The modeling of excimer laser particle removal from hydrophilic silicon surfaces

We summarize experimental results on the successful removal of submicron-sized polystyrene latex, carboxylate-modified latex, ${\mathrm{SiO}}_{\mathrm{2}},$ and ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ particles from hydrophilic silicon surfaces by excimer laser, using both dry and steam cleaning; the cleaning and damage thresholds have also been determined for these particles. Adhesion and removal models for an ideal sphere particle, that include van der Waals forces, hydrogen bonding, and thermoelastic effects, theoretically explain the laser cleaning results. Two models of the removal force due to the explosive evaporation of liquid film have been calculated and compared. The effects of both asperities on the particle surface and particle aggregation have also been considered. The results of the calculations show that even those surface asperities which are small compared with the particle dimension can cause a large reduction in both adhesion and thermoelastic removal forces. The theoretical predictions are consistent with the experimental observations.