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A semiconductor plant in Taiwan is using Liqui-Cel Membrane Contactors to remove dissolved gas from their ultra pure water (UPW) system. The UPW system purifies water used in the chemical mechanical polishing process (CMP) at the fab. United Purification Technologies (UPT) in Taiwan built the system.
The water system has two degasification stages. The first stage removes both carbon dioxide and oxygen from the water and the second stage is in the final polishing loop where additional oxygen is removed to <5 ppb.
The UPW system uses CEDI technology as the primary system to remove ions and charged particles from the water.
The feed water to the system is first treated by Reverse Osmosis (RO). RO membranes are designed to remove ions but gasses will freely pass through them. Analysis of the RO water found that about 7.5 ppm of carbon dioxide was present in the water. Outlet water quality in the fab cannot be achieved if CO2 loading is high on the CEDI system. In order to lower the ionic load into the CEDI system, Liqui-Cel Membrane Contactors were installed.
The first stage membrane contactor system operates at 29 m3/hr (128 gpm). This system is designed to remove 85% of the carbon dioxide in the water. It also lowers the dissolved oxygen to 6 ppb.
The conductivity measurement after the membrane contactor system is 8-10
祍
/cm. This allows the CEDI system to continuously produce water with an outlet resistivity of 16 mega ohm-cm or higher.
The second stage system operates at 32 m3/hr (141 gpm) and lowers the dissolved oxygen to <5 ppb.
The system was commissioned in August of 2003 and has been successfully operating continuously since then. Thomas Chen, President and General Manager of UPT, is pleased with the low maintenance and ease of operation of the Liqui-Cel system. He recommends that membrane contactors always be installed upstream of the CEDI to improve the water quality.
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