A Comprehensive Model for Cleaning Semiconductor Wafers

A comprehensive model for particle removal from surfaces, which encompasses two interdependent models - an adhesion model and a removal model, is presented. The adhesion model predicts adhesive interactions for particles on surfaces by coupling computer simulation with a van der Waals adhesion model. Particle and surface geometry, morphology, composition, and deformation characteristics are accounted for in this model. Comparison between experimental results and model predictions shows that the adhesion model can not only accurately predict the mean adhesion force for a system, but can capture the variation in adhesion force due to roughness effects. The removal model assesses rolling particle removal from surfaces using a critical particle Reynolds number approach. Variation in particle size, adhesion force, and the point around which rolling can occur are accounted for in this model. Data from the literature are used to validate the removal model. The removal model was used to assess particle removal during brush scrubbing of semiconductor wafer surfaces at operating conditions typical of commercial brush scrubbers. Results indicate: 1) the time-dependent nature of the flow can significantly affect particle removal in this system, 2) particle shape can significantly affect removal for particles having nominally the same size, and 3) brush-particle contact must occur for complete particle removal.