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Effective Diffusion Barrier for Metallic Thin Films

IP.com Disclosure Number: IPCOM000122184D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 3 page(s) / 102K

Publishing Venue

IBM

Related People

Madakson, P: AUTHOR

Abstract

The Cu-Au thin film structure is widely used in contact metallurgy with Cu providing conduction and Au for the protection of Cu against environmental corrosion and oxidation. However, even at relatively low temperatures, 200-300oC, severe interdiffusion of Cu and Au takes place. This changes the electrical and metallurgical properties of each metal so that Au no longer provides any protection of Cu. In packaging technology, where Au also provides good bonding properties for joints, Cu diffusion into Au reduces the rework capability of the Au. Ni and Co are widely used as diffusion barriers [1-3], but Ni is almost ineffective and, although Co is an effective barrier at temperatures below 400oC, it has corrosion problems. Electrolytic migration studies [4] revealed Ni to be effective for inhibiting dendrite growth.

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Effective Diffusion Barrier for Metallic Thin Films

      The Cu-Au thin film structure is widely used in contact
metallurgy with Cu providing conduction and Au for the protection of
Cu against environmental corrosion and oxidation.  However, even at
relatively low temperatures, 200-300oC, severe interdiffusion of Cu
and Au takes place. This changes the electrical and metallurgical
properties of each metal so that Au no longer provides any protection
of Cu.  In packaging technology, where Au also provides good bonding
properties for joints, Cu diffusion into Au reduces the rework
capability of the Au. Ni and Co are widely used as diffusion barriers
[1-3], but Ni is almost ineffective and, although Co is an effective
barrier at temperatures below 400oC, it has corrosion problems.
Electrolytic migration studies [4] revealed Ni to be effective for
inhibiting dendrite growth.  The use of Co-Ni alloy should also be
effective.

      This invention provides a new alloy of Ni and Co which, when
used as a sandwich layer between Cu and Au, or any other metallic
thin films, provides very effective diffusion barrier.  Without a
diffusion barrier, Cu and Au interdiffuse even at 150oC; at 400oC
complete interdiffusion occurs (see Fig. 1), and it is accompanied by
the formation of intermetallic compounds [1,5].  The formation of
compounds raises the resistivity of the Cu-Au thin film structure
from 2 to about 12 microOhm cm.  Fig. 2 shows that Ni is not
effective as a diffusion barrier between Cu and Au, and Fig. 3 shows
that Co is also not effective.

      Fig. 4 shows the Rutherford backscattering data from a sample
with 60%Co-40%Ni alloy layer sandwiched between Cu and Au.  It can be
seen that it is very effective in inhibiting the interdiffusion of Cu
and Au.  Unlike pure layers of Co or Ni, there is no evidence of Cu
or Au diffu...