Effect of plasma parameters on the structure of CNx layers deposited by DC magnetron sputtering

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CNx layers were grown on polished Si(100) wafers by reactive DC magnetron sputtering of a high purity graphite target by nitrogen ions. The deposited layers were characterized by XPS and FT-IR spectroscopy. The ‘as-prepared’ CNx layers contained approximately 20–40 at.% nitrogen measured by XPS. The large width and asymmetric shape of the C1s and N1s lines manifested several chemical bonding states of the constituents. The two major components of the N1s lines were assigned to the CN double bonds (N1 at 398.2 eV B.E.) and to the CN single bonds (N3 at 400.6 eV B.E.). The proportions of these line-components varied significantly with the preparation conditions and showed a correlation with the plasma parameters (electron density, ion current density and electron temperature) of the magnetron, as measured by a Langmuir-probe. The N3/N1 ratio increased with decreasing target-to-substrate distance. Significant differences were also observed in the 1100–1700 cm−1 region of the FT-IR spectra. For layers grown in the high electron-density plasma, a major increase in the intensity ratio of IR band at 1300 cm−1 to that at 1530 cm−1 was observed, which can be connected to the increase of the ratio of the sp3 type N to the sp2 type one in the CN clusters.