Modeling and simulation of feature-size-dependent etching of metal stacks

Aspect ratio dependent etching (ARDE) has often been observed in various et ching processes. During etching of metal films in a high density plasma rea ctor, this phenomenon is more prominent. With a high amount of ARDE present , the narrow spaces will not be cleared unless there is enough overetch, wh ich removes an excessive amount of the underlying layers. The main focus of this article is on the understanding of the mechanisms behind metal ARDE. The results from an extensive design of experiments on the subject were uti lized for this study. SPEEDIE, the Stanford etching and deposition profile simulator, was used to develop and test appropriate models. The Langmuir ad sorption model with added surface recombination of the adsorbed species, bo th etchants and inhibitors, was used to model the phenomenon. The added sur face recombination acts as the major species loss mechanism on the feature sidewalls. The simulation results indicate that a process with inhibitors, which are highly adhesive to the metal surface and which do not like to rec ombine with the etchants to form volatile products, will lead to a low degr ee of ARDE. This is in agreement with experimental results which showed tha t the addition of CHF3 to the Al etch process helps to reduce the ARDE in n arrow space regions. (C) 2001 American Vacuum Society.