Enhancement of Ag electromigration resistance by a novel encapsulation process

The Ag lines on Ti/SiO2/Si stack structures were fabricated by using conven tional photolithography and a reactive ion etch (RIE) in an O-2 plasma, and subsequently encapsulated by annealing in a flowing NH3 ambient. A thin Ti N(O) layer formed at the Ag surface and a Ti(O)/Ti5Si3 bilayer formed at th e initial Ti/SiO2 interface. Electromigration testing was performed on both bare and encapsulated Ag lines. A partial depletion region in the near-cat hode segment and its drift towards the anode were observed at the early sta ge for the bare Ag test lines. Afterwards, the side-by-side distribution of clusters of voids and hillocks was also noted in other segments. After the encapsulation process, the electromigration resistance of the Ag lints was significantly improved due to the inhibition of the surface diffusion of A g atoms by the encapsulation layer. This encapsulation process was also exp ected to address some other issues associated with the applications of the Ag metallization in advanced integrated circuits. (C) 2000 Elsevier Science B.V. All rights reserved.