24 March 2017 Experimental verification of on-product overlay improvement by intra-lot overlay control using metrology based grouping
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Abstract
For the sub-20 nm DRAM nodes, wafer-to-wafer (W2W) variation is one of the major contributors to on-product overlay (OPO). One way to reduce the W2W variation is by applying overlay corrections on wafer level on top of per lot / per chuck corrections. These overlay corrections can e.g. be based on measurements of the OPO on the wafers to be corrected prior to rework and re-exposure. Measuring OPO on every wafer is not preferred due to the resulting metrology cost increase. Hence, wafers are typically assigned to a limited amount of groups, which are in turn assigned one common correction set for all the wafers within a particular group. The common corrections are obtained from measuring wafers from the respective groups. In this paper, we present results obtained by a different approach, where the wafer grouping is deduced from metrology data that is available prior to the exposure of the lot. Aim of this approach is to balance overlay control and OPO metrology effort. We experimentally demonstrated the benefit of our approach on one of the critical layers of a sub-20 nm DRAM product of SK hynix. The experiment was executed in a rework scenario, which involves exposing and measuring OPO on selected send-ahead (SAHD) wafers, their subsequent rework, and re-exposure of the full lot using per-group corrections derived from the OPO measurements of the SAHDs. The results of this experiment indicate a promising OPO improvement. Simulations performed on additional lots and for 3 additional layers confirm the validity of our results.
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Honggoo Lee, Junghwan Moon, Jaesun Woo, Sangjun Han, Changrock Song, Marc Hauptmann, Weitian Kou, Alexander Ypma, Hyun-Woo Yu, Hank Han, Michiel Kupers, Paul Böcker, Daan Slotboom, "Experimental verification of on-product overlay improvement by intra-lot overlay control using metrology based grouping", Proc. SPIE 10147, Optical Microlithography XXX, 1014713 (24 March 2017); doi: 10.1117/12.2259846; https://doi.org/10.1117/12.2259846
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