Bilayer systems of tantalum or zirconium nitrides and molybdenum for optimized diamond deposition

Abstract

Thermo chemical computing validates the stability of different nitrides against Co, Mo, and methane up to 1150 K, showing the highest chemical stability against carburization for ZrN and TaN under static conditions. Single zirconium and tantalum nitrides layers have been sputtered onto WC–Co substrates as diffusion barriers and buffer layers under specific reactive sputtering conditions. To improve the nuclei density of diamond during CVD processing, a thin Mo extra layer has been added (< 500 nm). In this study, two bilayer systems have been tested: TaN–Mo and ZrN–Mo. Nano crystalline diamond has been grown under negative biased substrates. After diamond deposition, a massive carburization of molybdenum and tantalum nitride is observable whereas zirconium nitride is not. Nevertheless, a small amount of cobalt has migrated through the ZrN layer. The better efficiency of the ZrN layer to prevent diffusion of the Co element, leads to expect an increased adhesion of diamond on ZrN–Mo bilayer coating. A TEM study is done to improve understanding of phenomena occurring at the interfaces during process.