A finite element model has been used to study the distortion issues associated with nonuniform irradiation of an x-ray mask membrane. Results clearly demonstrate thar small changes in stress can lead to large in-place distortions unless the membrane field is uniformly exposed. If the mask membrane is uniformly exposed, the distortion can be minimized, allowing the mask to stay within its pattern placement error budget. The model has also been experimentally confirmed. While uniform exposure will be critical for controlling in-plane distortions, new issues such as resist processing and pattern registration within the membrane field must now be addressed.