Correlation between CF2 and CxFy densities in C4F8 plasmas

The densities of CF 2 and higher-order reaction products [C x F y (x ≥ 2)] in C 4 F 8 plasmas were measured by laser-induced fluorescence spectroscopy and quadrupole mass spectrometry, respectively. The CF 2 radical density had hollow-shaped spatial distributions (CF 2 density near the chamber wall was higher than that in the plasma column), indicating that CF 2 radicals were not the precursor for the deposition of fluorocarbon film but were produced from the surface of the chamber wall. The variations in the CF 2 and C x F y densities were examined as a function of residence time, at a fixed r.f. power and a fixed C 4 F 8 gas pressure. As a result, a correlation was found between the densities of CF 2 and C x F y . In addition, the variation in the deposition rate of the fluorocarbon film was similar to that in the C x F y density. From these experimental results, a recycling model of CF 2 radicals can be assumed as the mechanism of plasma-surface interaction in the C 4 F 8 plasma used in the present experiment. In this model, precursors for the deposition of fluorocarbon film are higher-order reaction products C x F y .