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

The copper interconnect technology is constrained by the significant current distribution due to the terminal effect for resistive thin seeds. As a result, the current in the wafer center can become insufficient for cathodic protection of thin copper seeds leading to center seed corrosion. To improve the current distribution, the exchange current density can be lowered e.g. by lowering the copper 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 trenches were performed. In addition, proposing a high acid chemistry that is also compatible with direct plating, would enable the in-situ copper seed formation and filling in one and the same process step for direct plating on non-copper seed.