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 electrode were analyzed using infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and thormogravimetric analysis (TGA). Polymer deposition rates decreased with an increase in substrate temperature indicating that reactant adsorption is the rate-limiting step. Films deposited on the powered electrode had an O/C ratio of 0.14, which was significantly higher than that of films deposited on the grounded electrode at elevated temperatures. Likewise, TR spectra of films on the powered electrode also showed significant contributions from C=O related groups. TGA data indicated that the powered electrode films had similar to 3% weight loss at 250 degrees C, while films deposited on the grounded electrode had similar to 1% weight loss at 250 degrees C. The thermal stability of films deposited on the grounded electrode was significantly enhanced when deposited at higher substrate temperatures. XPS analyses indicated a decrease in the F/C ratio of the deposited films with an increase in substrate temperature. TGA analyses indicated that weight loss below 250 degrees C was due primarily to the outgassing of low-molecular weight species from the fluorocarbon films. The higher weight loss region 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.