Low-hydroxyl defect-free quartz glass and preparation method thereof
By combining flame hydrolysis and vacuum dehydration heat treatment with hydrogen-loaded heat treatment, a defect-free quartz glass with low hydroxyl content was prepared, solving the problem of reduced transmittance and resolution in the existing technology and realizing the application of high-purity quartz glass in deep ultraviolet lithography equipment.
Patent Information
- Application Number
- CN202511914135.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-18
- Publication Date
- 2026-03-06
AI Technical Summary
Existing technologies make it difficult to prepare quartz glass with low hydroxyl content (less than 20 ppm) and no oxygen-deficient structural defects, resulting in decreased transmittance in the deep ultraviolet region and reduced resolution of imaging systems.
Porous silica substrates were prepared by flame hydrolysis. After vacuum dehydration heat treatment and transparent vitrification, they were heat-treated in a hydrogen atmosphere. The pressure and temperature were controlled to eliminate oxygen defects and keep the hydroxyl content below 20 ppm.
A low-hydroxyl, defect-free quartz glass was prepared, which improved the transmittance and resolution of the imaging system in the deep ultraviolet region and is suitable for deep ultraviolet lithography equipment.
Smart Images
Figure CN121609501A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of materials technology, specifically relating to a quartz glass and its preparation method. Background Technology
[0002] High-purity synthetic quartz glass has become the preferred material for lens elements used in high-resolution deep ultraviolet projection lithography equipment in the semiconductor field. Reports indicate that when quartz glass is exposed to linearly polarized deep ultraviolet laser beams, additional birefringence (polarization-induced birefringence) occurs at the exposure center and edges, leading to a reduction in imaging system resolution. Literature studies suggest that quartz materials with low hydroxyl content (less than 20 ppm) exhibit low birefringence damage upon contact with linearly polarized deep ultraviolet beams, making them suitable for immersion lithography systems.
[0003] Synthetic quartz glass with a low hydroxyl concentration of less than 20 ppm is generally manufactured using the soot process. First, a porous soot body is obtained by flame hydrolysis of silicon-containing raw materials, followed by sintering under vacuum to create a transparent glass material. However, quartz glass produced by this method often exhibits oxygen-deficient structural defects. Under 193 nm laser irradiation, these oxygen defects decompose to generate E-color centers, producing an absorption peak at 215 nm, thus reducing the transmittance of the quartz material in the deep ultraviolet region. Therefore, we need to find a method to prepare quartz glass with a low hydroxyl concentration of less than 20 ppm and free from oxygen-deficient structural defects. Summary of the Invention
[0004] The purpose of this invention is to provide a method for preparing low-hydroxyl, defect-free quartz glass, thereby obtaining quartz glass with less than 20 ppm of low hydroxyl content and no oxygen-deficient structural defects.
[0005] To achieve the above objectives, the following technical solution is adopted: A method for preparing low-hydroxyl, defect-free quartz glass includes the following steps: (1) Silicon tetrachloride undergoes flame hydrolysis in an oxyhydrogen flame to obtain a porous silica substrate; (2) The obtained porous silica substrate is subjected to vacuum dehydration heat treatment, heated to a temperature of 1400°C to 1500°C for transparent vitrification treatment, and then subjected to thermoforming and annealing treatment to obtain quartz glass body; (3) The obtained quartz glass is heat-treated for 150h to 500h in an atmosphere containing hydrogen, at a pressure of 0.1Mpa to 1.0Mpa and at a temperature of 520℃ to 680℃ to obtain low-hydroxyl defect-free quartz glass.
[0006] According to the above scheme, step (1) includes providing combustible gas and oxygen to the quartz lamp that forms an oxyhydrogen flame, wherein the combustible gas is one or any mixture of methane, carbon monoxide, and hydrogen.
[0007] According to the above scheme, the density of the porous silica substrate powder obtained in step (1) is 0.5 g / cm³. 3 Up to 1g / cm 3 .
[0008] According to the above scheme, the vacuum dehydration heat treatment in step (2) includes maintaining a temperature of 600℃-1200℃ and a vacuum pressure of less than 5 Pa for 24h to 72h.
[0009] According to the above scheme, the transparent vitrification process in step (2) includes: maintaining the vacuum pressure below 5 Pa, and raising the temperature to 1400°C to 1500°C at a rate of 0.5°C / min to 10°C / min to obtain quartz glass matrix.
[0010] According to the above scheme, the thermoforming process in step (2) includes: loading the quartz glass master material into a high-purity carbon material mold and placing it in a vacuum sintering furnace, maintaining it at a temperature of 1700°C to 1900°C for 0.5h to 2h to obtain a quartz glass block.
[0011] According to the above scheme, the annealing process in step (2) includes: placing the quartz glass block in an atmospheric pressure furnace or a vacuum furnace, maintaining it at a temperature of 1100 to 1250°C for at least 20 hours, and then slowly cooling it down to the strain point temperature for annealing.
[0012] According to the above scheme, the air pressure in step (3) is preferably maintained at 0.5 MPa to 1.0 MPa, the temperature is preferably maintained at 550°C to 650°C, and the time is preferably maintained at 200 to 300 hours.
[0013] The present invention also provides a low-hydroxyl defect-free quartz glass, which is prepared by the above-described method for preparing low-hydroxyl defect-free quartz glass, wherein the hydroxyl concentration of the low-hydroxyl defect-free quartz glass is less than 20 ppm.
[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The soot method is a conventional method for preparing low-hydroxyl quartz glass. While vacuum dehydroxylation reduces the hydroxyl content, it inevitably creates internal oxygen-deficient defects. It is well known that the presence of hydrogen molecules in quartz glass is essential, significantly improving its resistance to damage from 193 nm and 248 nm excimer laser irradiation. The researchers discovered that during high-temperature hydrogen heat treatment, hydrogen molecules can react with oxygen defects in the following way: H₂+ -Si-Si- → 2 Si-H, eliminating oxygen defects. However, excessively high temperatures can also lead to the following reaction: H₂+ -Si-O-Si- → Si-OH + SiH, increasing the hydroxyl content. This invention addresses the problem of oxygen defects in quartz glass prepared by the soot method by developing a hydrogen-loaded heat treatment method that not only eliminates oxygen defects in the quartz glass but also reduces the hydroxyl content to <20 ppm. Attached Figure Description
[0015] Figure 1 Fluorescence test pattern of the quartz glass obtained in Example 1.
[0016] Figure 2 Fluorescence test pattern of the quartz glass obtained in Example 2.
[0017] Figure 3 Fluorescence test pattern of the quartz glass obtained in Comparative Example 1.
[0018] Figure 4 Fluorescence test pattern of the quartz glass obtained in Comparative Example 2.
[0019] Figure 5 Fluorescence test pattern of the quartz glass obtained in Comparative Example 3.
[0020] Figure 6 Fluorescence test pattern of the quartz glass obtained in Comparative Example 4. Detailed Implementation
[0021] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.
[0022] A specific embodiment provides a method for preparing low-hydroxyl, defect-free quartz glass, comprising the following steps: (1) Silicon tetrachloride undergoes flame hydrolysis in an oxyhydrogen flame to obtain a porous silica substrate; alternatively, providing combustible gas and oxygen to a quartz lamp can form an oxyhydrogen flame, wherein the combustible gas can be one or any mixture of methane, carbon monoxide, and hydrogen; the final density is 0.5 g / cm³ obtained by adjusting the flame hydrolysis process. 3 Up to 1g / cm 3The porous silica-based powder will facilitate subsequent processes. The classic flame hydrolysis method can generate extremely high-purity SiO2 particles, and the reaction in a flame avoids container contamination. The resulting porous, low-density SiO2 powder pack is key to efficient subsequent dehydration and also provides a channel for hydroxyl diffusion.
[0023] (2) The obtained porous silica substrate is subjected to vacuum dehydration heat treatment at a temperature of 600℃-1200℃ and a vacuum pressure of less than 5 Pa for 24h to 72h; the vacuum pressure is maintained below 5 Pa, and the temperature is increased to 1400℃ to 1500℃ at a rate of 0.5℃ / min to 10℃ / min to obtain a transparent vitrification treatment to obtain a quartz glass matrix. Under a continuous high vacuum environment, the porous powder is sintered into a completely dense and transparent quartz glass. The vacuum environment can extract the gas in the sealed bubbles in the final stage of sintering and continue to inhibit the generation of hydroxyl groups.
[0024] Quartz glass matrix is loaded into a high-purity carbon material mold and placed in a vacuum sintering furnace. It is held at 1700℃ to 1900℃ for 0.5h to 2h to thermoform a quartz glass block. In the high-purity graphite mold, the viscosity of the quartz glass matrix is extremely low at this high temperature. Under vacuum and mold pressure, internal bubbles are further eliminated and homogenized.
[0025] Quartz glass blocks are placed in an atmospheric pressure furnace or a vacuum furnace and held at 1100 to 1250°C for at least 20 hours. They are then slowly cooled to the strain point temperature for annealing to obtain the quartz glass body. The quartz glass block formed at high temperature will generate thermal stress inside. Prolonged holding at high temperature relaxes its structure, and extremely slow cooling completely eliminates the thermal stress, resulting in a high-purity, dense quartz glass body with extremely low hydroxyl content and no macroscopic stress.
[0026] (3) The obtained quartz glass is heat-treated for 150 to 500 hours in an atmosphere containing hydrogen, at a pressure of 0.1 MPa to 1.0 MPa, and at a temperature of 520°C to 680°C to obtain low-hydroxyl, defect-free quartz glass. This hydrogen-loaded heat treatment is a key step in determining whether the quartz glass product has defect peaks and the concentration of hydroxyl groups. The above process range ensures that not only are oxygen defects in the quartz glass eliminated, but the hydroxyl content is also <20 ppm. In a more optimized scheme, the pressure is maintained at 0.5 MPa to 1.0 MPa, the temperature at 550°C to 650°C, and the treatment time at 200 to 300 hours. The high-pressure environment increases the concentration of hydrogen in the quartz glass, ensuring uniform and thorough treatment. The temperature of 520°C to 680°C is the optimal window for hydrogen molecules to have a sufficient diffusion coefficient in the quartz glass; if the temperature is too low, diffusion is too slow and takes a very long time; if the temperature is too high, it may lead to changes in the glass structure and an increase in the hydroxyl content. The processing time of 200 to 300 hours is to allow hydrogen sufficient time to diffuse throughout the entire glass body (especially for large samples) to ensure that all defects are eliminated by the reaction.
[0027] In this specific implementation, an infrared spectrophotometer is used to calculate and measure the hydroxyl content from the intensity of the OH stretching vibration band at 2.7 micrometers. The method for determining the presence of anoxic defects is as follows: a fluorescence spectrophotometer manufactured by HORIBA Scientific, specifically the FluoroMaX_PLUS, is used with a 248nm excitation source. Absorption peaks at 280nm to 300nm and 560nm to 600nm indicate the presence of anoxic defects.
[0028] Unless otherwise specified, all raw materials used in the specific implementation methods were obtained through commercial purchase.
[0029] Example 1 Silicon tetrachloride undergoes flame hydrolysis in an oxyhydrogen flame, resulting in silica microparticles that deposit on the target material, forming a structure with a density of 0.6 g / cm³. 3 A porous silica substrate was prepared. After vacuum dehydration heat treatment at 1100℃ and 2 Pa for 48 hours, the material was then heated to 1500℃ for vitrification to obtain a quartz glass matrix. The obtained quartz glass matrix was then placed in a high-purity graphite mold and heated to 1800℃ in an argon atmosphere in a vacuum furnace to obtain a cylindrical synthetic quartz block. Annealing was performed in an atmospheric pressure furnace, holding at 1200℃ for 48 hours, then slowly cooling to 1000℃, followed by rapid cooling to room temperature. The quartz glass block was then placed in a pressure vessel under a pure hydrogen atmosphere and heat-treated at 0.5 MPa and 600℃ for 200 hours.
[0030] A 20mm*20mm*50mm quadrangular prism sample was cut from the obtained synthetic quartz glass for fluorescence and hydroxyl concentration testing. The fluorescence results are as follows: Figure 1 As shown, there are no defect peaks and the hydroxyl concentration is 17 ppm, which is suitable for use in deep ultraviolet lithography.
[0031] Example 2 Silicon tetrachloride undergoes flame hydrolysis in an oxyhydrogen flame, resulting in silica microparticles that deposit on the target material, forming a structure with a density of 0.7 g / cm³. 3 A porous silica substrate was prepared. After vacuum dehydration heat treatment at 1100℃ and 2 Pa for 72 hours, the material was then heated to 1500℃ for vitrification to obtain a quartz glass matrix. The obtained quartz glass matrix was then placed in a high-purity graphite mold and heated to 1800℃ in an argon atmosphere in a vacuum furnace to obtain a cylindrical synthetic quartz block. Annealing was performed in an atmospheric pressure furnace, holding at 1200℃ for 48 hours, then slowly cooling to 1000℃, followed by rapid cooling to room temperature. The quartz glass block was then placed in a pressure vessel under a pure hydrogen atmosphere and heat-treated at 0.5 MPa and 600℃ for 300 hours.
[0032] A 20mm*20mm*50mm quadrangular prism sample was cut from the obtained synthetic quartz glass for fluorescence and hydroxyl concentration testing. The fluorescence results are as follows: Figure 2 As shown, there are no defect peaks and the hydroxyl concentration is 15 ppm, which can be used in the field of deep ultraviolet lithography.
[0033] Comparative Example 1 Repeat Example 1, with the heat treatment atmosphere of the resulting quartz glass being pure nitrogen, without hydrogen; everything else remains unchanged.
[0034] Its fluorescence results are as follows Figure 3 As shown, there are obvious oxygen defect peaks at 290nm and 580nm. Although the hydroxyl concentration is 17ppm, it cannot be used in the field of deep ultraviolet lithography.
[0035] Comparative Example 2 Repeat Example 1, but reduce the hydrogen-loaded heat treatment temperature of the resulting quartz glass to 500°C; all other conditions remain unchanged.
[0036] Its fluorescence results are as follows Figure 4 As shown, compared to Comparative Example 1, the intensity reduction of oxygen defect peaks at 290 nm and 580 nm is not significant, and defects still exist in large quantities, making them unsuitable for deep ultraviolet lithography. Comparative Example 3 Repeat Example 1, but reduce the hydrogen-loaded heat treatment time of the resulting quartz glass to 100 h; the rest remain unchanged.
[0037] Its fluorescence results are as follows Figure 5 As shown, compared to Comparative Examples 1 and 2, the oxygen defect peak intensities at 290 nm and 580 nm are significantly reduced, but the defects still exist. This indicates that a short heat treatment time cannot completely eliminate oxygen defects, making it unsuitable for deep ultraviolet lithography. Comparative Example 4 Repeat Example 1, but increase the hydrogen-loaded heat treatment temperature of the resulting quartz glass to 700°C; all other conditions remain unchanged.
[0038] Its fluorescence results are as follows Figure 6 As shown, there are no oxygen defect peaks, but its hydroxyl concentration is increased to 30 ppm, making it unsuitable for use in deep ultraviolet lithography.
[0039] The main process parameters and product characterization of specific embodiments and comparative examples are shown in Table 1.
[0040] Table 1
[0041] As can be seen from the characterization data in Table 1, in Example 2, the hydroxyl concentration did not increase after the hydrogen-loaded heat treatment time was increased to 300 h.
[0042] In Comparative Example 1, the hydroxyl concentration did not change after using a nitrogen atmosphere, but the oxygen defects could not be eliminated. This is because the lack of hydrogen molecules involved in eliminating oxygen defects in the quartz glass is a significant factor.
[0043] In Comparative Example 2, the hydrogen-carrying heat treatment was carried out at 500℃, but the oxygen defects in the quartz glass were not eliminated. This is because the reaction between H2 and oxygen defects is limited by its own chemical reaction kinetics; at too low a temperature, the oxygen defects hardly react. In Comparative Example 3, the hydrogen-carrying heat treatment was 100 h, and the oxygen defects in the quartz glass were not completely eliminated. This is because the entire process was limited by the speed of hydrogen diffusion, the treatment time was short, the concentration of central hydrogen molecules was low, and the oxygen defects were not completely reacted.
[0044] In Comparative Example 4, the hydrogen-carrying heat treatment was carried out at 700℃, which completely eliminated the oxygen defects in the quartz glass. However, the hydroxyl concentration increased significantly to 30ppm. This was because the temperature was too high, and H2 reacted with the unstable -Si-O-Si- to generate -OH and -SiH.
Claims
1. A method of producing low-hydroxy, defect-free quartz glass, characterized by, The method comprises the following steps: (1) flame hydrolysis of silicon tetrachloride in a hydrogen-oxygen flame to obtain a porous silica substrate; (2) vacuum dehydration heat treatment of the obtained porous silica substrate, transparent vitrification treatment at a temperature of 1400-1500 DEG C, then hot forming and annealing treatment to obtain a quartz glass body; (3) heat treatment of the obtained quartz glass body in a hydrogen-containing atmosphere, at a gas pressure of 0.1-1.0 MPa and a temperature of 520-680 DEG C for 150-500 h to obtain low-hydroxyl defect-free quartz glass.
2. The method for preparing low-hydroxyl, defect-free quartz glass as described in claim 1, characterized in that, Step (1) comprises supplying combustible gas and oxygen to a quartz lamp forming a hydrogen-oxygen flame, wherein the combustible gas is one or any mixture of methane, carbon monoxide and hydrogen.
3. The method for preparing low-hydroxyl, defect-free quartz glass as described in claim 1, characterized in that, The powder density of the porous silica substrate obtained in step (1) is 0.5 g / cm 3 to 1 g / cm 3 .
4. The method for preparing low-hydroxyl, defect-free quartz glass as described in claim 1, characterized in that, The vacuum dehydration heat treatment in step (2) comprises maintaining a temperature of 600-1200 DEG C and a vacuum pressure of 5 Pa or less for 24-72 h.
5. The method for preparing low-hydroxyl, defect-free quartz glass as described in claim 1, characterized in that, The transparent vitrification treatment in step (2) comprises maintaining a vacuum pressure of 5 Pa or less and heating to 1400-1500 DEG C at a rate of 0.5-10 DEG C / min to obtain a quartz glass precursor.
6. The method for preparing low-hydroxyl, defect-free quartz glass as described in claim 5, characterized in that, The hot forming treatment in step (2) comprises loading the quartz glass precursor into a high-purity carbon material mold and placing it in a vacuum sintering furnace at a temperature of 1700-1900 DEG C for 0.5-2 h to obtain a quartz glass block.
7. The method for preparing low-hydroxyl, defect-free quartz glass as described in claim 6, characterized in that, The annealing treatment in step (2) comprises placing the quartz glass block in a normal pressure furnace or a vacuum furnace at a temperature of 1100-1250 DEG C for at least 20 h, then slowly cooling to the strain point temperature for annealing treatment to obtain a quartz glass body.
8. The method for preparing low-hydroxyl, defect-free quartz glass as described in claim 1, characterized in that, The hydrogen-containing atmosphere in step (3) is pure hydrogen.
9. The method for preparing low-hydroxyl, defect-free quartz glass as described in claim 1, characterized in that, The gas pressure in step (3) is preferably 0.5-1.0 MPa, the preferred temperature is 550-650 DEG C, and the preferred time is 200-300 h.
10. A low-hydroxy, defect-free quartz glass, characterized by, The low-hydroxyl defect-free quartz glass is prepared by the method of any one of claims 1-9, and the hydroxyl concentration of the low-hydroxyl defect-free quartz glass is less than 20 ppm.