New developments at PTB in 3D-AFM with tapping and torsion AFM mode and vector approach probing strategy

G. Dai; W. Hässler-Grohne; D. Hüser; H. Wolff; J. Fluegge; H. Bosse

doi:10.1117/12.884657

10 June 2011 New developments at PTB in 3D-AFM with tapping and torsion AFM mode and vector approach probing strategy

G. Dai, W. Hässler-Grohne, D. Hüser, H. Wolff, J. Fluegge, H. Bosse

Proceedings Volume 8036, Scanning Microscopies 2011: Advanced Microscopy Technologies for Defense, Homeland Security, Forensic, Life, Environmental, and Industrial Sciences; 80360V (2011) https://doi.org/10.1117/12.884657
Event: SPIE Defense, Security, and Sensing, 2011, Orlando, Florida, United States

Abstract

A new 3D-AFM for true 3D measurements of nano structures has been developed at Physikalisch Technische-Bundesanstalt, the national metrology institute of Germany. In its configuration, two piezo actuators are applied to drive the AFM cantilever near its vertical and torsional resonant frequencies. In such a way, the AFM tip can probe the surface with a vertical and/or a lateral oscillation, offering high 3D probing sensitivity. For enhancing measurement flexibility as well as reducing tip wear, a so called "vector approach probing" (VAP) method has been applied. The sample is measured point by point using this method. At each probing point, the tip is approached towards the surface in its normal direction until the desired tip-sample interaction is detected and then immediately withdrawn from the surface. Preliminary experimental results show promising performance of the developed system. The measurement of a line structure of 800 nm height employing a super sharp AFM tip is performed, showing a repeatability of its 3D profiles of better than 1 nm (p-v). A single crystal critical dimension reference material (SCCDRM) having features with almost vertical sidewall is measured using a flared AFM tip. Results show that the feature has averaged left and right sidewall angles of 88.64° and 88.67deg;, respectively. However, the feature width non-uniformity may reach 10 nm within the measurement range of 1 μm. The standard deviation of the averaged middle CD values of 7 repeated measurements reaches 0.35 nm. In addition, an investigation of long term measurement stability is performed on a PTB photomask. The results shows that the 3D-AFM has a drift rate of about 0.00033 nm per line, which confirms the high measurement stability and the very low tip wear.

Citation Download Citation

G. Dai, W. Hässler-Grohne, D. Hüser, H. Wolff, J. Fluegge, and H. Bosse "New developments at PTB in 3D-AFM with tapping and torsion AFM mode and vector approach probing strategy", Proc. SPIE 8036, Scanning Microscopies 2011: Advanced Microscopy Technologies for Defense, Homeland Security, Forensic, Life, Environmental, and Industrial Sciences, 80360V (10 June 2011); https://doi.org/10.1117/12.884657

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