Traceable pico-meter level step height metrology

The atomic force microscope (AFM) increasingly being used as a metrology tool in the semiconductor industry where the features measured are at the nanometer level and continue to decrease. Usually the height sensors of the AFM are calibrated using step height specimens ranging from 8 nm to a few μm, however there are no calibration standards at the sub-nanometer level. Recently we have explored the use of stepped silicon single atom specimens as sub-nanometer height calibration artifacts. We have also developed a calibrated atomic force microscope (C-AFM), an AFM with direct traceability to the definition of length to calibrate standards for other AFMs. Earlier, we evaluated the step height of silicon single atomic steps along the (1 1 1) direction (with native oxide) using the C-AFM and obtained a value 304 ± 8 pm (k = 2). To validate the utility of these specimens and the applicability of our analysis technique, we conducted an industry comparison to determine the reproducibility of results obtained when using our procedure. The comparison included AFM vendors and semiconductor device manufacturers. The average standard deviation was 6 pm, and indicates that these specimens and our procedure could be used for sub-nanometer height calibrations. In this paper we will present our evaluation procedure, results of the comparison, and derivation of a value for Si(1 1 1) step height. We will also explore the trends in each participantʹs data, its effect on the calculation of the mean value, and implications on the reproducibility of our technique. Finally, we will outline the procedure for use of these specimens.