Correlation between CF2-and C2F4-concentrations in pulsed capacitively coupled CF4/H2 rf plasma

Abstract

The CF2 and C2F4 absolute concentrations were measured in pulsed low pressure CF4/H2 rf plasmas (13.56 MHz, CCP) by means of Infra-Red Tuneable Diode Laser Absorption Spectroscopy. For measurement of CF2 radicals the P2(21) line at 1096.3433 cm-1 was chosen with its calculated line strength of 4.09·10-20 cm/molecule. In case of C2F4 there is no detailed spectroscopic data available. Therefore, the C2F4 gas was produced by thermal decomposition of polytetrafluoroethylene for spectroscopic analysis. An absorption structure of several overlapping C2F4 lines was found around 1337.11 cm-1 and manually fitted. In pulsed plasma the time dependencies of the CF2 and C2F4 concentration correlated with each other. In plasma off-phase, the recombination of two CF2 radicals forming C2F4 was found to be dominant in CF2 kinetics, but of minor importance in C2F4 production