REACTIVE ION ETCH PROCESSES FOR AMORPHOUS-SILICON THIN-FILM TRANSISTORS - A SICL4 BASED CHEMISTRY

Plasma etching has emerged as a most critical process in preparing thin film transistors (TFT). Previously, various etching issues about the a-Si:H thin-film transistor have been studied with chlorofluorocarbon feed gases. Here, the authors have examined some of these issues with SiCl4 which is a nonchlorofluorocarbon gas. Results on reactive ion etching (RIE) of common thin-film transistor materials such as a-Si:H, SiN(x), and tantalum are discussed. Two mechanisms, i.e., etching and deposition, exist simultaneously in the process. The latter interferes with the former and lowers the net etch rate. SiCl4 etch processes are compared with CF2Cl2 processes. SiCl4 is a good chlorofluorocarbon-free gas in preparing thin-film transistors. TFT transfer characteristics with the n+ layer being etched with the SiCl4/CF4 RIE process also are discussed.