Electromigration of Ti–Au thin-film conductors at 180° C

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Abstract
A total of 394 test stripes on sapphire substrates were subjected to constant current density [(2−8)×106A/cm2] at 180 °C. Resistance was measured periodically during the test. Sixty‐eight percent of the samples were tested to open‐circuit failure. For the remainder, lifetimes were predicted on the basis of the time‐on‐test and the lifetime statistics of the actual failures. The principal results are as follows: (i) Lifetime varied about as the inverse fourth power of the current density, and was almost independent of the stripe cross‐sectional area per se. (ii) The initial slope of the resistance‐time curve is highly correlated with, and varies inversely as, the lifetime. (iii) The distribution of failure times in this batch of test stripes was very broad, some 10% failing at times less than one‐tenth the median time to failure (MTF), and about 4% at times greater than 10× the MTF. (iv) Estimates of performance under various conditions of service have been made. Operation at current densities above the mid 105 A/cm2 range at 100 °C are not recommended for high‐reliability applications.