This paper presents a new highly sensitive scatterometry based Probe-Pattern Grating (PPG) focus monitor and its printing assessment on an advanced exposure tool. The high sensitivity is achieved by placing transparent lines spaced at the strong focus spillover distance from the centerline of a 90 degree phase-shifted probe line that functions as an interferometer detector. The monitor translates the focus error into the probe line trench depth, which can be measured by scatterometry techniques. The sensitivity of the defocus measurement through scatterometry calibration is around 1.1nm defocus / nm trench depth. This result indicates that the PPG focus monitor from a single wafer focus setting can detect the defocus distance to well under 0.05 Rayleigh Units.

Date Published: 24 March 2008
PDF: 12 pages
Proc. SPIE 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 692225 (24 March 2008); doi: 10.1117/12.773191

Published in SPIE Proceedings Vol. 6922:
Metrology, Inspection, and Process Control for Microlithography XXII
John A. Allgair; Christopher J. Raymond, Editor(s)