Drawbacks to using NIST electromigration test structures to test bamboo metal lines

In this work the applicability of NIST electromigration test patterns when used to test “bamboo” metal lines is discussed. Wafer level tests on passivated and nonpassivated samples employing the Al-1%Si/TiN/Ti metallization scheme were performed. Straight metal lines 1000 μm long and 0.9 μm or 1.4 μm wide were tested at two different current densities, j=3 MA/cm2 and J=4.5 MA/cm2, keeping the stress temperature at T=230°C. The failures occurred mainly in the end segment areas and hindered the evaluation of the electromigration resistance of the test lines. In order to avoid this problem, completely different test patterns containing a number of geometrical variations should be defined