Compensator selection and accuracy analysis for extreme ultraviolet lithographic objective

Extreme ultraviolet (EUV) lithographic projection objective must be well-corrected for aberrations after optimization process. However, selecting compensators to allocate tolerances properly is also needed in consideration of manufacturability and expected performance. For an EUV lithographic projection objective with a numerical aperture of 0.33, six compensators are chosen based on the sensitivity to wavefront error and correlation, and then the tolerances of non-compensators are analyzed. Furthermore, a method based on Monte Carlo trials is presented to analyze the accuracy of compensators. Using this method, the accuracy of compensators is obtained. The result shows that the most rigorous thickness tolerances, decentering tolerances and tilt tolerances are in the range of ±2 μm, ±3 μm and ±5 μrad respectively, and the accuracy of thickness and decentering compensators is ±0.1 μm. The root mean square (RMS) wavefront error of the projection system is less than 1 nm in the probability of 97.7%.