ICMCTF2014 Session B1-4: PVD Coatings and Technologies

Self-lubricant coatings are getting more importance and application area. VN thin films forms vanadium oxide layer on the surface easily and can be used as a self-lubricant. Vanadium nitride thin films deposited on high speed steel substrates via closed filed unbalanced magnetron sputtering systems from high purity vanadium target and Ar/N₂ gas atmosphere at different bias frequency. In this work, we investigated microstructural, mechanical and tribological properties of VN thin films comparatively. X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to analyze the microstructure and elemental composition of the films. Pin-on-disc test system was used for analysis tribological properties.

Intrinsic stresses in thin films of refractory metals or other high melting temperature materials have previously been considered to originate from two additive mechanisms; compressive stress generated by ion bombardment induced point defects and tensile stress generated from attraction over grain boundaries [1]. The situation is remarkably different in low melting temperature materials where a compressive-tensile-compressive stress evolution with stress relaxation upon deposition interruptions is observed [2]. The latter parts of the stress evolution has been suggested to be the result of adatom diffusion into (and out from) grain boundaries [3]. We have previously shown that dense Mo thin films deposited at low temperature using energetic (<120 eV) vapor fluxes exhibit large, and film density dependent, compressive stresses (up to -3 GPa) with a stress free lattice parameter only slight larger than the bulk stress free lattice parameter. This implies that the film stress is not generated by defect creation in the grain bulk but by grain boundary densification [4]. In this work we demonstrate that this indeed is the case by showing that the compressive stress magnitude is linear function of the inverse grain radius (proportional to the grain boundary length) by depositing dense Mo films using energetic vapor fluxes onto seed layers with different grain sizes under otherwise identical deposition conditions. It is thus possible to conclude that compressive intrinsic film stresses are caused by atom insertion into grain boundaries and that this mechanism can be activated in both low and high melting temperature materials.

[1] G. C. A. M. Janssen and J.-D. Kamminga, Appl. Phys. Lett. 85, 3086 (2004).

[2] A. L. Shull and F. Spaepen, J. Appl. Phys. 80, 6243 (1996).

[3] E. Chason, J. W. Shin, S. J. Hearne, and L. B. Freund, J. Appl. Phys. 111, 083520 (2012).

[4] D. Magnfält, G. Abadias, and K. Sarakinos, Appl. Phys. Lett. 103, 051910 (2013).

The residual stress in polycrystalline thin films can be large and depend strongly on the growth conditions. For instance, stress in electrodeposited Ni films can be 500 MPa (tensile) if the film is grown rapidly and -500 MPa (compressive) if the film is grown slowly. Furthermore, the stress progresses through different stages (tensile and compressive) as the film thickens and the microstructure changes. We have developed a model for residual stress that focuses on the stress that develops at the point where two adjacent grains meet as they are growing (i.e., the triple junction where the surface intersects the top of the developing grain boundary). The model predicts that the stress depends on the rate at which the grain boundary height increases, scaled by the parameter D/RL where D is the effective diffusivity, R is the growth rate and L is the grain size. Predictions of the model are compared with real-time measurements of stress evolution obtained using wafer curvature. In addition to randomly-nucleated films, we present results on lithographically patterned films in which the island spacing and grain boundary kinetics are controlled by the geometry

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000

Molybdenum films are used as back-contact layers in solar cells and thin film transistor-liquid crystal displays. Corrosion has a major influence on the performance of these layers; however, it is challenging to select suitable alloying elements to enhance the corrosion behavior without deteriorating their electrical properties.

Within this work, Mo films with Ta contents ranging from 0 to 100 at.% have been deposited in a laboratory-scale unbalanced d.c. magnetron sputter system on glass substrates. All Mo‑Ta films investigated show a body-centered cubic solid solution, without significantly effecting the electrical resistivity. To determine the electrochemical and the oxidation behavior, current density vs. potential measurements and climatic chamber exposure tests were done. Current density vs. potential measurements in a ventilated 0.9 % NaCl solution at room temperature show that the corrosion current decreases by a factor of 10 from 0.2 µA/cm² for pure Mo to 0.02 µA/cm² for about 20 at.% Ta. X-ray photoelectron spectroscopy of films exposed to a relative humidity of 85% at 85°C for 168 h indicates formation of a few nanometer thin and dense Ta₂O₅-rich layers providing an efficient barrier for further oxidation.

Recently, the thin film metallic glass (TFMG) materials have attracted lots of attentions due to their amorphous structure and unique properties. In this work, four Zr-Ti-B-Si TFMGs were fabricated on Si wafer and AISI 420 stainless steel disk substrates using four pure targets by a co-sputtering system. The target power of Ti target was adjusted to achieve TFMGs with different Ti contents. The amorphous phase of TFMG was determined by the X-ray diffractometer (XRD). The microstructures of thin films were examined by the field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). A nanoindenter and scratch tester were used to evaluate the hardness and adhesion properties of TFMGs, respectively. The anti-corrosion properties of thin films were evaluated by the potentiodynamic polarization tests in 5.0 wt.% NaCl aqueous solution. Effects of Ti content on the microstructure, mechanical property and corrosion resistance of Zr-Ti-B-Si TFMGs were discussed in this work.

Keywords: Zr-Ti-B-Si, thin film metal glass, nanoindenter, scratch test, potentiodynamic polarization test

A series of Cr-Si-C-N thin films have been deposited by a pulsed DC reactive magnetron sputtering system with tetramethylsilane (TMS) gas addition as the Si and C source. The contents of Si and C in the thin film were increased by the TMS flow rate varied from 3 to 30 sccm. The hardness, adhesion and tribological properties were investigated by nanoindenter, scratch and wear test, respectively. The chemical composition and microstructure of Cr-Si-C-N thin films were determined by an Electron Probe Microanalyzer (EPMA), X-ray diffractometer (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), respectively. It was found that the nanocomposite microstructure was produced when the TMS flow rate increased to higher level. The hardness of thin film was strongly influenced by the TMS flow rate. Effects of Si and C contents on the microstructure and mechanical properties of Cr-Si-C-N thin films were further discussed in this work.