J. E. Greene

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...

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.

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...

REACTIVE MAGNETRON SPUTTER DEPOSITED CNX : EFFECTS OF N2 PRESSURE AND GROWTH TEMPERATURE ON FILM COMPOSITION, BONDING, AND MICROSTRUCTURE

The effects of growth processes on the chemical bond structure, microstructure, and mechanical properties of carbon–nitride (CNx) thin films, deposited by reactive magnetron sputtering in a pure N2 discharge, are reported. The film deposition rate RD increases with increasing N2 pressure PN2 while N/C ratios remain constant. The maximum N concentration was ∼35 at. %. RD was found to be dependent upon the film growth temperature Ts. For a given PN2, RD decreased slightly as Ts was increased from 100 to 600 °C. The variations in RD with both PN2 and Ts can be explained by ion‐induced desorption of cyano radicals CNx from both the target and growth surfaces during deposition. X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (FTIR) analyses showed that N atoms in films grown at Ts≳350 °C with low nitrogen partial pressures PN2, ∼2.5 mTorr, were bound to C atoms through hybridized sp2 and sp3 configurations. For low Ts=100 °C and higher PN2, 10 mTorr, triple‐bonded C≡N was detected ...

Polycrystalline TiN films deposited by reactive bias magnetron sputtering : effects of ion bombardment on resputtering rates, film composition, and microstructure

Transmission electron microscopy, x‐ray diffraction, and Rutherford backscattering have been used to investigate the effects of ion irradiation during growth on the deposition rate, composition, and microstructure of single‐phase polycrystalline NaCl‐structure TiNx films deposited by reactive magnetron sputtering with a negative substrate bias voltage Vs. The layers were deposited on thermally oxidized Si(001) substrates in mixed Ar+4% N2 discharges at a total pressure of 4.2 mTorr. Varying Vs between 0 and 1800 V resulted in incident ion‐to‐Ti atom flux ratios of 0.3 to 0.6 at the film growth surface and increases in the substrate temperature Ts (initially Ts=300 °C) of 40 to 200 °C. The Ti resputtering yield increased from ≤0.02 (Vs≤100 V) to 0.30 (Vs=1800 V) Ti atoms per incident ion (primarily Ar+), while the N/Ti ratio in as‐deposited films increased from 1.03 for Vs=0 V to 1.12 for 100 V≤Vs≤400 V and then decreased to ≂0.95 as Vs was raised to 1800 V. Trapped Ar concentrations ranged from ≤0.5 at.% ...

Use of an externally applied axial magnetic field to control ion/neutral flux ratios incident at the substrate during magnetron sputter deposition

The development and characterization of an ultrahigh vacuum ‘‘unbalanced’’ dc magnetron sputter deposition system with a variable external axial magnetic field for controlling the ion‐to‐neutral flux ratio at the substrate during deposition with low negative substrate biases is reported. The target assembly is a planar‐magnetron (PM) with a toroidal magnetic‐field electron trap created using a set of permanent magnets. A pair of Helmholtz coils, located outside the vacuum chamber, produces an additional magnetic field Bext which is uniform along the axis orthogonal to both target and substrate surfaces. The value and sign of Bext has a strong effect on the plasma density near the substrate, and hence on the ion flux Ji incident at the substrate, with only a minor effect on the target‐atom flux. For a Ti target sputtered in pure Ar at 20 mTorr with a target‐substrate separation of 6.5 cm, changing Bext from −50 G (opposing the field of the outer PM pole) to +600 G (reinforcing the field of the outer PM pol...

Average energy deposited per atom: A universal parameter for describing ion‐assisted film growth?

The average energy deposited per atom, 〈Ed〉=Ei(Ji/JMe), where Ei is the ion energy and Ji/JMe is the ratio of the accelerated‐ion to deposited‐thermal‐particle fluxes incident at the growing film, has been shown to be one of a set of parameters useful for describing the effects of low‐energy ion irradiation on film microstructure during ion‐assisted deposition. Recently, however, 〈Ed〉 has often been treated as if it were a fundamental, or universal, parameter. We have carried out experiments in which Ei (20–100 eV) and Ji/JMe (1–10) were varied independently during the deposition, at constant temperature, of polycrystalline Ti0.5Al0.5N films onto amorphous SiO2 substrates by ultrahigh vacuum reactive magnetron sputtering in pure nitrogen. Ion‐irradiation‐induced changes in film microstructure, texture, phase composition, and nitrogen‐to‐metal ratio were found to follow distinctly different mechanistic pathways depending upon whether Ei or Ji/JMe was varied, resulting in quite different properties for the ...

Synthesis of metastable epitaxial zinc‐blende‐structure AlN by solid‐state reaction

Epitaxial metastable zinc‐blende‐structure β‐AlN was synthesized by the solid‐state reaction between single‐crystal Al(001) and TiN(001) layers grown on MgO(001) by ultrahigh vacuum magnetron sputter deposition. At an annealing temperature Ta=600 °C, the interaction proceeded according to the following overall reaction: 4Al+TiN→Al3Ti+AlN, in which β‐AlN was formed pseudomorphically between cubic TiN and tetragonal Al3Ti layers. The lattice constant of β‐AlN was found to be 0.438 nm, which corresponds to a 3.3% lattice mismatch with the underlying TiN layer.

Growth of epitaxial TiN films deposited on MgO(100) by reactive magnetron sputtering: The role of low-energy ion irradiation during deposition

Abstract Plan-view and cross-sectional transmission electron microscopy have been used to investigate the role of low-energy ion irradiation in controlling the defect structure of epitaxial TiN(100). The films were deposited by reactive magnetron sputter deposition onto MgO(100) substrates at film growth temperatures T s between 550 and 850°C (0.26 to 0.35 of the melting point of TiN in K) and negative substrate biases V s between 0 and 500 V. Sputtering was carried out in pure N 2 atmospheres, the energy per N ion incident at the film surface was ∼ eV s 2 (N 2 + was the predominant ionic species), the incident ion to thermal-atom flux ratio for films grown with V s ≥100 V was ∼1.3, and the deposition rate was ∼1 monolayer s -1 (1.3 μm h −1 ). The primary defects observed in the films were dislocation loops on {111} planes. The number density n d of these loops decreased with increasing T s (e.g., for V s =0, n d ranged from 5×10 12 cm −2 at 550°C to 1.5×10 10 cm −2 at 850°C). However, n d also decreased rapidly with increasing V s at constant T s until a minimum defect density was attained at V s ∗ (T s ) after which n d incre ased again. Films grown at T s ≥750° C and V s =V s ∗ ≅ 300 V were essentially free of dislocation loops. On the other hand, films grown with T s C and V s ≥400 V (i.e., V s > V s ∗ ) exhibited very high dislocation loop densities, ≥5×10 12 cm −2 , together with the preci itation of N 2 gas bubbles. The net effect of ion irradiation on film microstructure depended upon a competition between the defect annihilation rate due to enhanced adatom mobilities during deposition and the collisionally-induced defect formation rate. The residual defect density was thus a function of both T s and V s . Under the proper growth conditions, ion irradiation led to a reduction in dislocation loop densities by more than 5 orders of magnitude. Cross-sectional micrographs of multilayer films grown as a function of V s at constant T s showed that n d increased or decreased (depending upon the direction of the change in V s ) abruptly and reversibly.