The high-kappa stack consisting of an optional nitride interfacial layer and a HfO2 layer was studied. The result shows that nitride or oxynitride interfacial layers can be controllably formed down to a few angstroms. The growth of both interfacial layers is self-limited. The introduction of nitric oxide with hafnium t-butoxide during the high-kappa deposition leads to smaller effective oxide thickness (EOT) and gate leakage current. EOTs below 1.0 nm have been achieved with this combination of sources. The beneficial effect of nitric oxide can be explained in terms of reduced interfacial EOT, reduction of carbon contamination, and possibly a small trace amount of nitrogen incorporation. (c) 2006 American Vacuum Society.