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A numerical model, based on the commercial code Fluent, was developed to study the effectiveness of protection schemes for extreme ultraviolet lithography ͑EUVL͒ photomasks in mask carriers against particle contamination under atmospheric pressure conditions. The model included the effect of gravity, diffusion, drag force, thermophoresis, and electrophoresis on the particles and was validated against experimental data. Due to good agreement, the model could be extended down to a particle size of 50 nm, which could not experimentally be detected. It was found that electrophoresis can offer very effective protection if the particle charge distribution is unipolar. Thermophoresis also showed very promising results, however, only a small fraction of the particles could be intentionally deposited within a particle trap, surrounding the mask. Maintaining the mask facing down mainly protects the mask against large gravity-driven particles, whereas the protection against small particles requires the use of phoretic contamination control.

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Electret filters are widely used in HVAC systems to decrease particulate matter in indoor environments. The previous standard in Europe for testing air filters for general ventilation was EN 779. In July 2018, it was replaced by the new international standard ISO 16890. One major change is the discharging process: It is now performed by treating the filters with saturated isopropyl alcohol (IPA) vapor. The process is intended to simulate a worst‐case scenario of the filtration efficiency due to the reduction of the electret effect. These minimal efficiencies are a principal part of the filter classification. Therefore, two round robin tests with different filter classes (F9 and F7 according to EN 779) and up to eleven participants were carried out to evaluate the new test method by comparing the filtration efficiencies and pressure drops before and after the IPA treatment. Pressure drop measurements showed no mechanical altering of the material due to the discharging process. The calculated filter classes had a maximum deviation of 5%. Even with different equipment, the results indicate that the new ISO 16890 seems to be a viable test standard and a decent replacement for previous national standards.

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