Spatial-frequency multiplication with multilevel interference lithography

The authors present a large-area spatial-frequency multiplication fabrication process for patterning one-dimensional periodic structures using multilevel interference lithography. In this process, multiple grating levels with different phase offsets are overlaid by aligning to a reference grating. Each grating level is pattern transfered into a single hard mask layer, effectively reducing the grating period. The linewidth of the grating lines is controlled with nanometer repeatability by plasma etching and an image-reversal process. The authors demonstrate overlay accuracy of $0.6±1.9nm$ over $16×12mm2$ for two levels of $200nm$ period gratings. Using this process, a subdiffraction-limited resolution grating with $100nm$ period is fabricated using light with $λ=351.1nm$⁠. This process can also be used to fabricate more complex periodic geometries.