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25 March 2008 Low-k n&k variation impact on CD accuracy of scatterometry
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Scatterometry is one of the advanced optical metrology techniques has been implemented in semiconductor manufacturing for monitoring and controlling critical dimensions, sidewall angle and grating heights as well as thicknesses of underlying films, due to its non-destructive nature, high measurement precision and speed. In traditional scatterometry approach, the optical properties (n&k's) of film stack have been used as fixed inputs in a scatterometry model, therefore, the process engineers have to assume that there is no significant impact on measurement results by small deviation from pre-extracted n&k's. However, n&k's of actual production wafers will always vary from the fixed values used in the model. The magnitude of the variations and its impact on the accuracy of scatterometry measurements has not been well-characterized yet. In this study, a low-k dielectric stack with noticeable n&k's variations was generated. The low-k dielectric stack has the refractive index (n) variation around 0.01 @ 633nm within a wafer, and is under two layers of patterned PR and BARC. Different scatterometry models with fixed and floated n&k's have been analyzed. Although comparable repeatability was obtained with either fixed or floated n&k's model, the correlation (R2) to CD-SEM result has been improved by floating n&k in the model in comparison to that of fixed n&k model. In this paper, we also discuss some differences in applying various optical models (i.e, EMA and Cauchy) in scatterometry measurements.
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Yan Chen, Masahiro Yamamoto, Dmitriy Likhachev, Gang He, Akihiro Sonoda, and Vi Vuong "Low-k n&k variation impact on CD accuracy of scatterometry", Proc. SPIE 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 69223R (25 March 2008);

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