A comparison of ns and ps steam laser cleaning of Si surfaces

We report a quantitative investigation on the efficiency of the steam laser cleaning process using ns and ps pulses. Well-characterized polymer partic les with a diameter of 800 nm dispersed on commercial Si wafers were chosen as a modeling contaminant system. As a result of our investigation, we sho w for the first time the feasibility of performing efficient steam laser cl eaning with ps laser pulses and compare the achieved efficiency with the on e obtained for ns pulses. For ns pulses, we found a cleaning fluence thresh old of 50 mJ/cm(2) that is independent of the pulse durations (2.5 ns and 8 ns) and the wavelengths (532 nm and 583 nm) used. The application of ps pu lses (FWHM = 30ps, lambda = 583 nm) lowered this threshold to 20mJ/cm(2). B oth cleaning thresholds are far below the melting thresholds for these lase r parameters. Cleaning efficiencies > 90% were reached for both pulse durat ions.