24 March 2016 Highly sensitive focus monitoring technique based on illumination and target co-optimization
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We present a cost-effective focus monitoring technique based on the illumination and the target co-optimization. An advanced immersion scanner can provide the freeform illumination that enables the use of any kind of custom source shape by using a programmable array of thousands of individually adjustable micro-mirrors. Therefore, one can produce non-telecentricity using the asymmetric illumination in the scanner with the optimized focus target on the cost-effective binary OMOG mask. Then, the scanner focus variations directly translate into easily measurable overlay shifts in the printed pattern with high sensitivity (ΔShift/Δfocus = 60nm/100nm). In addition, the capability of using the freeform illumination allows us to computationally co-optimize the source and the focus target, simultaneously, generating not only vertical or horizontal shifts, but also introducing diagonal pattern shifts. The focus-induced pattern shifts can be accurately measured by standard wafer metrology tools such as CD-SEM and overlay metrology tools.
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Myungjun Lee, Myungjun Lee, Mark D. Smith, Mark D. Smith, Pradeep Subrahmanyan, Pradeep Subrahmanyan, Ady Levy, Ady Levy, "Highly sensitive focus monitoring technique based on illumination and target co-optimization", Proc. SPIE 9778, Metrology, Inspection, and Process Control for Microlithography XXX, 977826 (24 March 2016); doi: 10.1117/12.2218647; https://doi.org/10.1117/12.2218647

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