Super-resolution near-field lithography using planar silver lenses: A review of recent developments

The near-field imaging properties of planar silver layers are reviewed here, with a view to identifying their potential and pitfalls for sub-100 nm photolithography. Initial studies have shown that half-pitch features of 60–70 nm can be achieved using simple contact exposure with low-cost mercury lamp sources, which is less than 1/5th of the exposure wavelength. Sub-100 nm isolated features and line pairs with sub-100 nm spacing have also been resolved, and conventional resolution limits are exceeded in these cases too. Multi-layer silver lenses have also been studied, as it has been predicted that these will improve image resolution for a fixed mask-resist separation. Initial experimental results are inconclusive, as roughness on the additional interfaces tends to mitigate the benefits of going to the laminated structure. Simulations have been used to support the findings of the silver-lens experiments, and it is predicted that sub-50 nm half-pitch resolution should be possible.