Three-Dimensional Current Density Distribution Simulations for a Resistive Patterned Wafer

A combined boundary element method (BEM)-finite element method (FEM) numerical approach is used for the simulation of current density and layer thickness distributions in a wafer plating reactor. The current and potential distribution effects due to the electrolyte resistivity are modeled with BEM, while the transient internal resistive 'terminal' effect of the wafer is modeled using FEM. A nonlinear Butler-Volmer type overpotential relation is considered to describe cathode kinetics. The declining internal wafer resistivity that is due to the growth of the initial copper seed layer, is modeled over a number of discrete time steps. Different contacting methods (4 or 8 contact points, ring contact) are investigated, and their terminal effect time is compared. The wafer consists of a ring-shaped current thief, with adjacent photoresist area's and a central electroactive patterned zone.