Minimizing mapping-induced OPD errors when testing aspheric mirrors
Extreme ultraviolet (EUV) projection systems are designed with mild aspheres so that the mirrors can be tested at the center of curvature without null optics. The elimination of the null optics improves the fundamental accuracy of the test. However, this test configuration is not stiginatic, and the rays from the test wavefront and reference wavefront will not trace the same optical path through the viewing system. Effectively, the test and reference wavefront are sheared in the exit pupil of the viewing system. This shear leads to an OPD contribution from the viewing system that we label the mapping error. For visible light metrology, this induced OPD error can be a significant fraction of the EUV wavelength. The origin of this OPD error is demonstrated using simple ray optics. Examples are presented illustrating the nature and magnitude of this error for off-axis aspheric sections. Methods for mininiizing this OPD error are suggested.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 310907
- Report Number(s):
- UCRL-JC-128288; CONF-980225-; ON: DE98058760
- Resource Relation:
- Conference: 23. SPIE annual international symposium on microlithography conference, Santa Clara, CA (United States), 22-27 Feb 1998; Other Information: PBD: 16 Mar 1998
- Country of Publication:
- United States
- Language:
- English
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