Forming gas anneal induced flat-band voltage shift of metal-oxide-semiconductor stacks and its link with hydrogen incorporation in metal gates

Detailed studies were performed on the forming gas anneal (FGA, 10% H2 in N2) induced flat-band voltage (Vfb) shift of Ru and Mo gated Metal-Oxide-Semiconductor (MOS) stacks. The dependence of the Vfb shift on the FGA temperature was studied on Ru gated stacks. For the first time, the FGA-induced Vfb decrease was also observed on Mo and MoOx gated stacks. The FGA-induced decrease in Vfb was found to be unstable as a low temperature N2 anneal could significantly restore the Vfb. Incorporation of hydrogen in the interfacial RuOx or MoOx layers is believed to be the main cause for the Vfb decrease, at least for relatively low FGA temperatures.