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Proceedings Paper

Simultaneous overlay and CD measurement for double patterning: scatterometry and RCWA approach
Author(s): Jie Li; Zhuan Liu; Silvio Rabello; Prasad Dasari; Oleg Kritsun; Catherine Volkman; Jungchul Park; Lovejeet Singh
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Paper Abstract

As optical lithography advances to 32 nm technology node and beyond, double patterning technology (DPT) has emerged as an attractive solution to circumvent the fundamental optical limitations. DPT poses unique demands on critical dimension (CD) uniformity and overlay control, making the tolerance decrease much faster than the rate at which critical dimension shrinks. This, in turn, makes metrology even more challenging. In the past, multi-pad diffractionbased overlay (DBO) using empirical approach has been shown to be an effective approach to measure overlay error associated with double patterning [1]. In this method, registration errors for double patterning were extracted from specially designed diffraction targets (three or four pads for each direction); CD variation is assumed negligible within each group of adjacent pads and not addressed in the measurement. In another paper, encouraging results were reported with a first attempt at simultaneously extracting overlay and CD parameters using scatterometry [2]. In this work, we apply scatterometry with a rigorous coupled wave analysis (RCWA) approach to characterize two double-patterning processes: litho-etch-litho-etch (LELE) and litho-freeze-litho-etch (LFLE). The advantage of performing rigorous modeling is to reduce the number of pads within each measurement target, thus reducing space requirement and improving throughput, and simultaneously extract CD and overlay information. This method measures overlay errors and CDs by fitting the optical signals with spectra calculated from a model of the targets. Good correlation is obtained between the results from this method and that of several reference techniques, including empirical multi-pad DBO, CD-SEM, and IBO. We also perform total measurement uncertainty (TMU) analysis to evaluate the overall performance. We demonstrate that scatterometry provides a promising solution to meet the challenging overlay metrology requirement in DPT.

Paper Details

Date Published: 23 March 2009
PDF: 9 pages
Proc. SPIE 7272, Metrology, Inspection, and Process Control for Microlithography XXIII, 727207 (23 March 2009); doi: 10.1117/12.814706
Show Author Affiliations
Jie Li, Nanometrics Inc. (United States)
Zhuan Liu, Nanometrics Inc. (United States)
Silvio Rabello, Nanometrics Inc. (United States)
Prasad Dasari, Nanometrics Inc. (United States)
Oleg Kritsun, GLOBALFOUNDRIES Inc. (United States)
Catherine Volkman, GLOBALFOUNDRIES Inc. (United States)
Jungchul Park, Spansion Inc. (United States)
Lovejeet Singh, Spansion Inc. (United States)

Published in SPIE Proceedings Vol. 7272:
Metrology, Inspection, and Process Control for Microlithography XXIII
John A. Allgair; Christopher J. Raymond, Editor(s)

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