The effect of grain-boundary migration upon hillock formation in unpassivated Al thin films during thermal cycling was studied. Hillocks occurred more frequently in films that underwent grain growth during thermal cycling, than in films which had a stable grain structure. The hillock frequency was at least 4 times greater in films which underwent grain growth; as judged by the number of hillocks which were observed per initial grain boundary triple-junction. The latter measure took account of the smaller initial grain size of films which experienced grain growth, and showed that grain-boundary migration itself enhanced the hillock frequency.

Study of the Effect of Grain Boundary Migration on Hillock Formation in Al Thin Films. D.Kim, W.D.Nix, R.P.Vinci, M.D.Deal, J.D.Plummer: Journal of Applied Physics, 2001, 90[2], 781-8