Wavefront aberration compensation of projection lens using clocking lens elements.

For extremely high-performance lithographic lenses, the edge level accuracy of the manufacturing process and multicompensation strategies must be applied. Element clocking can be effectively used to compensate for the low-order figure errors of the elements. Considering that commercial optical software is usually incapable of obtaining good convergence for clocking optimization, this paper proposes a mathematical model of a lithographic lens containing the errors of a surface figure, after which a clocking optimization algorithm is programmed. A clocking optimization instance proving that the clocking optimization algorithm is capable of finding the optimized angle of elements and that clocking is an effective compensation strategy. The calculated accuracy of the proposed mathematic model was found to be acceptable for clocking optimization.