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Production sequence of Si-spheres and interferometrical determination of the sphere volume

3D Nanometrology

Working Group 5.23

TRUE 3D METROLOGY OF NANOSTRUCTURES

 

This research task aims to develop reference 3D nanometrology, particularly the measurement of feature width, edge profile, sidewall angle, corner rounding, footing, contour, line edge/width roughness etc.


Our research activities in this task consist of:

  • advanced instrumentation of 3D/CD AFMs;
  • development of novel 3D-AFM probes;
  • new measurement and new 3D probing strategy;
  • new traceable route;
  • sub-nm accurate tip characterisation;
  • modelling of tip-sample interaction in 3D;
  • calibration services with the highest level of accuracy;


A representative metrology tool applied for this task is the 3D/CD-AFM developed at PTB. In this device, an air bearing stage with a motion range of 500 mm x 300 mm developed by the former surface imaging systems company (S.I.S.) is applied for positing very large samples such as photomasks.

  • 3D/CD-AFM for true 3D metrology of nanostructures
  • Novel “Vector Approaching Probing (VAP)” technique applied in the design for better 3D probing sensitivity and reduced tip wear;
  • Outstanding metrology performance in 3D measurement, with point-wise measurement repeatability reaches about 0.12 nm;
  • Air bearing stage with motion range of 500 mm x 300 mm (x, y) offers measurement capability on very large samples, e.g., photomasks;
  • Scanning range of the AFM module: 45 µm x 12 µm x 45 µm (x, y, z);
  • AFM measurements using flared tips, allowing measurements of vertical or even under cut surface;
  • AFM tip width accurately and traceably calibrated to the nature silicon lattice constant, offering accurate calibration of feature width and sidewall profiles;
  • Excellent extend ability of the tool for satisfying special metrology demands;
  • Metrology performance confirmed by the international comparison Nano6 and the PTB-NIST bilateral comparison.



Fig.1 (a) Photo of the base instrument Nanostation 300 developed by the former surface imaging systems company (S.I.S.);

(b) Photo of the 3D/CD-AFM module developed at PTB. The module is mounted to the measurement frame of the Nanostation 300 for the measurement of large samples.

Fig.2 Typical measurement performance of the 3D/CD-AFM shown as a profile measured on an IVPS-100 sample, where four profiles repeatedly measured are plotted, showing excellent measurement repeatability below 1 nm. Insets show the details of the feature at the marked areas.

For more details of this research task, please refer to some selected publications listed below:

  • Gaoliang Dai et al.  New developments at Physikalisch Technische Bundesanstalt in three-dimensional atomic force microscopy with tapping and torsion atomic force microscopy mode and vector approach probing strategy, J. Micro/Nanolith. MEMS MOEMS 11(1), (2012 ) 011004
  • Gaoliang Dai et al. Measurements of CD and sidewall profile of EUV photomask structures using CD-AFM and tilting-AFM, Meas. Sci. Technol. 25 (2014) 044002
  • Patent of a new 3D-AFM probe