Resistivity Reduction in Very Narrow Cu Wiring

Abstract

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 ...

Effectiveness of a periodic annealing method to coarsen Cu grains in very narrow trenches

“…The discrepancy of the increase ratio of the grain diameter between the simulation and the actual experiment can be attributed to impurity atoms. In the previous research, we analyzed by glow discharge mass spectrometry (GDMS) the impurities in Cu films formed by plating with and without additives using high-purity and low-purity plating materials [13].…”

“…The result showed that the total impurities in Cu films were decreased clearly by using the high purity plating materials. Especially, the amount of impurities like O, C, Cl, Ti and Fe, which may suppress grain growth during annealing, were reduced (see Table I in reference [13]). Resistivities as a function of holding time at the peak temperature for the 60 nm wide Cu wires made with additive-free plating using high-purity plating materials (6N electrolyte/8N anode process) and high-heating rate annealing at 1.7 K/s were also measured (see Fig.…”

“…Resistivities as a function of holding time at the peak temperature for the 60 nm wide Cu wires made with additive-free plating using high-purity plating materials (6N electrolyte/8N anode process) and high-heating rate annealing at 1.7 K/s were also measured (see Fig. 10 in reference [13]). Resistivities of 60 nm wide Cu wires formed with additive-free plating and high-heating rate annealing to both 573 K and 673 K decrease with increasing holding time and they have almost the same value for 10 min holding at peak temperature.…”

Screening of Undesirable Elements Raising the Electrical Resistivity in Very Narrow Cu Wires by Ab Initio Calculation

“…Experimental for evaluation of electrical resistivity and grain size.-We used a four-point probe method 15 and field emission transmission electron microscope (FE-TEM) observations respectively to measure electrical resistivity and grain size in the Cu wires. We fabricated Cu wire structures including Fe impurity as follows.…”