Modeling superconformal electrodeposition using the level set method

Superconformal deposition enables the void-free filling of high aspect ratio features such as trenches or vias in the Damascene metallization process. Superconformal electrodeposition, also known as superfill, occurs when particular combinations of chemical additives are included in the electrolyte. The additives enable preferential metal deposition at the bottom surface which leads to bottom up filling before the sidewalls close off. Two crucial mechanisms by which the additives enable superfill to occur are (i) accelerator behavior increasing the copper deposition rate as a function of coverage and (ii) conservation of accelerator coverage with increasing/decreasing interface area. Thus, the adsorbed catalytic accelerator species floats upon the growing metal/electrolyte interface. An effective modeling approach must accurately track the position of the interface as well as preserving surfactant coverage while the interface is advancing. This must be achieved in an Eulerian framework due to the necessity of modeling the diffusion of electrolyte species. To this end, the level set method is used to track the interface while a scalar variable approach governs the surfactant coverage. Modeling of additive accumulation and conservation on a deforming interface in conjunction with the level set method presents areas for novel numerical approaches. Several test cases are examined to validate the surface coverage model. Comparison of superfilling simulations with experimental results is also presented. (C) 2003 The Electrochemical Society.