Others may have a long way to go, however. He stressed that the learning curve from aluminum to copper is long, steep and expensive. Companies hoping to put off buying the pricey tools until the technology seems fairly stable might encounter a nasty surprise. While Hutcheson noted that chip companies with the most advanced copper programs may be seeing yields of 40 to 50 percent, that's significantly below the 60 to 70 percent range that today is considered desirable for leading-edge technology. Other chip companies that are just beginning their copper development efforts may have yields close to zero.
Yield is a touchy subject for fabs, and hard data on copper production has yet to be disclosed.
But it appears early results are disappointing. Copper interconnects require a manufacturing process significantly different from that of aluminum-based chips and therefore relatively untested. For most CMOS chips, aluminum lines are laid onto a dielectric bed, but copper lines are sprayed into a deep trench dug into the dielectric. Potential pitfalls abound. Often the molten copper is studded with tiny gaps, which drive up the chip's resistivity and must be filled with residual electrolyte solution from the electroplating process.