Metal gate work function tuning by Al incorporation in TiN

Titanium nitride (TiN) films have been used as gate electrode on metal-oxide-semiconductor (MOS) devices. TiN effective work function (EWF) values have been often reported as suitable for pMOS. For nMOS devices, a gate electrode with sufficient low EWF value with a similar robustness as TiN is a challenge. Thus, in this work, aluminum (Al) is incorporated into the TiN layer to reduce the EWF values, which allows the use of this electrode in nMOS devices. Titanium aluminum (TiAl), Al, and aluminum nitride (AlN) layers were introduced between the high-k (HfO2) dielectric and TiN electrode as Al diffusion sources. Pt/TiN (with Al diffusion) and Pt/TiN/TiAl/TiN structures were obtained and TiN EWF values were reduced of 0.37 eV and 1.09 eV, respectively. The study of TiN/AlN/HfO2/SiO2/Si/Al structures demonstrated that AlN layer can be used as an alternative film for TiN EWF tuning. A decrease of 0.26 eV and 0.45 eV on TiN EWF values were extracted from AlN/TiN stack and AlN/TiN laminate stack, respectively. AlN/TiN laminate structures have been shown to be more effective to reduce the TiN work function than just increasing the AlN thickness.