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2 June 2000 Improving stigmation control of the CD-SEM
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Production fads currently rely on CD-SEM metrology for linewidth control in lithography and etch. The quality of the measurement data is therefore directly tied to the quality of the SEM imaging and that of the electron beam. Experience has shown that even within a 12 hour period, the beam alignment can drift sufficiently to cause a shift of several nanometers in the measured CD. Furthermore, the alignment of the electron beam has traditionally been performed manually, with the quality of the SEM image then being dependent on the judgement of the operator. While this has been adequate in the past, the drive towards ever smaller geometries means that even slight changes in the beam spot can lead to unacceptable variation in the CD measurements. In this paper, we will describe how a more consistent electron beam can be achieved by obtaining quantitative feedback on its sharpness and eccentricity. Using this quantitative information removes the subjective nature of the manual beam alignment and requires less training on part of the users. Furthermore, this procedure results in beam conditions that are at least as good as the alignment performed by an experienced operator, and in fact generally improves the alignment when compared to that obtained by subjective judgement of the image quality. Once a baseline is established, SPC charts for the sharpness and eccentricity values can be used to track tool performance. If either value falls out of a specified range, the system can be flagged as having a problem and efforts to restore the image resolution can begin immediately, reducing the risk of erroneous measurements and thus preventing lots from being misprocessed or mistakenly reworked.
© (2000) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Bryan Choo, Shobhana Punjabi, Carmen Morales, Bhanwar Singh, Michael K. Templeton, and Mark P. Davidson "Improving stigmation control of the CD-SEM", Proc. SPIE 3998, Metrology, Inspection, and Process Control for Microlithography XIV, (2 June 2000);


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