Abstract: Apparatus is provided for guiding a pellicle-covered photomask or other flat object into viewing position for inspection upon a flat top plate of a stage below the objective of a microscope. The apparatus includes a pair of spaced parallel rails having inwardly extending upper and lower flanges that define opposed keyways in which keybars at the edges of a photomask-carrying paddle slide. To protect the pellicle membrane and to space the latter above the top stage top plate, at entrance ends of the rails, segments of the upper flanges are recessed greater than the width of the paddle to permit a vertical dropping movement of the leading end of paddle onto inlet horizontal guide surfaces. These guide surfaces are broad platforms on which may be deposited the leading end of the paddle.

Abstract: 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.