Flat-field anastigmatic mirror objective for high-magnification extreme ultraviolet microscopy

Mitsunori Toyoda

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)

Abstract

To apply high-definition microscopy to the extreme ultraviolet (EUV) region in practice, i.e. to enable in situ observation of living tissue and the at-wavelength inspection of lithography masks, we constructed a novel reflective objective made of three multilayer mirrors. This objective is configured as a two-stage imaging system made of a Schwarzschild two-mirror system as the primary objective and an additional magnifier with a single curved mirror. This two-stage configuration can provide a high magnification of 1500, which is suitable for real-time observation with an EUV charge coupled device (CCD) camera. Besides, since off-axis aberrations can be corrected by the magnifier, which provides field flattener optics, we are able to configure the objective as a flat-field anastigmatic system, in which we will have a diffraction-limited spatial resolution over a large field-of-view. This paper describes in detail the optical design of the present objective. After calculating the closed-form equations representing the third-order aberrations of the objective, we apply these equations to practical design examples with a numerical aperture of 0.25 and an operation wavelength of 13.5 nm. We also confirm the imaging performances of this novel design by using the numerical ray-tracing method.

Original languageEnglish
Pages (from-to)339-346
Number of pages8
JournalAdvanced Optical Technologies
Volume4
Issue number4
DOIs
Publication statusPublished - 2015 Aug 1

Keywords

  • Aberration theory
  • extreme ultraviolet
  • microscopy
  • multilayer mirror
  • soft X-ray

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics
  • Instrumentation

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