Material and electrical properties of HfxRuy and HfxRuyNz metals as gate electrodes for p-metal oxide semiconductor field effect transistor devices

Abstract

Material and electrical characterizations of sputter-deposited HfxRuy and HfxRuyNz gate electrodes atop atomic layer deposited HfO2 were performed with a focus on optimizing their compositions for suitable applications in p-metal oxide semiconductor field effect transistors (pMOSFETs), since Fermi level pinning is a more severe issue for higher work function metals. The alloys of HfxRuy with effective work functions (EWFs) ranging from 4.4 to 5.0 eV were achieved when the Ru metal ratio was varied from 53% to 74%. Nitrided hafnium ruthenium alloys, HfxRuyNz (0%–25% N), with EWFs of 4.9–5.2 eV were also synthesized. Among these materials, Hf0.26Ru0.74 and Hf0.05Ru0.77N0.18 were determined to have EWFs adequate for pMOSFET devices of 5.0 and 5.2 eV, respectively. The slightly higher than expected EWFs of these metal gates are attributed to the presence of oxygen. The depth profiling of the as-deposited gate stacks showed reasonably sharp interfaces between the gate electrode and the gate dielectric with the HfxRuy alloy exhibiting better interfacial properties. Upon annealing, the HfxRuy alloys were found to be more stable than the HfxRuyNz alloys on HfO2.