The trade-off between resist sensitivity and local critical dimension uniformity (LCDU) of contact hole (C/H) patterning is one of the most challenging issues facing cost effective high-numerical aperture (NA) high volume manufacturing. The focus margin at 0.55 NA is only 36% of that at 0.33 NA, which raises significant concerns about defocus-induced LCDU degradation. A chemically amplified resist (CAR_B) which resolved 24 nm pitch showed zero useful depth of focus (DOF) when considering LCDU specification for 32-nm pitch contact holes. If we relax the LCDU target to 18% of half pitch (or 2.88 nm), a useful DOF of 30 nm was obtained with CAR_B at 32 nm pitch contact hole. If we relax the LCDU target to 20% of half pitch (or 2.8 nm), a useful DOF of less than 10 nm was achieved with CAR_A for 28-nm pitch contact hole. Non-CAR positive-tone resist (PTR) was worse than CAR PTR in terms of LCDU at 32-nm pitch and 28-nm pitch dense contact holes. Non-CAR negativetone resist (NTR) has a demerit of ~8% lower NILS caused by usage of clear-tone mask. For sub 30-nm pitch dense contact hole patterning, it is highly recommended to develop positive-tone non-CAR material and to develop new additional processes that improve LCDU for high-NA implementation.
In this paper, we propose advanced overlay stability control improving conventional stability control, Baseliner™ and reference wafers with new vertical structure for effective stability control. We verify improved overlay stability control experimentally by using this stability control method. Also we suggest that additional improvements can be achieved by controllable process terms. For focus stability control, we make reference wafers which can measure overlay and focus simultaneously on the same wafer to minimize monitoring wafers.
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