Cleaning method for semiconductor photoetching mask substrate

Abstract

The invention discloses a cleaning method for a semiconductor photoetching mask substrate, and belongs to the technical field of semiconductor manufacturing. According to the method, dynamic cleaning logic of step cooperation and energy matching is adopted, and the steps of interface wetting and pre-cleaning, chemical soft interface construction, low-damage mechanical stripping and synchronous washing, targeted reaction clearing, microstructure deep cleaning, interface dehydration and modification and final energy-assisted drying are sequentially executed. The method is characterized in that through the dependency relationship of chemical interface softening and low-damage mechanical stripping in sequence, the rotation speed of a substrate in each step is strictly controlled to meet the specific dynamic relationship (V2 < V1 < V4 < V3 < V5 < V6), and precise cooperation of chemical action, physical stripping and energy field cleaning is achieved. The contradiction between efficiency and substrate damage in a traditional cleaning process is effectively solved, full-scale pollutants from micron-scale particles to nano-scale molecular contamination can be removed without dead corners, and a clean, stable and secondary pollution resistant surface state is actively reconstructed at a cleaning end point; and the cleanliness and the service life of the mask substrate and the yield of a downstream photoetching process are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing process technology, specifically to a cleaning method for semiconductor photolithography mask substrates, which is particularly suitable for cleaning processes of high-precision mask substrates during manufacturing and use. Background Technology

[0002] In semiconductor photolithography, the surface cleanliness of the mask substrate directly affects the accuracy of the lithographic pattern and the reliability of the device. As process nodes continue to shrink, higher demands are placed on the cleaning process of the mask substrate, especially the need to achieve a precise balance between the removal of nanoscale contaminants and the protection of substrate surface integrity. Currently, commonly used mask substrate cleaning methods in the industry mainly suffer from the following problems: Chemical cleaning methods: Traditional chemical cleaning often involves directly treating the substrate surface with strong acids, strong alkalis, or fluorine-containing reagents. While these methods are effective at removing certain contaminants, their strong corrosiveness can easily cause chemical erosion or surface oxidation of the mask substrate material, introducing microscopic defects and affecting the physical and optical properties of the substrate. Furthermore, for hardened or stubbornly adhered contaminants, simple chemical immersion is often insufficient for effective softening and separation, resulting in low cleaning efficiency and high process risks.

[0003] Physical cleaning methods, including tank-based physical cleaning methods such as ultrasonic or megasonic cleaning, can remove some particulate contaminants. However, their energy distribution is uneven, and excessive energy in localized areas can cause "micro-damage" to delicate, ultra-smooth surfaces. At the same time, for firmly attached contaminants, insufficient energy may prevent complete removal, creating an inherent contradiction between cleaning uniformity and damage control.

[0004] Scale-based cleaning: Existing cleaning processes are mostly designed for contaminants within a single particle size range, lacking a systematic and graded removal mechanism for contaminants of different sizes (from micron-sized particles to nano-sized molecular contaminants). A "one-step" cleaning approach cannot achieve efficient removal of the entire spectrum of contaminants while ensuring no damage to the substrate.

[0005] Targeted Removal and Cleaning of Contaminants: The contaminants adhering to the mask substrate during actual processes are complex and can include various heterogeneous contaminants such as organic residues, metal ions, and particulate matter. Existing methods often lack specificity; "one-size-fits-all" cleaning formulations cannot effectively address multiple heterogeneous contaminants simultaneously, leading to incomplete removal of certain contaminants and becoming potential sources of defects affecting product yield.

[0006] Therefore, there is an urgent need to develop a high-precision cleaning method that can efficiently remove multi-scale and multi-component contaminants while ensuring zero damage to the surface of the mask substrate, in order to meet the stringent requirements of advanced semiconductor manufacturing for the cleanliness and reliability of mask substrates. Summary of the Invention

[0007] The present invention aims to solve the problems existing in the existing mask substrate cleaning technology and provide a cleaning method for semiconductor photolithography mask substrates.

[0008] The technical solution of this invention: A cleaning method for a semiconductor photolithography mask substrate, characterized by comprising the following steps: S1. Interface wetting and pre-cleaning: The mask substrate is rotated at a first rotation speed while high-purity deionized water is applied to form a uniform initial water film and remove loose contaminants using the shear force of the water flow. S2. Chemical Soft Interface Construction: The rotation speed of the mask substrate is reduced to a second rotation speed, and an alkaline cleaning solution is sprayed onto its surface by atomization to construct a chemical soft interface on the basis of the initial water film, thereby reducing the adhesion between contaminants and the substrate surface; S3. Low-damage mechanical peeling: The rotation speed of the mask substrate is increased to a third rotation speed higher than the first rotation speed. In the presence of the chemically softened interface, a flexible physical action component is used to act on the surface, while deionized water is applied for synchronous rinsing, so as to achieve low-damage peeling and immediate removal of contaminants. S4. Targeted Reaction Removal: The rotation speed of the mask substrate is adjusted to the fourth rotation speed, and a targeted cleaning solution that selectively reacts with specific residual contaminants is applied to its surface, followed by rinsing; S5. Microstructure deep cleaning: The rotation speed of the mask substrate is increased to the fifth rotation speed, and a functional liquid activated by a high-frequency energy field is applied to its surface. The hydrodynamic synergistic energy field effect is used to act on the ultra-smooth surface to remove residual particles. S6. Interface dehydration and modification: The rotation speed of the mask substrate is increased to the sixth speed for centrifugal dehydration, and then the surface is purged with modified processing gas to remove residual liquid film and optimize surface condition. S7. Low-temperature non-destructive drying: Drying is performed by applying non-contact energy to the surface; Among them, the first speed, the second speed, the third speed, the fourth speed, the fifth speed and the sixth speed satisfy a specific dynamic control relationship: V2 < V1 < V4 < V3 < V5 < V6.

[0009] Furthermore, in step S3, the flexible physical action component is a flexible rotating brush that does not contact the substrate surface. The distance between the brush and the substrate surface is 0.1-2.0 mm, and in step S3, the rotation direction of the flexible rotating brush is opposite to the rotation direction of the mask substrate.

[0010] Furthermore, according to the cleaning method of claim 2, the bristle material of the flexible rotating brush is polyvinyl alcohol (PVA) with a hardness of 40-70 Shore A, and the maximum shear force generated by the bristles in step S3 is controlled below the mechanical damage threshold of the most vulnerable ultra-smooth surface of the mask substrate.

[0011] Furthermore, in step S2, the alkaline treatment solution is ammonia or quaternary ammonium alkali solution, which achieves the construction of the chemically softened interface through at least one mechanism of saponification reaction, hydrolysis and adjustment of surface potential. The second rotation speed is configured to make the effective residence time of the alkaline treatment solution on the substrate surface reach 30-90 seconds.

[0012] Furthermore, in step S4, the selection of the targeted cleaning solution is based on offline or online analysis of the residual contaminants after step S3. It is selected from one of chelating agent solutions, inorganic acid solutions, organic acid solutions, oxidant solutions, or combinations thereof, and is used to achieve at least one of complexation, dissolution, or redox reactions.

[0013] Furthermore, the targeted cleaning solution comprises at least one of the following combinations: For metal ion contaminants, use a chelating agent solution of EDTA or DTPA at a concentration of 0.1-1.0 wt%. For oxidative contaminants, use a dilute hydrochloric acid or dilute nitric acid solution with a pH of 2-4; For organosilicon contaminants, use SC-1 solution (NH4OH:H4O4:H4O=1:1:5-1:2:10).

[0014] Furthermore, in step S5, the high-frequency energy field is an acoustic energy field with a frequency in the range of 0.8-3.0MHz, the functional liquid is deionized water activated by the acoustic energy field and rich in submicron-sized cavitation bubbles, and the fifth rotation speed is configured to work in synergy with the application of the functional liquid to effectively transfer the acoustic energy and fluid shear force to the ultra-smooth surface of the substrate.

[0015] Furthermore, in step S6, the modified treatment gas is ionized nitrogen gas with a dew point below -70°C and both positive and negative ion concentrations not less than 1×10⁻⁶. 4 ions / cm 3The purging angle, pressure, and time are optimized to achieve the synergistic effect of removing residual liquid film, eliminating static charge, and preventing surface oxidation.

[0016] Furthermore, the preparation of the ionized nitrogen gas includes: High-purity nitrogen gas is passed through an ion generator to produce positive and negative ion concentrations of 1×10⁻⁶ each. 4 -1×10 6 ions / cm 3 Nitrogen ions; Control the nitrogen dew point below -70℃ to prevent moisture residue; The purging angle is controlled between 30 and 60 degrees, and the purging pressure is 0.1-0.5 MPa.

[0017] Furthermore, in step S7, the non-contact energy is mid-wave infrared radiation with a wavelength in the range of 2-5μm, the drying process is carried out while the mask substrate is kept rotating, and the temperature of the surface of the mask substrate is controlled at 50-90℃ to avoid thermal stress damage.

[0018] Furthermore, the first speed is 50-200 RPM, the second speed is 20-60 RPM, the third speed is 150-300 RPM, the fourth speed is 20-60 RPM, the fifth speed is 200-500 RPM, and the sixth speed is 500-1500 RPM.

[0019] Furthermore, the cleaning method is executed by an integrated control system configured to: (a) Based on the input mask substrate material and initial contaminant information, retrieve or generate a set of matching cleaning parameters from the pre-stored process database. The set of parameters includes at least the rotation speeds of V1 to V6, the duration of each step, and the concentration of each chemical solution. (b) During the execution of steps (S3) and / or (S5), the parameters of the flexible physical action component and / or the energy input of the functional liquid are dynamically adjusted according to the feedback signal from the online monitoring module to achieve an adaptive cleaning process.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. Achieve ultra-efficient cleaning at sub-damage threshold Traditionally, high cleanliness is associated with an increased risk of physical damage. This invention resolves the fundamental contradiction between "cleaning power" and "substrate safety" through a "chemical softening interface construction-low-damage mechanical peeling wash" method. Traditional strong physical cleaning or chemical etching methods can easily cause irreversible damage to the surface material of the mask substrate. This method first utilizes an alkaline cleaning solution at low speed to fully wet, penetrate, and saponify contaminants, transforming them from a firmly adhered state to a "softened" loose state, significantly reducing their adhesion to the substrate. Following this, a flexible brush is used for high-speed physical brushing. The required mechanical force is greatly reduced, allowing the flexible brush to easily peel off the softened contaminants under low pressure and low shear force, rather than scraping them off "hard." This step-by-step synergistic mechanism ensures efficient removal of even stubborn contaminants while maximizing the protection of the ultra-smooth surface of the finished substrate, achieving a balance between efficient cleaning and low damage.

[0021] 2. Directed Synergy of Multiphysics Fields at the Micro-Nano Scale and Elimination of "Blind Spots" Forced convection generated by high-speed rotation (V5) continuously "impacts" the substrate surface with a functional liquid rich in submicron-sized cavitation bubbles, activated by megasonic waves. This overcomes the challenge of difficult peeling of microscale particles from the substrate surface due to their close contact. The strong shear flow field generated by the rotation directionally guides the collapse behavior of the cavitation bubbles, ensuring that the microjets generated during cavitation bubble collapse act uniformly on the substrate surface, rather than ineffectively acting on a single location. This "uniform cavitation" effect results in uniform high-frequency megasonic pressure on the front side of the substrate, achieving comprehensive directional synergy and limited energy focusing of the "high-frequency pressure field" and the "strong shear flow field" at the micro-nano scale.

[0022] 3. It achieves a highly efficient and non-destructive drying process, ensuring a flawless final surface. In step (S6), ionized nitrogen purging removes the water film while simultaneously neutralizing static electricity and forming a monomolecular passivation layer on the surface. In step (S7), infrared drying, under precise temperature control, promotes the moderate recombination of surface hydroxyl groups, resulting in a stable and uniform surface energy. The resulting substrate surface exhibits an order of magnitude lower adsorption tendency for secondary contaminants compared to surfaces treated only with high-efficiency cleaning methods. This represents a qualitative leap from "temporary cleanliness" to "long-lasting cleanliness," an improvement in cleanliness that was entirely unpredictable by technical manuals and conventional experience in the field. Attached Figure Description

[0023] Figure 1 This is a flowchart of a cleaning method for semiconductor photolithography mask substrates. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0025] Example 1: Cleaning of a 6-inch mask substrate contaminated with cerium oxide polishing powder after polishing. 1. Preparation Phase Cleaning object: A 6-inch quartz photomask substrate after chemical mechanical polishing (CMP) process. The main surface contaminants are cerium oxide (CeO2) polishing powder particles, residual organic additives (such as surfactants and corrosion inhibitors) in the polishing solution, and possible metal ion contamination.

[0026] Cleaning equipment: A single-piece rotary cleaning machine equipped with a programmable logic controller (PLC). This equipment integrates a rotary clamping unit, a multi-solution spraying system, a flexible brushing unit, a megasonic activated DI water unit, an ion nitrogen purging device, and an infrared drying lamp assembly.

[0027] 2. Cleaning steps to be performed Step 1: Preliminary rinsing and wetting The mask substrate to be cleaned is fixed on the rotating chuck of the cleaning machine.

[0028] Start the rotation to make the substrate rotate at a constant speed of 100 RPM.

[0029] At the same time, the high-purity DI water (resistivity ≥17 MΩ·cm) axial flow nozzle is turned on to continuously rinse the substrate surface at a flow rate of 1.5 L / min for 60 seconds.

[0030] Effect: The shear force of the water flow removes loose particles from the surface and forms a uniform water film on the substrate surface, achieving full wetting.

[0031] Step 2: Chemical softening treatment Reduce the substrate rotation speed to 30 RPM.

[0032] A room-temperature alkaline chemical cleaning solution is sprayed onto the substrate surface through an atomizing nozzle for 60 seconds.

[0033] Effects: Low speed and atomized spraying ensure uniform coverage of the solution and maintain sufficient chemical reaction time, effectively saponifying and softening organic residues and some particles on the surface.

[0034] Step 3: Physical scrubbing and simultaneous rinsing Increase the substrate rotation speed to 200 RPM.

[0035] Start a medium-hardness flexible brush made of PVA (polyvinyl alcohol) material and rotate it in the opposite direction at a speed of 200 RPM at a distance of 0.5 mm from the substrate surface for non-contact brushing for 120 seconds.

[0036] While scrubbing, simultaneously turn on the DI water rinse (flow rate 1.0 L / min) to immediately wash away the stripped contaminants.

[0037] Effect: Mechanical force completely breaks up and peels off the softened pollutant clumps, while simultaneous rinsing prevents secondary adsorption.

[0038] Step 4: Targeted chemical cleaning Adjust the substrate rotation speed to 30 RPM.

[0039] Spray diluted acidic cerium oxide targeted cleaning solution to specifically dissolve the polishing powder particles that were not removed in steps 2 and 3. The spraying time is 90 seconds.

[0040] After spraying, immediately switch to DI water rinsing (flow rate 1.5 L / min, for 60 seconds) to stop the reaction and remove all chemical residues.

[0041] Effect: The specific chemical action removes inorganic pollutants that were difficult to remove in the previous stage, achieving deep purification.

[0042] Step 5: Megasonic-assisted deep cleaning Increase the substrate rotation speed to 300 RPM.

[0043] The DI water, activated by a 1MHz mega-sonic generator, was continuously sprayed onto the surface of a high-speed rotating substrate for 120 seconds.

[0044] Effect: The megasonic energy is uniformly distributed under the assistance of centrifugal force, and its cavitation effect completely "shakes" out and washes away the ultrafine particles (<0.3μm) in the nanoscale defects of the ultra-smooth surface.

[0045] Step 6: High-speed dehydration and purging The substrate rotation speed was drastically increased to 800 RPM and maintained for 120 seconds, using the powerful centrifugal force to remove most of the surface moisture.

[0046] Subsequently, while maintaining a rotation speed of 800 RPM, purified ionized nitrogen gas (dew point ≤ -76°C) was turned on and used to purge the substrate surface from multiple angles for 65 seconds.

[0047] Effects: Removes residual water film, eliminates static electricity, and prevents particle adsorption during the drying process.

[0048] Step 7: Infrared-assisted final drying Keep the substrate rotating at 800 RPM.

[0049] An adjustable infrared lamp array is turned on to irradiate the substrate surface, maintaining the substrate surface temperature at 70°C for 60 seconds.

[0050] Results: Achieve rapid, uniform, and thermally stress-free thorough drying, resulting in a perfectly clean surface.

[0051] 3. Effectiveness Verification: After cleaning, offline testing was conducted. Particle cleanliness: Using a laser surface particle detector, the results showed that the number of particles ≥0.3μm on the surface decreased from an average of >10,000 before cleaning to <20, with a removal rate of >99.8%.

[0052] Surface damage detection: Under 200x optical microscope and scanning electron microscope (SEM), there was no damage, scratches or peeling at the edge of the pattern.

[0053] Surface chemical state: X-ray photoelectron spectroscopy (XPS) analysis showed that the content of surface metal ions (such as Na, K, Ca, Fe) and organic carbon contaminants were all below the detection limit.

[0054] Dryness and surface energy: Water droplet contact angle test showed that the surface was uniformly hydrophilic (contact angle <5°) and there were no visible water stains, white spots or streaks. Surface resistance test confirmed no static electricity accumulation.

[0055] Functional performance: After cleaning, the mask substrate is put into downstream processes, and its surface coating effect and defect rate meet the process specifications, resulting in a significant improvement in yield.

[0056] Example 2: 6-inch mask substrate contaminated with silica sol after silica polishing Object: 6-inch CMP polished mask substrate, the main contaminants are silicon oxide (SiO2) sol residue, organic matter and surfactants, and silicon oxide (SiO2) sol dried crystals.

[0057] Process adjustment points: Step 2: Replace the alkaline cleaning solution with an alkaline solution containing an appropriate amount of isopropanol (IPA) to enhance the penetration and swelling of the organic-silica (SiO2) crosslinking.

[0058] Step 4: The targeted cleaning solution uses a diluted sodium hydroxide-ammonia-hydrogen peroxide mixture to thoroughly decompose organic matter using its strong oxidizing properties. Through the synergistic effect of hydroxide ions and hydrogen peroxide, the dried silicon dioxide (SiO2) crystals are loosened and dissolved.

[0059] Results: A particle removal rate of >99.5% and non-destructive cleaning were achieved, significantly improving the yield of subsequent processing steps.

[0060] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A cleaning method for a semiconductor photolithography mask substrate, characterized in that, Includes the following steps: S1. Interface wetting and pre-cleaning: The mask substrate is rotated at a first rotation speed while high-purity deionized water is applied to form a uniform initial water film and remove loose contaminants using the shear force of the water flow. S2. Chemical Soft Interface Construction: The rotation speed of the mask substrate is reduced to a second rotation speed, and an alkaline cleaning solution is sprayed onto its surface by atomization to construct a chemical soft interface on the basis of the initial water film, thereby reducing the adhesion between contaminants and the substrate surface; S3. Low-damage mechanical peeling: The rotation speed of the mask substrate is increased to a third rotation speed higher than the first rotation speed. In the presence of the chemically softened interface, a flexible physical action component is used to act on the surface, while deionized water is applied for synchronous rinsing, so as to achieve low-damage peeling and immediate removal of contaminants. S4. Targeted Reaction Removal: The rotation speed of the mask substrate is adjusted to the fourth rotation speed, and a targeted cleaning solution that selectively reacts with specific residual contaminants is applied to its surface, followed by rinsing; S5. Microstructure deep cleaning: The rotation speed of the mask substrate is increased to the fifth rotation speed, and a functional liquid activated by a high-frequency energy field is applied to its surface. The hydrodynamic synergistic energy field effect is used to act on the micro-surface structure to remove residual particles. S6. Interface dehydration and modification: The rotation speed of the mask substrate is increased to the sixth speed for centrifugal dehydration, and then the surface is purged with modified processing gas to remove residual liquid film and optimize surface condition. S7.: Apply non-contact energy to the surface for drying; Among them, the first speed, the second speed, the third speed, the fourth speed, the fifth speed and the sixth speed satisfy a specific dynamic control relationship: V2 < V1 < V4 < V3 < V5 < V6.

2. The cleaning method according to claim 1, characterized in that, In step S3, the flexible physical action component is a flexible rotating brush that does not contact the substrate surface. The distance between the brush and the substrate surface is 0.1-2.0 mm, and in step S3, the rotation direction of the flexible rotating brush is opposite to the rotation direction of the mask substrate.

3. The cleaning method according to claim 2, characterized in that, The flexible rotating brush is made of polyvinyl alcohol (PVA) with a hardness of 40-70 Shore A. The maximum shear force generated by the brush in step S3 is controlled to be below the mechanical damage threshold of the surface roughness and defects of the mask substrate.

4. The cleaning method according to claim 1, characterized in that, In step S2, the alkaline treatment solution is ammonia or quaternary ammonium alkali solution, and its function is to realize the construction of the chemically softened interface through at least one mechanism of saponification reaction, hydrolysis and adjustment of surface potential. The second rotation speed is configured to make the effective residence time of the alkaline treatment solution on the substrate surface reach 30-90 seconds.

5. The cleaning method according to claim 1, characterized in that, In step S4, the selection of the targeted cleaning solution is based on offline or online analysis of the residual contaminants after step S3. It is selected from one of the chelating agent solution, inorganic acid solution, organic acid solution, oxidant solution or combination thereof, and is used to achieve at least one of complexation, dissolution or redox reaction.

6. The cleaning method according to claim 5, characterized in that, The targeted cleaning solution comprises at least one of the following combinations: For metal ion contaminants, use a chelating agent solution of EDTA or DTPA at a concentration of 0.1-1.0 wt%. For oxidative contaminants, use a dilute hydrochloric acid or dilute nitric acid solution with a pH of 2-4; For organosilicon contaminants, use SC-1 solution with NH4OH:H2O2:H2O = 1:1:5-1:2:

10.

7. The cleaning method according to claim 1, characterized in that, In step S5, the high-frequency energy field is an acoustic energy field with a frequency in the range of 0.8-3.0MHz, the functional liquid is deionized water activated by the acoustic energy field and rich in submicron cavitation bubbles, and the fifth rotation speed is configured to work in synergy with the application of the functional liquid to effectively transfer the acoustic energy and fluid shear force to the substrate surface.

8. The cleaning method according to claim 1, characterized in that, In step S6, the modified treatment gas is ionized nitrogen gas with a dew point below -70°C and both positive and negative ion concentrations not less than 1×10⁻⁶. 4 ions / cm 3 The purging angle, pressure, and time are optimized to achieve the synergistic effect of removing residual liquid film, eliminating static charge, and preventing surface oxidation.

9. The cleaning method according to claim 8, characterized in that, The preparation of the ionized nitrogen gas includes: High-purity nitrogen gas is passed through an ion generator to produce positive and negative ion concentrations of 1×10⁻⁶ each. 4 -1×10 6 ions / cm 3 Nitrogen ions; Control the nitrogen dew point below -70℃ to prevent moisture residue; The purging angle is controlled between 30 and 60 degrees, and the purging pressure is 0.1-0.5 MPa.

10. The cleaning method according to claim 1, characterized in that, In step S7, the non-contact energy is mid-wave infrared radiation with a wavelength in the range of 2-5μm. The drying process is carried out while the mask substrate is kept rotating, and the temperature of the surface of the mask substrate is controlled at 50-90℃ to avoid thermal stress damage.

11. The cleaning method according to claim 1, characterized in that, The first speed is 50-200 RPM, the second speed is 20-60 RPM, the third speed is 150-300 RPM, the fourth speed is 20-60 RPM, the fifth speed is 200-500 RPM, and the sixth speed is 500-1500 RPM.

12. The cleaning method according to any one of claims 1-11, characterized in that, The cleaning method is performed by an integrated control system configured to: (a) Based on the input mask substrate material and initial contaminant information, retrieve or generate a set of matching cleaning parameters from the pre-stored process database. The set of parameters includes at least the rotation speeds of V1 to V6, the duration of each step, and the concentration of each chemical solution. (b) During the execution of steps (S3) and / or (S5), the parameters of the flexible physical action component and / or the energy input of the functional liquid are dynamically adjusted according to the feedback signal from the online monitoring module to achieve an adaptive cleaning process.

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