Electrical, structural, and chemical properties of HfO2 films formed by electron beam evaporation

Abstract

High dielectric constant hafnium oxide films were formed by electron beam (e-beam) evaporation on HF last terminated silicon (100) wafers. We report on the influence of low energy argon plasma (∼70 eV) and oxygen flow rate on the electrical, chemical, and structural properties of metal-insulator-silicon structures incorporating these e-beam deposited HfO2 films. The use of the film-densifying low energy argon plasma during the deposition results in an increase in the equivalent oxide thickness (EOT) values. We employ high resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and medium energy ion scattering experiments to investigate and understand the mechanisms leading to the EOT increase. We demonstrate very good agreement between the interfacial silicon oxide thicknesses derived independently from XPS and HRTEM measurements. We find that the e-beam evaporation technique enabled us to control the SiOx interfacial layer thickness down to ∼6 Å. Very low leakage current density (< 10-4 A/ cm2) is measured at flatband voltage +1 V into accumulation for an estimated EOT of 10.9±0.1 Å. Based on a combined HRTEM and capacitance-voltage (CV) analysis, employing a quantum-mechanical CV fitting procedure, we determine the dielectric constant (k) of HfO2 films, and associated interfacial SiOx layers, formed under various processing conditions. The k values are found to be 21.2 for HfO2 and 6.3 for the thinnest (∼6 Å) SiOx interfacial layer. The cross-wafer variations in the physical and electrical properties of the HfO2 films are presented. © 2008 American Institute of Physics.