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30 July 2002 Complex 2D pattern lithography at λ/4 resolution using chromeless phase lithography (CPL)
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Fostered by continued advancements in the field of optical extension technologies, optical lithography continues to extend far beyond what was thought possible only a few years ago. The application of chromeless phase lithography (CPL), or '100% transmission PSM,' has been used to demonstrate the potential for achieving quarter-wavelength optical lithography (k1 approximately 0.2). The ability to print 70 nm lines through pitch using a 248 nm, 0.70 NA wafer scanner, QUASAR off axis illumination, and a chromeless mask (CLM) has been demonstrated. However, it was confirmed by Chen, et al., that imaging complex 2D structures with high transmission CLM reticles involves very strong optical proximity effects. The need to use high NA wafer steppers with off-axis illumination in order to apply chromeless phase lithography exacerbates these effects. This phenomenon is further magnified and the interactions become more complex as the pitch between 2D structures is decreased. The nature of the proximity effects observed with chromeless phase lithography and the means to correct for them using various optical proximity correction (OPC) methods are described and explained. Patterns representing real device- like structures are used to demonstrate that data processing algorithms are feasible which can correct for the induced proximity effects and thus make it possible to incorporate CPL technology for low-k1 production lithography.
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Douglas J. Van Den Broeke, J. Fung Chen, Thomas L. Laidig, Stephen Hsu, Kurt E. Wampler, Robert John Socha, and John S. Petersen "Complex 2D pattern lithography at λ/4 resolution using chromeless phase lithography (CPL)", Proc. SPIE 4691, Optical Microlithography XV, (30 July 2002);

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