Micrometer-width damascene copper conductors at ≥10 MA/cm2

We have applied high amplitude (~10 MA/cm²) alternating current (AC) at 100 Hz and direct current (DC) to copper interconnect lines with widths in the few-micrometer range covered with a thick layer of SiO₂. Under our test conditions of Joule heating, the lines typically fail with lifetimes from 100 to 100,000 s, with a well-defined correlation between cyclic temperature range and the logarithm of lifetime. Post-test scanning electron microscopy (SEM) examination reveals substantial voiding and grain growth, particularly in AC tests at the higher cyclic temperature ranges. Lines without the full SiO₂ constraint fail much sooner than the constrained lines for similar cyclic temperature ranges. The less-constrained lines also had surface contours that were not present on the fully constrained lines. Optical observations during the tests indicate that the void generation behavior appears different during the AC and DC tests, with a saturation behavior occurring in the AC tests, sometimes long before failure. The distributed void density in our AC tests was at least as great as that in the DC tests.