ELECTROMIGRATION FAILURES IN LINE-STUD STRUCTURES AS A FUNCTION OF LINE LENGTH

Modern interconnect structures may be regarded as a large number of ba sic units: pairs of Al alloy lines at two levels interconnected by via s. Presently as many as six levels of wiring may be used. Generally th e vias present barriers to the transport of components of the alloy be tween levels. While it is recognized that the failure statistics of su ch structures are different from the conventional test structure, diff erent values of activation energy for failure have been reported. Cons equently, different interpretations may be made regarding mechanisms. Simulations are presented to demonstrate that differences between test structures can result in different measurements. It is shown that sim ple lines, passivated with native oxide, need to be longer than about seven times the critical length and lines terminate in pads at the ano de end about four times this length, if measurements of both lifetime and activation energy are to be representative of long lines. (C) 1997 Elsevier Science S.A.