| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 100 === Electrochemical deposition is commonly employed in the fabrication of copper interconnects owing to its low cost advantage and ease of mass production. To further down scaling the microelectronic device, more in-deep knowledge and process control concerning interconnect microstructure are required to improve device reliability. Copper film microstructure is known to be tailored by various process parameters such as electrodeposition overpotential, electrolyte composition, substrate and temperature. In this study, nanocrystalline copper films were fabricated by galvanostatic pulsed electrodeposition using an addictive-free sulfate solution as an electrolyte. In comparison, two types of substrate have been used: one is a commercial nickel foil with strong (200) texture and the other is copper film prepared by sputtering which has no preferred orientation. The electroplated copper films were deposited at -1C and 20C. The surface topology, morphology, crystallographic texture and twin spacing distribution of the copper films electrodeposited under various conditions were examined. In this experiment, we observed that as the deposition temperature decreases, the copper film showed an increase in the deposition overpotential and a decrease in surface roughness. The inheritance of substrate texture in the electrodeposited copper film was found to be tailored by deposition temperature. As the deposition temperature decreases, the deposits show less dependent on the crystallographic orientation of the substrate. It was also found that twin spacing lamella reduces with decreasing deposition temperature. We proposed that the increase of overpotential has significant influence on the nucleation behavior. The increase of overpotential leads to higher nucleation rate and lower growth rate of existing nuclei, thus a smoother surface was obtained. At lower deposition temperature, the probabilities of nucleus formation on varies planes are generally the same, thus the electrodeposited copper films did not show any preferred orientation. Finally, the decrease of twin spacing was believed to be associated with the increasing stress caused by high nucleation rate under low deposition temperature.
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