IMEC outlines nickel-silicide metal-gate CMOSLONDON Belgian research organization IMEC has presented on a scheme to use fully-silicided (FUSI) nickel-silicide metal gates with high-k dielectric CMOS transistors at the International Electron Devices Meeting.
IMEC (Leuven, Belgium) claims that its scheme has the advantage of simplicity with different forms of FUSI nickel-silicide used for both p- and n-type transistors. IMEC has used a NiSi gate for the NMOS transistor and a Ni2Si gate for the PMOS transistor on the hafnium-based HfSiON dielectric with a simultaneous two-step silicidation.
The potential of the approach has been demonstrated with a ring oscillator circuit, IMEC said. Alternative FUSI approaches such as adding ytterbium and nickel to Ni FUSI allowed further tuning of the work function to lower the threshold voltage, thus enabling dual gate CMOS technologies based on FUSI for the 45-nanometer manufacturing process node.
Doping, which has always been successful to set the work functions in conventional CMOS, appears to be ineffective for nickel FUSI gates and hafnium-based dielectrics. IMEC claimed that it has shown that the several phases of nickel silicide can be used to modulate the threshold voltage.
Since silicides inherently have narrow line width effects, controlling the effective ratio of Ni to Si thickness across all line widths is the key to successfully introducing this process in manufacturing. IMEC claims to have achieved this as a two-step FUSI process.
“We are pleased that over the last two years we’ve made considerable progress within our core program on one of the major bottlenecks in scaling CMOS beyond 45-nm,” said Luc Van den hove, vice president of silicon process and device technology at IMEC, in a statement. “Some concerns are still remaining such as thermal stability, reliability and process control but the results show that FUSI is a leading candidate for successful integration of hafnium-based dielectrics with metal gate electrodes for sub-45-nm,” he added.