In demanding vacuum coating processes, chamber cleanliness directly determines the base pressure, film purity, adhesion, and ultimate product performance. Routine daily cleaning is insufficient to remove stubborn contaminants accumulated over time. Thus, periodic deep cleaning is an indispensable procedure for maintaining high production standards. This article systematically elaborates on the professional procedures and key considerations for the deep cleaning of vacuum chambers.
I. Pre-Cleaning Preparation and Safety Protocols
System Venting and Power Isolation: Ensure all process cycles are complete and the chamber is returned to atmospheric pressure. Implement a full Lockout-Tagout procedure to isolate all power sources (high voltage, RF, heaters), gas supplies, and water lines, guaranteeing operational safety.
Component Removal and Zoning: Dismantle all removable internal components, such as substrate holders, shutters, evaporation boats, arc cathodes, baffles, and the sensor heads of quartz crystal micro monitors. This divides the chamber into two main cleaning areas: the “main body” and the “components,” facilitating more thorough cleaning.
Contaminant Analysis: Conduct a preliminary assessment of contaminant types, commonly including:
Polymerized Residues: Splatter from PVD sources or evaporants.
Inorganic Coatings: Thin films deposited on non-substrate areas (e.g., chamber walls).
Vacuum Pump Oil Residues: Hydrocarbon contamination due to backstreaming or pump failures.
Particulate Contaminants: Dust, fibers, or flaked-off film particles.
II. Cleaning Methods and Process Selection
Appropriate cleaning methods must be selected based on the specific contaminants, typically following a sequence from physical to chemical cleaning.
Physical Cleaning Methods
Dry Blasting / Bead Blasting: Uses fine, chemically inert media (e.g., alumina, sodium bicarbonate) at controlled pressure to impact chamber walls and heavy coatings. Effectively removes stubborn nodules and thick contaminants, creating a uniform matte surface.
Lint-Free Wipers and High-Purity Solvents: For large areas with general contamination, use non-woven wipers (e.g., polyester or lint-free cloths) moistened with high-purity solvents (e.g., Isopropyl Alcohol, Acetone, or specialized VOCs). Wipe in a unidirectional manner to avoid recontamination.
Chemical Cleaning Methods
Solvent Cleaning: Targeted oils and certain polymers can be addressed using specific solvents for immersion or wiping. Complete removal of the solvent is mandatory post-cleaning to prevent it from becoming a new contamination source and impeding vacuum attainment.
Chemical Soaking and Stripping: Immerse removed components in dedicated coating strippers or acidic/alkaline solutions (e.g., nitric acid, sodium hydroxide) to dissolve inorganic coatings and oxides. Strictly control concentration, temperature, and immersion time to avoid substrate corrosion. Follow with a thorough rinse using deionized water and rapid drying.
Surface Activation and Passivation
For stainless steel chambers, a passivation treatment may be applied after deep cleaning to form a dense chrom oxide protective layer, enhancing corrosion resistance and reducing outgassing rates.
III. Post-Cleaning Treatment and Verification
Ultrasonic Cleaning: For components with complex geometries, ultrasonic cleaning utilizes cavitation to effectively remove sub-micron particles from micropores and crevices.
Drying: All cleaned components must be dried using oil-free, dry nitrogen or air and immediately placed in an oven for baking at an appropriate temperature (e.g., 80-120°C) to thoroughly remove adsorbed moisture.
Reassembly and Leak Checking: Reinstall all dry and clean components back into the chamber. Before pumping down, briefly purge the chamber with high-purity nitrogen. Start the pumping system and perform a coarse leak check at the rough vacuum stage to ensure no leaks at all sealing surfaces and flange connections.
Performance Verification: Conduct a standard pump-down cycle, recording the pressure vs. time curve from rough to high vacuum, and compare it with pre-cleaning data. The ultimate base pressure and its stability are the most critical metrics for judging cleaning effectiveness. A blank deposition run (without substrates) can be performed, followed by monitoring with a QCM or surface analysis instruments for any abnormal outgassing or contaminant release.
Conclusion
Deep cleaning of a vacuum chamber is a systematic, precision engineering task, not merely a cleaning chore. It requires operators to have a profound understanding of contamination mechanisms, material compatibility, and process specifications. By establishing and strictly adhering to a standardized deep cleaning protocol, defect rates in production can be significantly reduced, thin-film performance repeatability enhanced, and equipment service life extended, thereby ensuring process superiority and product reliability in a competitive market.
—This article was published by magnetron sputtering coating equipment manufacturer Zhenhua Vacuum
Post time: Oct-31-2025