Zepler Institute(1), University of Southampton, Southampton SO17 1BJ, UK; Experimental Physics of EUV, JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany.
Zepler Institute(1), University of Southampton, Southampton SO17 1BJ, UK.
Ultramicroscopy. 2023 Jul;249:113720. doi: 10.1016/j.ultramic.2023.113720. Epub 2023 Mar 21.
Ptychography is a lensless imaging technique that is aberration-free and capable of imaging both the amplitude and the phase of radiation reflected or transmitted from an object using iterative algorithms. Working with extreme ultraviolet (EUV) light, ptychography can provide better resolution than conventional optical microscopy and deeper penetration than scanning electron microscope. As a compact lab-scale EUV light sources, high harmonic generation meets the high coherence requirement of ptychography and gives more flexibilities in both budget and experimental time compared to synchrotrons. The ability to measure phase makes reflection-mode ptychography a good choice for characterising both the surface topography and the internal structural changes in EUV multilayer mirrors. This paper describes the use of reflection-mode ptychography with a lab-scale high harmonic generation based EUV light source to perform quantitative measurement of the amplitude and phase reflection from EUV multilayer mirrors with engineered substrate defects. Using EUV light at 29.6nm from a tabletop high harmonic generation light source, a lateral resolution down to ∼88nm and a phase resolution of 0.08rad (equivalent to topographic height variation of 0.27nm) are achieved. The effect of surface distortion and roughness on EUV reflectivity is compared to topographic properties of the mirror defects measured using both atomic force microscopy and scanning transmission electron microscopy. Modelling of reflection properties from multilayer mirrors is used to predict the potential of a combination of on-resonance, actinic ptychographic imaging at 13.5nm and atomic force microscopy for characterising the changes in multilayered structures.
相移成像技术是一种无像差的成像技术，能够使用迭代算法对物体反射或透射的辐射的振幅和相位进行成像。在极紫外（EUV）光下工作时，相移成像技术可以提供比传统光学显微镜更高的分辨率，比扫描电子显微镜更深的穿透能力。作为紧凑型实验室级 EUV 光源，高次谐波产生满足相移成像的高相干性要求，与同步加速器相比，在预算和实验时间方面具有更大的灵活性。测量相位的能力使得反射模式相移成像成为一种很好的选择，可以对 EUV 多层镜的表面形貌和内部结构变化进行定量测量。本文描述了使用基于实验室级高次谐波产生的 EUV 光源的反射模式相移成像，对具有工程化衬底缺陷的 EUV 多层镜的振幅和相位反射进行定量测量。使用来自桌面高次谐波产生光源的 29.6nm 的 EUV 光，实现了低至 ∼88nm 的横向分辨率和 0.08rad 的相位分辨率（相当于 0.27nm 的形貌高度变化）。比较了表面变形和粗糙度对 EUV 反射率的影响，以及使用原子力显微镜和扫描透射电子显微镜测量的镜面缺陷的形貌特性。使用多层镜的反射特性建模来预测结合共振、光致相移成像（在 13.5nm 下）和原子力显微镜的潜力，以对多层结构的变化进行特性分析。
