Impact of Thermally Induced Structural Changes on the Electrical Properties of TiN/HfLaSiO Gate Stacks

概要

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Thermally induced structural changes in TiN/Hf(La)SiO gate stacks were investigated by back-side X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS). A distinct correlation between bottom oxide growth and an increase in equivalent oxide thickness (EOT) was confirmed under high-temperature annealing at over 850 °C regardless of La content. Back-side XPS also revealed that oxygen and nitrogen diffusion occurs, forming partially oxidized TiON layers at a metal/high-k interface under moderate annealing temperatures of approximately 600 °C, and that annealing at over 750 °C leads to the reduction of the oxide phase and produces a thinner inter-layer with a clear Ti--N bond feature. Moreover, with an increase in annealing temperature, a change in the local atomic configuration in the HfLaSiO dielectric layer was identified from oxygen K-edge spectra. This structural change induced by thermal reaction can be considered as a possible cause of the V_{\text{th}} instability of La-incorporated high-k gate stacks. On the basis of these findings on structural changes, the physical origins of the effective work function modulation of the gate stacks are discussed in detail.
2011-10-25