Mixing and matching deep-uv step-and-scan with i-line step and repeat

Abstract

This paper reviews all the major aspects of successfully implementing a “mix and match” (Deep-UV/l-line, stepper/scanner) strategy. The resolution and line width-control limits of I-line are quantified for a number of theprocess levels and compared with the capabilities of Deep-UV step-and-scan. This analysis predicts the typicalmix of steppers and scanners in a 256 MBit production line for 250 nm lithography. A step-by-step procedure toachieve and monitor successful matching is reviewed. The procedure begins by defining a “golden system”, which is used to produce reference wafers for the setup and monitoring of all the systems being mixed and matched. The reference wafers are used to ensure that the pre-aligners of the systems are calibrated and that offsets areadapted to allow the transfer of wafers between systems. The wafers are also used to match both wafer-stage gridand exposure-field distortions. The matching of both wafer-grid and stepper-field distortions are reviewed. Theimplementation of stage correction-tables is demonstrated. It is indicated that grid matching to better than 10 nmis achievable. It is also indicated that the dynamic scanning of a step-and-scan system allows the monitoring andcorrection of such typical stepper problems as field magnification and rotation. The critical aspects of multi-fieldmatching between stepper and scanner are analyzed. The key factors that allow the successful overlaying of large, single, scanned fields with multiple, small, stepped fields are reviewed. The total overlay accuracy achieved usingstep-and-scan, and “mix-and-match” is analyzed and demonstrated. © 1995 The Japan Society of Applied Physics.