Aluminum Electromigration Lifetime Variations with Linewidth: The Effects of Changing Stress Conditions

The electromigration behavior of aluminum in films deposited by In-Source evaporation has been examined for films with widths ranging from 2 to 5 ¿m and lengths ranging from 30-80 cm. The linewidth dependence of the lifetime was obtained for films subjected to steady direct current stressing as well as for films subjected to pulsed current stressing. The results indicate that the observed linewidth dependence is a function of the nature of the accelerated aging method employed. Those samples subjected to high frequency, (2MHz), low duty cycle pulses showed less linewidth dependence for lifetime than did those subjected to high duty cycle and steady direct current stressing. Measurements utilizing pulse nonlinearity testing show a correlation between the onset of degradation as evidenced by a change in the thermal time constant, and the nature of the applied current stress tests is proposed which may more accurately predict metallization lifetime under actual use conditions.