Plasma enhanced chemical etching at atmospheric pressure for crystalline silicon wafer processing and process control by in-line FTIR gas spectroscopy

In advanced in-line processing of crystalline silicon solar cells, there is a high interest in dry etching at atmospheric pressure as an alternative to the current technology, especially when combined with similar process technologies, as for example deposition techniques. Based on a linearly extended DC arc with a width of 150 mm at atmospheric pressure, an innovative plasma etching technology has been studied. The technology operates in a remote mode, avoiding plasma source damage due to chemical attack of the etching gas. Fluorine radicals generated from NF3 and SF6 downstream of the plasma source have been successfully used to etch (100)-mono-crystalline-Si wafers. Independent industrial tests for rear surface etching for edge isolation of 125 x 125 mm22 mono-crystalline silicon wafers have been carried out. Rear surface etching for edge isolation results in short circuit currents better than values achieved by laser edge isolation, whereas cell efficiencies are comparable to reference values. Fourier Transformed Infrared (FTIR) gas spectroscopy was applied to monitor the etching processes. This nondestructive in-line measurement method allows the instantaneous determination of the current etching rates.