System and method for projection lithography with immersed image-aligned diffractive element

Abstract

A novel system and method and computer program product for exposing a photoresist film with patterns of finer resolution than can physically be projected onto the film in an ordinary image formed at the same wavelength. A hologram structure containing a set of resolvable spatial frequencies is first formed above the photoresist film. If necessary the photoresist is then sensitized. An illuminating wavefront containing a second set of resolvable spatial frequencies is projected through the hologram, forming a new set of transmitted spatial frequencies that expose the photoresist. The transmitted spatial frequencies include sum frequencies of higher frequency than is present in the hologram or illuminating wavefront, increasing the resolution of the exposing pattern. These high spatial frequency transmitted waves can be evanescent, or they can propagate at a steeper obliquity in a higher index medium than is possible in a projected image. A further method is described for designing lithographic masks to fabricate the hologram and to project the illuminating wavefront. In other embodiments, a simple personalization based on Talbot fringes and plasmonic interference is performed.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates generally to lithographic formation of integrated circuit patterns, and more particularly to a method for generating the spatial frequency modulation of a lithographic pattern by projecting a light beam that has been modulated with a set of spatial frequencies through a hologram modulated by a signal having a second spatial frequency modulation.[0003]2. Description of the Prior Art[0004]The resolution of a lithographic image is limited by the wavelength of the light that forms it. Currently, source wavelengths shorter than λ=193 nm (e.g., as provided by an ArF excimer light source) are not contemplated for IC manufacture until the future era of soft x-ray lithography. Fortunately, wavelength is reduced inside a medium, and a favorable reduction of as much as 1.8× can potentially be obtained for propagating waves within photoresist films. This corresponds to an upper limit of 1.8 for the res...

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