Experimental and Theoretical Studies of Laser Cleaning Mechanisms for Submicrometer Particulates on Si Surfaces

Submicrometer (0.1-1 mu m) polystyrene and alumina particles were removed by single-shot nanosecond 248 nm KrF laser radiation from Si wafer surfaces with or without pre-deposited thin liquid layers. Nearly complete (> 90%) single-shot laser cleaning has been achieved for combinations of polystyrene and alumina particles, respectively, with 2-propanol and water used as liquid energy transfer media, while for other combinations cleaning was absent or incomplete. Time-resolved optical microscopy studies have for the first time revealed important transient microscopic interactions between these particles and Si substrates in the pre-deposited micron-thick liquid layers, resulting, in some of these cases, in significantly reduced particle-substrate coupling. The visualization results give insight into microscopic particle removal mechanisms relevant to our laser cleaning experimental conditions, which are discussed along with their theoretical analysis. Theoretical modeling has been performed to interpret these experimental results and to provide insight into microscopic particle removal mechanisms.