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Electromigration Performance of Fluorinated Aluminum Films for VLSI Applications

  • K. P. MacWilliams (a1), W. E. Yamada (a1), S. Brown (a1), G. K. Yabiku (a1), L. Lowry (a2) and M. Isaac (a1)...

Abstract

We have previously shown greatly enhanced resistance to stressinduced hillock formation through fluorine incorporation in aluminum films. Utilizing relatively low F incorporation (<0.1 atomic %), hillock formation density is reduced ∼10x over pure or similarly Cu-doped aluminum films. Electromigration tests were performed on a matrix of structures with varying topology (step heights and slopes) and fluorine incorporation dose. We find that although F improves the stress-induced hillock formation by an order of magnitude, the electromigration performance of flat structures is only slightly improved with F incorporation. Analyzing various step heights and step slopes, the nonfluorinated Al experienced a decreasing electromigration lifetime with increasing step height. However, the optimally implanted F samples showed almost no lifetime reduction with step coverages over a similar regime. In addition, scanning electron micrographs of the failed samples revealed that the failures of the fluorinated samples differ markedly from the non-fluorinated samples. Finally, SIMS profiles taken on F and Cu (for comparison) implanted samples reveal the fundamentally different nature of the two beneficial components: Cu redistributes relatively easily throughout the Al film to segregate to grain boundaries. In contrast, the F profile is extremely stable with simnilar anneals and provides its beneficial effect by forming a distributed refractory metal-like structure within the interconnect.

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