A high-quality quartz glass and its preparation method

Abstract

This invention discloses a method for preparing high-quality quartz glass, belonging to the field of quartz glass preparation technology. The method includes a sequentially performed mobile high-temperature pretreatment process, a mobile dehydroxylation process, and a mobile sintering process. By controlling parameters such as the temperature in the high-temperature zone of the sintering furnace, the movement rate of the porous material, and the atmospheric environment, efficient dehydroxylation and dense sintering of the quartz glass are achieved. Each process independently controls the heating and cooling rates, the rising and falling rates of the porous material, and the atmospheric parameters, ultimately obtaining high-quality quartz glass with low hydroxyl content and high density. This invention effectively solves the problems of incomplete dehydroxylation and poor consistency in traditional processes through mobile multi-stage process decoupling and precise parameter coordination, significantly improving product quality and production efficiency, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of synthetic quartz glass manufacturing, specifically to a high-quality quartz glass and its preparation method, particularly applicable to the dehydroxylation sintering preparation technology of extremely low hydroxyl quartz glass. Background Technology

[0002] Ultra-low hydroxyl quartz glass typically refers to quartz glass with a hydroxyl content of less than 1 ppm. Due to its excellent physical and chemical properties, especially its outstanding performance in optics, thermal, and electrical fields, it is widely used in many high-tech fields, including semiconductor lithography, laser optics, fiber optic communication, and aerospace. A few applications require quartz glass that meets several extreme performance indicators, such as ultra-high purity, ultra-low stress birefringence, and extreme optical homogeneity. Ultra-low hydroxyl quartz glass is usually prepared using a two-step method: first, a porous silica body is deposited, followed by high-temperature sintering to achieve vitrification.

[0003] Axial vapor deposition (VAD) or external vapor deposition (OVD) is the core process for the two-step preparation of high-quality quartz glass. The principle involves a high-temperature hydrolysis reaction between an oxyhydrogen flame and silicon-containing raw materials (such as SiCl4, SiHCl3, or D4), generating loose SiO2 particles. These particles are deposited and adhered to the periphery of an axially rotating seed rod or target rod through a "thermophoretic effect," growing along the axial or radial direction of the seed rod to form a porous body composed of submicron-sized SiO2 microparticles. This porous body is then transferred to a dehydroxylation sintering furnace, where it undergoes dehydroxylation and high-temperature vitrification using chlorine-containing gas, ultimately yielding quartz glass with extremely low hydroxyl content.

[0004] Typically, after deposition, the porosity of the porous body varies significantly along its diameter, usually being denser in the center and looser around the edges. During dehydroxylation of the porous body, the different pore sizes lead to varying gas reaction and diffusion rates. After dehydroxylation, the chlorine content inside the quartz glass reaches hundreds to thousands of ppm, with a chlorine concentration difference exceeding 10 ppm / mm between the center and the edges. Although subsequent dechlorination processes using vacuum or oxygen atmospheres can further reduce the chlorine content, they cannot alter the radial gradient distribution of chlorine, resulting in a low-center, high-edge distribution of stress birefringence and optical homogeneity (transmission wavefront). Although chlorine's contribution to the refractive index is much lower than that of transition metals, its concentration gradient can amplify the spatial differences in refractive index caused by uneven annealing temperatures. Experiments show that when the chlorine concentration gradient exceeds 10 ppm / mm, the refractive index homogeneity (Δn) significantly increases. max It may be from ±2×10 -6 Deteriorated to ±5×10 -6 Under the industrial standard of stress birefringence ≤ 5 nm / cm, the chlorine concentration gradient should be less than 5 ppm / mm; otherwise, the local birefringence value may exceed 10 nm / cm.

[0005] Chinese patent application CN114031274 A discloses a method for preparing continuous low-hydroxyl, highly uniform quartz glass, comprising the following steps: placing a silica porous body in a sintering furnace; heating the sintering furnace to a first temperature, introducing a dehydroxylation gas into the sintering furnace to react the hydroxyl groups doped in the silica porous body with halogen elements contained in the dehydroxylation gas to remove the hydroxyl groups; further heating the sintering furnace to a second temperature, continuing to introduce a protective gas into the sintering furnace to remove the halogen elements contained in the dehydroxylation gas; further heating the sintering furnace to the glass transition temperature to vitrify the silica porous body into quartz; cooling the sintering furnace and cooling the quartz until vitrification is complete. This method does not consider the radial gradient distribution of chlorine concentration caused by the non-uniform porosity of the porous body, and the uniformity and stress birefringence of the prepared quartz glass are unlikely to meet the requirements of extreme applications such as ultraviolet lithography machines.

[0006] Chinese patent application CN121181230 A discloses a method for preparing quartz glass for photolithography. The sintering furnace includes an upper high-temperature reaction zone and a middle high-temperature reaction zone. The upper high-temperature reaction zone is located above the middle high-temperature reaction zone and its temperature is 100℃-200℃ lower than that of the middle high-temperature reaction zone. During the sintering process, the silica porous material is first pretreated in the upper high-temperature reaction zone and then enters the middle high-temperature reaction zone for sintering. This preparation method addresses the problems of uniformity and defect control in atmospheric pressure sintering by controlling the dehydration and impurity removal reaction rates, achieving a better uniform distribution. However, the temperature gradient in the sintering furnace used in this method still exists vertically, which easily leads to uneven processing in both the pretreatment and sintering processes, making it difficult to control the final quality consistency of the quartz glass.

[0007] Chinese patent application CN119219316 A discloses an integrated sintering and sinking system and method for preparing photomask quartz substrates. The system develops an integrated sintering-sinking system where a quartz rod deposited via a VAD is driven by a driving mechanism to gradually descend. After sintering and densification in a sintering furnace, it gradually descends into a sinking furnace. The quartz rod, passing through a high-temperature environment from bottom to top, forms molten quartz that spreads out within the sinking mold. The resulting quartz substrate exhibits excellent performance, avoiding the problems of folding and tipping that can occur during sinking due to the large aspect ratio of the VAD-deposited quartz rod, which can lead to issues such as streaks, bubbles, poor uniformity, and high stress in the product. However, this system is complex in structure and difficult to operate, posing a challenge to the stable preparation of high-quality quartz glass.

[0008] Therefore, conventional dehydroxylation sintering processes are insufficient to produce high-quality quartz glass with ultra-low stress birefringence and extreme optical homogeneity. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method for preparing high-quality quartz glass, aiming to solve the problem of excessive radial gradient of chlorine concentration distribution in existing dehydroxylation sintering processes. This invention employs a mobile high-temperature pretreatment, mobile dehydroxylation, and mobile sintering process to achieve a radially uniform distribution of chlorine concentration, ultimately producing high-quality quartz glass with optical uniformity and stress birefringence properties that meet the requirements of high-end applications.

[0010] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0011] A method for preparing high-quality quartz glass includes a sequentially performed mobile high-temperature pretreatment step, a mobile dehydroxylation step, and a mobile sintering step.

[0012] S1. The mobile high-temperature pretreatment process includes the following steps: first, the temperature of the high-temperature zone of the sintering furnace is increased from the initial temperature to the first temperature at a first heating rate; then, the porous material is placed in an inert atmosphere and slowly lowered to the high-temperature zone of the sintering furnace at a first cooling rate until the porous material has completely passed through the high-temperature zone; subsequently, it is slowly raised to the initial position at a first heating rate. S2. The mobile dehydroxylation process includes the following steps: first, the temperature of the high-temperature zone of the sintering furnace is adjusted to the second temperature at a second heating or cooling rate; then, the porous material is placed in a mixed atmosphere of carrier gas and reactant gas and slowly lowered to the starting position at a second cooling rate. The temperature of the sintering furnace is slowly lowered to the high-temperature zone until the porous material has completely passed through the high-temperature zone, and then it is raised to the starting position at the second rising rate; S3, the moving sintering process includes the following steps: first, the temperature of the high-temperature zone of the sintering furnace is raised to the third temperature at the third heating rate, then the porous material is placed in an inert atmosphere and slowly lowered to the high-temperature zone of the sintering furnace at the third lowering rate until the porous material has completely passed through the high-temperature zone and completed vitrification, and then it is raised to the starting position at the third rising rate; S4, after sintering is completed, the temperature of the high-temperature zone of the sintering furnace is lowered to the starting temperature to obtain quartz glass.

[0013] The first heating rate of the mobile high-temperature pretreatment process is 1~10 ℃ / min, with the optimum being 5~10 ℃ / min.

[0014] The first temperature of the mobile high-temperature pretreatment process is 1100℃~1300℃, with the optimal temperature being 1200~1300℃.

[0015] The inert atmosphere of the mobile high-temperature pretreatment process is one or a mixture of Ar, He, and N2, with a flow rate of 1~5 slm (standard liter per minute).

[0016] The first descent rate of the mobile high-temperature pretreatment process is 0.5~2 mm / min, with an optimal rate of 0.5~1 mm / min.

[0017] The first rise rate of the mobile high-temperature pretreatment process is 10~30 mm / min, and the optimum is 10~20 mm / min.

[0018] The second heating or cooling rate of the mobile dehydroxylation process is 1~10 ℃ / min, with the optimum being 1~5 ℃ / min.

[0019] The second temperature of the mobile dehydroxylation process is 1100℃~1300℃, with the optimal temperature being 1100~1200℃.

[0020] The dehydroxylation gas used in the mobile dehydroxylation process is generally a mixture of carrier gas and reactant gas.

[0021] The dehydroxylation mixture in the mobile dehydroxylation process generally uses helium, argon, or nitrogen as the carrier gas, with helium being preferred.

[0022] The dehydroxylation mixture in the mobile dehydroxylation process typically contains F2, Cl2, Br, dichlorothioyl, or CO as the reaction gas.

[0023] The volume ratio of carrier gas to reactant gas in the mobile dehydroxylation process is 30:1 to 10:1.

[0024] The second descent rate of the mobile dehydroxylation process is 1~5 mm / min, with an optimal rate of 1~3 mm / min.

[0025] The second ascent rate of the mobile dehydroxylation process is 10~30 mm / min, with an optimal rate of 10~20 mm / min.

[0026] The third heating rate of the mobile sintering process is 1~10 ℃ / min, with the optimum being 1~5 ℃ / min.

[0027] The third temperature of the mobile sintering process is 1450℃~1550℃, with the optimal temperature being 1500~1550℃.

[0028] The inert atmosphere of the mobile sintering process is one or a mixture of Ar, He, and N2, with a flow rate of 1~5 slm.

[0029] The third descent rate of the mobile sintering process is 1~5 mm / min, with an optimal rate of 3~5 mm / min.

[0030] The third rise rate of the moving sintering process is 10~30 mm / min, with the optimum being 10~20 mm / min.

[0031] The fourth temperature after sintering, i.e. the starting temperature, is generally 1100℃~1200℃, with the optimal temperature being 1100℃~1150℃.

[0032] The high-quality quartz glass prepared by the above method has a radial chlorine concentration gradient ≤ 5 ppm / mm.

[0033] Compared with existing technologies, it has the following advantages:

[0034] (1) Before dehydroxylation, the porous body is subjected to mobile high-temperature pretreatment, which can improve the porosity uniformity of the porous body and is beneficial to improve the uniformity of gas or molecular reaction rate and diffusion rate in the subsequent dehydroxylation or high-temperature sintering process. The chlorine concentration gradient distribution of quartz glass can be optimized from 10 ppm / mm in the traditional process to 5 ppm / mm or even below 3 ppm / mm.

[0035] (2) Whether it is the dehydroxylation process or the high-temperature sintering process, the porous body is moved through the high-temperature zone, which can ensure that all parts of the porous body can pass through the high-temperature zone at a uniform speed, and ensure the uniformity of gas reaction and diffusion rate, thereby improving the consistency and uniformity of the internal quality of quartz glass.

[0036] (3) The three key steps of high temperature pretreatment, dehydroxylation and sintering are controlled independently, which avoids the problem of mutual interference between stages in the traditional process. It is especially beneficial to remove hydroxyl (-OH) step by step and suppress re-contamination, thereby obtaining quartz glass with lower hydroxyl content. Attached Figure Description

[0037] Figure 1 This is a simplified diagram of the mobile pretreatment and dehydroxylation stage of the sintering furnace of the present invention;

[0038] Figure 2 This is a simplified diagram of the high-temperature vitrification stage of the sintering furnace of the present invention;

[0039] Figure 3 The optical uniformity (transmitted wavefront) comparison diagram of the present invention is as follows: 1# - no mobile high-temperature pretreatment process was used, 2# - mobile high-temperature pretreatment process was used.

[0040] Figure 4 The diagram shows a comparison of stress birefringence in this invention. 1# - no mobile high-temperature pretreatment process was used, and 2# - a mobile high-temperature pretreatment process was used.

[0041] In the figure, 1—furnace body; 2—heating element; 3—quartz lining; 4—air inlet; 5—air outlet; 6—lifting and rotating motor; 7—seed rod; 8—loose body; 9—quartz glass. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Please see Figure 1 and Figure 2 The dehydroxylation sintering furnace consists of a furnace body 1, a heating element 2, a quartz liner 3, an air inlet 4, an air outlet 5, and a lifting and rotating motor 6. A loose body 8 with a seed rod 7 is suspended on the lifting and rotating motor 6 and descends at a certain speed. It passes through the high-temperature zone where the heating element 2 is located and finally undergoes high-temperature sintering and vitrification to obtain quartz glass 9.

[0044] Example 1

[0045] The VAD-deposited porous body is transferred into furnace 1 and subjected to a mobile dehydroxylation treatment: the initial temperature of the sintering furnace is 1150℃, and dehydroxylation gas is introduced, with helium as the carrier gas and Cl2 as the reaction gas, and the volume ratio of helium to reaction gas is 25:1; the porous body descends at a rate of 2 mm / min, and after all the porous body has entered the high-temperature zone to complete the dehydroxylation process, the porous body rises to the starting position at an upward rate of 15 mm / min.

[0046] Next, a moving sintering process is carried out: the temperature rate is set to 5 ℃ / min, and the sintering furnace is heated from 1150℃ to 1500℃, and helium gas is introduced; after the temperature reaches 1500℃, the porous material descends at a rate of 4 mm / min. After all the porous material enters the high-temperature zone and completes the sintering process, the quartz glass rises to the starting position at a rate of 10 mm / min.

[0047] After sintering, the temperature is reduced to the initial temperature of 1150℃, the quartz glass 9 is slowly raised, and cooled to room temperature.

[0048] The hydroxyl content of the above-mentioned quartz glass was detected using Fourier transform infrared spectroscopy (FTIR), and the results showed that the hydroxyl concentration was below 0.5 ppm, reaching the detection limit of Fourier transform infrared spectroscopy. The chlorine content distribution of the above-mentioned quartz glass was detected using electron probe microanalysis (EPMA), and the results showed that the radial gradient of chlorine concentration reached 10 ppm / mm.

[0049] Example 2

[0050] The VAD-deposited loose body is transferred into furnace 1 and subjected to mobile high-temperature pretreatment: the first heating rate is 10 °C / min, the first temperature is 1250 °C, helium gas is introduced at a flow rate of 1 slm; after the temperature reaches the first temperature, the loose body slowly descends at a first descent rate of 1 mm / min according to the set program. When all the loose body enters the high-temperature zone and completes the pretreatment process, the loose body rises to the starting position at a first ascent rate of 15 mm / min.

[0051] Next, a mobile dehydroxylation process is performed: the second cooling rate is set to 5 °C / min, so that the sintering furnace is cooled from 1250 °C to the second temperature of 1150 °C. Dehydroxylation gas is introduced, the carrier gas is generally helium, and the reaction gas is Cl2, with a volume ratio of helium to reaction gas of 25:1. After the temperature reaches the second temperature, the loose body descends at a rate of 2 mm / min. When all the loose body enters the high-temperature zone and completes the dehydroxylation process, the loose body rises to the starting position at a second rising rate of 15 mm / min.

[0052] Next, a moving sintering process is carried out: the third cooling rate is set to 5 °C / min, so that the sintering furnace is heated from 1150 °C to the third temperature of 1500 °C, and helium is introduced; after the temperature reaches the third temperature, the porous material descends at a rate of 4 mm / min. When all the porous material enters the high temperature zone and completes the sintering process, the quartz glass rises to the starting position at a third rising rate of 10 mm / min.

[0053] After sintering, the temperature was lowered to the fourth temperature of 1150℃, the quartz glass 9 was slowly raised, and cooled to room temperature.

[0054] The hydroxyl content of the above-mentioned quartz glass was detected using Fourier transform infrared spectroscopy (FTIR), and the results showed that the hydroxyl concentration was below 0.5 ppm, reaching the detection limit of Fourier transform infrared spectroscopy. The chlorine content distribution of the above-mentioned quartz glass was detected using electron probe microanalysis (EPMA), and the results showed that the radial gradient of chlorine concentration decreased to 4.5 ppm / mm.

[0055] Figure 3 and Figure 4 The data are measured data of transmission front and stress birefringence of quartz glass corresponding to Examples 1 (1#) and 2 (2#), respectively. Figure 3 It can be seen that by adopting the mobile high-temperature pretreatment process, the radial distribution gradient in front of the transmitted glass is significantly flattened. After conversion of the transmitted glass data, the optical uniformity values ​​are optimized from 19.93 ppm and 4.11 ppm to 7.35 ppm and 1.65 ppm, respectively; from Figure 4It can be seen that by adopting the mobile high-temperature pretreatment process, the radial distribution gradient of stress birefringence becomes significantly flatter, and the stress birefringence distribution gradient within the φ90 mm and φ40 mm diameters becomes significantly flatter. The stress birefringence value of the φ90 mm diameter decreases from 12.5 nm / cm to less than 2.5 nm / cm.

[0056] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0057] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0058] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-quality quartz glass, characterized in that, Includes the following steps: S1. The mobile high-temperature pretreatment process raises the temperature of the high-temperature zone of the sintering furnace from the starting temperature to the first temperature at the first heating rate. Then, the loose material is placed in an inert atmosphere and slowly lowered to the high-temperature zone of the sintering furnace at the first falling rate until the loose material has completely passed through the high-temperature zone. Then, it slowly rises to the starting position at the first rising rate. S2, Mobile dehydroxylation process: The temperature of the high-temperature zone of the sintering furnace is adjusted to the second temperature according to the second heating or cooling rate. Then, the loose material is placed in a mixed atmosphere of carrier gas and reaction gas and slowly lowered to the high-temperature zone of the sintering furnace according to the second lowering rate until the loose material has completely passed through the high-temperature zone. Then, it is raised to the starting position according to the second rising rate. S3. Moving sintering process: First, the temperature of the high temperature zone of the sintering furnace is raised to the third temperature at the third heating rate. Then, the porous material is placed in an inert atmosphere and slowly lowered to the high temperature zone of the sintering furnace at the third descent rate until the porous material has completely passed through the high temperature zone and completed vitrification. Then, it is raised to the starting position at the third rising rate. S4. After sintering is completed, the temperature of the high-temperature zone of the sintering furnace is reduced to the initial temperature to obtain high-quality quartz glass. The first heating rate is 1~10 °C / min, the first temperature is 1100 °C~1300 °C, the inert atmosphere in step S1 is one or a mixture of Ar, He, and N2, with a flow rate of 1~5 slm, the first descent rate is 0.5~2 mm / min, and the first ascent rate is 10~30 mm / min; the second heating or cooling rate is 1~10 °C / min, the second temperature is 1100 °C~1300 °C, the carrier gas is helium, argon, or nitrogen, the reactant gas is F2, Cl2, Br2, or CO, the volume ratio of the carrier gas to the reactant gas is 30:1~10:1, the second descent rate is 1~5 mm / min, and the second ascent rate is 10~30 mm / min; the third heating rate is 1~10 °C / min. The third temperature is 1450℃~1550℃, the inert atmosphere in step S3 is one or a mixture of Ar, He, and N2, the flow rate is 1~5 slm, the third descent rate is 1~5 mm / min, the third ascent rate is 10~30 mm / min, and the initial temperature is 1100℃~1200℃.

2. The method for preparing high-quality quartz glass according to claim 1, characterized in that, The first heating rate is 5~10 ℃ / min, the first temperature is 1200~1300℃, the first descent rate is 0.5~1 mm / min, and the first rise rate is 10~20 mm / min.

3. The method for preparing high-quality quartz glass according to claim 1, characterized in that, The second heating or cooling rate is 1~5 °C / min, the second temperature is 1100~1200 °C, the carrier gas is helium, the second descent rate is 1~3 mm / min, and the second ascent rate is 10~20 mm / min.

4. The method for preparing high-quality quartz glass according to claim 1, characterized in that, The third heating rate is 1~5 °C / min, the third temperature is 1500~1550 °C, the third descent rate is 3~5 mm / min, and the third rise rate is 10~20 mm / min.

5. The method for preparing high-quality quartz glass according to claim 1, characterized in that, The starting temperature is 1100℃~1150℃.

6. A high-quality quartz glass, characterized in that, It is prepared by any one of claims 1 to 5.

7. The high-quality quartz glass according to claim 6, characterized in that, The radial gradient of chlorine concentration in the quartz glass is ≤5 ppm / mm.

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