具不同金屬疊層結構的奈米線寬鋁導線之電性和可靠度研究

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研究生：	楊正鵬 Yang, Zheng-Peng
論文名稱：	具不同金屬疊層結構的奈米線寬鋁導線之電性和可靠度研究 Electrical properties and reliability of Aluminum nanowires with various metal stack structures
指導教授：	吳文發 Wu, Wen-Fa 張廖貴術 ChangLiao, Kuei-Shu
口試委員:	蘇俊榮 Su, Chun-Jung 吳其昌 Wu, Chi-Chang
學位類別：	碩士 Master
系所名稱：	原子科學院 - 工程與系統科學系 Department of Engineering and System Science
論文出版年：	2019
畢業學年度：	107
語文別：	中文
論文頁數：	81
中文關鍵詞：	鋁、奈米金屬線、可靠度、電致遷移、竹節狀
相關次數：	點閱：1 下載：0
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隨著尺寸縮小，銅導線因為電子散射效應以及厚的阻障層的影響，會隨著尺寸縮小而有等效電阻率大幅提高的問題。由於鋁金屬在散射效應的影響較小，並且不需要厚的阻障層，因此在電性方面是有機會代替銅金屬導線。而鋁導線在小尺寸下容易形成竹節狀結構，可以克服傳統鋁導線可靠度不佳的問題。此外，採用Al/air-gap連線系統，並具有較Cu/air-gap連線系統，製程簡易許多的優勢。
因為具備不同金屬底層的鋁導線會有不同的等效電阻率以及可靠度表現，本論文中，我們將用傳統的鋁導線製程來製作四種不同底層金屬結構的鋁導線(AlCu/TiN、Ti/AlCu/TiN、TiN/AlCu/TiN、Ti/TiN/AlCu/TiN)，過程中會對金屬薄膜做RTA退火並探討退火對於材料以及電性的影響。接著使用SiO2當硬遮罩以及電子束微影方式製作出奈米線寬的鋁導線，其討論的內容包含退火對於鋁薄膜的影響、鋁導線材料分析、線寬效應對於鋁導線電阻率的影響、電阻溫度係數、焦耳熱影響、奈米線寬鋁導線的可靠度、四種不同金屬疊層結構的比較、介電覆蓋層沉積後的材料擴散情況。
研究結果發現，高度60奈米、實際線寬從90奈米縮小至20奈米的鋁導線等效電阻率僅提升約30 ~ 38%。在240°C、電流密度107 A/cm2的加速破壞情況下，具Ti/TiN或TiN金屬底層、線寬30奈米鋁導線可以提升生存時間至少14倍以上。而在線寬30奈米鋁導線可靠度量測結果發現有兩種電阻變化率趨勢以及三種生存時間分佈。根據生存時間與電阻變化率趨勢可以推論，當鋁導線竹節狀結構程度較差的情況下，其生存時間較低，並且其破壞機制與傳統鋁導線相同，某個位置的空隙形成後會在短時間內快速成長 ; 當鋁導線竹節狀程度較高，甚至成為竹節狀結構，其空隙形成後成長速度緩慢，需要較長的時間才會斷線。由於大部分量測結果為竹節狀程度高或竹節狀結構的鋁導線，表示鋁導線在小尺寸下會因為晶粒結構的改變而改善可靠度，因此無論是在電性還是可靠度，鋁是具有潛力用以代替銅，成為金屬連線系統的候選材料。

Cu line resistivity is expected to increase dramatically with further scaling of Cu interconnect dimension due to thick barrier layer and electron scattering effects. Compared to Cu, Al has relatively low electron scattering effects and does not need thick barrier layers, and hence Al is one of the potential candidates for interconnect scaling. Al metal line with small line width is easy to form a bamboo-like grain structure and hence expected to have an enhancing electromigration (EM) performance. Furthermore, the fabrication of the Al/air gap interconnect needs fewer process steps than the Cu/air gap interconnect.
In this study, electrical properties and reliability of Al nanowires with various metal stack structures were investigated. AlCu/TiN, Ti/AlCu/TiN, TiN/AlCu/TiN, Ti/TiN/AlCu/TiN nanowires were fabricated by electron-beam lithography, SiO2 hard mask, and dry etching processes. Rapid thermal annealing (RTA) was used to improve properties of the metal films. The discussion topics include annealing effects on Al films, material properties of Al nanowires, line width effects on effective resistivities of Al nanowires, temperature coefficient of resistance (TCR), Joule heat effects, electromigration effects, and thermal diffusion effects of Al nanowires with dielectric capping layers.
Effective resistivities of Al nanowires increase only 30-38% as effective linewidth decreases from 90 nm to 20 nm. The lifetime of 30 nm Ti/TiN/Al/TiN and TiN/Al/TiN nanowires is 14 times longer than Al/TiN nanowires under stressing at 107 A/cm2 and 300°C. EM reliability of the 30 nm Al/TiN nanowires exhibits a trimodal failure distribution and two trends in resistance variation. EM performance is related to the degree of bamboo-like grain structure in the Al nanowire. A short lifetime is found for the Al nanowire with more grain boundary triple points. Voids are nucleated at the grain boundary triple points due to atomic flux divergence. The voids may serve as a source of vacancies, thus accelerating EM failure. Most Al nanowires have high bamboo-like grain structures and hence enhancing electromigration performance. Therefore, Al-based interconnect will be one of the potential interconnect candidates for further large-scale integration.

摘要.......................................................i
Abstract..................................................ii
致謝.....................................................iii
目錄......................................................iv
表目錄....................................................vi
圖目錄...................................................vii
第一章、簡介...............................................1
1 前言...................................................1
2 研究動機...............................................2
第二章、文獻回顧...........................................9
1 金屬導線之演變.........................................9
2 銅導線之物理極限......................................10
2.1 平均自由路徑 (Mean free path, MFP)..................10
2.2 Mattiessen’s Rule..................................11
2.3 散射效應............................................12
2.4 阻障層..............................................14
3 鋁金屬連線之結構......................................14
4 電致遷移效應..........................................16
5 竹節狀結構............................................18
6 近竹節狀結構..........................................21
7 金屬退火..............................................22
第三章、實驗方法與步驟....................................24
1 鋁導線製程流程........................................27
2 電性量測..............................................28
2.1 四點探針 (Four point probe, FPP)....................28
2.2電流 – 電壓 (I-V) 量測..............................28
2.3電致遷移量測.........................................30
3 物性分析..............................................31
3.1 X光繞射儀 (X-ray diffractometer, XRD)...............31
3.2 電子束離子束雙束系統 (Focus Ion Beam, FIB)..........31
3.3 穿透式電子顯微鏡....................................31
4 電致遷移統計分析......................................32
第四章、結果與討論........................................33
1 不同疊層鋁金屬薄膜性質................................33
1.1 不同疊層鋁金屬薄膜厚度..............................33
1.2 鋁金屬薄膜在不同退火條件下之片電阻值變化............38
1.3 退火後鋁金屬薄膜的XRD分析...........................41
1.4 退火後的鋁金屬薄膜晶粒尺寸..........................41
2 奈米線寬鋁導線結構分析................................43
3奈米線寬鋁導線之線寬對等效電阻率效應...................45
4 奈米線寬鋁導線在不同環境溫度下的特性分析..............48
5 鋁導線可靠度分析......................................53
5.1 焦耳熱對於奈米線寬鋁導線的影響......................53
5.2 電致遷移對於奈米線寬鋁導線的影響....................58
5.3 不同金屬疊層結構鋁導線的可靠度量測與比較............65
6 介電材料對於奈米線寬鋁導線的影響......................69
第五章、結論..............................................72
第六章、未來研究方向......................................73
參考文獻..................................................74
附錄一、鋁金屬薄膜TEM切割詳細圖片.........................78
                                

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