ISI Case Study
Using ISI, a customer correlated the aberration performance of high NA 248 nm scanners with the yield for critical layers. In particular, H/V astigmatism (Z5) was found to vary significantly between lithography tools. On the basis of ISI measurements, the lens astigmatism was adjusted in the field. The was done in one adjustment, and without significantly affecting other aberration terms, as verified by a post move ISI analysis.

As a result of the lens adjustment, the H/V CD bias showed a large improvement, and the yield at critical levels was increased by approximately 10%.

SMI Case Study
Photolithography tools often exhibit out of specification CD behavior caused by ‘hidden’ illuminator problems. Many illuminator set-up errors or aging phenomena are not detectable by standard acceptance tests. SMI gives a rapid check of illuminator health. In this example, SMI was used to detect a profile asymmetry that led to out of spec CD and in particular to line end shortening on a critical layer. In addition to the intensity profile, SMI provides many illuminator parameters that can be fed directly into photolithography simulators to find the optimum settings for a particular structure.