A Theoretical Analysis of Wafer Cleaning Using a Cryogenic Aerosol

Abstract

Cryogenic aerosol-based cleaning has been successfully used to remove contaminant particles from the surface of semiconductor wafers. The aerosol is generated by the expansion of an inert gas such as argon or nitrogen. Particles are dislodged by mechanical impact of the aerosol clusters, and their suspension and removal are effected by phenomena such as thermophoresis and turbulent lift in the flow stream over the wafer surface. This study presents a theoretical examination of the issues of aerosol generation and particle suspension and removal. The characteristics of aerosols generated in a freely expanding argon gas jet are studied using a coupled fluid flow-cluster formation model. The role of thermophoresis in particle suspension and removal is studied by examining the relative strengths of thermal, diffusional, and gravitational effects in the boundary layer over the wafer surface. To the extent possible, theoretical findings are supported by experimental observations.

Integrated Experimental and Numerical Study of Thermomechanical Resist Removal-Cleaning Performance Using Cryogenic Micro-Solid Nitrogen Spray

“…By utilizing high-speed micro-solid nitrogen spray, the complete chemical free, pure water free, ashing-less dry type thermomechanical resist removal-cleaning system would be developed. The present system is quite different from that of conventional cryogenic aerosol cleaning (2,3), it utilizes the micro-solid nitrogen (SN 2 ) which consists of the fine solid nitrogen particle produced by the high-speed collision of subcooled liquid nitrogen and the cryogenic gaseous helium (cryogen) (1). The photo resist can be removed and cleaned from wafer surface due to the interaction that the particle impingement of inertial forces and the rapid thermal contraction effect (thermomechanical effect) which is based on solid super high heat flux cooling.…”

Ultra-high heat flux cooling characteristics of cryogenic micro-solid nitrogen particles and its application to semiconductor wafer cleaning technology

“…The proposed system is quite different from that of conventional cryogenic aerosol cleaning [6,7] in that it utilizes micro-solid nitrogen (SN 2 ) which consists of fine solid nitrogen particles produced by the high-speed collision of subcooled liquid nitrogen and cryogenic gaseous helium (cryogen) through a two-fluid nozzle. Photo resist can be removed and cleaned from the wafer surface due to the interaction of the particle impingement of inertial forces and the rapid thermal contraction effect (thermomechanical effect of the resist), which is based on the ultra-high heat flux cooling effect of the inherent characteristics of cryogenic solid particles which accompany phase change.…”

Removal of biofilms using carbon dioxide aerosols

“…Both momentum transfer and solvent action can initiate the removal of surface contaminants; the CO 2 gas then carries them away from the surface. In addition, several other cleaning mechanisms such as shear stress forces generated by sublimation, thermal stress, and thermophoresis have been proposed, but any of these are not completely understood yet (Narayanswami, 1999;Okada, Kawata, & Sonoda, 2002).…”