Spectroscopic Study of the Interface Chemical and Electronic Properties of High-kappa Gate Stacks

Abstract

X-ray and ultraviolet photoemission spectroscopy has been combined with in-situ deposition to study the interface chemistry and electronic structure of potential high-κ gate stack materials. In addressing the interface stability of ZrO2 with respect to a Si substrate three issues are considered: 1) the development of the band offsets and electronic structure during the low temperature (T<300°C) growth processes, 2) variations in the band structure as effected by process conditions and annealing (T<700°C) and 3) the interface stability of Zr oxide films at high temperatures (T>700°C). To further explore low temperature effects, titanium, zirconium and hafnium oxides were deposited on ultra-thin (~0.5 nm) SiO2 buffer layers and metastable states have been identified which give rise to large changes in the band alignments with respect to the Si substrate. Also discussed is the band edge electronic structure of 1) nanocrystalline Zr, Hf and complex oxide high-κ dielectrics, and 2) non-crystalline Zr and Hf silicates and Si oxynitride alloys. Three issues are highlighted: Jahn-Teller term-splittings that remove band edge d-state degeneracies in nanocrystalline films, intrinsic bonding defects in ZrO2 and HfO2, and chemical phase separation and crystallinity in Zr and Hf silicate and Si oxynitride alloys. Finally, photoemission spectroscopy has been used to characterize a candidate gate stack including electron affinities and work functions, valence band maxima, band bending in the Si and fields in the oxide layers. The band offsets are constructed and the deviation from the Schottky-Mott (or electron affinity) model at each interface is discussed in terms of interface bonding and the resultant charge transfer.