Fourier transform infrared spectroscopy (FTIR) reveals structural changes in high and low, and on and off pulsed C2H2F4 ECR plasma deposited films upon thermal annealing. A significant improvement in thermal stability was achieved when the precursor now rate was increased to 50 standard cubic centimeters per minute for high/low pulsing. Evolution of CF3 groups attached to unfluorinated carbons has been identified as a low temperature loss mechanism in one of these films. Annealing produces shifts in asymmetric vs. symmetric CF2 stretch intensities, as well as initiating of CH stretches. In the 1400-2000 cm(-1) range, a systematic change from carbon-carbon double bonding structures to carbon-oxygen bonding structures results. These variations may be due to either additional oxygen absorption after annealing or reaction between oxygen and fluorocarbon network sites that were previously unavailable due to the steric hindrance. In most films, the thermal stability was dominated by oxygen and hydrogen uptake. The film with the highest oxygen and hydrogen content after annealing also had the lowest thermal stability. Thus, minimizing both CF3 and susceptibility to oxygen and water uptake by the deposited films would appear to be a valid strategy for increasing film thermal stability.