溫度與基板對脈衝電鍍製備銅膜微結構影響之研究

The Effects of Temperature and Substrate on Microstructure of Copper Films Prepared by Pulsed Electrodeposition

曾麗倩(Li-Chien Tseng)

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

電鍍製程擁有容易量產及低成本的經濟效益，因此被大量運用於製備積體電路中的銅金屬導線。因應微電子積體電路元件尺寸不斷的微縮，為了提升元件的可靠度，瞭解電鍍製程參數對銅金屬導線微結構的影響是一個重要的課題。銅的微結構與晶體成長的優選方向會受到電鍍時的過電位、電鍍液的成份、基板以及溫度的影響。在本研究中，主要是探討基板與電鍍液溫度對脈衝電鍍製程所製備銅金屬膜微結構之影響。本實驗所採用的基板，一為市售的鎳金屬箔，其具備很強的(200)晶體優選方向，另一基板為利用磁控濺鍍法在矽基板上沉積銅薄膜。電鍍液的溫度則控制在攝氏-1及20度。接著利用觀察不同條件下銅膜的表面形貌、優選方向及雙晶的間距作為探討。實驗結果發現，當溫度降低時，利用定電流模式下進行脈衝電鍍所鍍出的銅金屬膜其表面較為光滑，且在電鍍過程中整體的過電位也有所提升。推論降低溫度而造成的過電位上升使銅膜成核速率上升，進而使晶粒細化，而得到較為平整的表面。另外觀察到當電鍍液的溫度控制在攝氏20度時，初始電鍍的銅膜繼承了基板的優選方向，而當溫度下降時，初始電鍍的銅膜其基板效應較不明顯。導致此差異的主要原因在於溫度下降所造成的過電位提升使得各生長方向成核所需要的能量都大幅下降，導致晶粒各方向的成核速度沒有明顯差異而得到無特定優選方向的薄膜。最後也觀察到當溫度降低時，雙晶結構的間距大幅的下降。推論當溫度下降後，銅膜內的應力因在低溫電鍍下成核數量較多及晶界較多而有所提升，另外在低溫下，推測應力釋放將由差排滑移轉變成形成奈米雙晶的機制，使低溫下製備的銅膜內的雙晶結構更為緻密。

關鍵字

銅膜 ； 電鍍 ； 奈米雙晶 ； 低溫

並列摘要

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 -1C and 20C. 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.

並列關鍵字

copper film ； electrodeposition ； nanotwin ； low temperature

參考文獻

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