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Using of Oxygen Balance

Cr-O-Si cermet films are widely applied in microelectronics devices. Such layers were prepared by RF-sputtering of a Cr:O:Si target with a nominal atomic ratio of 1:1:1 onto thermally oxidised silicon wafers.

XP spectra of the characteristic lines (Cr2p, Si2p, O1s, C1s) were recorded. Ion bombardments were performed by 2 keV Ar+ ions. Composition, expressed in Oxide molar ratio, was calculated for assumed combinations: Cr2O3+SiO2, Cr2O3+Si and Cr+SiO. The Oxygen balance, the ratio of the measured and calculated (according to the assumed "stoichiometric" formula) oxygen concentrations, are depicted on the figure as a function of the bombardment time.

Oxygen balance

The chart revealed that the top surface is totally oxidised, i.e., Oobs/Ocal ≈ 1 for the assumed Cr2O3+SiO2. After 10 min bombardment, the top layer is removed and the former composition gives unrealistic oxygen deficiency. The composition of the layer is close to either of the Cr2O3+Si or Cr+SiO (or also CrO+Si) supposed structures. Further bombardment does not change the composition. Chemical shifts of the photoelectron lines will determine the correct chemical structure but this method can reduce the choice, discard unrealistic combinations and by this back the peak decomposition procedure.

I. Bertóti, A. Tóth, M. Mohai, R. Kelly, G. Marletta: Effect of Ion Bombardment on Cr-Si-O Layers: An X-ray Photoelectron Spectroscopic Study.
Thin Solid Films 241, 211 (1994).

I. Bertóti, A. Tóth, M. Mohai, R. Kelly, G. Marletta: He+ and Ar+ Bombardment Induced Chemical Changes in Cr-O-Si Layers.
Nucl. Instrum. Methods B 116, 200 (1996).