Abstract
The reactive etching mechanism of Nb and Nb205in CF4/O2RF plasma has been studied in a flexible diode reactor, with special emphasis on a thin film heating effect. Etch rates of both materials during reactive ion etching are determined by a combination of the ion bombardment enhanced etching mechanism and the chemical etching mechanism. In niobium, the chemical etching always dominates over the ion enhanced etching. Etch rates in the plasma etching mode are primarily due to the chemical etching mechanism. The activation energy in the chemical etching is estimated to be 0.22 and 0.11 eV for Nb and Nb2O5respectively. The Nb chemical reactivity (etch rate divided by a number density of the fluorine atoms) shows a substantial increase proportional to RF power and, surprisingly, to Nb film thickness. The thicker the film, the higher the etching rate observed during plasma etching. We argue that this is due to a temperature rise in a Nb film caused by the eddy current generated by the RF magnetic field (i.e., the RF inductive heating). An efficient thermal contact between a substrate and the substrate electrode is essential to achieve good etching uniformity and reproducibility, especially in etching metal films like niobium. Reactive plasma etching of both Nb and Nb2O5is contributed by chemical etching as well as ion-bombardment-enhanced etching, as in the case of silicon etching. The chemical etching mechanism predominates in plasma etching, but both chemical etching and ion-enhanced etching mechanisms are present in reactive ion etching. Competition between these two etching mechanisms determines the sidewall etch profile. The chemical reactivity of Nb exhibits a substantial increase proportional to RF power. This is attributed to the RF inductive heating due to the eddy current, which should be only effective in a highly conducting material such as metals, silicides, and heavily doped degenerate semiconductors. The RF inductive heating in Nb is so significant that Nb etching rates during plasma etching varies with a film thickness. The thicker the Nb film, the higher film temperature results from the inductive heating, leading to a higher etch rate. © 1984, The Electrochemical Society, Inc. All rights reserved.