Performing measurements of surface structures with the

Calibrated Atomic Force Microscope

R. Köning1, R. Dixson1, J. Fu1, V. W. Tsai2, T. Vorburger1

1 National Institute of Standards and Technology, Gaithersburg, MD 20899

2 Dept. of Material Engineering, University of Maryland, College Park, MD 20742

The use of the atomic force microscope (AFM) to characterize surface structures for industrial applications is rapidly increasing. To compare the results obtained by different instruments and to achieve high accuracy, the scales of an AFM must be calibrated. Perhaps the most convenient and most appropriate method is the use of a calibration standard. To avoid any possible contributions to the calibration uncertainty due to different interactions used by different measurement methods, the AFM standards should be calibrated by using an AFM. Therefore we have built a calibrated AFM (C-AFM). It has metrology traceable to the wavelength of light for all three axes. To demonstrate the performance of the C-AFM, step height (from 18 nm to 180 nm) and pitch measurements (from 200 nm to 20 mm) on commercially available calibration artifacts were taken. After optimizing the measurement procedure, the results of the step height measurement showed an excellent repeatability and agreed well with the values obtained by stylus measurements. The C-AFM measurements of pitch on several samples have been compared with a metrology optical microscope system (line scale interferometer) at NIST, and the observed agreement was well within the combined standard uncertainties.

Acknowledgments

We thank the NIST Office of Microelectronics Programs for partial support of this work through the National Semiconductor Metrology Program. J. S. Beers and W. B. Penzes performed measurements using the NIST linescale interferometer. T. B. Renegar measured the step height with the stylus profiler. Finally, the authors thank J. Dagata, L. Howard, F. Rudder and R. Young for valuable discussions.