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Proceedings Paper

Minimization of sidelobes in rectangular contact/via hole structures
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Paper Abstract

With the increased use of attenuated phase shift masks, high NA, and highly light sensitive resists, accurate printing of both rectangular holes and square holes concurrently becomes an increasing challenge. Because of the relative difference in the amount of light passing through a rectangular hole compared to a square hole, printing both with good fidelity, and without sidelobing of the rectangular structures, is challenging. Sidelobes can arise when the first order of diffracted light from neighboring structures constructively interferes with light from the 6% attenuated background. Optimization of process conditions for square hole printing often results in sidelobing in rectangular structures on the same chip. Common methods for reducing sidelobes are to increase mask bias or partial coherence. Contrast considerations and mask inspectibility requirements limit the mask bias that can be used for square holes, and increasing partial coherence reduces the depth of focus for isolated square holes. This paper presents simulation and experimental results showing the effects of illumination conditions and mask bias on overall process window, including the sidelobe margin for rectangular hole structures. Sidelobe printing in rectangular holes is found to be extremely pitch dependent, and relatively insensitive to width. As discussed in this paper, the optimal process window depends on many factors, including the layout (of squares as well as rectangles), resist choice, scanner aberrations (coma), and illumination conditions. As with many aspects of photolithography, development of an optimal process requires consideration of all factors and making specific tradeoffs to reach this goal.

Paper Details

Date Published: 21 March 2006
PDF: 12 pages
Proc. SPIE 6154, Optical Microlithography XIX, 61543Z (21 March 2006); doi: 10.1117/12.658784
Show Author Affiliations
Mary Coles, Texas Instruments Inc. (United States)
Mark Somervell, Texas Instruments Inc. (United States)

Published in SPIE Proceedings Vol. 6154:
Optical Microlithography XIX
Donis G. Flagello, Editor(s)

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