ELECTROMIGRATION IN 0.25 MU-M WIDE CU LINE ON W

Electromigration in isolated 0.25-1. 0 mu m wide pure Cu fine lines ha s been investigated using both resistance and edge displacement techni ques in the sample temperatures range 221-394 degrees C. The Cu lines, sandwiched with a top and bottom Ta layer, were 200 mu m long and wer e connected to underlying W bars on each end of the Cu line. Transmiss ion electron microscopy revealed that the microstructures of the 1 and 0.25 mu m wide lines were polycrystalline and bamboo-like grain struc tures, respectively. During electromigration, voids formed at the cath ode end while hillocks,stew at the anode end. The failure lifetimes we re correlated to the sizes of voids formed in the vicinity of the cath ode end of the line, and a distribution of multiple failure modes was found. A low value of electromigration activation energy, 0.81 +/- 0.0 5 eV, and a Linear relationship between failure lifetime and metal lin ewidth were found, despite the fact that these narrow lines were close to a perfect bamboo-like grained structure. These results suggest tha t the mass transport of Cu during electromigration primarily occurs al ong the sidewall surfaces of the lines. (C) 1997 Elsevier Science S.A.