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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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