Measurement of 28 nm particle removal from liquids by high purity filters
Don Grant – CT Associates, Inc., Eden Prairie, MN
The critical feature size of state-of-the-art semiconductor devices is on the order of 50 nm and expected to decrease to ~ 20 nm by 2015. Particles on the order of 1?2 the feature size in process liquids used during device manufacturing can reduce device manufacturing yield and finished device reliability. Microfilters and ultrafilters with pore size ratings below 50 nm are often used to control particle concentrations in these liquids. However, the ability of the filters to remove particles is typically measured using optical particle counters with a minimum detection limit of 50 nm or larger.
This paper describes a new technique that allows measurement of removal of particles as small as 10 nm in diameter from liquids. In this technique filters are challenged with particles ranging from 10 to 100 nm in diameter. Total particle concentrations ranging from 107/mL to1010/mL ? 10 nm are used. Filter inlet and outlet concentrations are measured using ultrafine atomization/scanning mobility particle sizing (UFA/SMPS), a recently developed technique. In this technique a very fine mist of particle-laden water is created, the water in the mist droplets is evaporated and sizes and numbers of the remaining particles are measured using a scanning mobility particle sizer. This technique allows very accurate resolution of particle size with 64 size channels between 10 and 100 nm.
Examples of retention of poly-dispersed polystyrene latex (PSL) and mono-dispersed 28 nm colloidal silica particles by filters with pore size ratings between 20 and 100 nm are shown. The effect of particle loading on retention by these filters is examined.
CTA publication #94: Poster presented at the North American Membrane Society 2010 Conference, Washington, DC, July 20, 2010