A fluid jet polishing method for a square quartz mask substrate

Abstract

The application discloses a kind of jet polishing processing methods of square quartz mask substrate, including the following steps: square quartz mask substrate is placed in single piece cleaning machine table, and is sequentially cleaned by two fluid, SPM solution and megasonic nozzle spray superpure water;Substrate is jet polished by megasonic nozzle spray silicon dioxide polishing solution, then is rinsed by megasonic nozzle spray superpure water;After being cleaned by ultrasonic nozzle spray SC-1 cleaning solution, it is rinsed by superpure water;After drying treatment, it is transported to next process.The application integrates jet polishing and cleaning function by single piece cleaning machine table, so that process integration is higher, reduces the demand of additional processing equipment and process, improves efficiency, reduces production cost;While improving the roughness of medium frequency and high frequency spatial frequency by jet polishing, the serious influence on surface flatness can be avoided, and product yield is improved.

Description

Technical Field

[0001] This invention relates to the field of quartz mask substrate surface treatment technology, and specifically to a jet polishing method for a square quartz mask substrate. Background Technology

[0002] With the rapid development of artificial intelligence computing, the demand for semiconductor devices is driven by the need for more advanced processes, smaller sizes, and higher energy efficiency. Extreme ultraviolet (EUV) lithography has become the preferred method for manufacturing chips at technology nodes below 7nm. EUV lithography uses EUV light with extremely short wavelengths as the exposure source. Since EUV light is absorbed by most materials, EUV masks employ a completely different reflective mask compared to deep ultraviolet lithography. The ultra-low thermal expansion square quartz mask substrate used as the mask requires a surface flatness of no more than 80nm and a surface spatial frequency roughness of no more than 0.15nm, which places extremely high demands on the manufacturing process.

[0003] For square quartz substrates with surface flatness requirements below 80nm, simple double-sided polishing is insufficient. Ultra-precision polishing technology with controllable removal effects is required, such as magnetorheological polishing, which achieves high-precision reshaping of surface shape errors. Magnetorheological polishing technology mainly uses a high-intensity gradient magnetic field to create a semi-solid magnetorheological flexible polishing film from the polishing slurry. Fine abrasive particles, being non-magnetic, are repelled by magnetic powder and precipitate and embed in the surface of the flexible polishing film. When the polishing slurry is carried by the polishing wheel into the narrow contraction area between the workpiece and the polishing wheel, the polishing motion path, the yield stress of the magnetorheological slurry, and the removal function are controlled by computer software. Through shear force, precise polishing of the workpiece surface is achieved.

[0004] Magnetorheological polishing slurry uses iron powder as the magnetic sensitive material and cerium oxide as the polishing abrasive. It also contains organic additives to improve dispersion. Post-processing cleaning requires the use of strong acidic and oxidizing chemicals to remove iron powder and organic matter. Then, hydrofluoric acid is used to remove embedded abrasive particles, preventing cerium oxide particles from contaminating the double-sided polishing machine. For high spatial frequency roughness requirements below 0.15 nm, magnetorheological polishing, which relies entirely on physical shearing, is insufficient to meet the required roughness. Therefore, a short double-sided polishing process is necessary to remove the surface layer created by magnetorheological polishing and achieve the desired roughness. After double-sided polishing, the square quartz substrate is cleaned and dried using a single-piece cleaning machine before subsequent testing.

[0005] During magnetorheological polishing, the magnetorheological fluid needs to maintain its viscosity and rheological properties. It often contains organic oily components and has a low water content. When polishing in a dry environment, the residual polishing fluid will dry and adhere to the substrate surface, forming a complex contamination layer of iron particles, iron ions, cerium oxide particles and organic matter. This requires a special cleaning machine and the use of various chemicals for cleaning, which increases the complexity of the process, the pressure on plant management, and the production cost.

[0006] Magnetorheological polishing (MRP) involves frequent reversals due to pseudo-random paths. Excessive acceleration and deceleration of the machine tool stage can easily cause vibrations that damage the machine tool's rigidity. Therefore, grating paths are commonly used in practical MRP polishing of quartz glass surfaces. MRP technology offers high determinism and precise material removal from the component surface. Flexible polishing heads cannot produce the smooth effect of random removal. The asymmetry of the removal function about its short axis results in tool marks on the superimposed component surface. The period of these tool marks is related to the processing spacing, introducing mid-frequency errors and causing a relatively high spatial frequency roughness. Furthermore, since physical polishing is the primary method, the removal rate must also be considered. Therefore, the cerium oxide particle size in the MRP polishing slurry cannot be too small, making it difficult to achieve low spatial frequency roughness. This can lead to a decrease in the quality of multilayer reflective films in subsequent coating deposition processes on square quartz substrates, and optical performance will also suffer from light intensity and energy loss and reduced image quality due to scattering.

[0007] Double-sided polishing technology is easily affected by the shape of the polishing pad and the surface condition of the polishing pad, making it difficult to achieve local surface shape control in the processing of square substrates. Furthermore, due to limitations in requirements for surface finish and the degree of subsurface damage, it mostly uses damping cloth polishing pads with low hardness and slightly higher compressibility. However, the four corner areas of the square substrate are subjected to higher compressive stress during processing, thereby increasing the removal rate and causing corner collapse. When used for processing substrates after magnetorheological polishing, the controllability of surface shape accuracy is low, easily leading to a decrease in the yield of surface flatness. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a jet polishing method for square quartz mask substrates. By combining a single-piece cleaning machine with jet polishing technology, the roughness of mid-frequency and high-frequency spatial frequencies can be improved with relatively low variation in surface flatness.

[0009] To address the aforementioned technical problems, this invention provides a jet polishing method for a square quartz mask substrate, comprising the following steps:

[0010] S1. Place the square quartz mask substrate on a single-piece cleaning machine and clean it sequentially by passing it through a two-fluid system, an SPM solution, and ultrapure water sprayed from a mega-sonic nozzle.

[0011] S2. The substrate is jet polished by a silicon dioxide polishing slurry sprayed through a megasonic nozzle, and then rinsed with ultrapure water sprayed through a megasonic nozzle.

[0012] S3. After cleaning with SC-1 cleaning solution sprayed through an ultrasonic nozzle, rinse with ultrapure water.

[0013] S4. After drying, it is transported to the next process.

[0014] This invention integrates jet polishing and cleaning functions into a single-piece cleaning machine, resulting in a higher degree of process integration. While improving the roughness of medium and high frequency spatial frequencies through jet polishing, it avoids serious impact on the surface flatness.

[0015] This invention includes a calibration process before jet polishing of a substrate with silica polishing slurry. This process tests the smoothing effect of different jet polishing times on the surface, thereby determining the jet polishing parameters that match the substrate condition. The calibration process allows for more accurate control of the jet polishing time, resulting in higher utilization efficiency of the polishing slurry and reduced consumable costs.

[0016] Furthermore, in S1, the two fluids are driven by nitrogen and ultrapure water with a flow ratio of (50-200):1, and the pressures of nitrogen and ultrapure water are independently selected from 0.1-0.3 MPa.

[0017] Furthermore, in S1, the SPM solution comprises sulfuric acid, hydrogen peroxide, and ultrapure water in a volume ratio of (3-5):1:(1-5);

[0018] The temperature of the SPM solution is 50-120℃.

[0019] Furthermore, in S1, the temperature of the ultrapure water sprayed by the megasonic nozzle is 50-90°C.

[0020] Furthermore, in S2, the silica polishing slurry is a silica sol composed of nano-silica, water, and an acid-base regulator, and the pH of the polishing slurry is 8-11.

[0021] Furthermore, the nano-silica D50 has a particle size distribution of 30-100nm, and the content of nano-silica in the polishing solution is 10-40wt%.

[0022] Furthermore, in S3, the SC-1 cleaning solution comprises ammonia, hydrogen peroxide, and ultrapure water in a volume ratio of 1:(0.5-2):(10-30);

[0023] The temperature of the SC-1 cleaning solution is 35-50℃.

[0024] Furthermore, in S3, the washing-rinsing process is repeated 1-3 times.

[0025] Furthermore, all of the aforementioned megasonic nozzles operate at frequencies of 0.95-1.5MHz.

[0026] Furthermore, in S4, the drying process is carried out by high-speed rotary spin drying at 1000-2000 rpm.

[0027] The beneficial effects of this invention are:

[0028] This invention integrates jet polishing and cleaning functions into a single-piece cleaning machine, resulting in higher process integration, reduced need for additional processing equipment and processes, improved efficiency, and lower production costs. While improving the roughness of medium and high frequency spatial frequencies through jet polishing, it avoids serious impact on surface flatness and improves product yield.

[0029] The jet polishing of this invention does not require changes in process parameters based on empirical models due to changes in the life cycle of polishing pad consumables. It only requires stabilizing the preceding magnetorheological processing and performing a one-time calibration process to stably use a fixed process scheme, thereby improving the utilization efficiency of polishing slurry and production stability. Attached Figure Description

[0030] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart of the jet polishing method for the square quartz mask substrate of the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. 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.

[0033] This embodiment relates to a jet polishing method for a square quartz mask substrate, comprising the following steps:

[0034] S1. Place the square quartz mask substrate on a single-piece cleaning machine and clean it sequentially by passing it through a two-fluid system, an SPM solution, and ultrapure water sprayed from a mega-sonic nozzle.

[0035] S2. The substrate is jet polished by a silicon dioxide polishing slurry sprayed through a megasonic nozzle, and then rinsed with ultrapure water sprayed through a megasonic nozzle.

[0036] S3. After cleaning with SC-1 cleaning solution sprayed through an ultrasonic nozzle, rinse with ultrapure water.

[0037] S4. After drying, it is transported to the next process.

[0038] This embodiment integrates jet polishing and cleaning functions into a single-piece cleaning machine, resulting in higher process integration. While improving the roughness of mid-frequency and high-frequency spatial frequencies through jet polishing, it avoids serious impacts on surface flatness. A calibration process is set before jet polishing the substrate with silica polishing slurry to test the smoothing effect of different jet polishing times on the surface, thereby determining the jet polishing parameters that match the substrate condition. The calibration process allows for more accurate control of the jet polishing time, resulting in higher utilization efficiency of the polishing slurry and reduced consumable costs.

[0039] In a preferred embodiment, in S1, the two fluids are driven by nitrogen and ultrapure water with a flow rate ratio of (50-200):1, and the pressures of the nitrogen and ultrapure water are independently selected from 0.1-0.3 MPa; the SPM solution includes sulfuric acid, hydrogen peroxide and ultrapure water in a volume ratio of (3-5):1:(1-5); the temperature of the SPM solution is 50-120°C; and the temperature of the ultrapure water sprayed by the megasonic nozzle is 50-90°C.

[0040] In a preferred embodiment, in S2, the silica polishing slurry is a silica sol composed of nano silica, water and an acid-base regulator, and the pH of the polishing slurry is 8-11; the nano silica D50 particle size distribution is 30-100nm, and the content of nano silica in the polishing slurry is 10-40wt%.

[0041] In a preferred embodiment, in S3, the SC-1 cleaning solution includes ammonia, hydrogen peroxide and ultrapure water in a volume ratio of 1:(0.5-2):(10-30); the temperature of the SC-1 cleaning solution is 35-50℃; and the cleaning-rinsing process is repeated 1-3 times.

[0042] In a preferred embodiment, all of the megasonic nozzles operate at a frequency of 0.95-1.5MHz, and all of the ultrapure water is water with a resistivity of 18 MΩ·cm (25°C).

[0043] In a preferred embodiment, in S4, the drying process is performed by high-speed rotary spin drying at 1000-2000 rpm.

[0044] Example 1

[0045] This embodiment relates to a jet polishing method for a square quartz mask substrate, see reference. Figure 1 It includes the following steps:

[0046] (1) Pre-cleaning of square quartz mask substrate

[0047] The square quartz mask substrate, after magnetorheological polishing, is sent to a single-piece cleaning machine. It is first rinsed with 0.2MPa nitrogen and ultrapure water (flow ratio of 50:1) for 120 seconds. Then, it is cleaned for 300 seconds with SPM solution at 70°C, with a volume ratio of sulfuric acid, hydrogen peroxide and ultrapure water of 3:1:3, through a side nozzle. Finally, it is rinsed with ultrapure water heated to 60°C online through a megasonic nozzle. After completion, the substrate is transferred to the next chamber for jet polishing.

[0048] (2) Time calibration of the effect of jet polishing

[0049] A silica polishing slurry with a D50 particle size of 80nm, a silica content of 20wt%, and a pH of 10.5 was pumped under a pressure of 0.2MPa and passed through a primary 1-micron filter. Then, a megasonic nozzle with a sound frequency of 1MHz, a power setting of 50W, and a jet flow rate of 1.5L / min was used. The nozzle oscillated back and forth at a substrate rotation speed of 60rpm to perform jet polishing on the pre-cleaned square quartz substrate for 3 minutes. This was followed by a 30-second ultrapure water rinse, and then a final cleaning. The final cleaning involved a 60-second chemical cleaning using a megasonic nozzle with a sound frequency of 1.5MHz, a power setting of 20W, a flow rate of 1.5L / min, and an SC-1 cleaning solution (ammonia, hydrogen peroxide, and ultrapure water in a 1:1:10 volume ratio at 40℃), followed by a 90-second rinse with room temperature ultrapure water. This cleaning cycle was repeated twice. Finally, the substrate was spin-dried at 1000rpm for 300 seconds. After the final cleaning, a high-precision white light interferometer was used to analyze the mid-frequency spatial roughness by power spectral density measurement, and an atomic force microscope was used to measure the high-frequency spatial roughness. The above process was repeated multiple times until the high-frequency roughness was less than 0.2 / nm and the mid-frequency roughness was less than 0.004 / nm, at which point the cycle ended. The cumulative jet polishing time of 18 minutes obtained at this point is considered the appropriate process time.

[0050] (3) Jet polishing of square quartz substrates

[0051] A silica polishing slurry with a D50 particle size of 80nm, a silica content of 20wt%, and a pH of 10.5 was used. After being pumped at a pressure of 0.2MPa and filtered through a 1-micron filter, a megasonic nozzle with a sound frequency of 1MHz, a power setting of 50W, and a jet flow rate of 1.5L / min was used. The nozzle oscillated back and forth at a substrate rotation speed of 60rpm to perform jet polishing on the pre-cleaned square quartz substrate for 18 minutes. The ultrapure water rinsing time was 30 seconds. After completion, the substrate was transferred to the next chamber for final cleaning.

[0052] (4) Final cleaning of square quartz substrate

[0053] The final cleaning of the square quartz substrate involved a 60-second chemical cleaning process using a megasonic nozzle (1.5MHz, 20W power, 1.5L / min flow rate) with SC-1 cleaning solution (ammonia, hydrogen peroxide, and ultrapure water in a 1:1:15 volume ratio) at 40°C. This was followed by a 90-second rinse with room-temperature ultrapure water. This cleaning cycle was repeated twice. Finally, the substrate was spin-dried at 1000rpm for 300 seconds. Afterward, the clean substrate was transferred to the unloading end of the cleaning machine for subsequent testing.

[0054] The surface flatness was measured using a high-precision laser interferometer. The PV value after magnetorheological polishing was 54 nm, and the PV value after jet polishing was 62 nm, with a change of less than 15%, still meeting the 80 nm requirement. Under white light interferometry testing, the mid-frequency spatial roughness was 9.42 nm and the RMS was 0.21 nm. Under atomic force microscopy testing, the high-frequency spatial roughness was 0.13 nm, all meeting the roughness requirements for extreme ultraviolet mask substrates.

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that step (2) calibration is omitted, and the silica polishing liquid used in step (3) jet polishing is replaced with ultrapure water, while other steps and parameters remain unchanged.

[0057] The surface flatness was measured using a high-precision laser interferometer. The PV value after magnetorheological polishing was 62 nm, and the PV value after the comparative implementation was 64 nm. Under white light interferometry testing, the mid-frequency spatial roughness was 38.63 nm, and the RMS was 0.32 nm. Under atomic force microscopy testing, the high-frequency spatial roughness was 0.27 nm. Compared to the embodiment, because jet polishing is not performed, the wet cleaning process has little impact on the surface flatness and does not significantly optimize the substrate roughness, failing to meet the technical requirements of subsequent applications. Therefore, the processing method of this embodiment can perform jet polishing and cleaning using a single-wafer cleaning machine, achieving improvement in mid-frequency and high-frequency spatial roughness with relatively low surface flatness variation, which is beneficial for obtaining a mask substrate with better roughness.

[0058] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A jet polishing method for a square quartz mask substrate, characterized in that, Includes the following steps: S1. Place the square quartz mask substrate on a single-piece cleaning machine and clean it sequentially by passing it through a two-fluid system, an SPM solution, and ultrapure water sprayed from a mega-sonic nozzle. S2. The substrate is jet polished by a silicon dioxide polishing slurry sprayed through a megasonic nozzle, and then rinsed with ultrapure water sprayed through a megasonic nozzle. S3. After cleaning with SC-1 cleaning solution sprayed through an ultrasonic nozzle, rinse with ultrapure water. S4. After drying, it is transported to the next process.

2. The jet polishing method for a square quartz mask substrate as described in claim 1, characterized in that, In S1, the two fluids are driven by nitrogen and ultrapure water with a flow ratio of (50-200):1, and the pressures of nitrogen and ultrapure water are independently selected from 0.1-0.3 MPa.

3. The jet polishing method for a square quartz mask substrate as described in claim 1, characterized in that, In S1, the SPM solution comprises sulfuric acid, hydrogen peroxide, and ultrapure water in a volume ratio of (3-5):1:(1-5); The temperature of the SPM solution is 50-120℃.

4. The jet polishing method for a square quartz mask substrate as described in claim 1, characterized in that, In S1, the temperature of the ultrapure water sprayed by the megasonic nozzle is 50-90℃.

5. The jet polishing method for a square quartz mask substrate as described in claim 1, characterized in that, In S2, the silica polishing slurry is a silica sol composed of nano-silica, water, and an acid-base regulator, and the pH of the polishing slurry is 8-11.

6. The jet polishing method for a square quartz mask substrate as described in claim 5, characterized in that, The nano-silica D50 has a particle size distribution of 30-100nm, and the content of nano-silica in the polishing solution is 10-40wt%.

7. The jet polishing method for a square quartz mask substrate as described in claim 1, characterized in that, In S3, the SC-1 cleaning solution comprises ammonia, hydrogen peroxide, and ultrapure water in a volume ratio of 1:(0.5-2):(10-30); The temperature of the SC-1 cleaning solution is 35-50℃.

8. The jet polishing method for a square quartz mask substrate as described in claim 1, characterized in that, In S3, the washing-rinsing process is repeated 1-3 times.

9. The jet polishing method for a square quartz mask substrate as described in claim 1, characterized in that, All of the aforementioned megasonic nozzles operate at frequencies of 0.95-1.5 MHz.

10. The jet polishing method for a square quartz mask substrate as described in claim 1, characterized in that, In S4, the drying process is carried out by high-speed rotary spin drying at 1000-2000 rpm.

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