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2 April 2020 AFM characterization for Gate-All-Around (GAA) devices
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As development of stacked Nanosheet Gate All-Around (GAA) transistor continues as the candidate technology for future nodes, several key process points remain difficult to characterize effectively. With the GAA device strategy, it is critical to have an inline solution that can provide a readout of physical dimensions that have an impact on the threshold voltage (VT) and yield. Metrology challenges for obtaining these metrics arise from increasingly dense arrays coupled with both high aspect ratios, high numbers of correlated parameters, and increasingly complex 3D geometries. Large area metrology structures can be used for 3D parameters’ process monitoring through techniques such as scatterometry and xray diffraction (XRD) which deliver averaged results over that area, but variation impacting specific devices cannot currently be understood without destructive cross-section. Prior work to characterize the dimensions of these GAA devices has primarily featured optical metrology, X-ray metrology, and critical-dimension scanning electron microscopy (CDSEM), but these techniques have their own challenges at the critical process points. Atomic force microscopy (AFM) had not been utilized due to the aspect ratios and small trench widths which were inaccessible to conventional techniques. However, due to recent advances in scanning and novel probe technologies, AFM is well-suited now to solve these local, three-dimensional challenges. Through this study, we demonstrate AFM characterization of a key process point in the GAA process flow for multiple structures with varying channel lengths, after epitaxial (epi) growth along the Si sidewall. The AFM scan results are compared to CDSEM images for top-down corroboration of topography and to other reference metrology for height correlation. The impact of measured variations in epi height to device performance is also reviewed.
Conference Presentation
© (2020) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Mary Breton, Jennifer Fullam, Dexin Kong, Daniel Schmidt, Andrew Greene, Julien Frougier, Sean Hand, Jason Osborne, Weijie Wang, and David Fey "AFM characterization for Gate-All-Around (GAA) devices", Proc. SPIE 11325, Metrology, Inspection, and Process Control for Microlithography XXXIV, 1132514 (2 April 2020);

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