J.-E. Sundgren

Structure and properties of TiN coatings

During the last few years there has been increasing interest in TiN thin films deposited by various physical vapour deposition methods. Since the films are grown by various techniques and using different process parameters the variation in the actual growth conditions is considerable. This gives rise to a large scatter in the microstructures and hence also in the properties of the films. In this paper reported microstructures of thin films of TiN are reviewed and are also correlated to physical properties such as the electrical resistivity and the hardness of the films. For example, one important microstructural feature is voids located in the grain boundaries. Such voids result in low hardness values and high resistivities. The origin of the various microstructures that are obtained is also discussed in terms of the growth conditions used. The voids mentioned above can, for example, occur because of deviation from stoichiometry, too low a substrate temperature or impurities in the films, but also because of substrate-induced growth effects specially if multiphase substrates such as high speed steels are used. In addition to single-phase TiN films, two-phase or multiphase films containing the phase Ti2N are also discussed. In many cases such films show extremely high film hardnesses. However, it is shown that the high hardnesses are mainly caused by the specific microstructures that can develop rather than by the Ti2N phase itself.

Growth of single‐crystal TiN/VN strained‐layer superlattices with extremely high mechanical hardness

Single‐crystal TiN/VN strained‐layer superlattices (SLS’s) with layer thicknesses lTiN =lVN =λ/2 (where λ is the period of the superlattice) ranging from 0.75 to 16 nm have been grown on MgO(100 ) substrates by reactive magnetron sputtering. Cross‐sectional transmission electron microscopy (TEM) and x‐ray diffraction examinations showed that the films were single crystals exhibiting coherent interfaces and several orders of superlattice reflections. There was no evidence in either plan‐view or cross‐sectional TEM analyses of misfit interfacial dislocation arrays. The primary defects observed were dislocation loops with a diameter of 8–10 nm extending through several layers and small defects with a diameter of 1–2 nm that were confined within single layers. Microindentation hardness values H, measured as a function of λ in films with a total thickness of 2.5 μm, increased from 2035±280 kg mm−2 for Ti0.5V0.5N alloys (i.e., λ=0) to reach a maximum of 5560±1000 kg mm−2 at λ=5.2 nm and then decreased rapidly t...

Oxidation of metastable single‐phase polycrystalline Ti0.5Al0.5N films: Kinetics and mechanisms

Metastable single‐phase, NaCl‐structure, polycrystalline Ti0.5Al0.5N alloy films have been shown to exhibit much better high‐temperature (750–900 °C) oxidation resistance than polycrystalline TiN films grown under similar conditions. The Ti0.5Al0.5N alloys, ≂3 μm thick, were deposited at temperatures between 400 and 500 °C on stainless‐steel substrates by dc magnetron sputter deposition in mixed Ar+N2 discharges with an applied negative substrate bias Vs of either 0 or 150 V. Oxidation in pure O2 initially occurred at a rate that varied parabolically with time. The oxide overlayers consisted of two partially crystalline sublayers, the upper one Al‐rich and the lower one Ti‐rich, with no measurable N concentrations in either. Inert‐marker transport experiments showed that oxidation proceeded by the simultaneous outward diffusion of Al to the oxide/vapor interface and inward diffusion of O to the oxide/nitride interface. The oxidation rate constant K increased with oxidation temperature Tox at a rate much h...

Development of preferred orientation in polycrystalline TiN layers grown by ultrahigh vacuum reactive magnetron sputtering

The preferred orientation of polycrystalline TiN films grown by ultrahigh‐vacuum reactive‐magnetron sputter deposition on amorphous SiO2 at 350 °C in pure N2 discharges was controllably varied from (111) to completely (002) by varying the incident ion/metal flux ratio Ji/JTi from 1 to ≥5 with the N+2 ion energy Ei maintained constant at ≂20 eV (≂10 eV per incident accelerated N). All samples were slightly over‐stoichiometric with N/Ti=1.02±0.03. Films deposited with Ji/JTi=1 initially exhibit a mixed texture with competitive columnar growth which slowly evolves into a nearly complete (111) texture at film thicknesses greater than 1 μm. However, films grown with Ji/JTi≥5 exhibit an essentially complete (002) preferred orientation from the earliest observable stages. The normalized XRD (002) intensity ratio in thick layers increased from ≂0 to 1 as Ji/JTi was varied from 1 to ≥5. Both (111) and (001) interplanar spacings remained constant as a function of film thickness yielding a lattice constant of 0.4240...

Microstructure modification of TiN by ion bombardment during reactive sputter deposition

Abstract Cross-sectional transmission electron microscopy has been used to investigate the effects of low energy (400 eV or less) ion irradiation during the growth of reactively sputtered TiN at temperatures between 300 and 900 °C. The films were deposited on high speed steel substrates in mixed ArN 2 discharges using an applied negative substrate bias voltage V s to vary the energy of impinging ions. The arrival rate ratio between ions and titanium atoms increased from 0.3 to 0.4 as V s was increased from 40 to 400 V. Films grown with V s ⩽ 200 V exhibited a columnar-like microstructure with a mixed (200)–(220) preferred orientation and the average column size increased with increasing T s . Both the width of the columns and the defect number density within each column were also influenced by ion bombardment. Raising V s above about 200 V resulted in a loss of preferred orientation together with an increasing dissolution of the columnar boundaries due to continuous renucleation during growth. Defect number densities in multilayer films were observed to vary abruptly and reversibly with changes in V s atall growth temperatures.

Mechanisms of reactive sputtering of titanium nitride and titanium carbide II: Morphology and structure

Titanium was reactively r.f. sputtered in mixed ArN2 and ArCH4 discharges onto substrates held at 775 K. The films obtained were characterized by scanning electron microscopy and X-ray diffraction and through measurements of the microhardness and electrical resistivity. The composition of the films was determined by Auger electron spectroscopy. The measurements show that the morphology of the deposits to a large extent influences the properties of the films obtained. For TiN coatings the electrical resistivity reaches the bulk resistivity only if coatings with the full bulk density are obtained. The difference observed in the lattice parameter for TiN thin film and bulk samples is explained using a grain boundary relaxation model. It is also shown that the heat of formation of the compounds plays an important role in the formation of carbide and nitride films. A high heat of formation promotes the development of large grains and dense structures.

Microstructure and physical properties of polycrystalline metastable Ti0.5Al0.5N alloys grown by d.c. magnetron sputter deposition

Metastable single-phase polycrystalline Ti0.5Al0.5N alloy films, approximately 3 μm thick, have been grown on stainless steel substrates by d.c. magnetron sputter deposition from a TiAl target in mixed Ar-N2 discharges. The deposition temperature was between 400 and 500 °C and the applied negative substrate bias Vs was varied from 0 to 250 V. Electron microprobe analyses, using pure elemental standards, showed that the film composition was independent of Vs to within the experimental accuracy, ±3 at.%. All films were found, based upon X-ray diffraction (XRD) and transmission electron microscopy (TEM), to have a B1 NaCl structure (AlN crystallizes in the wurtzite structure) with a (111) preferred orientation. The lattice parameter a0 of films grown at Vs < 80 V was 0.4176 nm and cross-sectional TEM showed that such films had a columnar structure exhibiting a high intercolumn, as well as intragrain, porosity. Increasing Vs above 80 V, however, resulted in a rapid increase in both a0 and the width of the XRD peaks, while the average grain size decreased from 105 nm at Vs=0 to about 35 nm. There was also a corresponding decrease in the void density at high substrate biases, the columnar structure was interrupted and the dislocation density increased. All these effects were associated with the introduction and/or agglomeration of ion-irradiation- induced defects in the films. The microindentation hardness of the films increased with increasing substrate bias and ranged from 1000 kgf mm−2 at Vs = 0 to 4200 kgf mm−2 at Vs = 250 V.

Structural and mechanical properties of carbon nitride CNx (0.2⩽x⩽0.35) films

This article reports on the structure and mechanical properties of CNx thin films deposited by unbalanced reactive magnetron sputtering of C in N2 discharges. The films were grown on Si(001) substrates kept at temperatures (Ts) between 150 and 600 °C. Depending on Ts, the films contained between 15 and 26 at. % N. X‐ray photoelectron spectroscopy of samples typically showed two peaks in the C 1s core level spectrum (centered at 284.5 and 286.2 eV) and two peaks in the N 1s core level spectrum (centered at 398.4 and 400.3 eV). This indicates that there are two types of C–N bonds where N is bonded to both sp2‐ and sp3‐coordinated C atoms in the as‐deposited films. Transmission electron microscopy showed that the films produced in the temperature range 200≤Ts≤600 °C had a highly textured, turbostraticlike structure with the c axis in the plane of the film. The basal planes in this structure were found to be buckled and bent due to incorporation of N in substitutional sites. By contrast, films produced at Ts=...

High‐flux low‐energy (≂20 eV) N+2 ion irradiation during TiN deposition by reactive magnetron sputtering: Effects on microstructure and preferred orientation

The effects of the incident ion/metal flux ratio (1≤Ji /JTi≤15), with the N+2 ion energy Ei constant at ≂20 eV (≂10 eV per incident accelerated N), on the microstructure, texture, and stoichiometry of polycrystalline TiN films grown by ultrahigh‐vacuum reactive‐magnetron sputtering have been investigated. The layers were deposited in pure N2 discharges on thermally oxidized Si(001) substrates at 350 °C. All films were slightly overstoichiometric with a N/Ti ratio of 1.02±0.03 and a lattice constant of 0.4240±0.0005 nm, equal to that of unstrained bulk TiN. Films deposited with Ji/JTi=1 initially exhibit a mixed texture—predominately (111), (002), and (022)—with competitive columnar growth which slowly evolves into a pure (111) texture containing a network of both inter‐ and intracolumn porosity with an average column size of ≂50 nm at t=1.6 μm. In contrast, films grown with Ji/JTi≥5 do not exhibit competitive growth. While still columnar, the layers are dense with an essentially complete (002) preferred o...

NANOINDENTATION STUDIES OF SINGLE-CRYSTAL (001)-, (011)-, AND (111)-ORIENTED TIN LAYERS ON MGO

The mechanical properties of (001)‐, (011)‐, and (111)‐oriented MgO wafers and 1‐μm‐thick TiN overlayers, grown simultaneously by dc magnetron sputter deposition at 700 °C in a mixed N2 and Ar discharge, were investigated using nanoindentation. A combination of x‐ray‐diffraction (XRD) pole figures, high‐resolution XRD analyses, and Auger electron spectroscopy was used to show that all TiN films were single crystals with N/Ti ratios of 1.0±0.05. The nanoindentation measurements were carried out using a three‐sided pyramidal Berkovich diamond indentor tip operated at loads ranging from 0.4 to 40 mN. All three orientations of MgO substrates, as‐received, exhibited identical hardness values as determined using the Oliver and Pharr method. After a 1 h anneal at 800 °C, corresponding to the thermal treatment received prior to film growth, the measured hardness of MgO(001) was 9.0±0.3 GPa. All TiN films displayed a completely elastic response at low loads. Measured hardness values, which decreased with increasin...