Supercritical fluids surface cleaning

The high diffiisivities and lack of surface tension associated with pure supercritical fluids makes them ideal for cleaning narrow gaps (typically less than a few thousands of an inch) in circuit boards of high value such as for satellite applications. Many of the contaminants are, however, ionic and carbon dioxide alone is not effective at extracting these species. Residue from surfactants need not be a problem as final washings with pure CO2 would clean the boards of remaining surfactant. 

Supercritical drying of porous silicon films on wafers has been particularly successful (see references in Table 1) and should be applicable to other physical forms such as membranes, microparticles, nanowire arrays, and nanoparticles. Of particular relevance in this regard is that the silicon MEMS community also utilizes this technique to avoid micromachined structure stiction, to clean silicon surfaces, and to improve device yield (Kim et al. 1998 Jafri et al. 1999 Namatsu et al. 1999). There are now commercially available systems for both silicon powder and wafer batch processing (Fig. 4). Supercritical fluids could also be utilized in the purification of porous silicon (Koynov et al. 2011). 

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