Soft X-Ray-Assisted Detection Method for Airborne Molecular Contamination (AMC) and its Applications to AMC Filtration Issues

Abstract

Airborne molecular contamination (AMC) represents a wide range of gas-phase chemical contaminants in cleanrooms. Because AMC can make defects of semiconductor chips by forming undesired nanoparticles and haze under ultra violet lights in the photolithography and change properties of semiconductor chips as dopants, developing methods for monitoring and controlling AMC is highly required in the semiconductor industry. This dissertation focuses on 1) the development of a detection method for AMC and 2) its applications to AMC related issues in the semiconductor industry. The detection method for AMC was developed by converting AMC into nanoparticles under soft X-ray irradiation and measuring them through the aerosol detection instrument, the scanning mobility particle sizer (SMPS). The soft X-ray-assisted detection method for AMC showed high sensitivity, e.g. down to ppt-level SO2. This soft X-ray-assisted detection method was firstly applied to evaluate the filtration efficiency of two AMC filters by measuring the concentration of SO2 downstream of the filters. This AMC detection method was also employed to develop materials, which emit VOCs lower than the conventional materials used in cleanrooms. The process for finding low-VOC replacements can be accelerated by screening candidate materials through this method. In addition, this AMC detection method was applied to measure outgassing from particulate air pollutants (PM2.5), which is a source of AMC. Using this method, a linear relationship was observed between the outgassing and PM2.5 mass loading on the filters. Subsequently, the soft X-ray-assisted detection method was used to study the removal of AMC and nanoparticles simultaneously using a single gas filter, granular activated carbon (GAC). The filtration efficiency of the GAC for 1.5-30 nm particles was investigated at different compositions and face velocities. In the present work, the GAC showed 90% filtration efficiency for sub-3 nm particles, in addition to its original gas adsorption efficiency. Furthermore, the penetration of toluene molecules through the GAC measured by the soft X-ray method was not changed when the GAC was challenged with or without nanoparticles. The results implied that the GACs can be used to remove both AMC and nanoparticles simultaneously.