Novel lithography approach using feed-forward mask-based wafer CDU correction increase fab productivity and yield
2009
The extension of ArF lithography through reduced k1, immersion and double patterning techniques makes lithography a
difficult challenge. Currently, the concept of simple linear flow from design to functional photo-mask is being replaced
by a more complex scheme of feedback and feed-forward loops which have become part of a complex computational
lithography scheme. One such novel lithography concept, called "holistic lithography", was recently introduced by
ASML, as a scheme that makes the lithography process a highly efficient solution for the scaled down geometries. This
approach encourages efficient utilization of computational lithography and the use of feed-forward and feed-back critical
dimension (CD) and overlay correction loops. As sub-nanometer feature dimensions are reached for 3x nodes, with k1
reaching the optics limitations, Mask error enhancement factor (MEEF) values grow fast, thus making mask uniformity
fingerprint and degradation throughout its life time a significant factor in printed CDU on the wafer. Whereas the
consensus is on the need for growing density of intra-field data, traditional critical dimension scanning electron
microscope (CDSEM) Feed backward loops to the litho-cell become unsuitable due to the high density CD measurement
requirements. Earlier publications proposed implementing the core of the holistic lithography concept by combining two
technologies: Applied Material's IntenCD TM and ASML DoseMapper . IntenCD metrology data is streamed in a feedforward
fashion through DoseMapper and into the scanner, to create a dose compensation recipe which improves the
overall CDU performance. It has been demonstrated that the IntenCD maps can be used to efficiently reduce intra-field
printed CDU on printed wafers.
In this paper we study the integration concept of IntenCD and DoseMapper in a production environment. We implement
the feed-forward concept by feeding IntenCD inspection data into DoseMapper that is connected to ASML's
TWSINCAN TM XT:1900i scanner. We apply this concept on printed wafers and demonstrate significant reduction in
intra-field CDU. This concept can effectively replace the feedback concept using send-ahead wafers and extensive
CDSEM measurements. The result is a significant cost saving and fab productivity improvement. By routinely
monitoring mask-based CDU, we propose that all photo-induced transmission degradation effects can be compensated
through the same mechanism. The result would be longer intervals between cleans, improved mask lifetime, and better
end of line device yield.
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