Cleaning Chips with CO2, Not H2O

Chipmaking is dirty business. The tiny circuits are printed on silicon by a process similar to printing photos from negatives. As in photography, images created by photolithography have to be developed with powerful chemicals--acids that can eat away at the silicon. But unlike photos, each chip is developed in many layers, from multiple images. As a result, semiconductor plants gulp thousands of gallons of noxious acids every day. And since the acid must be washed off with ultrapure water to avoid leaving behind even the smallest impurity, a typical chip factory consumes 4 million gallons of water a day.

Now, researchers at Los Alamos National Laboratory have found an alternative. It's not only cleaner but cheaper, and it doesn't need all that water. The secret? So-called supercritical carbon dioxide--CO2 under such high pressure that the gas turns into a liquid. In this state, it acts as a catalyst for solvents. Mix it with small amounts of solvent, and the combo removes silicon just as effectively as hydrochloric acid. What's neat about supercritical CO2, says Craig M.V. Taylor, who heads the Los Alamos project, is that the liquefied gas "leaves no residue," he explains, "so we don't have to rinse." Bye-bye to those 4 million gallons of water a day.

By Petti Fong

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