A 193 nm Optical CD metrology tool for the 32 nm node

摘要

A novel optical critical dimension (CD) metrology tool equipped with a 193 nm laser source and a high numerical aperture objective (NA=0.9) is under development at the Physikalisch-Technische Bundesanstalt (PTB), the National Metrology Institute of Germany. The CD tool is designed for characterization of photomasks up to 6-inch and offers "at-wavelength" measurements for current and future 193 nm lithography. Design, construction and realisation of the CD metrology tool is presented in this paper. The illumination system, which employs a multi-mode DUV fiber to reduce the lateral coherence of the laser beam, is detailed with numerical simulation and experimental investigation. Combined with precision optical modelling, this optical CD tool will be applicable for quantitative determination of the microstructures on 32 nm node photomasks with uncertainty less than 10 nm.