A study of electromigration in aluminum and aluminum-silicon thin film resistors using noise technique

Aluminum and aluminum-silicon (1%) thin film resistors, with and without an Si 3N 4 passivating layer, were characterized by means of noise measurements in a low-frequency range (10 mHz-1 Hz), during electromigration. Activation energies for Al test patterns were found to be E a =0.64 eV and E ap =0.88 eV for non-passivated and passivated samples respectively, whereas for AlSi (1%) test patterns, E a =0.94 eV and E ap =1.07 eV. After noise measurements the samples were subjected, to the same stress conditions, current density and temperature, as during the noise measurements for a period of 165 h. Then both percentage resistance variation and damage in the stripes were evaluated and correlated with the power spectral density of resistance fluctuations. As a result, by means of noise technique one is able to obtain activation energy values that are consistent with the subsequent modification undergone by the resistors, so that activation energies determined in this way can be used as “true” reliability parameters. The time interval necessary to obtain such parameters (about 10 h for each series) is much shorter than those required by traditional techniques.