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Politics : Formerly About Advanced Micro Devices
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To: RDM who wrote (54172)4/5/1999 4:43:00 AM
From: Process Boy  Read Replies (4) of 1573904
 
RDM - RE: <heard that the copper has less cross-talk between traces, but I have not heard a clear reason why.>

Theory in a nutshell: Cu inherently has lower resistance and carries a higher current load per cubic unit, which reduces parasitic capacitance vs. Al.

The longer a wire, the higher the resistance. However, the thicker the wire, the less resistance. Cu's lower specific resistance allows thinner wires with less parasitic capacitance (reduces cross-talk), and also allows higher speed (less RC delay).

Choice of dielectric material (material between the wires) is also a fundamental factor in determining RC effects.

Specific resistance values (rho) at 20deg C, (cmil)*(ohm/ft)

Cu - 10.4
Al - 17.0

As for your question: <quantitatively how much faster are copper wires than aluminum wires for a typical .18 micron process?>

This depends on the fundamental approach to improve overall speed of the circuit. Intel seems to contend at .18 that overall speed can be better enhanced by reducing gate delay in the transistors (stick with Al). AMD/MOT process evidently is endeavoring to improve overall processor speed by reducing RC delay (go to Cu), which allows for smaller pitches (tighter design rules) and reduces die size. Check out this post from Kash, and see if this sort of answers your question:

Message 8688672

As for which process will ultimately be faster, we will have to wait until closer to the end of life of the process. Still speculative at this point.

PB
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