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 a nd implemented in practical use. An industrial-grade KrF excimer laser is utilized to irradiate the solid surface to be cleaned. The nanosec ond-pulsed laser irradiation, shortly after the deposition of a thin l iquid film on the surface, induces explosive vaporization of the liqui d and removal of particulates (''steam cleaning''). The ultraviolet (U V) irradiation also causes ablative photodecomposition of organic film contaminants on the surface (''dry cleaning''). Hence, cleaning can b est be done with the combination of these two laser-cleaning modes. Th e excimer laser cleaning tool is constructed with an aim toward practi cal 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(2)/min. Semiconductor, metal, and ceramic sample surfaces , contaminated with 1-mu m sized alumina particles and micron-thick ep oxy films, are tested by laser cleaning. The effectiveness of laser cl eaning is compared with ultrasonic technique. The cleaning strategy an d the probability of thermal damage due to laser cleaning are discusse d.