Homogeneous and Heterogeneous Reaction Mechanisms in CH$_{3}$F-O$_{2}$ Inductively Coupled Plasmas

CH$_{3}$F/O$_{2}$ containing plasmas are used in selective Si$_{3}$N$_{4}$ etching over Si or SiO$_{2}$. Fundamental plasma studies in these gas mixtures are scarce. In this work, optical emission rare gas actinometry and a global chemistry model were employed to study inductively couple plasmas in CH$_{3}$F/O$_{2}$ gas mixtures. For constant CH$_{3}$F and O$_{2}$ flow rates, the absolute H, F and O atom densities increased linearly with power. The feedstock gas was highly dissociated and most of the fluorine and oxygen was contained in reaction products HF, CO, CO$_{2}$, H$_{2}$O and OH. Measured number densities as a function of O$_{2}$ addition to CH$_{3}$F/O$_{2}$ changed abruptly for H, O, and particularly F atoms (factor of 4) at 48{\%} O$_{2}$ A corresponding transition was also observed in electron density, electron temperature and gas temperature, as well as in C, CF and CH optical emission. These abrupt transitions were attributed to the reactor wall reactivity, changing from a polymer-coated surface to a polymer-free surface, and vice-versa, as the O$_{2}$ content in the feed gas crossed 48{\%}. Homogeneous chemistry dominates above 48{\%} O$_{2}$; a kinetic model with no adjustable parameters is in excellent agreement with the absolute F and H and relative HF number density dependence on power and pressure.