Yashiro Wataru, Ikeda Susumu, Wada Yasuo, Totsu Kentaro, Suzuki Yoshio, Takeuchi Akihisa
Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi, 980-8577, Japan.
WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi, 980-8577, Japan.
Sci Rep. 2019 Oct 1;9(1):14120. doi: 10.1038/s41598-019-50486-5.
X-ray reflectometry (XRR), a surface-sensitive technique widely used for characterizing surfaces, buried interfaces, thin films, and multilayers, enables determination of the electron density distribution perpendicular to a well-defined surface specularly reflecting X-rays. However, the electron density distribution parallel to the surface cannot be determined from an X-ray reflectivity curve. The electron density correlation in the lateral direction is usually probed by measuring the grazing-incidence small-angle X-ray scattering (GISAXS). GISAXS measurement, however, typically requires using a collimated X-ray point beam to distinguish the GISAXS from the specularly reflected X-rays, and so the sample must be scanned in the lateral direction with the point beam to investigate variations in the surface and interface morphology for a region larger than the size of the beam. In this paper, we report a new approach based on X-ray grating interferometry: an X-ray sheet beam is used instead of an X-ray point beam. A method using this approach can simultaneously provide one-dimensional real-space images of X-ray reflectivity, surface curvature, and 'dark-field' contrast with a field-of-view of more than a few millimetres. As a demonstration, a sample having a 400 nm line and space SiO pattern with a depth of 10 nm on its surface was used, and the dark-field contrast due to the unresolved line and space structure, creating GISAXS in the lateral direction, was successfully observed. Quantitative analysis of these contrasts provided the real-space distribution of the structural parameters for a simple model of the grating structure. Our study paves the way to a new approach to structure analysis, providing a quantitative way to investigate real-space variations in surface and interface morphology through wavefront analysis.
X射线反射测量法（XRR）是一种广泛用于表征表面、埋藏界面、薄膜和多层膜的表面敏感技术，它能够确定垂直于镜面反射X射线的明确表面的电子密度分布。然而，无法从X射线反射率曲线确定平行于表面的电子密度分布。横向的电子密度相关性通常通过测量掠入射小角X射线散射（GISAXS）来探测。然而，GISAXS测量通常需要使用准直的X射线点光束来区分GISAXS和镜面反射的X射线，因此必须用点光束在横向扫描样品，以研究比光束尺寸更大区域的表面和界面形态变化。在本文中，我们报告了一种基于X射线光栅干涉测量的新方法：使用X射线片状光束代替X射线点光束。使用这种方法的一种技术可以同时提供X射线反射率、表面曲率和“暗场”对比度的一维实空间图像，视场超过几毫米。作为演示，使用了一个表面具有400 nm线间距的SiO图案且深度为10 nm的样品，成功观察到了由于未分辨的线间距结构在横向产生GISAXS而导致的暗场对比度。对这些对比度的定量分析为光栅结构的简单模型提供了结构参数的实空间分布。我们的研究为结构分析开辟了一条新途径，通过波前分析提供了一种定量方法来研究表面和界面形态的实空间变化。
