It is well known that the energy E_pi delivered to the growing film by bombarding ions has a crucial effect on its structure and so on its physical and functional properties. In a collisionless discharge this energy can be determined from three easily measured quantities, i.e. the substrate bias U_s, the substrate ion current density i_s and the deposition rate a_D of the film, according to the formula E_pi = E_i ν_i/ν_c ~ U_s i_s/a_D, where E_i is the ion energy, ν_i and ν_c is the flux of ions and condensing particles, respectively. This means that E_pi strongly depends not only on U_s and i_s but also on a_D. This fact is of extraordinary importance in reactive deposition of compounds, such as nitrides, oxides, carbides, etc. A change in the partial pressure of reactive gas (N₂, O₂, CH₄, etc.), under constant deposition conditions, affects not only amount of reactive gas atoms in the growing films but it can also result in large changes in a_D and hence in the E_pi values. For instance, for nitrides a_D(Me) = (3-4) a_D(MeN) and for oxides even a_D(Me) = (10-15) a_D(MeO), where Me is a metal, MeN and MeO is a metal nitride and metal oxide, respectively.

This paper reports on the effect of the E_pi values on (1) development of the structure of nitrides, (2) desorption of N from reactively sputtered nitrides, (3) resputtering of the growing film and (4) mechanical properties of hard Ti(Al,V)N_x and Ti(Fe)N_x nitrides. Besides, it is shown that the delivered energy E_pi is necessary but not a sufficient condition to form the film with a maximum hardness H_max. To produce the film with H_max two conditions must be fulfilled: (1) the energy E_pi must be greater than E_pi,min and (2) the film must have an optimum structure.

Thin Ti_1-xAl_xN films, with 0≤x≤1.0 (0.7 µm thick), were deposited onto unheated silicon (100) substrates by reactive unbalanced magnetron sputtering at a bias voltage of -60 V in an Ar-N₂ gas mixture. The effects of aluminium concentration on the structural and mechanical properties of these films have been studied. The films were analyzed by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), cross-sectional scanning electron spectroscopy (SEM), atomic force microscopy (AFM) and nanoindentation measurements.

Ti_1-xAl_xN films were first analyzed by XPS in order to determine the chemical bonding configuration and the atomic concentration of elements. The XRD scans exhibited the structural changes in the Ti_1-xAl_xN films with different Al concentrations. It was found that at x < 0.3, the films were essentially B1-NaCl TiN. A two-phase structure of B1-NaCl (TiN) and Wurtzite (AlN) was observed in the range of x = 0.48-0.57. It is interesting to note that the nature of the AlN (002) orientation changes drastically at x=0.57. A single-phase structure of AlN was formed as x=1.0.

By nanoindentation measurements, it was observed that the hardness of the TiN film at x=0.0 was 23 GPa. The hardness was increased when the value of x increased and reached a maximum value of 32 GPa at x=0.48. With further increase in x, the hardness of the film dropped. The hardness had a lower value of 21 GPa for x=1.0.

The evolution of the microstructure of the films by cross-sectional SEM revealed that both TiN and AlN films had a columnar structure, while the film prepared at x=0.5 had a dense and fine grained structure. Further measurements by AFM indicated that the film at x=0.5 also showed the finest surface topography. By analysis, it is concluded that the maximum hardness coincides with a minimal grain size, which implies a high density of grain boundaries.

Elastic Properties of nc-TiN/a-Si₃N₄! Nanocomposite Films by Surface Brillouin Scattering *Nanocomposite (nc) films developed recently exhibit extremely high values of hardness¹. To model the behavior of the nanoindenter in case of such a nanocomposites, it is necessary to know the distribution of the elastic properties of the film at the vicinity of the surface. We used Surface Brillouin Scattering (SBS) to determine the elastic properties of the nc-TiN/a-Si₃N₄ film at depth from 50nm to 400 nm. In the case of nc-TiN/a-Si₃N₄ films, the Rayleigh mode can be clearly identified in the Brillouin spectra. Surface acoustic waves (SAW) velocity dispersion curve has been measured at the frequency range from 7.3 GHz till 17.6 GHz. At this frequency range velocity of the SAWs decrease from 5.69 km/s to 4.75 km/s. To model the variation of the elastic properties with depth we used an algorithm proposed by Glorieoux et al.² . Simulation shows that Rayleigh wave velocity increases from 3.5 km/s at the depth of 50 nm to 6.0 km/s at 400 nm. Our results demonstrate that the elastic properties of the film are highly inhomogeneous, and the velocity of Rayleigh wave increases with depth.

¹Veprek, S., The Search for Novel, Superhard Materials, Journal of Vacuum Science & Technology A 17 (5), 2401-2420, 1999.

²Glorieux, C., Gao, W., Kruger, S. E., Van de Rostyne, K., Lauriks, W., and Thoen, J., Surface Acoustic Wave Depth Profiling of Elastically Inhomogeneous Materials, J. Appl. Phys. 88 (7), 4394-4400, 2000.