The electromigration lifetime determined from the minimum time to failure in an acceleration test

Electromigration (EM) acceleration testing was performed on AlSiCu lines in 1550 samples, each having a length of 6 mm, under five different test conditions at 125-175 degrees C and with a current density of 0.4-1.0 MA cm -2 . The time to failure (TTF) showed a lognormal distribution. However, TTFs of lines whose cumulative failure was below 1% did not fit the lognormal curve and showed saturation at a minimum TTF for every test condition. Using the minimum TTFs, the activation energy and current density factor in Black's equation were calculated, for the first time, as 0.68 eV and 2.1 respectively. The presence of the minimum TTFs should correspond to the presence of the most vulnerable local structure in the lines. Therefore, the EM lifetime under an operational condition deduced using the minimum TTFs should be valid as a lifetime for lines in our LSI chips whose total length is over several metres.