Ian,
From your length article regarding copper interconnects, I do have a few comments:
...gigahertz parts...CMOS process using copper metallization, integrating six metal levels, a 0.2-micron drawn gate and a 0.12-micron effective channel length.
What is the big deal about this copper technology here? From 0.13um which is what IBM is describing, digital ICs can easily achieve 1 GHz, even with aluminum metallization.
ICs with inductors using copper technology for GPS system
These guys cannot be serious here, integrating inductors into an IC! For years, TRW has been using copper plating for their MMIC devices, highly integrated RF circuitry. That is probably a better solution for GPS.
"We are aggressively pursuing copper technology, but while copper solves a near-term problem, we think reducing the capacitance is even more of a critical issue because unless it is solved, chip performance, power and operating voltage ultimately will be limited by the interconnect," --- Robert Havemann of TI.
I agree with that comment. Notice he is hinting copper technology is not as beneficial as IBM has pointed out. He then changed the whole subject towards the dielectric material.
"We're aggressively investigating copper and dielectric materials, but we're still doing scaling of aluminum lines. We're trying to improve things by going to tall or high-aspect-ratio aluminum lines. That way, you gain performance advantages and get to keep your existing processes and production equipment." --- Mark Bohr of Intel.
If it ain't broke, why fix it! Remember, the name of the game is to make money.
"It's not actually the copper wires that are the main issue. It's the capacitance and that gets to the dielectric," --- Mark Pinto of Lucent.
Again, Mr. Pinto is emphasizing Mr. Havemann's comment.
"On most products, the most important capacitance is between metal lines on the same layers. If you use copper as the trace, it has about 30 percent less resistivity than aluminum, so you can make it 30 percent thinner. If the spacing is kept the same, the capacitance is reduced." --- Suresh Venkatesan of Motorola.
By making a trace thinner, you are risking design rule violation, besides most of the capacitance encountered by a gate is not in the metal trace but the semiconductor junction.
Over all, is copper really that good? Given that ICs today are limited by their power handling capacity, an increase in trace resistance does not really matter. Remember, it is not resistance of the trace but the capacitance that is governing how much power is dissipated in an IC.
John
East Greenwich, Rhode Island |
