Modeling of laser cleaning of metallic particulate contaminants from silicon surfaces

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Abstract
A model for laser-assisted particle removal was developed. The model was applied to micrometer-sized particles of gold, copper, and tungsten on silicon substrates. A two-dimensional heat transfer model is used to calculate the temperature profiles and the thermal expansion for the metallic particles and the silicon substrate irradiated with ultraviolet nanosecond laser pulses. The particle/substrate system was modeled as a simple spring oscillator under the sudden thermal expansion excitation pulse and a concept of degree of coupling between the laser induced thermal expansion associated frequency and the particle/substrate system is introduced. In terms of this degree of coupling a simple method to determine the most appropriate laser pulse duration is proposed. The theoretical results were compared with previously reported experimental observations. The experimental cleaning efficiency for the different particle materials and size distributions, as well as the possibility of substrate contamination due to metal evaporation are well accounted by the theoretical model.