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/cm2 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.

The focus of this paper is to introduce and describe a new technique for the determination of x-ray lithography mask distortions for pre- and post-irradiated membranes using a combination of numerical, analytical, and experimental methods. At the heart of this technique is a new test structure and fixture that allow for the accurate determination of material properties so that changes due to radiation exposure can then be incorporated into a finite element model to predict distortions. In addition, due to the size of the membranes used for the test structure, larger accumulated doses can be delivered in shorter periods of time. Once the material property and stress changes have been incorporated into numerical models, calculations can then be performed to simulate the effect of radiation on various membrane pattern areas and geometries.