Plasma chemistry in fluorocarbon film deposition from pentafluoroethane/argon mixtures

Plasma-enhanced deposition of fluorocarbon films was performed at 120 degrees C from a mixture of pentafluoroethane (CF3CHF2) and argon in a parallel plate plasma reactor. Mass spectrometry of the reactor effluent was used to gain an understanding of the plasma chemistry of this monomer. The monomer primarily dissociated into CF3. and CHF2. in the plasma. The results from mass spectrometry indicated that CHF2* was the primary precursor for deposition and that the fluorine radicals in the plasma were primarily scavenged as CF4 and HF. Monomer conversion (fraction of monomer fragmented) in the plasma was determined based on mass spectrometer partial pressure analysis of CH3CHF+ fragments' (parent molecule: CF3CHF2) before and after plasma ignition. The conversion correlated directly with both the applied power and the deposition rate. The overall gas phase reactions did not change significantly with rf power within our range of operation, indicating a common reaction mechanism at all powers. No significant change in the composition of the deposited films was found, as measured by x-ray photoelectron spectroscopy (XPS), supporting the common mechanism conclusion. Further, XPS studies showed a fluorine-to-carbon ratio between 1.05 and 1.15 suggesting extensive crosslinking of the polymer. Infrared spectra of the deposited films showed negligible CHx concentration despite the presence of hydrogen in the monomer. (C) 1999 American Vacuum Society. [S0734-2101(99)01906-5].