Modelling of laser cleaning of metallic particles on silicon substrates

Summary form only given. A two-dimensional model of the interaction between laser radiation and a particle-substrate system with was developed by solving the heat transfer equation using a semiimplicit finite difference method and calculating the thermal expansion of the particles and the substrate on the basis of their spatio-temporal temperature distribution. The particle-substrate system was modelled as a simple spring oscillator which experiences a sudden thermal expansion due to the laser induced heating. A new concept for the coupling between the laser induced thermal expansion associated frequency and the particle-substrate system, introduced in previous work, is used. The theoretical cleaning condition is established on the basis of the relation between the adhesion energy (van der Waals and H-bonds) and the energy acquired by the particle in the process. The theoretical predictions were compared with the results of mirage effect experiments, carried out to measure the fly of the particles from the substrate. Real-time measurements of the surface temperature during laser irradiation were done by monitoring the reflectivity of the surface. Theoretical predictions for the energy acquired by the particles and the substrate surface temperature obtained by the model were in good agreement with the experimental results. The better the coupling between the laser induced thermal expansion associated frequency and the particle-substrate system, the highest the particles jump away from the substrate (0.4 μm diameter W particles jump up to 1.mm against gravity).