Langmuir Probe Measurements in Inductively Coupled CF 4 ­ Ar Plasmas

Abstract

Technological advancement in the microelectronics industry requires an understanding of the physical and chemical processes occurring in plasmas of fluorocarbon gases used as etchants to optimize various operating parameters. This paper reports data on electron number density and temperature, electron energy distribution function (EEDF), and plasma potential measured using Langmuir probe in inductively coupled plasmas of mixtures of various compositions. The probe data were recorded at several radial positions providing radial profiles of these plasma parameters at 10-50 mTorr and 200 and 300 W of radio frequency (rf) power. The measurements indicate that the electron and ion number densities increase with power; the plasma potential and electron temperature decrease with an increase in pressure, and they depend weakly on rf power. The radial profiles show that the electron and ion number densities and the plasma potential peak at the center of the plasma and drop toward the wall. Within the experimental error, the electron temperature is nearly constant in the electrode region and decreases toward the wall. As the content increases in the mixture, the electron temperature increases but the electron density decreases. At low concentration, the electron and ion densities increase with pressure, but the densities are nearly independent of pressures at high concentrations. The EEDFs have a characteristic drop near the low energy end at all pressures and powers and their shapes represent a non-Maxwellian plasma. © 2002 The Electrochemical Society. All rights reserved.