Modelling of a large scale reactor for plasma deposition of silicon

Abstract

A 2D fluid model for RF discharges in a mixture of silane and hydrogen is applied to a cylindrically symmetric reactor with an electrode radius large compared to the electrode separation. In the model the electron kinetics are included by solving the two-term Boltzmann equation to obtain the electron energy distribution function. The chemistry is taken from the literature and only diffusive transport of the neutral species is considered. The plasma-wall interaction (including the deposition) is modelled by using surface reaction coefficients. As a result of the large depletion of silane, the uniformity of the deposition strongly depends on the type of gas inlet. Both a showerhead gas inlet system, where the powered electrode is perforated, and gas inlet through a ring shaped area around one of the electrodes are considered. As can be expected, both the discharge and the deposition are homogeneous in case of a shower inlet. The ring inlet leads to an almost pure hydrogen plasma in the centre, while at the edge of the electrodes a mixture of silane and hydrogen is present. As compared to a small scale reactor with a low depletion, the growth precursor shifts from SiH3 and higher silane radicals to SiH2.