Development of a high-speed nanoprofiler using normal vector tracing method for high-accuracy mirrors

Kohei Okuda; Takao Kitayama; Koji Usuki; Takuya Kojima; Kenya Okita; Junichi Uchikoshi; Yasuo Higashi; Katsuyoshi Endo

doi:10.1117/12.2029133

15 October 2013 Development of a high-speed nanoprofiler using normal vector tracing method for high-accuracy mirrors

Kohei Okuda, Takao Kitayama, Koji Usuki, Takuya Kojima, Kenya Okita, Junichi Uchikoshi, Yasuo Higashi, Katsuyoshi Endo

Proceedings Volume 8884, Optifab 2013; 888410 (2013) https://doi.org/10.1117/12.2029133
Event: SPIE Optifab, 2013, Rochester, New York, United States

Abstract

High-precision optical elements are used in various fields. Ultraprecise aspherical mirrors that offer nanofocusing and high coherence are used to concentrate high-brightness X-rays in developing third-generation synchrotron radiation facilities. In industry, extreme ultraviolet (wavelength: 13.5 nm) lithography, which is used to fabricate semiconductor devices, uses high-accuracy aspherical mirrors for its projection optical systems. The demand for rapid progress in nanomeasurement technologies is increasing because it is difficult to realize next-generation ultraprecise mirrors with the required precision by conventional processing. The measuring method itself requires superhigh precision. We developed an innovative nanoprofiler that can directly measure the figure of high-accuracy mirrors without using a reference surface. The principle of our measuring method is to determine the normal vectors by causing the optical paths of the incident and reflected light at the measurement point to coincide; it is based on the straightness of laser light and the accuracy of rotational goniometers. From the acquired normal vectors and their coordinates, the three-dimensional shape is calculated by a reconstruction algorithm. We measured concave spherical mirrors and compared the results with those using a Fizeau interferometer. The profiles of the mirrors were consistent within the range of error in their middle portions. In addition, we evaluated the performance of an airflow control unit by measuring a concave spherical mirror. This unit suppressed the influence of environmental change, and drastically improved the repeatability.

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Kohei Okuda, Takao Kitayama, Koji Usuki, Takuya Kojima, Kenya Okita, Junichi Uchikoshi, Yasuo Higashi, and Katsuyoshi Endo "Development of a high-speed nanoprofiler using normal vector tracing method for high-accuracy mirrors", Proc. SPIE 8884, Optifab 2013, 888410 (15 October 2013); https://doi.org/10.1117/12.2029133

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