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 investigation of the physics of particle removal from the particularly interesting surface of silicon we have deposited well-characterized spherical polymer and silica particles of different diameters ranging from several tens to hundreds of nanometers on commercial wafers. As a result of our systematic study we observe a sharp threshold of the steam cleaning process at 110 mJ/cm2 (λ=532 nm, FWHM=7 ns) which is independent of the size (for particles with diameters as small as 60 nm) and material of the particles. An efficiency above 90% after 20 cleaning steps is reached at a laser fluence of 170 mJ/cm2. Experiments with irregularly shaped alumina particles exhibit the same threshold as for spherical particles.