Interconnect Bonding
Conclusion We have demonstrated a high yielding bonding process for the fabrication of die-to-die interconnects in dense area arrays at 10µm pitch. Use of a mechanical key created by patterning an overcoat of BCB was found to improve yield. Bonded samples, underfilled with epoxy to prevent oxidation of Cu pads, were subjected to thermal cycling and humidity-temperature testing. No significant changes in performance occurred as a result of the test Cu-Cu thermocompression bonding resulted in demonstrated high yield on individual devices, but not on long runs of consecutive bonds. The lower average yield is due to the dishing obtained during the CMP of Cu pads. This dishing can be reduced by laying out the bond pad arrays so the area density of metal changes gradually between the array and field regions. Comparison of the electrical and shear test performance of Cu/Sn-Cu and Cu-Cu bonds shows that highly conductive (<100mΩ) and mechanically strong (8kg for ~6 mm x 5 mm die) bonds can be achieved in both metal systems. Low temperature bonding in Cu/Sn-Cu devices (at 210°C, below the melting point of tin) was demonstrated to produce high electrical yield, high shear strength and similar IMC formation to devices bonded at 300°C. Such a process may prove useful for bonding dice that have low thermal budgets such as memory or detectors.
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Acknowledgments
The authors gratefully acknowledge the financial support of DARPA. The authors thank RTI staff Scott Anderson and Targia Green for lithography, Dana Fox for cross-sectioning and SEM/EDS and Matt Fabean for electrical testing. The authors thank Russ A. Stapleton of LORD Corporation for underfill materials and discussions. References [1] 1. K. Tanida, M. Umemoto, Y Tomita, M. Tago, Y Nemoto, T. Ando, and K. Takahashi, Proc. of 2003 Electronic Components and Technology Conference, New Orleans, May 2003, pp. 1084-1089.
[2] A. Klumpp, R. Merkel, R. Wieland, and P. Ramm, Proc. of 2003 Electronic Components and Technology Conference, New Orleans, May 2003, pp. 1080-1083.
[3] S. Pozder, A. Jain, R. Chatterjee, Z. Huang, R. Jones, E. Acosta, B. Marlin, G. Hillman, M. Sobczak, G. Kreindl, S. Kanagavel, H. Kostner, S. Pargfrieder, Proc. of 11th IITC 2008, pp 46-48.
[4] J. Lannon Jr., C. Gregory, M. Lueck, A. Huffman, and D. Temple, Proc. of 2009 Electronic Components and Technology Conf., San Diego, May 26 - 29, 2009.
[5] A. Huffman, M. Lueck, C. Bower, D. Temple, Proc. 2007 Electronic Components and Technology Conference, Reno, NV, May 29 -June 1, 2007.
[6] J. Reed, M. Lueck, C. Gregory, A. Huffman, J. Lannon, and D. Temple, Proc. 2010 Electronic Components and Technology Conference, LV, NV, June, 2010.
[7] A. Huffman, J. Lannon, M. Lueck, C. Gregory, and D. Temple, Materials and Technologies for 3D Integration, MRS Symposium Proceedings, Vol. 1112, Boston, December 2008, pp 107-120.
[8] J. Reed, M. Lueck, C. Gregory, A. Huffman, J. M. Lannon, Jr., and D. Temple, Proc. of 13th IITC San Francisco, June 2010.
A B C A D C B
Fig 9. SEMs of samples bonded at 300°C (left) and 210°C (right). Region D marks the location of unreacted Sn.
Fig 10. Cross-sectional SEM of sample with 10µm pitch bonded at 210°C. 19
Fig. 11. Optical micrographs of a typical die from the qualification group (Device 501, 10µm pitch Cu/Sn-Cu bonded at 210°C) after shear testing. Left: Top die. Right: Bottom die.
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