Electrochemical Deposition in Deep Vias

Copper is used as interconnects on chips. It is laid down in deep vias by electrodeposition. For the simple case, the rate of electrodeposition on the shoulders is much greater than that at the bottom, and the via-mouth closes during the process and a bubble is captured inside. Approximate solutions to the electrodeposition process, when the transport is diffusion controlled and when it is reaction controlled, are obtained. It is shown that bubbles are easily captured in diffusion-controlled systems, but no bubbles are captured in the reaction-controlled system. However, the diffusion-controlled system has very low currents, low electrodeposition rates, and low production rates, and the reaction-controlled system has even lower rates. Based on these, the existing solutions to the bubble-capture problem are briefly reviewed to suggest that inducing natural convection appears most promising