Calibration strategies for overlay and registration metrology

Critical dimensions in current and next generation devices are driving the need for tighter overlay registration tolerances and improved overlay metrology tool accuracy and repeatability. Tool matching, performance evaluation, model-based metrology, and a move towards closed-loop image placement control all increase the importance of improved accuracy and calibration methodology. The National Institute of Standards and Technology (NIST) is introducing a calibrated overlay wafer standard. A number of calibration requirements must be addressed when using this standard, including identification of the best methods for evaluating measurement bias and uncertainties, proper data acquisition and analysis, and the best calibration strategy.