Interference lithography at EUV and soft X-ray wavelengths: Principles, methods, and applications

Interference lithography is an effective method of patterning periodic structures with limits set by light diffraction. Using this method at the short wavelengths of extreme ultraviolet (EUV) and soft X-ray provides additional advantages such as high photoresist absorption and low proximity effects. Operating at these short wavelengths, however, associates technical challenges such as light source, optics, transmission masks, and photoresists. Several research groups around the world have set up infrastructures to utilize interference lithography at this wavelength range for different applications. In this article we briefly review the works of these groups in terms of their light source, instrumentation, and achievements. We present more technical in-depth description of the illumination light source arrangements at our XIL-II beamline at the Swiss Light Source and the tabletop system at RWTH Aachen. We describe high-resolution mask fabrication and implementation, as well as achievements in photoresist patterning at cutting-edge resolutions. Moreover, we describe other methods of patterning at these wavelength regimes, such as Beyond EUV lithography, making tall nanostructures, and Talbot lithography. In addition, we show some of the applications of EUV-IL in nanoscience. (C) 2015 Elsevier B.V. All rights reserved.