Is your gas filter as clean as you think? Evaluation of UHP gas filters of differing membrane types for contamination contribution

The use of point-of-use (POU) filters will help achieve the most stringent purity requirements specified for the manufacture of future devices. Gas filter manufacturers will be faced with many challenges as tolerances to critical impurities and particles significantly decrease. Of all impurities, moisture concerns equipment and process engineers most. Moisture can interact with specialty gases to generate particles, which negatively impact other components such as mass flow controllers and transducers. Moisture in a corrosive gas can lead to corrosion and contribute to particulate contamination. Moisture adsorbs strongly to surfaces such as stainless steel; therefore, a filter that contributes a significant amount of moisture requires a significant amount of purge time, resulting in process delays. In this paper, two groups of filters undergo four performance-based evaluations: out-of-package initial outgassing, 24-hour ambient air exposure, flow/differential pressure determination and particle shed cleanliness. Group 1 (30 slpm) filters consisted of two metal and one ceramic filters while Group 2 (10-15 slpm) consisted of one prototype chromium, one nickel and two stainless steel filters. Results showed the nickel (group 1) and chromium (group 2) membranes contributed the least amount of contamination within their respective groups. The chromium membrane required the least purge time as it reached <10 ppb moisture concentration 90 minutes after installation on a gas panel.