Diagnosing and removing CD-SEM metrology artifacts

Background: Random and systematic errors found in CD-SEM tools affect the measurement of roughness in dramatically different ways than the measurement of the average critical dimension. Aim: In order to increase the accuracy of roughness measurements, monitor the health of CD-SEM tools, and improve CD-SEM tool matching, it is important to measure and remove the impact of random and systematic errors from the measurements. Approach: Several different CD-SEM tool systematic errors have been identified, but the scan error signature in particular was found to be very relevant. This signature is measured using the mean contour of many properly sampled features and can be used as the target edge for roughness calculations in order to remove this error. Results: Using six different CD-SEM tools and a large data set of across-wafer, across-scanner-field measurements of the same wafer, each CD-SEM tool was found to have a unique CD-SEM signature. Subtracting off this error signature significantly improved the accuracy of the roughness measurements and the CD-SEM tool-to-tool matching. It also identified one tool as being problematic, requiring further attention. Conclusions: Measurement and characterization of the CD-SEM scan error is a powerful tool, along with measurement and removal of random edge detection noise, for monitoring CD-SEM tool health, matching different CD-SEM tools, and improving the accuracy of line-edge and linewidth roughness measurements.