三維度電子構裝為次世代構裝最重要的一環，藉由垂直堆疊整合晶片，大幅提升構裝品效能，其優點為接合間距縮小使傳遞訊號間產生的能量耗損降低，進而提高傳導效率，並因其中單元構裝體積縮小，整體構裝中內體積使用率提高，於同體積構裝中可加入更多元件整合，整體效能大幅提升。三維度電子構裝之中包含三項重要技術:晶圓細化、直通矽晶穿孔、Cu對Cu接面接合，前兩者製程為單獨操作於獨立晶圓，後者製程為欲連接不同的晶圓於垂直方向。Cu對Cu接面接合目前存在兩種接合技術：直接擴散接合法、銲料接合法，前者需要極良好的表面性質，高熱處理溫度及額外施加壓力幫助接合。因此銲料接合法是相對於Cu對Cu接面接合較迅速且簡易的接合方法，其優點為低處理溫度，製程操作時間短，於熱處理時，使用銲料因熔融補平其不均等的接面性質。傳統Cu對Cu接面接合材料使用為Pb-Sn合金或者是Sn基無鉛合金，於本文當中我們嘗試以Ga金屬作為Cu對Cu接面材料使用，利用暫態液相接合法於等溫固化接合，實驗首先討論Cu/Ga二元界面反應，藉由塊材實驗討論於160、180、200、220、240、280與300 oC下反應於固定時間3、6、12、24、48小時，觀察生成相q-CuGa2與g3-Cu9Ga4界面金相結構和測量其動力學性質，建構出反應機制及理論，並對其中發現Cu基板窪地形貌現象，進而討論Ga金屬作為銲料時，基材前處理與飽和度計算，後建立Cu/Ga/Cu三明治結構模擬實際三維度Cu對Cu構裝應用，其結果生成Cu/g3-Cu9Ga4/q-CuGa2/liquid/q-CuGa2/g3-Cu9Ga4/Cu層狀結構。根據結果，實驗應用低溫製程(160 oC)製造出高溫Cu對Cu接點(254 oC)，並試圖修正及優化反應參數於實際應用。

Three-dimensional integrated-circuit (3D IC) packaging is the most important technology in the next generation semiconductor industry. By stacking and interconnecting chips vertically, the form factor of a package is significantly shrunk. Thus the efficiency is greatly enhanced, the power consumption is correspondingly reduced, and the integration property is tremendously improved as well. Currently the three key processes in 3D IC packaging are wafer thinning, through-silicon-via (TSV) formation, and Cu-to-Cu bonding. The former two are processes on the individual dies/wafers, while the latter is the process that vertically connects different dies/wafers. The Cu-to-Cu bonding can be achieved by direct diffusion bonding that the two pretreated Cu pad surfaces are pressed at high temperature and pressure. However, strict surface planarization of the Cu pads is required for the direct diffusion bonding. On the other hand, soldering is an alternative process for Cu-to-Cu bonding. By introducing foreign solder materials, the extremely high quality of Cu pads is not necessary. As a result, soldering is a much cheaper and faster process for Cu-to-Cu interconnection in 3D IC packaging in comparison with the direct diffusion bonding. Conventionally either Pb-Sn or Pb-free Sn-based alloys are employed in the soldering processes. In the research project, we proposed a novel Ga-based Cu-to-Cu soldering bonding interconnection. Combining with the unique bonding technique: transient liquid phase (TLP) bonding, the isothermal solidification of molten Ga at interface was examined. Specifically four types of Cu/Ga/Cu sandwich couples with different Ga thickness were prepared. The Ga layers are 10, 30, 50 and 60 micro-m-thick, respectively. Additionally, bulk Cu/Ga couples with unlimited Cu and Ga supplements were also prepared for comparison. All of the couples were then annealed at 160, 180, 200, 220, 240, 280 and 300 oC for various predetermined length of time ranging from 3 to 48 hours. Furthermore, the pre-treatment process added into the bulk experiments as bulk Cu/Pt/Ga couples. The interfacial morphologies as well as the compositions of the intermetallic compounds (IMCs) formed at the joints were analyzed with optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and electron probe microanalysis (EPMA), respectively. A thicker scalloped q-CuGa2 phase and a thinner planar g3-Cu9Ga4 phase were found at Ga-side and Cu-side, respectively, at the Cu/Ga interface. The original Cu/liquid/Cu couples transformed to Cu/g3-Cu9Ga4/q-CuGa2/liquid/q-CuGa2/g3-Cu9Ga4/Cu couples upon reactions. The two adjacent IMC layers grew thinker with reaction time. Eventually all liquid phase was consumed, and the two q-CuGa2 layers met each other and filled the gaps. The kinetics of phase transformation was discussed and reaction mechanism was proposed in the paper.

1. Kühne, S. and C. Hierold (2011), “Wafer-level bonding and direct electrical interconnection of stacked 3D MEMS by a hybrid low temperature process,”Sensors and Actuators A: Physical, 172(1) pp. 341-346.
2. Motoyoshi, Makoto (2009), “Trough-Silicon Via (TSV),”Proceedings of the IEEE, 97.
3. Lau, John H. (2011), “Overview and outlook of through-silicon via (TSV) and 3D integrations,”Microelectronics International, 28(2) pp. 8-22.
4. Chen, K. N., C. S. Tan, A. Fan and R. Reif (2004), “Morphology and Bond Strength of Copper Wafer Bonding,”Electrochemical and Solid-State Letters, 7(1) pp. G14-G16.
5. Ko, Cheng-Ta and Kuan-Neng Chen (2010), “Wafer-level bonding/stacking technology for 3D integration,”Microelectronics Reliability, 50(4) pp. 481-488.
6. Tang, Ya-Sheng, Yao-Jen Chang and Kuan-Neng Chen (2012), “Wafer-level Cu–Cu bonding technology,”Microelectronics Reliability, 52(2) pp. 312-320.
7. Bobzin, Kirsten, Erich Lugscheider, Felix Ernst, Reimo Nickel, Nazlim Bagcivan, Daniel Parkot, Arne Schlegel, Stefania Ferrara, Tatyana Kashko and Noémi Leick (2008), “Solders development and application process for a micro chip-camera,”Microsystem Technologies, 14(12) pp. 1887-1894.
8. Wu, C. M. L., D. Q. Yu, C. M. T. Law and L. Wang (2004), “Properties of lead-free solder alloys with rare earth element additions,”Materials Science and Engineering: R: Reports, 44(1) pp. 1-44.
9. Li, J. F., P. A. Agyakwa and C. M. Johnson (2011), “Interfacial reaction in Cu/Sn/Cu system during the transient liquid phase soldering process,”Acta Materialia, 59(3) pp. 1198-1211.
10. Agarwal, Rahul , Wenqi Zhang, Paresh Limaye and Wouter Ruythooren (2009), “High Density Cu-Sn TLP Bonding for 3D Integration,”Electronic Components and Technology Conference, pp. 345-349.
11. Zeng, Guang, Songbai Xue, Liang Zhang and Lili Gao (2011), “Recent advances on Sn–Cu solders with alloying elements: review,”Journal of Materials Science: Materials in Electronics, 22(6) pp. 565-578.
12. Alloy Phase Diagram, ASM HANDBOOK(1992), ASM International
13. Yole Developpement (2007), Market for 3D Packaging.
14. Abtewa, M. and G. Selvaduray (2000), “Lead-free Solders in Microelectronics,”Materials Science and Engineering, 27 pp. 95-141.
15. Hume-Rothery, W., G.W. Mabbott and K.K.C. Evans (1934), “The Freezing Points, Melting Points, and Solid Solubility Limits of the Alloys of Silver, and Copper with the Elements of the B Sub-Groups,”Philos. Trans. R. Soc.(London)A, 233 pp. 1-97.
16. Weibke, F. and Z. Anorg (1934), “Das Zustandsdiagramm des Systems Kupfer-Gallium,”Chem, 220 pp. 293-311.
17. Hume-Rothery, W. and G.V. Raynor (1937), “The constitution of the copper-gallium alloys in the region 18 to 32 atomic percent of gallium,”J. Inst Met., 61 pp. 205-222.
18. Andrews, K. W. and W. Hume-Rothery (1941), “On the Alpha/Beta Brass Type of Equilibrium,”Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 178(975) pp. 464-473.
19. Owen, E.A. and V.W. Rowlands (1940), “Solubility of certain elements in copper and in silver,”J. Inst Met., 66 pp. 361-378.
20. Betterton, J.O. and W. Hume-Rothery (1951-52), “The equlibrium diagram of the system copper-gallium in the region 30-100 at.-% gallium,”J. Inst Met., 80 pp. 459-468.
21. Massalski, T. B. (1958), “A massive transformation, β → αm, in Cu-Ga alloys,”Acta Metallurgic, 6 pp. 243-253.
22. Kittl, J.E. and T.B. Massalski (1964-65), “Modification of the Copper-Gallium Phase Diagram in the Region of the Zeta Phase,”J. Inst Met., 93 pp. 182-188.
23. Tikhomirova, O.I., M.V. Pikunov, I.D. Tochenova and I.P. Izotova (1969), “An investigation of structural transformation during the solidifiaction od copper-gallium alloys,”Sov. Mater. Sci, 5 pp. 355-358.
24. El-Boragy, M. and Konrad Schubert (1972), “Kristallstruktur von CuGa2,”Z. Metallkd, 63 pp. 52-53.
25. Stokhuyzen, R., J.K. Brandon, P.C. Chieh and W.B. Pearson (1974), “Copper-Gallium,g1-Cu9Ga4,”Acta Crystallogr. B, 30 pp. 2910-2911.
26. Subramanian, P.R., T.B Massalski and D.E.Laughlin (1988), “Thermodynamic Aspects of Massive Transformations in the CuGa and CuZn Systems,”Acta Matall, 36(4) pp. 937-343.
27. Zhang, Y. , J. B. Li, J. K. Liang, Q. Zhang, B. J. Sun, Y. G. Xiao and G. H. Rao (2007), “Subsolidus phase relations of the Cu–Ga–N system,”Journal of Alloys and Compounds, 438(1-2) pp. 158-164.
28. Li, J. B., L. N. Ji, J. K. Liang, Y. Zhang, J. Luo, C. R. Li and G. H. Rao (2008), “A thermodynamic assessment of the copper–gallium system,”Calphad, 32(2) pp. 447-453.
29. Simic, V. and Z. Marinkovic (1980), “Room temperature interactions in copper-metal thin film couples,”Journal of the Less-Common Metals, 72 pp. 133-140.
30. Simic, V. and Z. Marinkovic (1986), “Reactions of r.f.-sputtered copper layers with Cd, Ga, Ge, Sn and Zn,”Journal of the Less-Common Metals,, 116 pp. L7-L12.
31. Marinkovic, Z. and V. Simic (1992), “Comparative analysis of interdiffusion in some thin film metal couples at room temperature,”Thin Solid Films, 217 pp. 26-30.
32. Simic, V. and Z. Marinkovic (1998), “Review Room-temperature reactions in thin metal couples,”Journal of Materials and Science, 33 pp. 561-624.
33. Shackelford, James F. and William Alexander (2001), Materials Science and Engineering Handbook. Third Edition: CRC Press.
34. Gaskell, David R.,Introdution to the Thermodynamics of Materials. Fifth Edition: Taylor & Francis. Chapter 9.
35. Shewmon, Paul (1989), Diffusion In Solids Second edition: The Minerals, Metals & Materials Society. 10-17.
36. Dyvkov, V. I. (1986), “Reaction diffusion in heterogeneous binary systems Part 1.Growth of the chemical compound layers at the interface between two elementary substances: one compound layer ”J. Mater. Sci, 21 pp. 3078-3084.
37. Evans, U.R. (1960), The Corrosion and Oxidation of Metals,London: Edward Arnold.
38. Wang, Chao-Hong, Chen, Hsien-Hsin, Li, Po-Yi, and Po-Yen Chu (2012), “Kinetic analysis of Ni5Zn21 growth at the interface between Sn–Zn solders and Ni ”Intermetallics, 22 pp. 166-175.
39. Kim, H. K. and K. N. Tu (1996), “Kinetic analysis of the soldering reaction between eutectic SnPb alloy and Cu accompanied by ripening,”PhysRevB.
40. Perez, M. (2005), “Gibbs-Thomson effects in phase transformations,”Scripta Materialia, 52(8) pp. 709-712.
41. Schaefar, Matt, Raymond A. Fournelle and Jin Liang (1998), “Theory for intermetallic phase growth between cu and liquid Sn-Pb solder based on grain boundary diffusion control,”J. Electron. Mater, 27(11) pp. 1167-1176.
42. Cook, Grant O. and Carl D. Sorensen (2011), “Overview of transient liquid phase and partial transient liquid phase bonding,”Journal of Materials Science, 46(16) pp. 5305-5323.
43. Ipser, H., H. Flandorfer, Ch Luef, C. Schmetterer and U. Saeed (2006), “Thermodynamics and phase diagrams of lead-free solder materials,”Journal of Materials Science: Materials in Electronics, 18(1-3) pp. 3-17.
44. Laurila, T., V. Vuorinen and J. K. Kivilahti (2005), “Interfacial reactions between lead-free solders and common base materials,”Materials Science and Engineering: R: Reports, 49(1-2) pp. 1-60.
45. Lee, Hwa-Teng, Ming-Hung Chen, Huei-Mei Jao and Tain-Long Liao (2003), “Influence of interfacial intermetallic compound on fracture behavior of solder joints,”Materials Science and Engineering: A, 358(1-2) pp. 134-141.
46. W.D. Macdonald and T.W. Eagar (1998), “Isothermal Solidification Kinetics of Diffusion Brazing,”Metall Mater Trans A, 29A pp. 315-325.
47. Kuntz, M. L., Y. Zhou and S.F. Corbin (2006), “A Study of Transient Liquid-Phase Bonding of Ag-Cu Using Differential Scanning Calorimetry,”Metallurgical and Materials Transactions A, 37A pp. 2493-2504.
48. Lugscheider, E. and S. Ferrara (2004), “Characterisation and optimisation of innovative solders for transient liquid phase bonding and active soldering,”Advanced Engineering Materials, 6(3) pp. 160-163.
49. Qiao, X. and S.F. Corbin (2000), “Development of transient liquid phase sintered (TLPS) Sn–Bi solider pastes,”Materials Science and Engineering A, 283 pp. 38-45.
50. Keene, B.J. (1993), “Review of Data for the Surface Tension of Pure Metals,”International Materials Reviews, 38(No.4) pp. 157-192.
51. Rame, E. (1997), “The Interpretation of Dynamic Contact Angles Measured by the Wilhelmy Plate Method,”Journal of Colloid and Interface Science, 25 pp. 245-251.
52. Instruction Manual for SAT-5000. ver.1.12: Rhesca Co.
53. Nicolas, M. G. and C. F. Old (1979), “Review-Liquid embrittlement,”Journal of Materials and Science, 14 pp. 1-18.
54. Schaefer, Mathew , Werner Laub, Janet M. Sabee and Raymond A. Fournelle (1996), “A numerical method for predicting intermetallic layer thickness developed during the formation of solder joints,”J. Electron. Mater, 25(6) pp. 992-1003.
55. Shea, M. M. and N. S. Stoloff (1973), “Embrittlement of Beta-Brass Alloys by Liquid Metals and Aqueous Ammonia,”Mater. Sci. Eng, 12 pp. 245-253.
56. Narh, K. A., V. P. Dwivedi and J. M. Grow (1998), “The effect of liquid gallium on the strengths of stainless steel and thermoplastics,”Journal of Materials and Science, 33 pp. 329-337.
57. Deng, Yue-Guang and Jing Liu (2009), “Corrosion development between liquid gallium and four typical metal substrates used in chip cooling device,”Applied Physics A, 95(3) pp. 907-915.
58. Weast, Robert C. (1988), CRC Handbook of Chemistry & Physics CRC Press.
59. Tanaka, T., M. Matsuda, K. Nakao, Y. Katayama, D. Kaneko, S. Hara, X. Xing and Z. Qiao (2001), “Measurment of Surface Tension of Liquid Ga-Base Alloys by a Sessile Drop Method,”Zeitschrift für Metallkunde, 92(11) pp. 1242-1246.
60. Hardy, S.C. (1985), “The Surface Tension of Liquid Gallium,”J Cryst Growth, 71 pp. 602-606.
61. Sun, Shun-Ping , Dan-Qing Yi and Bing Zang (2010), “Calculation of surface tension of Al-Mg-Er ternary alloy based on Butler's equation,”The Chinese Journal of Nonferrous Metals, 20(5).
62. Picha, Radim, Jan Vrestal and Ales Kroupa (2004), “Prediction of alloy surface tension using a thermodynamic database,”Calphad, 28(2) pp. 141-146.
63. Hai, Yoon Park and Shik Jhon Mu (1982), “Thermodynamic and Transport Properties of Liquid Gallium,”Journal of Korea Nuclear Society, 14(No.1) pp. 10-16.
64. D. A. Harrison, D. Yan and S.B. Lairs (1977), “The surface tension of liquid copper,”J. Chem. Thermodynamics, 9 pp. 1111-1119.