Ultra-Low Copper Baths for Sub-35 nm Copper Interconnects

The copper interconnect technology is constrained by the non-uniformity of the current distribution over the wafer due to the terminal effect for resistive thin seeds. As a result, the current in the wafer center becomes insufficient to cathodically protect the copper seed leading to seed corrosion in this wafer area. To improve the current distribution, the exchange current density can be lowered e.g. by lowering the Cu2+ concentration. Our approach is to investigate and develop acid ultra-low copper baths with feature fill capability. For this goal, the optimum additives concentrations were sought and fill studies in 30 nm wide trenches were performed. Additionally, a low-copper/high-acid chemistry, that is also compatible with direct plating, was developed to enable the in-situ copper seed formation and filling in one process step for plating on non-copper seeds.