Influence of Capping Layer on Threshold Voltage for HKMG FinFET With Short Channel

The influence of SiO
₂
and SiN
_x
capping layer on threshold voltage (
${V}_{t}$
) for FinFET with TiAl-based metal gate (MG) is studied. After metal gate-stack formation, SiN
_x
capping is revealed to be able to serve as a new N source, resulting in the diffusion of N into the effective work function (EWF) TiN
_x
layer. Correspondingly, the accumulation of N in the TiN
_x
layer is demonstrated to be able to lower the EWF for both n- and p-FinFETs. Compared to SiO
₂
capping, SiN
_x
capping can induce
$\sim 100$
–150 mV
${V}_{t}$
lowering for short n- and p-FinFETs. No obvious
${V}_{t}$
shift is found for long-channel devices.