one of claims 1 to 5, wherein the content of Fe, Ni and Cu is 10 wtppb or less, respectively. 7. The diffusion coefficient of Na at 1000 ° C. is 1.
The heat-resistant synthetic silica glass for shielding impurity metals according to any one of claims 1 to 6, which has a density of x10 ^-10 cm ² / sec or less. 8. The heat-resistant synthetic silica glass for shielding an impurity metal according to claim 1, which has a viscosity of 10 ^11.6 poise or more at 1280 ° C. 9. (a) A step of producing an amorphous silica base material, that is, a soot body by a flame hydrolysis method using a silicon compound raw material, and (b) immersing the soot body in a solution of a zirconium compound and an aluminum compound. Thereby uniformly doping the soot body with zirconium and aluminum, (c) drying the soot body uniformly doped with zirconium and aluminum,
(D) a step of vitrifying the dried soot body under a reduced pressure atmosphere.
9. The method for producing a heat-resistant synthetic silica glass for shielding an impurity metal according to any one of 8 above.