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High Resolution reticle inspection is well-established as a proven, effective, and efficient means of detecting yield-limiting
mask defects as well as defects which are not immediately yield-limiting yet can enable manufacturing process
improvements. Historically, RAPID products have enabled detection of both classes of these defects. The newly-developed
Wafer Plane Inspection (WPI) detector technology meets the needs of some advanced mask manufacturers to
identify the lithographically-significant defects while ignoring the other non-lithographically-significant defects. Wafer
Plane Inspection accomplishes this goal by performing defect detection based on a modeled image of how the mask
features would actually print in the photoresist. This has the effect of reducing sensitivity to non-printing defects while
enabling higher sensitivity focused in high MEEF areas where small reticle defects still yield significant printing defects
on wafers.
WPI is a new inspection mode that has been developed by KLA-Tencor and is currently under test with multiple
customers. It employs the same transmitted and reflected-light high-resolution images as the industry-standard high-resolution
inspections, but with much more sophisticated processing involved. A rigorous mask pattern recovery
algorithm is used to convert the transmitted and reflected light images into a modeled representation of the reticle.
Lithographic modeling of the scanner is then used to generate an aerial image of the mask. This is followed by resist
modeling to determine the exposure of the photoresist. The defect detectors are then applied on this photoresist plane so
that only printing defects are detected. Note that no hardware modifications to the inspection system are required to
enable this detector. The same tool will be able to perform both our standard High Resolution inspections and the Wafer
Plane Inspection detector.
This approach has several important features. The ability to ignore non-printing defects and to apply additional effective
sensitivity in high MEEF areas enables advanced node development. In addition, the modeling allows the inclusion of
important polarization effects that occur in the resist for high NA operation. This allows for the results to better match
wafer print results compared to alternate approaches. Finally, the simulation easily allows for the application of
arbitrary illumination profiles. With this approach, users of WPI can make use of unique or custom scanner illumination
profiles. This allows the more precise modeling of profiles without inspection system hardware modification or loss of
company intellectual property.
This paper examines WPI in Die:Die mode. Future work includes a review of Die:Database WPI capability.
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