A chemical underlayer approach to mitigate shot noise in EUV contact hole patterning

Shot noise is a significant issue in EUV lithography, especially in printing small area features like contact holes. This brings about LCDU (Local CD Uniformity) issue and LCDU-sensitivity tradeoff. This paper describes efforts to alleviate this issue through a novel EUV Underlayer (UL) chemistry design approach. The novel component “buffer” was introduced into EUV UL formulations to balance back exposure energy from UL to the resist at different incident positions. Measured back exposure dose from UL shows much lower variation (6σ/mean) compared with shot noise of resist absorbed dose. Thus summed energy variation will be suppressed when counting back exposure effect of UL, namely shot noise is reduced. Through reported shot noise model, our calculation suggests 30% sensitivity improvement and 13.4% shot noise suppression can be expected. Actual lithographic evaluations demonstrated simultaneous LCDU and sensitivity improvement. The feasibility of 30% sensitivity improvement by Metal hard mask (MHM) material was tested. The combination of buffer functionalized UL and MHM was modeled.

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