Particle removal in linear shear flow

Abstract

In many industrial processes, particle contamination is becoming a major issue. Particle detachment from surfaces can be detrimental, e.g., during lithographic processing. During cleaning, however, detachment of particles is aimed for. However, until recently, only little was known on the mechanism of particle detachment due to flowing gasses. In high throughput applications, large gas velocities are likely to occur at certain locations in the system. It is important to test particle behavior experimentally under all conditions that may arise. Therefore, the aim of this study is to be able to predict the risk of particle detachment by modeling. For this purpose, particle-surface interaction is studied for micrometer-sized particles. Based on the particle Reynolds number, critical particle diameters were determined for which the flow-induced forces on the particles (drag and lift forces) are larger than the attractive forces between the particle and the surface (van der Waals force). Among the different possible particle motions (lift, sliding and rotation), particle rotation turns out to be the mechanism responsible for particle removal. A critical particle diameter was defined for which attractive and flow-induced forces are equal. Calculated values of the critical particle diameter agree with the experimental results within a few micrometers. This removal mechanism model can thus be used to calculate the cleaning efficiency of a flow, and for determining the probability of unwanted detachment of particles from surfaces in ultra-clean production or processing environments.