| Summary: | 碩士 === 國立清華大學 === 電子工程研究所 === 92 === As the integrated circuits (IC) step into deep sub-half-micron regime, devices dimensions are scaled down and the interconnect lines become thinner and narrower, the resistance and current density in the wire will increase, and the RC delay time and Joule heating increasing as well. The previous used aluminum interconnect line is going to suffer from high performance and interconnection reliability problems. Copper (Cu) has been considered as the most suitable interconnect metal to substitute aluminum (Al) due to its lower electrical resistivity and better susceptibility to electromigration failure. Copper wiring has become the main stream in IC interconnect especially as the integrated circuit processing goes beyond the 0.18 um technology node.
Among the various Cu deposition methods, electroplating has been adopted by most of the IC manufactures because of its low cost and higher throughput. By far, the most common electrolyte use in IC industries is copper sulfate (CuSO4). However, the as-deposited Cu films using CuSO4 exhibit a so-called self-annealing phenomenon, in which the grains in the films grow with time and the film resistivity changes. Therefore, post-deposition-anneal is generally required to stabilize the self-annealing effect. Researchers believed that the self-annealing effect is a result of high inner film stress. If one could deposit the Cu films with low stress through some kind of electrolyte, the self-annealing effect would then be eliminated and no post-deposition-anneal is required. Of course, the thermal budget in the IC manufacturing could be improved.
In this work, we compare the properties of as-deposited Cu films prepared using two different electroplating solutions: copper-hexafluoro-silicate (CuSiF6) and CuSO4. By mixing the CuSO4 and CuSiF6 with different mix ratios, the Cu films were deposited on seed-Cu/SiO2/Si substrates and SiO2/Si substrate with different barrier layer materials. We compared the stress, resistivity, self-annealing effect, microstructure, growth rate, impurity and reliability of the as-deposited electroplated Cu films. We found that the electroplated Cu films deposited using CuSiF6 exhibit lower resistivity, denser structure, lower stress and less-apparent self-annealing effect than those using CuSO4. Therefore, we concluded that CuSiF6 is one of promising electrolyte solution for future Cu electroplating in IC manufacturing.
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