Enhancement of cleaning efficiency by geometrical confinement of plasma expansion in the laser shock cleaning process for nanoscale contaminant removal

Abstract

It has been shown that the laser shock cleaning (LSC) process is effective for removing nanoscale particles from solid surfaces and thus has various potential applications in microelectronic manufacturing. In this work, we propose a simple method to amplify the shock wave intensity generated by laser-induced breakdown (LIB) of air. The suggested scheme employs a plane shock wave reflector which confines the plasma expansion in one direction. As the half of the LIB-induced shock wave is reflected by the reflector, the intensity of the shock wave propagating in the opposite direction is increased significantly. Accordingly, the enhanced shock wave can remove smaller particles from the surface than the existing LSC process. The LSC process under geometrical confinement is analyzed both theoretically and experimentally. Numerical computation of the plasma/shock behavior shows about two times pressure amplification for the plane geometry. Experiments confirm that the shock wave intensity is enlarged by the effect of geometrical confinement of the plasma and shock wave. The result of cleaning tests using polystyrene particles demonstrates that the particle removal efficiency increases by the effect of geometrical confinement.