Reactive ion etching processes for amorphous germanium alloys

This paper presents results on reactive ion etching (RIE) processes of amorphous germanium (a-Ge), germanium silicon alloys (a-GeSix) and germanium oxide (GeOx). Their process characteristics are compared with those of the amorphous silicon (a-Si) and silicon nitride (SiNx). Various combinations of feeding gases, i.e., from CF4, CF2Cl2, CH3F, and O2, over a pressure range of 100 to 300 mTorr and a power range of 500 to 1500 W were used in this study. The following conclusions are drawn from the results: 1) the a-Ge and a-GeSix etch mechanisms are similar to that of a-Si, but the former have higher etch rates than the latter; 2) a-Ge-Six etch rate falls between those of a-Ge and a-Si; 3) the GeOx etch mechanism is similar to that of SiNx; 4) although plasma phase chemistry, ion bombardment energy, and surface reactions are all important to the etch process, the film component selectivity is greatly dependent on the feeding gas; 5) to obtain a high etch selectivity between a-GeSix and PECVD SiNx a chlorine-containing gas has to be used; 6) RIE plasma damage to a-Si TFT is decreased when it is covered with an a-GeSix layer.