Ultra‐thin SiO₂ on Si IX: absolute measurements of the amount of silicon oxide as a thickness of SiO₂ on Si

Abstract

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.

Uncertainty in Quantification of Binary Alloy Films and Thickness Measurement of nm Oxide Films

“…Key comparison reference value and their associated uncertainties were determined from the weighted means and the expanded weighted standard deviations of the means. [7] The standard uncertainty in the measurement of thickness of nm silicon oxide films can be described by the following equation.…”

“…4, 8 nm. [7] u F : different peak shape algorithms u L : electron attenuation length u n and u θ have random contributions (type A) and the other terms largely involve systematic contributions (type B). u E is less than 0.025 nm and u A is negligible for an analyser with small cone entrance angle.…”

“…The measurand was the thickness of the silicon oxide layer on each of a total of 9 samples of nominal thicknesses in the range 1.5 to 8 nm on (100) and (111) Si substrates. [6,7] In this paper, the various methods to improve the measurement uncertainty in surface analysis and the roles of certified reference materials (CRMs) are described. Moreover, some details of recent activities of CCQM SAWG on the quantification of alloy films and the thickness measurement of ultra-thin oxide films are reviewed.…”

Angular accuracy and the comparison of two methods for determining the surface normal in a Kratos Axis Ultra X‐ray photoelectron spectrometer

“…However, both L and R o may be calibrated using reference samples and then d may be determined with significantly greater accuracy. [1,3] In this case, the accuracy of the angle of emission becomes the factor that limits the accuracy in determining d. [4] In the machining of these sophisticated spectrometers, one would expect the angles to have an accuracy of better than 0.5…”

Influence of contamination layer on thickness evaluation by X‐ray reflectometry

“…A comparison of the thickness determination of SiO 2 films (2–10 nm) on Si substrates was conducted using CCQM‐K32, P84, and P38 . The results revealed that there was an offset in the reported thickness values among the measurement methods.…”