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Ever-tightened design rules and ensuing aggressive OPC features pose significant challenges for wafer fabs in the pursuit
of compelling yield and productivity. The introduction of advanced reticles considerably augments the mask error
enhancement factor (MEEF) where progressive defects or haze, induced by repeated laser exposure, continue to be a
source of reticle degradation threatening device yield. High resolution reticle inspection now emerges as a rescue venue
for wafer fabs to assure their photomask integrity during intensive deep UV exposure. Integrated in the high resolution
reticle inspection, a MEEF-driven lithographic detector "Litho3" can be used run-time to group critical defects into a
single bin. Previous investigations evinced that critical defects identified by such detector were directly correlated with
defects printed on wafer, upon which fab users can make cogent decisions towards reticle disposition and cleaning
therefore reduce cycle time.
One of the challenges of implementing such detector resides in the lengthy set up of user-defined parameters, from
practitioner standpoint, can considerably extend reticle inspection time and inevitably delay production. To overcome
this, an automatic simulation program has been written to optimize Litho3 settings based off a pre-inspection in which
only default Litho3 values are needed. Upon completion of the pre-inspection, the images are then scanned and
processed to extract the optimal Litho3 parameters that are largely dependent upon the feature size characteristics and
local MEEF. Thus optimized Litho3 parameters can then be input into the recipe set up to enable a real-time inspection,
as such fab user can timely access the defect criticality information for subsequent defect disposition. In the interest of
printability validation, such defect information and associated coordinates can be passed onto defect review via XLINK
for further analysis. Corresponding MEEF values are also available for all identified critical defects. Through this
automatic program the set up time for Litho3 can be reduced by up to 90%.
For high capacity production fabs running a pre-inspection is deemed infeasible; this automatic optimization program
can also serve as a direct interpretation of any regular reticle inspection even without invoking Litho3 set up, yet in the
end provide output in the context of defect criticality. Results acquired from this program were found in good accordance
with those from the real-time Litho3 inspection, for both critical and non-critical layers of 90 nm design node. Such
capability allows detailed study of defect criticality in relation to its size, defect optical transmittance, residing surface,
its proximity to a printing pattern as well as lithography parameters such as NA and sigma. Furthermore, coupling this
automatic program with high resolution inspection also assists in determining lithography process window and an indepth
comprehension of defect progression mechanism.
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