Common Gas For Super ChipsCommon Gas For Super Chips

Carbon dioxide is very useful stuff. Without it, there would be no bubbles in your soda, your bread wouldn't rise, and your Pop Rocks wouldn't fizz. So it's no wonder scientists are finding that carbon dioxide could help build smaller and faster microchips.

Under just the right temperature and pressure, carbon dioxide becomes "supercritical"--a gas-liquid hybrid that functions as a fluid but with extremely low viscosity and no surface tension. In practice, that means supercritical carbon dioxide can flow through holes and channels so small that other liquids would get stuck in them.

Those properties are extremely attractive to researchers working to build smaller processors. Chipmakers create circuits by etching them into silicon with caustic chemicals, which then need to be washed away. In the past, they've used water to do so, but today's chips are so tiny and delicate that conventional washing can damage them or fail to get into all the nooks and crannies. So scientists at several labs across the United States are perfecting the use of supercritical carbon dioxide as a more gentle solvent, letting chip features shrink even more.

Once the tiny features are etched into a chip, supercritical carbon dioxide can also be used to refill them. "What we do is more or less the opposite of what everyone else does," says James Watkins, a professor of chemical engineering at the University of Massachusetts in Amherst, Mass. "We're interested in putting materials down."

Watkins and his team are perfecting chemical fluid deposition, where metals are dissolved into carbon dioxide, which is then poured into the silicon channels. Add a blast of hydrogen gas, and the metal precipitates out, neatly building the circuits. Watkins has already used the technique to lay wires as thin as 100 nanometers, and doesn't see an endpoint to how small the features can get. He says it will be only a few years before these techniques work their way out of the labs and into mass-market chipbuilding.