In this paper we will report on the most recent immersion scanner innovations to improve scanner matching overlay. These are realized by improvements in e.g. optical column distortion, wafer alignment and system-metrology. We will elaborate on scanner solutions for wafer handling/chucking of warped wafers. Furthermore, to enable cost-of-ownership reduction, system design implementations driving larger scanner productivity (wafer per hour) will be presented.
ASML’s 300mm scanner-systems are built on the TWINSCAN (XT/NXT) platform and yield high productivity levels for dry as well as immersion litho-scanners. NXT:1980Di immersion scanners yield productivity levels as high as 275wph while maintaining the overlay accuracy. The NXT:1980Di can be equipped with a new leveling mode that results in a significant reduction of the time that is spent on measuring the wafer focus height map. In the new leveling mode the focus height map is measured employing the full width of the level sensor and thereby minimizing the number of leveling scans. In this paper we describe the implementation of the LIL-method in the TWINSCAN platform design. Here, we report on the focus / leveling performance for both test as well as customer product wafers, and present a productivity outlook on the performance gain for a selected set of exposure use-cases.
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