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According to Moore's Law, as the feature size of semiconductor devices becoming smaller and smaller, the chip integration degree keeps increasing. In particular, accompanying with the development of high chip integration and unit size reduction, the metal interconnects, i. e. the wire bonding, are becoming a challenging problem. Copper wire is believed to be an excellent metal for wire bonding, instead of gold wire, due to its attractive advantages such as low cost, favorable electrical and thermal conductivities etc. However, the excess Cu/Al intermetallic compounds (IMC) at the interface of copper wire and aluminum pad will increase the contact resistance and reduce bonding strength. This can affect the properties and reliability of devices. Currently, the evolutions of the interfacial microstructures as well as the growth mechanism of Cu/Al IMC at the bonding interface under thermal condition are still unclear.In-situ transmission electron microscope (TEM) has high spatial resolution and strong analysis ability. With fast CCD cameras, TEM can also record the dynamic structure evolution of the sample in real time. Combined with multi-function holders, TEM can also exert diverse fields and loads on the sample and synchronously monitor their structures and component evolutions. Hence, in situ TEM provides an advanced technique to explore the structural evolution and growth mechanism of Cu/Al IMC.In this paper, the growth mechanism of Cu/Al IMC is investigated during the annealing temperature from 50-220 ℃ based on the in-situ high resolution transmission electron microscopy (in-situ HRTEM). Specifically, the dynamic growth and structural evolution of Cu/Al IMC during annealing are recorded in real time. Results show that the isolated Cu/Al IMC is distributed in the bonding interface before annealing. The main component of IMC is Cu9Al4, whereas the minor one of IMC is CuAl2. After annealing at 50-220 ℃ for 24 h, Cu/Al IMC near the Cu layer is Cu9Al4, while Cu-Al IMC apart from the Cu layer is CuAl2. Meanwhile, the reaction rates and the activation energy of Cu/Al IMC at different temperatures are calculated. Furthermore, the more accurate growth equation of Cu/Al IMC is also proposed based on the in-situ experimental results, which will benefit the optimization of bonding process and the reliability of Cu/Al wire bonding.
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Keywords:
- intermetallic compounds /
- Cu/Al wire bonding /
- growth process /
- in-situ transmission electron microscopy
[1] Khoury S L, Burkhard D J, Galloway D P, Scharr T A 1990 IEEE Electronic Components and Technology Conference Las Vegas, USA, May 20-23, 1990 p768
[2] Mori S, Yoshida H, Uchiyama N 1988 Proceedings of the 38th IEEE Electronics Components Conference Los Angeles, USA, May 9-11, 1988 p539
[3] Liu Y-L, Gui L-J, Jin S 2012 Chin. Phys. B21 096102
[4] Hang C J 2008 Ph. D. Dissertation (Harbin: Harbin Institute of Technology) (in Chinese) [杭春进 2008 博士学位论文 (哈尔滨: 哈尔滨工业大学)]
[5] Nguyen L T, McDonald D, Danker A R, Ng P 1995 IEEE Trans. Compon. Packag. Manuf. Technol. A 18 423
[6] Funamizu Y, Watanabe K 1971 Trans. Jpn. Inst. Met. 12 147
[7] Kim H J, Lee J Y, Paik K W, Koh K W, Won J, Choe S, Lee J, Moon J T, Park Y J 2003 IEEE Trans. Compon. Packag. Technol. 26 367
[8] Murali S, Srikanth N, Vath C J 2003 Mater. Res. Bull. 38 637
[9] Murali S, Srikanth N, Charles J V III 2004 Mater. Lett. 58 3096
[10] Ellis T W, Levine L, Wicen R, Ainouz L 2000 Proceedings of Semicon Conference Singapore, Singapore, May 8-11 p44
[11] Lu Y H, Wang Y W, Appelt B K, Lai Y S, Kao C R 2011 IEEE 61 st Electronic Components and Technology Conference (ECTC) Lake Buena Vista, USA, May 31-June 3, 2011 p1481
[12] Drozdov M, Gur G, Atzmon Z, Kaplan W D 2008 J. Mater. Sci. 243 6029
[13] Tan Y Y, Yong F K 2010 IEEE 17th International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA), Singapore, Singapore, July 5-9, 2010 p1
[14] Lee C C, Higgins L M 2010 Proceedings of IEEE 60th Electronic Components and Technology Conference (ECTC) Las Vegas, USA, June 1-4, 2010 p342
[15] Chen J, Lai Y S, Wang Y W, Kao C R 2011 Microelectron. Reliab. 51 125
[16] Zhang B, Wang T, Cong Y, Zhao M, Fan X, Wang J 2010 11th International Conference on Electronic Packaging Technology & High Density Packaging (ICEPT-HDP) Xi'an, China, August 16-19, 2010 p213
[17] Xu H, Liu C, Vadim V, Silberschmidt V V, Chen Z 2010 J. Electron. Mater 39 124
[18] Boettcher T, Rother M, Liedtke S, Ullrich M, Bollmann M, Pinkernelle A, Gruber D, Funke H J, Kaiser M, Kan L, Li M, Leung K, Li T, Farrugia M L, O'Halloran O, Petzold M, Ma Z B, Klengel R 2011 12th Electronics Packaging Technology Conference (EPTC) Singapore, Singapore, December 8-10, 2011 p585
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[1] Khoury S L, Burkhard D J, Galloway D P, Scharr T A 1990 IEEE Electronic Components and Technology Conference Las Vegas, USA, May 20-23, 1990 p768
[2] Mori S, Yoshida H, Uchiyama N 1988 Proceedings of the 38th IEEE Electronics Components Conference Los Angeles, USA, May 9-11, 1988 p539
[3] Liu Y-L, Gui L-J, Jin S 2012 Chin. Phys. B21 096102
[4] Hang C J 2008 Ph. D. Dissertation (Harbin: Harbin Institute of Technology) (in Chinese) [杭春进 2008 博士学位论文 (哈尔滨: 哈尔滨工业大学)]
[5] Nguyen L T, McDonald D, Danker A R, Ng P 1995 IEEE Trans. Compon. Packag. Manuf. Technol. A 18 423
[6] Funamizu Y, Watanabe K 1971 Trans. Jpn. Inst. Met. 12 147
[7] Kim H J, Lee J Y, Paik K W, Koh K W, Won J, Choe S, Lee J, Moon J T, Park Y J 2003 IEEE Trans. Compon. Packag. Technol. 26 367
[8] Murali S, Srikanth N, Vath C J 2003 Mater. Res. Bull. 38 637
[9] Murali S, Srikanth N, Charles J V III 2004 Mater. Lett. 58 3096
[10] Ellis T W, Levine L, Wicen R, Ainouz L 2000 Proceedings of Semicon Conference Singapore, Singapore, May 8-11 p44
[11] Lu Y H, Wang Y W, Appelt B K, Lai Y S, Kao C R 2011 IEEE 61 st Electronic Components and Technology Conference (ECTC) Lake Buena Vista, USA, May 31-June 3, 2011 p1481
[12] Drozdov M, Gur G, Atzmon Z, Kaplan W D 2008 J. Mater. Sci. 243 6029
[13] Tan Y Y, Yong F K 2010 IEEE 17th International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA), Singapore, Singapore, July 5-9, 2010 p1
[14] Lee C C, Higgins L M 2010 Proceedings of IEEE 60th Electronic Components and Technology Conference (ECTC) Las Vegas, USA, June 1-4, 2010 p342
[15] Chen J, Lai Y S, Wang Y W, Kao C R 2011 Microelectron. Reliab. 51 125
[16] Zhang B, Wang T, Cong Y, Zhao M, Fan X, Wang J 2010 11th International Conference on Electronic Packaging Technology & High Density Packaging (ICEPT-HDP) Xi'an, China, August 16-19, 2010 p213
[17] Xu H, Liu C, Vadim V, Silberschmidt V V, Chen Z 2010 J. Electron. Mater 39 124
[18] Boettcher T, Rother M, Liedtke S, Ullrich M, Bollmann M, Pinkernelle A, Gruber D, Funke H J, Kaiser M, Kan L, Li M, Leung K, Li T, Farrugia M L, O'Halloran O, Petzold M, Ma Z B, Klengel R 2011 12th Electronics Packaging Technology Conference (EPTC) Singapore, Singapore, December 8-10, 2011 p585
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