Spatial profiles of reactive intermediates in rf silane discharges

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Abstract
Spatial concentration profiles of ground-state SiH and electronically excited SiH* radicals are measured using laser-induced fluorescence and emission spectroscopy, respectively. The measurements are made in pure silane, as well as in mixtures with helium, hydrogen, and argon, in a capacitively coupled rf glow-discharge apparatus used for the deposition of a-Si:H. Low-power–low-depletion conditions are maintained throughout, whereas pressure is varied from 20 to 400 mTorr. Our observations indicate a close relationship between concentration profiles of the species and local electron energy distribution. We conclude that spatial concentration profiles represent stationary generation rates of the radicals. In the case of diluted silane the process is strongly influenced by diffusional transport of detected species to the deposition electrode. The dependence of this effect on dilution grade and buffer gas used is presented.