Energetic Deposition Conditions Research Articles

Effect of Al content on the hardness and thermal stability study of AlTiN and AlTiBN coatings deposited by HiPIMS

The microstructure, mechanical properties and thermal stability of AlTiN and AlTiBN coatings grown by reactive high-power impulse magnetron sputtering (HiPIMS) have been analyzed as a function of Al/(Al+Ti) ratio, x, between 0.5 and 0.8. The coatings were predominantly formed by a face-centered cubic Ti(Al)N crystalline phase, both with and without B, even for x ratios as high as 0.6, which is higher than the ratio typically encountered for AlTiN coatings deposited by reactive magnetron sputtering. B doping, in combination with the highly energetic deposition conditions offered by HiPIMS, results in the suppression of the columnar grain morphology typically encountered in AlTiN coatings. On the contrary, the AlTiBN coatings grown by HiPIMS present a dense nanocomposite type microstructure, formed by nanocrystalline Ti(Al)N domains and amorphous regions composed of Ti(Al)B2 and BN. As a result, high-Al content (x>0.6) AlTiBN coatings grown by HiPIMS offer higher hardness, elasticity and fracture toughness than AlTiN coatings. Moreover, the thermal stability and the hot hardness are substantially enhanced, delaying the onset of formation of the detrimental hexagonal AlN phase from 850 C in the case of AlTiN, to 1000 C in the case of AlTiBN.

Structure and Mechanical Properties of AlCrN Thin Films Deposited by Magnetron Sputtering

A magnetron sputtering system was used to deposit AlCrN thin films. Chemical compositions of the films were determined by both EDXS and RBS, while structures analyses were conducted by XRD in a Seifert XRD3000 diffractometer. Macroscopic residual stresses of films were determined by curvature measurements using DEKTAK IIA profilometer, while in-grain stresses were extracted by the “sin²Y method” from XRD measurements. A nanoindenter from CSM (Switzerland) was used to determine the hardness of the films. A CrN type FCC structure was obtained with a strong (200) fiber texture for the range of compositions Al1-xCrxNy(0.56 < x< 0.89) of interest here. The global stresses were compressive for all FCC films resulting from the high energetic deposition conditions used. In-grain compressive stresses were determined for the films with thickness < 500nm, while thicker films (> 500nm) showed tensile in-grain stresses. Stress-free lattice parameter a0strongly decreased from 4.13 to 3.97 A°. Hardness values were obtained in a range extending from 17 to 27 GPa with an increase obtained as Cr content increases and correlated to the residual-stress level.

Co-development of stress and texture in reactive magnetron sputtered TiN films revealed by in situ film stress measurements

Titanium nitride (TiN) films up to 100 nm thickness were deposited by reactive magnetron sputter deposition on silicon substrates while measuring the film force in situ. The energy per deposited atom supplied to the growing film by ion bombardment was varied in two ways: a) by changing the deposition pressure and b) by changing the bias voltage applied to the substrate. Both variations affected the film force, the microstructure and the film texture. More energetic deposition conditions led to a continuous build up of stress, a dense microstructure and a 001 film texture almost independent of film thickness. These findings lead us to conclude that a 001 film texture is more susceptible to stress generation by an ion bombardment than a 111 film texture. Further, from the similar effect of a pressure increase and a bias voltage decrease on the film growth and characteristics we identify ion–neutral charge transfer collisions in the substrate sheath as the mechanism by which the deposition pressure influences film characteristics.

Anisotropic strain-stress state and intermixing in epitaxial Mo(110)/Ni(111) multilayers: An x-ray diffraction study

The present study deals with the analysis of elastic strains and stresses in high-quality heteroepitaxial Mo/Ni superlattices with periods Λ lying in the range 4.8–27.6 nm. The strain-stress state in this lattice-mismatched system grown under energetic deposition conditions (ion beam sputtering) is rather complex, resulting from three contributions: (i) intrinsic (growth) stress due to atomic peening, (ii) coherency stresses of opposite sign in the two elemental layers due to the observed Nishiyama–Wassermann epitaxial relationship Ni[11¯0](111)∥Mo[001](110), and (iii) interfacial mixing. The measurement of the lattice parameters of Mo and Ni sublayers in various crystallographic directions was performed by x-ray diffraction, using the sin2 ψ method adapted for epitaxial layers. A large anisotropy of elastic strain and associated in-plane coherency stresses is revealed in the Mo sublayers, while for Ni sublayers no such behavior could be detected due to the superimposition of growth variants with threefold symmetry. Postgrowth ion irradiation with Ar ions at very low dose (∼0.2 dpa) was employed as a powerful tool to modify the intrinsic stress, thus providing additional data to be implemented in a triaxial strain-stress model, which enabled us to separate the different stress sources (intrinsic and coherency stresses) as well as to quantify the intermixing occurring during growth. This model, which has been successfully applied previously to Mo thin films, yields in the case of multilayer systems to the determination of the “stress-free and defect-free” lattice parameter, a0, i.e., solely linked to chemical mixing. The linear dependence of a0 with Λ observed in both sublayers reveals an interface-mediated chemical mixing mechanism, the extent of this interfacial mixing being much more pronounced in Mo sublayers than in Ni ones.

Stress evolution in magnetron sputtered Ti–Zr–N and Ti–Ta–N films studied by in situ wafer curvature: Role of energetic particles

Stress evolution during reactive magnetron sputtering of binary TiN, ZrN and TaN thin films as well as ternary Ti–Zr–N and Ti–Ta–N solid-solutions was studied using real-time wafer curvature measurements. The energy of the incoming particles (sputtered atoms, backscattered Ar, ions) was tuned by changing either the metal target (MTi=47.9, MZr=91.2 and MTa=180.9g/mol), the plasma conditions (effect of pressure, substrate bias or magnetron configuration) for a given target or by combining different metal targets during co-sputtering. Experimental results were discussed using the average energy of the incoming species, as calculated using Monte-Carlo simulations (SRIM code). In the early stage of growth, a rapid evolution to compressive stress states is noticed for all films. A reversal towards tensile stress is observed with increasing thickness at low energetic deposition conditions, revealing the presence of stress gradients. The tensile stress is ascribed to the development of a ‘zone T’ columnar growth with intercolumnar voids and rough surface. At higher energetic deposition conditions, the atomic peening mechanism is predominant: the stress remains largely compressive and dense films with more globular microstructure and smooth surface are obtained.

Film growth phenomena in high-energetic room temperature pulsed laser deposition on polymer surfaces

Coating of plastics by inorganic metal-based films requires profound knowledge about the phenomena occurring in connecting materials of very high and very low (visco-)elastic properties. Buckling and delamination are unwanted, stress-release induced effects leading to severe failure. To overcome the problem of delamination, higher energetic deposition conditions for strengthening the polymer surface by ion implantation are seen as a chance, but bear the risk of high film stresses and, thus, an increase of buckling. To understand these phenomena in pulsed laser deposition (PLD) the current work focuses on topographical, morphological and chemical investigations of polymers coated with thin interface films between 5 and 100 nm thickness. Applying this approach in the room temperature PLD (RT-PLD) enables the understanding of ion implantation during interface growth. The results reveal a strong chemical binding between implanted atoms and polymer chains as well as a hardening of the soft polymer surface, which increases the load capacity. Only very low changes of the surface topography after coating by wrinkling phenomena reveal scarce influence of the ion bombardment and high adhesion of the films.

Misfit-energy-increasing dislocations in vapor-deposited CoFe/NiFe multilayers

Recent molecular dynamics simulations of the growth of $[{\mathrm{Ni}}_{0.8}{\mathrm{Fe}}_{0.2}/\mathrm{Au}]$ multilayers have revealed the formation of misfit-strain-reducing dislocation structures very similar to those observed experimentally. Here we report similar simulations showing the formation of edge dislocations near the interfaces of vapor-deposited (111) [NiFe/CoFe/Cu] multilayers. Unlike misfit dislocations that accommodate lattice mismatch, the dislocation structures observed here increase the mismatch strain energy. Stop-action observations of the dynamically evolving atomic structures indicate that during deposition on the (111) surface of a fcc lattice, adatoms may occupy either fcc sites or hcp sites. This results in the random formation of fcc and hcp domains, with dislocations at the domain boundaries. These dislocations enable atoms to undergo a shift from fcc to hcp sites, or vice versa. These shifts lead to missing atoms, and therefore a later deposited layer can have missing planes compared to a previously deposited layer. This dislocation formation mechanism can create tensile stress in fcc films. The probability that such dislocations are formed was found to quickly diminish under energetic deposition conditions.

Simulated space environmental exposure of optical coatings for spacecraft solar rejection

Dielectric multilayers composed of niobium pentoxide and silicon dioxide, designed for broadband solar rejection, were exposed to a simulated space environment of ultraviolet light and low-energy (10-20-keV) electron radiation. Samples exhibited various degrees of exposure-induced absorption extending from the ultraviolet to the infrared. Processing variations were correlated to damage susceptibility, and methods were identified that produced parts that exhibited no degradation even though the same materials and coating design were used. Coatings prepared under energetic deposition conditions that provided the densest and most moisture-stable coatings exhibited the best stability to the exposure conditions used.

Atomic scale structure of sputtered metal multilayers

A combined theoretical and experimental approach has been used to study nanoscale CoFe/Cu/CoFe multilayer films grown by sputter deposition. Such films have applications in sensors that utilize the giant magnetoresistance effect, for example, read heads in high-density information storage devices. Atomistic simulations based on a molecular dynamics approach and an alloy form of the embedded atom method have been developed to accurately model the sputter deposition of the CoFe/Cu/CoFe multilayers. The simulations show that relatively flat interfaces are formed because of the energetic deposition conditions. However, significant intermixing at the CoFe-on-Cu interface, but not at the Cu-on-CoFe interface, was observed. An abnormal Fe depletion zone is also revealed at the CoFe-on-Cu interface. A three-dimensional atom probe method has been used for a nanoscale chemical analysis of the films. It provided direct verification of the simulations. The simulations have then been used to understand the mechanism responsible for the formation of the intermixing defects observed in the multilayers. A novel deposition technique is proposed which reduces both interfacial mixing and Fe depletion by controlling the incident adatom energies.

Review of advances in cubic boron nitride film synthesis

Abstract Cubic boron nitride (cBN) has a number of highly desirable mechanical, thermal, electrical, and optical properties. Because of this, there has been an extensive worldwide effort to synthesize thin films of cBN. Film synthesis is difficult in that without significant levels of ion bombardment during growth, only sp2-bonded BN forms, not sp3-bonded cBN. Recently there has been considerable progress in improving the deposition techniques and cBN film quality. In addition, progress has been made in understanding how energetic deposition conditions can lead to cBN formation. However, unanswered questions remain and process improvements are still needed. In this paper we critically and comprehensively review recent developments in cBN film synthesis and characterization. First, the structures and stability of the BN phases and characterization techniques are described. Next, the key experimental parameters controlling cBN film formation and synthesis techniques are discussed. Following a review of microstructure, the proposed mechanisms of cBN formation and the observed mechanical and electrical properties of cBN films are analyzed. We conclude by highlighting the current impediments to the practical realization of cBN-film technology.

Co thickness dependence of the microstructure of Pt/Co multilayers

We have studied with high resolution electron microscopy the microstructure of polycrystalline Pt/Co multilayers with between 13- and 18-Å-thick Pt and Co thicknesses up to 20 Å. For thin Co (∼4 Å), Pt/Co multilayers had (111)-fcc texture normal to the substrate and a coherent lattice with interplanar spacing of ∼2.2 Å, along the direction of chemical modulation. As the Co thickness increased, coherence was lost, and thicker Co layers had hcp structure with (002) texture, and the film surface roughness increased for less energetic deposition conditions. Coincident with a coherent structure (thin Co), Pt/Co multilayers have a large perpendicular magnetic anisotropy, important for their application in magnetic and magneto-optical devices.