Aluminum to copper

Microprocessors contain millions of tiny switches, or transistors, carrying instructions for computers and other electronic devices. Making the switches smaller and more numerous boosts performance, but increases the difficulty of wiring them together. The semiconductor industry has used aluminum wiring on chips for over 30 years. But the ever-shrinking universe of semiconductors has made aluminum more and more problematic, since it resists the flow of electricity as wires are made ever thinner and narrower.

Instead of attempting to drive subtractive-aluminum wiring beyond its reasonable limits, IBM has chosen to employ an additive-copper, dual-damascene wiring process for its high-performance sub-0.25-µm CMOS logic technologies.

Damascene-copper has several key performance and manufacturing advantages over subtractive-aluminum for sub-0.25-µm technologies:

• 40 percent lower sheet resistance (reduced reverse scaling requirements)
• Lower random and systematic defect density Lower resistance and capacitance variability
• Improved metal line/via/line photolithographic overlay
• Improved metal line and line/via/line electromigration reliability

This technology, which has copper line widths ranging from 270 nm to 810 nm, offers substantially lower BEOL resistance and capacitance as compared with similar subtractive-aluminum technologies and provides a clear technology path for IBM's future CMOS generations.