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30 December 1999 CD-SEM characterization of reticle-level pattern density effects
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Three 4X test reticles for 0.15 - 0.18 micrometer lithography are characterized using a critical-dimension scanning electron microscope (CD-SEM). The reticles, which contain metrology cells of isolated and nested lines, are manufactured with an i-line (365 nm) laser patterning tool and wet etch (reticle A), an e-beam patterning tool and dry etch (reticle B), and an e-beam patterning tool and wet etch (reticle C). We investigate the nature of pattern density-induced CD variations by studying groups of metrology cells with systematically varying linewidths and line spacings. The CD bias between nested and isolated lines is a smoothly increasing function of pattern density on reticles B and C. The CD signatures on reticle B exhibit strong microloading and loading signatures related to the plasma etch process. The bias characteristic on reticle A demonstrates a threshold effect, increasing sharply as the space between adjacent nested lines becomes less than approximately 600 nm. Matching images taken with secondary and backscattered electron spectra support the conclusion that the laser write process is resolution-limited at this pattern density. The SEM data is also compared to data from broad-band optical metrology tools to show that the optical response for dense features becomes unreliable when the feature spacing is less than approximately 600 nm.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Raymond Yip, Mico Chu, Steven Fu, Dave Castro, Waiman Ng, Geoffrey T. Anderson, Micheal J. Sherrill, Norman Chen, and Yao Ching Ku "CD-SEM characterization of reticle-level pattern density effects", Proc. SPIE 3873, 19th Annual Symposium on Photomask Technology, (30 December 1999);

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