X-ray photoemission and X-ray absorption studies of Hf-silicate dielectric layers

Photoelectron spectroscopy and X-ray absorption spectroscopy (XAS) measurements have been performed on HfSixOy and HfSixOyNz dielectric layers, which are potential candidates as high-k transistor gate dielectrics. The hafnium silicate layers, 3-4 nm thick, were formed by codepositing HfO2 and SiO2 (50%:50%) by MOCVD at 485 °C on a silicon substrate following an IMEC clean. Annealing the HfSixOy layer in a nitrogen atmosphere at 1000 °C resulted in an increase in the Si4+ chemical shift from 3.5 to 3.9 eV with respect to the Si0 peak. Annealing the hafnium silicate layer in a NH3 atmosphere at 800 °C resulted in the incorporation of 10% nitrogen and the decrease in the chemical shift between the Si4+ and the Si0 to 3.3 eV. The results suggest that the inclusion of nitrogen in the silicate layer restricts the tendency of the HfO2 and the SiO2 to segregate into separate phases during the annealing step. Synchrotron radiation valence band photoemission studies determined that the valence band offsets were of the order of 3 eV. X-ray absorption measurements show that the band gap of these layers is 4.6 eV and that the magnitude of the conduction band offset is as little as 0.5 eV.