奈米雙晶電鍍銅薄膜之腐蝕特性研究

Corrosion Properties of Nanotwinned Copper Films Prepared by Electrodeposition

楊智傑(Chih-Jie Yang)

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

在積體電路銅連結導線製程中，化學機械研磨是移除過多材料以及整平試片表面最重要的方法。而在化學機械研磨中採用的漿料卻為製程帶來了易腐蝕的不確定因素。化學腐蝕以及伽瓦尼腐蝕等常造成元件良率過低或是降低其可靠度，因此提高銅抗腐蝕能力成為極為重要的議題。
近年來奈米雙晶銅因具有高機械強度同時保有良好的電導率及抗電遷移的能力而被廣泛研究，但其抗腐蝕能力卻從未有人探討。因此本論文藉脈衝電鍍製程沉積具雙晶結構之銅膜，並研究雙晶結構是否能提升材料抗腐蝕能力。Benzotriazole (BTA)被廣泛應用在化學機械研磨中作為抗腐蝕劑，同時亦有應用在電鍍中作為添加劑以細化晶粒，使表面平整。但卻只有極少文獻對其作為添加劑是否能同時提升電鍍銅膜的抗腐蝕能力討論。因此於此本論文中亦針對以BTA作為添加劑的電鍍銅膜抗腐蝕能力做討論。
透過電化學極化測試、掃描式電子顯微鏡(SEM)、原子力顯微鏡(AFM)等分析發現，由脈衝法所製備的銅膜其抗腐蝕能力均優於由直流電鍍法所製備的銅膜。另外在電鍍時添加BTA的銅膜相較於未添加的銅膜也有著更好的抗腐蝕的能力。一般而言，表面平整度、材料優選方向、晶粒大小等均被認為是可能影響腐蝕的原因，前兩者在實驗設計時均已控制，而晶粒大小的差異亦無法解釋實驗所觀查到的結果。因此雙晶結構被認為是提升由脈衝電鍍銅膜抗腐蝕能力主要的因素。穿透式電子顯微鏡(TEM)分析亦證明利用脈衝電鍍製備之銅膜具有高密度雙晶結構。推測是由於雙晶結構在晶界交界處之晶界區域會轉換成較穩定的 coincidence site lattice (CSL)界面，使得銅膜抗腐蝕能力提升。此外，X光散射(XRD)分析指出電鍍時添加BTA的銅膜的結晶性較未添加的銅膜差，因此推論是BTA在電鍍時被嵌入鍍膜使得其結晶性較差，但卻更能抗腐蝕。

關鍵字

腐蝕 ； 奈米雙晶 ； 苯並三唑 ； 微結構

並列摘要

In copper interconnects of integrated circuit process technology, chemical mechanical polish (CMP) is the most important step to remove overburden material and planarize surface of metallization. However, the slurry adopted in CMP may introduce corrosion issue. Chemical and galvanic corrosions of copper interconnects during processing may cause the failure of device. Therefore, it is crucial to find a way to increase the corrosion resistance of copper interconnects.
Nanotwinned copper has received broad attention recently due to its high mechanical strength, reasonably low electrical resistivity, and better electromigration resistance. However, its corrosion resistance is yet to be investigated. In this thesis, the corrosion resistance of nanotwinned copper prepared by pulsed electrodeposition technique is studied. Benzotriazole (BTA) is widely applied as a corrosion inhibitor in CMP and an electrodeposition additive as a brightener. But there is only limited literatures addressing the corrosion resistance of copper films deposited with BTA. In this study, the corrosion resistance of copper films electrodeposited with BTA is investigated. From the results by electrochemical polarization, scanning electron microscope and atomic force microscopy, it was found that copper films prepared by pulsed electrodeposition technique as well as with BTA in electrolyte have better corrosion resistance than those deposited by direct current deposition and without BTA in the electrolyte. Surface roughness, crystal orientation, and grain size are known to affect the rate of corrosion. In this study, the former two are controlled in all specimens to minimize their influence on corrosion behaviors. Moreover, the grain size effect is unable to explain the observed corrosion properties of the copper films prepared by different methods. The existence of twin structures, confirmed by transmission electron microscopy, is thought to be associated with the increase of corrosion resistance. Twinning induced grain boundary segment transformation is speculated to be held responsible for better corrosion resistance. X-ray diffractions results indicate that copper films deposited with BTA have poor crystallinity due to BTA incorporation in the electrodeposited films. The incorporation of BTA was found to increase corrosion resistance of the electrodeposited copper films.

並列關鍵字

Corrosion ； Nanotwin ； Benzotriazole ； Microstructure

參考文獻

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