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Explain metal migration in interconnect.
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Metal migration or electro migration is the transport of metal ions through a conductor resulting from the passage of direct current. It is caused by a modification of the normally random diffusion process to a directional one caused by charge carriers. At high current densities, the aluminium atoms in a wire tend to migrate leaving a void that eventually (after some years of operation) grows to a discontinuity. This can result in the deformation of conductors and subsequent failure of circuitry. Factors that influence the electro migration rate are:

  1. Current density
  2. Temperature
  3. Crystal structure

If the current density J, of a current carrying conductor exceeds a threshold value, we find that the conductor atoms begin to dislocate and move in the direction of the current flow. If there is a constriction in the conductor, the conductor atoms move at a faster rate in the region of the constriction. This results in a weakening of the constriction, which eventually blows like a fuse. Metal migration is an important factor in determining the width of interconnects.

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