Minimization of residual stress in TSV interconnections by controlling their crystallinity

The crystallinity of electroplated copper thin-film interconnections varies drastically depending on its manufacturing process, and thus, their mechanical and electrical properties change significantly depending on their micro texture. These changes should cause the variation of the residual stress in the interconnections, and thus, electronic performance of devices and the lifetime of interconnections should vary depending on the amplitude of the residual stress around TSV structures. The main reasons for high residual stress is attributed to not only thermal stress but also the shrinkage of the interconnections during their thermal history. Since the crystallinity of the interconnections varies drastically depending on their electroplating process, the residual stress after high temperature annealing is a strong function of the crystallinity. In this paper, the dominant process factors for changing the crystallinity and the residual stress in the electroplated interconnections were investigated by varying the electroplating process parameters systematically. Finally, it was found that the control of the crystallinity of a seed layer material used for the electroplating is the most important factor for controlling the crystallinity and long-term reliability of thin electroplated interconnections.