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Characterization of tip form of CD-AFM with sub-nm accuracy for true 3D nanometrology

20.12.2018

In the frame of the European Metrology Programme for Innovation and Research (EMPIR) and within the project entitled “Traceable three-dimensional nanometrology (3DNano)”, a new method for characterizing the tip form has been developed recently. As the tip geometry fundamentally defines the tip sample probing in AFM measurements, this research directly meets the challenging demands on true 3D metrology of complex nanosystems of, for instance, the state-of-the-art EUV lithography and nanoelectronics industry.

A highly accurate reference standard referred to as IVPS100-PTB [1], which was jointly developed by the PTB and the company Team Nanotec before has been applied as the tip characterizer. The corner rounding of the line features of the standard was calibrated traceably to the silicon crystal lattice constant by means of high-resolution transmission electron microscope (HR-TEM) and 3D atomic force microscope (3D-AFM). This method offers a much better measurement accuracy in tip characterisation compared to conventional tip characterisation methods (e.g. microscopic techniques, blind tip characterisation technique and commercially available tip characterisers).

A comprehensive set of algorithms and software both for tip reconstruction and for tip correction have been realized. To enhance the metrology performance, algorithms are investigated and optimized carefully concerning different aspects such as the line-width roughness (LWR) of reference features, measurement noise, fitting and resampling.

Thorough experimental investigations have been carried out with three different tips: two CDR120 and one CDR70 from the company Team Nanotec. The standard deviation of 160 measurements of tip profiles obtained from one 3D-AFM image reaches 0.25 nm. The repeatability of the tip form of five repeated measurements using a same reference material reaches a standard deviation of 0.07 nm. The reproducibility of the tip form of 20 repeated measurements using different reference structures reaches 0.4 nm. The results indicate excellent metrology performance of the developed method, and thus setting a solid metrology fundament to achieve true 3D nanometrology.


    (a)                                                                                     (b)
Fig 1. Tip characterizer type IVPS100-PTB has been applied, shown as (a) a TEM image of the reference line feature and (b) determination of the corner rounding of the line feature. The result is traceable to the “Metre” via the silicon crystal lattice.


Fig.2. Reconstructed tip form of a CDR120 tip from two reference tip characterizers (Ref.1 and Ref.2), shown as (a) twenty tip forms obtained from twenty reference images; (b) zoomed-in view of the tip form at its left corner, showing a maximum deviation of 0.40 nm; (c) zoomed-in view of the tip form at the side, showing a maximum deviation of 0.15 nm.

Reference:

[1] Gaoliang Dai, Fan Zhu, Markus Heidelmann et al. 2015 Development and characterisation of a new line width reference material, Meas. Sci. Technol. 26, pp. 115006

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