NIL master manufacturing for optical gratings

Abstract

The production of surface relief gratings plays a crucial role in nano-structuring today. Applications range from laser mirrors to manufacturing of waveguides for mixed and augmented reality. Augmented (AR) and mixed reality (MR) applications have recently gained large interest. For in- and out-coupling optics, mainly Slanted Relief Gratings (SRG) are used. Nano-imprint lithography (NIL) is one way to produce such optical gratings.^{[1], [2], [3]} For this procedure, NIL master stamp is pressed into a polymer for replication of the pattern. These NIL master stamps have to be structured previous to the NIL process. The manufacturing of those masters is realized by a pattern transfer of a masked substrate by ion beam etching technology. This technology enables the tilting of the substrate in the respect to the ion beam, the so-called incident angle of the ions, and, hence, the slant angles can be defined. Additionally, applying different process parameters, such as ion energy, beam current density and the mixture of process gas, the ratio between the physical, anisotropic etching and chemical isotropic etching can be adjusted. This ratio defines the shape of the slanted gratings. Two types of ion beam process are available, the Reactive ion beam etching (RIBE) for structuring the complete substrate surface simultaneously and the reactive ion beam trimming (RIBT) a locally resolved etching method enabling manufacturing of slanted gratings with both varying slant angle and varying trench depth. This work shows process results for these two manufacturing approaches.