RADIATION DAMAGE-INDUCED CHANGES IN SILICON-NITRIDE MEMBRANE MECHANICAL-PROPERTIES

Traditional x-ray lithography mask radiation damage studies have conce ntrated on the pattern placement errors produced by stress changes wit hin the mask membrane. The usual approach is to measure the location o f fiducial marks on the mask membrane to measure the distortions for p re-and postirradiation. The measured distortions are not directly rela ted to changes in individual mechanical properties of the membrane mat erial. 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 mea surement of changes in the elastic modulus and Poisson's ratio as a fu nction of incident dose. It was found that the modulus of elasticity d ecreased 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 i nto a finite element model to numerically determine the resulting dist ortions and compare them with published experimental results. (C) 1995 American Vacuum Society.