Role of H₃⁺ions in deposition of silicon thin films from SiH₄/H₂discharges: modeling and experiments

A 1D fluid model including a detailed chemistry for silane-hydrogen discharges as well as surface reactions to account for deposition and etching processes has been implemented to study the effects of gas pressure (1 to 3.5 Torr) and silane concentration (2 to 10%) on the deposition rate of silicon thin films in a standard RF-PECVD reactor. The thickness of the films and their deposition rate as functions of the process conditions were determined from optical modelling of UV-visible spectroscopic ellipsometry measurements. The experimental values of the deposition rate were compared with results from the 1D fluid model. SiH3 radicals are found to be the main contributor to the computed deposition rates, while H3+ ions play the main role in the etching process. The study reveals that etching by hydrogen ions must be taken into account to reproduce properly the experimental deposition rate. In particular etching by H3+ ions must be taken into account to achieve a good agreement between the experimental and modelled values of the deposition rate as a function of the total gas pressure and the silane fraction in the discharge.