Electrical properties and temperature-humidity studies of fluorocarbon films deposited from pentafluoroethane/argon plasmas

Fluorocarbon films were deposited from pentafluoroethane/argon plasmas in a parallel plate reactor at operating pressures of 0.75 and 1 Torr, substrat e temperatures of 120, 180, and 240 degreesC, and applied powers between 10 and 30 W. These films were subjected to an 85 degreesC and 85% relative hu midity environment for 100 h to assess reliability. Infrared spectroscopy s howed no change in the bulk structure and composition of the deposited film s after temperature-humidity exposure. Also, no OH related peaks were detec ted in the infrared spectrum, suggesting negligible moisture absorption. In deed, moisture absorption studies showed less than 0.15 wt % increase for t he investigated deposition conditions, as measured by a quartz crystal micr obalance. Furthermore, humidity cycling studies indicated no chemisorption of water by the deposited films. Capacitance measurements of the fluorocarb on films yielded a dielectric constant ranging between 2.23 and 2.55 and a loss tangent on the order of 10(-2). The dielectric constant increased with an increase in deposition temperature and a decrease in operating pressure . The dielectric constant of the fluorocarbon films did not change after ex posure to the 85 degreesC/85% relative humidity environment, further confir ming the IR and moisture absorption results. However, X-ray photoelectron s pectroscopy (XPS) of the fluorocarbon films indicated a decrease in the F/C ratio and an increase in the O/C ratio after temperature-humidity exposure , which suggests that defluorination and oxidation occur primarily in the t op few monolayers of the deposited films. C 1s spectral analysis indicated a decrease in the relative concentrations of CF3,CF2, CF, and C-CFx moietie s and a dramatic increase in the C-C/C-H concentrations. These changes were attributed to the formation of a thin layer of low molecular weight oxidiz ed material, which could be dissolved by rinsing the film in an ethanol ult rasonic bath. (C) 2001 The Electrochemical Society.