Plasma-Wall Interactions in Dual Frequency Narrow-Gap Reactive Ion Etching System

The effects of plasma-wall interactions on the plasma chemistry in a dual frequency narrow-gap reactive ion etching (RIE) system is investigated as a function of electron density, residence time, and partial pressure of additive O2 gas. It is found that there is a critical point in the residence time, where the dissociation dominant region and the wall-interaction dominant region are separated. The net flux of chemically reactive species is estimated. The net flux of carbon-inclusive ions is of the order of 1016 cm-2s-1, and is larger than that of CF x radicals. Carbon-inclusive and silicon-inclusive ions dominate the total flux of chemically reactive species. The deposition rate of the fluorocarbon film is strongly dependent on the O2 partial pressure, and is controlled by the chemical etching with oxygen as well as the reduction of fluorocarbon radical density in the gas phase. Based on the estimation of the net flux of chemically reactive species and the effect of added oxygen, dominant chemical species that control the etching reaction in the RIE system are discussed.