ICMCTF2006 Session B1: Sputtering Coatings and Technologies

Special attention will be dedicated to Ti-Si-N and Ti-Si-Al-N films prepared under conditions out of thermodynamic equilibrium, and the formation of mixed phases. In order to explain the influence of Si → Ti substitution in the bulk stoichiometric B1 TiN, calculations using first principles density functional theory were performed. A 16-atomic supercell Ti₇SiN₈, which corresponds to the nominal composition of Ti_0.875Si_0.125N was used as a model. A lattice compression in result of Si-Ti substitution was obtained.

These results suggest that the subsequent formation of the nanocomposite of the type nc-MeN/a-Si₃N₄ results from ion irradiation induced effects and a driven Si surface segregation, leading to continuous renucleation during film growth. This mechanism explains the formation of a multiphase system, where the crystalline TiN, (Ti,Al)N and (Ti,Al,Si)N phases were identified by X-ray diffraction, when the surface mobility is not enough to obtain a complete thermodynamically driven segregation. XPS measurements show the absence of Titanium silicide and the formation of the amorphous Silicon nitride phase.

Regarding the ZrO_xN_y, thin films, the evolution of film properties as a function of the reactive gas flow (a mixture of oxygen plus nitrogen), revealed the development of three distinct growth modes. These changes are particularly evident in the film’s structure evolution, which revealed a change from fcc ZrN-type growth at low gas flows, to a structure similar to that of Zr₃N₄, with oxygen inclusions, at intermediate gas flows, to oxide-type structures at the highest flows. These structural changes were also confirmed by resistivity measurements, whose values ranged from 250-400 Ωcm for low gas flows and up to 106 Ωcm for the highest flow rates. Color measurements in the films revealed a change from bright yellow at low reactive gas flows, to red-brownish at intermediate flows and dark blue for films prepared at the highest flows. Mechanical properties also tend to follow these different behaviors.

Transparent highly conductive indium tin oxide (ITO) films for low cost applications were deposited by a reactive dual-magnetron sputter process using metallic targets. The magnetrons were equipped with rectangular (130 x 400 mm²) In/Sn targets (90 wt.-% In / 10 wt.-% Sn). A sine wave power supply was used at a frequency of about 70 kHz. All experiments were done in the transition mode at a constant argon flow of 40 sccm. The oxygen flow rate was varied between 35 and 70 sccm. The total pressure was kept constant at 0.4 Pa.

The films were deposited onto silicon and float glass substrates which were either moved in an oscillatory manner (dynamic deposition) or fixed in front of the targets (static mode) during deposition. A dynamic deposition rate of about 96 nmxm/min was obtained at an averaged power of 2 kW per cathode. The film thickness was adjusted to 500 nm. At an optimised Ar/O₂ gas flow ratio of 0.6 we found an electrical resistivity as low as 1x10^-3 Ωcm. The refractive index of these films was about 2.05 indicating a dense film structure. The optical absorption of k = 10^-2 is comparable to typical results of other groups. Moreover, the film texture and the mechanical stress were investigated by XRD methods.

Applying a static deposition we have achieved a lower electrical resistivity with a minimum value of 5x10^-4 Ωcm. In this case, the resistivity was not constant over the substrate but depends on the lateral position in front of the target. In order to explain this inhomogeneity we have performed spatially resolved Langmuir probe and OES measurements and related their results to film structure and properties. In order to improve the film properties at dynamic deposition the growth conditions have to be homogenised at all substrate positions.

Chromium diboride PVD coatings possess desirable combinations of properties (high hardness, wear resistance, chemical inertness, high thermal and electrical conductivity), which are attractive for a wide range of potential applications.

Pulsed magnetron sputtering (at 100 kHz frequency) of loosely-packed powder targets allowed deposition of stoichiometric CrB₂ coatings at low substrate temperatures (110-150°C). The structure, composition and mechanical properties of these coatings were found to be strongly dependent on the deposition process parameters. Investigation of the coating structure could explain certain differences between them, indicating directions for improvement and giving important information about the characteristics of the deposition process.

Characterization of the films was performed by cross-sectional and plan-view transmission electron microscopy techniques (electron diffraction and bright-field/dark-field imaging). Some results from XRD, RBS and nanoindentation studies of these films are also presented. The structures of coatings deposited with different parameters are investigated and compared; the reasons for the structural differences observed are discussed.

All coatings studied exhibited extremely fine, dense and uniform structure and morphology. For example, films deposited at 80% duty cycle (100 kHz frequency) onto negatively biased substrates (-30V DC) resulted in a crystalline, nanocolumnar structure (column width ~ 4-6 nm), which exhibits very strong preferred (001) orientation. Such coatings were also found to have highest hardness and better corrosion resistance. However, significant structural differences between these coatings were also evident. The structure of CrB₂ coatings, and changes that resulted from variation of deposition parameters (such as target voltage pulse regime, duty cycle and substrate biasing conditions), are discussed in detail.