Effective Work-Function Modulation by Aluminum-Ion Implantation for Metal-Gate Technology $(\hbox{Poly-Si/TiN/SiO}_{2})$

The impact of aluminum (Al) implantation into TiN/SiO
₂
on the effective work function (EWF) of poly-Si/ TiN/SiO
₂
is investigated. Al implanted at 5 keV with a dose of 5 times 10
¹⁵
cm
^-2
reduces the flatband voltage (V
_FB
) and the EWF of poly-Si/TiN/SiO
₂
stack by ~150 mV compared with the unimplanted poly-Si/TiN/SiO
₂
stack. This reduction of V
_FB
is found to be dose-dependent, which is correlated to the Al concentration at the TiN-SiO
₂
interface as evidenced by secondary-ion-mass-spectrometry profiles. The interface dipole created due to the Al presence at the metal-dielectric interface is believed to contribute to the observed V
_FB
(or EWF) reduction (or increase). This technique for EWF modulation is promising for further threshold-voltage (V
_t
) tuning without any process complexities and is quite significant for planar and multiple gate field-effect transistors on fully depleted silicon on insulator.