The capacitive coupled plasma (CCP) has been extensively used in the semiconductor industry because it has not only good uniformity, but also low electron temperature. But CCP source has some problems, such as difficulty in varying the ion bombardment energy separately, low plasma density, and high processing pressure, etc. In this reason, dual frequency CCP has been investigated with a separate substrate biasing to control the plasma parameters and to obtain high etch rate with high etch selectivity. Especially, in this study, we studied on the etching of SiO₂ by using the dual-frequency CCP source composed of high (27.12, 60, etc.) MHz/ low (2.0, etc.) MHz rf powers to control the ion flux and ion energy impacting on the substrate independently. By using the combination of high /low rf powers, the differences in the gas dissociation, plasma density, and etch characteristics were investigated.

For SiO₂ etching, fluorocarbon gases are commonly used, because a polymer film which decreases the etch rate is deposited on the silicon surface and enhances the etch selectivity to SiO₂ etching. Therefore, in addition to the frequency variation for SiO₂ etching, the plasma characteristics such as gas dissociation characteristics, plasma density, electron energy distribution, etc. were investigated by varying chemical composition of fluorocarbon gases. With the measurement of plasma characteristics, SiO₂ etching characteristics were also investigated and correlated with the variation of plasma characteristics. The etch rate was decreased with increase in C/F ratio in order of CF₄, C₂F₆, and C₄F₈ plasma, which forms a thicker fluorocarbon polymer on the SiO₂ surface. We observed the increase of CF₂ radicals in the higher C/F ratio plasma by using optical emission spectroscopy (OES). And the etch rates were increased with the low frequency (2 MHz) power for all fluorocarbon plasmas. When the low frequency power was increased, a steady-state fluorocarbon polymer thickness on the SiO₂ surface was reduced by the ion energy during the process, resulting in the increase of the etch rate. The X-ray photoelectron spectroscopic analysis on the surfaces etched by different low frequency powered conditions correlate with the results above.