Influence of beam incidence angle on dry laser cleaning of surface particles

Dry laser cleaning is envisaged by semiconductor companies to replace wet-cleans. The influence of beam incidence angle was studied in the case of the removal of weakly absorbing particles on absorbing Si wafers by 248 nm DUV light pulses. By decreasing the beam incidence angle from 808 to 108, the removal efficiency of 0.15–0.30 mm Si3N4 particles was increased by 30–45%, while no improvement was observed with 0.3 mm SiO2 particles. Based on theoretical calculations, it is proposed that the enhanced removal of particles at grazing incidence is caused by the horizontal component of the beam radiation pressure. The difference between Si3N4 and SiO2 particles is attributed to the influence of particle shape on van der Waals adhesion forces. q2000 Elsevier Science B.V. All rights reserved.