Control of a metal-electrode work function by solid-state diffusion of nitrogen

Abstract

\u3cp\u3eThe work function of a metal gate electrode has been adjusted with the introduction of nitrogen by solid-source diffusion from an over-stoichiometric TiN\u3csub\u3e1+x\u3c/sub\u3e layer. RBS measurements have shown that measurable concentrations of nitrogen can be diffused into a 10nm Ta layer at moderate anneal temperatures (>500°C), and that this concentration increases with temperature in the range 500-1000°C. Capacitance-voltage measurements have been carried out on 1Onm tantalum layers on Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e. These measurements have indicated that the work function of tantalum changes by -0.08eV due to the presence of the over-stoichiometric TiN\u3csub\u3e1+x\u3c/sub\u3e covering layer during anneal (800°C/30 inch). Similar C-V measurements have been carried out on 10nm molybdenum layers on SiO\u3csub\u3e2\u3c/sub\u3e and on Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e dielectrics. These have shown that the work function of molybdenum is substantially different for metal stacks with the TiN\u3csub\u3e1+x\u3c/sub\u3e covering layer after a similar anneal. The work function changes by -0.52eV for molybdenum on SiO\u3csub\u3e2\u3c/sub\u3e and by 1.1eV for molybdenum on Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e. The results suggest great potential for molybdenum as a candidate for a single-metal dual-work function approach to integrating metal gates into future CMOS technologies.\u3c/p\u3