Optimized registration model for 2:1 stepper field matching

In this study, a large field 1x stepper was matched to an advanced 5x reduction stepper using a 2:1 field matching scheme. The 1x field is a 44 X 22 mm rectangle that is symmetrically aligned to two 22 X 22 mm 5x reduction fields. Overlay measurements were collected at 33 sites per reduction field (or 66 sites per Ultratech field) and the resulting data was analyzed using a modified grid registration model that fully supports the 2:1 matching geometry. Two complementary optimization techniques were developed, the first of which assumes corrective action only on the 1x stepper. The more sophisticated approach supports corrective action on both the 1x and 5x reduction stepper. Next, both techniques were applied to the measured mix-and-match data with the results suggesting a specific set of corrective action that could be applied to the 1x and 5x reduction steppers. Based on these results, it was found that there is a substantial registration benefit to exerting simultaneous corrections on both stepper types as opposed to controlling each stepper individually.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.