| Description |
Following the progress of shrinking down the sizes of integrated circuit elements, optical lithography, which is the state of the art of patterning ever-small structures, has now almost reached its final limit. This limit to the size of the smallest feature that can be patterned using photolithography is imposed by the diffraction limit of light, generally accepted to be about half the wavelength of illumination. Absorbance Modulation Optical Lithography (AMOL) is a technique of super-resolution maskless photolithography with the potential to localize light to sub-diffraction limited spaces. AMOL uses a unique family of organic molecules called photochromes that can switch between two isomeric states based on the wavelength of photon that the states absorbs, a long wavelength photon (of wavelength λ2) and a short wavelength photon (of wavelength λ1). When a thin layer of this photochromic molecule, is subjected to simultaneous illumination by a focal spot at λ1 and a ring-shaped spot at λ2, it is rendered opaque everywhere except at very close to the center of the optical node in the ring shaped λ2 spot. This competing behavior of the absorbance of the layer to the two wavelengths and the state transitions allows only λ1 photons to penetrate through the λ2 node, creating a nanoscale illumination spot, the dimensions of which are far below the diffraction limit. A recording medium placed under this layer, such as photoresist can record this illumination. In this thesis, the development of AMOL as a cost effective super-resolution photolithography process is addressed. Firstly, an improvement to the AMOL process is affected by the removal of a barrier layer that was present in previous demonstrations in between the AML and the photoresist. Secondly, experimental verification of the AMOL feature-scaling trend is presented. Next, a comprehensive model to simulate the AMOL process is constructed using finite element method based full electromagnetic wave solutions. A couple of methods to realize AMOL patterning at very low light intensity levels are also demonstrated with both simulation and experimental verifications. Lastly, an optical system is described that is capable of extending the AMOL process to patterning aperiodic arbitrary features. |
