W. L. Gore & Associates and CT Associates have published a white paper describing a new method for measuring sub-50 nm particles in ultra-pure water (UPW) used in semiconductor processing and removing particles as small as 12 nm through a combination of ultrafiltration and microfiltration.
Semiconductor manufacturers need to know that their UPW systems can produce water that is free of small particles that can cause yield issues. As they move to smaller line widths, this critical particle size can be as small as 10 nm or less. Current particle counting instrumentation does not have the ability to measure particles this small, and semiconductor manufacturers need to know that the filtration strategy used in their UPW system is capable of capturing such small particles.
A particle detection technique has been developed that enables filter manufacturers to measure retention efficiency for such small, critical particle sizes in the laboratory environment. This technique relies on an innovative method for creating a precise aerosol from the UPW and evaporating the water in the aerosol. This leaves the particles from the UPW in the gas phase, where they can be accurately sized and counted using conventional aerosol particle detection instrumentation.
This method has been employed to evaluate the filtration performance of ultrafiltration filters typically employed in most UPW systems today. The testing demonstrates that although these ultra filters have high retention efficiency, some of these very small particles can still pass through and create a risk for the semiconductor manufacturer.
This test method was further used to show that a very high retention micro filter is able to retain a large fraction of the small particles as well. Finally, it was validated that an overall filtration system using both an ultra filter and a high retention micro filter in series shows superior retention performance for particles as small as 12 nm.
The new white paper, “Removal of 12 nm particles from UPW by a combination of Ultrafiltration and Microfiltration”, by Donald C Grant and Dennis Chilcote, CT Associates, and Uwe Beuscher, W. L. Gore and Associates, is available online in the May/June issue of ULTRAPURE WATER Journal.