Plasma reactor dry cleaning strategy after TiN, TaN and HfO2 etching processes

The authors have investigated the etch chamber recovery after TiN, TaN, and HfO2 metal gate etching processes. The deposits formed on the reactor walls after etching these materials in various chemistries have been analyzed by x-ray photoelectron spectroscopy. They found that after a complete polysilicon/metal/high-k gate stack patterning process, the reactor walls are typically covered by a composite layer such as SiOClx-MO-HfBClx (where M is the metal). The SiOClx layer is deposited on the reactor walls during silicon etching (HBr/Cl-2/O-2 plasma); it is subsequently covered by a halogen-rich metal oxide layer during the metal etch step and, finally, by a BClx polymer containing traces of Hf deposited during HfO2 etching (in a BCl3 plasma). They have then investigated the best plasma chemistry to clean the reactor walls after these processes. In particular, they have analyzed the efficiency of several plasma cleaning chemistries to remove each metal from the reactor walls. This allowed them to conclude that after a metal gate etching process, a two step cleaning strategy is required in most cases to remove the deposit from the reactor walls. A Cl-2 plasma is first used to remove the HfBClx layer and the Ta coatings (in the case of TaN etching), and it is followed by a SF6/O-2 plasma that is able to remove Ti and SiOClx deposits from the reactor walls. This two step cleaning strategy will always restore clean chamber conditions before processing the next wafer, thus ensuring a good wafer-to-wafer reproducibility. (c) 2008 American Vacuum Society.