Interface investigations of hydrogen plasma etched silicon surfaces for heterojunction silicon solar cell applications

Excellent carrier lifetime is obtained by applying a rapid low-temperature hydrogen plasma etch before the deposition of intrinsic amorphous silicon in an industrial ICPECVD reactor. The hydrogen etch process substitutes a conventional HF dip and removes surface oxides via the rapid hydrogen plasma. Process development details such as influence of the temperature, flow rate and power density on the lifetime are presented. Interface comparison is carried out on plasma etched and HF dipped samples by using transmission electron microscopy, electron energy loss spectroscopy and time-of-flight secondary ion mass spectroscopy. It is found that the interface is both hydrogen and oxygen rich compared to HF-etched reference samples. Epitaxial growth is suppressed. Using amorphous silicon suboxide for subsequent surface passivation, the plasma etched samples show excellent lifetimes of 6.1 ms on a 6 inch 1 Ωcm n-type wafer. This hydrogen plasma etch process may be an excellent alternative to conventional HF treatment for heterojunction silicon solar cell fabrication.