Influence of contamination layer on thickness evaluation by X-ray reflectometry

In this study, the effect of allowing for a contamination layer on a SiO₂ film/Si substrate system on thickness determination by X-ray reflectometry (XRR) was investigated. The calculated XRR profiles obtained using a calculation model that utilizes a contamination layer for analysis showed good agreement with measured profiles. Further, the obtained physical structures were promising and within acceptable limits. Where the existence of a contamination layer was ignored in the calculation process, a part of the thickness of the contamination layer was incorporated into the determined thickness of the SiO₂ layer. In that case, the evaluated thickness was proportional to the density ratio between the contaminated and SiO₂ layers. The results of investigation of the effect of X-ray energy on layer thickness determination indicated that the effects of contamination also depend on the X-ray energy used for XRR measurements. These effects increase in the case of experiments that employ X-ray energy with a high contrast for the contamination.