Application of rigorously optimized phase masks for the fabrication of binary and blazed gratings with diffractive proximity lithography

Abstract

Gratings with binary and blazed profiles and periods in the low micron and sub-micron range define a class of microstructures with a huge application potential. We present a mask based photolithographic fabrication method for these demanding grating geometries. It combines the advantages of electron beam lithography and holographic exposure, which are superior homogeneity, high resolution and pattern flexibility on one hand, and a fast, large aerial exposure with the option for smooth profiles on the other hand. This is accomplished by the use of an electron beam written phase mask which contains a very homogeneous pattern of diffractive features and is used for a full-field exposure in a proximity mask aligner. The key for the beneficial use of the technology is the proper design of the phase mask surface profile which can have a binary or multilevel geometry. Since the patterns to be exposed are periodic, this is also the case for the phase mask which allows calculating their physical light transmission with exact methods like rigorous coupled wave analysis. An optimization algorithm has been developed which can find mask geometries that synthesize a desired complex aerial image in the proximity distance of choice. Aerial images offering e.g. high resolution features, phase shifts, and tilted propagation directions can be realized that way. This technology has been successfully used to fabricate e.g. binary gratings of very high quality with a period of 800 nm as well as blazed gratings with a period of 3 µm

High-resolution proximity lithography for nano-optical components

“…8c) and asymmetric structures with steep sidewalls in thick resist have been demonstrated [158] by mask aligner lithography.…”

“…NFH has the potential to realize similar structures with very small periods [159]. Blazed gratings with micron-and submicron-scale periods can potentially be fabricated by RO-PSM [158] while both continuous profiles with steep sidewalls or binary high resolution sub-period features are feasible. The very broad range of two dimensional periodic structures can partially be addressed by all the approaches described, while the resolution and DOF limitations are in principle similar to one-dimensional pattern.…”

New Illumination Technology for Mask Aligner Lithography

“…like blazed gratings for beam deflection or splitting. Using a combination of a customized angular spectrum and a rigorously optimized photomask [3], the research team was also able to obtain promising experimental results and fabricated blazed gratings with a perpendicular back jump.…”

“…The work was developed within the project ultra optics "Fertigungstechnol- Fig. 3 A rigorously optimized photomask (left side) allows the generation of blazed pattern of 3 µm period and a perpendicular back jump in photoresist (right side) [3].…”

Photomask displacement technology for continuous profile generation by mask aligner lithography

“…Stuerzebecher et al have shown the application of rigorously optimized phase masks to fabricate binary and blazed grating with diffractive proximity lithography [12]. The phase mask generates a tilted light distribution which then propagates to the photoresist.…”