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As the dimensions of nanostructure rapidly shrink, the optical critical dimension (OCD) metrology, owing to its fast, non-destructive, and in-line-compatible features, has proved to be an effective tool to detect 3D periodic structure’s geometry at several nanometer-scale [1]. When the integrated circuit manufacturing enter the 3 nm technology node, Complementary FET (CFET) architectures, by utilizing shared gate for vertically stacked nanosheet n-FET and p-FET, have achieved notable reduction on average cell area, metal length and block-level area [2]. Because many metallic layers are not transparent to most optical wavelengths in CFET structures, and the gate oxide thickness and uniformity, the metal gate and inner spacer dimension uniformity are crucial during the process control [3], the sensitivity and precision of OCD metrology are very important and challenging. For instance, the inner spacers are formed by Atomic Layer Deposition (ALD) of spacer material on the recessed pockets of the SiGe superlattice formed by lateral over-etch during the source and drain etch process.The inner spacers insulate the metal gates and the source/drain terminals, which are decisive to the gate reliability and parasitic capacitance. Therefore, accurate control and measurement for inner spacers’ dimension uniformity is crucial to the manufacturing. In this paper, we will perform a study on the critical dimensions in CFET structures by using optical scatterometry simulation based on Rigorous Coupled Wave Analysis (RCWA). By tuning detection parameters, such as angle-of-incidence, illumination wavelength, polarization and scattering orders, we try to find an optimized parameter settings for measurement, and give recommendations for building OCD models of CFET structures.
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