A method for developing a mask substrate based on a slit nozzle

Abstract

The present application belongs to the technical field of photolithography in mask manufacturing, and particularly relates to a mask substrate developing method based on a slit nozzle. The present application adopts a bidirectional scanning mode to perform multiple cycle scanning development on the mask, and specifically includes a main developing stage and an overlap stage. The nozzle stops supplying liquid when reversing in the main developing stage, and the nozzle does not stop supplying liquid when reversing in the overlap stage. The number of cycle scanning in the overlap stage is greater than that in the main developing stage. The CD deviation is eliminated by stopping the liquid supply when reversing at both ends in the main developing stage, and the liquid supply is continuously supplied in the overlap stage, but a dilute developing solution is used for mild reaction, the alkaline developing solution is neutralized, and the residues are flushed, so that the developing defects such as developing residues, pinholes and bubbles are effectively reduced. The bidirectional scanning is adopted in the main developing stage, the air travel time is reduced, the liquid supply is not stopped in the overlap stage, the waiting time caused by starting and stopping of the liquid supply is avoided, and the total process time can be significantly shortened.

Description

Technical Field

[0001] This invention belongs to the field of photolithography technology in mask manufacturing, specifically relating to a mask substrate development method based on a slit nozzle. Background Technology

[0002] A photomask is a crucial pattern transfer tool in photolithography, its surface carrying the integrated circuit design pattern. During photomask manufacturing, after exposure, the photomask coated with photoresist needs to undergo a development process to reveal the pattern of the exposed area, forming a mask pattern for subsequent etching.

[0003] Critical Dimension (CD) is a core parameter for measuring the pattern accuracy of a photomask after development, typically referring to the width or spacing of photoresist lines. Development defects include unintended pattern anomalies such as developer residue, pinholes, bubbles, and watermarks. The uniformity of CD and the level of control over development defects directly determine the pattern quality of the photomask, thus affecting the performance and yield of the final chip product. Furthermore, throughput is a key indicator of manufacturing efficiency, typically referring to the number of photomasks processed per unit time. In the context of increasingly fierce competition in the semiconductor industry, improving throughput is crucial for reducing manufacturing costs and shortening delivery cycles.

[0004] Currently, mask development widely adopts slit nozzles, which have high liquid film coverage efficiency and development uniformity, and support two development methods: Puddle and Puddle-Less. The Puddle method achieves full reaction by allowing the liquid film to stand still, while the Puddle-Less method effectively inhibits the accumulation of by-products by continuously flowing and refreshing the developer.

[0005] Slit-nozzle-based mask development encompasses three parts: pre-development preparation, development execution, and post-development processing. In the development execution step, traditional methods typically employ unidirectional scanning. However, for mask substrate development, limitations imposed by the substrate and photoresist mean that during the nozzle's return from the second end to the first end, the developer on the mask substrate surface undergoes continuous reaction due to the time spent moving the nozzle. This leads to a continuous increase in the mean to target (MTT). Existing data shows that, with a target linewidth of 356.03 nm for the mask surface, unidirectional scanning has achieved a linewidth of 383.25 nm. Furthermore, in addition to the number of scans, unidirectional scanning also introduces another control variable: the developer's residence time on the mask substrate surface (Puddle), further increasing the difficulty of controlling the MTT.

[0006] Therefore, there is an urgent need for a development method that can increase production capacity and better control MTT. Summary of the Invention

[0007] This invention provides a mask substrate development method based on a slit nozzle. It aims to solve the problems of liquid film accumulation and uneven development caused by nozzle reversal in existing development processes, and to improve the uniformity and stability of the development process.

[0008] The method of this invention achieves process optimization for binary photomask manufacturing at the 180nm process node, and can be simultaneously applied to simplify the manufacturing processes of 28nm and 160nm phase-shifting photomasks, all achieving a target linewidth accuracy of ±1nm, and both have been put into mass production.

[0009] The technical solution of this invention is a mask substrate development method based on a slit nozzle, which uses a bidirectional scanning method to develop the mask, specifically including the following steps: (1) Main development stage Place the mask on the developing machine stage, control the nozzle to scan and continuously spray developer along the direction from the first end to the second end of the mask; when the nozzle reaches the second end, stop the liquid supply and complete the reversal, and resume the liquid supply after the nozzle leaves the second end, and scan and spray developer along the direction from the second end to the first end; when the nozzle reaches the first end, stop the liquid supply and complete the reversal again, resume the liquid supply and continue scanning towards the second end, and repeat this scanning cycle multiple times; (2) Overlap stage The nozzle is controlled to scan and continuously spray a mixture of developer and water along the direction from the first end to the second end of the mask. When the nozzle reaches the second end, the liquid supply is not stopped and the direction is changed. The mixture of developer and water is then scanned and sprayed along the direction from the second end to the first end. When the nozzle reaches the first end, the liquid supply is not stopped and the direction is changed. The scanning continues to the second end. This cycle is repeated multiple times.

[0010] The mask includes, but is not limited to, a 28nm phase-shifting mask, a 160nm phase-shifting mask, and a 180nm binary mask; the nozzle is a slit nozzle, the length of which is greater than the width of the mask perpendicular to the scanning direction, so as to cover the entire scanning width of the mask; the developer is a mixture of tetramethylammonium hydroxide (TMAH) or methyl isobutyl ketone (MIBK) and IPA with a mass fraction of 2.38%, wherein the volume ratio of MIBK to IPA is 1:1, 1:2, or 1:3.

[0011] The first end and the second end are opposite sides away from the edge of the mask, and are 10-12mm away from the edge of the mask.

[0012] Further, in step (1), the scanning speed is 40-60 mm / s, the length of the slit nozzle is 150-350 mm, the spray flow rate of the developer is 1800-2500 mL / min, and the number of cyclic scans is ≥4 times, preferably 4-6 times.

[0013] Further, in step (2), the scanning speed is 40-80 mm / s, 40-60, the spray flow rate of the mixture of developer and water is 1300-2500 mL / min, and the volume ratio of developer to water in the mixture of developer and water is 2:1-1:15; the number of cyclic scans is greater than the number of cyclic scans in the main development stage.

[0014] Furthermore, in step (2), during multiple cyclic scanning processes, the volume ratio of developer to water in the mixture of developer and water is controlled to decrease gradually within the range of 2:1 to 1:15.

[0015] Furthermore, the mask rotates 180° for each scanning cycle of the nozzle, requiring the length of the slit nozzle to be greater than the width of the mask perpendicular to the scanning direction, so as to cover the entire scanning width of the mask.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. Development capability comparable to unidirectional scanning: CD deviation is eliminated by stopping the liquid supply when the two ends are reversed in the main development stage, and the liquid supply is continuously supplied in the Overlap stage but a diluted developer is used for a mild reaction. Test data shows that the CD uniformity 3σ is optimized from 12.05nm to 7.37nm by the above development method, which is better than the level of unidirectional scanning.

[0017] 2. Improved developing capacity: The main developing stage adopts bidirectional scanning to reduce idle travel time. The liquid supply is not stopped throughout the Overlap stage, avoiding the waiting time for liquid supply start and stop. The total process time can be significantly shortened. At the same time, it avoids the deviation of CDMean value caused by waiting. Test data shows that when using the same amount of developer, the MTT of unidirectional scanning is about 14nm, while the MTT of bidirectional scanning is only 2nm.

[0018] 3. Effective reduction of development defects: During the Overlap stage, the mixing solution is continuously sprayed, and the alkaline developer is neutralized by deionized water and the residue is rinsed away, effectively reducing development defects such as developer residue, pinholes, and bubbles. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process of this invention.

[0020] Figure 2 This is a CD map distribution diagram from the development results of Example 2.

[0021] Figure 3 This is a CD map distribution diagram from the development results of Comparative Example 3. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The present invention provides a mask substrate development method based on a slit nozzle, comprising a main development stage and an overlap stage.

[0023] Example 1 I. Main Development Stage The main development stage employs a bidirectional scanning method. After the blank substrate is coated with photoresist, it enters a laser direct-write exposure machine for photolithography. After photolithography, the photomask (a binary photomask for the 180nm process node, measuring 152mm × 152mm × 6.35mm) is removed from the laser direct-write exposure machine and placed in an Smif (substrate cassette). Subsequently, it is transferred to the development stage, where a slit nozzle (250mm in length) is set to scan from the first end to the second end of the photomask (e.g., ...). Figure 1 As shown, the scanning process starts from one end of the mask and moves to the opposite end at a speed of 50 mm / s. Simultaneously, pure developer (TMAH, tetramethylammonium hydroxide 2.38 wt%) is continuously sprayed at a flow rate of 1800 mL / min to ensure the formation of a complete liquid film on the mask substrate surface. When the nozzle scans to the second end, the liquid supply system immediately stops supplying liquid. The nozzle completes a reversal action while the liquid supply is stopped and moves in the opposite direction to the first end. After the nozzle leaves the second end area, the liquid supply is resumed, and the developer continues to be sprayed to scan to the first end. When the nozzle scans to the first end, the liquid supply is stopped again, the reversal is completed, the liquid supply is resumed, and the scanning to the second end continues. This scanning cycle is repeated 4 times.

[0024] The first and second ends are opposite sides away from the edge of the mask, and are 10mm away from the edge of the mask.

[0025] The key to this control method is that the nozzle stops supplying liquid when it reverses at both ends, which can avoid liquid film accumulation and flow fluctuation caused by sudden changes in the direction of movement, thereby eliminating CD deviation at the reversal position. The scanning process from the second end back to the first end maintains normal liquid supply, ensuring uniform coverage of the developing liquid film on the mask surface.

[0026] II. Overlap Stage After the main development stage is completed, the Overlap stage begins. This stage also uses a bidirectional scanning method, as detailed below: The slit nozzle is set to scan from the first end of the mask to the second end at a scanning speed of 50 mm / s, while continuously spraying a mixture of developer and deionized water at a flow rate of 1800 mL / min. When the nozzle scans to the second end, the liquid supply is not stopped. The nozzle completes a reversal action while supplying liquid and moves in the opposite direction to the first end, continuing to spray the mixture of developer and deionized water to scan to the first end. When the nozzle scans to the first end, it completes a reversal action while supplying liquid and continues to scan to the second end. This scanning cycle is repeated 5 times. The volume ratio of developer (TMAH) to deionized water in the first to fifth cycles is 1:12.

[0027] The first and second ends are opposite sides away from the edge of the mask and are 10mm away from the edge of the mask to avoid the unstable initial flow rate of the liquid and ensure that the flow rate acting on the surface of the mask is stable.

[0028] The advantage of not stopping the fluid supply during this stage is as follows: 1. It avoids the waiting time required to resume liquid supply after the end has stopped, thus shortening the overall scanning time; 2. Continuous liquid supply ensures that the mixed solution is sprayed continuously and stably throughout the scanning path, and the mask surface is always in a uniform environment of diluted developer. At the same time, due to the shortened time, the impact on the mean value of CD is greatly reduced. 3. Continuous spraying keeps the mask surface moist, and the flowing deionized water washes away residual alkaline developer, effectively reducing development defects.

[0029] The development results are then tested and evaluated.

[0030] After development, the photomask was etched, stripped of its resist, and cleaned. It was then placed in a CD SEM and ADI instrument to test the CD value and defect. The results are as follows: CD Target: 354.43nm; CD Mean: 353.09nm; CD 3σ: 7.17nm; The number of defects is 1~2ea, and the size is generally less than 1μm; WPH: 1.8 tablets.

[0031] Example 2 I. Main Development Stage Same as Example 1.

[0032] II. Overlap Stage The specific process is the same as in Example 1, except that the volume ratio of developer TMAH to deionized water in the first to fifth cycles is 1:2, 1:5, 1:7, 1:10, and 1:12, respectively.

[0033] The development results are then tested and evaluated.

[0034] After development, the photomask was etched, stripped of its resist, and cleaned. It was then placed in a CD SEM and ADI instrument to test the CD value and defect. The results are as follows: CD Target: 354.43nm; CD Mean: 353.48nm; CD 3σ: 7.26nm; The number of defects is 1~2ea, and the size is generally less than 1μm; Example 3 All processes are the same as in Example 1, except that the mask rotates 180° each time the slit nozzle performs a bidirectional scan.

[0035] The development results are then tested and evaluated.

[0036] After development, the photomask was etched, stripped of its resist, and cleaned. It was then placed in a CD SEM and ADI instrument to test the CD value and defect. The results are as follows: CD Target: 354.43nm; CD Mean: 353.60nm; CD 3σ: 7.16nm; CD map as follows Figure 2 As shown, the Profile exhibits high symmetry.

[0037] The number of defects is 1~2ea, and the size is generally less than 1μm; Comparative Example 1 All processes are the same as in Example 1, except that during the main development stage, the liquid supply is not stopped when the slit nozzle scans to the first and second ends.

[0038] The development results are then tested and evaluated.

[0039] After development, the photomask was etched, stripped of its resist, and cleaned. It was then placed in a CD SEM and ADI instrument to test the CD value and defect. The results are as follows: CD Target: 354.43nm; CD Mean: 364.85nm; CD 3σ: 12.05nm; The number of defects is 1~2ea, and the size is generally less than 1μm; WPH: 1.4 tablets.

[0040] Comparative Example 2 All processes are the same as in Example 1, except that during the Overlap stage, the liquid supply stops when the slit nozzle scans to the first and second ends.

[0041] The development results are then tested and evaluated.

[0042] After development, the photomask was etched, stripped of its resist, and cleaned. It was then placed in a CD SEM and ADI instrument to test the CD value and defect. The results are as follows: CD Target: 354.43nm; CD Mean: 362.51nm; CD 3σ: 8.17nm; The number of defects is 36ea, and their size is generally greater than 2μm. Comparative Example 3 There is only a main development stage, and no overlap stage.

[0043] The development results are then tested and evaluated.

[0044] After development, the photomask was etched, stripped of its resist, and cleaned. It was then placed in a CD SEM and ADI instrument to test the CD value and defect. The results are as follows: CD Target: 354.43nm; CD Mean: 353.48nm; CD 3σ: 7.26nm; CD map as follows Figure 3 As shown, the profile is severely skewed.

[0045] Defect quantity 30ea, size 0.3-1μm; Comparative Example 4 All processes are the same as in Example 1, except that the number of loop scans in the Overlap phase is 2.

[0046] The development results are then tested and evaluated.

[0047] After development, the photomask was etched, stripped of its resist, and cleaned. It was then placed in a CD SEM and ADI instrument to test the CD value and defect. The results are as follows: CD Target: 354.43nm; CD Mean: 354.09nm; CD 3σ: 8.17nm; Defect quantity 40ea, size 0.3-1μm; Comparative Example 5 (Prior technology unidirectional scanning) I. Main Development Stage The main development stage uses a unidirectional scanning method. The mask is taken out from the laser direct writing exposure machine, placed in Smif, and then transferred to the development stage. A slit nozzle is set to scan from the first end to the second end of the mask at a scanning speed of 50 mm / s. At the same time, pure developer (TMAH, tetramethyl oxynitride) is continuously sprayed at a flow rate of 1800 mL / min to ensure that a complete liquid film is formed on the surface of the mask substrate.

[0048] II. Overlap Stage Same as Example 1.

[0049] The development results are then tested and evaluated.

[0050] After development, the photomask was etched, stripped of its resist, and cleaned. It was then placed in a CD SEM and ADI instrument to test the CD value and defect. The results are as follows: CD Target: 354.43nm; CD Mean: 369.3nm; CD 3σ: 11.38nm; Defect quantity 10ea, size 0.3-1μm; The method of this invention can perform development processing on phase shift masks, including but not limited to 28nm phase shift masks, 160nm phase shift masks, and 180nm binary masks. The examples and comparative examples only select one type as an illustration. By comparing the results of the examples and comparative examples, it can be seen that: For binary photomasks at the 180nm node, at least four main development stages and more than four overlap stage scans are typically required. When the liquid supply is not stopped during the main development stage when scanning to the first and second ends (Comparative Example 1), liquid film accumulation and flow fluctuations caused by abrupt changes in the direction of movement lead to deviations in the CD at the reversal position, with a CD uniformity of 3σ of approximately 12.05 mm. However, after stopping the liquid supply (Example 1), the 3σ is approximately 7.17 nm, and the uniformity is significantly improved. The production capacity also increases from 1.4 wafers in Comparative Example 1 to 1.8 wafers.

[0051] If the liquid supply is stopped in Comparative Example 2 during the Overlap stage, the CD Mean value is about 8 nm larger than that of the continuous liquid supply method in the Overlap stage of Example 1 of this invention. The single scan influence is about 2 nm, and the Mean value is more difficult to control. Example 1 requires less time for the same number of scans. If the scan time is controlled the same, more scans can be set, and the number of defects can be further reduced in high-order processes.

[0052] By employing the method described in Example 2, which adjusts the volume ratio of developer (TMAH) and deionized water during the overlap phase for each scan, the number of defects can be controlled to the order of 1-2 ea, and the CD Mean deviation is manageable. The TMAH:DIW ratio can be gradually reduced between 2:1 and 1:15.

[0053] Example 3 provides a further preferred solution: the mask can be rotated 180° each time the scanning direction is changed. Since the mask is square, and multiple scans are required in both the main development and overlap stages, in high-node mask manufacturing processes, the side that preferentially contacts the developer has a longer reaction time, while the side that lags behind in contact with the developer has a shorter reaction time. When the number of scans is not an integer multiple of 4, a biased distribution of the developed map may occur. Furthermore, because the slit nozzle is relatively long, its horizontal control relative to the mask is difficult, which also affects the CD profile during scanning. Therefore, by controlling the rotation angle during scanning and combining it with the biased state of the CD map, its distribution can be adjusted to obtain a controllable CD distribution result.

[0054] If the development process only uses the main development stage and has no overlap stage (Comparative Example 3), its particle control level is difficult to meet the industry standard of >300nm, less than 15ea, >1μm, and 0ea standard.

[0055] The number of scans in the Overlap stage must be greater than the number of scans in the main development stage; otherwise, the particle count is difficult to control. In Comparative Example 4, the number of scans in the Overlap stage was only 2, and the number of particles of 0.3~1μm in wet operation was 40ea, which cannot meet the industry standard of 15ea. If only 2 scans are performed in the Overlap stage, it basically does not have the effect of modifying defects, and the slit nozzle cannot be rinsed, making it difficult to control the particles generated in wet operation, thus resulting in defects such as development residue.

[0056] The main mechanism of the development process is that the developer reacts with the exposed photoresist and is then washed away. Therefore, using the same amount of developer in both the unidirectional scanning method of Comparative Example 5 and the bidirectional scanning method of this invention, the bidirectional scanning method is more efficient and faster. Furthermore, unidirectional scanning adds a puddling process compared to bidirectional scanning. This method, with repeated scanning, increases the puddling time variable in controlling the CD Mean value, making post-production equipment debugging more difficult and requiring more debugging time and a larger quantity of expensive source materials.

[0057] In summary, the developing method of the present invention achieves optimal results in terms of CD mean value, CD profile, defect quantity control, and production capacity.

Claims

1. A method for developing a mask substrate based on a slit nozzle, characterized in that, The photomask is developed using a bidirectional scanning method, specifically including the following steps: (1) Main development stage Place the mask on the developing machine stage, control the nozzle to scan and continuously spray developer along the direction from the first end to the second end of the mask; when the nozzle reaches the second end, stop the liquid supply and complete the reversal, and resume the liquid supply after the nozzle leaves the second end, and scan and spray developer along the direction from the second end to the first end; when the nozzle reaches the first end, stop the liquid supply and complete the reversal again, resume the liquid supply and continue scanning towards the second end, and repeat this scanning cycle multiple times; (2) Overlap stage The nozzle is controlled to scan and continuously spray a mixture of developer and water along the direction from the first end to the second end of the mask. When the nozzle reaches the second end, the liquid supply is not stopped and the direction is changed. The mixture of developer and water is then scanned and sprayed along the direction from the second end to the first end. When the nozzle reaches the first end, the liquid supply is not stopped and the direction is changed. The scanning continues to the second end. This cycle is repeated multiple times.

2. The mask substrate development method based on a slit nozzle according to claim 1, characterized in that: The mask includes, but is not limited to, a 28nm phase-shifting mask, a 160nm phase-shifting mask, and a 180nm binary mask; the nozzle is a slit nozzle, the length of which is greater than the width of the mask perpendicular to the scanning direction, so as to cover the entire scanning width of the mask; the developer is a mixture of tetramethylammonium hydroxide (TMAH) or methyl isobutyl ketone (MIBK) and IPA with a mass fraction of 2.38%, wherein the volume ratio of MIBK to IPA is 1:1, 1:2, or 1:

3.

3. The mask substrate development method based on a slit nozzle according to claim 1, characterized in that: The first end and the second end are opposite sides away from the edge of the mask, and are 10-12mm away from the edge of the mask.

4. The mask substrate development method based on a slit nozzle according to claim 1, characterized in that: In step (1), the scanning speed is 40-60 mm / s, the length of the slit nozzle is 150-350 mm, the spray flow rate of the developer is 1800-2500 mL / min, and the number of cyclic scans is ≥4 times, preferably 4-6 times.

5. The mask substrate development method based on a slit nozzle according to claim 1, characterized in that: In step (2), the scanning speed is 40-80 mm / s, 40-60, the spray flow rate of the mixture of developer and water is 1300-2500 mL / min, and the volume ratio of developer to water in the mixture of developer and water is 2:1-1:15; the number of cyclic scans is greater than the number of cyclic scans in the main development stage.

6. The mask substrate development method based on a slit nozzle according to claim 1 or 5, characterized in that: In step (2), during multiple cyclic scanning processes, the volume ratio of developer to water in the mixture of developer and water is controlled to decrease gradually within the range of 2:1 to 1:

15.

7. The mask substrate development method based on a slit nozzle according to claim 1, characterized in that: Each time the nozzle performs a scanning cycle, the mask rotates 180°. The length of the slit nozzle must be greater than the width of the mask perpendicular to the scanning direction in order to cover the entire scanning width of the mask.

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