Dimensional measurement sensitivity analysis for a MoSi photomask using DUV reflection scatterfield imaging microscopy

A critical challenge in optical critical dimension metrology, that requires high measurement sensitivity as well as high throughput, is the dimensional measurements of features sized below the optical resolution limit. This paper investigates the relationships among dimensional sensitivity and key illumination beam conditions (e.g., angular illumination, partial coherence) for photomask feature characterization. Scatterfield images at the edge areas of multiple line structures on a Molybdenum Silicide (MoSi) photomask are analyzed to establish sensitivity to dimensional changes. Actinic scatterfield imaging experiments for these features are performed using the NIST 193 nm Scatterfield Microscope, designed to enable engineered illumination beams at the target. Illumination configurations that improve sensitivity are identified from imaging edges of multiple line targets having linewidths and spaces of about 1/3 wavelength.