Optimizing 0.25-um lithography using confocal microscopy

Robert E. Colgan; Herschel M. Marchman

doi:10.1117/12.195829

7 December 1994 Optimizing 0.25-um lithography using confocal microscopy

Robert E. Colgan, Herschel M. Marchman

Proceedings Volume 2322, 14th Annual BACUS Symposium on Photomask Technology and Management; (1994) https://doi.org/10.1117/12.195829
Event: 14th Annual BACUS Symposium on Photomask Technology and Management, 1994, Santa Clara, CA, United States

Abstract

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 IIA^TM 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.

Citation Download Citation

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); https://doi.org/10.1117/12.195829

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