Observation of electromigration at low temperature

Electromigration and mean time-to-failure were investigated for unglassed thin Al stripes over the temperature range of 223 K to 347 K. Thermal effects are minimized by sinking heat from the linestrip through the substrate to a miniature cryogenic refrigerator. This test technique allows the investigation of structure and current interactions while suppressing the effects of an added temperature factor. The circuit was stressed by direct current densities greater than 4*10/sup 6/ A/cm/sup 2/. Electromigration damage was induced in a test stripe at temperatures near 0 degrees C. For the temperature range of 347 K to 267 K, an activation energy of 0.30 eV was calculated, indicating that surface migration is the dominant failure mechanism. For temperatures between 267 K and 223 K, a calculated activation energy of 0.12 eV suggests a different failure mechanism, which was subsequently identified as stripe separation from the substrate.<
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