Optical Imaging Metrology Calibration using High Voltage Scanning Electron Microscope at After-Development Inspection for Advanced Processes

On-product overlay (OPO) challenges are quickly becoming yield limiters for the latest IC technology nodes, requiring new and innovative solutions to meet the technology demands. One of the primary means for reducing OPO error is the measurement of the grid (on target) at after-develop inspection (ADI) correctly and accurately. To reduce the optical error in the measurement, signals from both high voltage scanning electron microscope (HV-SEM) technology and imaging based overlay (IBO) measurements at ADI can be leveraged. Using key performance indicators (KPIs) and information produced by multiple optical measurement conditions, it is possible to optimize SEM sampling across the wafer and to capture all relevant target deformations. The objective is to improve the accuracy of optical measurements by efficiently combining information from HV-SEM and optical metrology systems. This paper will demonstrate that the information extracted from electron-based metrology and IBO measurements can be used for direct measurement of target deformations, which feeds into advanced optical target diagnostics and utilized for de-correlation between asymmetries and overlay (OVL).