Silicon nanowire polarizers for far ultraviolet (sub-200 nm) applications: Modeling and fabrication

We have previously demonstrated a fabrication technique for the creation of silicon wire grid polarizers (WGPs) for far (deep) ultraviolet applications utilizing a shear-aligned cylinder-forming polystyrene- b -poly(n -hexyl methacrylate) diblock copolymer as a mask for reactive ion etching of an amorphous silicon substrate. In our current work, a numerical model is refined and applied to our experimental systems to describe the impact of wire height and periodicity, and tradeoffs between the two, on polarization efficiency. We focus our attention at a wavelength of 193 nm, the emission wavelength of the ArF excimer laser currently in use in advanced photolithographic processes. Through application of the model's predictions we have achieved marked improvement in the polarization efficiency of our WGPs by increasing the block copolymer molecular weight, thereby increasing the thickness of the Si wires, which compensates for a simultaneous increase in wire periodicity; the resulting arrays of parallel Si nanowires exhibit polarization efficiencies approaching 64% at 193 nm, a 68% relative increase over our previous Si WGPs.