A non-destructive blank mask cleaning system and cleaning process

Abstract

The present application relates to a kind of non-destructive blank mask cleaning system and cleaning process, cleaning process includes the following steps: blank mask is placed in supercritical carbon dioxide environment and is cleaned once;And the blank mask after cleaning once is treated with plasma, to achieve secondary cleaning.System includes: non-destructive cleaning module, it includes: supercritical carbon dioxide cleaning unit, it is configured to be cleaned once in supercritical carbon dioxide environment to blank mask;And low-temperature plasma processing unit, it is configured to be treated with low-temperature plasma in the mixed gas of oxygen and argon to blank mask, to achieve secondary cleaning.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and to a non-destructive blank mask cleaning system and cleaning process. Background Technology

[0002] A photomask is a core component of semiconductor photolithography, used to transfer design patterns onto the surface of a silicon wafer. Its surface cleanliness, roughness, and optical properties directly determine the quality of photolithography imaging and chip yield. As the substrate material before patterning, the blank mask easily adsorbs particulate contaminants, organic residues, and trace metal impurities during production, transportation, storage, and reuse. These contaminants must be removed through an efficient and gentle cleaning process while ensuring the mask surface remains undamaged and its optical performance remains stable.

[0003] Currently, the cleaning of blank masks mainly employs ultrasonic cleaning, chemical immersion, or mechanical brushing, which presents the following problems: Physical damage risk: Ultrasonic cavitation effects or mechanical brushing forces can easily generate micro-scratches or structural damage on the mask surface, affecting photolithography accuracy; Chemical corrosion: Traditional cleaning solutions (such as sulfuric acid, hydrogen peroxide, ammonia, etc.) are corrosive to mask materials (such as chromium, quartz, ruthenium, etc.), affecting mask lifespan with long-term use; Residual contamination: After cleaning, particles, water stains, or chemical substances are easily left behind, affecting the optical transmittance and reflectivity of the mask; Low efficiency: The multi-step cleaning process is complex and has a long cleaning cycle, making it difficult to meet the needs of high-efficiency production; Narrow applicability: Existing processes cannot effectively remove organic pollutants, particulate matter, and oxide layers simultaneously, often requiring multiple equipment combinations, increasing the risk of cross-contamination. Summary of the Invention

[0004] This invention provides a non-destructive blank mask cleaning system and cleaning process to solve the problems of physical damage, chemical corrosion, and residual pollution in existing cleaning methods.

[0005] The first aspect of this invention provides a non-destructive blank mask cleaning process, comprising the following steps: The blank mask was cleaned once in a supercritical carbon dioxide environment; and The blank mask after the first cleaning is subjected to plasma treatment to achieve a second cleaning.

[0006] Furthermore, in the aforementioned cleaning process, the cleaning pressure is 7.4~30MPa, the temperature is 32~60℃, and the time is 3~10min.

[0007] Furthermore, the supercritical carbon dioxide environment also includes 1-5 wt% ethanol or acetone, which together with the supercritical carbon dioxide form a supercritical mixed fluid. Supercritical carbon dioxide is carbon dioxide in a supercritical fluid state at a temperature above 32°C and a pressure above 7.4 MPa.

[0008] Furthermore, the plasma treatment employs a mixed gas of oxygen and argon for low-temperature plasma treatment, with temperatures below 80°C. The plasma treatment generates active free radicals, removing nanoscale organic residues and activating the surface, thus improving cleanliness. This unit works synergistically with the supercritical cleaning unit to achieve comprehensive removal of various contaminants.

[0009] Furthermore, the volume ratio of oxygen to argon is 1:(3~10).

[0010] Furthermore, the plasma processing power is 150~400 W, and the processing time is 1~5 min.

[0011] Furthermore, it also includes: The blank mask is pre-processed; the pre-processing includes surface condition detection and static electricity removal.

[0012] Furthermore, the surface condition detection employs a combination of laser scattering particle detection and high-resolution imaging to identify particles, defects, and roughness on the blank mask surface in real time, record initial contamination data, and screen out unqualified products.

[0013] Furthermore, the static removal process employs an ion wind static eliminator, which reduces the electrostatic potential on the mask surface to within ±50 V through the neutralization of positive and negative ions. This, combined with high-purity nitrogen purging, removes loose particles and reduces the risk of particle re-adsorption during subsequent cleaning processes.

[0014] Furthermore, it also includes: The blank mask after plasma treatment is dried.

[0015] Furthermore, the drying process is carried out under an inert gas atmosphere, specifically nitrogen, with a vacuum level of 10-100 Pa and a processing time of 1-3 min.

[0016] A second aspect of the present invention also provides a non-destructive blank mask cleaning system, comprising: Non-destructive cleaning module, comprising: The supercritical carbon dioxide cleaning unit is configured to perform a single cleaning of a blank mask in a supercritical carbon dioxide environment. Utilizing the high permeability and low surface tension of CO2 in a supercritical state (pressure can be set between 7.4 and 30 MPa, temperature between 32 and 60°C), the unit dissolves organic contaminants and removes particulate matter without damaging the mask surface structure. A small amount of co-solvent (such as ethanol or acetone) can be selectively added to enhance the solubility of specific contaminants; and The low-temperature plasma processing unit is configured to perform low-temperature plasma treatment on blank masks in a mixed gas of oxygen and argon for secondary cleaning. This non-destructive cleaning module avoids mechanical and chemical damage to the mask surface structure and materials while simultaneously removing multiple contaminants such as particles, organic residues, and oxide layers, achieving a particle removal rate of over 99.5%. It also reduces mask wear during cleaning, with surface roughness changes after a single cleaning cycle controlled within 0.1 nm, extending mask lifespan, reducing the defect rate caused by cleaning, and improving the stability of the photolithography process.

[0017] Furthermore, it also includes: A preprocessing module is configured to perform surface condition detection and electrostatic elimination on blank masks; and The drying module is configured to dry the blank mask by purging with inert gas in a vacuum environment. The drying module achieves traceless drying by purging with nitrogen in a vacuum environment, avoiding water stains.

[0018] Furthermore, it also includes: The online detection module is configured for real-time monitoring and feedback control of surface particle size, roughness, and optical properties before and after cleaning.

[0019] Furthermore, the online detection module includes a laser scattering particle detection unit and a spectral analysis unit, which are used to provide real-time feedback and adjust the process parameters of the preceding modules.

[0020] Furthermore, the non-destructive cleaning module, pretreatment module, drying module, and online detection module are connected via a closed-loop transmission chamber, forming a closed-loop cleaning system. The pretreatment module and the non-destructive cleaning module are connected via a closed transmission chamber to prevent secondary contamination. The pretreatment module uses an electrostatic eliminator to reduce the adhesion force on the mask surface, improving the efficiency of subsequent cleaning.

[0021] The present invention has at least the following beneficial effects: 1) The present invention avoids mechanical and chemical damage to the surface structure and materials of the mask, while simultaneously removing multiple contaminants such as particles, organic residues, and oxide layers, with a particle removal rate of over 99.5%. It also reduces the wear and tear on the mask during cleaning, with surface roughness changes after a single cleaning cycle controlled within 0.1 nm, extending the mask's lifespan and reducing the defect rate caused by cleaning, thus improving the stability of the photolithography process; 2) The present invention does not use strong acids or alkalis, and the supercritical CO2 is recyclable, resulting in no harmful waste liquid discharge. Attached Figure Description

[0022] To further illustrate the above and other advantages and features of the various embodiments of the present invention, a more specific description of the embodiments of the invention will be presented with reference to the accompanying drawings. It is to be understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by identical or similar reference numerals for clarity.

[0023] Figure 1 A flowchart illustrating the overall workflow of a non-destructive blank mask cleaning system in some embodiments of the present invention is shown. Detailed Implementation

[0024] It should be noted that the components in the accompanying drawings may be shown exaggerated for illustrative purposes and may not be to scale.

[0025] In this invention, the various embodiments are merely intended to illustrate the solutions of the invention and should not be construed as limiting.

[0026] In this invention, unless otherwise specified, the quantifiers “a” and “one” do not exclude scenarios involving multiple elements.

[0027] It should also be noted that, in the embodiments of the present invention, only a portion of the parts or components may be shown for clarity and simplicity. However, those skilled in the art will understand that, under the teachings of the present invention, the required parts or components can be added as needed for specific scenarios.

[0028] It should also be noted that within the scope of this invention, the terms "same", "equal", and "equal to" do not mean that the two values ​​are absolutely equal, but allow for a certain reasonable error. In other words, the terms also cover "substantially the same", "substantially equal", and "substantially equal to".

[0029] It should also be noted that in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not explicitly or implicitly suggest 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 the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] Furthermore, the embodiments of the present invention describe the process steps in a specific order. However, this is only for the convenience of distinguishing each step, and is not a limitation on the order of each step. In different embodiments of the present invention, the order of each step can be adjusted according to the process.

[0031] In the following examples, supercritical carbon dioxide is carbon dioxide in a supercritical fluid state with a temperature above 32°C and a pressure above 7.4 MPa.

[0032] The following embodiment provides a non-destructive blank mask cleaning process, including the following steps: The blank mask is pre-processed, including surface condition detection and static electricity removal. The blank mask was placed in a supercritical carbon dioxide environment for a single cleaning; during the single cleaning, the cleaning pressure was 7.4~30MPa, the temperature was 32~60℃, and the time was 3~10 min. The blank mask after the first cleaning is subjected to plasma treatment to achieve a second cleaning. The plasma treatment uses a mixture of oxygen and argon gas for low-temperature plasma treatment, with a temperature below 80℃, an oxygen to argon volume ratio of 1:(3~10), a plasma treatment power of 150~400 W, and a treatment time of 1~5 min. The blank mask after plasma treatment was dried under nitrogen atmosphere at a vacuum of 10-100 Pa for 1-3 min.

[0033] This embodiment also provides a non-destructive blank mask cleaning system. Figure 1 The overall workflow diagram of the non-destructive blank mask cleaning system is shown, including: Non-destructive cleaning module, comprising: A supercritical carbon dioxide cleaning unit, configured to perform a single cleaning of a blank mask in a supercritical carbon dioxide environment; and The low-temperature plasma processing unit is configured to perform low-temperature plasma processing on the blank mask in a mixture of oxygen and argon gas to achieve secondary cleaning. The preprocessing module is configured to perform surface condition detection and electrostatic elimination on the blank mask; A drying module configured to purge a blank mask with an inert gas in a vacuum environment; and The online inspection module is configured to detect surface particle size, roughness, and optical properties before and after cleaning and provide feedback control. The non-destructive cleaning module, pretreatment module, drying module, and online inspection module are connected via a closed transmission chamber, forming a closed-loop cleaning system.

[0034] In some embodiments, the supercritical carbon dioxide environment also includes 1-5 wt% ethanol or acetone, which together with the supercritical carbon dioxide form a supercritical mixed fluid.

[0035] Example 1 – Regular Maintenance and Cleaning of EUV High-Precision Masks This embodiment provides a non-destructive blank mask cleaning process, including: Pretreatment: Surface inspection and electrostatic elimination are performed; a laser scattering particle detector (such as KLA-TencorSurfscan) is used to detect surface particles and defects, and an ion wind electrostatic eliminator (set voltage ±5kV, ion balance ±20V) is used to reduce the electrostatic potential of the mask surface to within ±50V, and high-purity nitrogen (flow rate 50 L / min) is used to purge for 10 seconds. Supercritical carbon dioxide cleaning: pressure 15~20MPa, temperature 45~50℃, time 5~8min; Low-temperature plasma treatment: power 200~300W, oxygen / argon = 1:5, time 2~3min; Online detection: Particle removal rate can reach over 99.5%, surface roughness change is usually no more than 0.1nm, and optical reflectivity loss is less than 0.3%.

[0036] Example 2 – Intermediate Batch Cleaning in Mask Manufacturing This embodiment provides a non-destructive blank mask cleaning process, including: Pretreatment: Surface inspection and static elimination are performed; the pretreatment process in this embodiment is the same as in Embodiment 1; Supercritical carbon dioxide cleaning: pressure 10~15MPa, temperature 40~45℃, time 3~5min; Low-temperature plasma treatment: power 150~200W, oxygen / argon = 1:8, time 1~2min; Online inspection: Improves cleaning efficiency, suitable for mass production, and can process 4-6 masks per batch.

[0037] Example 3 – Mask Recycling and Reuse in Deep Cleaning This embodiment provides a non-destructive blank mask cleaning process, including: Pretreatment: Surface inspection and static elimination are performed; the pretreatment process in this embodiment is the same as in Embodiment 1; Supercritical carbon dioxide cleaning: pressure 20~25MPa, temperature 50~55℃, time 8~10min, with 5% ethanol added as a co-solvent; Low-temperature plasma treatment: power 300~400W, oxygen / argon = 1:4, time 3~5min; At the same time, an online detection module is activated to monitor the entire process and ensure that each mask can meet the factory-grade cleanliness standard after cleaning (e.g., particle count <10 / mask, particle size >0.1μm).

[0038] The structural advantages of the above embodiments are as follows: Modular design facilitates integration and maintenance; A closed transmission structure prevents cross-contamination; Integrating online detection and process control enhances automation levels. Each module is controlled independently, allowing for flexible adjustment of process parameters.

[0039] The functional advantages of the above embodiments are as follows: Non-destructive characteristics: The low surface tension (near zero) of supercritical CO2 can effectively eliminate surface tension damage during the drying process; plasma treatment is carried out at low temperature, without thermal damage; Highly efficient cleaning: The synergistic effect of supercritical cleaning and plasma treatment achieves simultaneous removal of particles and organic matter. By adjusting process parameters (such as supercritical CO2 pressure 10~25MPa, temperature 40~55℃, treatment time 3~10 minutes, plasma power 150~400W, time 1~5 minutes), the removal rate of particles with a diameter ≥0.1μm can reach over 99.5%, and the organic residue can be reduced to less than 5% of the original value. Surface integrity maintenance: After cleaning, the change in the Ra value of the mask surface roughness can be controlled within 0.1 nm (the original Ra value is usually 0.3-0.5 nm), and the changes in optical transmittance and reflectance can be less than 0.5%; Environmentally friendly: It does not use corrosive chemical solutions, supercritical CO2 can be recycled, and there is no harmful waste discharge; Wide process window: suitable for quartz substrates, glass substrates, and various coating masks (chromium, ruthenium, molybdenum silicide, etc.).

[0040] While some embodiments of the present invention have been described in this application, those skilled in the art will understand that these embodiments are merely illustrative. Numerous variations, alternatives, and improvements will arise in those skilled in the art under the teachings of this invention without departing from its scope. The appended claims are intended to define the scope of the invention and thereby cover methods and structures within the scope of the claims themselves and their equivalents.

Claims

1. A non-destructive blank mask cleaning process, characterized in that, Includes the following steps: The blank mask was cleaned once in a supercritical carbon dioxide environment. as well as The blank mask after the first cleaning is subjected to plasma treatment to achieve a second cleaning.

2. The non-destructive blank mask cleaning process according to claim 1, characterized in that, In the aforementioned cleaning process, the cleaning pressure is 7.4~30MPa, the temperature is 32~60℃, and the time is 3~10 min.

3. The non-destructive blank mask cleaning process according to claim 1, characterized in that, The supercritical carbon dioxide environment also includes 1-5 wt% ethanol or acetone.

4. The non-destructive blank mask cleaning process according to claim 1, characterized in that, In the plasma treatment, a mixture of oxygen and argon is used for low-temperature plasma treatment, with the temperature below 80°C; the plasma treatment power is 150~400 W, and the treatment time is 1~5 min.

5. The non-destructive blank mask cleaning process according to claim 4, characterized in that, The volume ratio of oxygen to argon is 1:(3~10).

6. The non-destructive blank mask cleaning process according to claim 1, characterized in that, Also includes: Preprocess the blank mask; The pretreatment includes surface condition detection and static electricity removal.

7. The non-destructive blank mask cleaning process according to claim 1, characterized in that, Also includes: The blank mask after plasma treatment is dried.

8. The non-destructive blank mask cleaning process according to claim 7, characterized in that, The drying process is carried out under an inert gas atmosphere, specifically nitrogen, with a vacuum level of 10-100 Pa and a processing time of 1-3 minutes.

9. A non-destructive blank mask cleaning system, characterized in that, include: Non-destructive cleaning module, comprising: A supercritical carbon dioxide cleaning unit, configured to perform a single cleaning of a blank mask in a supercritical carbon dioxide environment; and The low-temperature plasma processing unit is configured to perform low-temperature plasma processing on the blank mask in a mixture of oxygen and argon gas to achieve secondary cleaning.

10. The non-destructive blank mask cleaning system according to claim 9, characterized in that, Also includes: The preprocessing module is configured to perform surface condition detection and electrostatic elimination on the blank mask; as well as The drying module is configured to dry the blank mask by purging it with an inert gas in a vacuum environment.

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