REACTIVE MAGNETRON SPUTTERING OF HARD C-N AND Si-C-N FILMS AND THEIR PROPERTIES

J. Vlcek, M. Kormunda, J. Cizek and V. Hajek

Department of Physics, University of West Bohemia, Univerzitni 22, 306 14 Plzen, Czech Republic

E-mail: vlcek@kfy.zcu.cz, Fax: +420-19-7422825, Tel.: +420-19-7423136

ABSTRACT

C-N and Si-C-N films were deposited on Si(1,0,0) substrates using dc magnetron sputtering with a negative bias voltage on the substrate.

In the case of C-N films a high-purity graphite target was sputtered in pure nitrogen at a substrate temperature of 600 °C. The film characteristics were primarily controlled by the pressure, p, (0.05 - 5 Pa), the discharge current on the magnetron target, 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 mm thick, were found to be amorphous, and they possessed the N/C atomic concentration ratio (determined by ERD) up to 0.35, the hardness up to 40 GPa, the elastic recovery up to 85 %, and good adhesion. In order to clarify the complex relationship between the process parameters and the film characteristics, we systematically studied, using optical emission spectroscopy and electrical measurements under the same conditions, the density of N atoms and CN radicals near the substrate, and the kinetic energy and flux of ions bombarding the magnetron target and growing films. Good correlation between the N/CN concentration ratio in front of the substrate and the N/C atomic ratio in the films was found over a wide range of the investigated process parameters. We have shown that the C-N films have a high hardness only when the energy and flux of the nitrogen ions are sufficiently high for effective incorporation of nitrogen into the layers (and for ion-induced desorption and resputtering of hydrogen-containing species from them); such conditions require the pressures around 0.5 Pa and lower, and the U_b values between -500 and -700 V.

Si-C-N films of various compositions were produced by reactive dc magnetron co-sputtering of silicon and graphite in nitrogen-argon gas mixtures using a single sputter target with different Si/C area ratios. The total pressure and the discharge current on the magnetron target were held constant at p = 0.5 Pa and I_m = 1 A, and the substrate temperature was adjusted at 600 °C by an Ohmic heater or it was in the range from 135 to 210 °C without the heater. The negative substrate bias voltage was varied from a floating potential of about -20 V to -500 V. The film compositions (determined by RBS and ERD), and hence the surface bonding structure (XPS), the surface morphology (AFM) and mechanical properties (see our measurements of hardness, effective Young modulus, elastic recovery and friction coefficient), were primarily controlled by the Si fraction in the magnetron erosion track area (5 - 80 %) and by the Ar fraction in the gas mixture (0 - 75 %). Depending on the process parameters, ternary Si_xC_yN_z films within the composition range 9 £ x £ 35 at %, 6 £ y £ 61 at % and 26 £ z £ 52 at % were prepared possessing the hardness between 20 and 40 GPa.

Keywords: carbon-nitride films, silicon-carbon-nitride films, reactive magnetron sputtering, controlled film composition, hard protective layers.