ICMCTF2012 Session B1-3: PVD Coatings and Technologies

The processes and functions of MeN-(soft metal) nanocomposite films were first reviewed. Following that, the processing, structure, and multi-functional properties of TaN-Cu, TaN-Ag, and TaN-(Cu,Ag) nanocomposite films were discussed and compared. The TaN-(soft metal) films were prepared by a hybrid process that combines co-sputtering deposition and rapid thermal annealing. After the surface morphologies as well as the microstructures were analyzed and compared, the samples were examined for their tribological properties. It is found that the tribological properties could be improved when the soft metals were smeared out and functioned as solid lubricants. All TaN-(soft metal) nanocomposite thin films showed similar behaviors. However, it is found further that Cu-incorporated films could behave better under low load or low contact temperature while Ag-incorporated films could do better under high load or high temperature. For TaN-(Cu,Ag), the films might behave more like Ag-incorporated films. The samples were also tested for their anti-bacterial behaviors against Gram-negative (E. coli) and Gram-positive ( S. Aureus ) bacteria. It is found that the antibacteria efficiency against either E.coli or S. aureus can be much improved for TaN-(Cu,Ag), comparing with TaN-Ag or TaN-Cu films. The annealing temperature for TaN-(Cu,Ag) can be as low as 200 ^oC. Being annealed at this temperature, the film still shows good antibacterial behaviors against either bacterium. The synergistic effect due to the co-existence of Ag and Cu would be discussed.

Transition metal nitride and carbide coatings attracted a lot of attention in the last decades due to their good wear, erosion, corrosion and high temperature oxidation resistance. In this study, an alternative synthesis approach was used for the synthesis of carbide coatings in the W-C system. New W_xC_y coatings were synthesized by reactive magnetron sputtering technique with various target combinations and gas compositions on Si(100) and steel (100Cr6) substrates. Instead of the frequently used carbon sources such as WC(1:1) or graphite target, and CH₄ or C₂H₂ gases, a B₄C target was used as an alternative for C source and N₂ gas was fed through the chamber during deposition. For comparison, another set of coatings were synthesized using an additional graphite target together with allowing C₂H₂ gas feed instead of N₂ flow in order to see the effect of increasing C content in the coatings. We investigated the change in the phase composition, chemical bonding, hardness, room-temperature and high-temperature wear rates of these two sets of coatings. Scanning electron microscopy (SEM) was used to understand the effect of process parameters on surface roughness and microstructure of the films. The hardness values of the films were measured using the nano-indentation technique and, we used a high-temperature tribometer (up to 800°C) to investigate the wear-rates of the coatings. X-ray photo-electron spectroscopy (XPS) has been employed to understand the bonding states of tungsten and carbon as well as boron, nitrogen and oxygen on the as-deposited surfaces. Our results showed that the coatings are mostly combinations of W+WC, W+W₂C and BN in the case of N₂ flow. Coatings containing BN species are showing considerably good hardness (up to 31.5 GPa) and wear performances(up to 2.0x10^-7 mm³/Nm at room-temperature and 2.0x10^-6 mm³/Nm at 500^oC). Increasing the C content of the films in the second set of experiments did not cause a significant change on the wear rates but gave a gradual decrease to the hardness and friction coefficient of the films.

Reactive magnetron sputtering requires precise knowledge of the chemical and physical processes in the plasma itself as well as at the target surface. Therefore, a lot of investigations are focusing on the poisoning behavior in dependency of parameters like power density, reactive gas partial pressure, total pressure or magnetic field configuration. Especially the change of the magnetic field strength due to progressing target erosion has a pronounced influence on the target poisoning as well as plasma conditions and hence, on the plasma and film properties. To investigate this effect, voltage hysteresis curves were recorded while sputtering a Ta target in Ar-O2 atmosphere. The magnetic field strengths and DC current densities were subsequently varied from 45 to 90 mT and from 13 to 26 mA/cm², respectively. Due to these variations, a shift of the different sputtering regimes within the hysteresis can be detected. Selected points, referring to oxygen gas contents of 42, 70 and 100 % of the total gas flow, were used for the deposition and characterization of Ta₂O₅ thin films, which indicate hardness values in the range of 15 GPa, crystalline structure and high thermal stability. This comprehensive study of the sputtering behavior helped to gain well-founded knowledge of possible influences on the poisoning behavior of Tantalum as well as on the film formation processes of the resulting pentoxide.

For the Cu metallization in Si-based microelectronics technology, a layer of diffusion barrier is required to prevent detrimental reactions between Cu and Si. To cope with the miniaturization, however, manufacturing of reliable and extrathin barrier layer is even difficult. As a prospective solution, a barrierless interconnect with the concept of enhanced thermal stability Cu alloy films has been proposed. In this study, we report the excellent thermal stability of Cu(Ru), Cu(RuN_x) and Cu(ReN_x) films.

Cu alloy films added with dilute amounts of Ru, denoted as Cu(Ru), were deposited onto barrierless (100) Si substrates by magnetron co- sputtering. Cu alloy films with dilute Ru or Re deposited in Ar/N₂ ambient, are denoted as Cu(RuN_x) and Cu(ReN_x), respectively, Post- annealing was carried out under a vacuum condition in isothermal and cyclic modes up to 730°C. The films were characterized by EPMA and SIMS, XRD, FIB, and TEM to investigate the composition, crystallography and microstructure. The electrical resistivity of the film was measured by the four-point probe technique. The leakage currents were determined by measuring the current–voltage (I-V) curves of metal-oxide-semiconductors (MOSs) multilayer structures.

Cu(ReN_x) films exhibit a better thermal stability film which can stable up to 730°C for 1 hour without detectable copper silicide in XRD patterns. A dding such insoluble substances into Cu film can prevent the diffusion reaction between Cu and Si by inhibiting recrystallization and grain growth after annealing at high temperatures, as well as their nitrides . More detailed analytical results will be presented and discussed.

Keywords

Cu metallization, barrierless, thermal stability, insoluble substance, annealing

Aluminum nitride (AlN) is a well known, wide bandgap semiconductor which exhibits absorption in the far UV spectral range, while being totally transparent in the visible spectral region. In addition, it has excellent mechanical properties and substantial chemical and metallurgical stability making it suitable for various applications in coatings’ industry, especially if blended with Si [1]. As a covalent ceramic AlN is intrinsically brittle and the incorporation of a ductile metal (e.g. Er [2] or Ag [3]) is used to control its ductility and adhesion.

In this work we deal with the growth of AlN and Al-Si-N nanostructured films with Ag inclusions (AlN:Ag and Al-Si-N:Ag). The Ag into the AlN is distributed either as individual atoms (atomic dispersion) or as nanospheres or nanosheets (<2 nm). The atomically dispersed AlN:Ag and Al-Si-N:Ag films and the laminated structures were grown by Multi-Cathode Confocal Reactive Magnetron Sputtering (MCRMS) in (a) co-deposition of Ag and AlN or Al-Si-N using two magnetron sources, or (b) sequential growth of AlN or Al-Si-N and ultra-thin Ag layers (as thin as to approach the island coalescence threshold), respectively. On the other hand, the films with embedded Ag nanospheres were grown by Pulsed laser deposition (PLD) [4].

We investigate the effect of target power on the microstructure of the pure AlN films; AlN films can be either amorphous (a-AlN) or crystalline having the wurtzite crystal structure (w-AlN). In addition, we investigate the phases of Al-Si-N vs. the Si content and we study how the structures and the bonding of AlN and Al-Si-N change after the incorporation of Ag. For this purpose we used X-ray Diffraction (XRD), X-Ray Reflectivity (XRR) and Wavelength-Dispersive X-Ray Fluorescence (WD-XRF), using Bruker’s D8 and S4 instruments, in order to determine the film’s crystal structure, density and chemical state, respectively.

Finally, in order to determine the thermal stability of the films and the diffusion of Ag in a-AlN, w-AlN and Al-Si-N, we thermally annealed the produced films at various temperatures. We find that annealing at more than 600 ^oC results in outdiffusion of Ag on the surface.

[1] A. Pelisson-Schecker, H.J. Hug, J. Patscheider, J. Appl. Phys. 108, art. no. 023508 (2010).

[2] J.C. Oliveira, A. Cavaleiro, M.T. Vieira, Surf. Coat. Technol. 132, 99 (2000).

[3] Ch.E. Lekka, P. Patsalas, Ph. Komninou, G.A. Evangelakis, J. Appl. Phys. 109, art. no. 054310 (2011).

[4] A. Lotsari, G.P. Dimitrakopulos, Th. Kehagias, P. Kavouras, H. Zoubos, L.E. Koutsokeras, P. Patsalas, Ph. Komninou, Surf. Coat. Technol. 204, 1937 (2010).