Silicon oxides and oxynitrides are used for electronic application in wide scale. In the case of oxynitrides technology, the prime importance is to control the atomic concentration in thin SiO_xN_y layers. In the present paper we compare the depth profile analyses of oxides and oxynitrides using SIMS (Secondary Ion Mass Spectrometry) technique, which is ideally suited for nanostructure characterisation. A subnanometer depth resolution can be achieved with ultra-low energy (below 1 keV) ion beam due to atomic mixing reduction in sputtering process [1-2].

SiO₂ on Si samples were formed by thermal heating (800-1100^oC) of silicon wafers in oxygen flow. SiO_xN_y layers were obtained by nitrogen implantation followed by plasma oxidation process. The nitrogen plasma implantation was performed with NH₃ and pure N₂ plasma sources in 350^oC. Influence of r.f. power, used during implantation on the oxynitride layer properties, was studied. The SiO_xN_y and SiO₂ layers were 1, 2.5, 3.5, 4, 5 nm and 5, 15, 22, 50, 65, 85 nm thick respectively.

Ultra-low energy Ar⁺ ion beam (880 eV) was used in SAJW-05 SIMS analyser with quadrupole spectrometer. Quantitative atomic concentrations of N and O were calculated basing on Si₂N⁺ and Si₂O⁺ secondary ion currents according to Berkum [3]. Sputtering rate was calibrated basing on ellipsometry measurements. The obtained layers were also characterised by X-ray Photoelectron Spectroscopy.

Charge build-up effects during positive secondary ion detection were observed dependent of the SiO₂ layer thickness. The SiO_xN_y/Si interface regions show differences related to the kind of plasma and the r.f. power of nitrogen implantation used.

[1] J.B. Clegg, et al.; Surf.Interf.Anal. 14 (1987) 307

[2] P. Konarski et al.; Appl.Surf.Sci. 203-204 (2003) 354

[3] J.G.M. Berkum et al.; Appl.Surf.Sci. 203-204 (2003) 414

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