Case Study
Case Study: Removing Dissolved Oxygen From Ultrapure Water
Membrane Contactor system reduces dissolved oxygen concentration to 10 ppb.
Jesus Bujedo
Lucent Technologies
Madrid, Spain
Paul A. Peterson
Celgard Inc.
Charlotte, NC
At A Glance
The upltrapure water (UPW) used to rinse wafers must contain very low levels of dissolved gases such as oxygen, nitrogen and carbon dioxide. The Lucent Technologies fab outside of Madrid, Spain, used a two-phase upgrade project to remove dissolved oxygen from the UPW loop. After introducing a nitrogen sparging system to the loop, a membrane contactor degassing system was installed within the two-pass Reverse Osmosis system. It uses vacuum with a nitrogen sweep gas to reduce the dissolved oxygen level below 10 ppb from a 56 m3/hr UPW loop. It has run continuously, except for scheduled year-end downtime, since May 1995.
The increasing complexity and level of integration in ULSI devices is requiring higher levels of water purity. A typical wafer uses between 20 and 200 separate rinsing steps. Impurities in the rinse water such as particles, high dissolved oxygen content, organic contaminants and gas bubbles can cause defects. Controlling oxide formation on the wafer surface is one of the reasons for reducing residual dissolved oxygen levels. As chip line widths continue to decrease, the quality of the water and the dissolved oxygen content becomes more critical.
At the Lucent Technologies fab near Madrid, Spain, a two-phase plan was enacted to reduce dissolved oxygen levels below 10 ppb. The first step, in 1994, was to install a nitrogen sparger in the filtered water tank. The sparging system provided the first deoxygenation capability at the site and met the goals of the first phase. Using the nitrogen sparger, dissolved oxygen was reduced to 0.6-0.8 ppm.
The second phase of the plan was to lower the oxygen to <10 ppb. A study was launched to determine the best method to achieve this goal. The options included...
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Reprinted from Semiconductor International, October 1997 by Reprint Services. Copyright (C) Reed Business Information, a division of Reed Elsevier, Inc. All rights reserved. For reorders call Reprint Services 651.582.3800. For subscription information call 847.390.2219.
