Gold membranes with large arrays of sub-μm holes fabricated by wafer-scale Nanosphere Lithography

Gold membranes with large arrays of sub-μm holes were fabricated and optically characterized. The fabrication is a combination of a bottom-up, self-assembly based patterning technique, Nanosphere Lithography (NSL), and standard microfabrication. This was achieved by 1) up-scaling of the deposition of close-packed bead monolayers to 4" wafer substrates, 2) controlled bead size reduction, 3) etching of high aspect-ratio Si pillar arrays, 4) using the pillar arrays as a lift-off template, and 5) releasing the membranes by dry-etching. In this way, millimeter-size, 200 nm thick gold membranes with dense, short-range ordered hole arrays were fabricated. The array periodicity was either 428 nm or 535 nm, depending on the initial bead size. The hole diameter was tuned in the range of 150 nm to 250 nm. Optical transmission spectroscopy showed surface plasmon mediated extraordinary optical transmission (EOT) with an enhancement factor greater than two.