Resistance Degradation in Early Stage of Electromigration of Al(Cu) Metal lines

摘要

Resistance degradation in the early stage of electromigration of Al(Cu) metal lines has been investigated by using high resolution resistance measurement. The resistance variation due to Cu diffusion along the line was separated from that due to the thermal stress in the electromigration test. It was found that Cu diffusion along the line strongly depends on the metal line structure. In a wide line with polycrystalline structure, the resistance drop due to Cu diffusion is linearly increased with the test time. However, as the linewidth is reduced and the line becomes bamboo structure, most of resistance drop is ascribed to the thermal stress and Cu diffusion along the line is almost negligible. This finding indicates that the role of Cu in the electromigration reliability strongly depends on the line structure, and previous theory on the role of Cu in improvement of electromigraiton reliability can not simply apply to the metal line with bamboo structure.