High-resolution resistance measurements were performed on isolated Al lines in order to study the resistance changes which were caused by electromigration. The test structures consisted of a 1.5-diameter and 0.8-deep interconnect between 2 alloy metallization layers that were separated by a TiN layer. The latter acted as a diffusion barrier, to the electromigration process, where material could accumulate or be depleted and thus cause resistance changes. The latter changes were measured to a resolution of 10-9/s, at a resistance of 0.1. A direct current caused both increases and decreases in resistance, depending upon the current direction, and these recovered completely when the current was removed. The initial resistance changes were found to be proportional to t½; as expected for a diffusive electromigration process. Because the structure geometries and diffusion barriers were well defined, a quantitative analysis could be carried out. This was found to be most consistent with the assumption that Cu was the initial diffusing element.

G.B.Alers, A.S.Oates, N.L.Beverly: Applied Physics Letters, 1995, 66[26], 3600-2