Three-beam interference lithography: upgrading a Lloyd's interferometer for single-exposure hexagonal patterning.

Three-beam interference lithography is used to create hole/dot photoresist patterns with hexagonal symmetry. This is achieved by modifying a standard two-beam Lloyd's mirror interferometer into a three-beam interferometer, with the position of the mirrors chosen to guarantee 120 degrees symmetry of exposure. Compared to commonly used three-beam setups, this brings the advantage of simplified alignment, as the position of the mirrors with respect to the substrate is fixed. Pattern periodicities from several wavelengths lambda down to 2/3lambda are thus easily and continuously accessible by simply rotating the three-beam interferometer. Furthermore, in contrast to standard Lloyd's interferometers, only a single exposure is needed to create hole/dot photoresist patterns.