Using a dwell-time increase to compensate for SLM pixelation-limited diffraction efficiency in DMHL

Abstract

Dynamic maskless holographic lithography (DMHL) is a new micro-manufacturing technique that uses holograms to create patterns on a substrate instead of a mask. In DMHL, gratings and Fresnel lenses are displayed on nematic liquid crystal spatial light modulators (SLMs) to steer light to desired locations to expose sensitive photopolymers. Micro-manufacturing can be done in two modes, serial or parallel. Serial refers to a beam being scanned through a set of points and parallel refers to an entire intensity pattern being created at once. The field over which patterning can be performed is affected by the diffraction efficiency of the displayed hologram, the maximum possible spatial frequency of the SLM, and aliasing (light being steered to unintended spots due to mismatches between designed and displayed phase patterns). This paper presents a technique to compensate for these inherent inefficiencies by properly adjusting the amount of time spent by the beam at each point in the desired feature, the dwell-time, during the lithographic process. The relationship between the spatial frequency of the appropriate grating or Fresnel lens and the dwell time is discussed. Experiments are presented with and without this technique applied, and results show that feature uniformity is improved with dwell-time compensation.