Thickness Measurement of Ultra-thin TiO₂ Films by Mutual Calibration Method

Mutual calibration with length-unit traceable and zero-offset methods has been recently suggested as a reliable method to determine the absolute thickness of the ultra-thin oxide films. In this study, the thickness of the TiO2 film on Si (100) substrate was determined using the mutual calibration method. A series of ultra-thin TiO2 films were fabricated via atomic layer deposition. The thicknesses of the TiO2 films were measured by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and medium energy ion scattering spectroscopy (MEIS). The absolute thickness was determined by mutual calibration using a combination of high-resolution (HR)-TEM and MEIS. The thickness was also measured by mutual calibration employing a combination of HR-TEM and XPS to compare the two zero-offset methods (XPS and MEIS). A large offset difference of 0.45 nm was observed between the two data. This was related to the difference in the escape depth of the photoelectrons from the film and substrate in XPS analysis due to the surface contamination layer.