A method of forming a semiconductor structure includes annealing a surface of a substrate in an ambient of hydrogen to smooth the surface, pre-cleaning the surface of the substrate, depositing a high-κ dielectric layer on the pre-cleaned surface of the substrate, performing a re-oxidation process to thermally oxidize the surface of the substrate; performing a plasma nitridation process to insert nitrogen atoms in the deposited high-κ dielectric layer, and performing a post-nitridation anneal process to passivate chemical bonds in the plasma nitridated high-κ dielectric layer.