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Diffusion Barrier between Copper and Silicon

IP.com Disclosure Number: IPCOM000108739D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Ronay, M: AUTHOR

Abstract

In future devices copper conductors will replace aluminum ones due to their better conductivity and a lesser tendency to electromigration. The difficulty is that copper diffuses with extreme ease into silicon and this cannot be tolerated. The problem to be solved here is to find a diffusion barrier between copper and silicon which a. does not interact with silicon and b. into which copper does not diffuse up until at least 500oC.

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Diffusion Barrier between Copper and Silicon

       In future devices copper conductors will replace aluminum
ones due to their better conductivity and a lesser tendency to
electromigration.  The difficulty is that copper diffuses with
extreme ease into silicon and this cannot be tolerated. The problem
to be solved here is to find a diffusion barrier between copper and
silicon which
      a. does not interact with silicon and
      b. into which copper does not diffuse up until at least 500oC.

      Criterion "a" can be fulfilled by choosing a metal which does
not form a silicide with silicon up to at least 1,200o C.  This is
assured if the temperature of the lowest lying eutectic between the
metal and silicon is above that temperature.  In the past, diffusion
barriers were selected by trial and error.  The barriers to
interstitial diffusion were calculated theoretically and it was found
that the interstitial diffusion of one metal in another metal is a
rather complicated function of the elastic constants C11, C12, C44.
The bottom line is that large values of these elastic constants bring
with them large values of activation energies for the barrier to
interstitial diffusion, and a large activation energy requires high
temperatures to overcome, exactly the aim of good diffusion barriers.
Thus, to fulfill criterion "b" we have to find barriers with large
values of elastic constants.

      The metal that ideally fulfills these criteria is rhenium.  The
temperature of the lowest lying eutectic between silicon and rhenium
is 1380oC, and the values of the elastic constants are among the
largest...