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Unidirectional Growth of Microbumps on (111)-Oriented and Nanotwinned Copper

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Science  25 May 2012:
Vol. 336, Issue 6084, pp. 1007-1010
DOI: 10.1126/science.1216511

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Abstract

Highly oriented [111] Cu grains with densely packed nanotwins have been fabricated by direct-current electroplating with a high stirring rate. The [111]-oriented and nanotwinned Cu (nt-Cu) allow for the unidirectional growth of Cu6Sn5 intermetallics in the microbumps of three-dimensional integrated-circuit packaging; a uniform microstructure in a large number of microbumps of controlled orientation can be obtained. The high-density twin boundaries in the nt-Cu serve as vacancy sinks during the solid-state reaction between Pb-free solder and Cu and greatly reduce the formation of Kirkendall (or Frenkel) voids.

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