2 April 2014 Metrology of advanced N14 process pattern split at lithography
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In advanced semiconductor N14 processes, due to the requirement of shrinking pitches for increased densities, pattern split is introduced. However, each of the two pattern split methods, SADP (Self-Aligned Double Patterning) and LELE (Litho-Etch-Litho-Etch), can incur process variations that might cause “pitch walk” [1, 3]. Pitch walk is a by-product of line critical dimension (CD) and spacer error (in SADP) or overlay variations (in LELE). Pitch walk not only results in different line and spaces but also affect the later steps, for example, different etched depths due to loading effects. Because of those behaviors, it is therefore a requirement to control the CD for better uniformity. This paper demonstrates how to use SCD (Scatterometry Critical Dimension) metrology tools to measure the different critical dimensions and spaces to control CD and overlay at the same process step [2]. Traditionally, wafers have to go through both a CD metrology tool and an overlay tool in order to verify CD uniformity and grid uniformity. The methodology introduced in this paper can efficiently shorten cycle time since only the CD metrology tool will be used to verify both CD and overlay. SpectraShape™ is a proven optical CD platform based on spectroscopic ellipsometry and reflectometry. In optical model type metrology, pitch walk can be a challenging parameter to measure due to inherent low sensitivity. Hence this study is performed on the newest generation system, the SpectraShape™ 9010. A new, laser driven light source [4] on this SCD tool provides higher light intensity, producing better signal-to-noise ratios for critical device parameters. This paper explores the use of SCD to measure both resist and hard mask CD in a single step. In addition, results will be presented on using SCD to measure pitch walk, typically a low sensitivity parameter for optical CD metrology tools.
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Wei-Jhe Tzai, Wei-Jhe Tzai, Chia-Ching Lin, Chia-Ching Lin, Chien-Hao Chen, Chien-Hao Chen, Chun Chi Yu, Chun Chi Yu, Wei-Yuan Chu, Wei-Yuan Chu, Sungchul Yoo, Sungchul Yoo, Chien-Jen Huang, Chien-Jen Huang, Chao-Yu Cheng, Chao-Yu Cheng, Hsiao-Fei Su, Hsiao-Fei Su, "Metrology of advanced N14 process pattern split at lithography", Proc. SPIE 9050, Metrology, Inspection, and Process Control for Microlithography XXVIII, 90502R (2 April 2014); doi: 10.1117/12.2046617; https://doi.org/10.1117/12.2046617

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