24 March 2017 Reducing the impact of etch-induced pattern shift on overlay by using lithography and etch tool corrections
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Abstract
With shrinking design rules, the overall patterning requirements are getting aggressively tighter and tighter. For the 5-nm node and beyond, on-product overlay below 2.5nm is required. Achieving such performance levels will not only need optimization of scanner performance but a holistic tuning of all process steps. In previous work, it has been shown that process-induced pattern asymmetry has significant impact on overlay performance at wafer edge and can be partially compensated by applying high-order scanner corrections or optimizing metrology targets. Today, we present the reduction of process-induced pattern asymmetry in a tunable etch system and demonstrate the related on-product overlay improvement combined with scanner corrections.

In our work we utilize etch tools (Lam Kiyo® conductor etch systems) with proprietary edge tuning technology that can be used to reduce the etch-related asymmetry at the wafer edge. In combination to this unique method, we evaluate the impact of high order corrections per exposure field to compensate for process asymmetry at the wafer edge with a state-of-the-art 1.35 NA immersion scanner (NXT:1970Ci).

The study is done on dedicated test wafers with 10-nm logic node design. We use angle-resolved scatterometry (YieldStar® S-250), atomic force microscopy, and SEM cross-sections to characterize process asymmetry. We present experimental investigation of the effect of etch tuning and scanner corrections on the pattern shift and the resulting overlay. In particular, we present results showing a reduction of etch-induced pattern shift by 12nm at wafer radius 147mm.

Results show that asymmetry can be addressed by both, litho compensation and etch tuning, and bring on-product overlay down to the required level. We discuss the benefit of the correction techniques especially for thick hard mask layers (the pattern shift scales linear with hard mask thickness) and evaluate a combined correction scenario, where preventive etch tuning and feed-back based scanner corrections are used. We conclude that a holistic tuning of all process steps will be required to fulfill overlay requirements of future nodes.
© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Michael Kubis, Rich Wise, Charlotte Chahine, Katja Viatkina, Samee Ur-Rehman, Geert Simons, Mircea Dusa, David Hellin, Daniel Sobieski, Wenzhe Zhang, Christiane Jehoul, Patrick Jaenen, Philippe Leray, "Reducing the impact of etch-induced pattern shift on overlay by using lithography and etch tool corrections", Proc. SPIE 10147, Optical Microlithography XXX, 101470H (24 March 2017); doi: 10.1117/12.2260000; https://doi.org/10.1117/12.2260000
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