A kinetic study of the plasma-etching process. I. A model for the etching of Si and SiO2 in CnFm/H2 and CnFm/O2 plasmas

Abstract

A kinetic model of the plasma‐etching process has been developed to describe the etching of Si and SiO₂ in C_nF_m/O₂ and C_nF_m/H₂ plasmas (C_nF_m ≡CF₄, C₂F₆). The model has obtained good agreement with experiment for demonstrating the selective etching of SiO₂ in C_nF_m/H₂ plasmas, and the enhancement of the etch rate of Si in C_nF_m/O₂ plasmas. Good agreement is also obtained with mass spectroscopic measurements of neutral species from a CF₄/H₂ plasma. Results from the model indicate that the adsorption of atomic hydrogen on silicon surfaces from C_nF_m/H₂ plasmas, which then reacts with adsorbed fluorine, can significantly effect the selectivity of etching SiO₂ with respect to Si. Similarly, the adsorption of atomic oxygen, which then reacts with adsorbed carbon thereby cleansing the surface, may be responsible for the large etch rates of Si seen in C_nF_m/O₂ plasmas. The selectivity of etching SiO₂ in C_nF_m/H₂ plasmas has been found to be a sensitive function of the C/F ratio of the carbon‐bearing molecules which desorb from the surface, and a C/F ratio of 0.5 shows best agreement with experiment. Results from the model favor ion drift as a dominant mechanism by which radicals are transported to the surface.