Reproducibility of electromigration measurements

The reproducibility of median-time-to-failure (t50) measurements was determined in an interlaboratory experiment in which 11 laboratories and a reference laboratory took part. Each laboratory used a method of its choosing to test equivalent samples under the same conditions of current density and oven temperature. The between-laboratory reproducibility of t50measurements normalized to one metallization temperature was dependent on current-density stress: at 1.0 MA /cm²it was within 15 percent, while at 2.5 MA/cm²it was generally within 50 percent. The primary source for variability is in estimating the temperature rise of the test metallization due to joule heating. Recommendations are given for the design and test of electromigration test structures to improve the reproducibility of t50measurements.