Compositionally graded hafnium silicate studied by chemically selective scanning tunneling microscopy

Taking a tradeoff between channel carrier mobility and overall k value into account, compositionally graded ultrathin (1-2 nm) hafnium silicate has been investigated and suggested as an interfacial layer for an alternative high-permittivity (high-k) gate dielectric. Attempts to confirm whether a compositional gradation could occur in such a thin thickness range were performed by thermal annealing of 1-ML-thick Hf deposited on 1-nm-thick SiO2 in an ultrahigh vacuum chamber. Compositionally graded features varying from topmost HfOx-like to SiO2-like at the interface with Si could be analyzed with subnanometer resolution by scanning tunneling microscopy utilizing a local variation in the position of the conduction-band minimum within the insulator band gap as an identifier. (C) 2002 American Institute of Physics.