Back-end-of-line compatible contact materials for carbon nanotube based interconnects

Abstract

Carbon nanotube (CNT) based interconnects with different metal–CNT contacts were prepared and characterized. All investigated contact materials are compatible with the back-end-of-line processing. For interconnect applications the length of the metal–CNT contact interface has to be extremely short, and has to have a low contact resistance. In order to provide a reliable interface between the metal and the CNTs the applied metal should form stable carbides. Indeed, Ta and Ti are beneficial in terms of contact resistance for the top metallization with Ta even outperforming Ti. However, those materials are non-noble metals and hence can oxidize. Besides the metals Ta and Ti, also their metal nitrides were investigated as bottom metallization. They outperform the pure metals since TaN and TiN are more resistant towards oxidation during subsequent processing steps. However, an extremely thin Ta layer also proves beneficial since in this case the formation of a conductive TaC during the CNT growth process is feasible. Unfortunately, insufficiently controlled oxidation processes occur which impairs the reproducibility and hence causes the average via to have a higher resistance.