Overlay error budgets for a high-throughput SCALPEL system

The implementation of SCALPEL for post-optical production lithography generations, including mix-and-match options, involves unique issues in alignment and overlay. SCALPEL's use of stitching modifies the familiar analysis of overlay errors. Stitching may produce a small, localized image-placement error, but it creates negligible fixed image distortion. It also allows sub-field placement adjustments to correct some of the distortion errors in mix-and-match optimization. SCALPEL can use existing off-axis alignment sensor technologies, but a preferred electron back-scatter technique offers robustness and versatility. For high-throughput operation, a form of global alignment similar to that of full-field tools is likely, but implemented with the dynamic alignment mark scanning capabilities available in the writing strategy. Finally, it is expected that wafer-heating correction issues will factor into the coupled development of optimum writing and alignment strategies, possibly introducing novel mixed operating modes of fine alignment. We shall discuss our present overlay error budgets, representing these unique challenges and opportunities for developing a high-throughput SCALPEL tool.