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10 May 2005 Application of optical CD for characterization of 70nm dense lines
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CD and line shape control face tougher technology requirements as the drive towards feature size reduction continues down to the 70nm regime. This poses new challenges not only for the lithography process, but also the metrology tool used to qualify the process. Smaller CDs mean smaller tolerances which puts a premium on the ability of metrology to precisely measure these dimensions. Also the trend towards more sampling and entire wafer uniformity mapping to increase yields makes sampling time a consideration. In this paper, we discuss Nanometrics’ Optical CD technology and its application towards the qualification of a scanner exposure system at 140nm pitch resolution (70nm line-spaces). This OCD technique uses normal incidence polarized reflectometry and a form of the Rigorous Coupled-Wave Analysis (RCWA) to do real-time regression. It is a fast and non-destructive method of measuring grating structures which provides complete interfield and intrafield spatially distributed profiles for all fitted OCD parameters. Analysis of spatially distributed data is critical in separating the sources of error that contribute to scanner qualification as a complete litho system Wafers with 70nm dense (L/S=1:1) horizontal and vertical lines of resist on BARC were measured for this study. The fields on these wafers were exposed under various defocus conditions, producing small to large changes in the grating profiles. OCD measurements show good sensitivity to all fitted parameters; CD, CD profiles and film thickness. The focus fingerprint is clearly identified in a wafer uniformity map, amid other inter-field and intra-field contributions. Dynamic repeatability and total test reproducibility metrics are introduced and discussed to quantify the reliability and resolution of the OCD to measure these lines.
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Beverly Cheung, Mircea Dusa, Ton Kiers, and Hugo Cramer "Application of optical CD for characterization of 70nm dense lines", Proc. SPIE 5752, Metrology, Inspection, and Process Control for Microlithography XIX, (10 May 2005);


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