Optimization of silicon etch rate in a CF4/Ar/O2 inductively coupled plasma

We use a fluid plasma model coupled with Maxwell's equations to analyze the influence of various parameters on the silicon etching rate by inductively coupled low-pressure plasma (ICP) generated in a CF4/O2/Ar mixture. These parameters include different argon and oxygen fractions in the feedgas, the gas residence time, and the discharge power. The simulation results show that the optimal etching rate is obtained when the gas residence time in the reactor is comparable to the time scale of dissociation reactions of feedgas CF4. We find that the etch rate remains almost constant for argon fraction in the mixture <50% and decreases for larger argon fractions. Based on these results, we discuss the influence of the argon fraction on the energy efficiency of the fluorine atoms formation in the ICP reactor. It is found that, for the conditions of our studies, there is the optimal etch rate for the oxygen fraction in the mixture of ∼5%. We demonstrate that the conventional explanation of this result is not applicable to the diffusion-controlled discharges and propose an alternative explanation. Finally, the increasing etching rate is obtained for the discharge power in the range of 102–103 W.