Large-Scale Filter Testing for High-Purity Gas Supply Systems Used in Semiconductor Processing

Abstract

The development of controlled aerosol generation technology at pressure has made possible fundamental performance measurements on commercial and developmental filters over a wide range of operating conditions. Aerosols were generated by dispersing sodium chloride solution into dry, clean nitrogen at pressure using a modified TSI, Inc. constant output atomizer. The size distributions of the aerosols were measured using a TSI, Inc. differential mobility particle sizer. The geometric mean particle diameter x _g and geometric standard deviation of the aerosols were found to vary with atomizer operating condition. The diameter x _g was found to depend upon the nitrogen pressure and solution concentration in the atomizer. The salt concentration was varied from 0.001 to 0.1 g/cm³. The aerosol size distribution deviated from log-normal behavior at each operating condition. The size distributions were stable and reproducible. The pressurized aerosols were then used as particle challenges in large-scale performance tests of two ultrahigh-efficiency filters. Tests were performed on complete Alter cartridges in a large-scale recirculating flow apparatus. Aerosol concentration in the Alter effluent was measured using a TSI, Inc. condensation nucleus counter and a Particle Measuring Systems, Inc. optical particle counter. The results indicate negligible penetration or bypassing of particles for each of the test cartridges. Concentrations of less than 3x 10⁻⁴/cm³ were measured for all particles as small as 0.02 μm in the effluent gas. The introduction of sodium chloride challenge did not substantially change the particle concentration in the effluent gas.