17 May 1994 Optimizing numerical aperture and partial coherence to reduce proximity effect in deep-UV lithography
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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.'
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Raymond A. Cirelli, Eric L. Raab, Robert L. Kostelak, Sheila Vaidya, "Optimizing numerical aperture and partial coherence to reduce proximity effect in deep-UV lithography", Proc. SPIE 2197, Optical/Laser Microlithography VII, (17 May 1994); doi: 10.1117/12.175438; https://doi.org/10.1117/12.175438
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