Microscopic detection of membrane surface defects through interference patterns

摘要

Transparent membranes are examined with a microscope having coaxial brightfield illumination fitted with a narrow bandwidth filter to convert polychromatic light from a source to substantially monochromatic light. Light reflecting off of the surfaces of the membrane recombine to create an interference pattern, including observable fringes in the region of membrane surface aberrations. Membranes which may be examined include pellicles used to cover photomasks and photo-resist layers. If a photo-resist layer is examined, a filter is selected to provide essentially monochromatic light at a wavelength to which the resist is insensitive.