Uncertainty of Film Structures Evaluated by X-Ray Reflectivity

X-ray reflectivity (XRR) is a powerful technique for evaluating nanometer scale film structures. In principle, it is rested on interference of X-rays reflected on surface and interface of the film stacks. If we have a proper structural model for film stacks, calculation of XRR pattern is a physically well-defined procedure based on the Fresnel formula that only needs well known physical constants, wavelength of X-ray and refractive indices of film materials for X-ray. Therefore, XRR is capable of providing standard nano-film thickness ensuring SI unit traceability. We discuss roots of errors for the evaluated film structures, for example, miss-alignment of sample positions andso on. We also present several trials to diminish uncertainties of measured film structures.