Difluorocarbene Emission Spectra from Fluorocarbon Plasmas and its Relationship to Fluorocarbon Polymer Formation

Abstract

The principal feature of the emission spectra from tetrafluoroethylene, perfluoropropene, perfluorobutene 2 and perfluorocyclobutene excited in a quartz flow tube electrodelessly at 13,56 MHz consisted of the intense system of bands due to the transition between 240 and 420 nm. Similar excitation of CF4 yielded bands between 180 nm and 240 due to CF(B2Δ -Xzπ) transition, possibly the CF(A2Σ -X2π) transition and bands due to the transition. Addition of hydrogen to CF4 reduced the fluorine atom emission intensity and increased the transition intensity. HF emission appeared after addition of 8% hydrogen. Addition of oxygen to CF4 reduced the intensity of the transition and increased the fluorine atom emission. The transition band system was also observed from rf excited plasma of trifluoroethylene, cis and trans 1,2 difluoroethylene but not from 1.1 difluoroethylene or monofluoroethylene. Using a parallel plate plasma reactor excited capacitively a rf frequency with perfiuoropropane, the deposition rate of fluorocarbon polymer was found to be a linear function of the CF2 emission between 50 and 200/watts of power and several flow rates. The polymer deposition rate was also a linear function of the fluorine atom emission intensity under these conditions, however, the slope of the two curves differed. These in situ optical spectroscopy results are consistent with plasma chemistry models previously derived from mass spectrometric studies of effluents from similar plasma systems. Clearly emission spectroscopy provides a viable alternative as a diagnostic tool for the control of plasma polymerization processes. © 1982, The Electrochemical Society, Inc. All rights reserved.