Measurements of metal gate effective work function by x-ray photoelectron spectroscopy

We developed a method to measure effective work function of metal gate in contact with high-k dielectric. The method was based on the deposition of ultrathin (1-5 nm) continuous and very uniform layers of metal on high-k gate stack (HfO2) by pulsed laser deposition and in situ measurements by x-ray photoelectron spectroscopy. This approach was applied to investigate the evolution of work function during silicidation reaction between Ni overlayer and thin Si/HfO2/Si(100). The effect of dopants on fully silicided gate formation and work function modulation was also explored. The effective work function of NiSi, Ni2Si, and Sb-doped Si gate electrodes on HfO2 dielectric was found to be 4.4, 4.5-4.7, and 4.2 eV, respectively. Ge interlayer at the NiSi/HfO2 interface showed no significant effect. These values were in a good agreement with C-V measurements performed ex situ on metal-oxide-semiconductor capacitors. (c) 2007 American Institute of Physics.