Atomic force microscopy

Development and research in nanotechnology has increased the need for accurate nanometre scale measurements in research institutes and industry. Different kinds of Scanning Probe Microscope (SPM) measurements are commonly used in many institutes and companies. Scale errors of uncalibrated SPMs typically range from 2 % to 20 %. In addition, measurement errors may cause distortions in the measured figure, which might be difficult to detect from the figure. ​Calibration is the best way to check the accuracy and stability of the instrument. New, more advanced SPMs have increased measurement precision, but the development does not remove need for calibration. Especially in all quantitative form measurements, the measurements should be traceable to the definition of the metre. Calibration can be done with calibrated transfer standards. Official calibration certificate guarantees traceability to the definition of the metre.  

Our services for SPMs MAFM.JPG

In order to guarantee accurate and reliable dimensional measurements at nanometre range, VTT MIKES provides customers traceable measurements at nanometre range using a calibrated Atomic Force Microscope (AFM). In addition, we calibrate SPM transfer standards.​ Measurement uncertainty can be given to all our measurement results. The uncertainty depends on the object being measured. For example, it is possible to reach less than one nanometre uncertainty when measuring groove depth.

Scanning probe microscopes (SPMs) can be calibrated using several kinds of transfer standards [1], which can be calibrated at VTT MIKES. 1D and 2D gratings are calibrated either by laser diffraction or by metrology atomic force microscope (MAFM). Pitch and orthogonality of the grid can be measured. Step height standards or z scale of 1D or 2D gratings can be calibrated. 

Calibration itself gives information about the accuracy of the instrument. Accuracy of the measurement can be further increased by correcting with software the errors detected in the calibration. With different measurements we can reveal several error sources; x, y and z scale errors, nonlinearity of the scales, orthogonality errors, out-of-plane errors, among others.   
 

Calibration services for SPM standards.

 Measurement / standard Property  Range Uncertainty
1D grid (diffraction measurement)​Pitch300 nm – 10 µm50 – 100 pm
2D grid (diffraction measurement) 
Pitch
Orthogonality 
300 nm – 10 µm 50 – 100 pm
1D grid (AFM measurement)​Pitch, p
Orthogonality
100 nm – 10 µm 

10 nm – 2 µm
100 µm × 100 µm
Q [3.4; 0.2 p/µm] nm 
14 mrad
Q [2; 0.2 h/µm] nm
5 nm
Step height standard 10 nm – 2 µmQ [2; 0.2 h/µm] nm
Flatness standard 100 µm × 100 µm5 nm

 

Our AFM (PSIA XE-100 AFM) is regularly calibrated interferometrically and using a grating calibrated by laser diffraction. Hence, the results measured by our AFM are traceable to the definition of the metre. The xy-movements of the AFM are mechanically separated from the z-movements. This increases the linearity of the movements, decreases out of plane movements and eliminates cross-talk. The structure of the device allows rather large samples to be measured; also measurements can be performed using the most usual measurement modes: contact, non-contact, tapping and lateral force. The measurement results can be analysed using SPIP software (The Scanning Probe Image Processor SPIPTM, http://www.imagemet.com). 
 

Properties of the AFM at VTT MIKES (table) and traceability chain of SPM measurements (diagram).SPM_traceability_4.jpg

PropertyData
Model​PSIA XE-100
Sample size<100 mm × 100 mm
Sample thickness<20 mm
Sample mass<500 g
Measurement range (xy)90 µm × 90 µm
Measurement range (z)12 µm
Resolution (xy)0.15 nm
0.02 nm (low voltage mode)
Resolution (z)0.05 nm
0.01 nm (low voltage mode)
Uncertainty (k=2),
x and y directions
Q [3; 2 L/µm] nm *
Uncertainty (k=2), z direction Q [3; 2 L/µm] nm *
 * Q [x; y] = (x2 + y2)1/2

 

 

  1. V. Korpelainen and A. Lassila, Calibration of a commercial AFM: traceability for a coordinate system, Meas. Sci. Technol. 18, 395 (2007). https://doi.org/10.1088/0957-0233/18/2/S11 
  2. J. Seppä, V. Korpelainen, S. Bergstrand, H. Karlsson, L. Lillepea, and A. Lassila, Intercomparison of lateral scales of 
    scanning electron microscopes and atomic force microscopes in research institutes in Northern Europe, Meas. Sci. Technol. 25, 044013  (2014). https://doi.org/10.1088/0957-0233/25/4/044013
  3. V. Korpelainen, V. Linko, J. Seppä, A. Lassila, and M. A. Kostiainen, DNA origami structures as calibration standards for nanometrology, Meas. Sci. Technol. 28, 034001 (2017). https://doi.org/10.1088/1361-6501/28/3/034001


Contact

  • Virpi Korpelainen, Senior Research Scientist, tel. +358 50 410 5504, email Virpi.Korpelainen(at)vtt.fi  

 

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