Method of designing a projection system, lithographic apparatus and device manufacturing method
First Claim
1. A method of designing a projection system for a lithographic projection apparatus, comprising:
- obtaining a projection system starting configuration comprising a plurality of surfaces and having a merit function value corresponding to a local minimum in a merit function space;
inserting two additional surfaces at a reference surface in the starting configuration, with a separation between the additional surfaces and between the additional surfaces and the reference surface, with the optical material between the additional surfaces being substantially the same as that at the reference surface and with the curvatures of the two additional surfaces being substantially the same as the curvature of the reference surface to generate a saddle point configuration of a projection system corresponding to a saddle point in merit function space, wherein the saddle point has a Morse Index value of 1;
perturbing the saddle point configuration and performing optimization on at least one side of the saddle point to obtain a new projection system configuration having a merit function value corresponding to a local minimum in the merit function space;
increasing the separation between the two inserted surfaces and between the inserted surfaces and the reference surface at which they were inserted; and
outputting the resulting projection system configuration.
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Accused Products
Abstract
Optimization of a projection system is performed to obtain a starting configuration that is at a local minimum of the merit function or simply a previously known minimum system is used as the starting configuration. A zero-thickness meniscus lens is inserted at a surface in the local minimum starting configuration with N surfaces to construct a saddle point with Morse Index=1 having N+2 surfaces. The saddle point is perturbed and optimization is performed on both sides of the saddle, and the distances at the two surfaces that have been introduced are increased, to generate two new configurations, m1 and m2, that are new minima in the merit function. Each resulting configuration is output, e.g., as a table of parameters specifying the projection system or as a computer file for use in making an actual projection system.
26 Citations
21 Claims
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1. A method of designing a projection system for a lithographic projection apparatus, comprising:
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obtaining a projection system starting configuration comprising a plurality of surfaces and having a merit function value corresponding to a local minimum in a merit function space; inserting two additional surfaces at a reference surface in the starting configuration, with a separation between the additional surfaces and between the additional surfaces and the reference surface, with the optical material between the additional surfaces being substantially the same as that at the reference surface and with the curvatures of the two additional surfaces being substantially the same as the curvature of the reference surface to generate a saddle point configuration of a projection system corresponding to a saddle point in merit function space, wherein the saddle point has a Morse Index value of 1; perturbing the saddle point configuration and performing optimization on at least one side of the saddle point to obtain a new projection system configuration having a merit function value corresponding to a local minimum in the merit function space;
increasing the separation between the two inserted surfaces and between the inserted surfaces and the reference surface at which they were inserted; and
outputting the resulting projection system configuration. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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Specification