The linewidth measurement capability of the model-based library (MBL) matching technique was evaluated experimentally. This technique estimates the dimensions and shape of a target pattern by comparing a measured SEM image profile to a library of simulated line scans. The simulation model uses a non-linear least squares method to estimate pattern geometry parameters. To examine the application of MBL matching in an advanced lithography process, a focus-exposure matrix wafer was prepared with a leading-edge immersion lithography tool. The evaluation used 36 sites with target structures having various linewidths from 45 to 200 nm. The measurement accuracy was evaluated by using an atomic force microscope (AFM) as a reference measurement system. The results of a first trial indicated that two or more solutions could exist in the parameter space in MBL matching. To solve this problem, we obtained a rough estimation of the scale parameter in SEM imaging, based on experimental results, in order to add a constraint in the matching process. As a result, the sensitivity to sidewall variation in MBL matching was improved, and the measurement bias was reduced from 22.1 to 16 nm. These results indicate the possibility of improving the CD measurement capability by applying this tool parameter appropriately.

Date Published: 24 March 2008
PDF: 11 pages
Proc. SPIE 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 69221T (24 March 2008); doi: 10.1117/12.772088

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