Opaque quartz glass and methods for manufacturing it

Abstract

Opaque quartz glass, characterized in that the average diameter of the bubbles contained therein is 1 µm or less, and the density is 2.16 to 2.19 g / cm³ 3 where the whiteness is 90% or more at a thickness of 10 mm and the reflectance of light with a wavelength of 0.2 to 3 µm is greater than 85% at a thickness of 3 mm, wherein the average diameter of the bubbles is determined by cutting a sample, viewing at least 20 bubbles on the cut surface using a scanning electron microscope, processing the images obtained of the bubbles and measuring the area “A” of each bubble, wherein an average value “D” of the bubbles is determined by the following equation (1): D = ( 4 × A / π ) 1 / 2

Description

Technical field

[0001] The present invention relates to an opaque quartz glass with excellent heat radiation blocking properties and excellent light blocking properties, and to a method for manufacturing it. In particular, the present invention relates to an opaque quartz glass blank that can be applied to components of a semiconductor manufacturing device, to components for optical instruments, or the like, and to a manufacturing method for it. Technical background

[0002] Quartz glass is used for various purposes, such as in lighting equipment, optical components, semiconductor manufacturing equipment, and physical or chemical facilities, because it exhibits excellent light transmission, heat resistance, and chemical resistance. For example, opaque quartz glass with embedded bubbles is used for flanges and core tubes in semiconductor processing equipment because it has excellent heat radiation blocking properties. And because it also has excellent light shielding properties, it can be used in components of optical devices, such as a reflector base material for a projector light source lamp.

[0003] Opaque quartz glass is made white by creating bubbles within it. The shape of these bubbles can be broadly classified as amorphous (i.e., non-spherical) or spherical, depending on the manufacturing method. In the manufacturing process for amorphous bubbles, the average particle size of the bubbles can be easily reduced, and the baked surface of the resulting opaque quartz glass exhibits excellent smoothness. However, if the resulting opaque quartz glass is sintered until the bubbles are almost closed, the density of the bubbles becomes low. Consequently, the whiteness and infrared reflectance of the opaque quartz glass are reduced, leading to the problem of mechanical stress concentration at the bubble's edge and a decrease in the mechanical strength of the opaque quartz glass.

[0004] Opaque quartz glass, composed of perfectly spherical bubbles, exhibits excellent mechanical strength because the bubbles have no edges, preventing stress concentration at their periphery. However, reducing the diameter of the bubbles that make the quartz glass opaque is challenging. Furthermore, the baked surface of opaque quartz glass eventually becomes rough and uneven. When used as a flange in a device, the contact area is insufficient, leading to leakage. Similarly, when used as a reflector base material, light from the lamp can leak, potentially damaging the electronic components within the projector.

[0005] In the manufacturing process for an opaque quartz glass blank in which bubbles are amorphous (non-spherical), a shaped body of amorphous silica powder is heated to a temperature equal to or lower than its melting point, and the heat treatment is then interrupted before complete compaction and partial firing, as described in patent document 1 (JP patent JP 3 394 323 B2). This manufacturing process is not preferred because it is difficult to obtain a large blank using this method, and because the possible size of the opaque quartz glass is limited.

[0006] Patent document 2 (JP patent JP 3 043 032 B2) describes a method for producing an opaque quartz glass blank with spherically shaped bubbles. This method involves adding a foaming agent such as silicon nitride to crystalline or amorphous silicon and heating and melting it with an oxyhydrogen flame. This manufacturing process allows for the production of a large, opaque quartz glass blank. Prior art documents, patent documents [Patent document 1] Japanese patent JP 3 394 323 B2 [Patent document 2] Japanese patent JP 3 043 032 B2 Description of the invention Problem statement

[0007] The present invention is based on the finding that the heat radiation blocking properties, light shielding properties, and the mechanical strength and roughness of the baked surface of a large opaque quartz glass blank are closely related to the average diameter of the bubbles contained therein. The invention provides for an opaque quartz glass with the aforementioned excellent properties, wherein the average diameter of the bubbles is used as a parameter index for obtaining an opaque quartz glass with the aforementioned desirable properties. Problem solving

[0008] The present invention provides for an opaque quartz glass containing bubbles whose mean diameter is controlled to less than 1 µm, thereby preventing stress concentration at the bubble ends and consequently increasing the strength of the opaque quartz glass material. Furthermore, it prevents an increase in surface roughness caused by the firing process of the quartz glass blank. The density of the product is 2.16 to 2.19 g / cm³. 3 , the whiteness at a thickness of 10 mm is 90% or more, the reflectance of light with a wavelength of 0.2 to 3 µm at a thickness of 3 mm is 85% or more, the flexural strength is 75 MPa or more and the surface roughness Ra is 0.5 µm or less.

[0009] Furthermore, the present invention provides a manufacturing process for the opaque quartz glass blank in which a silica powder slurry with a silica powder concentration of 45 to 75 wt% is subjected to wet pulverization by applying bead mill pulverization, ball mill pulverization, vibratory mill pulverization and attritor pulverization or a combination thereof, and then the slurry is subjected to spray-drying granulation to produce substantially spherical, granulated silica particles with a mean particle diameter of 2 to 8 µm, a standard deviation of the particle size of the pulverized powder of 3 to 7 µm and a BET-specific surface area of ​​2 to 9 m². 2 / g to produce. The prepared slurry is then subjected to spray drying to obtain granulated silica particles. The granulated silica particles are then molded and fired.

[0010] The mean diameter of the bubbles in the resulting opaque quartz glass blank is determined as follows.

[0011] First, the opaque quartz glass blank is cut to obtain a sample. Then, using a desktop scanning electron microscope, 20 or more bubbles appearing at the cut surface of the sample are observed, images of the bubbles appearing at the surface are obtained, and the images of the bubbles are processed to obtain the cross-sectional area “A” of each bubble and to calculate the mean “D” according to the following equation (1): D=(4×A / π)1 / 2

[0012] For example, the TM4000 Plus from Hitachi, Ltd. can be used as a scanning electron microscope for measuring the cross-sectional area “A”.

[0013] The whiteness of the opaque quartz glass is measured as the brightness according to JIS Z 8722 (Japanese industry standard), and a Konica Minolta color difference meter (CR-400) is used as the measuring instrument.

[0014] The opaque quartz glass of the present invention is produced as follows. A silica powder slurry, in which silica powder is dispersed in water, is prepared. The slurry is then wet-milled to achieve a mean particle size of the powdered silica powder of 2 to 8 µm, a standard deviation of the particle size of 3 to 7 µm, and a BET-specific surface area of ​​2 to 9 m². 2 / g to obtain. The slurry is subjected to spray drying to obtain granulated silica particles. The granulated silica particles are then press-molded and fired.

[0015] The features of the opaque quartz glass of the present invention are as follows.

[0016] It is essential that the mean diameter of the bubbles should be 1 µm or less. If the mean diameter of the bubbles is greater than 1 µm, the whiteness of the opaque quartz glass will be low and the flexural strength insufficient. Furthermore, the surface roughness of the baked surface will increase.

[0017] The density of the opaque quartz glass is preferably in the range of 2.16 to 2.19 g / cm³. 3 If the density is lower than 2.16 g / cm³ 3 If the density is greater than 2.19 g / cm³, the flexural strength is reduced and insufficient. 3 In this case, the whiteness and reflectance of the opaque quartz glass are reduced, which is not advantageous.

[0018] The method for producing the opaque quartz glass of the present invention is described in greater detail below.

[0019] In the process for producing an opaque quartz glass of the present invention, a slurry of silica powder dispersed in water is wet-pulverized, wherein the average particle size of the pulverized powder is 2 to 8 µm or less, the standard deviation of the particle size of the pulverized powder is 3 to 7 µm, and the BET-specific surface area is 2 to 9 m². 2 / g.

[0020] Furthermore, the opaque quartz glass of the present invention is obtained by melting the granulated powder obtained by subjecting the slurry to a spray-drying granulation process.

[0021] The following sections describe the steps in greater detail. For all processes, it is essential to select suitable equipment to prevent contamination during operation. Metal contamination should be strictly avoided to ensure that the concentration of metal impurities in the opaque quartz glass of the final product is less than 1 ppm. (1) Selection of the raw material for silica powder

[0022] No specific requirements are given regarding the production method for the silica powder; for example, an amorphous silica powder produced by hydrolyzing silicon alkoxide, a silica powder produced by hydrolyzing silicon tetrachloride with an oxygen acid flame, or similar products may be used.

[0023] Alternatively, silica powder produced by pulverizing natural quartz or pyrogenic silicon dioxide can be used.

[0024] The average particle size of the silica powder is preferably 100 µm or less, and better 60 µm or less. If the average particle size is greater than 300 µm, the wet pulverization of the silica powder takes a long time, which reduces productivity and increases production costs, thus being disadvantageous. (2) Preparation of the slurry

[0025] The concentration of the silica powder slurry, in which silica powder is dispersed in water, is 45 to 75 percent by weight, and preferably 60 to 70 percent by weight. If it is greater than 75 percent by weight, the viscosity of the slurry becomes high, and wet pulverization cannot be carried out. If the concentration is less than 45 percent by weight, the amount of water becomes too large, requiring excessive heat for drying, which is disadvantageous because it reduces productivity and increases production costs. (3) Wet pulverization of the slurry

[0026] The silica powder slurry, with its controlled concentration, is subjected to wet milling using one or more different types of beads, selected from quartz glass beads, zirconia beads, silicon carbide beads, or aluminum oxide beads with an average particle size of 0.1 mm to 3 mm. The average particle size of the powdered silica in the slurry is 2 µm to 8 µm. If the average particle size of the powdered silica is greater than 8 µm, the mean diameter of the bubbles in the opaque quartz product becomes quite large. Conversely, if the mean diameter of the silica is less than 2 µm, the viscosity of the slurry becomes high, reducing the productivity of the opaque quartz blank, which is undesirable.

[0027] The standard deviation of the particle size of the powdered silica powder is 3 to 7 µm. If the standard deviation is greater than 7 µm, the viscosity of the slurry becomes high, which is disadvantageous because it reduces productivity. If the standard deviation is less than 3 µm, the density of the resulting opaque quartz glass product becomes low.

[0028] The BET-specific surface area of ​​the pulverized powder contained in the slurry after wet pulverization is preferably 2 m². 2 / g or more. In particular, it amounts to 4 m 2 / g or more, preferably wet pulverization is carried out until they reach 6 m 2 / g or more. If the BET-specific surface area is less than 2 m². 2 If the granulation yield is less than / g, the strength of the granulated powder is reduced and the granulated powder collapses, thus reducing the granulation yield.

[0029] If the BET-specific surface area is greater than 9 m² 2 If / g is present, the formability in the compression molding process deteriorates, which is disadvantageous.

[0030] No specific requirements are given regarding the method of wet pulverization of the slurry; for example, bead mill pulverization, ball mill pulverization, vibratory mill pulverization, attritor pulverization, or another method may be used. In particular, bead mill pulverization or a combination of bead mill and ball mill pulverization is preferred. (4) Spray drying granulation

[0031] The prepared silica powder slurry is then spray-dried to obtain a granulated powder that is essentially spherical and has an average particle size of 30 to 200 µm and a water content of 3 percent by weight or less.

[0032] If the average particle size of the granulated powder is less than 30 µm, the powder will dissipate during the compression molding process, reducing the yield. If the average particle size is greater than 200 µm, the compression molding process will not function correctly. And if the water content is greater than 3% by weight, the fluidity of the granulated powder will be reduced, resulting in poor uniformity of the molded products, which is detrimental. (5) Pressing and firing the granulated silica powder

[0033] An opaque quartz glass blank can be obtained by compression molding. The resulting granulated silica powder is formed into a desired shape and subjected to firing. The pressure applied during compression molding is preferably 10 to 300 MPa. If it is less than 10 MPa, the molded product simply collapses, resulting in a low yield from the molding process. If the applied pressure is greater than 300 MPa, a large-scale production line is required, which reduces productivity and increases manufacturing costs, thus being disadvantageous.

[0034] The resulting shaped product is baked by atmospheric baking and / or vacuum baking. The maximum baking temperature is between 1300°C and 1500°C, preferably between 1350°C and 1450°C, and even better between 1380°C and 1430°C.

[0035] If the baking temperature is too high, the whiteness and reflectance will be low. Conversely, if the baking temperature is too low, the density and flexural strength of the opaque quartz glass product will be reduced.

[0036] The opaque quartz glass blank produced by the process described above is processed to obtain desired products using processing machines such as band saws, wire saws or core drills. (6) Purity of the opaque quartz glass obtained

[0037] The purity of the resulting opaque quartz glass can be controlled by selecting the quality of the silica powder used as raw material. With the exception of the components of the beads used in the pulverizing medium, the purity of the product is almost identical to that of the raw silica powder. Advantages of the invention

[0038] The opaque quartz glass blank of the present invention exhibits excellent heat radiation blocking and excellent light blocking properties and can be used, in particular, for various core tubes, auxiliary components, and glass bells used in semiconductor manufacturing, for example, for processing silicon wafers. It can also be used as a material for a core tube, a flange, a thermal insulation fin, a crucible for melting silicon, and the like. Furthermore, it can be used as a reflector base material for a light source lamp of a projector in an optical device. Preferred embodiment of the invention

[0039] The present invention will now be described by means of examples, although the present invention is not limited to these examples.

[0040] A desktop scanning electron microscope used as a measuring instrument for the average particle size of the bubbles is the “TM4000 Plus” from Hitachi, Ltd. And a color difference meter used for measuring whiteness is the “CR-400” from Konica Minolta. (Examples 1-3)

[0041] A slurry in which silica powder is dispersed in water at a concentration of 45 to 75 wt% is subjected to wet pulverization, which is bead mill pulverization, ball mill pulverization, vibratory mill pulverization, attritor pulverization, or a combination thereof, to achieve an average particle size of 2–8 µm, a standard deviation of the particle size of the pulverized powder of 3–7 µm, and a BET-specific surface area of ​​solids contained in the slurry of 2–9 m². 2 to obtain / g.

[0042] Spray drying and granulation is carried out to obtain a silica powder with an average particle size of 30 to 200 µm and a water content of 3% by weight or less. The granulated silica powder is then press-molded and fired to produce an opaque quartz glass blank.

[0043] The properties of the resulting opaque quartz glass are given in Table 1. The average diameter of the bubbles in the opaque quartz glass is 1 µm or less, and the density is 2.16–2.19 g / cm³. 3 , the whiteness at a thickness of 10 mm is 90% or more, the reflectance of light with a wavelength of 0.2-3 µm is 85% or more, the flexural strength is 75 MPa or more and the surface roughness Ra of the baked area is 0.5 µm or less.

[0044] The weight of the resulting opaque quartz glass blank is 70 kg, and the bubbles of the opaque quartz glass blank can be determined by visual observation to be evenly distributed, which is also aesthetically pleasing. (Comparative example 1)

[0045] A slurry in which silica powder is dispersed in water at a concentration of 45 to 75 wt% is subjected to wet pulverization, which may be bead mill pulverization, ball mill pulverization, vibratory mill pulverization, attritor pulverization, or a combination thereof, to achieve an average particle size of 9 µm, a standard deviation of the particle size of the pulverized powder of 3–7 µm, and a BET-specific surface area of ​​solids in the slurry of 2–9 m². 2 to obtain / g.

[0046] Spray-drying granulation is carried out to obtain a silica powder with an average particle size of 30 to 200 µm and a water content of 3% by weight or less. The granulated silica powder is then press-molded and fired to produce an opaque quartz glass blank containing air bubbles with a mean diameter of 2 µm and a density of 2.16–2.19 g / cm³. 3 to obtain.

[0047] The whiteness at a thickness of 10 mm is 83%, which is below the lower limit of 90% of the present invention. The reflectance of light with a wavelength of 0.2 to 3 µm at a thickness of 3 mm is 50%, which is below the lower limit of 80% of the present invention. The flexural strength is 67 MPa, and the surface roughness Ra of the baked surface is 1.5 µm, which is above the upper limit of the present invention. (Comparative example 2)

[0048] A slurry in which silica powder is dispersed in water at 45 to 75 wt% is subjected to wet pulverization to achieve an average particle size of 2-8 µm, a standard deviation of the particle size of the pulverized powder of 2 µm, and a BET-specific surface area of ​​solids obtained in the slurry of 2-9 m². 2 / g to obtain. After wet pulverization by bead mill pulverization, ball mill pulverization, vibratory mill pulverization, attritor pulverization or a combination thereof, spray drying granulation is carried out, the average being essentially spherical.

[0049] Granulated powder with a particle size of 30 to 200 µm and a water content of 3% by weight or less is obtained and fired after compression molding. The measurement results given in Table 1 show that the average particle size of the bubbles in the quartz glass is 0.9 µm, and the density is 2.10 g / cm³. 3 The whiteness is 92% at a thickness of 10 mm, the reflectance of light with a wavelength of 0.2 to 3 µm is 62% at a thickness of 2 mm, and the flexural strength is 65 MPa. The surface roughness Ra of the baked surface is 0.8 µm, which is above the upper limit of 0.5 µm of the present invention, meaning that the flatness is insufficient. (Comparative example 3)

[0050] A slurry in which silica powder is dispersed in water at 45 to 75% by weight has an average particle size of 2 to 8 µm, a standard deviation of the particle size of the pulverized powder of 3 to 7 µm, and a BET-specific surface area of ​​solids contained in the slurry of 2 to 9 m². 2 / g. After wet pulverization by bead mill pulverization, ball mill pulverization, vibratory mill pulverization or attritor pulverization, spray drying granulation is carried out to obtain an essentially spherical shape.

[0051] A granulated powder with an average particle size of 30 to 200 µm and a water content of 3 wt% or less was press-molded and then fired at 1510°C to obtain an opaque quartz glass with the properties of Table 1.

[0052] The average particle size of the bubbles in the obtained opaque quartz glass is 0.8 µm, and the density is 2.20 g / cm³. 3 The flexural strength is 80 MPa, the surface roughness Ra of the baked surface is 0.5 µm, the whiteness at a thickness of 10 mm is 79%, and the reflectance of light with a wavelength of 0.2 µm to 3 µm at a thickness of 2 mm is 40%. Table 1 Average diameter of bubbles (µm) Density (g / cm³) 3 ) Reflectance (%) White (%) Three-point bending strength (MPa) Roughness of the baked surface (µm) Ra (µm) Rmax Example 1 1,0 2,17 86 90 80 0,5 0,6 Example 2 0,9 2,19 87 91 78 0,4 0,5 Example 3 0,8 2,16 88 93 85 0,4 0,5 Comparative example 1 2,0 2,18 50 83 67 1,5 3,0 Comparative example 2 0,9 2,10 62 92 65 0,8 1,5 Comparative example 3 0,8 2,20 40 79 80 0,5 0,6 Industrial applicability

[0053] The opaque quartz glass blank according to the present invention is a large opaque quartz glass blank with excellent heat radiation shielding properties and excellent light blocking properties, wherein the baked surface is smooth and has a low roughness Ra. The opaque quartz glass can be used in various industrial fields and, in particular, in components of semiconductor manufacturing machines and optical devices.

Claims

[1] Opaque quartz glass, characterized by that the average diameter of the bubbles contained therein is 1 µm or less, the density 2.16 to 2.19 g / cm 3 the whiteness at a thickness of 10 mm is 90% or more, and the reflectance of light with a wavelength of 0.2 to 3 µm at a thickness of 3 mm is over 85%, wherein the average diameter of the bubbles is determined by cutting a sample, observing at least 20 bubbles on the cut surface using a scanning electron microscope, processing obtained images of the bubbles, and measuring the area "A" of each bubble, wherein an average value "D" of the bubbles is determined by the following equation (1): D=(4×A / π)1 / 2 [2] Opaque quartz glass according to claim 1, wherein the flexural strength is equal to or greater than 75 MPa. [3] Opaque quartz glass according to claim 1 or 2, wherein the surface roughness Ra of the baked surface is equal to or less than 0.5 µm. [4] Opaque quartz glass according to any one of claims 1 to 3, wherein the proportion of each metal impurity is less than 1 ppm. [5] A method for producing the opaque quartz glass according to claims 1 to 4, comprising the steps of preparing a silica powder slurry having a silica powder concentration of 45 to 75 wt% and subjecting the slurry to wet pulverization by applying bead mill pulverization, ball mill pulverization, vibration mill pulverization and attritor pulverization or a combination of these, the slurry then being subjected to spray-dry granulation to obtain substantially spherical granulated silica particles having an average particle diameter of 2 to 8 µm, a standard deviation of the particle size of the pulverized powder of 3 to 7 µm and a BET specific surface area of ​​2 to 9 m 2 / g, the prepared slurry is subjected to spray drying to obtain granulated silica particles, and the granulated silica particles are press-molded and fired. [6] A method for producing the opaque quartz glass according to claim 5, wherein one or more beads for wet grinding are selected from quartz glass beads, zirconium beads, silicon carbide beads and alumina beads having an average particle size of 0.1-3 mm.