High speed low power optical detection of sub-wavelength scatterer

Optical detection of scatterers on a flat substrate, generally done using dark field microscopy technique, is challenging since it requires high power illumination to obtain sufficient SNR (Signal to Noise Ratio) to be able to detect sub-wavelength particles. We developed a bright field technique, based on Fourier scatterometry, with special illumination and detection control to achieve this goal with a power level that can be sustained by most substrates including polymers. The performance of the system in a roll-to-roll line in production environment and strict throughput requirement is shown.