Investigation of etching optimization in capacitively coupled SF6–O2 plasma

Abstract

The selective etching process is widely used for achieving the desired etch rate in semiconductor fabrication. Parameters such as input power, operating pressure, gas mixture, chamber geometry, and amplitude of the radio-frequency voltage govern the etch rate and etch quality in plasma. In this work, we experimentally investigated the optimum plasma etching conditions required to achieve an anisotropic etch profile and analyzed how the optimum etching can be carried out using an appropriate operating pressure and oxygen concentration. Optical emission spectroscopy was used to measure the concentrations of oxygen and fluorine, and Langmuir probe was used to measure the electron density in the plasma. The oxygen concentration was varied from zero to 100 vol. % for pressures in the range of 20–600 mTorr. The optimum etch conditions are used to study the ion energy distribution given by Kawamura et al., Plasma Sources Sci. Technol. 8, R45 (1999). The results suggest that in addition to O2% and pressure, the DC bias is another crucial parameter for achieving the optimum etch conditions.