Scanning coherent diffractive imaging methods for actinic EUV mask metrology
Scanning coherent diffractive imaging methods for actinic EUV mask metrology
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用于光化 EUV 掩模计量的扫描相干衍射成像方法
DOI：
10.1117/12.2219937
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Y. Ekinci
中科院分区：
文献类型：
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作者：
P. Helfenstein;I. Mohácsi;R. Rajendran;Y. Ekinci
为了在即将到来的技术节点中成功实施极紫外（EUV）光刻，需要克服的一个主要挑战是稳定可靠的掩模缺陷检测和表征。我们最近推出了反射模式 EUV 掩模扫描无透镜成像工具 (RESCAN)，该工具安装在瑞士光源的 XIL-II 光束线上，并显示 EUV 掩模上测试图案的重建航拍图像。 RESCAN 使用扫描相干衍射成像 (SCDI) 方法来获取 EUV 光掩模的光化航空图像，并设计用于 20 nm 晶圆分辨率。我们的 SCDI 算法通过使用通过有限照明扫描样本收集的超定衍射数据迭代解决相位问题来重建测量的样本。它可以提供高分辨率的 EUV 光掩模的相位和振幅航空图像，而无需使用高 NA（数值孔径）镜头。扫描显微镜和全视场显微镜的分辨率受光斑尺寸或透镜的数值孔径 (NA) 限制，与此相反，我们的方法可实现的分辨率取决于探测器噪声和探测器的数值孔径 (NA)。为了提高我们工具的分辨率，我们使用新的探测器和算法升级了 RESCAN。在这里，我们展示了使用晶圆分辨率高达 10 nm 的新工具获得的结果。我们相信，我们的原型的实现标志着克服依赖成像光学的方法所施加的限制迈出了重要一步，并为光化掩模计量提供了可行的解决方案。
For the successful implementation of extreme ultraviolet (EUV) lithography in the upcoming technology nodes, a major challenge to overcome is the stable and reliable detection and characterization of mask defects. We have recently presented a reflective mode EUV mask scanning lensless imaging tool (RESCAN) which is installed at the XIL-II beamline of the Swiss Light Source and showed reconstructed aerial images of test patterns on EUV masks. RESCAN uses scanning coherent diffractive imaging (SCDI) methods to obtain actinic aerial images of EUV photomasks and was designed for 20 nm on-wafer resolution. Our SCDI algorithm reconstructs the measured sample by iteratively solving the phase-problem using over-determined diffraction data gathered by scanning across the specimen with a finite illumination. It provides phase and amplitude aerial images of EUV photomasks with high resolution without the need to use high NA (numerical aperture) lenses. Contrary to scanning microscopy and full-field microscopy, where the resolution is limited by the spot size or NA of the lens, the achievable resolution with our method depends on the detector noise and NA of the detector. To increase the resolution of our tool, we upgraded RESCAN with a new detector and algorithms. Here we present the results obtained with the new tool that is capable of up to 10 nm on-wafer resolution. We believe that the realization of our prototype marks a significant step towards overcoming the limitations imposed by methods relying on imaging optics and shows a viable solution for actinic mask metrology.