Calibration procedures for atomic force microscopes (NT TR 536)

Abstract

  This report documents the results of Nordtest project 1596-02 carried out by the Swedish national metrology institute (SP), Toponova AB and the Danish Institute of Fundamental Metrology (DFM) in year 2002. More than 8 years of research in calibration of atomic force microscopes (AFM) has been condensed in to two procedures for calibration of metrology grade AFM instruments. The greatest success of the project is that DFM in September 2002 has – as one of the first laboratories in the world – successfully passed a technical assessment for using one of these procedures for accredited (i.e. traceable) AFM measurements. It was found that the calibration procedures in particular for the lateral plane with some limitations could also be used for non-metrology grade AFMs if these are properly designed and linearised. In the vertical direction this is more dubious since measurements of roughness in the 1-10 nm range gave unacceptable differences in the results for two non-metrology grade AFMs and a metrology AFM. The calibration procedures were successfully tested on an interference microscope and it was shown that equivalence between AFM and interference microscope measurements can be established through appropriate filtering, at least in the 1-10 nm range (vertical). In conclusion there is a need to assess roughness measurement in the nanometer range with atomic force microscopes more carefully. Also more research is required in order to establish standardised procedures for making comparisons between AFM and interference microscope data.