15 March 2016 Overcoming low-alignment signal contrast induced alignment failure by alignment signal enhancement
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Abstract
Overlay is one of the key factors which enables optical lithography extension to 1X node DRAM manufacturing. It is natural that accurate wafer alignment is a prerequisite for good device overlay. However, alignment failures or misalignments are commonly observed in a fab. There are many factors which could induce alignment problems. Low alignment signal contrast is one of the main issues. Alignment signal contrast can be degraded by opaque stack materials or by alignment mark degradation due to processes like CMP. This issue can be compounded by mark sub-segmentation from design rules in combination with double or quadruple spacer process. Alignment signal contrast can be improved by applying new material or process optimization, which sometimes lead to the addition of another process-step with higher costs. If we can amplify the signal components containing the position information and reduce other unwanted signal and background contributions then we can improve alignment performance without process change. In this paper we use ASML's new alignment sensor (as was introduced and released on the NXT:1980Di) and sample wafers with special stacks which can induce poor alignment signal to demonstrate alignment and overlay improvement.
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Byeong Soo Lee, Young Ha Kim, Hyunwoo Hwang, Jeongjin Lee, Jeong Heung Kong, Young Seog Kang, Bart Paarhuis, Haico Kok, Roelof de Graaf, Stefan Weichselbaum, Richard Droste, Christopher Mason, Igor Aarts, Wim P. de Boeij, "Overcoming low-alignment signal contrast induced alignment failure by alignment signal enhancement", Proc. SPIE 9780, Optical Microlithography XXIX, 97800B (15 March 2016); doi: 10.1117/12.2220587; https://doi.org/10.1117/12.2220587
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