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7 December 1994 Optimizing 0.25-um lithography using confocal microscopy
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With a 325 nm confocal microscope including a 0.95 N.A. lens and special threshold algorithms, linewidths to 0.25 micrometers and below are easily imaged without special preparation or harm to the sample. The enhanced resolution of a 325 nm laser system provides a point resolution of approximately 0.2 micrometers . This resolution is achieved by the tightly focused beam and the symmetrical arrangement of the laser and photomultiplier system. The point resolution of a confocal microscope is about 30% better than a conventional scope. In this new study, we have developed a unique 2-stage calibration technique to extend the range of the 325 nm confocal microscope below 0.2 micrometers and were able to use the system to optimize a new 0.25 micrometers lithography process. This paper presents data that qualified at 0.25 micrometers linewidth wafer process using a SiScan IIATM confocal laser microscope (now offered by Optical Associates, Inc.) with a 325 nm imaging laser and correlating the results against other instruments. This was a single layer process where the metrology resolution and precision were shown to be below 5 nm, 3 sigma. Very repeatable results were obtained when using bottom focus and center out measurement algorithms. In addition to wafers processing, this system is an excellent metrology tool for reticles and photomasks.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Robert E. Colgan and Herschel M. Marchman "Optimizing 0.25-um lithography using confocal microscopy", Proc. SPIE 2322, 14th Annual BACUS Symposium on Photomask Technology and Management, (7 December 1994);

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