Novel Lithography Approach Using Feed-Forward Mask-Based Wafer CDU Correction Increases Fab Productivity and Yield

摘要

The extension of ArF lithography through reduced k_1, 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? 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? 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.