A relatively new method of removing hydrocarbon and silicone grease stains from silicon wafer surfaces is discussed. In this technique, high purity liquid or gaseous CO2 is expanded in a special nozzle to form a high speed jet. The jet contains numerous small diameter particles of solid CO2. The CO2 particles, referred to as snow, strike the surface and remove adherent particles (even submicron sizes), hydrocarbon stains such as fingerprints and noseprints, and silicone grease. Indeed, CO2 snow cleaning of clean wafer surfaces has led to sizable reductions in the adventitious hydrocarbons; in one case, the reduction was about 60%. Surface analysis of clean and contaminated silicon wafers indicates that CO2 snow cleaning causes no apparent chemical interactions and leaves no detectable residues.
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Sherman et al. (1990) studied this question.