30 July 2002 System design of a 157-nm scanner
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Abstract
Two key technologies of 157nm exposure tools are projection optics and the environment control with highly purified gasses. For the projection optics, the NA is required to be extremely high even from the beginning to meet the accelerated ITRS roadmap, while compensating for the chromatic aberration issues with a line selected laser. In addition, the NIST has raised an issue of intrinsic birefi-ingence with the CaF2 materials, which has serious effects on the image quality if left uncorrected. We have found answers to suppress the intrinsic birefringence effects in the practical sense for the newly designed high NA system. One solution is to optimize the combination of the rotational positions of [1 11] crystals used for the projection optics, and to combine some [100] crystals with [1 11] crystals. Looking at the environmental control issue, there are two points. One is the purging of the constantly-sealed projection optics. We have experimented on the components in the projection optics, and have achieved the purging target for them. The second point is the purging around the reticle and the wafer both of which are continually carried in and out. We have got a practical solution, partial purge system, through simulations and basic experiments using a mock-up. The partial purge mechanism is effective in keeping the environment at high purity, capable of assuring the target purging level. It can also solve the problem of lens contamination due to outgas from the resist.
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Hideki Nogawa, Hideki Nogawa, Hideo Hata, Hideo Hata, Michio Kohno, Michio Kohno, } "System design of a 157-nm scanner", Proc. SPIE 4691, Optical Microlithography XV, (30 July 2002); doi: 10.1117/12.474609; https://doi.org/10.1117/12.474609
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