A composite cleaning method for calcium fluoride optical lenses

Abstract

This invention relates to the field of cleaning calcium fluoride optical lenses, and discloses a composite cleaning method for calcium fluoride optical lenses. The method includes: pre-purging the calcium fluoride optical lens with dry nitrogen gas, performing a primary dissolution and wiping process with electronic-grade acetone solution, and a secondary displacement wiping process with electronic-grade anhydrous ethanol, followed by drying with dry nitrogen gas; placing the dried calcium fluoride optical lens onto a vacuum sample stage and evacuating it; introducing high-purity argon gas into an ion source; controlling the ion energy and beam current density to bombard the calcium fluoride optical lens with an ion beam; and monitoring the temperature stability of the vacuum sample stage during the bombardment process to complete the composite cleaning. This invention combines chemical solvent wiping with low-energy ion beam physical bombardment, effectively removing contaminants from the calcium fluoride surface while avoiding surface scratches and thermal stress cracking caused by conventional cleaning. This results in a clean optical surface with high surface activity, improving the adhesion of subsequent deposited optical thin films.

Description

Technical Field

[0001] This invention relates to the field of cleaning calcium fluoride optical lenses, specifically a composite cleaning method for calcium fluoride optical lenses. Background Technology

[0002] Currently, calcium fluoride crystals possess excellent broadband light transmission properties and are widely used in precision optical systems. This material exhibits perfect cleavage and is relatively soft. Calcium fluoride is sensitive to changes in environmental temperature and humidity and has a high coefficient of thermal expansion. These physical and chemical properties require calcium fluoride optical lenses to have high surface cleanliness and structural integrity before coating.

[0003] To address the processing requirements of the aforementioned calcium fluoride optical lenses, the relevant processes primarily employ single physical or chemical cleaning methods. Operators use specific chemical solvents to wipe the surface of the calcium fluoride optical lenses. Some processes utilize ultrasonic cleaning equipment, immersing the calcium fluoride optical lenses in a liquid medium and using the mechanical force generated by cavitation to remove surface particles. Other processes involve setting up a plasma source within a vacuum chamber, using a conventional energy ion beam to bombard the surface of the calcium fluoride optical lenses.

[0004] Existing cleaning technologies have limitations. Manual wiping alone has limited cleaning capabilities and cannot achieve atomic-level surface cleanliness. Ultrasonic cleaning, with its mechanical impact on soft crystals, easily induces internal microcracks. Conventional ion beam bombardment generally has high energy parameters; high-energy ion impacts cause physical damage and increase roughness, while also inducing thermal stress leading to cleavage surface cracking. Furthermore, mechanical equipment is difficult to integrate with various specifications of calcium fluoride optical lenses. If environmental barriers occur between the cleaning and coating processes, the highly reactive cleaned surface easily reabsorbs moisture and impurities from the air. These factors degrade the substrate surface condition, ultimately reducing the adhesion of the optical thin film.

[0005] Therefore, the present invention provides a composite cleaning method for calcium fluoride optical lenses to overcome the shortcomings of the prior art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a composite cleaning method for calcium fluoride optical lenses, which solves the problem that existing cleaning methods cannot achieve the high cleanliness required before optical coating without damaging the fragile surface of calcium fluoride.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A composite cleaning method for calcium fluoride optical lenses, the composite cleaning method comprising the following steps: The calcium fluoride optical lens to be cleaned was first purged with dry nitrogen, then dissolved and wiped with electronic grade acetone solution, then replaced with electronic grade anhydrous ethanol, and finally dried with dry nitrogen. The calcium fluoride optical lens, after the aforementioned drying treatment, is placed on the vacuum sample stage of the magnetron sputtering and ion beam assisted coating system and evacuated. High-purity argon gas is introduced into the ion source, and the ion energy and beam current density are controlled to bombard the calcium fluoride optical lens with an ion beam. At the same time, the temperature of the vacuum sample stage is monitored and stabilized by a thermocouple during the bombardment process, thereby completing the composite cleaning of the calcium fluoride optical lens.

[0008] By employing the above technical solution, this invention combines liquid-phase chemical displacement cleaning with vacuum physical sputtering cleaning to obtain a non-destructive and clean optical surface. The specific cleaning mechanism and steps are as follows: The first step is to pre-purge with dry nitrogen gas to remove large dust particles adhering to the surface of the calcium fluoride optical lens, preventing dust from scratching the calcium fluoride surface during subsequent contact operations.

[0009] The second step involves using an electronic-grade acetone solution to perform a primary dissolution and wiping of the surface, allowing the acetone molecules to dissolve the processing grease and organic contaminants on the surface of the calcium fluoride optical lens.

[0010] The third step involves using electronic-grade anhydrous ethanol for a secondary replacement wipe to replace the residual acetone solution on the surface and remove trace amounts of moisture, preventing residual stains caused by uneven solvent evaporation.

[0011] The fourth step involves bombarding the calcium fluoride surface with a low-energy argon ion beam in a vacuum environment. Argon ions, accelerated by an electric field, bombard the surface of calcium fluoride, generating physical sputtering through kinetic energy transfer, and stripping away any remaining gas adsorption layer and deposits. By limiting the range of ion energy and beam current density, the sputtering energy acts on the surface deposits without damaging the internal lattice of the calcium fluoride. Simultaneously, a thermocouple is used to maintain a constant temperature on the sample stage, eliminating thermal stress caused by temperature changes, preventing cleavage surface cracking, and obtaining a clean optical surface with surface activity.

[0012] Preferably, the operations of pre-purging with dry nitrogen, primary dissolution wiping with electronic-grade acetone solution, secondary replacement wiping with electronic-grade anhydrous ethanol, and drying with dry nitrogen are all performed in a clean bench with a temperature of 15-25°C, a humidity of 30%-50%RH, and a cleanliness level of Class 1000.

[0013] By adopting the above technical solution, a constant temperature, humidity and cleanliness environment is set to prevent calcium fluoride crystals from absorbing moisture from the air and deliquescing, thereby reducing secondary pollution of particulate matter in the environment.

[0014] Preferably, the step of pre-purging with dry nitrogen includes: using a nitrogen gun equipped with a high-efficiency air filter, introducing dry nitrogen with a purity of 99.999%, controlling the nozzle to be 2-3 cm away from the surface of the calcium fluoride optical lens, and gently purging the entire surface at an angle of 25-35 degrees for 30 seconds.

[0015] By adopting the above technical solution, the inclined airflow uses the horizontal component force to push the particles away from the surface, avoiding the particles from adhering to the surface caused by vertical sweeping.

[0016] Preferably, the step of using electronic-grade acetone solution for primary dissolution wiping includes: taking a brand-new polypropylene-handled optical swab, immersing the tip of the swab in electronic-grade acetone solution until slightly moistened, applying pressure to prevent the swab from bending, and wiping from the center of the calcium fluoride optical lens in a continuous, uninterrupted unidirectional spiral motion towards the outer edge, covering the entire optical surface; the step of using electronic-grade anhydrous ethanol for secondary replacement wiping includes: using a brand-new polypropylene-handled optical swab dipped in electronic-grade anhydrous ethanol, and wiping again from the center of the calcium fluoride optical lens towards the outer edge in a spiral motion, following the same trajectory and pressure as the primary dissolution wiping.

[0017] By adopting the above technical solution, the operating pressure is limited to prevent the cotton swab rod from bending and to prevent scratches from the calcium fluoride crystal; the unidirectional spiral trajectory causes contaminants to migrate to the edge of the calcium fluoride optical lens to prevent cross-contamination; and the completely overlapping replacement trajectory ensures that anhydrous ethanol effectively replaces acetone.

[0018] Preferably, the step of drying with dry nitrogen includes: immediately using dry nitrogen to gently blow from top to bottom onto the surface of the calcium fluoride optical lens until no liquid reflection or traces are observed, ensuring complete drying.

[0019] By adopting the above technical solution, combined with the effect of gravity and forward airflow, the remaining liquid is detached from the surface, preventing local accumulation of liquid.

[0020] Preferably, the vacuuming step includes: evacuating the vacuum chamber to a background vacuum of (1.0–5.0) × 10⁻⁶ using a molecular pump assembly. -3 Pa.

[0021] By adopting the above technical solutions, the content of water vapor and impurity gases in the vacuum chamber is reduced, the scattering of the ion beam by the impurity gases is reduced, and the bombardment efficiency is improved.

[0022] Preferably, the parameters for ion energy and beam current density are: ion energy controlled within the range of 50–110 eV, and beam current density controlled within the range of 0.1–0.5 mA / cm². 2 Within the range.

[0023] By adopting the above technical solution, the ion energy within this range ensures that argon ions have the kinetic energy to clean the surface adsorption layer, while avoiding excessive kinetic energy that could damage the integrity of the calcium fluoride crystal structure.

[0024] Preferably, the flow rate of high-purity argon gas introduced into the ion source is set to 3–8 sccm; the temperature of the vacuum sample stage is stabilized in the range of 60–90°C; and the processing time of the ion beam bombardment is set to 120–240 s.

[0025] By adopting the above technical solution, the limited gas flow rate maintains a stable plasma density; the constant temperature accelerates the desorption rate of moisture on the surface of the calcium fluoride optical lens and reduces the stress inside the crystal.

[0026] Preferably, during the ion beam bombardment process, the ion source and sample stage are rotated and monitored through the chamber observation window. The surface of the calcium fluoride optical lens exhibits a uniform pale blue glow without any abnormal discharge points.

[0027] By adopting the above technical solution, the sample stage rotates to form a uniform bombardment surface, avoiding the accumulation of local charge that could cause discharge and break down the surface.

[0028] Preferably, after the cleaning step is completed, the ion source is turned off and a high vacuum is maintained. Then, without breaking the vacuum, the process is directly switched to the ion beam-assisted deposition coating procedure to begin depositing the required optical thin film.

[0029] By adopting the above technical solution, the surface of calcium fluoride is isolated from the outside atmosphere, preventing the re-adsorption of moisture and hydrocarbons, thereby improving the adhesion and optical performance of the subsequently deposited film.

[0030] This invention provides a composite cleaning method for calcium fluoride optical lenses. It has the following beneficial effects: 1. This invention employs a composite cleaning method combining chemical solvent replacement wiping with physical ion beam bombardment. The initial nitrogen pre-purging and solvent wiping steps remove dust and organic contaminants from the surface of calcium fluoride, reducing the processing load and duration of subsequent ion beam bombardment. This reduces the risk of thermal damage to the calcium fluoride crystals, and the continuous process steps also reduce secondary pollution in intermediate stages.

[0031] 2. This invention controls the energy and current density of the ion beam to a low level, and, in conjunction with temperature monitoring of the vacuum sample stage, ensures that the sputtering kinetic energy of the ion beam is used only to remove residual deposits on the surface. This avoids physical sputtering damage and thermal stress cracking on the calcium fluoride surface caused by high-energy ion bombardment, thus maintaining the flatness and structural integrity of the crystal surface.

[0032] 3. In this invention, after ion beam bombardment is completed in a vacuum environment, the process directly proceeds to the thin film deposition procedure without breaking the vacuum. Ion bombardment treatment can strip the trace gas adsorption layer on the surface of calcium fluoride and activate the surface chemical bonds. The non-vacuum operation isolates the treated highly active surface from the external atmosphere, preventing environmental moisture and impurities from re-adhering, thereby improving the adhesion of the subsequently deposited optical thin film. Attached Figure Description

[0033] Figure 1 This is a bar chart comparing the contact angle changes of calcium fluoride optical lenses at different cleaning stages in embodiments of the present invention. Figure 2 This is a trend graph showing the effect of different ion energies on the surface roughness of calcium fluoride optical lenses in embodiments of the present invention. Figure 3 This is a comparison chart showing the effects of the cleaning methods of the embodiments of the present invention and the comparative examples on the roughness and macroscopic defect rate of calcium fluoride optical lenses. Figure 4 This is a comparison diagram of the water droplet contact angle on the surface of calcium fluoride optical lenses after cleaning by the methods of the embodiments of the present invention and the comparative examples. Figure 5 This is a rating comparison chart showing the impact of the cleaning methods of the embodiments of the present invention and the comparative examples on the adhesion of the subsequent antireflection film. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0036] The calcium fluoride optical lens to be cleaned (CAS No. 7789-75-5) used in the embodiments and comparative examples of this invention are commercially available conventional precision optical components. The 99.999% pure dry nitrogen (CAS No. 7727-37-9), 99.999% pure high-purity argon (CAS No. 7440-37-1), electronic-grade acetone (CAS No. 67-64-1), and electronic-grade anhydrous ethanol (CAS No. 64-17-5) used are all commercially available conventional reagents. The optical swabs used are commercially available brand-new polypropylene rod dust-free swabs, with the polypropylene material having a CAS No. 9003-07-0.

[0037] The Class 1000 clean bench, the nitrogen gun equipped with a high-efficiency air filter, and the magnetron sputtering and ion beam assisted coating system (which integrates a vacuum molecular pump pump unit, a vacuum sample stage with heating and rotation functions, and a low-energy ion source device) used in the embodiments and comparative examples of this invention are all conventional and commonly used equipment available in the art.

[0038] Examples 1-3: Example 1: This embodiment provides a composite cleaning method for calcium fluoride optical lenses, including the following steps: Precision manual wiping: In a clean bench with a temperature of 15℃, humidity of 30%RH and a cleanliness level of 1000, the operator wears powder-free nitrile gloves and a mask.

[0039] Dry nitrogen pre-purging: Place the calcium fluoride optical lens to be cleaned on the workbench, use a nitrogen gun equipped with a high-efficiency air filter, introduce dry nitrogen with a purity of 99.999%, keep the nozzle 2-3 cm away from the surface of the calcium fluoride optical lens, gently blow the entire surface at a 25-degree angle, and the purging time is 30 seconds.

[0040] First-stage dissolving and wiping: Take a brand-new polypropylene optical swab and immerse the tip of the swab in an electronic-grade acetone solution until slightly moistened. Apply pressure to prevent the swab from bending and, starting from the center of the calcium fluoride optical lens, wipe outwards in a continuous, uninterrupted unidirectional spiral motion, covering the entire optical surface.

[0041] Secondary replacement wiping: Using a brand-new polypropylene optical swab dipped in electronic-grade anhydrous ethanol, wipe the calcium fluoride optical lens again from the center outward in a spiral trajectory, following the same path and pressure as the primary dissolution wiping.

[0042] Drying: Immediately use dry nitrogen gas to gently blow from top to bottom over the surface of the calcium fluoride optical lens until no liquid reflection or traces are observed, ensuring it is completely dry.

[0043] Low-energy ion beam bombardment: Mounting and Vacuuming: The calcium fluoride optical lens, which has undergone the aforementioned manual treatment and drying, is rapidly mounted onto the vacuum sample stage of the magnetron sputtering and ion beam assisted coating system. The base vacuum of the vacuum chamber is evacuated to 1.0 × 10⁻⁶ using a molecular pump assembly. - 3 Pa.

[0044] Parameter settings and cleaning: High-purity argon gas is introduced into the ion source at a flow rate of 3 sccm. The ion energy is controlled at 50 eV, and the beam current density is 0.1 mA / cm². 2The ion source and sample stage were started and rotated. The bombardment time was set to 120 seconds, and the temperature of the vacuum sample stage was monitored and stabilized at 60°C using thermocouples.

[0045] Process monitoring and subsequent coordination: During the bombardment process, the surface of the calcium fluoride optical lens exhibited a uniform pale blue glow, with no abnormal discharge points, as monitored through the chamber observation window. After the cleaning step was completed, the ion source was shut off, maintaining a high vacuum. Subsequently, without breaking the vacuum, the process was directly switched to the ion beam-assisted deposition coating procedure to begin depositing the required optical thin film.

[0046] Example 2: This embodiment provides a composite cleaning method for calcium fluoride optical lenses, including the following steps: Precision manual wiping: In a clean bench with a temperature of 20℃, humidity of 40%RH and a cleanliness level of 1000, the operator wears powder-free nitrile gloves and a mask.

[0047] Dry nitrogen pre-purging: Place the calcium fluoride optical lens to be cleaned on the workbench, use a nitrogen gun equipped with a high-efficiency air filter, introduce dry nitrogen with a purity of 99.999%, keep the nozzle 2-3 cm away from the surface of the calcium fluoride optical lens, gently blow the entire surface at a 30-degree angle, and the purging time is 30 seconds.

[0048] First-stage dissolving and wiping: Take a brand-new polypropylene optical swab and immerse the tip of the swab in an electronic-grade acetone solution until slightly moistened. Apply pressure to prevent the swab from bending and, starting from the center of the calcium fluoride optical lens, wipe outwards in a continuous, uninterrupted unidirectional spiral motion, covering the entire optical surface.

[0049] Secondary replacement wiping: Using a brand-new polypropylene optical swab dipped in electronic-grade anhydrous ethanol, wipe the calcium fluoride optical lens again from the center outward in a spiral trajectory, following the same path and pressure as the primary dissolution wiping.

[0050] Drying: Immediately use dry nitrogen gas to gently blow from top to bottom over the surface of the calcium fluoride optical lens until no liquid reflection or traces are observed, ensuring it is completely dry.

[0051] Low-energy ion beam bombardment: Mounting and Vacuuming: The calcium fluoride optical lens, which has undergone the aforementioned manual treatment and drying, is rapidly mounted onto the vacuum sample stage of the magnetron sputtering and ion beam assisted coating system. The base vacuum of the vacuum chamber is evacuated to 3.0 × 10⁻⁶ using a molecular pump assembly. - 3 Pa.

[0052] Parameter settings and cleaning: High-purity argon gas is introduced into the ion source at a flow rate of 5 sccm. The ion energy is controlled at 80 eV, and the beam current density is 0.3 mA / cm². 2 The ion source and sample stage were started and rotated. The bombardment time was set to 180s, and the temperature of the vacuum sample stage was monitored and stabilized at 75℃ via thermocouples.

[0053] Process monitoring and subsequent coordination: During the bombardment process, the surface of the calcium fluoride optical lens exhibited a uniform pale blue glow, with no abnormal discharge points, as monitored through the chamber observation window. After the cleaning step was completed, the ion source was shut off, maintaining a high vacuum. Subsequently, without breaking the vacuum, the process was directly switched to the ion beam-assisted deposition coating procedure to begin depositing the required optical thin film.

[0054] Example 3: This embodiment provides a composite cleaning method for calcium fluoride optical lenses, including the following steps: Precision manual wiping: In a clean bench with a temperature of 25℃, humidity of 50%RH and a cleanliness level of 1000, the operator wears powder-free nitrile gloves and a mask.

[0055] Dry nitrogen pre-purging: Place the calcium fluoride optical lens to be cleaned on the workbench, use a nitrogen gun equipped with a high-efficiency air filter, introduce dry nitrogen with a purity of 99.999%, keep the nozzle 2-3 cm away from the surface of the calcium fluoride optical lens, gently blow the entire surface at a 35-degree angle, and the purging time is 30 seconds.

[0056] First-stage dissolving and wiping: Take a brand-new polypropylene optical swab and immerse the tip of the swab in an electronic-grade acetone solution until slightly moistened. Apply pressure to prevent the swab from bending and, starting from the center of the calcium fluoride optical lens, wipe outwards in a continuous, uninterrupted unidirectional spiral motion, covering the entire optical surface.

[0057] Secondary replacement wiping: Using a brand-new polypropylene optical swab dipped in electronic-grade anhydrous ethanol, wipe the calcium fluoride optical lens again from the center outward in a spiral trajectory, following the same path and pressure as the primary dissolution wiping.

[0058] Drying: Immediately use dry nitrogen gas to gently blow from top to bottom over the surface of the calcium fluoride optical lens until no liquid reflection or traces are observed, ensuring it is completely dry.

[0059] Low-energy ion beam bombardment: Mounting and Vacuuming: The calcium fluoride optical lenses, which have undergone the aforementioned manual processing and drying, are rapidly mounted onto the vacuum sample stage of the magnetron sputtering and ion beam assisted coating system. The base vacuum of the vacuum chamber is then evacuated to 5.0 × 10⁻⁶ using a molecular pump assembly. - 3 Pa.

[0060] Parameter settings and cleaning: High-purity argon gas is introduced into the ion source at a flow rate of 8 sccm. The ion energy is controlled at 110 eV, and the beam current density is 0.5 mA / cm². 2 The ion source and sample stage were started and rotated. The bombardment time was set to 240 seconds, and the temperature of the vacuum sample stage was monitored and stabilized at 90°C using thermocouples.

[0061] Process monitoring and subsequent coordination: During the bombardment process, the surface of the calcium fluoride optical lens exhibited a uniform pale blue glow, with no abnormal discharge points, as monitored through the chamber observation window. After the cleaning step was completed, the ion source was shut off, maintaining a high vacuum. Subsequently, without breaking the vacuum, the process was directly switched to the ion beam-assisted deposition coating procedure to begin depositing the required optical thin film.

[0062] Comparative Examples 1-4: Comparative Example 1: Compared with Example 2, the difference is that this comparative example only performs a precise manual wiping step on the calcium fluoride optical lens, without performing the subsequent low-energy ion beam bombardment step.

[0063] Comparative Example 2: Compared with Example 2, the difference is that this comparative example does not perform a precise manual wiping step, but directly puts the dirty calcium fluoride optical lens into the vacuum chamber and uses the ion source parameters of Example 2 for long-term single ion source cleaning. All other steps and parameters are the same.

[0064] Comparative Example 3: Compared with Example 2, the difference is that in the low-energy ion beam bombardment step, the anode voltage of the ion source is adjusted to generate conventional high-energy ion energy of 130eV, and the sample stage is not precisely controlled at 75°C. All other steps and parameters are the same.

[0065] Comparative Example 4: Compared with Example 2, the difference is that this comparative example does not perform the combined cleaning steps of precision manual wiping and low-energy ion beam bombardment, but directly uses the conventional ultrasonic cleaning method to treat the calcium fluoride optical lens to be cleaned.

[0066] Test Examples 1-5: Test Example 1: Verification of the graded cleaning mechanism and surface activation process (contact angle tracking test) Five samples of calcium fluoride optical lenses from the same production batch that have not undergone any cleaning treatment were selected as initial state test samples and numbered as Sample 1 to Sample 5.

[0067] Using a contact angle meter, at room temperature (20℃, 40% relative humidity), multiple drops of 2μL deionized water were applied to the center and edge regions of each sample. After the droplets stabilized, the instrument was used to collect the droplet profiles and calculate the contact angle values, recording the initial contact angle data.

[0068] The first step of precise manual wiping was completed according to the parameters and operating method described in Example 2. After wiping, the above 5 samples were placed on the contact angle measuring instrument platform, and the same deionized water volume and fitting method as in step 2 was used for testing. The contact angle data after the completion of the manual wiping stage was recorded.

[0069] The five samples that had completed the above tests were loaded into the vacuum system, and the second step of the low-energy ion beam bombardment procedure described in Example 2 was continued. After the system returned to normal pressure, the samples were removed and immediately transferred to the contact angle measuring instrument for a final test. The final contact angle data after the entire composite cleaning process was completed were recorded.

[0070] Table 1. Contact Angle Tracking Test Data for Calcium Fluoride Optical Lenses at Different Cleaning Stages (Unit: °) in conclusion: According to Table 1 and Figure 1 Data from Figure 1 The bar chart distribution clearly shows that the contact angle of the samples exhibits a distinct stepwise decreasing trend across the three treatment stages. The untreated calcium fluoride optical lenses (samples 1 to 5) initially show the highest bar height, with contact angles fluctuating between 77.8° and 82.1°, demonstrating significant hydrophobic properties and reflecting the adsorption of organic hydrocarbon pollutants and processing residues from the environment on the crystal surface. After a single, precise manual wipe in the first step, the corresponding bar height in the chart generally decreased, and the contact angle dropped to the range of 63.5° to 67.1°. The data changes at this stage indicate that through the graded physical dissolution and displacement by acetone and anhydrous ethanol, the macroscopic particulate matter and the layer of large molecular organic pollutants on the surface of the calcium fluoride optical lenses were stripped away. The contact angle failed to decrease further because manual wiping is a macroscopic physical process; the energy is insufficient to break the chemical bonds between the calcium fluoride surface and the monomolecular contaminant layer, and trace molecular residues inevitably remain during solvent evaporation, keeping the surface in a weakly hydrophilic state.

[0071] After the second step of low-energy ion beam bombardment, Figure 1The corresponding column height decreased, and the contact angle of all samples dropped below 10° (extremely low at 6.7°), indicating a transformation from hydrophilic to superhydrophilic surface state. Based on the cleaning mechanism, low-energy argon ions (80 eV) transferred momentum to the calcium fluoride surface in a vacuum environment. This energy level was insufficient to induce cascade collisions of lattice atoms, avoiding increased roughness and sputtering damage, but just exceeded the desorption threshold of surface adsorbates. The ion beam not only removed microscopic molecular-level contaminants remaining from manual wiping but also excited high-density dangling bonds on the calcium fluoride lattice surface, resulting in surface chemical activation. The high surface energy matrix state strongly attracted polar molecules, macroscopically manifesting as a superhydrophilic phenomenon where the water droplet contact angle dropped to below 10°. The step-down characteristic shown in the graph confirms the synergistic effect of the manual wiping pretreatment reducing contamination load and the low-energy ion beam end activation in terms of physical mechanism, demonstrating the feasibility of the two-stage treatment logic of this scheme.

[0072] Test Example 2: Verification of Low-Energy Ion Beam Energy Threshold and Non-Destructive Mechanism (Numerical Test of Roughness Variation) Twenty calcium fluoride optical lenses that had undergone the first step of manual wiping were selected and randomly divided into five test groups, with four lenses in each group, corresponding to ion energy test conditions of 50eV, 80eV, 110eV, 130eV, and 150eV.

[0073] The initial surface roughness Rq value of each sample was measured using a white light interferometer. Measurements were taken at fixed points in the center and surrounding area of ​​each sample surface, and the fitted mean value was recorded as the initial roughness data for that sample.

[0074] Five groups of samples were sequentially loaded into a vacuum chamber for ion beam cleaning. The ion source anode voltage was adjusted to generate ion energies of 50 eV, 80 eV, 110 eV, 130 eV, and 150 eV, respectively, while other conditions were kept constant at a beam current density of 0.3 mA / cm². 2 Argon flow rate 5 sccm, processing time 180 s, temperature control 75℃.

[0075] After the bombardment process is completed, the samples are removed, and the surface roughness Rq value is remeasured in the original test area using a white light interferometer. The roughness difference (ΔRq) before and after cleaning for each sample is calculated, and the data are summarized.

[0076] Table 2. Changes in surface roughness (Rq) of calcium fluoride optical lenses before and after bombardment with different ion energies. (Unit: nm) in conclusion: According to Table 2 and Figure 2 The data shows that when the ion energy is set within the range of 50 eV to 110 eV, from Figure 2The graph shows hollow dots representing individual sample distribution and solid broken lines representing the mean trend, both located below the dashed 0.01nm lossless baseline. The mean data marked in the graph rises smoothly from 0.0037nm to 0.0090nm without exceeding the limits, and the vertical line segments representing the error range are short, indicating high data consistency. This graph characteristic confirms that the kinetic energy carried by the incident argon ions only completed the momentum exchange and desorption of surface organic matter and water molecules, without reaching the displacement threshold required to break the calcium fluoride lattice bonds, thus achieving fidelity in the physical morphology of the calcium fluoride crystal surface.

[0077] When the ion energy is increased to 130 eV and above Figure 2 The mean value trend line in the graph shows a significant steep upward trend, directly crossing the non-destructive baseline. The two sets of mean values ​​marked at 130 eV and 150 eV jump to 0.0852 nm and 0.1510 nm respectively, while the corresponding hollow dots show a significantly wider vertical dispersion, reflecting the instability and increased dispersion of roughness changes. Due to the high thermal expansion coefficient and soft lattice of calcium fluoride, high-energy ions exceeding 130 eV disrupt the ionic bonds between surface atoms, triggering a physical sputtering stripping effect. Simultaneously, the excessive momentum transfer is converted into localized thermal stress, exacerbating the roughening of the microstructure. The graph clearly defines the ion energy threshold for cleaning the surface of calcium fluoride materials, verifying that precisely reducing the ion beam energy to 80 eV can completely isolate sputtering damage.

[0078] Test Example 3: Comparison Test of Surface Topography Fidelity and Physical Non-destructive Testing Twenty-eight calcium fluoride optical lenses from the same batch were selected as test samples and divided into seven groups of 40 lenses each, corresponding to the cleaning conditions of Examples 1 to 3 and Comparative Examples 1 to 4, respectively.

[0079] The initial surface roughness Rq value of each sample was measured using a white light interferometer. Multiple tests were performed on a fixed test area on the surface of each sample, and the fitted mean value was recorded as the initial roughness data of the sample before cleaning.

[0080] The corresponding sample groups were cleaned according to the specific steps and parameters described in Examples 1 to 3 and Comparative Examples 1 to 4.

[0081] After the bombardment process is completed, the samples are removed, and the surface roughness Rq value is remeasured in the original test area using a white light interferometer. The roughness difference (ΔRq) before and after cleaning is calculated for each sample, the data are summarized, and the average change value for each group is calculated.

[0082] After cleaning, each group of samples was transferred to a high-intensity light inspection table. A high-intensity parallel light source was turned on, and quality inspectors, using both the naked eye and a 100x handheld optical magnifying glass, inspected each calcium fluoride optical lens, examining its surface and interior. The number of samples in each group exhibiting cleavage microcracks, edge chipping, or surface whitening defects was counted, and the macroscopic defect incidence rate for each group was calculated.

[0083] Table 3. Data on the impact of cleaning methods on the roughness and macroscopic defect rate of calcium fluoride optical lenses. in conclusion: According to Table 3 and Figure 3 The data shows that the mean roughness difference ΔRq of samples 1 to 3 before and after cleaning ranged from 0.0038 nm to 0.0086 nm. Figure 3 The graph is represented by three light gray pillars corresponding to the left main axis scale, with extremely low heights; simultaneously, the defect rate line corresponding to the right secondary axis and marked with a diamond shape remains steadily at a data point of 0.0% within the example area. This graph characteristic verifies the physically non-destructive nature of the composite cleaning mechanism. Through prior manual wiping to remove macroscopic particles, combined with low-energy ion beam bombardment between 50 eV and 110 eV, the momentum transfer provided by the ion source is confined to the surface molecular desorption level. Supplemented by a temperature control mechanism, thermal stress within the lattice material is eliminated, allowing the calcium fluoride crystal surface to achieve chemical activation while avoiding microscopic dislocations and macroscopic cleavage.

[0084] Comparative Example 1 only used manual wiping. Figure 3 The corresponding column height was the lowest, with a data label showing 0.0017 nm, and the defect rate indicated by the diamond-shaped data points was 0.0%, proving that the energy of a single physical wipe was mild and would not damage the substrate, but this failed to achieve a thorough surface activation effect. Comparative Example 4 used conventional ultrasonic cleaning. Figure 3 The defect rate curve rises sharply to a peak of 77.5% here, with the corresponding dark gray bar indicating that ΔRq reaches 0.0487nm. Ultrasonic waves induce cavitation bubbles in the liquid, causing collapse and generating high-pressure shock waves. Calcium fluoride, as a soft crystal with perfect cleavage properties, struggles to absorb high-frequency mechanical stress, leading to rapid propagation of microcracks along the crystal direction and resulting in macroscopic damage.

[0085] Comparative Example 3 used a 130 eV high-energy ion beam without temperature control. Figure 3 The dark gray column representing ΔRq in the middle suddenly jumps to a global maximum of 0.1123 nm, and the defect rate corresponding to the right axis also rises to 42.5%. High-energy ions directly penetrate the surface of the calcium fluoride optical lens, causing a sputtering and peeling effect, which damages the microscopic flatness. At the same time, thermal accumulation induces local thermal stress, leading to cracking of the calcium fluoride optical lens. Comparative Example 2 omits the manual pre-wiping step and directly performs long-term bombardment. Figure 3The graph shows that the ΔRq column height increased to 0.0241 nm, with the line curve rising and resulting in a defect rate of 12.5%. Large hydrocarbon particles adhering to the surface formed a micromask effect during ion bombardment, inducing uneven etching. Prolonged plasma irradiation caused uncontrolled localized temperature rise in the substrate, leading to secondary material damage. The intuitive correspondence between the bar chart and the line graph clearly defines the physical effects of each cleaning method on the substrate, demonstrating the necessity of low-energy range limitation, pre-wiping and decontamination, and precise temperature control in protecting the calcium fluoride optical substrate.

[0086] Test Example 4: Surface Limit Cleanliness Comparison Test Thirty-five calcium fluoride optical lenses from the same batch were selected as test samples and divided into seven groups of five lenses each, corresponding to the cleaning conditions of Examples 1 to 3 and Comparative Examples 1 to 4, respectively. All samples were stored in a cleanroom with the same temperature and humidity for 24 hours before the experiment.

[0087] The samples to be tested were processed according to the operating procedures described in each embodiment and comparative example. Samples involving a vacuum treatment step were transferred to the contact angle testing stage within 5 minutes after exiting the chamber to avoid secondary adsorption of hydrocarbons from the air. Comparative example samples not involving vacuum treatment were also tested within 5 minutes after processing.

[0088] Surface contact angle was tested using a fully automated contact angle measuring instrument. The seated drop method was used, in which a 2-microliter droplet of deionized water was dispensed through the instrument's injection system. After the droplet contacted the surface of the calcium fluoride optical lens, it was allowed to stand for 3 seconds to reach a spreading equilibrium state.

[0089] High-resolution side projection images of the droplets were captured using the built-in CCD camera system of the testing instrument. The droplet profile was edge-fitted using the tangent method, and the angle formed by the gas-liquid interface and the solid-liquid interface at the three-phase interface was measured and recorded as the contact angle value at that test point.

[0090] For each sample, five locations were evenly selected across the four quadrants and the center point for measurement. After discarding the data with the largest deviation, the arithmetic mean of the remaining test values ​​was taken as the final contact angle result for that sample. After the test was completed, the data distribution range and mean of each group of samples were summarized.

[0091] Table 4. Water droplet contact angle data on the surface of calcium fluoride optical lenses after each cleaning method. in conclusion: According to Table 4 and Figure 4 The data showed that the average water droplet contact angle on the surface of the calcium fluoride optical lenses prepared in Examples 1 to 3 was significantly reduced to the range of 4.92° to 7.88°. Figure 4In the test, the single-sample hollow dots representing these three sets of measurements, after being arranged horizontally in a regular pattern, clearly and entirely fall within the bottom light gray superhydrophilic activation zone (<10°). The error bars have a very small span, and the mean value displayed on the data labels is stably limited below the limit threshold line. The test results verify that this composite cleaning method achieves the ultimate cleanliness and high-energy state activation of the substrate surface. The manual wiping step, as a pre-process, removes macroscopic particles and thick layers of grease from the surface, eliminating the shielding effect of large-sized contaminants on subsequent vacuum processes. Low-energy ion beam bombardment in a vacuum environment further removes the single-molecule-level hydrocarbons remaining in the shallow surface layer. Argon ions in the energy range of 50eV to 110eV break the van der Waals force connection between the residual organic molecules and the calcium fluoride lattice through momentum transfer, exposing a large number of dangling bonds on the surface. The increase in the density of surface dangling bonds increases the free energy of the material surface, enabling deionized water droplets to quickly overcome surface tension and establish wetting and spreading at the solid-liquid interface, which is physically manifested as a decrease in the macroscopic contact angle value.

[0092] Comparative Example 1 only used physical manual wiping treatment. Figure 4 The zigzag node is at a high position of 65.50°. Organic solvents can dissolve macroscopic oil stains, but cannot overcome the chemical bonding force formed between the underlying organic molecular layer and the calcium fluoride surface. The residual hydrocarbon molecular layer exhibits stable hydrophobic properties, limiting the surface activation level. Comparative Example 2 omitted the pre-wiping step and directly bombarded the substrate with an ion source, and the average contact angle remained at 41.54°. Large-sized dirt particles attached to the surface formed a micro-mask shielding area during ion bombardment, consuming the kinetic energy of the plasma, resulting in a heterogeneous state of alternating hydrophobic and hydrophilic states on the substrate micro-surface, which could not bring the overall macroscopic contact angle to the limit threshold. Comparative Example 4 used ultrasonic cleaning, and its average contact angle remained at 57.84°. The ultrasonic cavitation effect was insufficient to remove strongly adhered micro-organic matter. Comparative Example 3 used 130eV high-energy ion bombardment, and the contact angle dropped to 16.64°, but from Figure 4 It is evident that neither the scatter plot nor the mean label broke through the 10° baseline. High-energy ions caused physical sputtering damage to the calcium fluoride substrate during the stripping of contaminants. The disruption of the surface lattice structure and micro-roughening created a structural trapping effect, hindering the continuous spreading of the droplet front. The test data demonstrate the engineering effectiveness of the synergistic mechanism of pre-treatment physical decontamination and low-energy ion bombardment in eliminating multi-level contamination and increasing surface free energy.

[0093] Test Example 5: Comparison Test of Subsequent Process Strengthening Effects (Film Adhesion Test) The calcium fluoride optical lens samples that had been processed according to the cleaning procedures of Examples 1 to 3 and Comparative Examples 1 to 4 were grouped into groups of 5 lenses each.

[0094] All samples were loaded together into the sample holder of the ion beam assisted deposition (IBAD) vacuum coating system, ensuring the consistency of position and angle of each sample during the subsequent coating process. The vacuum system was then activated, and the chamber's base vacuum was evacuated to 1.0 × 10⁻⁶. -4 Below Pa.

[0095] A standard multilayer antireflection film was deposited on the surface of all samples. The deposition process parameters were uniformly set as follows: an electron beam evaporation source was used, with Ta₂O₅ as the high-refractive-index material and MgF₂ as the low-refractive-index material. The film thickness was precisely controlled to match the design using an optical film thickness monitoring system. Throughout the deposition process, an ion source was activated to assist deposition, with the ion energy set at 150 eV to enhance film density.

[0096] After the coating is completed, all samples are removed and placed in a room temperature environment for 24 hours to completely release the internal stress of the film.

[0097] Referring to the US military standard MIL-F-48616 adhesion test standard, 3 MScotch 610 tape was cut and its tacky side was firmly attached to the surface of the antireflection membrane of each sample with stable pressure. The tape was repeatedly pressed with an eraser to remove air bubbles and ensure that the tape was in complete contact with the membrane layer.

[0098] Hold the tape on the film surface for 60 seconds. Then, quickly and steadily peel the tape off at a 90-degree angle perpendicular to the film surface.

[0099] Using a 10x stereomicroscope, examine the areas where the tape has peeled off and the extent of film detachment on the inner side of the tape. Grade the detached film area according to its percentage: Grade 0 (no detachment), Grade 1 (detachment area < 5%), Grade 2 (5% ≤ detachment area < 15%), Grade 3 (15% ≤ detachment area < 30%), Grade 4 (30% ≤ detachment area < 50%), Grade 5 (detachment area ≥ 50%). Record the grade for each sample.

[0100] Table 5. Rating of the impact of each cleaning method on the adhesion of the subsequent antireflection film. in conclusion: According to Table 5 and Figure 5 According to the data, all calcium fluoride samples treated by the composite cleaning method of Examples 1 to 3 had an adhesion rating of 0 after subsequent coating and tape pull-out test. Figure 5In the diagram, the three light gray average bars representing the embodiment are completely aligned with the zero-point baseline of the Y-axis, and the rhomboid dots above them are also all concentrated there, indicating that an extremely strong bond has been formed between the film layer and the substrate, achieving the highest adhesion standard of zero detachment. The composite cleaning method, through the synergistic effect of physical wiping and low-energy ion bombardment, thoroughly removes macroscopic and microscopic contaminants from the calcium fluoride surface and simultaneously activates the substrate surface. A clean substrate with high surface free energy provides ideal nucleation sites for the initial atoms of subsequent thin film materials, promoting the formation of dense chemical bonds between the deposited atoms and the substrate rather than simple physical adsorption, thereby constructing a robust film-substrate interface transition layer.

[0101] In contrast, all comparative samples exhibited varying degrees of film detachment. Comparative Example 1, which underwent only manual wiping, had an average rating as high as 3.4, indicating that the residual monomolecular organic contaminant layer formed a physically weak boundary layer, hindering direct bonding between the film and the substrate. Comparative Example 2, which omitted pre-wiping and directly bombarded the substrate, had a rating of 2.8 reflecting the unevenness of surface cleanliness. The localized contamination residue areas caused by the micromask effect became weak points in adhesion, preferentially peeling off under stress. Comparative Example 4, which used ultrasonic cleaning, had an average rating as high as 4.6, indicating insufficient removal capacity for strongly adhering contaminants and also failing to provide suitable interface conditions for coating. Comparative Example 3, which used high-energy ion bombardment, had the worst adhesion rating, with an average of 4.4. This is because high-energy ions exceeding the threshold caused irreversible subsurface damage to the calcium fluoride lattice, forming a loosely structured interface layer with numerous dislocations. Although the surface may be clean, this fragile damaged layer itself cannot withstand the internal stress and external tensile stress of the film, causing the film to peel off along with the damaged substrate. From the perspective of subsequent process applications, this set of test data verifies the importance of the composite cleaning method of this invention in achieving extreme cleanliness while ensuring the physical integrity of the substrate. This is a key prerequisite for ensuring the stable and reliable performance of thin films in sensitive optical components.

Claims

1. A composite cleaning method for calcium fluoride optical lenses, characterized in that, Includes the following steps: The calcium fluoride optical lens to be cleaned was first purged with dry nitrogen, then dissolved and wiped with electronic grade acetone solution, then replaced with electronic grade anhydrous ethanol, and finally dried with dry nitrogen. The calcium fluoride optical lens, after the aforementioned drying treatment, is placed on the vacuum sample stage of the magnetron sputtering and ion beam assisted coating system and evacuated. High-purity argon gas is introduced into the ion source, and the ion energy and beam current density are controlled to bombard the calcium fluoride optical lens with an ion beam. At the same time, the temperature of the vacuum sample stage is monitored and stabilized by a thermocouple during the bombardment process, thereby completing the composite cleaning of the calcium fluoride optical lens.

2. The composite cleaning method according to claim 1, characterized in that, The operations of pre-purging with dry nitrogen, primary dissolution wiping with electronic-grade acetone solution, secondary replacement wiping with electronic-grade anhydrous ethanol, and drying with dry nitrogen are all performed in a clean bench with a temperature of 15–25°C, a humidity of 30%–50%RH, and a cleanliness level of Class 1000.

3. The composite cleaning method according to claim 1, characterized in that, The step of pre-purging with dry nitrogen includes: Using a nitrogen gun equipped with a high-efficiency air filter, introduce dry nitrogen gas with a purity of 99.999%. Control the nozzle to be 2-3 cm away from the surface of the calcium fluoride optical lens, and gently blow the entire surface at an angle of 25-35 degrees for 30 seconds.

4. The composite cleaning method according to claim 1, characterized in that, The step of using electronic-grade acetone solution for primary dissolution and wiping includes: Take a brand new polypropylene optical swab, immerse the tip of the brand new polypropylene optical swab in an electronic grade acetone solution until slightly moistened, apply pressure to prevent the swab from bending, and wipe from the center point of the calcium fluoride optical lens outward in a continuous, uninterrupted unidirectional spiral trajectory to cover the entire optical surface. The step of using electronic-grade anhydrous ethanol for secondary replacement wiping includes: Using a brand-new polypropylene optical swab dipped in electronic-grade anhydrous ethanol, wipe the calcium fluoride optical lens again from the center outwards in a spiral pattern, following the same trajectory and pressure as the first-stage dissolution wiping.

5. The composite cleaning method according to claim 1, characterized in that, The step of drying using dry nitrogen includes: Immediately use dry nitrogen gas to gently blow from top to bottom over the surface of the calcium fluoride optical lens until no liquid reflection or traces are observed, ensuring it is completely dry.

6. The composite cleaning method according to claim 1, characterized in that, The vacuuming step includes: evacuating the vacuum chamber to a background vacuum of (1.0~5.0)×10 using a molecular pump assembly. -3 Pa.

7. The composite cleaning method according to claim 1, characterized in that, The parameter ranges for ion energy and beam current density are as follows: Ion energy is controlled within the range of 50–110 eV, and beam current density is controlled within the range of 0.1–0.5 mA / cm². 2 Within the range.

8. The composite cleaning method according to claim 7, characterized in that, The flow rate of high-purity argon gas introduced into the ion source is set to 3–8 sccm; The temperature of the vacuum sample stage is stable within the range of 60–90°C; The processing time for the ion beam bombardment is set to 120–240 s.

9. The composite cleaning method according to claim 1, characterized in that, During the ion beam bombardment, the ion source and sample stage are rotated and monitored through the chamber observation window. The surface of the calcium fluoride optical lens exhibits a uniform pale blue glow with no abnormal discharge points.

10. The composite cleaning method according to claim 1, characterized in that, After the cleaning step is completed, the ion source is turned off and a high vacuum is maintained. Then, without breaking the vacuum, the process is directly switched to the ion beam-assisted deposition coating procedure to begin depositing the required optical thin film.

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