基于散射场层析广义椭偏仪的三维纳米结构测量理论与方法

A novel optical instrument named generalized ellipsometer with scatterfield tomography (GEST) is proposed. Based on the conventional ellipsometry and by introducing a high numerical-aperture microscopic lens with its back focal plane rapidly scanned by an illumination beam, GEST can obtain the scatterfield distrubtution of a sample at multiple illumination incidence angles, with each scatterfield point represented by a 4×4 Mueller matrix. Therefore, GEST can provide much more useful information about the sample. Accordingly, in this project, we propose to utilize GEST to realize a fast, low-cost, nondestructive, and accurate measurement of complex three-dimensional nanostructure profiles. We will focus on the investigations including the scatterfield modeling of nanostructures and the GEST-based measurement mechanism, the profile reconstruction and the uncertainty estimation, the key techniques and prototype development of the instrument, and the experiment on nanostructure profile measurements. We will emphasize on the fundamental theories and key techniques in the optical scatterfield modeling of nanostructures, the robust profile reconstruction, and the system calibration and error compensation in instrumentation, and develop a GEST prototype instrument. It is expected that the exploratory research in this project will expand the application of conventional optical metrology in nanomanufacturing, and provide a novel principle and a new means for the in-line measurement in high-volume nanomanufacturing.

提出研制一种称为散射场层析广义椭偏仪的新型光学仪器，以传统椭偏仪为基础，引入高数值孔径显微物镜并实现照明光束在物镜后焦面的快速扫描层析，获取多入射角下样品的完整散射场分布，且每一处分布都包含一个4×4阶的Mueller矩阵，从而可以获得极为丰富的测量信息。本项目以此为出发点，提出利用散射场层析广义椭偏仪，实现复杂三维纳米结构形貌的快速、低成本、非破坏、精确测量。提出开展纳米结构光学散射场建模与测量机理、三维形貌重构与测量不确定度评估、仪器实现关键技术与原理样机研制、以及纳米结构三维形貌测量应用实验等研究工作。着重解决纳米结构光学散射场快速准确建模求解、三维形貌快速鲁棒重构、仪器系统标定与误差补偿等基础理论和技术难题，研制一套具有自主知识产权的散射场层析广义椭偏仪原理样机，以促进传统光学测量技术在纳米制造领域中的扩展应用，为批量化纳米制造中的在线测量提供新原理、新途径和新工具。

光学散射仪作为集成电路(IC)制造工艺线上的一种重要测量设备，具有非破坏性、测量速度快等优点。传统光学散射仪在测量时仅使用了简单周期性结构的单一散射场（即零级衍射光）信息，因此只能获得周期性结构在测量光斑内的少量统计参数，如平均意义下的光栅结构关键尺寸、高度、侧壁角等，从而很大程度上限制了其在复杂三维纳米结构测量中的应用。.鉴于此，本项目提出并研制了一种散射场层析广义椭偏仪，该新仪器将传统广义椭偏仪与衍射光学层析技术相结合，借由入射光斑在高数值孔径物镜后焦面扫描，可以获得待测纳米结构多光谱、多入射角、多方位角的测量信息，进而准确重构出待测纳米结构的三维形貌参数。在光学散射逆问题求解过程中，为了减少系统正向建模的复杂度并提高计算效率，提出了一种减基-边界元方法，相较于传统的边界元方法可以将计算效率提高数倍甚至数十倍。通过建立偏振光与纳米结构相互作用的散射近场、远场成像的完整矢量模型，探索了不同类型样品在不同测量配置及噪声水平下的测量灵敏度。在此基础上开展实验研究，实现了纳米压印工艺中硅基光栅模板、光刻工艺中光刻胶光栅、闪存刻蚀工艺中高深比深沟槽等典型纳米结构的准确测量，阐明了散射场层析广义椭偏仪在三维纳米结构形貌测量应用中的潜力，有望推动我国纳米测试计量技术的完善和发展，并促进传统光学测量技术在纳米材料与纳米制造领域中的扩展应用。