Nonconventional applications of Mueller matrix-based scatterometry for advanced technology nodes

The semiconductor industry continues to drive patterning solutions that enable devices with higher memory storage capacity, faster computing performance, and lower cost per transistor. These developments in the field of semiconductor manufacturing along with the overall minimization of the size of transistors require continuous development of metrology tools used for characterization of these complex three-dimensional device architectures. Optical scatterometry or optical critical dimension (OCD) is one of the most prevalent inline metrology techniques in semiconductor manufacturing because it is a quick, precise, and nondestructive metrology technique. However, at present OCD is predominantly used to measure the feature dimensions such as line-width, height, side-wall angle, etc. of the patterned nanostructures. Use of optical scatterometry for characterizing patterning process errors such as pitch-walking, overlay, etc. is fairly limited. Characterization of process-induced errors is a fundamental part of process yield improvement. It provides process engineers with important information about process errors, and consequently helps optimize materials and process parameters. Scatterometry is an averaging technique and extending it to measure the position of local process-induced errors and feature-to-feature variation is extremely challenging. This report is an overview of applications and benefits of using optical scatterometry for characterizing defects such as pitch-walking, overlay, and fin bending for advanced technology nodes beyond 7 nm. Currently, the optical scatterometry is based on conventional spectroscopic ellipsometry and spectroscopic reflectometry measurements, but generalized ellipsometry or Mueller matrix (MM) spectroscopic ellipsometry data provide important, additional information about complex structures that exhibit anisotropy and depolarization effects. In addition, the symmetry-antisymmetry properties associated with MM elements provide an excellent means of measuring asymmetry present in the structure. The useful additional information as well as symmetry-antisymmetry properties of MM elements is used to characterize fin bending, overlay defects, and design improvements in the OCD test structures are used to boost OCDs' sensitivity to pitch-walking. In addition, the validity of the OCD-based results is established by comparing the results to the top down critical dimension-scanning electron microscope and cross-sectional transmission electron microscope images.