Nonlinear processes to extend interferometric lithography

Saleem H. Zaidi; Steven R. J. Brueck

doi:10.1117/12.351110

25 June 1999 Nonlinear processes to extend interferometric lithography

Saleem H. Zaidi, Steven R. J. Brueck

Proceedings Volume 3676, Emerging Lithographic Technologies III; (1999) https://doi.org/10.1117/12.351110
Event: Microlithography '99, 1999, Santa Clara, CA, United States

Abstract

The linear-systems spatial frequency limit of diffraction- limited optical lithography is approximately NA/(lambda) , where NA is the optical system numerical aperture, and (lambda) is the exposure wavelength. Optical resolution enhancement techniques such as optical proximity correction, phase-shifts masks and off-axis illumination extend this resolution towards 2NA/(lambda) . Interferometric lithography (IL) for periodic patterns and imaging interferometric lithography for arbitrary patterns extends the frequency space coverage out towards the free-space linear systems transmission limit of 2/(lambda) . By taking advantage of inherent processing nonlinearities, higher spatial frequencies available by IL are reported. The first process is a variant of spatial frequency doubling in which two maskless IL processes combined with a moire alignment scheme are used to form a spatial frequency doubled grating at a period of d/2, where d is the original grating period. A first grating is written at period d, and linewidth approximately d/4, and transferred to a thin nitride film. A second IL grating, at the same period but shifted in phase by (pi) , is then interpolated to divide the period by two. A moire interference scheme is used to ensure proper alignment over large areas. This process has been used to frequency double a 360-nm period at I-line exposure to 180-nm period that was transferred into Si using KOH etching with the nitride film as the etch mask. A second example, using photoresist nonlinearities, is the formation of nanoscale square vias in a single photoresist level. This structure is formed by sequence including exposure of a grating, partial development of the resist, exposure of a second grating at right angles.

Citation Download Citation

Saleem H. Zaidi and Steven R. J. Brueck "Nonlinear processes to extend interferometric lithography", Proc. SPIE 3676, Emerging Lithographic Technologies III, (25 June 1999); https://doi.org/10.1117/12.351110

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