Issues on thickness measurements of nm HfO₂ film by X-ray photoelectron spectroscopy

Abstract

In the mutual calibration for determination of ultrathin oxide film thickness, the thickness measured by X-ray photoelectron spectroscopy (XPS) has been known to be representative offset traceable. The offset traceability of XPS has been proved in the Consultative Committee for Amount of Substance (CCQM) pilot study P-190. For the analysis of nm HfO₂ film thickness by XPS, a general equation is used involving the relative peak intensity (R_o) of pure HfO₂ film and the substrate. The difference in the surface polarity of HfO₂ film and substrate induces different amount of surface carbon contamination, which leads to the error in R_o value. In the plot of XPS and reference thickness of HfO₂ films, the correction for the carbon contamination results in the offset value of -0.014 nm, while a larger offset value of -0.219 nm was measured without the carbon correction. Furthermore, different from the thickness measurement of SiO₂ film, the reference geometry configuration is not important factor for the thickness measurement of ultrathin amorphous HfO₂ films.