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Proceedings Paper

Effect of metrology time delay on overlay APC
Author(s): Alan Carlson; Debra DiBiase
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Paper Abstract

The run-to-run control strategy of lithography APC is primarily composed of a feedback loop as shown in the diagram below. It is known that the insertion of a time delay in a feedback loop can cause degradation in control performance and could even cause a stable system to become unstable, if the time delay becomes sufficiently large. Many proponents of integrated metrology methods have cited the damage caused by metrology time delays as the primary justification for moving from a stand-alone to integrated metrology. While there is little dispute over the qualitative form of this argument, there has been very light published about the quantitative effects under real fab conditions - precisely how much control is lost due to these time delays. Another issue regarding time delays is that the length of these delays is not typically fixed - they vary from lot to lot and in some cases this variance can be large - from one hour on the short side to over 32 hours on the long side. Concern has been expressed that the variability in metrology time delays can cause undesirable dynamics in feedback loops that make it difficult to optimize feedback filters and gains and at worst could drive a system unstable. By using data from numerous fabs, spanning many sizes and styles of operation, we have conducted a quantitative study of the time delay effect on overlay run- to-run control. Our analysis resulted in the following conclusions: (1) There is a significant and material relationship between metrology time delay and overlay control under a variety of real world production conditions. (2) The run-to-run controller can be configured to minimize sensitivity to time delay variations. (3) The value of moving to integrated metrology can be quantified.

Paper Details

Date Published: 12 July 2002
PDF: 16 pages
Proc. SPIE 4692, Design, Process Integration, and Characterization for Microelectronics, (12 July 2002); doi: 10.1117/12.475656
Show Author Affiliations
Alan Carlson, New Vision Systems (United States)
Debra DiBiase, New Vision Systems (United States)

Published in SPIE Proceedings Vol. 4692:
Design, Process Integration, and Characterization for Microelectronics
Alexander Starikov; Alexander Starikov; Kenneth W. Tobin, Editor(s)

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