A practical excimer laser-based cleaning tool for removal of surface contaminants

A laser-cleaning tool capable of removing surface contaminants such as submicron-sized particulates and organic films has been constructed and implemented in practical use. An industrial-grade KrF excimer laser is utilized to irradiate the solid surface to be cleaned. The nanosecond-pulsed laser irradiation, shortly after the deposition of a thin liquid film on the surface, induces explosive vaporization of the liquid and removal of particulates (“steam cleaning”). The ultraviolet (UV) irradiation also causes ablative photodecomposition of organic film contaminants on the surface (“dry cleaning”). Hence, cleaning can best be done with the combination of these two laser-cleaning modes. The excimer laser cleaning tool is constructed with an aim toward practical use: It includes a computer-controlled laser beam scanning system and a stable liquid film deposition unit, providing a cleaning rate of over 200 cm /min. Semiconductor, metal, and ceramic sample surfaces, contaminated with 1-μm sized alumina particles and micron-thick epoxy films, are tested by laser cleaning. The effectiveness of laser cleaning is compared with ultrasonic technique. The cleaning strategy and the probability of thermal damage due to laser cleaning are discussed