Monitoring of Fermi level variations at metal/high-k interfaces with in situ x-ray photoelectron spectroscopy

A method to monitor Fermi level changes at the metal/high-k interface depending on the materials of choice and peculiarities of interface formation is presented. The method is based on the deposition of ultrathin (1-5 nm) continuous and very uniform layers of Si, metal (Ni) or/and a dopant (Sb and Ge) marker layer on high-k (HfO2) by pulsed laser deposition (PLD) and insitu x-ray photoelectron spectroscopy (XPS) measurements. Core level binding energy shifts following Fermi level (work function) change at metal/dielectric interface were monitored. The method was applied to investigate the work function (WF) change during the silicidation reaction between thin Ni overlayer on thin Si/HfO2/Si(100) as well as the effect of the dopants on fully-sillicided (FUSI) gate formation and work function modulation. It was found that the effective work function in contact with HfO2 was 4.4 eV, 4.5-4.7 eV, and 4.2 eV for NISI, Ni2Si, and Si+Sb, respectively, These values are in a good agreement with electrical measurements on MOS devices. Germanium interlayer at NiSi/HfO2 interface produces no effect on FUSi workfunction.