隨著電子構裝技術的精進，電子產品的微型化伴隨導線高電流密度，會引發「電遷移效應」－原子因通電而造成的擴散現象，本研究探討在打線接合中最有潛力來取代傳統金線的銀與銅之銀銅合金。過去文獻曾報導通電造成「合金過飽和」的現象，然而關於電遷移對合金影響的討論較少，本研究以通電中臨場掃描式電子顯微鏡 (in situ SEM)結合通電中臨場同步輻射X光繞射實驗 (in situ XRD)來探討電遷移對銀銅合金的影響。本實驗銀銅合金組成特意選擇為在銀銅二元相圖上是單相區的Ag97Cu3與兩相區的Ag75Cu25。臨場SEM結果顯示通電後Ag97Cu3 與Ag75Cu25皆有晶粒成長的現象，且在Ag75Cu25中觀察到噴泉狀 (micro-fountain)與麵條狀不曾觀察到的微結構，顯示傳統電遷移理論無法完整解釋發生的機制。臨場XRD分析顯示在通電過程中晶格處於一個晶格膨脹的狀態，且晶格膨脹程度隨電流密度增加而增加，應變量也隨之上升。Ag75Cu25通電後晶格膨脹之應變量大於Ag97Cu3晶格膨脹之應變量，而Ag75Cu25中富銀相通電引發之應變量又大於富銅相通電引發之應變量，表示銀原子與銅原子間存在著不均勻的應力分佈，而該應力梯度很有可能為造成臨場SEM觀察到晶粒成長、麵條狀微結構的主要原因。除此之外，通電後引發的應變量對合金微結構的改變與試片的失效時間有很大的影響，應變越大，失效時間越快。結合SEM與XRD結果顯示單相區的Ag97Cu3較兩相區的Ag75Cu25擁有更加的抗電遷移能力。

As the technologies in microelectronic industry are being developed, miniaturization of electronic products is inevitable. However, as miniaturization requires much smaller interconnects, the current density goes up, as well as the probability of circuit failure induced by electromigration. In this study, Ag-Cu alloys were investigated since silver and copper are best potential metals to replace traditional gold wires for wire bonding. The phenomenon of alloy supersaturation after current stressing is being studied yet there are not much researches about the electromigration on alloys. The compositions of Ag-Cu alloys were chosen to be one-phase alloy Ag97Cu3 and two-phase alloy Ag75Cu25. Microstructure evolution and crystal structure of Ag97Cu3 and Ag75Cu25 under 4x〖10〗^5 A/cm^2 current stressing were investigated using in-situ SEM and in-situ XRD analysis. Significant coarsening of Ag-rich grains and Cu-rich grains were observed for both Ag97Cu3 and Ag75Cu25 under current stressing. In Ag75Cu25, the microstructure became noodle-like pattern after current stressing for 260 minutes, where copper is the major atom with little silver atoms. In situ XRD analysis indicated that both Ag97Cu3 and Ag75Cu25 experienced lattice expansion during current stressing, and the lattice expansion strain induced by current stressing of Ag75Cu25 was higher than that of Ag97Cu3. Besides, the induced strain of silver atoms was higher than that of copper atoms in Ag75Cu25, indicating that there was a non-uniform lattice expansion of silver and copper atoms, which established a stress gradient between silver and copper atoms. Such strain energy gradient might be the driving force of grain growth and the noodle-like pattern. Our experiments also revealed that the higher the strain induced during current stressing, the shorter the failure time. Combining the in-situ SEM results and in-situ XRD results suggest that one-phase alloy Ag97Cu3 shows better electromigration resistance than two-phase alloy Ag75Cu25.

1. Mack, C.A., Fifty Years of Moore's Law. Ieee Transactions on Semiconductor Manufacturing, 2011. 24(2): p. 202-207.
2. Zeng, K. and K.N. Tu, Six cases of reliability study of Pb-free solder joints in electronic packaging technology. Materials Science & Engineering R-Reports, 2002. 38(2): p. 55-105.
3. Tu, K.N., Recent advances on electromigration in very-large-scale-integration of interconnects. Journal of Applied Physics, 2003. 94(9): p. 5451-5473.
4. Koeninger, V., H.H. Uchida, and E. Fromm, Degradation of gold-aluminium ball bonds by aging and contamination. Ieee Transactions on Components Packaging and Manufacturing Technology Part A, 1995. 18(4): p. 835-841.
5. Noolu, N., et al., Phase transformations in thermally exposed Au-Al ball bonds. Journal of Electronic Materials, 2004. 33(4): p. 340-352.
6. Gan, C.L., et al., Future and technical considerations of gold wirebonding in semiconductor packaging - a technical review. Microelectronics International, 2014. 31(2): p. 121-128.
7. A.R. Grone, “Current-induced Marker Motion in copper”, Journal of Physics and Chemistry of Solids, Vol. 20, No. 1-2, 1961, pp. 88-93
8. H. B. Huntington and A.R. Grone, “Current-induced Marker Motion in Gold Wires”, Journal of Physics and Chemistry of Solids, Vol. 20, No. 1-2, 1961, pp. 76-87
9. Fiks, V.B., ON THE MECHANISM OF THE MOBILITY OF IONS IN METALS. Soviet Physics-Solid State, 1959. 1(1): p. 14-28.
10. Sorbello, R.S., Theory of electromigration, in Solid State Physics, Vol 51: Advances in Research and Applications, H. Ehrenreich and F. Spaepen, Editors. 1998. p. 159-231.
11. Sanchez, J.E., L.T. McKnelly, and J.W. Morris, MORPHOLOGY OF ELECTROMIGRATION-INDUCED DAMAGE AND FAILURE IN AL-ALLOY THIN-FILM CONDUCTORS. Journal of Electronic Materials, 1990. 19(11): p. 1213-1220.
12. Bennett, C., A. Nowick, and J. Burton, Diffusion in Solids, Recent Developments. JJ Burton, 1975.
13. Ladani, L.J., Numerical analysis of thermo-mechanical reliability of through silicon vias (TSVs) and solder interconnects in 3-dimensional integrated circuits. Microelectronic Engineering, 2010. 87(2): p. 208-215.
14. Tu, K.N., Reliability challenges in 3D IC packaging technology. Microelectronics Reliability, 2011. 51(3): p. 517-523.
15. Ho, P.S. and T. Kwok, ELECTROMIGRATION IN METALS. Reports on Progress in Physics, 1989. 52(3): p. 301-348.
16. Hu, C.K. and J.M.E. Harper, Copper interconnections and reliability. Materials Chemistry and Physics, 1998. 52(1): p. 5-16.
17. Chen, C., H.M. Tong, and K.N. Tu, Electromigration and Thermomigration in Pb-Free Flip-Chip Solder Joints, in Annual Review of Materials Research, Vol 40, D.R. Clarke, M. Ruhle, and F. Zok, Editors. 2010. p. 531-555.
18. Huang, A.T., K.N. Tu, and Y.-S. Lai, Effect of the combination of electromigration and thermomigration on phase migration and partial melting in flip chip composite SnPb solder joints. Journal of Applied Physics, 2006. 100(3).
19. Ye, H., C. Basaran, and D. Hopkins, Thermomigration in Pb-Sn solder joints under joule heating during electric current stressing. Applied Physics Letters, 2003. 82(7): p. 1045-1047.
20. Tan, C.M. and A. Roy, Electromigration in ULSI interconnects. Materials Science & Engineering R-Reports, 2007. 58(1-2): p. 3-75.
21. Lloyd, J., K.-N. Tu, and J. Jaspal, The physics and materials science of electromigration and thermomigration in solders. MECHANICAL ENGINEERING-NEW YORK AND BASEL-MARCEL DEKKER-, 2004: p. 827-850.
22. Huntington, H.B., Diffusion in Solids：Recent Developments. 1975, New York.
23. Tu, K. Electromigration in VLSI of thin film interconnects. in Fifth International Conference on Thin Film Physics and Applications. 2004. International Society for Optics and Photonics.
24. Cho, J. and C.V. Thompson, GRAIN-SIZE DEPENDENCE OF ELECTROMIGRATION-INDUCED FAILURES IN NARROW INTERCONNECTS. Applied Physics Letters, 1989. 54(25): p. 2577-2579.
25. Sanchez, J.E., L. McKnelly, and J. Morris, Morphology of electromigration-induced damage and failure in Al alloy thin film conductors. Journal of electronic materials, 1990. 19(11): p. 1213-1220.
26. Morris Jr, J., et al., The role of microstructure in thermal fatigue of Pb-Sn solder joints, in Solder Joint Reliability. 1991, Springer. p. 225-265.
27. Frear, D., et al., Microstructurally based finite element simulation of solder joint behavior. 1996, Sandia National Labs., Albuquerque, NM (United States).
28. Lee, T.Y., et al., Electromigration of eutectic SnPb solder interconnects for flip chip technology. Journal of Applied Physics, 2001. 89(6): p. 3189-3194.
29. Ye, H., C. Basaran, and D.C. Hopkins, Pb phase coarsening in eutectic Pb/Sn flip chip solder joints under electric current stressing. International Journal of Solids and Structures, 2004. 41(9-10): p. 2743-2755.
30. Wu, A.T., et al., Electromigration-induced microstructure evolution in tin studied by synchrotron x-ray microdiffraction. Applied Physics Letters, 2004. 85(13): p. 2490-2492.
31. Wu, A.T., et al., Electromigration-induced grain rotation in anisotropic conducting beta tin. Applied Physics Letters, 2005. 86(24).
32. Galyon, G.T., Annotated tin whisker bibliography and anthology. IEEE Transactions on Electronics Packaging Manufacturing, 2005. 28(1): p. 94-122.
33. Lee, B.-Z. and D. Lee, Spontaneous growth mechanism of tin whiskers. Acta Materialia, 1998. 46(10): p. 3701-3714.
34. Boettinger, W., et al., Whisker and hillock formation on Sn, Sn–Cu and Sn–Pb electrodeposits. Acta Materialia, 2005. 53(19): p. 5033-5050.
35. Suganuma, K., et al., Sn whisker growth during thermal cycling. Acta materialia, 2011. 59(19): p. 7255-7267.
36. Lin, S.-k., et al., Mechanical deformation-induced Sn whiskers growth on electroplated films in the advanced flexible electronic packaging. Journal of materials research, 2007. 22(07): p. 1975-1986.
37. Liu, S.H., et al., Tin whisker growth driven by electrical currents. Journal of Applied Physics, 2004. 95(12): p. 7742-7747.
38. Baated, A., et al., Whisker growth behavior of Sn and Sn alloy lead-free finishes. Journal of electronic materials, 2011. 40(11): p. 2278-2289.
39. Liu, C.Y., et al., Microstructure-electromigration correlation in a thin stripe of eutectic SnPb solder stressed between Cu electrodes. Applied Physics Letters, 1999. 75(1): p. 58-60.
40. Liu, Y.H. and K.L. Lin, Damages and microstructural variation of high-lead and eutectic SnPb composite flip chip solder bumps induced by electromigration. Journal of Materials Research, 2005. 20(8): p. 2184-2193.
41. Yang, D., et al., Microstructural evolution and atomic transport by thermomigration in eutectic tin-lead flip chip solder joints. Journal of Applied Physics, 2007. 102(4).
42. Ouyang, F.-Y., K.N. Tu, and Y.-S. Lai, Effect of electromigration induced joule heating and strain on microstructural recrystallization in eutectic SnPb flip chip solder joints. Materials Chemistry and Physics, 2012. 136(1): p. 210-218.
43. Gupta, D., K. Vieregge, and W. Gust, Interface diffusion in eutectic Pb-Sn solder. Acta Materialia, 1998. 47(1): p. 5-12.
44. Yang, Q.L. and J.K. Shang, Interfacial segregation of Bi during current stressing of Sn-Bi/Cu solder interconnect. Journal of Electronic Materials, 2005. 34(11): p. 1363-1367.
45. Chan, Y.C. and D. Yang, Failure mechanisms of solder interconnects under current stressing in advanced electronic packages. Progress in Materials Science, 2010. 55(5): p. 428-475.
46. Yeh, E.C.C., et al., Current-crowding-induced electromigration failure in flip chip solder joints. Applied Physics Letters, 2002. 80(4): p. 580-582.
47. Rinne, G.A., Issues in accelerated electromigration of solder bumps. Microelectronics Reliability, 2003. 43(12): p. 1975-1980.
48. Chiu, Y.-T., et al., Supersaturation induced by current stressing. Scripta Materialia, 2011. 65(7): p. 615-617.
49. Chiu, Y.-T., K.-L. Lin, and Y.-S. Lai, Dissolution of Sn in a SnPb solder bump under current stressing. Journal of Applied Physics, 2012. 111(4).
50. Wang, T.-H. and K.-L. Lin, The Dissolution and Supersaturation of Zn in the Sn9Zn Solder Under Current Stressing. Journal of Electronic Materials, 2016. 45(1): p. 164-171.
51. Chen, W.-Y., et al., Anisotropic dissolution behavior of the second phase in SnCu solder alloys under current stress. Scripta Materialia, 2013. 68(5): p. 317-320.
52. Chiu, T.-C., Y.-T. Chiu, and K.-L. Lin, Electro-dissolution of the Bi second phase in Sn5Bi solder alloy. Materials Letters, 2015. 160: p. 309-313.
53. Lin, S.-k., et al., Ab initio-aided CALPHAD thermodynamic modeling of the Sn-Pb binary system under current stressing. Scientific Reports, 2013. 3.
54. Lee, A., et al., Synchrotron x-ray microscopy studies on electromigration of a two-phase material. Journal of Applied Physics, 2007. 102(5).
55. Chiu, Y.-T., et al., Electrorecrystallization of Metal Alloy. Journal of Alloys and Compounds, 2013. 549: p. 190-194.
56. Chen, K., et al., In situ measurement of electromigration-induced transient stress in Pb-free Sn-Cu solder joints by synchrotron radiation based x-ray polychromatic microdiffraction. Journal of Applied Physics, 2009. 106(2).
57. Wu, A.T., et al., In situ observation of stress evolution in pure tin strip under electromigration using synchrotron radiation x-ray. Journal of Materials Research, 2010. 25(2): p. 292-295.
58. Chen, K., et al., Plastic deformation in Al (Cu) interconnects stressed by electromigration and studied by synchrotron polychromatic x-ray microdiffraction. Journal of Applied Physics, 2008. 104(1).
59. Wang, P.C., et al., Topographic measurement of electromigration-induced stress gradients in aluminum conductor lines. Applied Physics Letters, 2000. 76(25): p. 3726-3728.
60. Aguilar, M., et al., Electromigration in gold thin films. Thin Solid Films, 1998. 317(1-2): p. 189-192.
61. Kao, H.K., et al., Relationship between copper concentration and stress during electromigration in an Al(0.25 at.% Cu) conductor line. Journal of Applied Physics, 2003. 93(5): p. 2516-2527.
62. National Synchrotron Radiation Research Center” Synchrotron Light Source”.