Theory And Method Of Nanostructure Metrology Using Generalized Ellipsometry

Nanomanufacturing referes to the manufacturing of products with feature dimensions at the nanoscale. It is of great importance for the fast, inexpensive, nondestructive, precise and accurate measurement of the structural parameters of nanostructures, in order to support the nanomanufacturing process to be controllable, predictable, repeatable and scalable and guarantee the nanotechnology-based products to be reliable, repeatable, economical and large-scale manufacturing. Although both SEM and AFM tools can achieve nanoscale measurement, they are in general time-consumed, expensive, complex to be operated, and hard to realize on-line integrated measurement. In contrast, the optical scatterometry tools have drawn more and more attention in semiconductor manufacturing due to their attractive advantages, such as high throughput, low cost and non-destruction. Moreover, they are well suited for use in integrated metrology applications.The conventional ellipsometric scatterometry can only change two measurement conditions, i.e., the wavelength and incidence angle, and obtain only two measurement parameters, i.e., the amplitude ratio and phase shift, in each combination of above two measurement conditions. In contrast, the generalized ellipsometry (GE) can change one more measurement condition, i.e., the azimuthal angle, and obtain a4x4Mueller matrix in each combination of the three measurement conditions. Hence, more information about the sample under measurement can be obtained by GE. More sensitive measurement is also expected to be achieved by choosing appropriate ranges of the three measurement conditions and make full use of the measurement information contained in the Mueller matrices. Accordingly, theory and method of nanostructure metrology using GE are explored in the dissertation, of which the main contents and innovations include:The optical model of the nanostructure is established based on the rigorous coupled wave analysis (RCWA) with the depolarization effect taken into account in the meanwhile. The established optical’ model reveals the relation between the Mueller matrix and the structural parameters of the nanostructure, the material optical constants, the measurement conditions, as well as the parameters that induce depolarization effect.Two novel parameter extraction methods, termed the fitting error interpolation based library search and the correction based library search respectively, are proposed to figure out the issue that the measurement accuracy of conventional library search method is fundamentally limited by the grid interval of the pre-generated signature library. Experiments performed on a photoresist grating sample have demonstrated that the proposed two parameter extraction methods can achieve much more accurate measurement with negligible computational penalty to the conventional library search method in the parameter extraction.The error sources and categorization in the GE-based nanostructure metrology is investigated. A generalized first-order error propagating formula is derived to reveal the mechanism of error propagation in the GE-based nanostructure metrology. According to the first-order error propagating formula, detailed formulations for the estimation of random and systematic errors that are propagated into the final extracted parameters are further derived. Then, a novel measurement configuration optimization method based on the minimization of the norm of a model error propagating matrix is proposed to find an optimal combination of the incidence and azimuthal angles, with which more accurate measurement can be achieved.An experimental platform for the GE-based nanostructure measurement is developed. The sources and estimation of random and systematic errors in the measured Mueller matrices are investigated. The validity of the proposed theory and method associated with optical modeling, parameter extraction, error analysis and measurement configuration optimization have been fully demonstrated by using the developed experimental platform.The proposed theory and method in this dissertation will provide the theoretical foundations for the in-depth understanding of the mechanism of nanostructure measurement by GE. The GE-based nanostructure metrology will provide a novel means for fast, inexpensive, nondestructive, precise and accurate measurement of the nanostructures in high-volume nanomanufacturing. It is also expected to have a promising application prospects in the on-line process monitoring and control in high-volume nanomanufacturing.