Correlation between CF2 and CxFy densities in C4F8 plasmas

The densities of CF2 and higher-order reaction products [CxFy(x greater than or equal to 2)] in C4F8 plasmas were measured by laser-induced fluorescence spectroscopy and quadrupole mass spectrometry, respectively. The CF2 radical density had hollow-shaped spatial distributions (CF2 density near the chamber wall was higher than that in the plasma column), indicating that CF2 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 CF2 and CxFy densities were examined as a function of residence time, at a fixed r.f. power and a fixed C4F8 gas pressure. As a result, a correlation was found between the densities of CF2 and CxFy. In addition, the variation in the deposition rate of the fluorocarbon film was similar to that in the CxFy density. From these experimental results, a recycling model of CF2 radicals can be assumed as the mechanism of plasma-surface interaction in the C4F8 plasma used in the present experiment. In this model, precursors for the deposition of fluorocarbon film are higher-order reaction products CxFy. (C) 2000 Elsevier Science S.A. All rights reserved.