A new mechanism of laser dry cleaning

The dry laser cleaning arises due to thermal expansion of the substrate and/or particle, when the corresponding acceleration (breaking) force produces work sufficient to overcome the adhesion energy. The previous examinations of the dry cleaning were done for two mechanisms: 1) expansion of absorbing particle on the transparent substrate and 2) expansion (thermal deformation) of the absorbing substrate with non-absorbing particle. Nevertheless using model with conventional mechanism based on the 1D surface expansion, one can find (for the smooth laser pulse) threshold fluence by the order of magnitude higher than experimental one. In the present paper, we discuss the new mechanism for situation when the particle is heated due to thermal contact with substrate, and additional thermodeformation effect, caused by optical enhancement. It is shown that these effects can be responsible for relatively small threshold fluence for laser cleaning of SiO2 particles (with size 0.5-1.0 mum) from the surface of Si by ns-excimer laser pulse.