Evaluating the Registration of Mirror-Image Photoresist Stencils

Abstract

In photoetching of metal foils, control of hole shape and size can be improved by exposing photoresist on both sides behind registered mirror-image masks. The improvement so obtained is sensitive to the accuracy of registration of the two masks. By using a photoresist producing a stencil which remains undistorted, even when severely undercut, registration can easily be checked. With a calibrated eyepiece micrometer scale, the apparent shift was noted when the microscope was successively focused on the lOp and bottom stencils. The construction of a special multi-image test pattern for checking both x and y displacement, control checks of the method, and observations on two pairs of masks are described. The method seemed to be simple and effective.