COHERENCE AND STRUCTURAL DESIGN OF FREESTANDING GRATINGS FOR ATOM-WAVE OPTICS

Improvements in electron-beam writing techniques have allowed us to co mpensate for electron-beam system drift, making feasible tile exposure of 800 x 800 mu m gratings with period as small as 0.14 mu m. Placeme nt errors due to drift, calibration errors, and nonplanar substrates a re measured with verniers. Gratings patterned with interferometric pho tolithography provide an absolute reference for a measure of stage non linearity (runout.) Simulation of fracture formation in silicon nitrid e films has given us a tool for the prediction of structures that will fail during fabrication, and a way of evaluating stress relief patter ns in arbitrary structures. We have used two sets of simple patterns t o identify tile critical stress intensity factors in thin, free-standi ng films of nonstoichiometric silicon nitride.