Thermal stability of fluorocarbon films deposited from pentafluoroethane/argon plasmas

Fluorocarbon films were deposited from pentafluoroethane/argon mixtures in a parallel-plate reactor at a pressure of 1 Torr and substrate temperatures between 120 and 210 degrees C. Films deposited on substrates placed on the heated, grounded electrode as well as films formed on the powered electrod e were analyzed using infrared spectroscopy, X-ray photoelectron spectrosco py (XPS), and thormogravimetric analysis (TGA). Polymer deposition rates de creased with an increase in substrate temperature indicating that reactant adsorption is the rate-limiting step. Films deposited on the powered electr ode had an O/C ratio of 0.14, which was significantly higher than that of f ilms deposited on the grounded electrode at elevated temperatures. Likewise , TR spectra of films on the powered electrode also showed significant cont ributions from C=O related groups. TGA data indicated that the powered elec trode films had similar to 3% weight loss at 250 degrees C, while films dep osited on the grounded electrode had similar to 1% weight loss at 250 degre es C. The thermal stability of films deposited on the grounded electrode wa s significantly enhanced when deposited at higher substrate temperatures. X PS analyses indicated a decrease in the F/C ratio of the deposited films wi th an increase in substrate temperature. TGA analyses indicated that weight loss below 250 degrees C was due primarily to the outgassing of low-molecu lar weight species from the fluorocarbon films. The higher weight loss regi on between 320 and 425 degrees C was ascribed to polymer degradation due to scission of main chain C-C bonds and to evolution of HF and CO2. (C) 2000 The Electrochemical Society.