Atomic hydrogen temperature in silane plasmas used for the deposition of a-Si:H films

Abstract

Atomic hydrogen temperature in a silane plasma used for the deposition of a-Si:H films was measured using a two-photon laser-induced fluorescence technique. The temperature was found to be 2200±600 K and higher than both the parent-gas temperature and the atomic hydrogen temperature in a hydrogen plasma. We considered the mechanism of atomic hydrogen temperature determination in the plasma as follows. Hydrogen atoms generated by the dissociation of gas molecules due to electron impact in the plasma have a kinetic energy of several eV, which they then lose through collisions with gas molecules. At the same time, they disappear from the plasma due to chemical reactions and diffusion before thermal equilibrium with gas molecules has been established. Thus, an atomic hydrogen temperature higher than that of gas molecules becomes the equilibrium value in the plasma. We show, in the new experiment, that this model provides a good estimation of atomic hydrogen temperature in the plasma under various conditions of silane-hydrogen mixtures.