This article describes how an uncertainty analysis may be performed on a scatterometry measurement. A method is outlined for propagating uncertainties through a least-squares regression. The method includes the propagation of the measurement noise as well as estimates of systematic effects in the measurement. Since there may be correlations between the various parameters determined by the measurement, a method is described for visualizing the uncertainty in the extracted profile. The analysis is performed for a 120 nm pitch grating, consisting of photoresist lines 120 nm high, 45 nm critical dimension, and 88◦ sidewall angle, measured with a spectroscopic rotating compensator ellipsometer. The results suggest that, while scatterometry is very precise, there are a number of sources of systematic errors that limit its absolute accuracy. Addressing those systematic errors may significantly improve scatterometry measurements in the future.
Proceedings Title: Metrology, Inspection, and Process Control for Microlithography XXIII
Conference Dates: February 22-27, 2009
Conference Location: San Jose, CA
Pub Type: Conferences
accuracy, optical critical dimension metrology, scatterometry, traceability, uncertainty analysis