Automated CD SEM Tilt: Ready for primetime, a fast in-line methodology for differentiating lines vs. spaces

摘要

One of many challenges the process or metrology engineers face is incorrect flagging on the processcontrol chart. It could either be a result of an un-optimized recipe that measures the wrong feature (a spaceinstead of line) or a feature placement error due to tool limitation. This can be a costly problem in the fabwhere processes are put on hold, feedback loops are corrupted and backlogs are built up unnecessarily.Often many hours must be spent by operators re-inspecting lots and process or metrology engineers requalifyingthe recipes. Most CD SEMs use algorithms employing pattern matching and contrast differenceto differentiate between line and space. However, the shrinking node requirement, limited contrast betweenline and space images and the 1:1 line and space ratios have revealed limitations of these algorithms.Recently, a metrology solution using beam tilt on the KLA-Tencor ECD-2 has been developed to tackle theproblem of dense line or dense trench array measurements. This methodology is a line vs. space detectionmechanism that precedes the metrology measurement. This application is quick and oblivious to lowcontrast differences between line/space and to systematic errors that occur with narrow feature positioning.Whether or not the specified feature type for measurement is centered in the field of view, it always detectsthe requested feature type and sets the metrology measurement to be made accordingly and thereforesignificantly reducing false negatives and false positives. This application also allows for greater tolerancein recipe setup and placement error, and thus lightens the burden of recipe creation on the novice user. Thistechnique can also be incorporated into waferless design based metrology where limited prior knowledge ofthe wafer is one of the requirements.