Preparation method of high-density opaque quartz glass

Abstract

The invention relates to a preparation method of high-density opaque quartz glass, and belongs to the technical field of quartz glass production. The preparation method comprises the following steps: crushing, pickling and drying natural quartz or quartz glass with the SiO2 content of more than 99.99%, mixing with hafnium oxide powder, putting into a vacuum electric melting furnace, melting quartz sand into a quartz glass hydrothermal solution at the temperature of 1700-1750 DEG C, and cooling to obtain the high-density opaque quartz glass. The interior of the prepared opaque quartz glass is almost free of any pores, and the density can reach a theoretical value of quartz glass density of 2.20-2.21 g / cm < 3 >; the full spectrum transmittance of a 5mm cut slice is less than 1%; the problem that semiconductor devices are polluted in the production process due to the fact that the content of air holes in an existing non-transparent quartz glass production method is too high is solved, and the method is particularly suitable for semiconductor production and use.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing high-density opaque quartz glass, and belongs to the technical field of quartz glass production. BACKGROUND

[0002] Opaque quartz glass is a kind of quartz glass material with low light transmittance. The total spectral transmittance of a 5mm thin sheet of the material can reach <2%, which can effectively block thermal radiation. In addition, the quartz glass material itself has good high-temperature resistance (can withstand 1100℃), and the main chemical component of the quartz glass is SiO2, which will not cause pollution to semiconductor devices such as single crystal silicon wafers (Si element), so opaque quartz glass is often used to make heat shielding devices in the semiconductor industry. Quartz glass is a transparent material in itself. Common opaque quartz glass is a kind of porous quartz glass material, which appears milky white in appearance. When light penetrates, it undergoes repeated refraction, reflection and scattering on the surface of the pores, so that the intensity of the light finally penetrating the quartz glass is reduced to <2%, thereby realizing the function of blocking thermal radiation. Due to the internal porosity, the density of this porous opaque quartz glass material is generally 1.90~2.19g / cm3. The manufacturing process of the porous opaque quartz glass material is usually gas melting process and electric melting process. The gas melting process is to first mix a foaming agent into quartz sand, and then melt the quartz sand at high temperature with a hydrogen-oxygen flame, during which the foaming agent forms bubbles with a diameter >20μm in the quartz glass, obtaining opaque quartz glass. The electric melting process is to crush the quartz glass and press it into a green body, and then sinter it at high temperature in an electric furnace in an atmosphere or certain gas environment to densify it. During the sintering process, a small amount of gas with the same composition as the sintering atmosphere is enclosed inside, forming a porous opaque quartz glass.

[0003] However, this porous opaque quartz glass needs to be cut and processed before actual use, and the pores in it will be exposed on the cross section of the material, forming open pores, and external foreign matter will enter these pores during the processing process and be difficult to completely remove. During the processing of semiconductor devices, these foreign matters will continuously and slowly fall off. Even a very small amount of foreign matter will contaminate the single crystal silicon wafer, resulting in product defects or scrap. On the other hand, when using porous opaque quartz glass as a material for sealing applications, a step of flame polishing is often included, i.e. melting the surface layer of the component with a high-temperature flame to eliminate the open pores on the surface. However, during the acid etching process of semiconductor devices, the closed pores below the surface after flame polishing will be exposed again, and will trap some unwanted debris, dust or other foreign matter, becoming a new source of contamination. SUMMARY

[0004] The present application aims to provide a high-density opaque quartz glass manufacturing method with high density and no air hole generation to solve the problem of excessive air holes in existing opaque quartz glass, which leads to product defects or scrapping, The technical scheme of the present application is: A high-density opaque quartz glass manufacturing method, characterized in that it comprises the following steps: 1) crushing natural quartz or quartz glass with SiO2 content > 99.99% into quartz sand or quartz glass crushing material with particle size of 100-250 μm; after acid washing and drying with acid solution containing hydrogen fluoride in a conventional manner, the quartz sand or quartz glass crushing material is put into a mixer with hafnium oxide powder with particle size of 1-5 μm at a weight ratio of 100:0.5-2, and mixed at a speed of 10-200 revolutions per minute for 24-48 hours to obtain a mixture; 2) putting the mixture into a crucible, placing the crucible in a vacuum electric furnace, then vacuumizing the furnace to an air pressure of 5-10 Pa, and then heating the furnace to 1700-1750 ℃ and keeping the temperature for 12-24 hours until the mixture is completely melted to form a quartz glass melt; during the process, the air pressure in the furnace is kept at 5-10 Pa; 3) stopping heating and keeping the air pressure in the vacuum electric furnace unchanged until the quartz glass is completely cooled to obtain a high-density opaque quartz glass product.

[0005] Invention mechanism: Hafnium oxide is a light-transmitting high-refractive material (light-transmitting range 230-7000 nm, refractive index about 2.0 at a wavelength of 500 nm). Since its melting point is 2758±25 ℃, which is much higher than that of quartz glass and natural quartz, hafnium oxide can stably maintain its phase unchanged during melting, forming a clear HfO2 / SiO2 two-phase interface in the quartz glass. When light passes through the two-phase interface from the SiO2 phase into the HfO2 phase, and from the HfO2 phase into the SiO2 phase, another part of the light is refracted due to the difference in refractive index between the two sides of the interface (refractive index refers to the ratio of the propagation speed of light in vacuum to the propagation speed of light in medium, the refractive index of quartz glass is 1.45-1.46, and the refractive index of hafnium oxide is 2.0-2.2), and another part of the light returns to the original medium and is reflected. Due to the random distribution of the HfO2 / SiO2 two-phase interface in the high-density opaque quartz glass material, the light is scattered when passing through, which macroscopically appears to be scattered, making the material appear opaque and milky white. The more dispersed the hafnium oxide in the quartz glass, the larger the HfO2 / SiO2 two-phase interface area, and the stronger the light scattering effect, and the lower the light transmittance of the high-density opaque quartz glass material.

[0006] To make HfO2 evenly dispersed in quartz glass, the two raw materials need to be mixed thoroughly before melting. The purpose is to make HfO2 powder evenly wrapped around the surface of quartz sand particles and remain in the quartz glass in situ during the subsequent melting process. The dispersion of HfO2 in the product depends on the size of the quartz sand particles. The finer the quartz sand particles, the larger the total surface area, the more HfO2 is dispersed, the larger the total area of the HfO2 / SiO2 two-phase interface, the stronger the scattering when light transmits, the lower the total spectral transmittance of the high-density opaque quartz glass product, and the better the effect of heat radiation isolation. Quartz sand or quartz glass sand with a particle size of <100 μm is easily dissolved and lost by hydrofluoric acid during pickling, so it is not preferred. Quartz sand with a particle size of >250 μm is too coarse, which is not conducive to the dispersion of HfO2, and the product has high transmittance, so it is not preferred. Therefore, the particle size of the quartz sand or quartz glass broken material of the present application is preferably 100-250 μm.

[0007] The ratio of quartz sand and hafnium oxide powder is determined by the particle size of the hafnium oxide powder. When the particle size of the hafnium oxide powder is 1-5 μm, an incorporation of 1% can form enough HfO2 / SiO2 two-phase interface in the quartz glass, so it is preferred. However, if the hafnium oxide powder is too fine, such as 50 nm, it will be difficult to disperse due to particle agglomeration, and the appearance of the product will turn gray-black, so it is not preferred.

[0008] The particle size of the hafnium oxide powder is fine, the surface energy of the particles is high, and it is easy to agglomerate and difficult to disperse. The more hafnium oxide agglomerates in the high-density opaque quartz glass product, the higher the light transmittance of the material. Therefore, fast particle impact speed and long time are needed during mixing to break up most of the hafnium oxide agglomerates. The mixer used in the present application is a planetary rotation mixer. The tank body rotates around the axis while rotating around the shaft, and the inside is lined with polyurethane, Teflon or other wear-resistant organic coating. The lining material is preferably polyurethane. The metal content of the organic material is small. If it is mixed into the quartz sand after wear, it will also decompose and react to generate gas products during the melting process. During the mixing process, the quartz sand and hafnium oxide powder collide at high speed, the agglomerated hafnium oxide powder is broken up and evenly attached to the surface of the quartz sand. During this process, the temperature of the lining material will be too high due to friction, which will cause aging and accelerate wear. Therefore, the mixer of the present application is preferably water-cooled or air-cooled, and the mixing speed is first set to 100-200 rpm for 5-20 min, then the mixing speed is set to 4-10 rpm for 20-60 min to cool down, and this process is repeated, i.e. intermittent high-speed mixing, until the hafnium oxide powder is fully dispersed. If the mixing time is too short or the mixing speed is too slow, there will be more hafnium oxide powder in the form of agglomerates in the product, which will lead to insufficient dispersion and result in high light transmittance of the product. Deionized water can also be added during mixing for wet mixing, but the mixed product needs to be dried, which increases the risk of introducing contamination; the present application preferably uses dry mixing for 24-48 hours.

[0009] The mixture is fed into an electric melting furnace, where the quartz sand is completely melted into quartz glass hydrothermal fluid under a vacuum of 5-10 Pa and a high temperature of 1700-1750℃. The melting time is determined by the total weight of the mixture; the more mixture, the longer the melting time. Melting approximately 100 kg of mixture takes about 24 hours. During melting, the temperature of the mixture needs to exceed its theoretical melting point of 1713℃ to melt. Due to limitations in temperature measurement methods, there is a certain deviation between the displayed temperature of the electric melting furnace and the actual temperature of the raw material being melted. The displayed temperature of the electric melting furnace varies greatly depending on the structure of the furnace, but it is generally within the range of 1700-1750℃. The furnace pressure needs to be maintained at a vacuum of 5-10 Pa during the melting stage. In this stage, the gas-liquid inclusions in the quartz sand vaporize and expand, and are then expelled due to the vacuum environment, thus preventing the formation of bubbles. The lower the gas pressure inside the electric furnace, the less gas is trapped, and the fewer and smaller the bubbles in the product. Therefore, the present invention preferably uses 5-10 Pa.

[0010] The advantages of this invention are: This invention adds hafnium oxide to quartz glass, creating a uniformly distributed interface between the SiO2 and HfO2 phases within the glass. When light passes through, it undergoes repeated refraction, reflection, and scattering at this interface, reducing the intensity of light penetrating the quartz glass and thus achieving opacity and blocking thermal radiation. The high-density opaque quartz glass prepared by this invention contains almost no pores, achieving a density equivalent to the theoretical value of quartz glass density (2.20~2.21 g / cm3). Its full-spectrum transmittance in a 5mm slice is <1%. This invention solves the problem of excessive pore content in existing opaque quartz glass production methods, which leads to contamination of semiconductor devices during production, making it particularly suitable for semiconductor manufacturing needs. Attached Figure Description

[0011] Figure 1 This is the process flow diagram for this application.

[0012] Figure 2 These are microscope images of the high-density opaque quartz glass products described in this application, by [Author Name]. Figure 2 As can be seen, the quartz glass, being transparent, cannot be directly observed and appears as a black background in the photograph. HfO2 is uniformly dispersed in the quartz glass in a three-dimensional white honeycomb pattern. No pores or bubbles are visible through the quartz glass, indicating that the high-density, opaque quartz glass material prepared by the method of this invention is completely dense with zero porosity.

[0013] Figure 3 Microscopic images of products with insufficiently dispersed HfO2 powder, by Figure 3 As can be seen, when the mixture is not fully mixed, some HfO2 will form white clumps in the product because it is not completely dispersed.

[0014] Figure 4 The transmittance curve of the high-density opaque quartz glass product of the present application with a thickness of 5 mm is shown in the following table: Figure 4 It can be seen that the transmittance of the high-density opaque quartz glass product is 0.2-0.5% in the visible light and infrared light wavelength range of 380-3000 nm, which is better than the index requirement of "the spectral transmittance in the wavelength range of 380-3000 nm should be less than 1.0%" in "GB_T_42800-2023 High-purity opaque quartz glass". It shows that the heat radiation isolation performance of the high-density opaque quartz glass material prepared by the method of the present application meets the requirements of opaque quartz glass heat isolation devices in the semiconductor industry.

[0015] Figure 5 The transmittance curves of high-density opaque quartz glass products melted with different amounts of hafnium oxide are shown in the following table: Figure 5 It can be seen that the greater the amount of incorporation, the lower the transmittance of the product. When the incorporation ratio is greater than or equal to 1%, the transmittance of the product hardly changes.

[0016] Figure 6 The transmittance curves of high-density opaque quartz glass products melted with different particle sizes of quartz sand are shown in the following table: Figure 6 It can be seen that the smaller the particle size of the quartz sand, the lower the transmittance of the product.

[0017] Figure 7 The transmittance curves of high-density opaque quartz glass products melted with different mixing speeds of the mixed material are shown in the following table: Figure 7 It can be seen that the higher the speed, the lower the transmittance of the product.

[0018] Figure 8 The transmittance curves of high-density opaque quartz glass products melted with different mixing times of the mixed material are shown in the following table: Figure 8 It can be seen that the longer the mixing time, the lower the transmittance of the product. DETAILED DESCRIPTION Example 1

[0019] The preparation method of the high-density opaque quartz glass comprises the following steps: First, natural quartz with a SiO2 content of >99.99% is crushed into quartz sand with a particle size of 100-150 μm, and is subjected to acid washing and drying with a hydrogen fluoride-containing acid solution in a conventional manner; then the quartz sand and hafnium oxide powder with a particle size of 5 μm are put into a mixer with air cooling at a weight ratio of 100:2. First, high-speed mixing is carried out at 100 revolutions per minute for 20 minutes, and then low-speed mixing is carried out at 10 revolutions per minute for 60 minutes to reduce the temperature. This is repeated, and the mixed material is obtained after mixing for 24 hours. 2kg of the mixture was put into a crucible, and the crucible was placed in a vacuum electric furnace, and then vacuumized to 5 Pa, and then heated to 1700 DEG C to melt the quartz sand into a quartz glass solution, and kept for 12 hours to completely melt the mixture to form a quartz glass melt; the heating was stopped until the quartz glass was completely cooled to obtain high-density opaque quartz glass products with a density of 2.20 g / cm3, and the transmittance of 380 nm-3000 nm was 0.3-0.8%. Example 2

[0020] The quartz glass waste or offcut produced by processing with a SiO2 content of 99.99% was crushed into quartz glass crushed material with a particle size of 180-250 μm; the quartz glass crushed material and hafnium oxide powder with a particle size of 3 μm were put into a mixer with air cooling in a weight ratio of 100:1 after being pickled with an acid solution containing hydrofluoric acid and dried in a conventional manner. First, high-speed mixing was carried out at 150 rpm for 10 min, and then low-speed mixing was carried out at 10 rpm for 30 min to cool down, and the process was repeated, and the mixture was obtained after mixing for 36 hours. 20kg of the mixture was put into a crucible, and the crucible was placed in a vacuum electric furnace, and then vacuumized to 8 Pa, and then heated to 1720 DEG C to melt the mixture into a quartz glass solution, and kept for 18 hours to completely melt the mixture to form a quartz glass melt; the heating was stopped until the quartz glass was completely cooled to obtain high-density opaque quartz glass products with a density of 2.20 g / cm3, and the transmittance of 380 nm-3000 nm was 0.3-0.8%. Example 3

[0021] The preparation method of the high-density opaque quartz glass comprises the following steps: First, natural quartz with a SiO2 content of >99.99% was crushed into quartz sand with a particle size of 250 μm; the quartz sand and hafnium oxide powder with a particle size of 1 μm were put into a mixer with air cooling in a weight ratio of 100:0.5 after being pickled with an acid solution containing hydrofluoric acid and dried in a conventional manner. First, high-speed mixing was carried out at 200 rpm for 5 min, and then low-speed mixing was carried out at 10 rpm for 60 min to cool down, and the process was repeated, and the mixture was obtained after mixing for 48 hours. 100kg of the mixture was put into a crucible, and the crucible was placed in a vacuum electric furnace, and then vacuumized to 10 Pa, and then heated to 1750 DEG C to melt the quartz sand into a quartz glass solution, and kept for 24 hours to completely melt the mixture to form a quartz glass melt; the heating was stopped until the quartz glass was completely cooled to obtain high-density opaque quartz glass products with a density of 2.20 g / cm3, and the transmittance of 380 nm-3000 nm was 0.2-0.7%.

Claims

1. A method of making high density, non-transparent quartz glass, characterized by: It comprises the following steps: 1) crushing natural quartz or quartz glass with SiO2 content >99.99% into quartz sand or quartz glass crushing material with particle size of 100-250 μm; drying after acid pickling with acid liquid containing hydrogen fluoride acid in a conventional manner, then putting the quartz sand or quartz glass crushing material and hafnium oxide powder with particle size of 1-5 μm into a mixer in a proportion of 100:0.5-2 by weight, mixing for 24-48 hours to obtain a mixture; 2) putting the mixture into a crucible, then placing the crucible in a vacuum electric furnace, then vacuumizing to 5-10 Pa of air pressure in the furnace, and melting the quartz sand into quartz glass solution under the condition of 1700-1750 ℃ and heat preservation for 12-24 hours to completely melt the mixture and form a quartz glass melt; 3) stopping heating after melting, keeping the air pressure in the vacuum electric furnace unchanged until the quartz glass is completely cooled to obtain high-density opaque quartz glass finished product.

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