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 particles 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 show for the first time the feasibility of performing efficient steam laser cleaning with ps laser pulses and compare the achieved efficiency with the one obtained for ns pulses. For ns pulses, we found a cleaning fluence threshold 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 pulses (FWHM = 30ps, lambda = 583 nm) lowered this threshold to 20mJ/cm(2). Both cleaning thresholds are far below the melting thresholds for these laser parameters. Cleaning efficiencies > 90% were reached for both pulse durations.