New way of measuring particles in water for semicon production

Method can remove particles as small as 12nm through a combination of ultrafiltration and microfiltration

Removal of particles as small as 12nm has been demonstrated

W L Gore & Associates and CT Associates have developed a new method for measuring sub-50nm particles in ultra-pure water (UPW) used in semiconductor processing. It can also remove particles as small as 12nm 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 could otherwise cause yield issues. As they move to smaller line widths, this critical particle size can be as small as 10nm 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.

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.

The method, published in a recent white paper*, has been employed to evaluate the filtration performance of ultrafiltration filters typically used in most UPW systems. The testing shows that although these ultra filters have high retention efficiency, some very small particles can still pass through and create a risk for semiconductor manu-facturers. The 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 12nm.

* Removal of 12 nm particles from UPW by a combination of Ultrafiltration and Microfiltration, by D C Grant, D Chilcote, and U. Beuscher, Ultrapure Water Journal, May/June, p17, 2012.