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

摘要

The CF2 and C2F4 absolute concentrations were measured in pulsed low pressure CF4/H2 rfplasmas (13.56 MHz, CCP) by means of Infra-Red Tuneable Diode Laser AbsorptionSpectroscopy. For measurement of CF2 radicals the P2(21) line at 1096.3433 cm -1 was chosen withits calculated line strength of 4.09·10 -20 cm/molecule. In case of C2F4 there is no detailedspectroscopic data available. Therefore, the C2F4 gas was produced by thermal decomposition ofpolytetrafluoroethylene for spectroscopic analysis. An absorption structure of several overlappingC2F4 lines was found around 1337.11 cm -1 and manually fitted. In pulsed plasma the timedependencies 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, butof minor importance in C2F4 production.