Reconsider the depolarization behavior of copper electrodeposition in the presence of 3-mercapto-1-propanesulfonate

3-mercapto-1-propanesulfonate (MPS) accelerates the copper deposition rate through making the reduction of cupric ions into cuprous ions be kinetically favorable in the two-step, single-electron-transfer route. The depolarization ability of MPS shows a strong dependence on current density and its accelerating characteristic declines with the current density. The fading depolarization phenomenon is a critical reason for the void formation under the high current density plating condition although employing higher current densities to shorten the plating time for copper damascene process is the objective to push forward. Consequently, the polarizing species suppressing the deposition rate at the corner and sidewall of the vias should be strong enough to prevent copper from growing too fast, and the concentration of depolarizing additives may also need to increase to promote the growth rate at the bottom. Careful reconsideration of additives should be done to achieve the void-free filling at high current density electrodeposition.