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Requirements coming from the customer, as well as internal needs of improvements consequent to the increasing
complexity of the layout of the newest devices, lead to the necessity of exploring all the potential improvements
achievable at the mask manufacturing inspection process.
A key point to manage for the better DB inspections is that of being able to achieve a proper matching between the
images to be compared, tasks which is accomplished by the tool architecture by means of a pre-swath calibration process
on which the quality of the focus is playing a relevant role. From here the decision to focus on this parameter aiming of
working out and evaluate a different approach to be used to set the scanning focus on the inspection tool moving from
the vendor theory based on the edge speed on a specific test plate to a new one based on intensity measurements into
specific features on a purposely designed test vehicle.
A matter of relevant importance for mask makers, either for the smoothness of the inspection process or for the
homogeneity of the quality of the products being delivered, but on which any tool vendor likes providing official
commitments, is that of correlating the overall performance of similar tools. This was accomplished with the new
approach with two different tools achieving optical images with similar grey scale distributions into the most critical
features. Moreover, the improvement of the matching of the images being compared allows extending the usage of the
tool for products for which the complexity of the layout forced the inspection with different pixels or with more
advanced tools, with a positive impact either on costs or on the cycle time of the masks being delivered.
A careful assessment-verification of the shadowing limitation induced by the frame of the pellicle was another task
successfully carried out with the new methodology, with some improvement regarding the inspectable area.
The extended its usage the wider the field of application will become, but few advantages can be appreciated since the
beginning: the focus will be set on a production like layer, its choice will not be depending on a human decision, it will
be a simple, fast and reliable process runable at any time and at any operating level.
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