Ultrathin SiO₂ on Si IV. Intensity measurement in XPS and deduced thickness linearity

Abstract

The procedures for measuring the intensities and for subsequent calculation of the thickness of thermal SiO 2 layers on Si in the range 0.3-8 nm have been evaluated to determine the best measurement protocols. This work is based on earlier work where the measurements for (100) and (111) Si surfaces indicate the need to work at a reference geometry. In the spectra, the Si 2p peaks may be separated clearly into the substrate Si and the overlayer SiO 2 but it is recommended here that, for accuracies better than 1%, the interface oxides are also analysed. The analysis here is for thermal oxides. Oxides grown by other routes may require a modification of this analysis. It is shown that, in evaluating the data to determine the layer thickness, the failure to remove x-ray satellites or the use of a straight-line background will both lead to unacceptable errors that may exceed 5%. On the other hand, if a Shirley background is used consistently for both the peak area analysis and for evaluation of the ratio of intensities for bulk SiO 2 and Si, R o , the results should be linear over the above range to within ±0.025 nm. This excellent result includes the non-linearities arising from elastic scattering effects and the data reduction method. Equations are provided, together with a value of R o for Mg and Al x-rays, to calculate the oxide thicknesses with the above linearity. In order to determine the oxide thickness accurately, the relevant inelastic mean free paths also must be known. Theoretical evaluations are only accurate to 17.4% and so better values need to be obtained by calibration. This paper provides the infrastructure to do this. Crown

X-ray metrology for advanced microelectronics

“…The inelastic mean free path of Si-2p photoelectrons in the SiON films depends on the photoelectron kinetic energy and on the chemical composition of the SiON films. In this study we considered that this value is independent of the nitrogen content in the SiON films and is equal to l SiON = l SiO2 = 2.964 nm [28]. The SiON film thickness monitored using XPS metrology agrees quite well with thickness values measured using conventional spectroscopic ellipsometry (SE) (Fig.…”

Ultrathin SiO2 on Si. VII. Angular accuracy in XPS and an accurate attenuation length

“…This and other small non-linearity contributions are contained within š0.025 nm. 15 Thus, in Table 2. Summary of results using homogenised data for the average values of m and c by method in ascending order of offset value with the standard deviation of the results and, in brackets, standard deviations of the means -an update of Table 13 terms of the standard uncertainty, the total uncertainty will be 0.66% at 8 nm but rising to 0.76% at 3 nm and 1.05% at 1.5 nm with these uncertainties doubled for 95% confidence.…”

Angle-resolved environmental X-ray photoelectron spectroscopy: A new laboratory setup for photoemission studies at pressures up to 0.4 Torr

“…30 The binding energy difference between the two signals is in agreement with the values reported in the literature. 30,31 No peaks, which can be assigned to silicon with oxidation state between 0 and +4, 30,31 were revealed by the curve-synthesis procedure. An example of fitted Si 2p XP-signal is reported in Figure 7(a).…”

“…As extensively reported in the literature, 3,27,30,31 calculating the ratio of the intensities of the oxide and elemental silicon peaks (R = I SiO 2 /I Si ) allows the determination of the thickness of the oxide layer (d SiO 2 ) according to the equation…”