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研究生： 林冠斈
Lin, Kuan-Hsueh
論文名稱： 臨界應變誘發電遷移-重新檢視Blech效應
The Blech Effect Revisited: Critical Lattice Strain-induced Electromigration
指導教授： 林士剛
Lin, Shih-kang
學位類別： 碩士
Master
系所名稱： 工學院 - 材料科學及工程學系
Department of Materials Science and Engineering
論文出版年： 2020
畢業學年度： 108
語文別： 英文
論文頁數： 87
中文關鍵詞： 臨場通電實驗 、結晶繞射分析 、晶格應變 、鋁 、電遷移
外文關鍵詞： In-situ current stressing experiment, XRD analysis, lattice strain, aluminum, electromigration
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    • 隨著大數據世代的演進，自駕車、智慧城市、自動化科技已成未來資訊世代的代表產品。為此，更快速的傳輸科技與更耐用的電子產品成為一大需求，近來的5G技術之起步正是其中一大標的。5G技術包含三大重點特色:提升的傳輸頻寬、機器間的資訊交換與更低的傳遞延遲。資訊傳輸的基本來自於電子訊號在元件內與元件間傳遞。低延遲的快速傳輸意味著電子訊號不會在這些過程中受干擾、損失或延遲。元件內與元件間的訊號傳輸主要由許許多多的金屬導線來完成，這些導線主要是鋁、銅與其他些許高導電性的金銀等材料。電子訊號的干擾通常來自這些金屬導線發生微結構的改變進而影響訊號的傳輸行為。在通電的過程當中，電遷移現象是其中一個主要原因。電遷移現象描述導線在承受高密度的電流時，金屬導線上會在陰極端出現孔洞，陽極端出現凸塊進而影響導線的訊號傳輸。在1976年，Blech在鋁金屬導線上發現電遷移現象要發生須滿足一臨界電流密度與長度乘積之值，成為往後在金屬導線設計上的重要法則。然而，此法則在材料機制的解釋上並不完備。本研究利用臨場通電觀測搭配材料為結構的分析方法，設計不同長度的鋁金屬導線施作大量通電測試。藉由繞射的分析，發現電遷移微結構的變化，與材料的應變行為有極大關聯，當材料通電時的臨場應變達到一個臨界值時，電遷移會在此情形下發生，並且使材料發生永久性的結構改變。進一步的第一原理計算發現此應變會大大降低材料的遷移屏障，提升材料遷移的可能性。在穿透式電子顯微鏡的進一步觀測下，雖在缺陷的差排密度分析上看不出顯著的差異，但在高密度電流通電的實驗組中，發現在鋁系統中極難形成的雙晶結構。加上繞射分析的永久性結構變化，說明了高密度電流的施加，電遷移的過程會使材料發生微觀尺度下的差排累積，進而促成巨觀尺度下發現的孔洞與凸塊，使微結構改變。

    Since the technology development goes into the 5th generation. Requirement of low latency and highly functionalized devices increases. Moore’s law and More than Moore’s become important discipline in the IC industry. In the IC industry, the System in Package (SiP) concept results in the development of 2.5D and 3D IC. Upon the road to ultimate goal of the design, the reliability and efficiency is subjected to the current-induced issues such as Joule heating and electromigration (EM). In this thesis, the EM-resist design is reviewed, and the Blech effect is emphasized, followed by the investigation of the length-dependent EM occurrence in aluminum by current stressing experiments. In the experiment, the synchrotron X-ray was used as analyzing tool for the strain evolution during the in-situ current stressing process. From the strain to time profile, the steady state strain during the process and the residual strain after current ceased is defined for further quantitative study. By plotting the derived steady state strain and residual against the hillocks formation on the aluminum thin film, a critical steady-state strain around 0.008±0.0003 was found to trigger the EM hillocks formation, for the strip length ranging from 500 to 20000 μm. Further first principle calculation of the migration barrier under different strain state has been done to explain the critical strain. To conclude the whole thesis, the Blech effect is revisited that it is the critical strain instead of the current density-length product that results in EM. In the future work, the detailed study on the defect structure that causes the residual strain is suggested. On the other hand the relation between the critical strain 0.008±0.0003 and physical property of aluminum need to be investigated for the further application in to other industrial material systems and structures.

    摘要 I Abstract II 致謝 III Table of Content IV List of Tables VII List of Figures VIII Chapter I: Introduction 1 I.1 Background: Technology trends in semiconductor industry 1 I.2 Extending Moore’s Law from industrial perspectives 5 Chapter II: Literature review 11 II.1 Electromigration effect 11 II.2 Predicting the lifetime of a metal strip 12 II.3 Lengthening MTTF by increasing EM-resistance 13 II.3.1 Tuning the EM-resistance by grain engineering 14 II.3.2 Alloying effect one the electromigration behavior. 16 II.3.3 Liner used in dual-damascene Cu interconnections 17 II.3.4 Length-dependent design implementing Blech effect 18 II.4 Blech effect 20 II.4.1 Blech effect and the critical Blech product for electromigration 20 II.4.2 Back-stress model for Blech effect 22 II.5 Synchrotron-based analysis on electromigration 24 II.5.1 Synchrotron-based stress and defects measurements 25 II.5.2 Non-uniform stress-strain induce electromigration 26 II.5.3 Current-induced deformation in copper system: an EBSD study 31 Chapter III: Motivation: electromigration effect in aluminum for different strip length 34 Chapter IV: Experimental methods 35 IV.1 Sample preparation 35 IV.2 In-situ observation with synchrotron XRD 36 IV.3 Microstructure observation 39 IV.4 Ab-initio calculation for diffusion barrier 41 IV.5 Data processing and quantitative study 42 IV.5.1 Big data generated from repeated and different experiment group 42 IV.5.2 Quantitative study 44 Chapter V: Experimental results and discussion 48 V.1 Sample benchmark 48 V.1.1 As-deposit sample lattice constant 48 V.1.2 Sample electric resistance and surface morphology 49 V.1.3 Thermal expansion of sample holder at different applied voltage 50 V.1.4 Sub-micron structure of as-deposited sample 51 V.2 Blech product at different length scale: SEM observation 54 V.3 Voltage drop-induced lattice strain evolution during current stressing 55 V.3.1 Strain evolution during current stressing 55 V.3.2 Hillocks formation on different applied voltage 56 V.3.3 Voltage-induced different cases of microstructure changes on Al film 58 V.3.4 Voltage drop-induced hillocks formation after current stressing 58 V.4 Structure change after hillocks formation and lattice strain-induced hillocks formation during current stressing 61 V.5 Sub-micron microstructure observation by TEM 64 V.5.1 Grain structure change after interaction with thermal and electrical field 64 V.5.2 Defect structure analysis 67 V.6 TEM observation of hillocks formation 72 V.7 Lattice strain induces enhanced diffusivity by ab-initio calculation 74 V.8 Criteria for electromigration: comparison with Blech product 75 Chapter VI: Conclusion 76 Chapter VII: Outlook 78 Chapter VIII: Reference 79 Chapter IX: Appendix 82 IX.1.1 Strain evolution data 82 IX.1.2 TEM and IFFT analysis for ｛111｝ plane 86

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