Reactive ion etching mechanism of plasma enhanced chemically vapor deposited aluminum oxide film in CF4/O2 plasma

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Abstract
Aluminum oxide film prepared by plasma enhanced chemical vapor deposition (PECVD) is one of the promising candidates for an etch mask or an etch barrier material in very large scale integrated fabrication. We have investigated the reactive ion etching mechanism of the PECVD aluminum oxide films in the CF4/O2 plasma. The dependences of the aluminum oxide etch rate on the atomic fluorine concentration and the incident particle bombardment energy are studied at various etching conditions. The etch products and their depth distribution are also determined by analyzing the surface layer of the etched aluminum oxide films with Auger electron spectroscopy. The CF4/O2 plasma fluorinates the aluminum oxide surface layer through the particle bombardment activated reaction, producing etch products in the form of AlF3 or AlOXFY, which is nonvolatile but has a higher sputtering yield than aluminum oxide. The reactive ion etching of aluminum oxide proceeds by the formation and the sputter removal of the etch product. The etch rate strongly depends on the particle bombardment energy because it determines not only the formation rate but also the removal rate of the etch products. However, the atomic fluorine concentration has little effect on the etch rate because the consumption rate of fluorine radicals is so low that they are always superfluous under any experimental conditions.