3 March 2010 High fluence testing of optical materials for 193-nm lithography extensions applications
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Abstract
As next generation immersion lithography, combined with double patterning, continues to shrink feature sizes, the industry is contemplating a move to non-chemically amplified resists to reduce line edge roughness. Since these resists inherently have lower sensitivities, the transition would require an increase in laser exposure doses, and thus, an increase in incident laser fluence to keep the high system throughput. Over the past several months, we have undertaken a study at MIT Lincoln Laboratory to characterize performance of bulk materials (SiO2 and CaF2) and thin film coatings from major lithographic material suppliers under continuous 193-nm laser irradiation at elevated fluences. The exposures are performed in a nitrogen-purged chamber where samples are irradiated at 4000 Hz at fluences between 30 and 50 mJ/cm2/pulse. For both coatings and bulk materials, in-situ laser transmission combined with in-situ laser-induced fluorescence is used to characterize material performance. Potential color center formation is monitored by ex-situ spectrophotometry. For bulk materials, we additionally measure spatial birefringence maps before and after irradiation. For thin film coatings, spectroscopic ellipsometry is used to obtain spatial maps of the irradiated surfaces to elucidate the structural changes in the coating. Results obtained in this study can be used to identify potential areas of concern in the lens material performance if the incident fluence is raised for the introduction of non-chemically amplified resists. The results can also help to improve illuminator performance where such high fluences already occur.
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V. Liberman, S. Palmacci, G. P. Geurtsen, M. Rothschild, P. A. Zimmerman, "High fluence testing of optical materials for 193-nm lithography extensions applications", Proc. SPIE 7640, Optical Microlithography XXIII, 76402Z (3 March 2010); doi: 10.1117/12.853094; https://doi.org/10.1117/12.853094
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