ON EFFECTS OF INITIAL CF4 + CHF3 + O2 MIXTURE COMPOSITION ON PLASMA PARAMETERS AND REACTIVE-ION ETCHING OF SILICON

In this work, we discussed how the CF4/CHF3 ratio in CF4 + CHF3 + O2 gas mixture does influence steady-state plasma composition and silicon etching kinetics in a conventional reactive-ion process. Plasma diagnostics by double Langmuir probes delivered the information on electro-physical plasma parameters and provided input data for the modeling of plasma chemistry. As a result, we confirmed basic properties of CF4 + O2 and CHF3 + O2 plasmas known from previous works as well as analyzed formation/decay kinetics for plasma active species in the three-component gas mixture. In particular, it was found that the substitution of CF4 by CHF3 at fixed content of oxygen in a feed gas a) causes weak changes in electron temperature and plasma density; b) leads to an increase in plasma polymerizing ability; and c) sufficiently (by more than 3 times) reduces F atom density. The last effect was confirmed by the satisfactory agreement with experimental data obtained using the optical emission actinometry method. Etching experiments indicated a monotonic decrease in Si etching rate toward CHF3-rich plasmas, from 140 nm/min down to 65 nm/min. The analysis of etching kinetics allowed one to conclude that a) the dominant etching mechanisms is the ion-assisted chemical reaction; and b) the effective reaction probability keeps the nearly constant value, in spite of increasing polymer deposition rate. This effect may reflect the change in passivation of polymer-free surface by oxygen atoms. For citation: Efremov A.M., Bobylev A.V., Kaznacheeva E.M., Kwon K.-H. On effects of initial CF4 + CHF3 + O2 mixture composition on plasma parameters and reactive-ion etching of silicon. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2025. V. 68. N 1. P. 39-47. DOI: 10.6060/ivkkt.20256801.7096.