電鍍溫度與電流密度對銅奈米線微結構影響之研究

Influence of electrodeposition temperature and current density on microstructure of Cu nanowires

盧逸滄(Yi-Cang Lu)

指導教授 ： 廖建能

國立清華大學/工學院/材料科學工程學系/碩士(2012年)

摘要

銅常使用於積體電路中，作為連結各元件的導線，而隨著奈米製程的引進，瞭解銅在奈米尺度下所呈現的性質也日趨重要，因此近年來有關奈米線的研究也愈來愈多。材料特性與材料微結構有密切的關係，例如不同的結晶方向會使材料呈現不同的機械性質及導電性質，對於銅在積體電路及奈米元件的應用上扮演了重要角色。雙晶是材料常見的微結構之一，有文獻指出，若在銅內部引入了奈米雙晶結構，不僅能大幅提升銅的機械強度，同時也保持了良好的導電性，且奈米雙晶結構的存在也能夠使銅的抗電遷移性質提升。電鍍過程中，電流密度及電鍍液溫度影響了銅原子在沉積過程的成核行為，進而影響銅的微結構生成。電流的波形也是影響材料微結構的重要因素，而文獻也指出，採用脈衝電流的電鍍製程有較高的機率製備出雙晶銅。然而目前關於電鍍液溫度及電流密度對材料結晶方向及雙晶結構生成的研究，仍是以電鍍銅膜較多。關於電鍍奈米線的資訊較為缺乏，其中有關脈衝電鍍系統的研究為數更是稀少，故本實驗致力於研究在脈衝電鍍系統中，電鍍液溫度及電流密度對銅奈米線的結晶方向及雙晶結構生成之影響。
本實驗分別利用 x-ray 結晶繞射儀及穿透式電子顯微鏡分析銅奈米線的結晶方向及雙晶結構生成的情形。研究結果發現，在高電流密度下，降低電鍍液溫度有助於提升銅奈米線的 (111) 晶面繞射強度，同時奈米線內部的平均雙晶間距也會下降；而在低溫環境中，提高電流密度也會提升銅奈米線的 (111) 晶面繞射強度，而奈米線內部的平均雙晶間距也隨之下降。電流密度及電鍍液溫度對銅奈米線微結構的影響機制可由在不同電鍍條件下所造成的工作電壓變化，結合應力累積與應力釋放的理論來探討。

關鍵字

銅奈米線 ； 結晶方向 ； 雙晶結構

並列摘要

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.

參考文獻

10. Pang, Y.T., G.W. Meng, Y. Zhang, Q. Fang, and L.D. Zhang, Copper nanowire arrays for infrared polarizer. Applied Physics A: Materials Science & Processing, 2003. 76(4): p. 533-536.

1. Tu, K.N., Recent advances on electromigration in very-large-scale-integration of interconnects. Journal of Applied Physics, 2003. 94(9): p. 5451.

2. Chen, K.C., W.W. Wu, C.N. Liao, L.J. Chen, and K.N. Tu, Observation of atomic diffusion at twin-modified grain boundaries in copper. Science, 2008. 321(5892): p. 1066-9.

3. Lu, L., Y. Shen, X. Chen, L. Qian, and K. Lu, Ultrahigh strength and high electrical conductivity in copper. Science, 2004. 304(5669): p. 422-6.

4. Lu, L., X. Chen, X. Huang, and K. Lu, Revealing the Maximum Strength in Nanotwinned Copper. Science, 2009. 323(5914): p. 607-610.