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September 17, 2001
Volume 79, Number 38
CENEAR 79 38 p. 10
ISSN 0009-2347
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Supercritical CO2 is latest technique for stripping semiconductor wafers


Add a new use--semiconductor cleaning--to the many emerging industrial applications for supercritical carbon dioxide.

CO2 producer Air Products & Chemicals and SC Fluids, a private equipment maker in Nashua, N.H., have teamed up to complete the development of supercritical CO2 as a photoresist stripping agent for semiconductor wafers.

7938NOTW9 NEW HOME Air Products will install a CO2 cleaning machine at its research labs in Allentown, Pa.
Air Products says it will bring its experience in the supply, delivery, and storage of high-pressure, high-purity bulk gases to the semiconductor industry. As part of the agreement, Air Products will install one of SC Fluids' cleaning machines at its R&D facility in Allentown, Pa.

Supercritical CO2 is a strong solvent that has been used for years in applications such as caffeine and hops extraction. But its "green" nature is giving rise to novel new uses in, for example, chemical synthesis and dry cleaning (C&EN, July 16, page 27).

David Mount, SC Fluids' vice president of strategic development, says CO2 offers environmental and cost benefits to the semiconductor industry, but that they are actually secondary. The main driver in electronics, according to Mount, is that existing wet-chemical stripping techniques are reaching their theoretical limits as circuit line architecture gets smaller and smaller. "We think that at 0.18 mm and below, wet chemistry just won't clean these things out because of surface tension and capillary force," he says.

Supercritical CO2, on the other hand, has "zero surface tension," he says. "There are no features we cannot wet."

SC Fluids has a development relationship with IBM and last week shipped a "beta" version of its cleaning machine to IBM's research complex in East Fish-kill, N.Y. It's also working with ATMI, a top supplier of specialty materials and equipment to the semiconductor industry.

At least one other company--Supercritical Systems of Fremont, Calif.--is pursuing CO2 technology as well. Last year, it formed a joint development venture with Praxair, one of Air Products' industrial gases rivals; soon after, it was acquired by Tokyo Electron Ltd., a big semiconductor equipment company.

Supercritical Systems President Max Biberger says the company continues to actively advance its technology and equipment. However, he says it isn't providing progress updates "until the product is ready."

Providers of conventional cleaning chemicals are watching intently. Dana Durham, director of Ashland Specialty Chemical's ACT unit, a leading supplier of photoresist strippers, acknowledges that the new technology could be a threat. However, he points out that the new machines both rely on traditional chemicals to do the cleaning job effectively.

A month ago, Durham says, Ashland launched an agreement with a semiconductor equipment supplier aimed at developing chemistry that will work with CO2 systems. "CO2 technology is not proven, but if it's successful, we want to be one of the first players," he says.

Chemical & Engineering News
Copyright © 2001 American Chemical Society

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