Overcoming the far-field diffraction limit via absorbance modulation

Abstract

Diffraction limits the resolution of far-field lithography and imaging to about half of the wavelength, which greatly limits the capability of optical techniques. The proposed technique with absorbance modulation aims to get around the diffraction limit by using wavelength-selective chemistry to confine light to nanoscale dimension. Absorbance modulation lithography and imaging is a near-field technique that does not require scanning of a tip in close proximity or fabrication of a physically small aperture. Near-field apertures are dynamically generated in the photochromic absorbance modulation layer (AML) with only far-field illuminations. In this thesis, the concept of absorbance modulation is explained and in-house simulation models are discussed in detail. One-dimensional experimental demonstrations of absorbance modulation lithography achieved line exposures with widths of about one tenth of the exposure wavelength. In order to extend absorbance modulation to two-dimension, a binary diffractive-optical element that generates a focused round spot at one wavelength, aligned with the central node of a ring-shaped spot at another wavelength was designed and fabricated. Lithography and imaging results applying this diffractive optical element showed evidence of point-spread function compression in lithography and contrast enhancement in imaging.