Experimental and theoretical study of a magnetron DC-PECVD acetylene discharge
Identification of the deposition precursors and film growth mechanisms
This work focuses on the film deposition mechanisms in a low-pressure argon-acetylene magnetron assisted plasma via Particle-in-Cell Monte-Carlo simulation in combination with a chemical surface model including saturated and dangling bond sites to account for the film growth mechanisms involving reactive radical species. A main point of interest was to find out whether the film growth is dominated by ions, by radicals or by target sputtering. Predictions were made regarding the equilibrium coverage and the deposition profile at equilibrium for various acetylene ratios by varying the initial surface coverage of dangling bonds, fitting its evolution with time and extrapolating predictions to discharge powers. These predictions were tested against experimental a-CH film characterizations, including RBS/ERDA, XPS, Raman, and profilometer measurements. Even if high uncertainty remains, we demonstrated that films deposited on a grounded substrate facing the target have Gaussian deposition profiles which can be reproduced quantitatively for various C2H2 ratios. This model could be used to accelerate the search for optimal deposition parameters for more complex deposition configurations without relying on costly trial-and-errors, and to get a clearer understanding on the underlying processes which is hard to obtain with in-situ experiments for PECVD.