A precision fabrication method for photolithography mask substrates

Abstract

This invention relates to a precision processing method for photolithographic mask substrates, comprising: cleaning the photolithographic mask substrate blank using single-slot multi-frequency ultrasonic cleaning; polishing the photolithographic mask substrate blank to its full aperture using a planetary double-sided polishing machine to obtain a preliminary photolithographic mask substrate shape; rapidly removing the shallow damaged layer of the preliminary photolithographic mask substrate shape by high-frequency vibration etching with a hydrofluoric acid mixture; correcting the surface shape of the preliminary photolithographic mask substrate shape and removing surface defects using a double-sided polishing machine; detecting the double-sided surface shape of the preliminary photolithographic mask substrate shape after surface defect removal using a laser interferometer; deterministically correcting local surface shape errors of the preliminary photolithographic mask substrate shape through sub-aperture polishing; and controlling the surface roughness of the corrected preliminary photolithographic mask substrate shape to the sub-nanometer level using an ultra-smooth polishing process to obtain the photolithographic mask substrate. This method reduces the number of traditional iterative polishing cycles, shortens the processing cycle, and avoids surface damage caused by traditional long-term mechanical grinding.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material preparation technology, and more specifically to a precision processing method for photolithographic mask substrates. Background Technology

[0002] As the core carrier of mask patterns in chip manufacturing, the surface quality and surface accuracy of photolithography mask substrates directly affect the pattern transfer accuracy of photolithography processes. Currently, high-end photolithography mask substrate blanks are mainly made of quartz glass, and their manufacturing process must meet stringent requirements of flatness ≤0.1µm and surface roughness ≤0.2nm. Traditional processing methods mainly rely on double-sided polishing technology, gradually approaching the target accuracy through multiple iterations of polishing, but this method has the following significant drawbacks:

[0003] 1. Low efficiency: Multiple polishing processes result in long processing cycles, and each polishing requires re-clamping and inspection, introducing human error;

[0004] 2. Insufficient yield: During the iteration process, the subsurface damage layer accumulates, and surface defects (such as scratches and pits) are difficult to completely eliminate, resulting in a low final yield.

[0005] 3. Unstable surface shape control: Double-sided polishing makes it difficult to balance full-diameter surface shape correction and local error compensation, requiring manual experience to adjust parameters, resulting in poor consistency.

[0006] Existing technologies include improving surface roughness by optimizing polishing slurry formulations and reducing surface damage by using chemical mechanical polishing (CMP), but they have not solved the problem of high-precision surface shape correction efficiency; at the same time, they have not solved the problem of simultaneous convergence of surface shape and ultra-high surface quality.

[0007] Therefore, there is an urgent need for a deterministic polishing method that can improve processing efficiency, surface accuracy, and surface quality through coordinated convergence. Summary of the Invention

[0008] Therefore, the purpose of this invention is to propose a precision processing method for photolithography mask substrates to solve the defects existing in the processing of photolithography mask substrates.

[0009] The technical solution of this invention is a precision processing method for a photolithographic mask substrate, comprising the following steps:

[0010] S1 uses multi-frequency ultrasonic cleaning to clean the photolithography mask substrate blank;

[0011] S2 uses a planetary double-sided polishing machine to rapidly polish the entire diameter of the photolithography mask substrate blank using a fixed program, thereby obtaining the prototype of the photolithography mask substrate.

[0012] S3 rapidly removes the shallow damage layer of the photomask substrate prototype by high-frequency vibration etching of a hydrofluoric acid mixture, thus obtaining a photomask substrate prototype without a damage layer.

[0013] S4 uses a double-sided polishing machine and a fixed program to correct the surface shape of the photolithography mask substrate prototype in S3 and remove surface defects.

[0014] S5 uses a laser interferometer to detect the double-sided surface shape of the photolithographic mask substrate prototype in S4 after removing surface defects;

[0015] Based on the detection results of S5, S6 performs deterministic correction of the local surface shape error of the photolithography mask substrate prototype through a single processing step and sub-aperture polishing;

[0016] S7 uses an ultra-smooth polishing process to control the surface roughness of the modified photomask substrate prototype in S6 to the sub-nanometer level, thus obtaining the photomask substrate.

[0017] According to the precision machining method of the present invention, in S1, a single-tank multi-frequency ultrasonic cleaner is used to perform multi-frequency ultrasonic cleaning on the photolithography mask substrate blank. The selected frequencies are 40KHZ, 80KHZ, 120KHZ, 170KHZ, and 240KHZ. The temperature range for cleaning the photolithography mask substrate blank at multiple frequencies is 60℃-80℃.

[0018] According to the precision machining method of the present invention, ultrasonic cleaning includes five frequency stages: 40kHz, 80kHz, 120kHz, 170kHz, and 240kHz, with cleaning temperature gradients of 70℃, 65℃, and 60℃; a single-tank overflow mode is adopted, and residual particles are finally removed by spray cleaning, with a spray time of ≥20 seconds.

[0019] According to the precision machining method of the present invention, the planetary double-sided polishing machine in S2 adopts a fixed machining program. After a fixed machining time, the component is completed and no inspection is required after removal. The polishing liquid is a 5%-10% concentration cerium oxide particle suspension, and the pressure is controlled at 30-50 kPa.

[0020] According to the precision machining method of the present invention, the hydrofluoric acid mixture in S3 is made by mixing hydrofluoric acid, nitric acid and deionized water in a volume ratio of 0.4:1:2, with a corrosion temperature ≤20℃ and a time ≤10 minutes.

[0021] According to the precision machining method of the present invention, the double-sided polishing machine in S4 is dressed using a customized composite dresser. Every 30 hours, the customized composite dresser is used to perform a fixed program dressing, with a dressing pressure of 50-80 kPa. After dressing, the surface shape error of the polishing disc is ≤0.02 mm.

[0022] According to the precision machining method of the present invention, in S6, the prototype photolithography mask substrate after surface shape detection in S5 is subjected to sub-aperture polishing correction, and the correction time for a single side is ≤30 minutes.

[0023] According to the precision machining method of the present invention, the airbag polishing technology achieves a removal efficiency of 30mm. 3 The sub-diameter polishing disc rotation speed is 1500-2000 r / min, the pressure is 50-100 N, and the polishing solution is a 1% concentration cerium oxide solution.

[0024] According to the precision machining method of the present invention, the ultra-smooth polishing in S7 uses a nano-particle polishing slurry with a particle size of 20-80 nm and a concentration of 0.05%-0.2%.

[0025] According to the precision machining method of the present invention, the polishing tool for ultra-smooth polishing rotates at a speed of ≥6000 r / min, and the modified photolithography mask substrate prototype in S6 is supported by a U-shaped pad for back protection during component processing.

[0026] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This invention rapidly removes macroscopic defects through full-diameter polishing, combined with localized correction through sub-diameter polishing. The overall efficiency is significantly improved through this process flow. The processing procedure is essentially fixed, requiring only one inspection to meet the final requirements, greatly reducing the number of traditional iterative polishing steps and shortening the processing cycle. The hydrofluoric acid mixture, through high-frequency vibration corrosion, can rapidly remove shallow surface defects within 10 minutes, improving the efficiency of the initial polishing stage and avoiding rework later.

[0028] 2. The laser interferometer of this invention detects the polishing of the mating part diameter, realizes the deterministic correction of surface shape error, and uses a fixed program to adjust at fixed processing intervals to ensure the performance consistency of the polishing tool.

[0029] 3. Ultra-smooth polishing uses nano-grade cerium oxide polishing slurry (particle size 20-80nm), with a surface roughness (Ra) ≤0.2nm and a defect density ≤0.1 defects / cm². 2 It meets the requirements for photolithography mask substrates for processes below 7nm.

[0030] 4. Single-tank multi-frequency ultrasonic overflow cleaning removes contaminants in stages (40kHz for grease removal → 80kHz for particulate removal → 240kHz for nano-residue removal), combined with spray cleaning, improving surface cleanliness by 50%. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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 the provided drawings without creative effort.

[0032] Figure 1 A flowchart of a precision processing method for a photolithographic mask substrate provided by the present invention;

[0033] Figure 2 The diagram illustrates the cleaning process of a single-tank multi-frequency ultrasonic cleaner.

[0034] Figure 3 A schematic diagram of the planetary double-sided polishing machine is shown.

[0035] Figure 4 The diagram illustrates the state of high-frequency vibration corrosion of a hydrofluoric acid mixture.

[0036] Figure 5a The diagram illustrates the machining process for correcting a double-sided polishing machine;

[0037] Figure 5b A schematic diagram of the modified pellet base gear base is shown;

[0038] Figure 5c A schematic diagram of a convex trimming head is shown;

[0039] Figure 5d A schematic diagram of the concave trimming head is shown;

[0040] Figure 6a The machining diagram of the sub-diameter polishing machine is shown;

[0041] Figure 6b The diagram illustrates the placement of support pads during sub-diameter polishing.

[0042] Figure 7a A schematic diagram of the immersion tank in the ultra-smooth process is shown;

[0043] Figure 7b The diagram shows a top view of the immersion tank used in the ultra-smooth process;

[0044] Figure 7c An enlarged schematic diagram of the photolithographic mask substrate and the extension block base in the immersion tank is shown.

[0045] Figure 7d The tooling diagram in the ultra-smooth process is shown. Detailed Implementation

[0046] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0047] In existing technologies, the surface roughness of photolithography mask substrates is improved by optimizing the polishing slurry formulation, but the problem of surface shape correction efficiency is not solved; chemical mechanical polishing (CMP) is used to reduce subsurface damage, but deterministic correction of local errors cannot be achieved.

[0048] Therefore, the technical solution of the present invention is a precision processing method for a photolithographic mask substrate, see appendix. Figure 1 This includes the following steps:

[0049] S1 uses multi-frequency ultrasonic cleaning to clean the photolithography mask substrate blank;

[0050] S2 uses a planetary double-sided polishing machine to rapidly polish the entire diameter of the photolithography mask substrate blank using a fixed program, thereby obtaining the prototype of the photolithography mask substrate.

[0051] S3 rapidly removes the shallow damage layer of the photomask substrate prototype by high-frequency vibration etching of a hydrofluoric acid mixture, thus obtaining a photomask substrate prototype without a damage layer.

[0052] S4 uses a double-sided polishing machine and a fixed program to correct the surface shape of the photolithography mask substrate prototype in S3 and remove surface defects.

[0053] S5 uses a laser interferometer to detect the double-sided surface shape of the photolithographic mask substrate prototype in S4 after removing surface defects;

[0054] Based on the detection results of S5, S6 performs deterministic correction of local surface shape errors of the photolithography mask substrate prototype through a single processing step and sub-aperture polishing. Based on the spatial frequency domain distribution characteristics of the component surface shape, it plans the path of the polishing tool to achieve rapid convergence without edge effects. Simultaneously, polishing tools of different sizes are integrated to enable quick tool replacement.

[0055] S7 employs an ultra-smooth polishing process to control the surface roughness of the modified photomask substrate prototype in S6 to the sub-nanometer level, thus obtaining the photomask substrate. The polishing tool achieves a linear speed of 20 m / s relative to the device, and the gap between the polishing tool and the device reaches more than 10 μm, without direct contact with the device. The program runs for 10 minutes to correct surface defects.

[0056] This invention utilizes full-aperture polishing to rapidly remove macroscopic defects, combined with sub-aperture polishing for localized correction, reducing the number of traditional iterative polishing cycles and shortening the processing time. High-frequency vibration etching with a hydrofluoric acid mixture efficiently removes the surface damage layer within 10 minutes, avoiding surface damage caused by prolonged mechanical grinding. Laser interferometer detection, combined with sub-aperture polishing, enables deterministic correction of surface shape errors. A custom full-aperture dresser with a fixed program corrects the polishing disc morphology, reducing surface shape errors after double-sided polishing.

[0057] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0058] In an embodiment of the present invention, in S1, multiple sets of ultrasonic cleaners connected in series are used to perform multi-frequency ultrasonic cleaning on the photolithography mask substrate blank. The selected frequencies are 40KHZ-240KHZ, and the temperature range for cleaning the photolithography mask substrate blank at multiple frequencies is 60℃-80℃.

[0059] Advantageously, ultrasonic cleaning includes five frequency stages: 40kHz, 80kHz, 120kHz, 170kHz, and 240kHz, with cleaning temperature gradients of 70℃, 65℃, and 60℃; finally, residual particles are removed by spray cleaning, with a spray time of ≥20 seconds.

[0060] In the embodiments of the present invention, the planetary double-sided polishing machine in S2 adopts a fixed program for processing. After a fixed processing time (the fixed program is double-sided polishing with fixed pressure, speed and processing time), the component is processed and no inspection is required after removal. The polishing liquid is a 5%-10% concentration cerium oxide particle suspension, and the pressure is controlled at 30-50 kPa.

[0061] In one embodiment of the present invention, the hydrofluoric acid mixture in S3 is a mixture of hydrofluoric acid, nitric acid, and deionized water in a volume ratio of 0.4:1:2, with a corrosion temperature ≤20°C and a corrosion time ≤10 minutes.

[0062] In the embodiment of the present invention, the double-sided polishing machine in S4 uses a customized composite dresser. Every 30 hours, a fixed procedure is used (after processing the double-sided polishing machine three times (30 hours) according to a fixed procedure, the disc surface is dressed, and the dressing procedure is based on a fixed pressure, rotation speed and dressing time) to ensure the consistency of the polishing tool's performance; the dressing pressure is 50-80 kPa, and the surface shape error of the polishing disc after dressing is ≤0.05 μm.

[0063] In S6, the prototype photolithographic mask substrate after surface shape detection in S5 undergoes sub-aperture polishing correction, with a single-sided correction time of ≤30 minutes. The sub-aperture polishing disk rotates at 1500-2000 r / min, the pressure is 50-100 N, and the polishing slurry is a 1% concentration cerium oxide solution.

[0064] In the embodiments of the present invention, the ultra-smooth polishing in S7 uses nano-sized cerium oxide polishing slurry with a particle size of 20-80 nm and a concentration of 0.05%-0.2%. The polishing disc for ultra-smooth polishing rotates at a speed ≥6000 r / min, utilizing non-contact polishing. The high-speed wheel drives the polishing slurry to flow, and the nano-abrasives in the polishing slurry are removed by impacting the surface of the component with high kinetic energy.

[0065] In S6, the modified lithography mask substrate prototype is supported by a U-shaped pad during processing, which protects the back side of the component processing.

[0066] The specific steps of using this invention are as follows:

[0067] Step S1: Multi-frequency ultrasonic cleaning:

[0068] Equipment configuration: tandem ultrasonic cleaner (single-tank multi-frequency ultrasonic cleaner), see [link / reference] Figure 2 It includes three cleaning tanks (first cleaning tank 101, second cleaning tank 102, and third cleaning tank 103) and a spray tank 104. Each of the four tanks is connected by an inlet pipe 105 and an outlet pipe 106. Each cleaning tank has a control panel (first cleaning tank control panel 1011, second cleaning tank control panel 1021, and third cleaning tank control panel 1031). The spray tank 104 has a spray tank control panel 1041, and the spray tank 104 contains a spray nozzle 1042.

[0069] Operating procedures:

[0070] First, open the valve of the inlet pipe 105 and fill the three ultrasonic cleaning tanks with deionized water, then close the valve of the inlet pipe 105.

[0071] Place the blanks P into the blanks in sequence:

[0072] First cleaning tub 101: Set the temperature to 70℃ on the control panel, and set the frequencies to 40kHz and 80KHz respectively. Clean for 30 seconds at 40kHz and 30 seconds at 80KHz to remove grease and large particulate contaminants.

[0073] Second cleaning tank 102: Set the temperature to 65℃ on the control panel, and set the frequencies to 120kHz and 170KHz respectively. Add neutral cleaning agent, clean for 18 seconds at 120kHz and 12 seconds at 170KHz to remove submicron particles.

[0074] Third cleaning tank 103: Set the temperature to 60℃ and the frequency to 240kHz on the control panel, and perform overflow cleaning for 20 seconds to remove nanoscale residues.

[0075] 1042 spray cleaning: Deionized water spray for 20 seconds at a pressure of 0.2 MPa to thoroughly remove surface deposits.

[0076] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0077] Step S2: Full-caliber double-sided polishing:

[0078] See attached equipment. Figure 3 The planetary double-sided polishing machine includes a double-sided polishing cylinder (201), a connecting block (202), an upper polishing disc (203), a component placement fixture (204), an outer ring gear (205), a lower polishing disc (206), an inner ring gear (208), a selection spindle (209), a polishing fluid tank (210), a polishing fluid pipe (211), a dresser (212), a dressing pellet (213), a gear base (214), a convex dressing head (215), a concave dressing head (216), and P1 is a prototype of a photolithography mask substrate.

[0079] The upper polishing disc 203 rotates at 20 r / min (clockwise), and the lower polishing disc 206 rotates at 40 r / min (counterclockwise); the inner ring gear 208 rotates at 15 r / min, and the outer ring gear 205 rotates at 20 r / min, with a pressure of 40 kPa; the polishing solution is 8% cerium oxide (5 μm particles) + deionized water, with a flow rate of 200 mL / min.

[0080] Then, the multiple photolithography mask substrate blanks P cleaned in step S1 are placed into the component placement fixture 204. Then, the double-sided polishing cylinder 201 is started. The double-sided polishing cylinder 201 drives the upper polishing disk 203 to descend together until the upper polishing disk 203 contacts the photolithography mask substrate blank P and then stops descending. Then, the valve switch of the polishing liquid pipeline 211 is opened to let the 5%-10% cerium oxide polishing liquid flow into the polishing liquid tank 210, then into the upper polishing disk 203 through the polishing liquid tank 210, and then into the lower polishing disk 206 through the upper polishing disk 203.

[0081] Open the setup program, the upper polishing disk 203 rotates clockwise, the lower polishing disk 206 rotates counterclockwise, the outer ring gear 205 and the inner ring gear 208 drive the component placement fixture 204 to rotate counterclockwise. Under the action of relative motion and pressure, the upper and lower surfaces of the photolithography mask substrate blank P are polished simultaneously to obtain the photolithography mask substrate prototype P1.

[0082] Processing results: Surface roughness Ra decreased from the initial 1.5μm to 0.5μm, and flatness error was ≤0.3μm.

[0083] Step S3: Corrosion by hydrofluoric acid mixture:

[0084] See Appendix for mixture preparation. Figure 4 The components include a 301 drain pipe, a 302 hydrofluoric acid mixing tank, a 303 photolithography mask substrate placement position, a 304 mixing tank control panel, and a 305 liquid level sensor; the ratio of hydrofluoric acid to nitric acid to deionized water is 0.4:1:2 (volume ratio), the temperature is 18℃, and the etching time is 8 minutes.

[0085] Specifically, 15L of deionized water, 7.5L of nitric acid, and 0.75L of hydrofluoric acid are added to the hydrofluoric acid mixing tank 302. A level sensor 305 is installed in the hydrofluoric acid mixing tank 302. When the hydrofluoric acid mixture reaches the level set by the level sensor 305, the drain pipe 301 opens the valve to discharge the mixture above the level sensor position. The four photolithography mask substrate prototypes P1 processed in step S2 are placed in the photolithography mask substrate placement position 303. Then, the mixing tank control panel 304 is turned on. The temperature of the hydrofluoric acid mixture is set to 18°C ​​and the etching time of the hydrofluoric acid mixture on the surface of the photolithography mask substrate is set to 8 minutes. Then, the program is run to quickly remove the surface damage layer to obtain the photolithography mask substrate prototype P2.

[0086] Corrosion effect: Removes surface crack layer (depth ≤ 50nm), providing a uniform substrate for subsequent correction.

[0087] Step S4: Surface shape correction and polishing, using... Figure 3 The diagram shows a planetary double-sided polishing machine.

[0088] The surface shape of the photolithographic mask substrate prototype P2 was corrected using a double-sided polishing machine, such as... Figure 5a As shown, the shape of the composite structure trimmer (212) is selected according to the surface shape of the photolithography mask substrate (see Appendix for trimmer head). Figure 5c and 5dIf the surface of the photomask substrate is convex, select the concave trimming head 216 for the corresponding trimming polishing pad; if the surface is concave, select the convex trimming head 215 for the corresponding trimming polishing pad. The trimming pressure is 60 kPa, the trimming time is 15 minutes, and the surface shape error of the polishing pad is corrected to 0.03 μm. Figure 5b The trimmed pellet 213 and gear base 214 are shown.

[0089] Specifically, the rotational speed of the inner ring gear 208 is set to -5 r / min, the rotational speed of the outer ring gear 205 is set to 10-15 r / min, the rotational speed of the upper polishing disc 203 is set to 5-10 r / min, the rotational speed of the lower polishing disc 206 is set to 20-30 r / min, and the pressure is set to 50-80 kPa. Then, the four dressing bases 214 are evenly distributed between the inner ring gear 208 and the outer ring gear 205, so that the inner ring gear 208 and the dressing base 214 mesh. The outer ring gear 205 meshes with the dressing base 214 gear, and the double-sided polishing cylinder 201 is started. The double-sided polishing cylinder 201 drives the upper polishing disc 203 to descend together until the upper polishing disc 203 contacts the dressing pellet 213 and then stops descending. Then the valve switch of the polishing liquid pipeline 211 is opened, and the cerium oxide polishing liquid with a concentration of 6-10% flows into the polishing liquid tank 210, then flows into the upper polishing disc 203 through the polishing liquid tank 210, and then flows into the lower polishing disc 206 through the upper polishing disc 203.

[0090] When the setup program is opened, the upper polishing disc 203 rotates clockwise and the lower polishing disc 206 rotates counterclockwise. The outer ring gear 205 and the inner ring gear 208 drive the dressing base 214 to rotate counterclockwise. Under the action of relative motion and pressure, the surfaces of the upper and lower polishing discs are dressed.

[0091] After finishing, the double-sided polishing cylinder 201 is activated, causing the upper polishing disk 203 to rise until it reaches its upper limit and stops. The four finishing device bases 214 are then removed. Next, the photolithography mask substrate prototype P2, etched in step S3, is subjected to step S2 to correct the surface shape of the photolithography mask substrate. After polishing, the flatness error is ≤0.1μm, and surface defects (scratches, pits) are reduced by 80%.

[0092] Step S5: Laser Interference Surface Shape Detection:

[0093] Detection method: The double-sided surface shape was detected using a TAKY laser interferometer in multi-plate separation mode, and a surface shape error distribution map was generated (local maximum error +0.15μm).

[0094] Step S6: Local correction of sub-aperture, see appendix Figure 6aThe sub-diameter polishing machine includes a 601 guide rail, a 602 motor, a 603 sub-diameter cylinder, a 604 ejector pin, a 605 sub-diameter polishing disc, a 606 immersion fixture, a 607 slide table, and a 608 component placement support pad.

[0095] First, after surface shape detection in step S5, optical tape is applied to the back side (B side) of the photolithography mask substrate prototype P2. Then, the photolithography mask substrate prototype P2 with protective tape is placed in the immersion fixture 606. Next, the guide rail 601 and slide table 607 are moved to position the starting point of the photolithography mask substrate prototype. Then, the ejector pin 604 is moved, simultaneously driving the sub-aperture polishing disk 605 to move slowly until the sub-aperture polishing disk 605 contacts the surface of the photolithography mask substrate prototype and stops moving. Next, a pre-prepared 1% cerium oxide polishing solution is poured into the immersion fixture 606. The pressure of the sub-aperture cylinder 603 is set to 50N-100N, and the rotation speed of the sub-aperture polishing disk 605 is set to 1500-2000 r / min. Then, the processing program is run. The airbag polishing technology achieves a removal efficiency of 30mm. 3 / min.

[0096] When processing the first surface A of the photolithography mask substrate prototype, the following method is used: Figure 6b After tooling processing, the component is removed, and the surface is cleaned with polishing powder. Then, the B side is processed according to the above processing steps for the A side. When processing the A side, the optical tape side of the B side of the photolithography mask substrate is placed on the component placement support pad 608. When quickly correcting the surface shape of the A side of the photolithography mask substrate, since the B side of the photolithography mask substrate is placed on the large flat support pad 608, the protective layer of the photolithography mask substrate directly contacts the large flat surface of the pad, thus protecting the B side.

[0097] Polishing solution: 1% cerium oxide solution, correction time 25 minutes / side.

[0098] Correction effect: Local protrusion areas (error +0.15μm) are corrected to within ±0.03μm.

[0099] Step S7: Ultra-smooth polishing (see...) Figure 7a , Figure 7b , Figure 7c , Figure 7d )

[0100] Tooling: 701 Immersion tank, 702 Extension block, 703 Extension block base, 704 Component placement support U-shaped pad, 705 Base.

[0101] Ultra-smooth polishing is used to control the surface quality of the photolithography mask substrate. Figure 7dThe tooling first places the substrate placement support ring-shaped pad 704 on the base 705 (the base 705 has a channel for polishing fluid to flow out). Then, after processing in step S6, the photolithography mask substrate, without a protective layer to improve the surface quality of the non-processed surface, is directly placed on the component placement support ring-shaped pad 704. The support ring-shaped pad 704 has a light-transmitting hole, with a supporting element outside the light-transmitting aperture and a suspended element inside the light-transmitting aperture, so that the light-transmitting aperture on the back of the photolithography mask substrate is suspended to protect the surface. Then, the extension block base 703 is moved to extend the extension block. The top plate supports the sides of the photomask substrate to ensure that the components are fixed when the photomask substrate is processed. Then, a polishing powder with a particle size of 20-80nm and a concentration of 0.05-0.2% nano-particle polishing slurry is prepared and poured into the immersion tank 701. The polishing tool rotates at 6000-8000r / min and there is a gap of ≥10μm between the polishing tool and the components. The surface layer of the substrate is removed and repaired at the nanoscale through the fluid between the photomask substrate and the polishing tool, and the surface of the components achieves ultra-smoothness and extremely low defects and roughness requirements.

[0102] Tooling and parameters: The substrate was suspended and supported by a U-shaped pad; the polishing tool rotation speed was 7000 r / min; the polishing slurry was 0.1% cerium oxide (50 nm particle size); the processing pressure was 3 kPa; and the processing time was 10 minutes. Final specifications: Surface roughness Ra = 0.18 nm, defect density 0.01 defects / cm². 2 Flatness ≤ 0.08μm.

[0103] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0104] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0105] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method of precision processing of a photolithography mask substrate, characterized by, Includes the following steps: S1 uses multi-frequency ultrasonic cleaning to clean the photolithography mask substrate blank; S2 uses a planetary double-sided polishing machine to rapidly polish the photolithography mask substrate blank throughout its entire diameter using a fixed program, thereby obtaining a prototype of the photolithography mask substrate. S3 rapidly removes the shallow damage layer of the photomask substrate prototype by high-frequency vibration etching of a hydrofluoric acid mixture, thus obtaining a photomask substrate prototype without a damage layer. S4 uses a double-sided polishing machine and a fixed program to correct the surface shape of the photolithography mask substrate prototype in S3 and remove surface defects. S5 uses a laser interferometer to detect the double-sided surface shape of the photolithographic mask substrate prototype in S4 after removing surface defects; Based on the detection results of S5, S6 performs deterministic correction of the local surface shape error of the photolithography mask substrate prototype through a single processing step and sub-aperture polishing; S7 uses an ultra-smooth polishing process to control the surface roughness of the modified photomask substrate prototype in S6 to the sub-nanometer level, thus obtaining the photomask substrate. Ultrasonic cleaning includes five frequency stages: 40kHz, 80kHz, 120kHz, 170kHz, and 240kHz. The cleaning temperature gradient is 70℃, 65℃, and 60℃. A single-tank overflow mode is adopted, and residual particles are finally removed by spray cleaning with a spray time of ≥20 seconds. The S2 planetary double-sided polishing machine adopts a fixed processing program. After a fixed processing time, the component is processed and no inspection is required after removal. The polishing fluid is a 5%-10% concentration of cerium oxide particle suspension, and the pressure is controlled at 30-50 kPa. The hydrofluoric acid mixture in S3 is a mixture of hydrofluoric acid, nitric acid, and deionized water in a volume ratio of 0.4:1:

2. The corrosion temperature is ≤20℃ and the time is ≤10 minutes. In S6, the photolithography mask substrate prototype after S5 surface shape detection is polished and corrected to a sub-aperture, with a single-sided correction time of ≤30 minutes. The airbag polishing technology achieves a removal efficiency of 30 mm³ / min, with a sub-diameter polishing disc rotation speed of 1500-2000 r / min, a pressure of 50-100 N, and a 1% concentration cerium oxide solution as the polishing fluid. The S7 uses a nano-particle polishing slurry for ultra-smooth polishing. The nano-particle size of the polishing slurry is 20-80nm, and the concentration is 0.05%-0.2%.

2. The method of claim 1, wherein the method further comprises: The S4 double-sided polishing machine uses a custom composite dresser for dressing. Every 30 hours, the custom composite dresser is used for a fixed program dressing, with a dressing pressure of 50-80 kPa. After dressing, the surface shape error of the polishing disc is ≤0.02 mm.

3. The method of claim 1, wherein the method further comprises: The polishing tool for ultra-smooth polishing has a rotation speed of ≥6000r / min. The modified photolithography mask substrate prototype in S6 is supported by a U-shaped pad for back protection during component processing.

Images