Mass transfer and current distributions in metallization processes for the electronics industry

Electrodeposition of copper onto a patterned surface is considered via a multiple-length scale approach. The wafer-length-scale (decimeters) current distribution is governed primarily by the electrical fields and by the convective mass transfer of the reactants to the cathode surface. However, commercial plating tools are designed to minimize the electrical field non-uniformities. The fluid flow design of these tools is carried out by relying on empirical methods. Thus an accurate experimental or numerical method for investigating laminar and turbulent fluid flows is required. Feature scale (sub-micron) current distribution is governed predominantly by the diffusion of the reactants and the reaction kinetics at the cathode's surface.; The effects of laminar and turbulent flow from a rectangular cross-section impinging jet on mass transport to an isolated, flush-mounted, thin line electrode (100 μm in the flow direction) were investigated. The experimental method was based on an electrochemical measurement procedure and produced mass transfer results that are more sensitive to fluid flow conditions compared with the experimental approaches taken by others. The effects of different fluid flow rates (laminar, transition, and turbulent) were examined. Furthermore, the numerical simulations of fluid flow yielded results that were in good agreement with the experimental analysis.; Feature-scale events during the electrodeposition process were analyzed via a 2-D numerical approach. On this length scale, convection and electrical potential effects were neglected. The short length scale problem was thus reduced to solving the diffusion equation for cupric ions and the possible additive species. Complications arising from the moving-boundary nature of this problem were alleviated via a multi-scale approach with respect to time. This simplified the moving boundary problem considerably by decoupling the unsteady diffusion and moving boundary phenomena. Thus, the behavior of current distributions on the diffusion time scale was considered on a fixed geometry. Similarly, long time—or feature filling time scale—events, specifically the metal deposit uniformities, were treated via a quasi-steady state approach, where the concentration fields were assumed to be at steady profiles at each intermediate shape of the cathode.