Immersion Effects on Lithography System Performance

摘要

The immersion effects on lithography-system performance have been investigated using a ASML TWINSCAN® XT:1250Di immersion-ArF scanner (NA=0.85) and Tokyo Electron CLEAN TRACK® ACT12 at IMEC. Effects of immersion-induced-temperature change and effects of material-top surface are discussed in this paper. The wafer-stage temperature is measured during the leveling-verification tests and compared with the observed residual-focus-error change. The results indicate that stage-temperature change under an immersion environment can induce a focus change. In this paper, it was proved that the improved-temperature-control stage is effective to mitigate the immersion-specific focus change. The immersion effect on overlay is also investigated as a function of material top surface. It was demonstrated that the effect of material-receding-contact angles on the grid-residual errors (non-correctable errors) is small in the latest-immersion-hardware configuration of the scanner. However, there was a tendency that material with a smaller-receding-contact angle has a larger-wafer scaling although it is a correctable parameter. This can be caused by the first-layer wafer shrinkage due to more water evaporation on the more-hydrophilic surface. The immersion effect on scanner-dynamic performance is then investigated by changing the material-top surface and the scan speed of the scanner. It was turned out that the scan synchronization is not much affected by differences of material receding-contact-angles for the new configuration of the scanner. Moving-standard deviation of the synchronization error in scanning direction (y-direction) is slightly more affected by increased scanning speed, although it stays within specification even at a maximum scan speed of 500 mm/sec. Finally the immersion effects on resist-profile uniformity are examined. It was found that lower-leaching-film stacks (with a top coat or a lower leaching resist) seem to mitigate the variation of resist-profile uniformity.