Effective Work Function Modulation by Aluminum Ion Implantation on Hf-Based High- $k$/Metal Gate pMOSFET

The impact of aluminum (Al) implantation into TiN/HfO
₂
/ SiO
₂
on the effective work function is investigated. Al implanted through poly-Si cannot attain sufficient flatband voltage (V
_FB
) shift unless at higher implantation energy. Al implanted through TiN at 1.2 keV with a dose of 5 × 10
¹⁵
cm
^-2
raised the V
_FB
to about 250 mV compared with a nonimplanted gate stack. Moreover, the V
_FB
shift can be up to about 800 mV at 2 keV with the same dose level accompanied with slightly equivalent oxide thickness penalty and gate leakage current degradation. Optimized process window to control Al diffusion depth was essential to minimize these impacts.