INFLUENCE OF Ar/He RATIO ON PLASMA COMPOSITION AND SILICON ETCHING KINETICS IN CF4- AND C4F8- BASED TERNARY MIXTURES

The investigation of plasma electro-physical parameters, gas phase composition and reactive-ion etching kinetics of silicon in CF4 + Ar/He and C4F8 + Ar/He mixtures with variable ratio of inert components was carried out. The combination of plasma diagnostics tools (Langmuir probes, optical emission spectroscopy) with modeling of plasma chemistry allowed one a) to figure out how the Ar/He ratio influences densities of active species (fluorine atoms, polymerizing radicals and positive ions) determining the overall plasma-surface interaction result; b) to divide contributions of physical and chemical etching pathways; and c) to analyze the etching mechanism in terms of effective reaction probability. It was shown that the substitution of argon by helium produces several common features, such as a decrease in both electron temperature and electron density, а transition toward lower dissociation degrees for multi-atomic species that results in decreasing densities of less saturated fluorocarbon radicals and fluorine atoms as well as a fall of Si etching rate that follows the kinetics of heterogeneous reaction Si + xF → SiFx. The growth of corresponding reaction probabilities demonstrate an agreement with decreasing amount of deposited polymer in the case of CF4 + Ar/He plasma, but contradicts with increasing polymerizing impact in C4F8 + Ar/He plasma. The last phenomenon probably reflects an enforcement of F atom flux (compared with that determined by F atom density in plasma) at the polymer/Si interface. The reason is the formation of F atoms in polymer layer of increasing thickness due to its de-fluorination by the ion bombardment. For citation: Efremov A.M., Betelin V.B., Kwon K.-H. Influence of Ar/He ratio on plasma composition and silicon etching kinetics in CF4- and C4F8- based ternary mixtures. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2025. V. 68. N 6. P. 41-51. DOI: 10.6060/ivkkt.20256806.7181.