19 March 2015 Scatterometry or imaging overlay: a comparative study
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Abstract
Most fabrication facilities today use imaging overlay measurement methods, as it has been the industry’s reliable workhorse for decades. In the last few years, third-generation Scatterometry Overlay (SCOL™) or Diffraction Based Overlay (DBO-1) technology was developed, along another DBO technology (DBO-2). This development led to the question of where the DBO technology should be implemented for overlay measurements. Scatterometry has been adopted for high volume production in only few cases, always with imaging as a backup, but scatterometry overlay is considered by many as the technology of the future. In this paper we compare imaging overlay and DBO technologies by means of measurements and simulations. We outline issues and sensitivities for both technologies, providing guidelines for the best implementation of each. For several of the presented cases, data from two different DBO technologies are compared as well, the first with Pupil data access (DBO-1) and the other without pupil data access (DBO-2). Key indicators of overlay measurement quality include: layer coverage, accuracy, TMU, process robustness and robustness to process changes. Measurement data from real cases across the industry are compared and the conclusions are also backed by simulations. Accuracy is benchmarked with reference OVL, and self-consistency, showing good results for Imaging and DBO-1 technology. Process sensitivity and metrology robustness are mostly simulated with MTD (Metrology Target Designer) comparing the same process variations for both technologies. The experimental data presented in this study was done on ten advanced node layers and three production node layers, for all phases of the IC fabrication process (FEOL, MEOL and BEOL). The metrology tool used for most of the study is KLA-Tencor’s Archer 500LCM system (scatterometry-based and imaging-based measurement technologies on the same tool) another type of tool is used for DBO-2 measurements.

Finally, we conclude that both imaging overlay technology and DBO-1 technology are fully successful and have a valid roadmap for the next few design nodes, with some use cases better suited for one or the other measurement technologies. Having both imaging and DBO technology options available in parallel, allows Overlay Engineers a mix and match overlay measurement strategy, providing back up when encountering difficulties with one of the technologies and benefiting from the best of both technologies for every use case.
© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Simon C. C. Hsu, Simon C. C. Hsu, Yuan Chi Pai, Yuan Chi Pai, Charlie Chen, Charlie Chen, Chun Chi Yu, Chun Chi Yu, Henry Hsing, Henry Hsing, Hsing-Chien Wu, Hsing-Chien Wu, Kelly T. L. Kuo, Kelly T. L. Kuo, Nuriel Amir, Nuriel Amir, } "Scatterometry or imaging overlay: a comparative study", Proc. SPIE 9424, Metrology, Inspection, and Process Control for Microlithography XXIX, 942409 (19 March 2015); doi: 10.1117/12.2085950; https://doi.org/10.1117/12.2085950
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