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The difficulties encountered during lithography of state-of-the-art 2D patterns are
formidable, and originate from the fact that deep sub-wavelength features are being
printed. This results in a practical limit of k1 ≥0.4 as well as a multitude of complex
restrictive design rules, in order to mitigate or minimize lithographic hot spots. An
alternative approach, that is gradually attracting the lithographic community's
attention, restricts the design of critical layers to straight, dense lines (a 1D grid), that
can be relatively easily printed using current lithographic technology. This is then
followed by subsequent, less critical trimming stages to obtain circuit functionality.
Thus, the 1D gridded approach allows hotspot-free, proximity-effect free lithography
of ultra low- k1 features. These advantages must be supported by a stable CD control
mechanism. One of the overriding parameters impacting CDU performance is photo
mask quality. Previous publications have demonstrated that IntenCDTM - a novel,
mask-based CDU mapping technology running on Applied Materials' Aera2TM aerial
imaging mask inspection tool - is ideally fit for detecting mask-based CDU issues in
1D (L&S) patterned masks for memory production. Owing to the aerial nature of
image formation, IntenCD directly probes the CD as it is printed on the wafer.
In this paper we suggest that IntenCD is naturally fit for detecting mask-based CDU
issues in 1D GDR masks. We then study a novel method of recovering and
quantifying the physical source of printed CDU, using a novel implementation of the
IntenCD technology. We demonstrate that additional, simple measurements, which
can be readily performed on board the Aera2TM platform with minimal throughput
penalty, may complement IntenCD and allow a robust estimation of the specific
nature and strength of mask error source, such as pattern width variation or phase
variation, which leads to CDU issues on the printed wafer. We finally discuss the
roles played by IntenCD in advanced GDR mask production, starting with tight
control over mask production process, continuing to mask qualification at mask shop
and ending at in-line wafer CDU correction in fabs.
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