Oxygen Transfer from Metal Gate to High-k Gate Dielectric Stack: Interface Structure & Property Changes

Photoelectron spectroscopy and transmission electron microscopy provide clear experimental evidence to show that oxygen initially present in the W gate layer of a metal/high-k gate stack is transferred to the substrate and increases the interfacial oxide during post-deposition thermal processing. Oxide interface layer growth was reduced, but still occurred, if a TaN barrier layer was used to cap the W gate metal, thus minimizing atmospheric oxygen incorporation. Our results suggest that oxygen is incorporated into the W layer (perhaps at grain boundaries and interfaces) during or immediately after its deposition, thus providing a source for subsequent oxidation of the underlying layers. This effect, which may be exhibited by other high workfunction metals besides W, may be an important contributor to the Vfb instability observed in scaled PMOS devices based on the metal/high-k gate stacks