基于离焦扫描穆勒显微镜的纳米结构缺陷检测理论与方法研究

In order to achieve effective process control, fast, non-destructive, and precise nanoscale defect inspection is of great importance in high-volume nanomanufacturing. Conventional optical microscopy based defect inspection encounters severe challenges when dealing with deep subwavelength defects, such as the ultra-weak scattering intensity from the defects and the disturbance from a complicated noisy environment. In this project, we combine conventional optical microscopy with Mueller matrix ellipsometry, and meanwhile introduce the through-focus scanning technique, and propose to conduct the exploratory research on theory and method for the inspection of defects in nanostructures by through-focus scanning Mueller microscopy (TSMM). We will take full advantage of the rich information contained in the through-focus imaging Mueller matrices collected by TSMM, and emphasize on the fundamental theories and key issues in nanoscale defect inspection by TSMM, such as the optical modeling of the three-dimensional scattering field of nanostructures that contain defects, the extraction of characteristic parameters associated with the defects from the collected redundant data, and the identification and classification of the defects in nanostructures under a complicated noisy environment. It is expected that the exploratory research in this project will offer theoretical bases for the in-depth understanding of nanoscale defect inspection by TSMM, and will provide a fast, inexpensive, non-destructive, and precise inspection method for deep subwavelength defects emerged in the manufacturing processes of advanced technology nodes. The exploratory research in this project is also expected to expand the application of traditional optical inspection techniques in the field of nanomanufacturing.

为了实现有效的工艺监控，在批量化纳米制造中对纳米结构缺陷进行快速、非破坏性的精确检测具有非常重要的意义。传统光学显微成像技术在检测深亚波长结构缺陷时面临着诸如缺陷本身散射信号十分微弱与复杂噪声环境干扰等严峻挑战。为此，本项目将传统显微成像技术与穆勒矩阵椭偏仪相结合，并引入离焦扫描技术，提出开展基于离焦扫描穆勒显微镜的纳米结构缺陷检测理论与方法的探索性研究。将充分利用离焦扫描穆勒显微镜所测得的成像穆勒矩阵离焦分布图中包含的丰富测量信息，着重研究并解决含缺陷纳米结构三维散射场光学特性建模、冗余数据中纳米结构缺陷相关联特征参量提取、复杂噪声环境下纳米结构缺陷甄别等基础理论与关键问题，为深入认识和解释基于离焦扫描穆勒显微镜的纳米结构缺陷检测提供理论基础，为先进技术节点下纳米制造中的深亚波长纳米结构缺陷检测提供一种快速、低成本、非破坏性的精确检测新方法，扩展传统光学检测技术在纳米制造领域的应用。

对于集成电路的大批量制造产线，由于不可避免地存在工艺参数偏差或者环境中引入的污染，因此需对加工的微纳结构图形中可能存在的结构缺陷进行快速准确检测，以保证最终产品的性能和良率。常用的电子束检测和光学显微成像技术，受限于检测速度或者分辨率，难以满足制造产线中的深亚波长下的纳米结构缺陷检测要求。为此，本项目结合光学显微成像和穆勒矩阵椭偏仪各自的优势，并引入离焦扫描技术，提出并研制了一种离焦扫描穆勒显微镜的新型光学仪器，在此基础上开展了纳米结构缺陷检测理论与方法的探索性研究，并取得了以下重要研究成果：. (1) 建立了光与纳米结构作用的散射近场、远场成像的全矢量的理论计算模型。系统研究了不同测量条件和不同噪声水平下，纳米结构缺陷与穆勒矩阵图像之间的联系及灵敏度特性，揭示了基于离焦扫描穆勒显微镜的纳米结构缺陷检测机理；. (2) 提出了基于二阶差分和高斯卷积的穆勒矩阵图像处理算法，有效地去除了纳米结构穆勒矩阵图像中背景图形的散射信号的影响，并增强了缺陷信号的信噪比，进一步提升了缺陷检测的灵敏度和范围；. (3) 提出了基于主成分分析法和支持向量机，以及卷积神经网络的两种缺陷自动分类方法，利用带缺陷纳米结构的穆勒矩阵图像作为输入，实现了对其结构缺陷的特征提取以及缺陷类型的快速准确自动分类；. (4) 自主研制了一台离焦扫描穆勒显微镜原理样机，可以实现单次测量获得样品的穆勒矩阵图像，且测量时间约10s。利用研制的离焦扫描穆勒显微镜首次实现了带有不同类型典型缺陷的纳米结构样品的准确检测，展示了其在先进技术节点下纳米制造过程中的纳米结构缺陷检测应用中的潜力。. 项目所研制的离焦扫描穆勒显微镜具有测量信息全、速度快、灵敏度高等优势，有望为大批量集成电路制造过程中的深亚波长下的纳米结构缺陷检测提供一种快速、低成本、非破坏性的精确检测新方法。