Optical 3-D nanostructure metrology utilizes a model-based metrology approach to determine critical dimensions (CDs) that are well below the inspection wavelength. Our project at the National Institute of Standards and Technology is evaluating how to attain key CD and shape parameters from engineered in-die capable metrology targets. More specifically, the CDs are determined by varying the input parameters for a physical model until the simulations agree with the actual measurements within acceptable error bounds. As in most applications, establishing a reasonable balance between model accuracy and time efficiency is a complicated task. A well-established simplification is to model the intrinsically finite 3-D nanostructures as either periodic or infinite in one direction, reducing the computationally expensive 3-D simulations to usually less complex 2-D problems. Systematic errors caused by this simplified model directly influence the fitting of the model to the measurement data and are expected to become more apparent with decreasing lengths of the structures. In this paper we investigate these effects, and will report experimental set-ups, e.g., the used illumination numerical apertures and focal ranges, that can increase the validity of the 2-D approach.
Mark-Alexander Henn, Bryan M. Barnes, and Hui Zhou, "Evaluating the effects of modeling errors for isolated finite 3D targets," Proc. SPIE 10145, Metrology, Inspection, and Process Control for Microlithography XXXI, 101451E (Presented at SPIE Advanced Lithography: March 02, 2017; Published: 30 March 2017); https://doi.org/10.1117/12.2262544.
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