Comparison of composition and bonding states of constituents in CNx layers prepared by d.c. plasma and magnetron sputtering

Abstract

Layers of CNx were grown on polished Si(100) wafers and cleaved NaCl(100) substrates by reactive sputtering of graphite in d.c. nitrogen plasma and also by d.c. or r.f. magnetron sputtering of graphite in N2. The deposited layers were studied in situ by XPS and ex situ by Fourier transform infrared spectroscopy (FTIR). Direct current plasma deposition resulted in brown transparent layers of high nitrogen content, close to CN with 1 : 1 stoichiometry, as determined by XPS. Direct current magnetron sputtering resulted in layers with slightly lower nitrogen content. The grey opaque CNx layers deposited by r.f. magnetron sputtering contained only 33–38 at.% N. The broad C 1s and N 1s lines manifested several bonding states. The relative intensities of the component peaks varied with the preparation conditions. Differences were observed also in the 1000–1700 cm−1 region of the FTIR spectra. Assignments of the various photoelectron peak components were proposed, based on published results and measurements on model compounds and binding energy separations between the related C 1s and N 1s lines. It was deduced that the concentration ratio of sp3-type C–N clusters to that of the sp2-type clusters was significantly higher for the r.f. magnetron-sputtered layers than for the d.c. plasma-deposited layers. The observed differences can be explained by the specificity of unbalanced magnetron sputtering, providing an increased amount of plasma ions and intensive bombardment of the as-deposited material at the growing surface. The increase of the ratio of sp3-type C–N clusters to the sp2-type C N clusters can be enhanced further for the r.f. magnetron-sputtered samples by applying a negative bias to the substrate. Copyright © 2000 John Wiley & Sons, Ltd.