Influence of the oxygen concentration of atomic-layer-deposited HfO2 gate dielectric films on the electron mobility of polycrystalline-Si gate transistors

Abstract

The influence of the ozone concentration (150–370g∕m3) during the atomic layer deposition of HfO2 gate dielectrics on the dielectric performance of the films and the device performance of metal-oxide-semiconductor field effect transistor (MOSFET) grown on Si was studied. The use of a lower ozone concentration (150g∕m3) produced a HfO2 film with a stoichiometric oxygen concentration, whereas a higher ozone concentration (390g∕m3) produced an oxygen excess HfO2 film. An almost identical Dit to that of the SiO2 gate dielectric film was obtained from the stoichiometric HfO2, whereas the oxygen excess HfO2 gate dielectric produced a much higher Dit with the polycrystalline-Si electrode. The investigation of the interface states using x-ray photoelectron spectroscopy revealed that the excessive oxygen incorporated during the film growth made the interfacial reaction and oxidation serious. This increased the interface trap density and degraded the interface properties. Accordingly, an electron effective mobility of ∼65% of the MOSFET with SiO2 as a gate dielectric was obtained from the stoichiometric HfO2 gate dielectric film. The effective mobility from the MOSFET with the oxygen excess HfO2 film was only ∼45%. The 35% loss of the effective mobility for the stoichiometric HfO2 MOSFET appeared to be due to factors such as carrier scattering by fixed charges and long range optical phonons.