Laser removal of contaminant films from metal surfaces

Abstract

In precision cleaning operations, it is essential to remove all traces of organic films and other contaminants, such as particles and fibers, from critical aerospace components. In the past, this was accomplished effectively with powerful solvents such as CFC-113, which can no longer be used because of its adverse effects on the environment. Among many alternative cleaning technologies under investigation, use of lasers to remove contaminants has recently shown promise in several applications, particularly in the area of particle removal from semiconductor surfaces for microcircuit manufacture. We present here, results of some of the first definitive studies of removal of organic films from metal surfaces using pulsed lasers. The substrate metals included aluminum and stainless steel, test coupons of which were contaminated with controlled amounts of organic substances (oils and greases) that might be present from normal use or handling of parts made from these materials. The test coupons were laser cleaned with short pulses having wavelengths selected to span a range of physical removal mechanisms from photo-chemical ablation to pure thermal effects (248, 355, and 1064 nm). Cleaning thresholds were measured using sloped irradiance profiles and post-test SEM observation of the position of the boundary between cleaned and uncleaned zones. These test results were combined with engineering studies of optical fiber beam delivery approaches in the design of a system for precision cleaning of the inside surfaces of metal tubes. Quantitative results of the laser cleaning tests and their implications for optical fiber-based laser cleaning systems are presented.In precision cleaning operations, it is essential to remove all traces of organic films and other contaminants, such as particles and fibers, from critical aerospace components. In the past, this was accomplished effectively with powerful solvents such as CFC-113, which can no longer be used because of its adverse effects on the environment. Among many alternative cleaning technologies under investigation, use of lasers to remove contaminants has recently shown promise in several applications, particularly in the area of particle removal from semiconductor surfaces for microcircuit manufacture. We present here, results of some of the first definitive studies of removal of organic films from metal surfaces using pulsed lasers. The substrate metals included aluminum and stainless steel, test coupons of which were contaminated with controlled amounts of organic substances (oils and greases) that might be present from normal use or handling of parts made from these materials. The test coupons were laser clean...