Bilayer metal gate electrodes with tunable work function: Adhesion and interface characterization

摘要

The dependence of Pt film thickness and forming gas annealing on the interface fracture properties and interface composition of Ti/Pt bilayer gate electrode films on a HfO2 gate dielectric are reported. These fracture properties and composition results are directly compared to work function tuning behavior witnessed in metal-oxide semiconductor (MOS) capacitors fabricated from the same films. The interface fracture energy of the metal bilayer/gate dielectric interface is strongly dependent on thickness after a forming gas anneal but shows no thickness dependence in the as-deposited case. The flat-band voltage increases abruptly and then remains constant as the thickness of the Pt film is increased in the as-deposited case but varies gradually with increasing Pt thickness after a forming gas anneal. Angle-resolved x-ray photoelectron spectroscopy characterization of the resulting fracture surfaces confirms that Ti diffusion to the metal bilayer/gate dielectric interface is responsible for these effects.