The electromigration characteristics of copper metallization are not just dependent upon the quality of the deposition techniques, but also on the geometry of the structure. To analyze the differences of copper metallization deposited by different techniques and their geometries, an experiment was carried out by using copper lines with the width at the minimum groundrules in both single and dual damascene processes. The samples were processed with the same diffusion barriers / adhesion layers, copper seed layers, and then the bulk copper was filled by different techniques: a) Physical Vapor Deposition (PVD), b) Chemical Vapor Deposition (CVD) and Electro-Plated (EP). Damascene copper lines were planarized and patterned by a chemical-mechanical polishing (chem-mech) process. The mean-time-to-failure (MTTF) were found to be different depending on the deposition technique and also their geometries. When the electron flow was from the bottom level upward, the failure mechanism was via depletion. When the electron flow was from the upper level downward, the failure mechanism was line depletion. The MTTF data of the copper lines which were deposited by different techniques also indicated that EP copper has the highest MTTF, followed by the CVD copper, and last was PVD copper. This phenomenon is also confirmed by the differences in thermal activation energies and the grain size distributions of PVD, CVD and EP copper.
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