PLASMA PARAMETRS AND SILICON ETCHING KINETICS IN CF4 + C4F8 + O2 MIXTURE: EFFECT OF CF4/C4F8 MIXING RATIO

Abstract

In this work, we investigated the influence of fluorocarbon component ratio in the CF4 + C4F8 + O2 gas mixture on electro-physical plasma parameters, steady-state densities of active species and silicon etching kinetics under typical reactive-ion process conditions. The combination of plasma diagnostics (double Langmuir probes, optical emission spectroscopy) and plasma modeling confirmed known peculiarities of plasma chemistry of individual fluorocarbons in the presence of oxygen as well as provided an extended analysis of both fluorine and oxygen atom kinetics in the three-component gas mixture. It was shown that the substitution of CF4 by C4F8 at the constant fraction of O2 a) causes the weak disturbance in electrons- and ions-related plasma parameters (electron temperature, electron density, ion energy flux); b) provides drastically increasing density of polymerizing CFx (x = 1, 2) radicals; and c) results in monotonically decreasing F atoms density. The latter is due to simultaneous changes in both F atom formation rate and their loss frequency, especially in C4F8-rich plasmas. From experiments, it was found that Si etching rate is by more than 85% controlled by its chemical component (in a form of ion-stimulated heterogeneous reaction Si + xF → SiFx) and decreases with increasing C4F8 fraction in a feed gas. The change in effective reaction probability contradicts with the growth of polymer deposition rate and film thickness (as it follows from changes in gas-phase plasma characteristics) but may reflect the weakening of surface passivation by oxygen atoms. For citation: Efremov A.M., Bobylev A.V., Kwon K.-H. Plasma parametrs and silicon etching kinetics in CF4 + C4F8 + O2 mixture: effect of CF4/C4F8 mixing ratio. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 6. P. 29-37. DOI: 10.6060/ivkkt.20246706.6982.