Paper TF-ThP17
Silicon Carbonitrides: On the Attainability of Stable Compounds with High Nitrogen Content

Thursday, October 18, 2007, 5:30 pm, Room 4C

During the last decade great efforts have been made to synthesize pure Si-C-N compounds using various precursor based techniques. These still ongoing activities were mainly stimulated by the expected attainability of materials combining the properties of silicon carbide and silicon nitride. However, most of the approaches result in compounds of deficient nitrogen content and considerable hydrogen and oxygen content, respectively. In contrast, high-purity thin films with tailored elemental composition can be achieved directly from the elements using either RF magnetron sputtering, ion implantation or the combination of both methods. In the latter cases, severalfold implantation at different energies calculated from Monte-Carlo-simulations is necessary in order to synthesize layers with homogeneous element depth-distribution up to the surface. The availability of this powerful preparation tool motivated us to study the ternary Si-C-N phase diagram in more detail. Therefore, the main stoichiometry-defining parameters for sputtering (Si/C target area ratio, N partial pressure, substrate temperature) and ion implantation (energy and fluence) have been varied systematically in order to attain a chosen composition. The chemical composition of the Si-C-N films was characterized by means of X-ray photoelectron spectroscopy (XPS). In addition, Auger electron spectroscopy (AES), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy were used to achieve a comprehensive characterization. For quantification XPS and AES data were calibrated with absolute concentration values from non-Rutherford backscattering spectrometry (n-RBS). Resonant nuclear reaction analysis (NRRA) provides non-destructive depth profiles of ¹⁵N. The morphology after subsequent annealing was studied by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM).
 
As one prominent result the N content of 57.4 at.% required for the formation of Si-C-N compounds on the tie line Si₃N₄ - C₃N₄ cannot be reached for Si/C ratios ≤1, whereas stoichiometric Si₂CN₄ can be easily achieved in a reproducible manner. Obviously the compound formation does not follow a simple Si by C substitution. In conclusion these results might give reason to speculate on the attainability of pure C₃N₄.