Direct patterning of micro-optical structures by combined nanoimprinting and lithography

The driving force behind combining the nanoimprinting and photolithography is to effectively utilize the advantages of both patterning techniques simultaneously. Conventional shadow-mask UV-lithography can be used to pattern micron-scale structures uniformly over large areas, whereas nanoimprinting enables patterning of nanoscale features, which can also be tilted or round-shaped. We present the work on direct patterning of micro-optical structures by combined nanoimprinting and lithography using modified mask aligner, hybrid mask mold and directly patternable, UV-curable materials. Patterning of structures is carried out in wafer-level fashion. Hybrid mask mold fabrication can be realized for example by modifying conventional shadow-mask using focused ion beam (FIB) milling, or by patterning a mold area on shadow-mask surface by nanoimprinting. One of the advantages of proposed fabrication method is that there is no need for reactive ion etching (RIE) process steps. We present also near-field holography (NFH) as a method of grating mold fabrication. Fabricated micro-optical structures include directly patterned waveguides with light coupling gratings, and also pyramid-shaped gratings which show antireflection properties in the mid-infrared spectral region.