NONLINEAR RESISTANCE BEHAVIOR IN THE EARLY STAGES AND AFTER ELECTROMIGRATION IN AL-SI LINES

A common result obtained in electromigration experiments carried out o n Al-Si lines using different high resolution resistometric methods, i s 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 attr ibuted to the attainment of a steady state of vacancy concentration du ring and after electromigration. This paper shows how even small abrup t temperature steps, always present at the beginning and after electro migration tests, are the triggering events for different, often revers ible, 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 t he hydrostatic stress of passivated lines. The relaxation of the hydro static stress could be coupled with a void volume change, and the tota l resistance is a function of both the hydrostatic stress (through res istivity) and of void volume. However, we demonstrate that in our expe riments the effect of hydrostatic stress relaxation on resistance vari ations is negligible with respect to the action of precipitation-disso lution. These non-linear, thermally induced effects, however, do not e xclude possible simultaneous resistance changes due to the accumulatio n/relaxation of the electromigration damage. Experimental results are collected by means of different, complementary techniques. (C) 1996 Am erican Institute of Physics.