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Manufacturing industry quartz glass and articles thereof

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The present invention relates to transparent quartz glass of high purity produced by molding powdery amorphous silica, and sintering and fusing the molded article of amorphous silica. Particularly, the present invention relates to pure transparent quartz glass which contains less impurities like alkalis respectively at a content of not more than 1 ppm, contains less water, and has high heat resistance, thereby being useful for a photomask and other uses in semiconductor production.

Conventionally, transparent quartz glass is produced by a process of melting powdery quartz crystal in vacuo in a furnace, a process of melting powdery quartz crystal by oxyhydrogen flame, or a like process. However, the conventional processes employ powdered natural quartz crystal, whereby the resulting quartz glass is not satisfactory to meet the severe requirements for high purity for highly integrated LSI, even though the quartz glass has high heat resistance.

Although the powdered natural quartz crystal is treated for high purity, not all of the undesired impurities can be removed to respective contents of not higher than 1 ppm at the moment. To obtain higher purity of the quartz glass, processes are investigated, including a VAD process which sinters deposited synthetic amorphous silica, and a sol-gel process which sinters powdery amorphous silica obtained by hydrolysis of a silicic acid alkoxide.

However, the synthetic powdery amorphous silica, although it can be produced in higher purity, gives quartz glass inferior in heat resistance to the one obtained from natural quartz material, disadvantageously.

This disadvantage is presumed to be due to water included during the synthesis of the quartz glass, or the structure of the glass. To offset the above disadvantage, a process is proposed for producing the glass by crystallizing amorphous silica and then fusing it.

This process, which employs a crystallization promoter such as alkali or alumina, involves a problem of contamination with impurities which affect adversely the transparency to lower the quality of the product. The impurities cannot readily be eliminated. For example, elimination by heat treatment requires long time to lower the productivity. Another process is proposed in which powdery amorphous silica is converted to powdery cristobalite and then it is fused.

This process requires much time for grinding the powdery crystal, and resulting ground matter is poor in moldability disadvantagesouly, and is not suitable for industrial production.

The present invention intends to provide a pure transparent quartz glass which is as pure as the one produced from the synthetic silica, containing impurities like alkali metals respectively at a content of not higher than 1 ppm, and further has heat resistance as high as the one produced from the powdery natural quartz crystal. The present invention also intends to provide a process for producing the above pure transparent quartz glass without contamination by impurities and at high productivity.

The pure transparent quartz glass of the present invention is produced by molding powdery amorphous silica into an article, converting the molded powdery amorphous silica into crystalline molded silica of high-temperature type cristobalite structure, and then fusing the crystalline molded silica, the quartz glass containing Li, Na, Mg, Ca, K, Al, Ti, Cr, Ni, Zn, Zr, Mo, Fe, and Cl respectively at a content of not higher than 1 ppm, and an OH group at a content of not higher than 20 ppm, and having a viscosity of 10 The process for producing the pure transparent quartz glass of the present invention comprises steps of molding powdery amorphous silica into an article, converting the molded powdery amorphous molded silica in a vacuum or a helium atmosphere into crystalline molded silica of high-temperature type cristobalite structure with simultaneous sintering , and then fusing the crystalline molded silica into glass, wherein the molded silica is converted into the crystalline molded silica without addition of any crystallization promoter like an alkali metal compound or alumina.

With any of the above specified impurities contained at a content of higher than 1 ppm, the quartz glass tends to decrease the light transmissivity, and is not suitable for the production of semiconductors.

The respective contents of the above impurities are preferably not higher than 0. The pure transparent quartz glass of the present invention contains an OH group at a content of not higher than 20 ppm. At a higher content thereof, the quartz glass tend to decrease its heat resistance, and tends to deform at a higher temperature, disadvantageously.

The content of the OH group is preferably not higher than 10 ppm. The pure transparent quartz glass of the present invention has a viscosity of 10 The quartz glass having the viscosity of lower than 10 The viscosity is preferably not lower than 10 The process for producing the pure transparent quartz glass of the present invention comprises steps of molding powdery amorphous silica into an article, converting the molded powdery amorphous silica in a vacuum or a helium atmosphere into crystalline molded silica of high-temperature type cristobalite structure with simultaneous sintering, and then fusing the crystalline molded silica, wherein the molded silica is converted into the crystalline molded silica without addition of any crystallization promoter like an alkali metal compound or alumina.

In the aforementioned process, the powdery amorphous silica is sintered at the heat treatment for converting it into high-temperature type cristobalite crystal structure.

The powdery amorphous silica as the starting material for the above process is prepared by reacting an aqueous solution of alkali metal silicate with an acid and purifying the resulting silica. With such a starting material, impurity removal from the produced quartz glass can be omitted.

The heat treatment for the crystal structure conversion is conducted in a vacuum or helium atmosphere, because heat treatment in other atmosphere e,g. The respective steps of the process for the pure transparent quartz glass of the present invention are described below in detail. The starting powdery material, namely powdery amorphous silica, may be prepared by any method which is capable of giving amorphous silica in high purity.

The method includes hydrolysis of silicic acid alkoxide, hydrolysis of silicon tetrachloride by oxyhydrogen flame, acid treatment of an aqueous alkali silicate solution, and so forth. Of these method, the acid treatment of alkali silicate solution is suitable for obtaining powdery amorphous silica having high purity and high moldability. The powdery silica obtained as above has an average particle diameter ranging preferably from 0.

Such satisfactory powdery silica can be obtained by control of the conditions of production thereof and selection of the produced powdery matter. The resulting powdery silica is molded by press-molding by use of a mold tool, slip cast molding in which a powder-containing slurry is poured into a gypsum or plastic mold tool, and the slurry is solidified therein, or a like molding method. The molding may be conducted by any method provided that the powdery pure amorphous silica can be molded without contamination by impurities.

A binder or the like additive may be added to the improve the strength of the molded product. Preferably, however, no additive like a binder is added to avoid the contamination with impurities.

The aforementioned molded article is heated to crystallize the constituting powdery amorphous silica to convert it into powdery high-temperature type cristobalite and to sinter it.

Before this crystallization step, pretreatment such as heat drying or binder removal may be conducted without any adverse effect. In conventional processes, addition of powdery cristobalite or a crystallization promotor such as an aluminum compound and an alkali compound to the amorphous silica was proposed for promoting the conversion to the cristobalite structure.

The addition of the foreign matter, however, necessitates an impurity removal step as described above. In the present invention, no additive is added for promotion of crystallization, and crystallization is allowed to proceed with retention of the purity of the powdery starting material, thus no post-treatment such as impurity removal being required. The process of the present invention utilizes rearrangement of amorphous structure on heating. Therefore, the atmosphere for the heating is not specially limited.

However, to minimize the size and number of pores in the formed crystal, the heating is preferably conducted in a vacuum or a helium gas atmosphere. The vacuum in the present invention means a pressure of 10 -1 torr or higher vacuum, more preferably 10 -2 torr or higher vacuum.

An excessively low or high treating temperature retards the rearrangement. A further higher temperature causes melting of the crystal. The crystalline matter obtained by the above conversion is further heated to a higher temperature to fuse the crystal into glass. The fused matter is held at a temperature above the melting point for a predetermined time for complete fusion. The time for the fusion depends on the temperature and the shape of the molded article.

If the heating temperature is such that the molded article is fused instantaneously, the fused matter need not be kept at that temperature. The gas bubbles remaining in the fused glass depend on the structure of the crystalline matter before the fusion thereof. The fusion may be conducted in an inert gas atmosphere such as helium, argon, and nitrogen, in a vacuum, or in any other atmosphere.

The present invention provides pure quartz glass from powdery pure amorphous silica without contamination with impurity. Therefore, no treatment is required for impurity removal in the present invention. Since the amorphous silica is converted during the sintering into the crystal of cristobalite structure, water is removed to result in the low OH group content of not more than 20 ppm, and the resulting glass has a structure approximate to crystal. Accordingly, the viscosity of the quartz glass at a high temperature is improved, and the pure quartz glass of the present invention has a viscosity of 10 The present invention is described below in more detail by reference to Examples without limiting the invention thereto.

The analysis and the measurements are conducted as described below. The impurities in the latter hydrofluoric acid solution is analyzed by means of ICP-mass apparatus atomic absorption-mass spectrometer: Model TQ-2, Fison Instrument Co. The viscosity is derived according to a beam bending method by heating a piece of glass and measuring the deformation thereof.

Then the silica was washed twice, each with 10 times amount of pure water. The above extraction-washing operation was conducted repeatedly five times. Water was removed therefrom, and the powdery silica was dried. The resulting molded article had a bulk density of 1. Then the electric furnace was cooled, and the specimen was taken out.

The obtained glass had very few gas bubbles and had high transparency. The starting powdery amorphous silica was molded into an article in the same manner as in Example 1. The molded article was sintered and fused in the same manner as in Example 1. The calcined powdery silica was pulverized by means of a ball mill made of quartz to have an average diameter of 0.

The powdery amorphous silica was molded with a mold tool of the same material as that in Example 1 into a molded article of mm in diameter and 10 mm in thickness. The molded article had a bulk density of 1. As shown in Table 1, transparent silica glass containing less impurities like alkalis and having high viscosity at high temperature could be produced from powdery amorphous silica of high purity by molding, heating, crystallizing, and fusing it.

The starting powdery amorphous silica prepared in Example 1, without molding, was heat-treated for conversion into cristobalite crystal structure. The heat-treated powdery matter was subjected to molding process. However, the molding was not successful.

Therefore, the subsequent steps of molding, sintering, and fusion could not be conducted. As described in detail, the quartz glass prepared according to the present invention is transparent glass having high purity and having excellent characteristics in high temperature viscosity. The process of the present invention provides transparent quartz glass of high purity at a low cost.

Effective date : Year of fee payment : 4. Year of fee payment : 8. Year of fee payment : Pure transparent quartz glass is provided by molding powdery amorphous silica into an article, converting the molded powdery amorphous silica into crystalline silica of high-temperature type cristobalite structure, and then fusing the crystalline silica, the quartz glass containing impurities respectively at a content of not higher than 1 ppm, and an OH group at a content of not higher than 20 ppm, and having a viscosity of 10 The quartz glass is transparent and has high purity, and is excellent in high temperature viscosity characteristics.

The quartz glass can be produced at a low cost. Field of the Invention The present invention relates to transparent quartz glass of high purity produced by molding powdery amorphous silica, and sintering and fusing the molded article of amorphous silica.

The present invention also relates to a process for producing the pure transparent quartz glass. Description of the Related Art Conventionally, transparent quartz glass is produced by a process of melting powdery quartz crystal in vacuo in a furnace, a process of melting powdery quartz crystal by oxyhydrogen flame, or a like process.

Preparation of Starting Powdery Material The starting powdery material, namely powdery amorphous silica, may be prepared by any method which is capable of giving amorphous silica in high purity. Molding of Powdery Silica The resulting powdery silica is molded by press-molding by use of a mold tool, slip cast molding in which a powder-containing slurry is poured into a gypsum or plastic mold tool, and the slurry is solidified therein, or a like molding method. Sintering and Conversion of Molded Amorphous Silica The aforementioned molded article is heated to crystallize the constituting powdery amorphous silica to convert it into powdery high-temperature type cristobalite and to sinter it.

Fusion of Crystal The crystalline matter obtained by the above conversion is further heated to a higher temperature to fuse the crystal into glass. Molding of Starting Powdery Amorphous Silica The starting powdery amorphous silica was molded into an article in the same manner as in Example 1.

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The present invention relates to a method of manufacturing a silica powder by a sol-gel method, wherein A suspension in water of a first material based on silica, gelled suspension, the gel is dried obtained and fractionated the dry gel into a powder comprised of silica granules. It also relates to the use of such a powder for producing an optical fiber preform. A silica powder manufacturing process is known in particular from French patent FR-B The suspension is conducted as exemplified in said patent, substantially free from chlorine particles. Indeed, the production of silica particles is performed by oxidation, generally in the presence of hydrogen and oxygen, silicon chloride SiCl 4. The particles obtained directly after such fabrication are described as "acids" since they comprise chlorine in the form of hydrochloric acid.

US5665133A - Process for production of pure transparent quartz - Google Patents

Heretofore, a crucible, a jig or the like which is useful for production of a semiconductor single crystal, has been produced by melting a natural quartz powder obtained by pulverizing natural quartz. However, natural quartz contains various metal impurities even when it is of good quality, and, as such, has not been fully satisfactory from the viewpoint of the purity. Especially for a high purity single crystal required along with the progress in high performance in the semiconductor industry, inclusion of metal impurities adversely affects the performance of a semiconductor, and a crucible, a jig or the like which is feared to bring about inclusion of metal impurities or the like, can not be used. Accordingly, for glass products to be used in the semiconductor industry or the like, a very strict control is carried out with respect to their quality. Such high purity glass is produced mainly by e. However, the method 1 has a problem that there is a limit in reduction of the content of minor impurities, and the method 2 has a problem that the production cost is extremely high. By the method 3 wherein a silica gel, particularly a silica gel powder prepared by using a silicon alkoxide as the staring material, is used, it is possible to obtain a synthetic quartz glass having a low content of minor impurities inexpensively as compared with the method 2 , but this method 3 does not necessarily satisfy the required level.

US5643347A - Process for manufacture of silica granules - Google Patents

The present invention relates to transparent quartz glass of high purity produced by molding powdery amorphous silica, and sintering and fusing the molded article of amorphous silica. Particularly, the present invention relates to pure transparent quartz glass which contains less impurities like alkalis respectively at a content of not more than 1 ppm, contains less water, and has high heat resistance, thereby being useful for a photomask and other uses in semiconductor production. Conventionally, transparent quartz glass is produced by a process of melting powdery quartz crystal in vacuo in a furnace, a process of melting powdery quartz crystal by oxyhydrogen flame, or a like process. However, the conventional processes employ powdered natural quartz crystal, whereby the resulting quartz glass is not satisfactory to meet the severe requirements for high purity for highly integrated LSI, even though the quartz glass has high heat resistance. Although the powdered natural quartz crystal is treated for high purity, not all of the undesired impurities can be removed to respective contents of not higher than 1 ppm at the moment. To obtain higher purity of the quartz glass, processes are investigated, including a VAD process which sinters deposited synthetic amorphous silica, and a sol-gel process which sinters powdery amorphous silica obtained by hydrolysis of a silicic acid alkoxide.

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This application is a Continuation-in Part of U. This application also claims the benefit of U. Provisional Patent Application No. In glass applications such as liquid crystal panels, optical communication devices for instance optical filters and optical switches, recording medium, halogen and High Intensity Discharge HID lamps etc. High-energy laser systems employ multiple large pieces of optical quality glass, sometimes thousands of large size laser glass pieces, and it is imperative for the pieces to have consistent optical quality. Glass compositions, similarly to fused quartz compositions, are characterized by a few fundamental properties affecting the manufacturing of or the properties of products employing the compositions, i. The effect of OH hydroxyl on viscosity of glass or quartz is widely known. As seen from the Figure, viscosity of glass drastically drops with increased hydroxyl concentration. If glass or quartz has batch-to-batch or within-batch variations in the OH level, it will result in inconsistent manufacturability and product quality. From a lamp manufacturer's perspective, variations in the glass properties impact the yields of the high-speed lamp production lines, requiring undesirable and frequent adjustments made to the equipment to account for the variations in the glass properties.

CROSS-REFERENCE TO RELATED APPLICATION

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The use of hazardous or toxic waste to make a glass material a useful product is provided for herein, however, vitrification of hazardous waste for purposes of containment is excluded, see References to Other Classes below. Included within the scope of the class definition are:.

The invention relates to a thermal processing jig for use in manufacturing semiconductor devices and a method of manufacturing such jig. As integrated circuit semiconductor devices acquire higher and higher circuit densities, extremely clean manufacturing environmental conditions are required to ensure that the semiconductor devices are free of contamination of impurity materials that cause imperfection and deterioration of the devices if introduced during manufacture of the devices. Such impurity metals for example include Fe, Cu, Cr, Ni, etc. Accordingly, jigs for use in the thermal processing of semiconductor wafers must be made from clean or pure materials, so that the jigs will not emit impurity materials onto wafers while the wafers are exposed to the jigs at high temperatures. Thus, in the thermal processing of a semiconductor wafer or substrate for growing a layer on the surface thereof for example, it is customary to use jigs made from high purity quartz SiO 2 or high purity silicon carbide SiC which contains only negligible amount of impurity metals. In the processes of growing a layer on the semiconductor wafer and in the heat treatment of the wafers, a furnace tube is often utilized, which consists of a quartz tube and a heater wound on the exterior of the quartz tube. Such a jig for the heat treatment is called a wafer boat. Conventionally, such a furnace tube and a wafer boat as mentioned above are made from quartz since quartz is relatively easy to fabricate and not too expensive.

Sep 9, - Pure transparent quartz glass is provided by molding powdery amorphous into an article, converting the molded powdery amorphous silica in a vacuum . of production thereof and selection of the produced powdery matter.

BACKGROUND OF THE INVENTION

Glass materials are often used in pharmaceutical packaging. Because of this, extractable substances e. Glass particle generation due to delamination is one of the major concerns in pharmaceutical packaging industries when Type I and Type II glasses are used as the container for pharmaceutical products. Delamination occurs when top layers of a glass separate at a scale that is barely visible or invisible to the naked eyes as shown in FIG. The particles become suspended in drug solutions, posing a serious risk to the consumer. Glasses without chemical modifiers e. Thus, such glasses have generally not been used to manufacture pharmaceutical packaging. Providing coated articles, however, are cumbersome and expensive and, therefore, not widely accepted in the pharmaceutical packaging market.

US5082484A - Apparatus for making quartz glass crucibles - Google Patents

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The invention pertains to a process for the production of silica granulate by mixing silicic acid powder with a liquid. Silica powders can be produced by means of gas-phase reactions such as by the hydrolysis of silicon halides or organic silicon compounds.

Quartz glass crucibles are used to hold molten silicon during the growing of a silicon crystal rod. Such quartz glass crucibles are manufactured by an apparatus having a rotation table which reciprocally moves between a feeding and shaping station and a heating and fusing station. A predetermined volume of grain material is fed into one of the rotation crucibles and shaped by a shaping means so as to form a shaped body therein at the feeding and shaping station, while the shaped body in the other rotation crucible is heated and fused so as to form a quartz glass crucible therein at the heating and fusing station.

The invention relates to methods for producing high-density ceramic materials based on quartz glass - quartz ceramics with open porosity close to zero. Such material will find wide application for products operating in difficult thermal and climatic conditions. Currently, methods for producing quartz ceramics and articles from it for the manufacture of steel pouring glasses and dispensers in metallurgy are well known R.

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  1. Samuzragore

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