Does Pressure Drop Correlate with Filter Lifetime of Sub-50NM Filtration Solutions?
ABSTRACT
Contamination control in semiconductor unit processes relies on various filtration solutions. These solutions are very effective at capturing contaminants by leveraging a variety of sieving and non-sieving forces over their effective lifetime. A filter’s lifetime is difficult to predict without robust in process monitoring as it depends heavily on a variety of factors, such as the incoming
contamination level, consistency in contaminant levels across batches, volume of material being filtered, and type of contaminant of concern.
Historically, for > 0.5 µm filters, monitoring pressure drop across the filter was an effective way to indicate the end of life of a filter. When an increase in the pressure delta across the filter housing was observed, that indicated that the filter was clogging and should be changed. However, this method of monitoring filter lifetime may not be relevant in the nanoscale range where diverse types of contaminants, such as particles, metals, organics, complexes, etc., are not solely removed by size-exclusion.
In this study we examine how pressure drop and retention change with continuous nanoparticle loading of ≤50 nm polytetrafluoroethylene (PTFE) membranes. We continuously spiked de-ionized water (DIW) with a challenge nanoparticle and flowed it through a filter membrane, where the change in pressure and downstream particle counts were continuously recorded.
We ran two tests with different types of standard particles and differently rated filter media to evaluate the pressure and retention correlation. First, a 50 nm rated membrane was challenged with 90 nm polystyrene latex (PSL) beads over a period of loading. Results showed that as monolayer coverage surpassed 1%, an increase in downstream particle concentration was seen, even though no change in pressure differential was observed (Figure 1). For the second test, we chose a <5 nm pore size rated membrane and challenged it with 20nm Gold (Au) nanoparticles (Figure 2) and we observed a similar trend to the 90nm PSL test – the loss of filter retention is seen well before an impact of the pressure drop of the system.
Together these results indicate that monitoring pressure changes to determine filter end of life is risky for ≤50nm filters, as contaminant breakthrough will occur well before any indication of a change in the pressure drop across the filter.
BIOGRAPHY
Nicole Williams is a Solutions Engineer at Entegris, providing technical expertise and application support for liquid filtration and purification products used in wet etch and clean processes. Her work focuses on helping customers maintain chemical purity, improve process yield and reliability, and address complex challenges. Nicole enjoys collaborating with cross functional teams to turn technical insights into practical solutions.