State-of-the-art pattern registration tools have to fulfill stringent requirements both in terms of reproducibility and accuracy, as photomask sets are often fabricated in a distributed fashion worldwide and yet have to perfectly match in their respective overlay properties. One option to calibrate the various metrology tools with respect to each other is to utilize a standard, a "golden mask." Alternatively, "self-calibration" strategies can be employed, which offer certain distinct advantages. This concept of calibration is illustrated by several examples. Merit functions are defined to compare the quality of the calibration procedures, and it is shown how they can be used to optimize the calibration with respect to its efficiency in filtering measurement noise. A symmetry based analysis is introduced to reveal systematic weaknesses of potential calibration sequences, also indicating the necessary steps to overcome these problems. An extension of the theory is given that allows to suppress a certain class of systematical errors, and it is studied under which conditions it can be applied.

Date Published: 11 May 2009
PDF: 12 pages
Proc. SPIE 7379, Photomask and Next-Generation Lithography Mask Technology XVI, 737914 (11 May 2009);

Published in SPIE Proceedings Vol. 7379:
Photomask and Next-Generation Lithography Mask Technology XVI
Kunihiro Hosono, Editor(s)