In situ study of processes taking place on silicon surface during its bombardment by CF_x/Ar ions: Etching versus polymerization

The application of a Kaufman ion source in the study of the etching/polymerization processes taking place at the surface of a silicon substrate being exposed to ion beams generated from CF₄/Ar gas mixtures is reported. The processes were analyzed by means of in situ mass and energy spectroscopy of the secondary ions sputtered from the substrate surface and the charge-exchange ions, respectively. These analytical methods confirmed the growth of the polymer C-F thin films on the silicon surface at higher concentrations of CF₄ in the mixture. It was found that there existed a primary beam threshold energy above which the polymer thin film stopped growing and the etch yield of silicon atoms was increased. The simplified activated growth model presented here describes this behavior qualitatively as a competition between creative and destructive processes leading to deposition and removal of the thin polymer film, respectively.