High-Performance Mo/Si and W/B4C Multilayer Mirrors for Soft X-Ray Imaging Optics

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Soft x-ray projection lithography and microscopy demand high-throughput, diffraction-limited imaging systems.
• Achieving this requires optical elements with high normal incidence reflectivity and precisely controlled d-spacing.
• Matching optical element properties to ray-tracing designs is crucial for system performance.

Purpose of the Study:

• To present techniques for fabricating high-performance multilayer coatings for soft x-ray imaging.
• To detail methods for optimizing d-spacing uniformity and inter-mirror matching.
• To introduce a characterization method for multilayer coatings on curved surfaces.

Main Methods:

• Development of Mo/Si and W/B4C multilayer coatings for high normal incidence reflectivity at specific wavelengths (13 nm and water window region).
• Implementation of methods to achieve ±0.4% d-spacing uniformity and ±0.5% inter-mirror d-spacing matching.
• Utilizing cylindrical witness optics with precalculated properties for simulating and characterizing final optics on curved surfaces.

Main Results:

• Achieved >60% normal incidence reflectivity at 13 nm for Mo/Si coatings.
• Achieved >2.7% normal incidence reflectivity in the water window region for W/B4C coatings.
• Demonstrated methods for obtaining high d-spacing uniformity and accurate inter-mirror matching.

Conclusions:

• The presented techniques enable the production of advanced multilayer coatings essential for high-performance soft x-ray imaging systems.
• Precise control over optical element properties is achievable, meeting the stringent requirements of lithography and microscopy.
• The developed characterization method provides a reliable way to assess coatings on curved optics.