Mechanism of silicon film deposition in the RF plasma reduction of silicon tetrachloride

Plasma-chemical reduction of SiCl4 in mixtures with H2 and Ar has been studied by optical emission spectroscopy (OES) and laser interferometry techniques. It has been found that the Ar:H2 ratio strongly affects the plasma composition as well as the deposition (rD) and etch (rE) rates of Si:H,Cl films and that the electron impact dissociation is the most important channel for the production of SiClx species, which are the precursors of the film growth. Chemisorption of SiClx and the reactive surface reaction SiClx + H --> -SiCl(x-1) + HCl are important steps in the deposition process. The suggested deposition model gives rD~ [SiClx][H], in agreement with the experimental data. Etching of Si:H,Cl films occurs at high Ar:H2 ratio when Cl atoms in the gas phase become appreciable and increases with increasing Cl concentration. The etch rate is controlled by the Cl atom chemisorption step.