A sophisticated chemical mechanical polishing (CMP) technology with in-line optical-thickness verification was developed for shallow-trench isolation formation in gate-all-around field-effect transistors with a multilayered Si/SiGe superlattice. The CMP tools were equipped with in-line optical critical dimension (OCD) measurement and a torque current monitor of the CMP turn-table motor for endpoint detection (EPD). In this study, model-based OCD fitting was applied to estimate the thicknesses of complex multilayered films: a SiN stopper on a thin SiO₂ buffer layer over a Si/SiGe/Si/SiGe/Si/SiGe superlattice epitaxially grown on a Si substrate. Immediately after the CMP with the electrical EPD and the in-line OCD measurement, the over-polished thickness of the SiN stopper was within 3 nm on the fin-patterned Si/SiGe superlattice despite the change in the SiO₂–CMP rate during continuous wafer processing. This nondestructive CMP control method improves the efficiency and quality of the CMP process in GAAFET fabrication.

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