A study of particle removal based on Monte Carlo simulation of ion interactions

In this paper, the fundamental forces acting on a particle close to a substrate are reviewed. Using experimental results, an attempt is then made to describe the actual particle removal mechanism in wet processes which seems to obey a dynamic process: competition between the substrate etching rate and particle speed back to the substrate due to the attractive forces. A simplified new static model based on a Monte Carlo simulation is proposed here and compared to the results obtained by the conventional DLVO theory. Because the actual size of the counter-ions and the inter-ion correlation are neglected in the DLVO theory, the repulsion pressure acting on the particle is underestimated in this model for distances lower than 5 nm. The consequence is that a lower particle/substrate distance is necessary to overcome the van der Waals attraction. The new Monte Carlo simulation presented here is also able to predict the experimental results obtained when the size and valence of the counter-ions are varied.