Advanced Oxidation for Semiconductor Water Recycle

The semiconductor industry is a large volume user of very high purity water used to fabricate wafers and chips. Depending on the type of microprocessor chip, the purity may require resistivity of 18 megohms, or greater, and a TOC concentration of less than 5 ppb. As the wafer size increases, and the geometry becomes narrower, the volume-demand for ultrapure water increases. A large semiconductor facility may require 100 million gallons per month of make-up water, with the cost of water and POTW disposal nearly $0.5 million. It costs another $20.00 per 1,000 gallons to make this water ultrapure.

The increased demand for ultrapure water has caused the semiconductor industry to evaluate methods to recycle this water. The need is driven by the high cost of purification and rapidly escalating POTW fees, as well as the capital investment required to expand an existing deionized (DI) water system to meet increased production needs.

Another strong influence is regional sensitivity to water conservation and environmental impact. The semiconductor industry acknowledges its need to become environmentally friendly.

A growing strategy involves recycling the rinse water back to the DI system. Since a portion of the rinse stream contains solvents and surfactants, i.e. IPA, acetone, methanol, acetic acid, used to clean the chip, they must be destroyed before this water can be reused in the DI system. The difficulty is that many of these contaminants cannot effectively be removed by conventional technologies like reverse osmosis (RO), ion exchange, activated carbon and filtration.

The UV/Oxidation Technology offered by Calgon Carbon Corporation is a proven process for destroying a broad range of organic compounds. The process creates no harmful emissions, by-products or secondary streams, and is synergistic with all of the other unit operations.

The process uses proprietary, high-energy lamps (kilowatts), which emit ultraviolet radiation through quartz sleeves to the contaminated water. The key to this process is the addition of hydrogen peroxide into the water ahead of the lamps. In this photochemical oxidation reaction, the ultraviolet radiation breaks down the hydrogen peroxide to form hydroxyl radicals:

H₂0₂ + UV-> 2(•OH)

These radicals oxidize the organic contaminants in rapid reactions to C0₂ and water. The result is water that is completely free of organic contaminants or contains low molecular-weight organic acids that can be removed by ion exchange beds.

Installations of this modular system include a major semiconductor facility in the Southwest United States. Calgon Carbon Corporation's patented system is recycling 375 gpm back to the DI pretreatment, where it is blended with incoming city water. Lower water costs and enhanced environmental quality are two major benefits to the end user.

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