Measurement of Gate-Oxide Film Thicknesses by X-ray Photoelectron Spectroscopy

摘要

X-Ray Photoelectron Spectroscopy (XPS) is being used to an increasing extent for the characterization of new gate-oxide materials, particularly for the determination of film composition, uniformity, and thickness. A key parameter for film-thickness measurements by XPS is the effective attenuation length (EAL) for a particular material, photoelectron energy, and measurement configuration. Due to the effects of elastic scattering on signal-electron trajectories, the EAL generally differs from the corresponding electron inelastic mean free path (IMFP) and is a function of film thickness and electron emission angle. We present calculations of EALs for four proposed gate-oxide materials: zirconium dioxide, hafnium dioxide, zirconium silicate, and hafnium silicate. These EALs were obtained from the NIST Electron Effective-Attenuation-Length Database that uses an analytical expression derived from solution of the Boltzmann equation within the transport approximation. The EALs were computed for the relevant photoelectron lines excited by Al characteristic x rays and for a range of film thicknesses and emission angles of practical relevance. The EALs were compared with the corresponding IMFPs to determine the magnitudes of the correction for elastic-scattering effects in each gate-oxide material. For common measurement conditions, this correction varied between 12 % and 20 %.