A theoretical analysis of wafer cleaning using a cryogenic aerosol

Cryogenic aerosol-based cleaning has been successfully used to remove conta minant particles from the surface of semiconductor wafers. The aerosol is g enerated by the expansion of an inert gas such as argon or nitrogen. Partic les are dislodged by mechanical impact of the aerosol clusters, and their s uspension and removal are effected by phenomena such as thermophoresis and turbulent lift in the flow stream over the wafer surface. This study presen ts a theoretical examination of the issues of aerosol generation and partic le suspension and removal. The characteristics of aerosols generated in a f reely expanding argon gas jet are studied using a coupled fluid flow-cluste r formation model. The role of thermophoresis in particle suspension and re moval is studied by examining the relative strengths of thermal, diffusiona l, and gravitational effects in the boundary layer over the wafer surface. To the extent possible, theoretical findings are supported by experimental observations. (C) 1999 The Electrochemical Society. S0013-4651(97)10-018-0. All rights reserved.