A Tertiary Current Distribution Model for the Pulse Plating of Copper into High Aspect Ratio Sub‐0.25 μm Trenches

Electrodeposition of copper into sub-0.25 μm features has been studied theoretically and experimentally. A physically based two-dimensional (2D) pseudo-steady state and a one-dimensional (1D) unsteady-state mass-transfer model have been developed to study the effect of important parameters on the step coverage, evolution of copper deposits in damascene features, and deposition rate inside high aspect ratio single and dual damascene features. An analytical model that assumes linear deposition kinetics and a fixed boundary also has been developed and found to be in good agreement with the numerical results of the free boundary models to about 50% filling of the feature. A new criterion, based on the pulse plating parameters, for optimizing the opposing trends in step coverage and the deposition rate is also given. Copper has been deposited into submicron features, by dc and pulse plating, using an alkaline bath. Deposit evolution inside trenches has been studied by performing sequential plating experiments. Copper deposits with good morphology and resistivity were obtained using the alkaline bath. Experimental observations have been compared to the model trends and found to be in good agreement. Pulse plating experiments show that the deposit quality and the step coverage are improved over dc plating. Slanting the sidewalls also improves step coverage as shown by 2D model calculations.