A Study on Radical Fluxes in Silane Plasma CVD from Trench Coverage Analysis

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Abstract
The precursors of the a-Si:H film in SiH4 plasma-enhanced CVD are investigated by use of trench coverage analysis. The cross sectional profile of deposited film in a trench is simulated by a direct Monte-Carlo method using the radical sticking probability β as an adjustable parameter. A comparison with the experimental results has shown that the trench coverage profiles are reproduced well by the model if two kinds of radicals, i.e., SiH3 and SiH2, are deposited independently on the substrate with the respective sticking probabilities of 0.1 and 1.0. The experimentally observed dependence of the trench profile on the plasma condition can be explained by the change in the radical deposition ratio, which becomes SiH3/SiH2=1/1 in pure SiH4 at low rf power and decreases to 1/2-1/3 in SiH4 diluted in Ar at high rf power. The above change in the contribution of two kinds of radicals to the deposition is also supported by the chemical kinetic calculation of the gas phase reactions and the radical transport to the substrate.