Monitoring printing fidelity with image correlation measurements on the CD SEM

Abstract

A promising use for image and waveform correlation measurements now possible on modern CDSEMs is to monitor pattern fidelity in printing for multiple structural dimensions. This work explores some ofthese possibilities specifically for image correlation. Two different CDSEM-based pattern recognition engines and off-line image correlation with several image enhancement techniques are examined. The printing fidelity of an unassisted cross as a function of stepper focus and dose is studied because the variations of the structural details demonstrate many of the issues of concern in lithography today. Strategies for extracting the most information with the least beam writing are also explored. In some examples the pattern recognition score is directly interpretable in terms ofprinting fidelity. With additional calibration overhead associated with a particular lithography process, scores can be interpreted in terms ofprinting variables such as defocus and dose. The conflict in goals for using image correlation for navigation versus monitoring pattern fidelity is also discussed.