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Solute Additions to Restrict Electromigration in Thin Films

IP.com Disclosure Number: IPCOM000075073D
Original Publication Date: 1971-Jul-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Rosenberg, R: AUTHOR [+3]

Abstract

Failure of solid state devices by electromigration in metal conductor leads has led to serious reliability problems. Electromigration flux can be represented by the expression; (Image Omitted) where D is the diffusivity of the atomic specie and F is the driving force for migration produced by an electron atom collision. Damage in a film has been related to the divergence of this quantity, which results in mass depletion at local sites in the film. Two ways to reduce failure are to decrease the absolute magnitude of Ja, or to reduce div Ja, either independently or in concert.

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Solute Additions to Restrict Electromigration in Thin Films

Failure of solid state devices by electromigration in metal conductor leads has led to serious reliability problems. Electromigration flux can be represented by the expression;

(Image Omitted)

where D is the diffusivity of the atomic specie and F is the driving force for migration produced by an electron atom collision. Damage in a film has been related to the divergence of this quantity, which results in mass depletion at local sites in the film. Two ways to reduce failure are to decrease the absolute magnitude of Ja, or to reduce div Ja, either independently or in concert.

The objective of this publication is to set forth selection rules for addition of solutes to metal stripes to decrease D and, thus, Ja. From past work, R. Rosenberg and L. Berenbaum Applied Physics Letters, 12, 201 (1968), it has been shown that migration takes place generally in grain boundaries. Thus, the effectiveness of the solute depended on its ability to interact with grain boundary defects that behave as preferred diffusion paths. Consideration should be given to the partitioning of solute between the lattice and the grain boundary, the maximum solubility of the solute in the boundary (S(b) degrees), the binding energy (B(NS) between the solute and the boundary defects (ledges, dislocations), and the binding energy (B(VS)) between the solute and the diffusing species (vacancies, jogs). Figs. A and B show a representative series of curves for the reduction in electromigration rate, Ja/Jo, as a function of S degrees, B(NS) and B(VS). Fig. C shows the projected temperature dependence of Ja on the same parameters. From these curves, restriction of electromigration can be accomplished by solute fulfilling the following criteria.

1) The atom fraction of solute in the boundary should be greater than 10/-2/ at all times. This indicates high partition energy, P, and low heat of mixing, Delta H(m), to get maximum amount of solute at particular nominal compositions in the crystalline lattice. A primary factor for high P is the "size facto...