Deep subwavelength patterning via absorbance modulation

Creating very small structures in the resist exceeding diffraction limit is becoming a bottle-neck in lithography especially for nanoscale features. A novel optical lithography technique that has the ability to overcome the diffraction barrier is Absorbance Modulation Interferometric-Lithography (AMIL). Feasibility of this technique is experimentally verified. In this approach of absorbance modulation, a standing wave at wavelength lambda 2 (633nm) is overlaid with a uniform beam from a light-emitting diode with a center wavelength at lambda1 (310nm). Both beams illuminate a photoresist film overcoated with a photochromic layer. This photochromic layer localizes the transmitted light at lambda1 to subwavelength spatial dimensions. The subwavelength lines are spaced by a diffraction-limited grating period. In order to generate dense lines, the sample is mounted on a single-axis high precision scanning stage that will enable multiple exposures.