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As double patterning techniques such as spacer double/quadruple patterning mature, ArF water immersion lithography
is expected to be applied down to the 1x nm hp node or beyond. This will necessitate precise process control solutions
to accommodate extremely small process windows. In the case of spacer double/quadruple patterning in particular, CD
uniformity of the final feature is strongly related to the lithography performance of the initial pre-spacer feature. CD
uniformity of the resist image is affected by many sources. In the case of the exposure tool, CD error on the reticle, as
well as exposure dose and focus errors are the key factors. For the resist process, heterogeneity of the stacked resist film
thickness, post exposure bake (PEB) plate temperature, and development all have an impact. Furthermore, the process
wafer also has error sources that include under-layer non-uniformities or wafer flatness. Fortunately, the majorities of
these non-uniformities are quite stable in a volume production process.
To improve and maintain the CD uniformity, a technique to calculate exposure dose and focus correction values
simultaneously using the measured resist image feature was reported previously [1]. Further, a demonstration of a
correction loop using a neural network calculation model was reported in SPIE 2010 [2], and the corrected CD
uniformity was less than 1.5 nm (3 sigma) within a wafer. For further improvement, a demonstration of precise dose
and focus control using high order field-by-field correction was then reported at SPIE 2011[3]. In that work, the interand
intra-field CD uniformities reported were less than 1 nm (3 sigma) respectively. A key aspect of this method is the
simultaneous compensation of dose and focus offsets, which successfully maximizes the process margin of a target
pattern. The Nikon CDU Master then derives the optimal control parameters for each compensation function in the
scanner using the exposure dose and focus correction data, with the NSR-S620 scanner having the capabilities to also
control higher order dose and focus distribution. This high degree of controllability ultimately enables precise
correction of the complicated CD error distribution that is caused by heterogeneities in the process.
In this work, this correction concept was expanded to include contact hole CD uniformity optimization and quick
correction method using the AMI-3500 auto macro inspection tool. A 3D contour analysis method is used for contact
hole CDs measured by CD-SEM. The contact hole CD is then corrected directly without using any other monitor
pattern features. Further, using the Nikon AMI-3500 system, it is possible to successfully extract the adjustment
components using the optical diffraction image. Since the AMI measurement time is very quick (just a few minutes), a
regular correction loop using the AMI may be a promising solution for system auto correction in an IC manufacturing
facility.
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