Superfilling of Cu-Ag for metal interconnection was investigated in cyanide-based electrolyte. Superfilling was successfully achieved using the combination of KSeCN and thiourea. The trenches having widths in a range between 120 nm and 1.7 μm (depth: 400 nm) were filled without any voids. The continuous acceleration effect of KSeCN on Cu-Ag electrodeposition in the concentration range between 3.75 and 20 μM was confirmed, and thus the accumulation of KSeCN at the bottom of trench was surmised to be the main reason of Cu-Ag superfilling. Dissimilar to the previous superfilling of Ag or Au, which could be characterized as the fast surface diffusion of KSeCN, remarkable bumps and convex profiles at the corners of low-aspect-ratio trenches were developed. The proposed formula has led to defect-free superfilling of Cu-Ag with the Ag concentration in the range of 4.6 to 7.9 atom%.

The dimensions of Cu interconnections in electronic devices have been rapidly reduced to achieve high integration. The continual down scaling considerably increases both the electrical resistivity and the probability of electromigration failure. The addition of a secondary metal into Cu can improve the resistance against electromigration. However, the co-deposition of a secondary metal inevitably reduces the electrical conductivity. Thus, the main consideration in alloying with Cu is to find a secondary metal that shows the lowest resistivity. Ag has been known as the most appropriate. In this research, the superfilling of Cu-Ag and its mechanism are investigated. The area reduction at the surface with negative curvature induces the accumulation of adsorbed accelerators, finally resulting in local increment of the deposition rate of Cu-Ag at the bottom of a trench. Additionally, the microstructure of Cu-Ag film is investigated, and it is confirmed that Cu-Ag film exhibits superior oxidation resistance and mechanical strength without severe deterioration of the electrical conductivity compared to pure Cu.Cu has been widely used to fabricate the metal interconnections in various electronic devices through the damascene process, which involves the deposition of an intermetallic dielectric, the patterning of trenches or vias through lithography, the deposition of diffusion barrier and Cu seed layers, the electrodeposition of Cu, and chemical mechanical planarization (CMP) in sequence. 1-3 As the dimensions of electronics have been continually reduced to the nanoscale range, the development of new conducting materials with improved electrical conductivity and enhanced electromigration resistance and mechanical strength are now needed to achieve high-speed and reliable electronic microprocessors. 4-8

Pulse deposition, which has an advantage to apply relatively high current density by supplement of Cu ions during off-time, was applied to deposit 250 nm Cu film. The microstructural change during off-time was to be investigated. The differences between constant potential and pulse deposition were due to the change during off-time. The application of pulse deposition led to the increase in the Cu͑111͒ intensity and the reduction in the film resistivity compared to constant potential deposition. The film characteristics were further improved as the duty cycle decreased. The change during the off-time was verified to be grain growth in contact with the electrolyte. Additionally, it was clarified that the grain growth completed in a second, unlike self-annealing process, which proceeded for tens of hours, and affected within about 2.0 nm of Cu film from the surface. Under optimum conditions, pulse deposition led to 50% enhancement in Cu͑111͒ intensity and 30% reduction in resistivity compared to the constant potential deposition.

One of the main concerns in fabricating Cu interconnections is a significant increase in resistivity. Thus, pulse-reverse electrodeposition was implemented in an attempt to improve the properties of Cu films. The influences of the anodic step in pulse-reverse electrodeposition were intensively investigated by varying the anodic potential and time (the amount of anodic charge). It was confirmed that the anodic step affected the grain size as well as surface roughness and the change rates of these properties were determined by the anodic potential. The conflicting effects between grain size and surface roughness resulted in the lowest resistivity at an optimum amount of anodic charge. The contributions of the grain size and surface roughness were taken into account to explain the resistivity behavior depending on the anodic charge. A theoretical approach was applied to complement the qualitative findings and it was well-matched with the experimental results.

The adsorption mechanism of thiourea (TU) and its effect on Cu electrodeposition were verified using TU derivatization. Contrary to the previously reported behavior of TU as an inhibitor, TU either promoted or inhibited Cu reduction according to the derivatization time. During the short derivatization time, the adsorbed TU with low surface coverage was oxidized to spontaneously reduce Cu 2+ to Cu + , thereby, accelerating the Cu deposition. However, TU inhibited the Cu deposition as the coverage of TU-Cu + increased with the derivatization time. Furthermore, a deterioration in the resistivity of the Cu film, which occurred when TU was added, was largely improved by the derivatization method while maintaining an enhancement in the film hardness. TU derivatization resulted in a 9.2% enhancement in the film hardness and only a 26.0% deterioration in the film resistivity compared to those of Cu films deposited in the absence of TU, which were not simultaneously obtainable upon the direct addition of TU to the deposition bath.