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Maskless, Direct Deposition of Copper onto Aluminum Bond Pads for Flip Chip Applications

Published online by Cambridge University Press:  10 February 2011

M. Fang
Affiliation:
University of Missouri-Rolla, Rolla, MO 65409
T. O'Keefe
Affiliation:
University of Missouri-Rolla, Rolla, MO 65409
M. Stroder
Affiliation:
Brewer Science Inc., Rolla, MO, 65401
W. Shih
Affiliation:
Brewer Science Inc., Rolla, MO, 65401
M. O'Keefe
Affiliation:
Air Force Research Lab, Wright-Patterson AFB, OH 45433
R. Strawser
Affiliation:
Air Force Research Lab, Wright-Patterson AFB, OH 45433
D. Via
Affiliation:
Wright St. University, Dayton, OH 45435.
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Abstract

Flip chip interconnection of integrated circuits (IC) for packaging applications such as direct chip attachment use Pb-Sn solders as the connection between the die and the substrate. Underbump metallization is typically used to transition from the non-solderable Al bond pad on the IC to a solderable surface such as copper using traditional blanket metal deposition, photolithography and etching procedures. In this study, we report for the first time the use of a novel process for selectively depositing adherent copper directly onto aluminum thin films, eliminating the need for adhesion promoting transition layers and additional patterning steps. Utilizing copper bearing organic solutions and standard electroless and electrolytic copper plating baths, as-deposited and annealed sputter deposited Al-x%Cu (x = 0 to 2) thin films were coated with metallic copper. An increase in the organically deposited copper nucleation site density was observed with increasing copper concentration in the sputtered aluminum/copper thin films. Preliminary results using focused ion beam microscopy indicated that dissolution of the aluminum oxide surface and subsequent deposition of copper by cementation occurs in the non-conducting organic solution at sub-micron reaction lengths. Qualitative adhesion testing of samples resulted in the majority of films passing the tape test. Demonstration of the process using 50 micron diameter vias in BCB coated flip chip test vehicles from MCNC will be presented.

Type
Research Article
Copyright
Copyright © Materials Research Society 1998

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References

REFERENCES

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