Overlay accuracy: a metal layer study

Andrew Habermas; Bradley A. Ferguson; Joel L. Seligson; Elyakim Kassel; Pavel Izikson

doi:10.1117/12.473466

16 July 2002 Overlay accuracy: a metal layer study

Andrew Habermas, Bradley A. Ferguson, Joel L. Seligson, Elyakim Kassel, Pavel Izikson

Proceedings Volume 4689, Metrology, Inspection, and Process Control for Microlithography XVI; (2002) https://doi.org/10.1117/12.473466
Event: SPIE's 27th Annual International Symposium on Microlithography, 2002, Santa Clara, California, United States

Abstract

While overlay precision has received much focus in the past, overlay accuracy has become more significant with shrinking process budgets. One component of accuracy is the difference between pre-etch (DI) and post-etch (FI) overlay, which is a function of wafer processing parameters. We investigated a specific case of overlay between metal and contact layers of a 0.16 mm SRAM process. This layer was chosen because a significant amount of wafer contraction was observed between DI and FI, resulting in as much as 30nm of DI-FI overlay difference. The purpose of the study was to characterize the systematic DI-FI differences and gain understanding of the wafer processing parameters that affect the DI-FI differences. A designed experiment showed how certain overlay mark widths were less sensitive to processing parameters. AFM profiles of the prior-level overlay marks identified issues with mark widths 1.0um or smaller. By performing localized etches on the inner vs. outer marks of the overlay targets, it was noted that the majority of the wafer contraction was induced by etching the outer (prior level) mark. Production measurements at photo and etch showed the wafer contraction to be fairly stable over a month timeframe and independent of device and exposure tool, though large fluctuation shifts in wafer contraction were noted over a nine-month period. The methods used in this study can be helpful in understanding other DI-FI processing issues.

Citation Download Citation

Andrew Habermas, Bradley A. Ferguson, Joel L. Seligson, Elyakim Kassel, and Pavel Izikson "Overlay accuracy: a metal layer study", Proc. SPIE 4689, Metrology, Inspection, and Process Control for Microlithography XVI, (16 July 2002); https://doi.org/10.1117/12.473466

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