Chapter 17 – Cleaning Using Argon/Nitrogen Cryogenic Aerosols

Aerosol jet cleaning of surfaces has become a promising technique for the anhydrous removal of particles, or other undesired materials such as films or layers. This chapter describes the methods used to produce argon/nitrogencryogenic aerosol jets, approximate operating costs, and some examples of the effectiveness of these aerosols in removing silicon wafer surface contamination. However, the technique is applicable in removing contaminants in other areas. Although operating conditions for a cleaning tool are presented, these conditions are merely illustrative, and should serve only as an approximate guide in generating cryogenic aerosols for cleaning. In production process, a pressurized mixture of high-purity gaseous argon and nitrogen is first filtered and then pre-cooled in a cryogenic heat-exchanger. The argon/nitrogen mixture may be pre-cooled to a temperature slightly above the argon dew point in the cryogenic cooler. The pre-cooled mixture is then expanded in a free jet to a lower pressure. The associated Joule-Thomson cooling condenses and solidifies microscopic argon particles in the free jet. Argon liquefaction first occurs in the cryogenic cooler, then argon droplets are formed through subsequent atomization in the nozzle.