Plasma reactor dry cleaning strategy after TaC, MoN, WSi, W, and WN etching processes

Abstract

Reproducibility of plasma etching processes is a critical issue for metal/high-k gate stack patterning because of progressive modification of the reactor wall conditions. Periodic dry cleaning of the etching chamber in appropriate plasma chemistry allows the achievement of acceptable reproducibility. The authors have used quasi in situ x-ray photoelectron spectroscopy to analyze the coatings formed on the walls of an industrial inductively coupled plasma reactor during the etching of TaC, MoN, WSi, W, and WN materials in various chemistries. Metallic residues containing Ta, Mo, or W are generally detected after the etching process, and the main factors responsible for their deposition are identified. They have then investigated the best plasma chemistry to clean each of these deposits. It is concluded that fluorine-based cleaning (eventually preceded by a chlorine cleaning step if Hf-based high-k dielectric is introduced in the stack) is efficient to remove the coatings formed on the reactor walls after metal gate stack etching. However, AlFx (YFx) residues are formed on the Al2O3 (Y2O3) reactor walls. Alternatively, the authors show that an efficient reactor cleaning strategy providing good wafer-to-wafer reproducibility (without AlFx or YFx residues) is a two-step SF6∕Cl2 process followed by SiCl4∕Cl2 plasma, whatever the materials in the high-k metal gate stack (poly-Si, TiN, TaC, TaN, MoN, W, WN, WSi, and HfO2).