Some indications of different film forming radicals in a-Si:H deposition by the glow discharge and thermocatalytic CVD processes

In this paper we present some experimental results which support the hypothesis that different film forming radicals (precursors) are responsible for the deposition of hydrogenated amorphous silicon (a-Si:H) films by the plasma enhanced chemical vapor deposition (PECVD) and thermocatalytic chemical vapor deposition (TCCVD). Indications for the above conjecture come from investigations and comparison of the growth of a-Si:H films prepared by the two methods. Basic differences in the silane dissociation process and subsequent radical collisions in the gas phase obviously produce different precursors. These produce deviations during the coalescence phase of the initial film growth and a very different effect of hydrogen dilution on the film preparation. As a result dense high quality a-Si:H is formed in both methods at quite different optimum substrate temperatures (∼250°C and ∼400°C) and with large differences in hydrogen content (∼10 and ∼2 at.%, respectively).