A cleaning method for a mask cleaning machine cavity

Abstract

The application discloses a cleaning method for a mask cleaning machine cavity, and belongs to the technical field of semiconductor cleaning equipment maintenance. The cleaning method is aimed at the problem that the inner wall of an old cleaning machine cavity is roughened due to long-term chemical corrosion and is prone to accumulate ammonium salt crystalline substances and organic residues. The cavity is subjected to multi-stage flushing and wiping by using hot water with different temperatures in sequence, so that the crystalline substances embedded in the microscopic depressions are effectively dissolved and removed. Then, the cavity is wiped by using a flexible wiping member soaked with an organic solvent, so that the organic residues are completely removed and secondary scratches on the fragile cavity surface during the wiping process are avoided. The cleaning method cooperatively uses multi-stage hot water cleaning and organic solvent cleaning, effectively removes stubborn contaminants in the cleaning machine cavity, and improves the cleaning success rate of the mask and the effective utilization rate of the machine.

Description

Technical Field

[0001] This invention relates to the field of semiconductor cleaning equipment maintenance technology, and in particular to a method for cleaning the cavity of a mask cleaning machine. Background Technology

[0002] In semiconductor photolithography, the photomask serves as a crucial carrier for pattern transfer, and its surface cleanliness directly impacts exposure quality and product yield. During the wafer fabrication process, photomasks require periodic cleaning using cleaning equipment, and the cleanliness of the cleaning equipment chamber itself is a prerequisite for ensuring effective photomask cleaning.

[0003] For long-term photomask cleaning equipment, especially older machines that have been in operation for more than fifteen years, the inner wall of the cavity is constantly subjected to the erosion and immersion of high-temperature chemical reagents such as strong sulfuric acid and strong alkali, resulting in a significant reduction in the strength of the surface material. Under microscopic observation, the inner surface of the cavity has been eroded into an uneven surface, forming numerous tiny pits and gaps.

[0004] The roughened cavity surface easily accumulates chemical crystals and organic residues. Currently, the industry standard for cleaning cavities is to use a lint-free cloth with water. However, this method has extremely limited effectiveness in removing these stubborn deposits. On the one hand, the microscopic depressions on the surface of old cavities allow crystals and organic residues to become embedded within them, making it difficult for conventional wiping methods to effectively reach and remove these deposits. On the other hand, during wiping, the lint-free cloth can cause detached crystal particles to move across the rough cavity surface, resulting in secondary scratches on the already fragile surface and further exacerbating the surface roughness.

[0005] The increased surface roughness of the cavity and the insufficient cleaning effect create a vicious cycle, making it easier for contaminants to accumulate inside the cavity. Eventually, these contaminants will fall off during the cleaning process and adhere to the surface of the mask, requiring the mask to be reworked and cleaned. In severe cases, it can even produce fog-like defects, endangering the yield of customers' products.

[0006] Therefore, there is an urgent need for a cleaning method that can effectively remove chemical crystals and organic residues from the cavity of old cleaning machines without causing secondary damage to the cavity surface. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this application is to provide a cleaning method for the cavity of a mask cleaning machine, which solves the problems in the prior art where old cleaning machine cavities are difficult to effectively remove crystals and organic residues due to rough inner surface erosion, conventional wiping methods easily cause secondary scratches on the cavity surface, and incomplete cleaning leads to mask contamination.

[0008] To achieve the above and other related objectives, this application provides a method for cleaning the cavity of a mask cleaning machine, comprising the following steps: The cavity is rinsed and wiped in multiple stages with hot water of different temperatures in sequence to remove the crystals; The cavity is wiped with a flexible wiping tool soaked in organic solvent to remove organic residues.

[0009] Preferably, the hot water at different temperatures includes at least hot water at a first temperature and hot water at a second temperature, wherein the first temperature is higher than the second temperature; The multi-stage rinsing and wiping includes: First, use hot water at the first temperature to spray and rinse the cavity multiple times; Then, using hot water at the second temperature, wipe with a flexible wiping tool while simultaneously spraying and rinsing; Finally, wipe the corners of the cavity with a wiping material that has been moistened with hot water at the second temperature.

[0010] Preferably, the step of using hot water at the first temperature to perform multiple spraying and rinsing is performed at least three times, with each rinsing lasting at least 5 minutes. After each rinsing, the reduction of crystals is observed and confirmed by shining a strong flashlight on the water, with the end point being the disappearance of crystals in the empty areas of the cavity.

[0011] Preferably, the first temperature is between 45°C and 55°C, and the second temperature is between 35°C and 45°C.

[0012] Preferably, the first temperature is 50°C and the second temperature is 40°C.

[0013] Preferably, the wiping step using a flexible wiping tool soaked in organic solvent is repeated at least three times, and the cleaning endpoint is confirmed by observing with a strong flashlight to ensure that there is no organic residue in the cavity and the flexible wiping tool used.

[0014] Preferably, the organic solvent is anhydrous isopropanol.

[0015] Preferably, the flexible wiping element is a dust-free cloth.

[0016] Preferably, the hot water is provided by a dedicated water gun branching off from the main hot water pipe of the cleaning machine, and the temperature of the hot water is controlled by the machine's programming.

[0017] Preferably, the cleaning method further includes: periodically polishing the cavity with sandpaper.

[0018] Preferably, the crystals are ammonium salt crystals.

[0019] As described above, the cleaning method for the cavity of the mask cleaning machine provided in this application has the following beneficial effects: The cleaning method for the cavity of a mask cleaning machine provided in this application addresses the problem of difficult removal of crystals and organic residues due to the rough inner surface erosion of old cleaning machine cavities. It effectively removes stubborn crystals embedded in microscopic depressions by sequentially rinsing and wiping the cavity with hot water at different temperatures in multiple stages. To address the issue of secondary scratches on the cavity surface caused by conventional wiping methods, a flexible wiping tool soaked in organic solvent is used for wiping, thoroughly removing organic residues while avoiding damage to the already fragile cavity surface. Ultimately, this method solves the problem of mask contamination caused by incomplete cavity cleaning, improving the success rate of mask cleaning and the effective utilization rate of the machine. Attached Figure Description

[0020] Figure 1 This is a graph showing the percentage of ammonium salt crystals dissolved over time under different hot water conditions.

[0021] Figure 2 The image shows the 4C test results of 37 sample cavities collected after using the cleaning method of Example 1.

[0022] Figure 3 The image shows the 4C test results of 37 sample cavities collected after using the cleaning method of Example 2.

[0023] Figure 4 The image shows the 4C test results of 37 sample cavities collected after using the cleaning method of Comparative Example 1.

[0024] Figure 5 The image shows the 4C test results of 246 sample cavities collected after using the cleaning method of Example 1.

[0025] Figure 6 The image shows the 4C test results of 253 sample cavities collected after using the cleaning method of Comparative Example 2.

[0026] Figure 7 The image shows the 4C test results of 246 sample cavities collected after using the cleaning method of Comparative Example 3. Detailed Implementation

[0027] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present application.

[0028] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application.

[0029] This application provides a method for cleaning the cavity of a mask cleaning machine, used to remove chemical crystals and organic residues accumulated in the cavity of a mask cleaning machine that has been in service for a long time. Due to years of exposure to strong sulfuric acid, strong alkali, and other chemical reagents, the inner wall surface of this cavity is corroded and becomes uneven, forming numerous microscopic depressions, which easily accumulate ammonium salt crystals and organic residues.

[0030] The raw materials used in the embodiments and comparative examples of this application are as follows: Hot water is deionized water with a conductivity not exceeding 6 μS / cm; Anhydrous isopropanol is electronic-grade anhydrous isopropanol used in semiconductor processes. Its purity is not less than 99.9%, water content is less than 0.1%, and metal ion content is less than 10 ppd. High-powered flashlight: White light (6000K cool white light; general macroscopic inspection), full spectrum: 420nm~680nm; Special sandpaper: HT4528D-10-1, a 360-grit diamond scrubbing pad with a fiber-free construction. Example 1

[0031] This embodiment uses the cleaning method provided in this application to clean the cavity of a mask cleaning machine that has been in service for more than 15 years. The specific steps are as follows: S1, Equipment Modification The cleaning machine was modified by branching off a dedicated rinsing pipeline from the existing hot water main, and connecting a dedicated water gun to this pipeline. The hot water is obtained by heating deionized water (DIW) with a conductivity not exceeding 6μS / cm. The hot water temperature can be set and adjusted via a programmable control unit on the machine, allowing operators to output hot water at different temperatures according to cleaning needs.

[0032] S2, Multi-stage hot water rinsing and wiping During cleaning, the cavity is first sprayed and rinsed with hot water at the initial temperature. The initial temperature of the hot water is set to 50°C through the machine program, so as to utilize the thermal energy and dissolving capacity of the hot water to gradually dissolve and loosen the ammonium salt crystals adhering to the inner surface of the cavity.

[0033] The spray rinsing was performed three times, each lasting five minutes. After each rinse, the operator used a strong flashlight to illuminate the inner surface of the cavity and observe the reduction of crystals. After the first rinse, large areas of crystals began to detach or their volume decreased significantly; after the second rinse, most of the crystals in the empty areas of the cavity were removed, with only small pieces remaining in some areas; after the third rinse, the crystals in the empty areas of the cavity had basically disappeared. If crystals remained in some areas, one or more additional rinses were performed until the crystals in the empty areas were completely gone.

[0034] After the crystals disappear in an open area, the hot water temperature is adjusted to a second temperature via machine programming. This second temperature is 40°C lower than the first temperature, allowing operators to perform manual wiping in subsequent steps.

[0035] Using hot water at a second temperature, while continuing to spray and rinse, the operator wipes the inner surface of the cavity with a lint-free cloth. At this time, the water rinsing and wiping are carried out simultaneously, and the residual micro-crystals that have been loosened by the hot water are further removed under the combined action of the impact of the water flow and the mechanical wiping force of the lint-free cloth.

[0036] Subsequently, the operator used a lint-free cloth soaked in hot water at a second temperature to wipe each corner of the cavity one by one. Corner areas are where crystals easily accumulate and are difficult to cover directly by spraying; manual wiping ensures that the crystals in these areas are thoroughly removed. During the wiping process, the operator continuously used a strong flashlight to observe and confirm that no crystals remained in any corner.

[0037] S3, organic solvent wiping After the multi-stage hot water rinsing and wiping steps are completed, wait for the surface temperature of the cavity to drop to room temperature or close to room temperature before wiping with organic solvents.

[0038] The organic solvent used in this embodiment is anhydrous isopropanol (IPA), preferably electronic-grade anhydrous isopropanol for semiconductor processes, with a purity of not less than 99.9%, a water content of less than 0.1%, and a metal ion content of less than 10 ppb, which can be directly purchased commercially. Using high-purity anhydrous isopropanol for wiping can effectively remove organic residues while avoiding secondary contamination of the cavity due to impurities in the solvent itself.

[0039] Use anhydrous isopropyl alcohol to moisten a lint-free cloth and wipe the entire inner surface of the cavity. The wiping process is repeated three times: the first wipe mainly removes large areas of organic residue; the second wipe focuses on cleaning stubborn residues in specific areas; the third wipe is used to check for any remaining residues and ensure that no organic residue is missed.

[0040] After each wipe, the operator uses a strong flashlight to illuminate the inner surface of the cavity for observation and to check the condition of the used lint-free cloth. After the third wipe, if no visible organic residue remains on the inner surface of the cavity under the strong flashlight and the surface of the used lint-free cloth is clean and free of dirt, it is determined that the organic residue has been completely removed, and the organic solvent wiping step is complete.

[0041] S4. Regular grinding and polishing In addition, to prevent the re-adhesion of crystals and organic matter on the rough surface of the cavity caused by long-term chemical erosion, machine maintenance personnel regularly perform grinding and polishing on the inner surface of the cavity. Special sandpaper with a grit of 280 is used for grinding, evenly grinding along the cavity surface until the surface feels smooth and shows no obvious unevenness or reflective differences under strong flashlight illumination. After grinding and polishing, the cavity is rinsed with hot water to remove grinding debris, and then the above-mentioned multi-stage hot water rinsing and wiping, along with organic solvent wiping steps, are performed again to restore the cavity to a clean state. Regular grinding and polishing effectively reduces the surface roughness of the cavity, reducing the probability of contaminant adhesion in subsequent production, thereby ensuring the long-term stable operation of the machine and the success rate of mask cleaning. Example 2

[0042] This embodiment also provides a cleaning method, which cleans the old cleaning machine cavity of the same specifications and the same degree of contamination as in Embodiment 1 using the same method.

[0043] During cleaning, hot water at the first and second temperatures is used to spray and rinse the cavity. The number of rinses and the duration are the same as the hot water rinsing steps in Example 1. The inner surface of the cavity is wiped with a lint-free cloth soaked in anhydrous isopropanol. The number of wipes and the operation method are the same as the organic solvent wiping steps in Example 1, but the hot water at the first temperature is 45°C and the hot water at the second temperature is 35°C. Example 3

[0044] This example is an experiment on the dissolution efficiency of ammonium salt crystals by hot water at different temperatures.

[0045] To verify the dissolution effect of hot water at different temperatures on ammonium salt crystals in the cavity, and to provide a basis for determining the optimal range of the first and second temperatures, the following comparative experiment was conducted.

[0046] Several stainless steel test pieces of the same material as the cavity of the mask cleaning machine were selected. An equal amount of ammonium salt crystals were coated on the surface of each test piece. They were placed in a constant temperature and humidity environment for the same amount of time to allow the crystals to fully adhere to the surface of the test pieces, so as to simulate the crystal accumulation state on the surface of the old cavity.

[0047] The test pieces coated with crystals were divided into six groups and immersed in deionized water at 35℃, 40℃, 45℃, 50℃, 55℃, and 60℃, respectively, while maintaining consistent stirring or continuous water flow conditions. Samples were taken at regular intervals to measure the ammonium salt content in the water, and the crystal dissolution efficiency was calculated. The experimental results are shown in Table 1 and... Figure 1 As shown.

[0048] Table 1 0 0 0 0 0 0 0 5 34 42 50 58 66 74 10 50 61 68 76 83 89 20 65 78 84 89 93 96 30 73 87 91 95 97 98.5 45 79 93 96 98 99.2 99.8 60 83 96 98 99.2 99.8 100 Figure 1The graph shows the dissolution efficiency of ammonium salt crystals with dissolution time under hot water conditions of 35℃, 40℃, 45℃, 50℃, 55℃ and 60℃. The horizontal axis represents dissolution time in minutes, and the vertical axis represents ammonium salt dissolution efficiency, which is the percentage of dissolved crystals relative to the total initial crystal mass.

[0049] From Table 1 and Figure 1 It can be seen that the dissolution efficiency reaches 99.2% after 60 minutes at 50℃, 99.5% after 50 minutes at 55℃, and 99.7% after 40 minutes at 60℃. Although experimental data shows that the ammonium salt dissolution rate is faster at 60℃, this application sets the first hot water temperature at around 50℃ based on a comprehensive optimization choice considering the material properties of the mask cleaning machine cavity, operational safety, energy consumption control, and the overall synergy of the cleaning process. The mask cleaning machine cavity is usually equipped with components such as polymer sealing rings, precision coatings, or sensors. Long-term contact of these materials with 60℃ hot water will accelerate aging, deformation, or lead to a decrease in sealing performance. At 50℃ for 60 minutes, the hot water already achieves a dissolution efficiency of over 99.2%, fully meeting the quantitative requirements for ammonium salt removal at the cleaning endpoint. While further increasing the water temperature to 60℃ could shorten the dissolution time, the thermodynamic marginal benefit diminishes, while the heating energy consumption increases significantly, which is not economical for large-scale maintenance scenarios in semiconductor production lines. In cleaning open or semi-open cavities, 60°C hot water generates a large amount of high-temperature steam, increasing the risk of burns to operators and making prolonged handheld spraying or deep cleaning within the cavity difficult. 50°C falls within the warm range, allowing operators to work continuously while wearing basic protective gloves, improving process operability. Furthermore, this invention employs a two-stage temperature control strategy. If the first temperature is 60°C, the cavity surface temperature becomes too high, easily creating significant thermal stress on the cavity wall when transitioning to the second temperature stage of 35°C to 45°C. Additionally, the high-temperature surface encountering the lower-temperature water flow will produce a large amount of condensation, interfering with visual judgment and cleaning effectiveness. 50°C, as the starting temperature, provides a smoother transition to the subsequent medium-temperature stage, helping to maintain a stable physical cleaning environment. Excessively high water temperatures also accelerate water evaporation; if dissolved trace impurities dry rapidly on the cavity surface, they may form new particle deposits. Physical cleaning at 50°C, combined with physical cleaning under strong flashlight detection, ensures that ammonium salts are fully dissolved and promptly rinsed or wiped away, avoiding secondary residues caused by rapid drying at high temperatures. Comparative Example 1

[0050] This comparative example uses the same method as Example 1 to clean the cavity of an old cleaning machine with the same specifications and degree of contamination as Example 1.

[0051] During cleaning, hot water at the first and second temperatures is used to spray and rinse the cavity. The number of rinses and the duration are the same as the hot water rinsing steps in Example 1. The inner surface of the cavity is wiped with a lint-free cloth soaked in anhydrous isopropanol. The number of wipes and the operation method are the same as the organic solvent wiping steps in Example 1, but the hot water at the first temperature is 35°C and the hot water at the second temperature is 35°C. Comparative Example 2

[0052] This comparative example uses deionized water (DIW) rinsing alone to clean the cavity of an old cleaning machine of the same specifications and degree of contamination as in Example 1.

[0053] During cleaning, the cavity is sprayed with hot water at the same temperature as the first and second temperatures in Example 1. The number of sprays and the duration are the same as the hot water rinsing steps in Example 1, but no organic solvent wiping steps are performed. Comparative Example 3

[0054] This comparative example uses anhydrous isopropyl alcohol (IPA) to wipe the cavity of an old cleaning machine of the same specifications and degree of contamination as in Example 1.

[0055] During cleaning, only a lint-free cloth moistened with anhydrous isopropyl alcohol is used to wipe the inner surface of the cavity. The number of wipes and the operation method are the same as the organic solvent wiping steps in Example 1, but the hot water rinsing step is not performed.

[0056] Cleaning effect verification To verify the cleaning effects of Examples 1, 2, and Comparative Examples 1 to 3, particle detection methods were used for evaluation.

[0057] The specific method is as follows: After cleaning, a surface particle detector is used to detect particles on the inner surface of the cavity in Examples 1, 2, and Comparative Examples 1 to 3, and the number of particles with a diameter greater than or equal to 0.4 μm is counted. Figure 2 The image shows the 4C test results of 37 sample cavities collected after using the cleaning method of Example 1; Figure 3 The image shows the 4C test results of 37 sample cavities collected after using the cleaning method of Example 2; Figure 4 The image shows the 4C test results of 37 sample cavities collected after using the cleaning method of Comparative Example 1. Figure 5 The image shows the 4C test results of 246 sample cavities collected after using the cleaning method of Example 1. Figure 6 The image shows the 4C test results of 253 sample cavities collected after using the cleaning method of Comparative Example 2. Figure 7 The image shows the 4C detection results of 246 sample chambers collected after using the cleaning method of Comparative Example 3. In the above figure, the horizontal axis represents the sample used, and the vertical axis represents the particle count.

[0058] from Figures 2 to 4 It can be seen that the method of Example 1 resulted in the lowest particle count after cleaning, achieving the required high cleanliness. The method of Example 2, due to the lower hot water temperature compared to Example 1, led to insufficient dissolution, resulting in an increased particle count after cleaning, but the cleanliness was still acceptable. The method of Comparative Example 1, due to the further decrease in hot water temperature compared to Example 2, resulted in even less complete dissolution, with a large amount of ammonium salt crystals remaining, further increasing the particle count after cleaning, and failing to meet the cleanliness requirements.

[0059] from Figures 5 to 7 It can be seen that: Example 1, which uses a combination of DIW rinsing and IPA wiping, has an average particle count of 1.39 particles, significantly lower than Comparative Example 2 (1.56 particles) and Comparative Example 3 (2.08 particles); the maximum particle count in Example 1 is only 8 particles, significantly lower than Comparative Example 2 (13 particles) and Comparative Example 3 (20 particles). Comparative Example 2 uses only deionized water, and almost no organic residue is removed. Comparative Example 3 uses only isopropanol, which has the ability to dissolve organic matter, but because the inorganic salt barrier in the cavity is not removed, the isopropanol cannot fully contact the underlying organic residue, resulting in incomplete cleaning. This indicates that the cleaning method provided in this application is significantly superior to any single cleaning method in terms of cleaning effect and cleaning stability.

[0060] Based on the experimental data from Examples 1 to 3 and Comparative Examples 1 to 3, it can be seen that: on the one hand, selecting a suitable hot water temperature is crucial for thoroughly removing crystals; on the other hand, rinsing with hot water alone or wiping with IPA alone cannot achieve the cleaning effect of the combined method of this application.

[0061] The above results fully demonstrate that this application, through the combination of "multi-stage rinsing and wiping with hot water at different temperatures" and "wiping with flexible wiping parts soaked in organic solvents," effectively removes stubborn ammonium salt crystals and organic residues from the cavity of old cleaning machines, solving the problem of poor performance of single cleaning methods in the prior art.

[0062] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for cleaning the cavity of a mask cleaning machine, characterized in that, Includes the following steps: The cavity is rinsed and wiped in multiple stages with hot water of different temperatures in sequence to remove the crystals; The cavity is wiped with a flexible wiping tool soaked in organic solvent to remove organic residues.

2. The cleaning method according to claim 1, characterized in that, The hot water at different temperatures includes at least hot water at a first temperature and hot water at a second temperature, wherein the first temperature is higher than the second temperature. The multi-stage rinsing and wiping includes: First, use hot water at the first temperature to spray and rinse the cavity multiple times; Then, using hot water at the second temperature, wipe with a flexible wiping tool while simultaneously spraying and rinsing; Finally, wipe the corners of the cavity with a wiping material that has been moistened with hot water at the second temperature.

3. The cleaning method according to claim 2, characterized in that, The step of using hot water at the first temperature to spray and rinse multiple times shall be performed at least three times, with each rinsing lasting at least 5 minutes. After each rinsing, the crystal reduction shall be observed and confirmed by shining a strong flashlight on the surface. The rinsing shall end when the crystals in the empty areas of the cavity disappear.

4. The cleaning method according to claim 2 or 3, characterized in that, The first temperature is between 45℃ and 55℃, and the second temperature is between 35℃ and 45℃.

5. The cleaning method according to claim 1, characterized in that, The wiping process using a flexible wiping tool soaked in organic solvent is repeated at least three times, and the cleaning endpoint is reached by observing with a strong flashlight to confirm that there is no organic residue in the cavity and the flexible wiping tool.

6. The cleaning method according to claim 1 or 5, characterized in that, The organic solvent is anhydrous isopropanol.

7. The cleaning method according to claim 1, characterized in that, The flexible wiping component is a dust-free cloth.

8. The cleaning method according to claim 1, characterized in that, The hot water is supplied by a dedicated water gun branching off from the main hot water pipe of the cleaning machine, and the temperature of the hot water is controlled by the machine's programming.

9. The cleaning method according to claim 1, characterized in that, Also includes: The cavity should be sanded and polished regularly.

10. The cleaning method according to any one of claims 1 to 9, characterized in that, The crystals are ammonium salt crystals.

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