Absorbance-modulation optical lithography

We describe a new mode of optical lithography called absorbance-modulation optical lithography (AMOL) in which a thin film of photochromic material is placed on top of a conventional photoresist and illuminated simultaneously by a focal spot of wavelength lambda(1) and a ring-shaped illumination of wavelength lambda(2). The lambda(1) radiation converts the photochromic material from an opaque to a transparent configuration, thereby enabling exposure of the photoresist, while the lambda(2) radiation reverses the transformation. As a result of these competing effects, the point-spread function that exposes the resist is strongly compressed, resulting in higher photolithographic resolution and information density. We show by modeling that the point-spread-function compression achieved via AMOL depends only on the absorbance distribution in the photostationary state. In this respect, absorbance modulation represents an optical nonlinearity that depends on the intensity ratio of lambda(1) and lambda(2) and not on the absolute intensity of either one alone. By inserting material parameters into the model, a lithographic resolution corresponding to lambda(1)/13 is predicted. (c) 2006 Optical Society of America.