Impact of additional factors in threshold voltage variability of metal/high-k gate stacks and its reduction by controlling crystalline structure and grain size in the metal gates

We have clarified that, in a metal/high-k gate stack, as well as the variability introduced by random dopant fluctuations (RDF), the threshold voltage variability (TVV) is attributable to the crystal structure and grain size in the metal gate. We have successfully eliminated this additional factor by reducing the grain size in the metal gate. We demonstrated that the incorporation of C into TiN metal gates transforms the crystalline film into an amorphous one, effecting a reduction in the TVV in HfSiON pFET devices. We observed that the TVV of C-incorporated TiN devices was dominated by RDF, indicating that the additional factor due to the metal gate had been diminished.