Abstract: Misalignment modes are combinations of rigid-body perturbations to the optical elements that comprise an optical system. Comparison of misalignment modes associated with metrology data and projection-camera performance can be used to increase the sensitivity of metrology measurements to specific camera-performance specification such as chief- ray distortion. Selection of measurable misalignment modes in the case of metrology and interesting misalignment modes in the case of camera performance is based on a determination of whether a mode can 'fit' into a projection camera given actuator-stroke and mirror tilt bounds. Measurement and interest subspaces are next compared using distance between subspaces. As an example of this type of analysis, we find that exit-pupil wavefront measurements can be made more sensitive to chief-ray distortion if these measurements are collected at field positions outside the ring field of view of an extreme ultraviolet lithography projection camera. !12
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