Current and resistivity dependence of electromigration from a statistical analysis of metallization failure data

Abstract

The time-to-failure among indentically produced linear metallization tracks deposited on a single wafer has been found to vary when they are subjected to current stress at a temperature of 270°C. This variation is accounted for by the statistical variation in resistivity and cross-sectional area and hence current density among the indentically produced tracks. The variation in cross-sectional area is principally caused by local over or under etching and mask misalignment during exposure. Resistivity variation may be due to the random introduction of defects and vacancies during deposition. Statistical distributions are formulated for the variations in resistance and time-to-failure and these fit the experimental data well. From such distributions, the exponent of the current dependence has been found to be 2 for plain tracks and 2.14 for stepped tracks and for both cases linearly dependent on the resistivity.