Abstract
Copper is often used as a interconnect material with the introduction of nano-processing. Therefore, it is important to understand the properties of copper in nanoscale, such as nanowires. Properties of material are closely related to its microstructure. For example, different crystal orientation may affect mechanical and electrical properties of materials and their applicability on integrated circuits and nano-devices. Twin structure is one of the microstructure in material. Nano-twinned copper is known to have high mechanical strength, decent electrical conductivity, and better electromigration resistance. During electrodeposition, deposition parameters such as current density and deposition temperature can greatly influence the microstructure of deposited material. Current waveform is also a factor which may affect the microstructure of deposited materials. It is generally believed that pulsed electrodeposition is an appropriate method to deposit twinned copper films. However, research about the influence of deposition temperature and current density for microstructure is mostly related to copper thin film system. The studies on the electrodeposited nanowires are limited especially for the pulsed electrodeposition system. Therefore, the objective of this study is to investigate how deposition temperature and current density affect crystal orientation and formation of twinning structure of copper nanowires in pulsed electrodeposition system. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to analyze the crystal orientation and twin structure formation of copper nanowires, respectively. Experiment results show that the (111) crystal plane diffraction intensity of copper nanowires increases, but the average twin spacing of copper nanowires decreases with the decrease of electrolyte temperature. Moreover, with increasing current density, the (111) crystal plane diffraction intensity of copper nanowires increases, while the average twin spacing of copper nanowires decrease. The relationship between electrodeposition parameters and microstructure of copper nanowires is discussed by considering the working voltage variation at different deposition conditions and the stress induction / relaxation theory.