Electroplated Cu films with different plating conditions and thicknesses are characterized to study the stress and texture evolution involved in the transition of the microstructure during self-annealing. Grain growth during the process induces stress in the film in the tensile direction. Degradation of the (111) texture and enhancement of the (200) texture are observed in the films during the microstructural transition. The rate of self-annealing increases dramatically as the plating current density increases. Self-annealing is significantly retarded in thinner films and in films plated with pulse reverse current. A strong correlation between stress and texture development is demonstrated for all electroplated Cu films under self- and thermal annealing conditions. This correlation is explained by the surface/interface energy and strain energy in anisotropic metal films. Due to the mechanical anisotropy of Cu, the orientation with the lowest total energy changes from (111) to (200) as the dominant energy that determines the film texture changes from surface/interface related to strain related. The texture remains unchanged until the biaxial stress in the film exceeds a critical value. Above the level of critical stress, the (111) texture starts to degrade and the (200) starts to become enhanced, which reduces the strain energy in the film. Different amounts of stress develop in Cu films during thermal annealing depending on the barrier layers; the stress is largest with TaSiN, medium with Ta and smallest with TaN. This suggests that film stress and texture are also affected by the Cu/barrier interface bond strength.
The integration of Cu interconnections will require sophisticated structures to prevent Cu from coming into contact with devices. The barriers for Cu also must have good adhesion with dielectric and Cu, and yield desirable microstructure of Cu. This paper discusses several critical barrier requirements and compares the properties of Ta and Ti/TiN barrier systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.