No abstract

Low resistivity Cu wires were obtained by high heating rate, short time, and low temperature annealing even at a temperature 100 K lower and for a time 67% shorter than the conventional H 2 annealing temperature and time. This was due to promotion of the grain growth by the release of grain boundary energy when the heating rate to the peak temperature was set at 1.7 K/s. Resistivity of Cu wires made by the new process at 573 K was lower than that of wires made by conventional H 2 annealing at 673 K for 30 min.

Low resistivity 60 nm wide Cu wires were realized by the combination of lessening impurities through additive-free plating using high-purity plating materials and high-heating rate annealing. Resistivity values of Cu wires made with the new method were about 14% lower than those made by conventional plating with additives and high-heating rate annealing at the same temperature. The resistivity values were also found to be more than 50% lower than those for Cu wires made by plating with additives using low-purity plating materials (3N/4N) and by long-time annealing at low heating rate of 0.1 K/s in H 2 atmosphere. . This paper is part of the JES Focus Issue on Electrochemical Processing for Interconnects.Resistivity increase in very narrow Cu wires is becoming a critical issue for the realization of high speed ULSIs. This is mainly due to the fact that electron scattering occurs both at grain boundaries and side walls. 1-5 Electron scattering at side walls will be determined by their areas, i.e., width and height of a trench. However, it is possible to reduce grain boundary scattering by uniform grain size coarsening of Cu wires.To lower resistivity, uniform coarsening of grain sizes is mandatory. We have investigated the effects of the purity of plating materials, i.e., anode and electrolyte on the microstructure and resistivity of very narrow Cu wires less than 100 nm, and found that grain size increases and resistivity decreases with increasing the purity of plating materials. 6 It is also found that high heating rate annealing in vacuum enhances the grain growth by utilizing grain boundary energy, resulting in low resistivity Cu wires. 7,8 A large grain boundary energy could remain in the Cu wires when heating rate is very high and it would act as a driving force for the grain coarsening during the isothermal stage at the peak temperature. These results imply that further resistivity reduction could be realized by combining very high-purity plating with high-heating rate annealing.In this paper, we have investigated the resistivity of 60 nm wide Cu wires prepared using a new fabrication method which combines reducing the impurities in Cu wires by additive-free plating using highpurity plating materials (8N anode / 6N electrolyte) with high heating rate (1.7 K/s). We compared the new fabrication method wires with Cu wires made by plating with additives using high-purity (8N anode / 6N electrolyte) and conventional purity(4N anode/3N electrolyte) plating materials, and with high-heating rate (1.7 K/s) and low-heating rate (0.1 K/s) annealing. ExperimentalPlating with additives and additive-free plating have been done as shown Figure 1. Additives, an organic accelerator, organic suppressor, organic leveler, and 50 ppm Cl − ions were added to the plating solution for plating with additives, while only 50 ppm Cl − ions were added to the electrolyte without organic additives in the case of additivefree plating. Figure 1a shows the cross-sectional structure of a test element group (TEG). The trench width was from 50 ...