19 March 2015 Simulation of AIMS measurements using rigorous mask 3D modeling
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Abstract
Aerial image measurement system (AIMSTM) has been widely used for wafer level inspection of mask defects. Reported inspection flows include die-to-die (D2D) and die-to-database (D2DB) methods. For patterns that do not repeat in another die, only the D2DB approach is applicable. The D2DB method requires accurate simulation of AIMS measurements for a mask pattern. An optical vectorial model is needed to depict the mask diffraction effect in this simulation. To accurately simulate the imaging results, a rigorous electro-magnetic field (EMF) model is essential to correctly take account of the EMF scattering induced by the mask topography, which is usually called the mask 3D effect.

In this study, the mask 3D model we use is rigorous coupled-wave analysis (RCWA), which calculates the diffraction fields from a single plane wave incidence. A hybrid Hopkins-Abbe method with RCWA is used to calculate the EMF diffraction at a desired accuracy level while keeping the computation time practical. We will compare the speed of the hybrid Hopkins-Abbe method to the rigorous Abbe method.

The matching between simulation and experiment is more challenging for AIMS than CD-SEM because its measurements provide full intensity information. Parameters in the mask 3D model such as film stack thickness or film optical properties, is optimized during the fitting process. We will report the fitting results of AIMS images for twodimensional structures with various pitches. By accurately simulating the AIMS measurements, it provides a necessary tool to perform the mask inspection using the D2DB approach and to accurately predict the mask defects.
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Chih-Shiang Chou, Hsu-Ting Huang, Fu-Sheng Chu, Yuan-Chih Chu, Wen-Chun Huang, Ru-Gun Liu, Tsai-Sheng Gau, "Simulation of AIMS measurements using rigorous mask 3D modeling", Proc. SPIE 9424, Metrology, Inspection, and Process Control for Microlithography XXIX, 94241A (19 March 2015); doi: 10.1117/12.2085113; https://doi.org/10.1117/12.2085113
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