Universal threshold for the steam laser cleaning of submicron spherical particles from silicon

The efficiency of the "steam laser cleaning" process is examined. For the i nvestigation of the physics of particle removal from the particularly inter esting surface of silicon we have deposited well-characterized spherical po lymer and silica particles of different diameters ranging from several tens to hundreds of nanometers on commercial wafers. As a result of our systema tic study we observe a sharp threshold of the steam cleaning process at 110 mJ/cm(2) (lambda = 532 nm, FWHM = 7 ns) which is independent of the size ( for particles with diameters as small as 60 nm) and material of the particl es. An efficiency above 90% after 20 cleaning steps is reached at a laser f luence of 170 mJ/cm(2). Experiments with irregularly shaped alumina particl es exhibit the same threshold as for spherical particles.