Results from a study conducted between National Metrology Institutes (NMIs) for the measurements of the absolute thicknesses of ultra-thin layers of SiO 2 on Si are reported. These results are from a key comparison and associated pilot study under the auspices of the Consultative Committee for Amount of Substance. 'Amount of substance' may be expressed in many ways, and here the measurand is the thickness of the silicon oxide layers with nominal thicknesses in the range 1.5-8 nm on Si substrates, expressed as the thickness of SiO 2 . Separate samples were provided to each institute in containers that limited the carbonaceous contamination to approximately <0.3 nm. The SiO 2 samples were of ultra-thin on (100) and (111) orientated wafers of Si. The measurements from the laboratories which participated in the study were conducted using ellipsometry, neutron reflectivity, X-ray photoelectron spectroscopy or X-ray reflectivity, guided by the protocol developed in an earlier pilot study. A very minor correction was made in the different samples that each laboratory received. Where appropriate, method offset values attributed to the effects of contaminations, from the earlier pilot study, were subtracted. Values for the key comparison reference values (agreed best values from a Consultative Committee study) and their associated uncertainties for these samples are then made from the weighted means and the expanded weighted standard deviations of the means of these data. These results show a dramatic improvement on previous comparisons, leading to 95% uncertainties in the range 0.09-0.27 nm, equivalent to 0.4-1.0 monolayers over the 1.5-8.0 nm nominal thickness range studied. If the sample-to-sample uncertainty is reduced from its maximum estimate to the most likely value, these uncertainties reduce to 0.05-0.25 nm or ∼1.4% relative standard uncertainties. The best results achieve ∼1% relative standard uncertainty. It is concluded that XPS has now been made fully traceable to the SI, for ultra-thin thermal SiO 2 on Si layers, by calibration using wavelength methods in an approach that may be extended to other material systems.

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Comparing with much valuable research on vibrational spectroscopy on low-k dielectrics in different substrates, this paper investigates the vibrational spectroscopy of low-k and ultra-low-k dielectric materials on patterned wafers. It is found that both Raman and FTIR spectroscopy are necessary as complement to characterize low-k and ultra-low-k dielectric materials on patterned wafers. Significant differences in the Raman and FTIR spectra between low-k and ultra-low-k dielectric materials are also observed. Moreover, Raman spectroscopy has an advantage in analyzing the mixed structure of low-k/ultra-low-k and Cu at nanometer-scaled sizes. The results in this paper show that Raman combined with FTIR spectroscopy is an effective tool to characterize dielectric thin film properties on patterned wafers.

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