Angular effect in laser removal of spherical silica particles from silicon wafers

In this study, laser cleaning efficiencies to remove 2.5 mum particles have been investigated with different incident angles ranging from 0 degrees to 60 degrees. It is found that when the laser light irradiated normally to the substrate surface, the particle could be removed most efficiently. In this direction, the cleaning efficiency was also most sensitive to the light intensity. A sharp drop of cleaning efficiency occurred with a small change of the incident angle. Theoretical calculations based on the Lorentz-Mie theory and an accurate solution of the boundary problem, indicate that the light intensity near the contacting point is sensitive to the incident angle even though the incident light is uniform. (C) 2001 American Institute of Physics.