24 May 2004 Are ambient SO2 levels a valid indicator of projected acid gas filter life?
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The requirement to extend existing lithography equipment working levels and life has required manufacturers and end users to extend their filtration requirements beyond airborne base gases. Due to the effect acid gases can have on optics, masks, reticles, steppers, wafers, and metrology tools, they have become a more important molecular airborne contaminate to remove from inside a fab. SO2 is known to be especially problematic within the cleanroom and exposure tool environment. However, a host of other molecular acids can also be found, some of which are present at considerably higher concentrations; the most prevalent of which are oxides of nitrogen, NOx. Although the removal of NOx contaminants is currently not considered to be as critical as SO2, its presence can have a significant impact on acid gas sensitive applications. Several of these applications are addressed in this work in order to point out that NOx contaminants do pose a problem, especially when considering the performance of acid gas chemical filters. More importantly, this preliminary work puts forth the recommendation that in addition to SO2, the concentration of other acid gases should be taken into account when acid gas chemical filter efficiency and life estimates are being made.
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Andrew J Dallas, Andrew J Dallas, Lefei Ding, Lefei Ding, Jon Joriman, Jon Joriman, Brian Hoang, Brian Hoang, Jonathan G Parsons, Jonathan G Parsons, Kevin Seguin, Kevin Seguin, } "Are ambient SO2 levels a valid indicator of projected acid gas filter life?", Proc. SPIE 5375, Metrology, Inspection, and Process Control for Microlithography XVIII, (24 May 2004); doi: 10.1117/12.534102; https://doi.org/10.1117/12.534102

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