Minimizing overlay measurement errors

Nigel P. Smith; Gary R. Goelzer; Michael Hanna; Patrick M. Troccolo

doi:10.1117/12.148972

4 August 1993 Minimizing optical overlay measurement errors

Nigel P. Smith, Gary R. Goelzer, Michael Hanna, Patrick M. Troccolo

Proceedings Volume 1926, Integrated Circuit Metrology, Inspection, and Process Control VII; (1993) https://doi.org/10.1117/12.148972
Event: SPIE'S 1993 Symposium on Microlithography, 1993, San Jose, CA, United States

Abstract

This paper is a continuation of our earlier work which investigated means of reducing Tool Induced Shift (TIS) in overlay tools. In this paper we show that there can be significant errors in the measurements from a tool that shows zero TIS. These errors arise from proximity effects within the measurement target. Improving the resolution of the instrument reduces these errors, although this is counter to the current trend of the industry. We present the results of detailed comparisons of two measurement objectives. These have the same magnification but different numerical aperture so that they differ in resolution and depth of field. We will show that the lowest measurement error are achieved by acquiring all images from a common focal plane, even when the target marks are displaced vertically by more than 2 micrometers . Both objectives perform equally well, although we had expected that increasing the depth of field would provide benefits. The data shows that increasing the resolution of the microscope will allow the high accuracy and precision required for the future to be achieved without sacrificing an ability to measure the deepest structures likely to be met in these processes.

Citation Download Citation

Nigel P. Smith, Gary R. Goelzer, Michael Hanna, and Patrick M. Troccolo "Minimizing optical overlay measurement errors", Proc. SPIE 1926, Integrated Circuit Metrology, Inspection, and Process Control VII, (4 August 1993); https://doi.org/10.1117/12.148972

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