The surface preparation techniques practiced in solar cell manufacturing have fundamentally stemmed from those applied in the past and present for circuit board and related manufacturing processes. Early silicon wafer cleaning processes, for example, have technologically progressed from aqueous, or wet, chemical cleaning and etching approaches to a wide range of alternative dry processes. The latter include gas-phase atmospheric plasma discharges for both two-dimensional and three-dimensional surfaces for removing organic-based layers and residues. These atmospheric plasma regimes are also found being used in conjunction with supercritical phase carbon dioxide fluid (“snow cleaning”) devices for removing particle contaminations where wet chemical approaches can either not be employed or are being reduced due to VOC emission issues.
Taking a look at the wider scope of surface modification challenges in solar cell manufacturing, typical wafer preparation protocols include edge etching and cleaning, metal oxide removal, the removal of organic and inorganic contaminations, thin film layer etching (polymer layers, silicon nitride, silicon oxide, polyimide), removal of photoresist, surface ashing and descumming, surface roughening to improve bondability, and surface activation to improve liquid wettability and wetting uniformity.
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