Photoemission Study of Metal/HfSiON Gate Stack

Chemical bonding features in metal (TiN or Ru)/HfSiON gate stacks and electrical potential changes due to dipoles at the metal/dielectric interfaces have been studied by back-side x-ray photoemission measurements of the samples after wet-chemical removal of Si substrate. The photoemission threshold of the metal gate measured through the ultrathin dielectric layer confirms that the potential change of the gate metals, which is nearly equivalent to the difference in the flat-band voltage shift between capacitors with SiO2 and HfSiON, is caused by electron transfer from the HfSiON layer to the metal gate near the interface. From the recovery in the gate potential induced by oxygen incorporation into HfSiON, oxygen vacancies in the HfSiON layer are likely to be possible origin of the gate potential change. Also, from the experimental fact that the gate potential change becomes significant with decreasing thickness of the interfacial SiO2 layer below 3.5nm in Ru/HfSiON/SiO2 gate stacks, it is suggested that the generation of oxygen vacancies in HfSiON caused by oxidation reaction of Si substrate through ultrathin SiO2 layer plays an important role on the electron transfer near the Ru/HfSiON interface.