Abstract
A new resolution enhancement method named SPLIT (Superimposition of Phase-shifting Layer for Image Transformation) is proposed. In the new method, top-layer resist patterns act as clear phase shifters for bottom-layer exposure. Since the phase shifters are closely contacted on the bottom-layer resist, very fine patterns are printed just under edges of top-layer shifter patterns. Theoretical resolution limit is infinitely small if the bottom-layer resist is infinitely thin. Using THMR iP3300 and KRF-M60G as the top- and the bottom-layer resists, feasibility of the new method is investigated. The top-layer shifter patterns are printed by projection exposure using blue light with a wavelength of 480 nm. The bottom layer is exposed to flood UV light with a wavelength of and 254 nm. As a result, 130-nm line pairs with a pitch of 240 nm are successfully printed.
