Evaluation of NbN thin films grown by MOCVD and plasma-enhanced ALD for gate electrode application in high-k/SiO2 gate stacks

NbN was deposited by plasma-enhanced ALD (atomic layer deposition) as well as MOCVD (metal organic chemical vapour deposition) as gate electrode for MOS capacitors with SiO2 and HfO2 as dielectric. Finally, different contact materials were deposited on the NbN electrodes and the gate stacks were annealed. Dependent on the applied dielectric and the composition of the contact materials, variation in work function, increase in EOT, and even oxide degradation occurs after thermal treatment. This can be related to chemical reactions due to interdiffusion between the NbN gate electrode, the contact material and the gate dielectric. Employing PEALD (plasma-enhanced atomic layer deposition) for NbN electrode deposition on HfO2 and poly-Si as contact material, however, degradation can be significantly reduced and the work function remains stable at 4.8 eV. This makes NbN deposited by PEALD an attractive gate electrode material for future low power consuming PMOS-transistors.