Reactive magnetron sputtering of CNx films: Ion bombardment effects and process characterization using optical emission spectroscopy

CNx films were deposited on Si(100) substrates at a substrate temperature o f 600 degrees C using dc magnetron sputtering of a high-purity graphite tar get in pure nitrogen. The film characteristics were primarily controlled by the pressure, p, (0.05-5 Pa), the discharge current on the magnetron targe t, I-m, (0.5-3 A), and the rf induced negative substrate bias voltage, U-b, (-300 to -1200 V). The films, typically 1-2 mu m thick, were found to be a morphous, and they possessed the N/C atomic concentration ratio up to 0.35, the hardness up to 40 GPa, the elastic recovery up to 85%, and good adhesi on and promising tribological properties. The energy and flux of ions bomba rding the target and the growing films were evaluated on the basis of the d ischarge characteristics measured for both the dc magnetron discharge and t he rf discharge in the deposition zone. Optical emission spectroscopy was u sed to study the behavior of significant atomic and molecular species, such as N, N-2, N+, N-2(+), CN, C, and C-2, near the substrate and in the plasm a bulk. The measurements indicated that both dc and rf discharges are mutua lly coupled. We confirmed that CN radicals and N atoms are the principal pr ecursors for reactive magnetron sputtering of the CNx films. Good correlati on between the N/CN concentration ratio in the deposition zone and the N/C atomic ratio in the films was found over a wide range of the investigated p rocess parameters. We have shown that the CNx films have a high hardness on ly when the energy and flux of the nitrogen ions are sufficiently high for effective incorporation of nitrogen in the layers; such conditions require the pressures lower than 0.5 Pa and the U-b values between -500 and -700 V. It has been proved that the frequently used deposition parameters such as I-m, U-b, p, and T-s, do not generally suffice to satisfactorily characteri ze the film growth process. (C) 1999 American Institute of Physics. [S0021- 8979(99)01119-6].