There is a clear demand from the industry for continuous measurement and control of airborne molecular contamination (AMC). Therefore, a three year project (MetAMC) was started in May 2013 within the European Metrology Research Programme (EMRP)*. The project is coordinated by MIKES and it aims to measure AMCs at trace levels in clean room environments by mainly laser methods. It encompasses a multitude of national metrology institutes* and other stakeholders.
Recent progress in laser-based quantitative molecular spectroscopy has brought the detection limits of typical contaminants to a level that meets the industrial need for AMC measurements. However, the high adsorptivity of the common AMCs combined with their very low concentration make sampling, transportation and generation of calibration gases challenging, which are addressed by the project as well. To meet the goals, the following tasks will be performed during the project:
- Compare state of the art optical spectroscopic techniques for AMC measurements.
- Optimizing the techniques in clean room measurement campaigns at collaborator facilities.
- Develop AMC detection techniques beyond the current state-of-the-art.
- Create reference materials at relevant concentration levels traceable to the SI-units.
The results of the project will be very essential in the semiconductor industry, in microfabrication, and for manufacturers of optical instrumentation. In addition to developing new measurement instruments and services, the project will provide good practice guides on detection and generation of AMCs, organize workshops and training courses as well as help standards organizations to produce new standards.
Current research highlights
Key to successful spectroscopic detection of AMCs is the existence of strong and relatively isolated transitions that are accessible using preferably commercial off-the-shelf laser sources. Therefore, two investigations have been made: Potential spectral windows were identified for five pre-selected analytes (NH3, HCl, HCOH, HF and HBr) from simulations performed using spectral databases as a first step. Secondly, a survey on the availability of suitable commercial lasers or frequency conversion-based light sources was carried out. A questionnaire concerning the most important AMCs and their detection limits was sent to stakeholders, who found NH3, HF and HCl to be the three most important AMCs. These analytes met the aforementioned criteria — commercial light sources and strong absorption features with minimal interferences are available — and were selected for further studies.
Estimates for the minimum detectable amount fraction were performed for the selected AMCs. It was found that these analytes are within nominal anticipated measurement capabilities of the project partners. We expect to measure the concentration of these analytes with detection limits better than 1 nmol/mol (ppbv) for a 5-min averaging time.
Ultrasensitive laser techniques (photoacoustic spectroscopy and different cavity-enhanced techniques) will be further developed for the detection of the selected analytes. Two good practice guides will be published in 2016 evaluating the applicability of these techniques for practical AMC monitoring. The AMCs for dynamic generation will be selected later.
*The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.
Information on MetAMC and the partners can be found on the project homepage http://www.ptb.de/emrp/metamc.html
Further information: Tuomas Hieta, email@example.com, p. 02950 54458