Monte Carlo-fluid model of chlorine atom production in Cl2, HCl, and CCl4 radio-frequency discharges for plasma etching

Chlorine chemistries are often used for the radio-frequency (rf) discharge plasma etching of compound semiconductors, metals, and silicon. A variety of gas mixtures are used as Cl atom donors, many of which have different electron transport coefficients. In this article we computationally investigate 13.56 MHz rf discharges sustained in He/Cl2, He/HCl, and He/CCl4 gas mixtures in the context of plasma etching. The study is performed using a Monte Carlo-fluid hybrid model of rf discharges. We find that the Cl atom production efficiency is surprisingly similar in these mixtures, while the details of the electron transport (sources of ionization, locations of attachment, electronegativity) dramatically differ. We also find that even at the low pressures of interest (0.25–1 Torr) attachment in He/HCl mixtures is dominated by vibrationally excited HCl, in analogy to high-pressure discharge devices.