Tracking down sources of carbon contamination in EUVL exposure tools

Optics in EUVL exposure tools are known to suffer reflectivity degradation, mostly from the buildup of carbon. The sources of this carbon have been difficult to identify. The vacuum cleanliness in the preproduction micro-exposure tools is monitored with a residual gas analyzer, but they have not shown carbon-containing species in sufficient concentration to account for the observed carbon buildup seen in these tools. We have developed a technique based on cryo trapping followed by gas chromatography with mass spectrometry analysis that is more sensitive to less-volatile compounds. We will present sample data on typical vacuum systems as well as a preliminary analysis of the Intel micro-exposure tool.