Space-invariant multiple-beam achromatic EUV interference lithography

We report the production of two-dimensional periodic patterns with defined cell shapes, such as arrays of circular rings, with multiple-beam extreme ultraviolet (EUV) interference lithography. The method combines coherent and incoherent addition of interference fields in a single exposure step to produce high-resolution, space-invariant intensity patterns. The use of wideband light, instead of highly monochromatic sources like lasers, eliminates the periodic variation of the intensity pattern as multiple beams interfere. The technique is especially useful in the EUV region as the undulator sources in that wavelength range provide radiation with relatively wide bandwidth. In demonstration experiments nanometer scale arrays of circular rings and dots in PMMA resist were obtained. The technique has potential for use in applications where periodically repeated cell structures are needed such as display units, optical filters, electronic memory and logic circuits and magnetic storage devices.