Cu-11 Chip Fabrication, IBM

Amongst the smallest and most technologically advanced microprocessors being produced today are those from IBM. Research scientists here have pioneered technology to replace the aluminium interconnects (a microchip's internal wiring between individual transistors) with copper. Copper is one of the best electrical conductors there is (2nd only to silver and gold). Its electrical resistivity is 40% lower than aluminium. Thus, by using copper, the microscopic wiring inside a chip and be shrunk yet further to produce faster, more powerful chips.

This copper technology is used together with IBM's 0.13 micron fabrication process. This allows features on the chip to be as small as 0.11 micron and the chip to contain 40 million gates. Each gate has a 27 picoseconds delay (for a 2 input NAND gate). All chips have base of transistors with a layer of interconnecting wires stacked above. IBM's Cu-11 technology allows for 7 levels of this copper wiring.

This Cu-11 technology is already being used for the production of custom chips (ASICs). It will also be used to produce future generations of the Power4 processors which power the RS/6000 and AS/400 lines of computers.

The other technologies which are being used in IBM's newest chips are as follows:

Low-k dielectric
This material replaces the usual silicon dioxide in insulating the individual wires and circuits. It leads to a 36% reduction in capacitance, thus allowing thinner and more closely spaced copper wires. While IBM's technique is proprietary, the low-k material is a commercially available SiLK semiconductor dielectric produced by The Dow Chemical Company.

Silicon on Insulator (SOI)
Instead of the transistors being placed directly onto the silicon substrate, the substrate is first coated with an insulator (silicon oxide). A thin layer of silicon is then placed on top of this insulator.

Silicon Germanium (SiGe)
This is used instead of the more expensive and unreliable gallium arsenide.

Links:
Cu-11 Fabrication, IBM: www.chips.ibm.com/products/asics