Intel Corp (INTC)

[chipguy]

Chipguy was explaining earlier that it is getting harder to hit the tight pitch metal layers with copper, so folks are moving to Al for M1...
No news on what INTC is doing at 45nm in this regard.

No that isn't quite what I said. The problem is that with
copper interconnect metal is surrounded by a barrier layer
to keep the copper from diffusing into the silicon. The
thickness of this barrier doesn't scale with feature size
well so the narrow lower level wires have less and less
copper at their core as feature size shrinks which drives
up effective resistivity. At some point aluminum becomes
better for the lowest level(s) of interconnect because its
resistivity is less than small cross section copper wires
which are have nearly as much barrier material as copper.
There are a few other effects like electron scattering off
the barrier/copper interface which make it even worse
than a simple cross section area ratio would suggest