Toward traceability for at-line AFM dimensional metrology

Abstract

The in-line and at-line measurement tools for critical dimension (CD) metrology in semiconductor manufacturing are technologically advanced instruments that exhibit excellent measurement repeatability - below one nanometer in some cases. Accuracy, however, is largely dependent upon the availability of traceable standards. Because the standards requirements of this fast-paced industry are particularly demanding and application-specific, metrology traceability is sometimes lacking. International SEMATECH (ISMT) and the National Institute of Standards and Technology (NIST) are working together to improve this situation. We are developing a reference measurement system (RMS) at ISMT using a critical-dimension atomic force microscope (CD-AFM). We are performing measurements needed to establish the traceability chain and develop uncertainty budgets for this tool. Monitoring of tool performance has been improved and we have performed preliminary checks of lateral and vertical scale calibration. Preliminary uncertainty budgets for pitch and height measurements have been developed. At present, the standard uncertainty due to scale calibration and non-linearity is estimated to be approximately 0.2 percent for pitch measurements and 0.5 percent for step height measurements. Our initial checks of scale calibration were performed using samples for which a full traceability chain is not available. We expect to reduce these uncertainties once we are able to use samples with a complete traceability chain. Ultimately, our major objective in developing an RMS is to provide a traceable metrology reference for other major projects at ISMT - including CD-SEM benchmarking, AMAG wafer development, and overlay tool benchmarking.