We describe the fabrication of slotted, free-standing structures used as amplitude gratings in a separated-beam interferometer. Improvements in electron-beam writing techniques have allowed us to compensate for electron-beam system drift, making practical the exposure of 800xX00 mu m gratings with period as small as 0.14 mu m. Alignment marks are used for periodic drift compensation. Finite element analysis of fracture formation in silicon nitride films gives us a tool for the prediction of structural failure in arbitrarily shaped free-standing structures.