Optimizing numerical aperture and partial coherence to reduce proximity effect in deep-UV lithography

Raymond A. Cirelli; Eric L. Raab; Robert L. Kostelak; Sheila Vaidya

doi:10.1117/12.175438

17 May 1994 Optimizing numerical aperture and partial coherence to reduce proximity effect in deep-UV lithography

Raymond A. Cirelli, Eric L. Raab, Robert L. Kostelak, Sheila Vaidya

Proceedings Volume 2197, Optical/Laser Microlithography VII; (1994) https://doi.org/10.1117/12.175438
Event: SPIE's 1994 Symposium on Microlithography, 1994, San Jose, CA, United States

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.'

Citation Download Citation

Raymond A. Cirelli, Eric L. Raab, Robert L. Kostelak, and 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); https://doi.org/10.1117/12.175438

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