Abstract
The difference in critical dimension between isolated and dense features of the same coded size in a circuit pattern must be minimized to enhance circuit performance. Altering the numerical aperture (NA) and partial coherence ((sigma) ) of an exposure system can help reduce this `proximity effect.' Using a state-of-the-art (variable NA, variable (sigma) ) deep- UV stepper (248 nm exposure wavelength), we exposed silicon wafers under a wide range of lithographic conditions. After measuring the linewidths with a scanning electron microscope and electrical probe, we plotted the linewidth as a function of pitch for various settings of NA and (sigma) . We present these results and compare them to data simulated using SPLAT and Prolith/2 modeling software. We show that partial coherence settings in the 0.6 - 0.74 range give excellent linewidth control for circuit designs with 0.30 micrometers design rules without any proximity correction. We also show that off-axis illumination techniques can worsen the `proximity effect.'
Published Version
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