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 V_fb instability observed in scaled PMOS devices based on the metal/high-k gate stacks.