Optical characterization of multi-NST nanowire test structures using Mueller matrix spectroscopic ellipsometry (MMSE) based scatterometry for sub 5nm nodes

With the rapid advancement of the CMOS technology in the semiconductor industry, innovative device fabrication techniques have led to the development of Nanosheet (NS) FETs and Nanowire (NW) FETs with sub nm dimensions. The application of Mueller Matrix Spectroscopic Ellipsometry (MMSE) based scatterometry simulations to characterize these complex 3D structures is described. Optical model-based simulations were used to investigate sensitivity and limitations of MMSE to characterize small changes in the etching of these NWTS structures. Cross-sectional Scanning Electron Microscopy and Tunneling Electron Microscopy provided a reference technique for the scatterometry simulations. Additionally, sensitivity to the nanowire test structure shape, size of holes, nanosheet thicknesses of each layer and the rounding at the top of the structure were investigated. As a result of this study, we find that Mueller Matrix scatterometry has the sensitivity to monitor dimensional changes during the progression of the selective SiGe etch for the sub surface nanowires and thus provide a reliable measurement method for process control.