Influence of Thermal-Mechanical Effects on Resistance Changes During and After Electromigration Experiments

This paper is focused on the non-linear resistance behaviours often detected by means of high resolution resistometric methods both at the very beginning of an electromigration (EM) test, and after the high stressing current inducing EM is switched off. It is shown that temperature steps, always present at the beginning or after EM, are the triggering events for different, often reversible, physical phenomena contributing to resistance changes. Precipitation-dissolution of alloyed elements is perhaps the most important one, while other mechanisms, like the combined effect of hydrostatic stress relaxation and void volume change, should cancel out. These effects, however, don't exclude a possible simultaneous effect on the resistance of accumulation/relaxation of EM damage. Experimental results are collected by means of different, complementary techniques

Non-Linear Resistance Behaviour in the Early Stages and After Electromigration in Al-Si Lines

A common result obtained in electromigration experiments carried out on Al-Si lines using different high resolution resistometric methods, is a monotonous non-linear resistance increase at the very beginning of the high current electromigration test, and a decrease after the high stressing current is switched off. These effects have often been attributed to the attainment of a steady state of vacancy concentration during and after electromigration. This paper shows how even small abrupt temperature steps, always present at the beginning and after electromigration tests, are the triggering events for different, often reversible, physical phenomena contributing to non-linear resistance changes. Precipitation - dissolution of alloyed elements appears to be the most significant one. Abrupt temperature changes also induce a change of the hydrostatic stress of passivated lines. The relaxation of the hydrostatic stress could be coupled with a void volume change, and the total resistance is a function of both the hydrostatic stress (through resistivity) and of void volume. However, we demonstrate that in our experiments the effect of hydrostatic stress relaxation on resistance variations is negligible with respect to the action of precipitation - dissolution. These non-linear, thermally induced effects, however, do not exclude possible simultaneous resistance changes due to the accumulation/relaxation of the electromigration damage. Experimental results are collected by means of different, complementary techniques