Cu/SiO2混合接合製程為現今半導體封裝中能夠實現三維積體電路的重要接合方法之一，銅接合因其優秀的導電與導熱表現而成為主要訊息傳輸位置，接合材料亦須足夠的機械強度以支撐結構，藉由高密度雙晶晶界的引入不但能夠提升純銅的機械強度，還能同時避免韌性的損失，以優化銅接合之產品品質與效能，由於銅接合主要藉由擴散接合方法形成，而其接合品質與強度備受重視，因此擴散接合中退火製程參數的控制成為影響接合品質的重要因素之一。

本研究針對一般銅/一般銅與奈米雙晶銅/奈米雙晶銅進行接合，分別經不同退火製程，探討基材與接合界面之性質。首先，藉由FIB之離子影像觀察接合基材之晶粒形貌，之後再以EBSD進行結晶取向分析及晶界分析，接著藉由SE及FIB之離子影像進行接合界面之孔洞分析、觀察接合界面之形貌變化，最後，以奈米壓痕量測基材與接合界面之剛性，探討不同退火製程參數對於一般銅與奈米雙晶銅的接合品質與強度之影響。

實驗結果顯示，退火溫度與時間的提高會使基材發生晶粒成長，一般銅之晶粒成長速率為0.49μm/hr1/2，奈米雙晶銅之晶粒成長速率為0.17μm/hr1/2；退火製程亦促進原子的擴散，使界面處孔洞逐漸消失、界面發生Zig-zag effect、界面處的晶粒成長，界面機械性質隨之提升，其中具{111}優選方位之奈米雙晶銅接合經250℃ 3小時退火後擁有最佳的接合品質。

In semiconductor packaging industry, Cu/SiO2 hybrid bonding has been developed to achieve three-dimensional integrated circuits (3D ICs). It is the key issue to control the annealing process which significantly affects the reliability of Cu-to-Cu bonding acting as conductive layer in Cu/SiO2 hybrid bonding. In this study, the quality of Cu-to-Cu bonding was investigated by analyzing the microstructure and mechanical property of matrix and interface, respectively. The microstructure was characterized by scanning electron microscope (SEM) together with electron backscattering diffraction (EBSD) and by focused ion beam (FIB). Then, the mechanical property was measured by nanoindentation technique (NID). The results show that the quality of Cu-to-Cu bonding can be improved as increasing annealing time and temperature.

1. R. Reif, A. Fan, K.N. Chen and S. Das, Fabrication technologies for three-dimensional integrated circuits. in Proceedings International Symposium on Quality Electronic Design. 18-21 March 2002. San Jose, CA, USA: IEEE.
2. S. Chen, S. Thijs, D. Linten, M. Scholz, G. Hellings and G. Groeseneken, ESD protection devices placed inside keep-out zone (KOZ) of through Silicon Via (TSV) in 3D stacked integrated circuits. in Electrical Overstress / Electrostatic Discharge Symposium Proceedings. 9-14 September 2012. Tucson, AZ, USA: IEEE.
3. P. Ramm, J.J.-Q. Lu and M.M. Taklo, Handbook of wafer bonding. John Wiley & Sons. Weinheim, Germany, 2011.
4. A. Fan, Copper Wafer Bonding. Electrochemical and Solid-State Letters, 2(10): p. 534, 1999.
5. X. Zhang, A. Misra, H. Wang, T.D. Shen, M. Nastasi, T.E. Mitchell, J.P. Hirth, R.G. Hoagland and J.D. Embury, Enhanced hardening in Cu/330 stainless steel multilayers by nanoscale twinning. Acta Materialia, 52(4): p. 995-1002, 2004.
6. L. Lu, R. Schwaiger, Z.W. Shan, M. Dao, K. Lu and S. Suresh, Nano-sized twins induce high rate sensitivity of flow stress in pure copper. Acta Materialia, 53(7): p. 2169-2179, 2005.
7. L. Lu, X. Chen, X. Huang and K. Lu, Revealing the Maximum Strength in Nanotwinned Copper. Science, 323(5914): p. 607-610, 2009.
8. D.F. Lim, J. Wei, K.C. Leong and C.S. Tan, Cu passivation for enhanced low temperature (⩽300°C) bonding in 3D integration. Microelectronic Engineering, 106: p. 144-148, 2013.
9. K.N. Chen, C.S. Tan, A. Fan and R. Reif, Morphology and Bond Strength of Copper Wafer Bonding. Electrochemical and Solid-State Letters, 7(1): p. G14, 2004.
10. C.S. Tan and R. Reif, Silicon Multilayer Stacking Based on Copper Wafer Bonding. Electrochemical and Solid-State Letters, 8(6): p. G147, 2005.
11. C.-M. Liu, H.-w. Lin, Y.-C. Chu, C. Chen, D.-R. Lyu, K.-N. Chen and K.N. Tu, Low-temperature direct copper-to-copper bonding enabled by creep on highly (111)-oriented Cu surfaces. Scripta Materialia, 78-79: p. 65-68, 2014.
12. C.-M. Liu, H.-W. Lin, Y.-S. Huang, Y.-C. Chu, C. Chen, D.-R. Lyu, K.-N. Chen and K.-N. Tu, Low-temperature direct copper-to-copper bonding enabled by creep on (111) surfaces of nanotwinned Cu. Scientific Reports, 5(1): p. 9734, 2015.
13. Y. Kagawa, N. Fujii, K. Aoyagi, Y. Kobayashi, S. Nishi, N. Todaka, S. Takeshita, J. Taura, H. Takahashi, Y. Nishimura, K. Tatani, M. Kawamura, H. Nakayama, T. Nagano, K. Ohno, H. Iwamoto, S. Kadomura and T. Hirayama, Novel stacked CMOS image sensor with advanced Cu2Cu hybrid bonding. in 2016 IEEE International Electron Devices Meeting (IEDM). 3-7 December 2016. San Francisco, CA, USA: IEEE.
14. R.H. Pry and R.W. Hennig, On the use of electrical resistivity as a measure of plastic deformation in copper. Acta Metallurgica, 2(2): p. 318-321, 1954.
15. P.V. Andrews, M.B. West and C.R. Robeson, The effect of grain boundaries on the electrical resistivity of polycrystalline copper and aluminium. The Philosophical Magazine: A Journal of Theoretical Experimental and Applied Physics, 19(161): p. 887-898, 1969.
16. E.A. Brandes and G. Brook, Smithells metals reference book. Elsevier. Great Britain, 2013.
17. T.H. Courtney, Mechanical behavior of materials. Waveland Press. UK, 2005.
18. K. Lu, L. Lu and S. Suresh, Strengthening Materials by Engineering Coherent Internal Boundaries at the Nanoscale. Science, 324(5925): p. 349-352, 2009.
19. A.P. Sutton, Interfaces in Crystalline Materials. Monographs on the Physice and Chemistry of Materials: p. 414-423, 1995.
20. K.-C. Chen, 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, 321(5892): p. 1066-1069, 2008.
21. C. Ryu, A. Loke, T. Nogami and S.S. Wong, Effect of texture on electromigration of CVD copper. in IEEE INTERNATIONAL RELIABILITY PHYSICS PROCEEDINGS. Citeseer.
22. C.-H. Tseng, K.N. Tu and C. Chen, Comparison of oxidation in uni-directionally and randomly oriented Cu films for low temperature Cu-to-Cu direct bonding. Scientific Reports, 8(1): p. 10671, 2018.
23. K.-C. Chen, W.-W. Wu, C.-N. Liao, L.-J. Chen and K.N. Tu, Stability of nanoscale twins in copper under electric current stressing. Journal of Applied Physics, 108(6): p. 066103, 2010.
24. T.-C. Liu, C.-M. Liu, H.-Y. Hsiao, J.-L. Lu, Y.-S. Huang and C. Chen, Fabrication and Characterization of (111)-Oriented and Nanotwinned Cu by Dc Electrodeposition. Crystal Growth & Design, 12(10): p. 5012-5016, 2012.
25. C.-H. Tseng, I.H. Tseng, Y.-P. Huang, Y.-T. Hsu, J. Leu, K.N. Tu and C. Chen, Kinetic study of grain growth in highly (111)-preferred nanotwinned copper films. Materials Characterization, 168: p. 110545, 2020.
26. C.-T. Ko and K.-N. Chen, Wafer-level bonding/stacking technology for 3D integration. Microelectronics Reliability, 50(4): p. 481-488, 2010.
27. J.-Y. Juang, C.-L. Lu, Y.-J. Li, K.N. Tu and C. Chen, Correlation between the Microstructures of Bonding Interfaces and the Shear Strength of Cu-to-Cu Joints Using (111)-Oriented and Nanotwinned Cu. Materials (Basel, Switzerland), 11(12): p. 2368, 2018.
28. S. Ryu, K. Lu, X. Zhang, J. Im, P.S. Ho and R. Huang, Impact of Near-Surface Thermal Stresses on Interfacial Reliability of Through-Silicon Vias for 3-D Interconnects. IEEE Transactions on Device and Materials Reliability, 11(1): p. 35-43, 2011.
29. F. Zong, N. Zhou, J. Niu and Z. Sun, Study on bond pad damage issue in bare Cu wire bonding on SMOS8MV wafer technology. 2015 16th International Conference on Electronic Packaging Technology (ICEPT): p. 108-113, 2015.
30. Y.-S. Tang, Y.-J. Chang and K.-N. Chen, Wafer-level Cu–Cu bonding technology. Microelectronics Reliability, 52(2): p. 312-320, 2012.
31. Y. Zhao, T.A. Furnish, M.E. Kassner and A.M. Hodge, Thermal stability of highly nanotwinned copper: The role of grain boundaries and texture. Journal of Materials Research, 27(24): p. 3049-3057, 2012.
32. D. Xu, V. Sriram, V. Ozolins, J.-M. Yang, K.N. Tu, G.R. Stafford, C. Beauchamp, I. Zienert, H. Geisler, P. Hofmann and E. Zschech, Nanotwin formation and its physical properties and effect on reliability of copper interconnects. Microelectronic Engineering, 85(10): p. 2155-2158, 2008.
33. C. Chen, C. Liu, H. Lin, Y. Huang, Y. Chu, D. Lyu, K. Chen and K.N. Tu, Low-temperature and low-pressure direct copper-to-copper bonding by highly (111)-oriented nanotwinned Cu. in 2016 Pan Pacific Microelectronics Symposium (Pan Pacific). 25-28 Jan. 2016.
34. J.W. Huang, K.C. Shie, H.C. Liu, Y.J. Li, H.Y. Cheng and C. Chen, Copper-to-copper direct bonding using different (111) surface ratios of nanotwinned copper films. in 2019 International Conference on Electronics Packaging (ICEP). 17-20 April 2019.
35. F. Pukelsheim, The Three Sigma Rule. The American Statistician, 48(2): p. 88-91, 1994.
36. H. Xiao, W. Han, Y. Ming, Z. Ding and Y. Duan, A Sensitivity Analysis-Based Parameter Optimization Framework for 3D Printing of Continuous Carbon Fiber/Epoxy Composites. Materials, 12(23): p. 3961, 2019.
37. B. Rebhan, J. Svoboda and M. Panholzer, A thermodynamic study of voiding phenomena in Cu–Cu thermo-compression wafer bonding. Microsystem Technologies, 24(1): p. 815-822, 2018.
38. T. Shimatsu, R.H. Mollema, D. Monsma, E.G. Keim and J.C. Lodder, Metal bonding during sputter film deposition. Journal of Vacuum Science & Technology A, 16(4): p. 2125-2131, 1998.
39. H.R. Peng, M.M. Gong, Y.Z. Chen and F. Liu, Thermal stability of nanocrystalline materials: thermodynamics and kinetics. International Materials Reviews, 62(6): p. 303-333, 2017.
40. S. Lagrange, S.H. Brongersma, M. Judelewicz, A. Saerens, I. Vervoort, E. Richard, R. Palmans and K. Maex, Self-annealing characterization of electroplated copper films. Microelectronic Engineering, 50(1): p. 449-457, 2000.
41. N. Alshwawreh, M. Militzer, D. Bizzotto and J.C. Kuo, Resistivity-microstructure correlation of self-annealed electrodeposited copper thin films. Microelectronic Engineering, 95: p. 26-33, 2012.
42. H. Frost and M. Ashby, Deformation-Mechanism Maps: The Plasticity and Creep of Metals and Ceramics. Oxford, UK.: Pergamon Press.
43. H.L. Leong, C.L. Gan, C.V. Thompson, K.L. Pey and H.Y. Li, Application of contact theory to metal-metal bonding of silicon wafers. Journal of Applied Physics, 102(10): p. 103510, 2007.
44. R.L. Norton, Cam design and manufacturing handbook. Industrial Press Inc., New York, 2002.
45. R.B. Bird, W.E. Stewart and E.N. Lightfoot, Transport phenomena. Vol. 1, John Wiley & Sons. USA, 2006.
46. W.L. Chiu, K.W. Chou and H.H. Chang, Nanotwinned Copper Hybrid Bonding and Wafer-On-Wafer Integration. in 2020 IEEE 70th Electronic Components and Technology Conference (ECTC). 3-30 June 2020. Orlando, FL, USA: IEEE.
47. P.M. Agrawal, B.M. Rice and D.L. Thompson, Predicting trends in rate parameters for self-diffusion on FCC metal surfaces. Surface Science, 515(1): p. 21-35, 2002.