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Proceedings Paper

Nonlinear processes to extend interferometric lithography
Author(s): Saleem H. Zaidi; Steven R. J. Brueck
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Paper 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.

Paper Details

Date Published: 25 June 1999
PDF: 8 pages
Proc. SPIE 3676, Emerging Lithographic Technologies III, (25 June 1999); doi: 10.1117/12.351110
Show Author Affiliations
Saleem H. Zaidi, Univ. of New Mexico (United States)
Steven R. J. Brueck, Univ. of New Mexico (United States)


Published in SPIE Proceedings Vol. 3676:
Emerging Lithographic Technologies III
Yuli Vladimirsky, Editor(s)

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