Mercury-Sensitized Hydrogen Radical Photoetching of Undoped Hydrogenated Amorphous Silicon and Crystalline Silicon

An etching study for undoped a-Si:H films and c-Si has been carried out by using Hg-sensitized H radicals in H2 gas under UV-light irradiation with a low pressure mercury lamp. It has been found that the etch rate of undoped a-Si:H increases with decreasing substrate temperature and H2 flow rate, as well as with increasing UV-light intensity. Concerning H2 gas pressure dependence, a maximum etch rate was observed at around 0.1 Torr. An adsorbed layer, composed of H2 molecules, H radicals, Hg atoms and photoexcited Hg atoms, can be considered to be formed on the surface. The adsorbed layer irradiated with UV light may supply a sufficient number of H radicals near the surface to rapidly cut off the Si network, leading to the formation of volatile SiH x .