Investigation of Low-Temperature Hydrogen Plasma-Etching Processes for Silicon Wafer Solar Cell Surface Passivation in an Industrial Inductively Coupled Plasma Deposition Tool

A hydrofluoric-acid (HF)-free hydrogen plasma dry etching process prior to the deposition of intrinsic amorphous silicon onto thin n-type planar Czochralski silicon wafers is developed. The influence of substrate temperature, hydrogen flow rate, and power density on the passivation quality is investigated. Advanced characterization using spectroscopic ellipsometry and transmission electron microscopy shows the impact of the etching conditions, especially the temperature and gas flow rates, on the surface quality and interface properties. It is found that the native oxide can only be removed effectively when wafers are subjected to higher temperature or lower hydrogen flow rate. The hydrogen, oxygen, and carbon concentration profiles at the a-Si/c-Si interface of the plasma-etched samples are studied and compared with the traditionally HF cleaned interface to gain a better understanding of the reasons for the superior passivation quality.