By: Sverre Sjøthun, March 23, 2001 Print this article
IBM Fellow Lubomyr Romankiw succeeded in electroplating narrow wires of copper onto thin film heads for storage, using a masking method that deposited the copper only in circuit patterns where it was needed. Next, his team devised a means of depositing a complex copper structure on polyamide, a compound used as an electrical insulator in silicon chips. Now, they sought a technique that would deposit very thin, even layers of copper both horizontally and in the vertical "vias" that link different layers of metal.
That search had a surprise ending. The simplest approach was thought to be chemical vapor deposition (CVD), which involved deposition of solid copper from a gas. In case that didn't work, electrochemical researchers headed by Romankiw examined two other possibilities. The first, electroless plating, exposes a wafer to a chemical "reducing agent" in an electrochemical "bath" containing copper ions; the agent releases copper ions from the compounds and onto the wafer. The second possibility, electrolytic plating, uses the wafer as the negative terminal of a power supply and a similar bath.
But instead of a reducing agent supplying the necessary electrons, it is the power supply that does the job together with another electrode that completes the electrical circuit. Despite being the betting favorites, CVD and electroless plating encountered severe problems. "The technology that worked was electrolytic plating," says Panos Andricacos, whose team of electrochemists at Watson and their colleague from East Fishkill, Cyprian Uzoh, pioneered the new methodology. "It has a faster rate of deposition and the evenness of the copper film is better."
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What does the future hold?