Wafer scale fabrication of submicron chessboard gratings using phase masks in proximity lithography

One and two dimensional grating structures with submicron period have a huge number of applications in optics and photonics. Such structures are conventionally fabricated using interference or e-beam lithography. However, both technologies have significant drawbacks. Interference lithography is limited to rather simple geometries and the sequential writing scheme of e-beam lithography leads to time consuming exposures for each grating. We present a novel fabrication technique for this class of microstructures which is based on proximity lithography in a mask aligner. The technology is capable to pattern a complete wafer within less than one minute of exposure time and offers thereby high lateral resolution and a reliable process. Our advancements compared to standard mask aligner lithography are twofold: First of all, we are using periodic binary phase masks instead of chromium masks to generate an aerial image of high resolution and exceptional light efficiency at certain distances behind the mask. Second, a special mask aligner illumination set-up is employed which allows to precisely control the incidence angles of the exposure light. This degree of freedom allows both, to shape the aerial image (e. g. transformation of a periodic spot pattern into a chessboard pattern) and to increase its depth of focus considerably. That way, our technology enables the fabrication of high quality gratings with arbitrary geometry in a fast and stable wafer scale process.