Cu direct electrodeposition using step current for superfilling on Ru-Al2O3 layer

• Ru-Al2O3 ratio and deposition condition affected terminal effect and superfilling.
• Step current electrodeposition succeeded Cu superfilling on Ru-Al2O3 layers.
• Formation of a conducting layer is critical to superfilling on resistive-substrate.

A Ru-Al2O3 layer can be used as an integrated material in a diffusion barrier and a Cu seed layer for Cu electrodeposition. This layer can effectively inhibit the formation of Cu silicide, and it is also applicable to Cu direct electrodeposition. Because the electrical conductivity of the Ru-Al2O3 layer is relatively high compared to the Cu seed or pure Ru layer, the ohmic drop within the wafer, known as the terminal effect, should be investigated. In this study, the superfilling of Cu on the Ru-Al2O3 layers and the terminal effect of Cu electrodeposition are reported. Electrodeposition with constant current results in severe variations in both the deposition amount and Cu property within the wafer. Step current electrodeposition is adopted to solve these problems. At the initial stage, a high current density is briefly applied to render enough overpotential on the whole wafer inducing substantial nucleation. This is followed by a low current density for stable growth and superfilling of Cu with a small terminal effect. The changes in superfilling according to the conditions of the first step and the composition of the Ru-Al2O3 are clarified. Under the optimal conditions, the successful superfilling is obtained with small variation in the deposition amount within the wafer.