CD (Critical Diminsion) measurements have been extracted from SEM (Scanning Electron Microscopy) and HRTEM (High Resolution Transmission Electron Microscopy) images of the same set of monocrystalline silicon features having linewidths between 40 nm and 240 nm. The silicon features are incorporated into a new test structure that has been designed to facilitate this type of CD-metrology study. Major improvements to previously reported high-resolution transmission-electron microscopy (HRTEM) sample-preparation and fringe-counting procedures have been implemented. The purpose of the work was to make a preliminary assessment of the calibraiton statistics of SEM transfer-metrology when HRTEM is used as primary metrology in CD reference material calibration. The linearity and correlation of the regression between HRTEM and SEM measurement was very encouraging. However, further study of the cliabration statistics, from which uncertainty estimates of the SEM-CD measurments was obtained, revealed small but significant test-chip-to-test-chip variability of the SEM-to-HRTEM offset at the low single-digit nanometer level. Further measurements made the case that this unanticipated variability originated in differences in the hydrocarbon deposition rates that were imparted by the SEM tool during the measurement cycle. This is considered a very useful finding because modern SEM tools, which can reduce hydrocarbon deposition below levels that were encountered here by almost an order of magnitude, are now becoming available. The results reported here provide a strong indication that HRTEM-SEM-based calibration approaches offer great promise for single-nanometer-level uncertainty.
Citation: IEEE Transactions on Instrumentation and Measurement
Pub Type: Journals