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Lateral Tip Control Effects in CD-AFM Metrology: The Large Tip Limit



Ronald G. Dixson, Ryan Goldband, Ndubuisi G. Orji


Critical dimension atomic force microscopes (CD-AFMs) use flared tips and two-dimensional sensing and control of the tip-sample interaction to enable scanning of features with near-vertical or even reentrant sidewalls. Features of this sort are commonly encountered in semiconductor manufacturing and other nanotechnology industries. The National Institute of Standards and Technology (NIST) has experience in the calibration and characterization of CD-AFM instruments and in the development of uncertainty budgets for typical measurands in semiconductor manufacturing metrology. Sidewall sensing in CD-AFM usually involves lateral dither of the tip, which was the case in the first two generations of instruments. Current, third generation instruments also utilize a control algorithm and fast response piezo actuator to position the tip in a manner that resembles touch-triggering of coordinate measuring machine (CMM) probes. All methods of tip position control, however, induce an effective tip width that is larger than the actual geometrical tip width. NIST has been investigating the dependence of effective tip width on the dither settings and lateral stiffness of the tip, as well as the possibility of material effects due to sample composition. We have concluded that these effects will not generally result in a residual bias, provided that the tip calibration and sample measurement are performed under the same conditions. To further validate our prior conclusions about the dependence of effective tip width on lateral stiffness, we recently performed experiments using a very large non-CD tip with an etched plateau of approximately 2 µm width. The lateral stiffness of these tips is nearly three orders of magnitude larger than typical CD-AFM tips – and the results supported our prior conclusions about the expected behavior for larger tips.
Proceedings Title
SPIE Proceedings: Scanning Microscopies 2015
Conference Dates
September 29-October 1, 2015
Conference Location
Monterey , CA
Conference Title
Scanning Microscopies 2015


CD-AFM, dither, metrology, CD, linewidth, tip width, calibration, traceability


Dixson, R. , Goldband, R. and Orji, N. (2015), Lateral Tip Control Effects in CD-AFM Metrology: The Large Tip Limit, SPIE Proceedings: Scanning Microscopies 2015, Monterey , CA, [online], (Accessed May 21, 2024)


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Created October 21, 2015, Updated November 10, 2018