Abstract

Abstract We have examined the determining factor of the effective work function (EWF) for an n-channel MOSFET (n-type EWF) in TiAlC/TiN metal gates on high-k gate dielectrics (HK). From electrical and physical evaluations of the bottom TiN between HK and TiAlC (BTM-TiN), the obtained results suggest that the dominant factor for the n-type EWF of TiAlC/TiN metal gates is not the fixed charge in the gate dielectric but the vacuum work function of BTM-TiN. It was found that TiN with low oxygen content has a vacuum work function of 3.8 eV, suitable for an n-channel MOSFET although TiN has been believed to be suitable for a p-channel MOSFET. We also found that its vacuum work function increases with increasing oxygen content. Based on these results, we proposed an oxygen scavenging from BTM-TiN(O) by Al in TiAlC as a novel mechanism for the n-type EWF for TiAlC/TiN metal gates.