The impact of TiN capping Layer on NiSi, CoSi/sub 2/, and Co/sub x/Ni/sub 1-x/Si/sub 2/ FUSI metal gate work function adjustment

The impact of TiN capping layer on dual work functions of Ni, Co, and Co-Ni fully silicided (FUSI) metal gates was investigated. It was found that the TiN capping layer significantly altered the distribution of both n- and p-dopants during the FUSI process, which in turn changed the work functions of both As-doped and B-doped in the three FUSI metal gate systems. The work function tuning was found to have a linear relationship with the change of dopant level at the silicides/dielectric interface after adding TiN capping layer. The investigation of TiN capping layer on FUSI provided some insights on work function tuning mechanism in FUSI systems. This work also suggested a new methodology for optimizing the nMOS and pMOS work functions for CMOS device applications.