Patterning a 50-nm period grating using soft x-ray spatial frequency multiplication

Abstract

Soft x-ray spatial frequency multiplication is a technique that has the capability of reducing by a factor of 2 or more the finest period grating that can be written by other methods. We describe two geometries for this technique: a single-grating geometry that requires spatially coherent illumination, and a two-grating geometry that can be used with incoherent illumination. Starting with a parent grating of period p and area A, gratings of period p/2, p/4, p/6 over an area A/3, A/5, A/7, respectively, can be printed in the single-grating geometry. The two-grating geometry produces the same final grating periods for parent gratings of period p, but the final grating area is limited only by the sizes of the parent gratings. As an initial demonstration of this technique, we have used the single-grating geometry to pattern a 50-nm period grating in polymethylmethacrylate over an area of 30 μm×100 μm, starting with a 100-nm period parent grating with an area of 90 μm×100 μm. The x-ray source was a synchrotron undulator at λ=18 Å and required a 5-min exposure time. Recent developments in coherent radiation from x-ray undulator sources will give shorter exposure times and permit larger areas to be patterned in the single-grating geometry.