cd-sem (critical dimension sem)

CD-SEM (Critical Dimension Scanning Electron Microscope) is a specialized SEM optimized for automated, high-throughput measurement of feature linewidths on semiconductor wafers. **Principle**: Electron beam scans across feature edge. Secondary electron signal profile shows edges as bright peaks. Distance between edges = CD measurement. **Resolution**: Sub-nanometer measurement precision. Beam landing energy typically 300-800 eV to minimize charging and damage. **Automation**: Fully automated pattern recognition, navigation, and measurement on production wafers. Measures hundreds of sites per wafer. **Recipe-driven**: Measurement recipes define sites, features, and measurement algorithms. Run unattended in production. **Measurement types**: Line width, space width, line-edge roughness (LER), line-width roughness (LWR), hole/contact diameter. **Top-down imaging**: Views wafer from above. Measures in-plane dimensions. Cannot directly measure 3D profiles (height, sidewall angle). **Accuracy vs precision**: High precision (repeatability) for process monitoring. Absolute accuracy requires calibration to reference standards or TEM. **Charging effects**: Low beam energy and charge compensation (flood gun) needed for insulating surfaces. **Applications**: After-develop inspection (ADI), after-etch inspection (AEI), process monitoring, OPC verification. **Vendors**: Hitachi High-Tech, Applied Materials (formerly KLA), ASML. **Throughput**: 30-60 wafers per hour depending on measurement density.