Dry laser cleaning of particles from solid substrates: Experiments and theory

The experimental analysis of dry laser cleaning efficiency is done for cert ified spherical particle (SiO2, 5.0, 2.5, 1.0, and 0.5 mum) from different substrates (Si, Ge, and NiP). The influence of different options (laser wav elength, incident angle, substrate properties, i.e., type of material, surf ace roughness, etc.) on the cleaning efficiency is presented in addition to commonly analyzed options (cleaning efficiency versus laser fluence and pa rticle size). Found laser cleaning efficiency demonstrates a great sensitiv ity to some of these options (e.g., laser wavelength, angle of incidence, e tc.). Partially these effects can be explained within the frame of the micr oelectronics engineering (MIE) theory of scattering. Other effects (e.g., i nfluence of roughness) can be explained along the more complex line, relate d to examination of the problem "particle on the surface" beyond the MIE th eory. The theory of dry laser cleaning, based on one-dimensional thermal ex pansion of the substrate, demonstrates a great sensitivity of the cleaning efficiency on laser pulse shape. For the reasonable pulse shape this theory yields the threshold fluence by the order of magnitude larger than the exp erimental one. At the same time the theory, which takes into account the ne ar-field optical enhancement and three-dimensional thermal expansion effect s, yields the correct values for threshold. (C) 2001 American Institute of Physics.