High-resolution grayscale patterning using extreme ultraviolet interference lithography

•Demonstration of grayscale patterning by EUV interference lithography.•Patterned blazed gratings of period 100 nm, equivalent to 10,000 lines/mm density•Arrays of nested troughs produced by overlay exposure of non-multiple periodicities

Grayscale patterning is technologically relevant in the fabrication of micro-optics elements, microfluidics, micro-electromechanical devices, to name a few. So far, the state-of-the-art is limited to micrometric scale, which is of interest for optical applications in the visible spectrum. In this work, we used extreme ultraviolet light and an interference lithography method to demonstrate the feasibility of grayscale patterning with high lateral and vertical resolution. A double exposure was carried out on poly(methyl methacrylate) photoresist using periodic lines/spaces of two different pitches (100 nm and 50 nm). The resulting morphology of photoresist after development, analyzed by scanning electron microscopy and atomic force microscopy, showed that a dense one-sided blaze profile consisting of three grayscale levels was obtained. The equivalent groove density of the blazed grating was 10,000 lines/mm, which is a remarkable achievement of significant interest for applications such as high resolution and high efficiency diffraction optics. Furthermore, combinations of overlay from non-multiple pitches (100 nm and 80 nm) was accomplished and unconventional structures with nested trenches with total period of 400 nm were obtained.

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