Development of soft-X-ray multilayer polarizing elements amd their application to soft-X-ray ellipsometry

本项目的目标是：1.通过将软X射线多层偏振元件的性能提高到实用水平，建立软X射线偏振测量和控制系统。与此平行的是，优化多层的材料对及其周期厚度以增加可用的波长区域。然后，使用高性能的偏振器，3.软X射线。椭偏测量法将作为一种新的高精度表面分析方法而发展起来。本研究历时两年，总结如下1.自支撑MO/Si多层膜由波长为13 nm的Lambda/4和Lambda/2板构成。在KEK2光子工厂使用反射式多层偏振器的旋转分析器椭偏测量仪对偏振性能进行了评估。多层膜是针对水窗口区域的波长而开发的，在那里反射率仍然保持在几个%的水平。根据光学准则，将Sc与Cr、Ni、Si、C和Al配对，制备了100对的多层膜，结果表明Sc/Cr是表现出最佳周期性的一对。在进一步提高溅射速率稳定性和衬底温度为70oC左右的条件下，250对Sc/Cr在3.1 nm波长下的反射率最高，达到15%。采用消光比为0.001的偏光片，用软X射线椭偏仪对40 nm厚的钼层样品进行了研究。这揭示了入射角响应中的类共振结构，通过边界粗糙的单层模型分析，预计厚度为0.001 1 nm，折射率为0.001，消光比为0.0001的灵敏度是极高的。

This project aims 1. establishments of polarization measurements and control in the soft X-ray by improving performances of soft X-ray multilayer polarizing elements to a practical level. In parallel to this, 2. material pairs of the multilayers and their period thicknesses are optimized to increase a wavelength region available. Then, with the high performance polarisers, 3. soft X-ray. ellipsometry will be developed as a new precision method of surface analysis. The two-year research is summarized in the following.1. Free standing MO/Si multilayers were developed as lambda/4 and lambda/2 plates at a wavelength of l3nm. The polarization performance was evaluated by rotating analyser ellipsometry with use of reflection multilayer polarizer at the photon factory, KEK.2. Multilayers were developed for the wavelengths of the water window region where the reflectances still remain at a level of a few %. Based on a optical criteria, Sc was paired with Cr, Ni, Si, C, and Al to fabricate multilayers of 100pairs, which revealed Sc/Cr as a pair showing the best periodicity. Further fabrication with improved stability of the sputtering rate and with optimized substrate temperature of around 70oC, Sc/Cr of 250 pairs showed the highest reflectance of 15% at a wavelength of 3.1nm.3. With polarisers of 0.001 extinction ratio, a sample of 40nm thick Mo layer was studied by soft X-ray ellipsometry. This revealed resonance like structures in the angle of incidence response where extremely high sensitivities of 0.0 1nm for the thickness, 0.001 for the refractive index, and 0.0001 for the extinction ratio were expected by analysis with a single layer model with rough boundaries.