In conventional semiconductor processes, gross photoresist scum has been detected with inspections using optical microscope or secondary electron microscope; trace molecular contamination or photoresist residue could be removed during wafer processes employing vigorous thermal, chemical, plasma or ion beam steps and thus had negligible effects on semiconductor manufacture. However, advanced semiconductor technology has become increasingly sensitive to molecular contamination that might be difficult to detect with traditional inspection and analysis techniques. Direct surface analysis by TOFSIMS provides sensitive detection of both elemental and molecular contamination that may be originated from environmental sources or from wafer fabrication processes. Monolayer level molecular contamination and very thin photoresist scum that were not detectable with conventional inspection techniques have been characterized with TOFSIMS in this paper. Detrimental effects of the very thin photoresist scum have been demonstrated with a 130 nm technology process. Cleaning process to remove molecular contamination was validated with TOFSIMS analysis. Detection of very thin photoresist scum can be accomplished with TOFSIMS imaging analysis. © 2003 American Institute of Physics