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Monitoring airborne molecular contamination (AMC) at the parts per trillion (ppt) level in cleanroom environments, scanner applications and compressed gas lines is essential for processes, equipment and yield-control. For the operation of EUV tools, in particular, volatile organic contamination is known to have as much impact as condensable organic compounds, which requires a suitable sampling and measurement methodology. Some of the current industry standards use sample traps comprised of porous 2,6-diphenylene-oxide polymer resin, such as Tenax®, for measuring volatile organic ( 6 C atoms, about toluene and higher) AMC. Inherent problems associated with these traps are a number of artifacts and chemical reactions that reduce accuracy of reported organic AMC concentrations. The break-down of the polymeric material forms false positive artifacts when used in the presence of reactive gases, such as nitrous acid and ozone, which attack and degrade the polymer to form detectable AMC. Most importantly, these traps have poor capture efficiency for volatile organic compounds (VOC). To address the disadvantages of polymer-based sample traps, we developed a method based on carbonaceous, multi-layered adsorbent traps to replace the 2,6-diphenylene-oxide polymer resin sample trap type. Along with the new trap’s ability to retain volatile organics, the trap was found to provide artifact-free results. With industry trends towards detecting more contaminants while continuously reducing required reporting limits for those compounds, artifact-free and accurate detection of AMC is needed at the parts per quadrillion (ppq) level. The proposed, multi-layered trap substantially increases laboratory productivity and reduces cost by eliminating the need to analyze condensable and volatile organic compounds in two separate methods. In our studies, even some organic compounds with six C-atoms, that are part of exposure tool OEM requirements, were not effectively retained by polymeric traps, but were fully retained on the multi-layered adsorbent trap. This demonstrates that the standard trap used in the industry will result in significantly underreporting actual AMC concentrations for volatile organic compounds, including some siloxanes (TMS, HMDSO, D3). Performance of the proposed trap was excellent at both zero and 50% relative humidity, an important metric, as the trap is used for AMC detection in dry supply gases and humidified environments. Retention of all organic compounds was quantitative for more than 30 liters of air, sufficient for ppq-level detection limits. Desorption efficiency was 94% for C26 compounds. Pressure drop through the new trap was comparable to that of polymer-based traps and much lower than other, commercially available carbonaceous traps. Precision of repeated analyses was 5%, a very good result. Resolution of IPA and acetone was complete and that of a mix of halogenated refrigerants was much improved over existing methods. We propose to adopt this methodology as a new industry standard to overcome widespread inaccuracy in the reporting of volatile organic AMC and false positive condensable AMC.

The measurement of parts-per-trillion (ppt) level acidic and basic airborne molecular contamination (AMC) is essential for process protection and yield control in semiconductor photo-lithography and adjacent applications. Real-time monitoring solutions are highly desired, as they provide instantaneous and continuous measurement. However, even the most advanced monitors cannot achieve detection limits in the low parts-per-trillion (ppt) range and many restrictions apply for the detection of acidic AMC. High cost of ownership is another disadvantage. Discontinuous sampling with sample traps is capable of achieving ppt-level measurement, but the currently accepted methods use sample traps filled with de-ionized water (impingers) to capture soluble acidic and basic AMC. Several inherent disadvantages of these methods result in inconsistent data and increased detection limits. Some proprietary solid state solutions have been reported, but involve complex preparation, have high background signals and require 24-72 hour sample duration, or they are protected trade secrets that are not available as an industry standard. To eliminate these disadvantages, we developed a liquid-free sample trap that allows parts-per-quadrillion level (ppq) measurement of acidic and basic AMC within one work shift, typically a 4-6 hour sample period. The traps can easily be manufactured and prepared in small lab operations, are sealed and protected from the outside and operator handling in the field, have months of shelf life and show high capture efficiencies while minimizing reactions and artifacts. Capacity results for the liquid-free base trap using ammonia (NH 3 ) as a test gas yielded more than 200 ppb-h at 100% capture efficiency without any moisture (simulating sampling of CDA or N 2 ) and 350 ppb-h at 40% RH. The capacity results for sulfur dioxide (SO 2 ) were highly dependent on moisture content of the sample gas and yielded 5 ppb-h at 90% capture efficiency and 0% RH, but increased exponentially to more than 1200 ppb-h at 40% RH. Performance testing indicates that the liquid-free trap provides both more precise and more accurate results for NH 3 , SO 2 and HF in comparison to standard impinger in lab testing, with a relative standard deviation not exceeding 8% and capture efficiency greater than 95% for all three compounds. Acetic acid was the only compound that shows slightly decreased performance but still maintained a precision and accuracy comparable to the other compounds tested. In-field validation deployment to external and internal customers in parallel with standard wet impingers resulted in less than 10% difference between the traps, providing the necessary evidence that liquid-free traps are suitable for replacement of and better than wet impingers.