Calibration strategies for overlay and registration metrology

Abstract

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.

Certification of Standard Reference Material® 5000: Calibrated Overlay Wafer Standard

“…There are different strategies one can implement in using an artifact to calibrate a tool or a tool set [1]. It can be used as 1) a calibration artifact or 2) a verification artifact.…”

“…This allows for an unknown wafer to be measured without regard to knowing the specific tool. The formulas to combine the individual measurements into a tool set calibration are available in Reference [1]. To determine the CU for the tool set, the tool set variance is combined in RSS with the rest of the relevant uncertainty components.…”