Diffraction Based Overlay Metrology for Double Patterning Technologies
2009
The extension of optical lithography to 32nm and beyond is made possible by Double Patterning Techniques
(DPT) at critical levels of the process flow. The ease of DPT implementation is hindered by increased significance of
critical dimension uniformity and overlay errors. Diffraction-based overlay (DBO) has shown to be an effective
metrology solution for accurate determination of the overlay errors associated with double patterning [1, 2] processes. In
this paper we will report its use in litho-freeze-litho-etch (LFLE) and spacer double patterning technology (SDPT),
which are pitch splitting solutions that reduce the significance of overlay errors. Since the control of overlay between
various mask/level combinations is critical for fabrication, precise and accurate assessment of errors by advanced
metrology techniques such as spectroscopic diffraction based overlay (DBO) and traditional image-based overlay (IBO)
using advanced target designs will be reported. A comparison between DBO, IBO and CD-SEM measurements will be
reported. . A discussion of TMU requirements for 32nm technology and TMU performance data of LFLE and SDPT
targets by different overlay approaches will be presented.
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