Influence of Triple Junction Structure on Cu Segregation in Al Thin Films

Abstract

Al thin films, used as interconnects in integrated circuit devices, are subject to voiding failures due to electromigration and stress. Electromigration is a diffusion process and voids are known to form at points of flux divergence such as triple junctions. Void formation in Al-Cu films has also been associated with 9θ-phase (Al2 Cu) precipitates [1], which form preferentially at grain boundaries and triple junctions. Some triple junctions are favored as nucleation sites [2], presumably due to energetic differences arising from the crystallographic nature of the junctions. Their character can be calculated from the crystallographic orientations of the surrounding grains and the associated grain boundary dislocation networks [3]. Bollmann's method of analysis results in two categories of triple lines: I-lines - the special case where the grain boundary dislocations balance; and U-lines - the general case where the dislocation arrays do not balance. U-lines should have higher energies than I-lines and should therefore behave differently [3, 4]. This paper investigates the relationship between triple-line character and the location of Al2 Cu precipitates at certain triple junctions in Al-lCu thin films.