The Characterization of the Residual Film Formed By Plasma Etching of Polysiloxane Spin-on-Glass on Aluminum

The etching of polysiloxane spin-on-glass (SOG) layers on aluminum by a fluorine-based plasma has been studied by Auger electron spectroscopy. The etching of such film by CF₄, CHF₃, and C₂F₆ is characterized by a residual film formation which is significantly thicker than the residues found after etching, under identical conditions, of a chemically vapor deposited (CVD) silicon dioxide on aluminum. A study of the residual layer composition is presented for various film structures, processing, and etching conditions for three types of reactive ion etching (RIE) systems operating at high, medium, and low pressures. The results indicate the presence of fluorocarbon polymer-like residual films, typical for each one of the systems. The thicker residual layer was found for SOG films on aluminum etched at high pressure. The film structure, as found by Auger electron spectroscopy, is of fluorocarbon material on an aluminum oxide. The formation of such residual layer can be reduced by decreasing the gas pressure in the system and increasing the bias between the sample and the plasma during etching. For the films etched in the very low pressure range, about 2–3 mt, the residual film is thin, 0.5–1.0 nm, and is not much different from those found for CVD oxide. The results are also compared to the residues found after etching similar films on silicon.