Abstract
Higher resolution demands for semiconductor lithography may be fulfilled by higher numerical aperture (NA) systems. However, NAs more than the photoresist refractive index (~1.7) cause surface confinement of the image. In this paper we describe how evanescent wave coupling to effective gain medium surface states beneath the imaging layer can counter this problem. We experimentally demonstrate this at λ = 405 nm using hafnium oxide on SiO2 to enhance the image depth of a 55-nm line and space pattern (numerical aperture of 1.824) from less than 40 nm to more than 90 nm. We provide a design example at λ = 193 nm, where a layer of sapphire on SiO2 counters image decay by an effective-gain-medium resonance phenomena allowing evanescent interferometric lithography to create high aspect ratio structures at NAs of 1.85 (26-nm resolution) and beyond.
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