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Traditionally, definition of mask specifications is done completely by the mask user, while characterization of the mask
relative to the specifications is done completely by the mask maker. As the challenges of low-k1 imaging continue to
grow in scope of designs and in absolute complexity, the inevitable partnership between wafer lithographers and mask
makers has strengthened as well. This is reflected in the jointly owned mask facilities and device manufacturers'
continued maintenance of fully captive mask shops which foster the closer mask-litho relationships. However, while
some device manufacturers have leveraged this to optimize mask specifications before the mask is built and, therefore,
improve mask yield and cost, the opportunity for post-fabrication partnering on mask characterization is more apparent
and compelling.
The Advanced Mask Technology Center (AMTC) has been investigating the concept of assessing how a mask images,
rather than the mask's physical attributes, as a technically superior and lower-cost method to characterize a mask. The
idea of printing a mask under its intended imaging conditions, then characterizing the imaged wafer as a surrogate for
traditional mask inspections and measurements represents the ultimate method to characterize a mask's performance,
which is most meaningful to the user. Surrogate wafer print (SWaP) is already done as part of leading-edge wafer fab
mask qualification to validate defect and dimensional performance.
In the past, the prospect of executing this concept has generally been summarily discarded as technically untenable and
logistically intractable. The AMTC published a paper at BACUS 2007 successfully demonstrating the performance of
SWaP for the characterization of defects as an alternative to traditional mask inspection [1]. It showed that this concept is
not only feasible, but, in some cases, desirable.
This paper expands on last year's work at AMTC to assess the full implementation of SWaP as an enhancement to mask
characterization quality including defectivity, dimensional control, pattern fidelity, and in-plane distortion. We present a
thorough analysis of both the technical and logistical challenges coupled with an objective view of the advantages and
disadvantages from both the technical and financial perspectives. The analysis and model used by the AMTC will serve
to provoke other mask shops to prepare their own analyses then consider this new paradigm for mask characterization
and qualification.
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