Electromigration drift velocity in Al-alloy and Cu-alloy lines

Abstract

Electromigration has been investigated using both drift velocity and resistance techniques in pure Al, Al(Cu), pure Cu, Cu(Mg), Cu(Zr), and Cu(Sn) isolated lines overlapping W studs (vias between metallization levels), or lines overlaying a W underlayer line. The phenomenon of void growth was investigated in sections of lines which extended past the cathode terminal to form reservoirs through which no current flowed. This has been modeled using the electromigration-induced vacancy wind. The activation energy for electromigration was found to be 0.60 eV and 0.9 to 1.1 eV for multigrained and bamboo-grained pure Al structures, respectively, and 0.77 eV for multigrained pure Cu thin film lines. The drift velocity of Cu alloys has been investigated using Mg as the solute, which enhances the Cu drift velocity, while Zr or Sn drastically reduce the Cu migration rate.