June 5, 2012 — W. L. Gore & Associates and CT Associates developed a method for measuring <50nm particles in ultra-pure water (UPW) used in semiconductor processes, and removing particles as small as 12nm, through a combination of ultrafiltration and microfiltration.
Small particles contaminating UPW can cause defects on the semiconductor wafer, and must be removed by filtration. At leading-edge nodes, semiconductor UPW must be free of particles above 10nm in diameter. Conventional particle counting instrumentation cannot measure particles this small.
W.L. Gore and CT Associates developed a particle detection technique that allows filter makers to measure retention efficiency for such small particle sizes in the lab. A precise aerosol is created from the UPW and evaporates the water, leaving the particles behind in the gas phase. These particles can then be accurately sized and counted using conventional aerosol particle detection instrumentation.
This method was used to evaluate filters from common UPW systems at semiconductor fabs. Although ultra filters have high retention efficiency, some very small particles can still pass through and create defects.
The test method showed that a very high retention micro filter is able to retain a large fraction of the small particles as well.
The researchers concluded that an overall filtration system using both an ultra filter and a high-retention micro filter in series will better retain defect-causing particles from UPW, in sizes as small as 12nm diameter.
W.L. Gore and CT Associates share the results of this study in a white paper, “Removal of 12nm particles from UPW by a combination of Ultrafiltration and Microfiltration,” by Donald C Grant and Dennis Chilcote, CT Associates, Inc., and Uwe Beuscher, W. L. Gore and Associates, Inc., is available online in the May/June issue of ULTRAPURE WATER Journal, http://www.ultrapurewater.com/UPW/Default.aspx, and will be presented at the ULTRAPURE WATER-Micro conference, November 13-14, in Phoenix, AZ.
W. L. Gore & Associates Inc. supplies PTFE-based filtration media for semiconductor, electronics, ultrapure water and high-purity chemical applications. To learn more, visit gore.com.