Soft X-ray-assisted detection method for airborne molecular contaminations (AMCs)

Airborne molecular contaminations (AMCs) represent a wide range of gaseous contaminants in cleanrooms. Due to the unintentional nanoparticle or haze formation as well as doping caused by AMCs, improved monitoring and controlling methods for AMCs are urgent in the semiconductor industry. However, measuring ultra-low concentrations of AMCs in cleanrooms is difficult, especially, behind a gas filter. In this study, a novel detection method for AMCs, which is on-line, economical, and applicable for diverse AMCs, was developed by employing gas-to-particle conversion with soft X-ray, and then measuring the generated nanoparticles. Feasibility study of this method was conducted through the evaluations of granular-activated carbons (GACs), which are widely used AMC filter media. Sulfur dioxide (SO₂) was used as an AMC for the feasibility study. Using this method, the ultra-low concentrations of SO₂ behind GACs were determined in terms of concentrations of generated sulfuric acid (H₂SO₄) nanoparticles. By calculating SO₂ concentrations from the nanoparticle concentrations using empirical correlation equations between them, remarkable sensitivity of this method to SO₂ was shown, down to parts-per-trillions, which are too low to detect using commercial gas sensors. Also, the calculated SO₂ concentrations showed good agreement with those measured simultaneously by a commercial SO₂ monitor at parts-per-billions.