Traceable thickness measurement of ultra-thin HfO₂ films by medium-energy ion scattering spectroscopy

The thicknesses of a series of ultra-thin HfO2 films were precisely determined by mutual calibration by x-ray photoelectron spectroscopy (XPS) and x-ray reflectometry (XRR) in the recent Consultative Committee for Amount of Substance (CCQM) pilot study P-190. From these well-defined reference film thicknesses, the measurement capability of medium-energy ion scattering spectroscopy (MEIS) for the thickness of HfO2 films was investigated. The film thicknesses determined by MEIS showed a small difference, within 2%, from the reference thicknesses and an offset value of 0.017 nm. The MEIS thicknesses can also be determined by mutual calibration between the transmission electron microscopy (TEM) thicknesses and the MEIS intensity ratios in the region of the substrate and HfO2 film. From linear fitting with the reference thicknesses, the MEIS thicknesses determined by mutual calibration showed a slope value of 1.011 and an offset value of 0.015 nm. As a result, MEIS can be a traceable method to determine the absolute thickness of ultra-thin HfO2 films, and a zero-offset method for application of the mutual calibration method.