Practical considerations for Wafer-Level Electromigration Monitoring in high volume production
South Lake Tahoe, CA(2006)
Abstract
Reliability monitoring is an important part of process control in high volume production. For the back end of line (BEOL), a wafer-level electromigration (WL-EM) test is usually the method of choice to get a good indication of process variation (Schuster, 2001). In this work we present practical normalization procedures to ensure an appropriate wafer to wafer comparison which is independent of variation in cross-sectional area as well as of the initial resistance spread. The measurements have been performed on a commercially available 300mm multi-side probe station, using custom-made software to implement the current ramp and resistance measurement. The test conditions were achieved through Joule heating; the test structures used were 800mum long single lines (no vias) in metal 1 to metal 3, varying in width from 0.14mum to 10mum. After several normalization steps described in this paper we found a strong activation energy dependence on line width. This dependence was linked to issues in temperature investigation using a constant TCR value. Additionally we found a simple way to estimate the current density exponent by optimizing the Arrhenius relation. Overall a comprehensive guideline for constant current WL-EM is presented
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Key words
current density,electromigration,reliability,semiconductor device manufacture,0.14 to 10 micron,300 mm,arrhenius relation,joule heating,activation energy dependence,current density exponent,current ramp,custom-made software,high volume production,initial resistance spread,multiside probe station,resistance measurement,wafer-level electromigration monitoring,process control,process variation,activation energy,cross sectional area
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