13 May 2013 Simulation based optimization of scatterometric signatures by designed near field structures
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Abstract
Scatterometry is a well-established optical metrology method used in research as well as in industrial applications to precisely characterize small structures. The method is based on a comparison of the measured scattered light field to the rigorously simulated scattered light field based on a model of the real structure. Although in recent time this method has been steadily improved and extended to characterize structures down to sub-lambda size, the sensitivity towards the parameters of interest is generally decreasing for smaller structures, which makes the characterization more and more difficult. Opposed to other efforts based on changing the measurement configuration or combining different measurement methods, we have chosen to address the fundamental cause of this loose of information: As known from theory the electromagnetic near field is directly dominated by currents and charge-separations in the illuminated structure, while the far field is produced by its corresponding near field and is not directly linked to the charges and currents induced in the structure. For that reason the transition from the near field to the far field, which is accessible in a scatterometric measurement, causes information loss about the structure. In our approach we directly influence the near field with the introduction of additional structures in the direct vicinity of the sub-lambda grating to be characterized. With rigorous electromagnetic simulations we optimize the design of these near field structures to increase the information content of the scatterometric signatures which can be detected in the far field region. We show the optimization of scatterometric signatures for a silicon line grating and compare the gain of information obtained by the near field design. Understanding the influence of the near field on the scatterometric signatures can help to address the increasing demand on quality management caused by the constant miniaturization in industrial applications.
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V. Ferreras Paz, V. Ferreras Paz, K. Frenner, K. Frenner, W. Osten, W. Osten, } "Simulation based optimization of scatterometric signatures by designed near field structures", Proc. SPIE 8789, Modeling Aspects in Optical Metrology IV, 87890S (13 May 2013); doi: 10.1117/12.2020569; https://doi.org/10.1117/12.2020569
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