装置計測
Research on Improvement of X-ray Reflectivity Method for High-Precision Surface-Interface Structure Analysis
2021 年 52 巻 p. 81-111
詳細
2021 年 52 巻 p. 81-111
X-ray scattering spectroscopy is a powerful tool for investigations on rough surface and interface structures of multilayered thin film materials 1-33), and X-ray reflectometry is used for such investigations of various materials in many fields. In many previous studies in X-ray reflectometry, the X-ray reflectivity was calculated based on the Parratt formalism 1), coupled with the use of the theory of Nevot and Croce to include roughness 2). However, the calculated results of the X-ray reflectivity done in this way often showed strange results where the amplitude of the oscillation due to the interference effects would increase for a rougher surface.
Because the X-ray scattering vector in a specular reflectivity measurement is normal to the surface, it provides the density profile solely in the direction perpendicular to surface. On the other hand, diffuse scattering can provide information about the lateral extent of the roughness. In contrast to previous calculations of the X-ray reflectivity, in the present analysis we consider the effect of a decrease in the intensity of penetrated X-rays due to diffuse scattering at a rough surface and rough interface. We show that the strange result has its origin in the limitation of the currently used equation in the value of the reflection coefficient because of a lack of consideration of diffuse scattering.
The analyzed results of XRR showed that the effective roughness measured by XRR might depend on the angle of incidence. Then we introduced the effective roughness with depending on the incidence angle of X-ray. The new improved XRR formalism derived more accurate surface and interface roughness with depending on the size of coherent X-rays probing area, and derived the roughness correlation function and the lateral correlation length. In this review, an improved XRR formalism, considering the diffuse scattering and the effective roughness, is presented. The calculated reflectivity obtained by the use of this accurate reflectivity equation gives a physically reasonable result, and should enable the structure of buried interfaces to be analyzed more accurately.
