Cell projection e-beam lithography for optical metastructures

It is widely recognized that Variable Shaped Beam (VSB) lithography is suitable for device prototyping and low volume production in fields like compound semiconductor fabrication, optics and in an increasing number of photonic applications such as photonic integrated circuits, metalenses or photonic crystals. However, the resulting write time for real device manufacturing of optical metastructures and the related costs are often the limiting factor for a wider usage of the technology. Cell Projection (CP), a special exposure mode in Vistec VSB lithography tools, offers the means to overcome these limitations by exposing complex individual shapes in a single exposure shot. In this paper, we focus on the generation and fabrication of an effective-index metastructure for the substitution of thin film anti-reflective (AR) coatings and the layout generation for application specific optical phase profiles e.g. for beam shaping. In this context, CP can be a very useful technology [1], specifically for the efficient exposure of highly repetitive structures on mesoscopic areas necessary for metamaterial applications [2]. To achieve ideal optical phase profiles an optimal combination of the number of exposure cells (in the order of 10⁹) and the design of these cells (in the order of 20 layout variations) are required. Therefore, computer simulations were performed to optimise the metastructure layout (period and diameter of exposure shots) and automated computer-aided design routines were implemented to create application-specific layout files such as lenses or beam shapers.