Traditional x-ray lithography mask radiation damage studies have concentrated on the pattern placement errors produced by stress changes within the mask membrane. The usual approach is to measure the location of fiducial marks on the mask membrane to measure the distortions for pre-and postirradiation. The measured distortions are not directly related to changes in individual mechanical properties of the membrane material. To isolate the individual mechanical parameters this study has utilized a silicon nitride membrane structure in the form of a bridge with lithographically patterned strain gauges to allow independent measurement of changes in the elastic modulus and Poisson’s ratio as a function of incident dose. It was found that the modulus of elasticity decreased by 37% for an incident dose of 114 kJ/cm(2) while the Poisson ratio for the material remained unchanged within the accuracy of the experiment. The results of these measurements have been incorporated into a finite element model to numerically determine the resulting distortions and compare them with published experimental results.