Semi-quantitative Analysis Techniques for AMC Monitoring

The control of airborne molecular contamination (AMC) continues to grow as a requirement for all advanced semiconductor manufacturing. With more fabs using copper processing and 300 mm wafers and as we move past the 90 nm technology node, the requirements for AMC control are becoming more stringent. Most AMC control specifications call for levels to be at or below 1 part per billion (ppb) for the target contaminants and verifying of achievement and maintenance of these levels can be a very expensive proposition if real-time monitoring is an option being considered. There are a number of real-time monitoring technologies available that can measure at sub-ppb levels, however, they can cost upwards of US$20,000 per monitoring location. Due to the large investments required in terms of equipment, supplies, and personnel, manufacturers are looking for lower-cost AMC monitoring options that can still provide information relevant to the protection of processes and materials. There are a number of "semi quantitative" analysis techniques being used for AMC monitoring. By this we refer to those analytical techniques that provide quantitative information on environmental air quality, but do not measure specific contaminants. These techniques can involve passive or real-time monitoring using devices such litmus paper, witness wafers, impingers, multi-sorbent tubes, surface contamination monitors, and reactivity monitors. Semi quantitative AMC monitoring techniques are being used to establish AMC fingerprints or baselines for facilities, as part of an "early warning" system to identify and track AMC events, and for benchmarking various control strategies. This paper examines a number of these semi quantitative techniques being used today and discuss their relative strengths and weaknesses with regards to AMC monitoring. A relative cost comparison was offered