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Proceedings Paper

Stress inspection for overlay characterization
Author(s): David M. Owen
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Paper Abstract

The understanding and control of stresses accumulated during device fabrication is becoming more critical at advanced technology nodes. Within-wafer stress variations cause local wafer distortions which in turn present challenges for the management of overlay and depth of focus during lithography. This paper describes the use of a comprehensive stress inspection technology, the Coherent Gradient Sensing (CGS) interferometer, for the characterization of stress-induced overlay errors. Using CGS, stresses and wafer distortions induced by any upstream process (or series of processes) can be measured, and the relative contribution of stress-induced overlay associated with individual processes can be evaluated. The CGS technology has two key features that enable the application of stress metrology to lithographic overlay: 1) whole-wafer stress measurement with approximately 800,000 points on a 300mm wafer, 2) patterned wafer stress measurement that is highly insensitive to variations in device structures or materials, such that any location within a die or wafer can be characterized without the need for traditional test structures. Fundamentally, thin-plate theory relates the in-plane stresses in a thin film structure to in-plane strains and displacements. The in-plane displacements in the film due to stress are related to the lithographic overlay. The approach presented here demonstrates the relationship between stress gradients are related to in-plane displacements. Data from case-studies are presented that further shows the correlation between in-plane displacements, measured from wafer distortion and traditional measurement of overlay targets.

Paper Details

Date Published: 10 April 2013
PDF: 7 pages
Proc. SPIE 8681, Metrology, Inspection, and Process Control for Microlithography XXVII, 86812T (10 April 2013); doi: 10.1117/12.2025310
Show Author Affiliations
David M. Owen, Ultratech, Inc. (United States)


Published in SPIE Proceedings Vol. 8681:
Metrology, Inspection, and Process Control for Microlithography XXVII
Alexander Starikov; Jason P. Cain, Editor(s)

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