Nanostep and Film-coatings thickness traceability

摘要

Nanosteps are important features in nanometrology. They are used for comparison of measurement accuracy in nanometer range at different laboratories and countries with different measurement methods. However, the nanosteps usually used for these purposes have both flats of the same material (homogeneous), which do not reveal the possible bias in measurement uncertainty for different measurement methods. The latter is especially important for measurement traceability of thin coating nanosteps on different substrates (heterogeneous). We have found that combined (homogeneous/heterogeneous) standards are more effective in traceability flowcharts. In addition, non-informative influence quantities and statistically evaluated surface roughness should be limited or compensated in thin film-coating thickness measurements. The consistency criterion can show the bias between different interferometric, contact stylus, and atomic force microscopy (AFM) measurement systems. However, this criterion is a conditional one. The contact measurements with small measuring force are more consistent for the heterogeneous nanosteps than are the interferometric non-contact measurements. We have proved also that AFM rectangular cantilever has different bending constants at higher more sensitive modes, which is important in permanent and tapping applications within the repulsive (contact) and attractive (non-contact) regimes. Besides that, the real coatings and substrates may have significant surface roughness (technological and functional), which can change the contact deformation and adhesion. We have derived simple theoretical proportions between the true RMS (R_(q)) and mean arithmetic (R_(a)) roughness parameters at different statistical distributions of irregularities and surface profiles, and compared them to the experimental data. These and other presented developments are helpful for improving traceability in the thin film-coatings thickness measurement.