Laser interference lithography with highly accurate interferometric alignment

Three dimensional photonic crystals, e.g. for obtaining the so-called woodpile structure, can, among others, be fabricated by vertical stacking of multiple gratings. One of the requirements for obtaining a full photonic bandgap in such a photonic crystal is an accurate angular and lateral alignment of the successive gratings. Using laser interference lithography at 266 nm wavelength, we fabricated gratings in silicon with periods down to 300 nm. We present a method for aligning further grating exposures with respect to this grating with a 0.001 degree angular and a few nanometers lateral resolution