A comparison of CF4, CBrF3 and C2Br2F4 plasmas: Physical parameters and densities of atomic species

In this work, we performed the comparative study of CF 4 , CBrF 3 and C 2 Br 2 F 4 inductively coupled low temperature plasmas under typical reactive-ion etching conditions. The research scheme included plasma diagnostics by Langmuir probes, optical emission spectroscopy and 0-dimensional (global) modeling for CF 4 plasma. The latter was to verify the experimental data for their relevancy. The main focus was on electrons- and ions-related plasma characteristics as well as on densities of F and Br atoms which do work as chemical etchants for Si-based materials. It was found that all three plasma systems exhibit similar changes of above parameters vs. gas pressure. Principal features of CBrF 3 and C 2 Br 2 F 4 plasmas in respect to CF 4 are a) lower electron temperatures; b) higher plasma densities and electronegativities; and c) reduced densities of F atoms with the condition of [F] > [Br]. The last phenomenon is probably due to Br 2 + F → BrF + Br reaction mechanism supported by the fast 2Br → Br 2 recombination on chamber walls. Hence, the combination of higher ion density and lower F atoms density in bromine-containing gases provides their advantage in neutral/charged ratios and thus, in the etching anisotropy. • ICP plasma of bromofluorocarbons CBrF 3 and C 2 Br 2 F 4 were compared with CF 4 plasma. • Bromofluorocarbons ICP plasma have lower electron temperatures than CF 4 plasma. • Plasma densities in CBrF 3 and C 2 Br 2 F 4 plasma are several times higher than in CF 4 . • CBrF 3 and C 2 Br 2 F 4 plasma have 5 times lower neutral/charged ratios than CF 4 plasma. • Fluorine concentration in CBrF 3 and C 2 Br 2 F 4 plasmas is higher than Br concentration.