Nanoscale Particle Removal Using Wet Laser Shockwave Cleaning

Abstract

A physical scalable Wet Laser Shockwave Cleaning (WLSC) process is presented for the removal of nanoscale particles, particularly organic nanoparticles, from Si wafers. The WLSC takes advantage of a very thin water film on the surface to increase the drag force by three orders of magnitude, reduce the adhesion force, utilize the double layer repulsive force and eliminate the capillary force. The removal of polystyrene latex (PSL) and silica particles of different sizes was investigated and compared with the original dry Laser Shock Cleaning (LSC). PSL particles as small as 28 nm were successfully removed using the proposed WLSC. The removal mechanism for the wet laser shockwave cleaning was investigated. Numerical computation of the laser-induced hydrodynamics and shadowgraphic imaging of the water film motion were used. The analysis suggests that the water film moves at a speed as high as 35 m/s as the impinging shockwave exerts a hydrodynamic drag force on the water film and consequently a sufficient removal force on the particle.