Optimization of positive novolak-based resists for phase-shift mask technology

Peggy M. Spragg; Giang T. Dao; Steven G. Hansen; Robert F. Leonard; Medhat A. Toukhy; Rajeev R. Singh; Kenny K.H. Toh

doi:10.1117/12.130325

1 June 1992 Optimization of positive novolak-based resists for phase-shift mask technology

Peggy M. Spragg, Giang T. Dao, Steven G. Hansen, Robert F. Leonard, Medhat A. Toukhy, Rajeev R. Singh, Kenny K.H. Toh

Proceedings Volume 1674, Optical/Laser Microlithography V; (1992) https://doi.org/10.1117/12.130325
Event: Microlithography '92, 1992, San Jose, CA, United States

Abstract

Various methods for the application of phase-shift mask (PSM) technology have been discussed, and for non-periodic features such as isolated contact holes, the "rim-shifter" and "out-rigger" methods show particular promise. While both approaches can improve process latitude, they introduce a new complication in the form of secondary illumination intensity lobes which can degrade lithographic performance. The present work specifically addresses whether an optimal "high contrast" resist process for conventional lithography will also be optimal for processes using rim-shifters and subresolution out-rigger shifters in the production of isolated trenches and contact holes. Simulations using SAMPLE and SPLAT show that for a given mask design, high contrast processes can amplify the secondary lobes and therefore may not be optimal. The reason for the enhanced printing of the secondary lobes is traceable to the higher Exposure Margin (defined as the ratio dose-to-size/dose-to-clear) associated with high contrast processes. Such processes require high exposures (relative to the clearing dose) to achieve the target developed dimension and so the secondary lobes are, in a sense, overexposed. Because the preferred mask designs are still evolving, it is uncertain whether secondary lobe printing will be an important factor in process optimization; however, the present work suggests that the problem is minimized by using positive resist systems with high surface inhibition and high transparency at the exposing wavelength. These are the same qualities which maximize profile-related defocus latitude with conventional masks. Lithographic results are presented showing superior performance of a photoresist formulated with these characteristics over conventional materials.

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Peggy M. Spragg, Giang T. Dao, Steven G. Hansen, Robert F. Leonard, Medhat A. Toukhy, Rajeev R. Singh, and Kenny K.H. Toh "Optimization of positive novolak-based resists for phase-shift mask technology", Proc. SPIE 1674, Optical/Laser Microlithography V, (1 June 1992); https://doi.org/10.1117/12.130325

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