A.J. Perry

Young's modulus of TiN, TiC, ZrN and HfN☆

Abstract The Youngs modulus of group IVB nitride and TiC films coated onto stainless steel substrates by reactive sputtering has been derived from their flexural resonance frequemcy. The values found for stoichiometric ZrN and HfN are 460 GPa and 380 GPa respectively. A wide range of TiN compositions was studied: the modulus increases steadily with nitrogen level to be about 640 GPa at the stoichiometric composition. A limited number of TiC samples has been measured; taking existing literature values into account a value for the stoichiometric phase of 460 GPa is derived.

A contribution to the study of poisson's ratios and elasticconstants of TiN, ZrN and HfN

Abstract The elastic constants of the group IVB nitrides TiN, ZrN and HfN have beenstudied by X-ray residual stress measurements. Films of the nitrides were deposited onto stainless steel substrates by reactive sputtering and then vacuum annealed. They were studied using Cr Kα radiation and the five available diffraction peaks (111) to (222). Poissons ratios for bulk material are 0.30, 0.19 and 0.35 for the three nitrides respectively, indicating that the first and last are nearly isotropic which requires ν to be ⅓. Values of the X-ray elastic constants and anisotropy factors were also derived.

Variations in the reflectance of TiN, ZrN and HfN

Abstract The gold-like color and high hardness of the group IVB nitrides have allowed their use as scratch-resistant decorative coatings. The color can be varied with composition and mode of preparation. In the present work, TiN, ZrN and HfN films with different nitrogen-to-metal ratios were prepared on stainless steel by reactive sputtering. Half of each sample was vacuum annealed at 900°C for 1 h. The lattice parameters, reflectance and color were determined. The lattice parameters remained above equilibrium even after tempering. The experimental reflectance curves were analyzed in terms of the reflectance minima (between the screened Drude plasma edge and the onset of interband transitions) and the value of the reflectance at a photon energy of 1 eV (which is representative of the relaxation behavior). For all three nitrides the reflectance minimum is reduced to lower values of photon energy and reflectance as the nitrogen content is increased through the stoichiometric point. The reflectance at 1 eV increases concurrently. The degree of yellowness increases with nitrogen content, but no consistent effect of tempering could be defined. The behavior is described as the combined result of charge transfer from the metal to the metalloid atom (thus changing the effective density of conduction electrons) and of varying concentrations of vacancies and interstitials.

The chemical analysis of TiN films: A round robin experiment

Abstract Two series of titanium nitride films have been prepared under different conditions by reactive d.c. bias magnetron sputtering. They have been studied by X-ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA), Auger electron spectroscopy (AES), X-ray diffraction (XRD) and gravimetric oxide chemical analyses, in a round robin experiment, to compare the reliability of the techniques in characterizing films quantitatively. The EPMA, AES and chemical analyses (where applied) of the samples produce consistent data. However, a discrepancy was found between AES and XPS data in one series of samples. XRD shows considerable deviations from equilibrium in the lattice parameters, negating its use in analysis.

The relationship between residual stress, X-ray elastic constants and lattice parameters in TiN films made by physical vapor deposition

Abstract The lattice parameters as measured by a traditional X-ray diffraction (XRD) study are affected by the residual stress in accordance with the crystallographic elastic constants. The present work reports a study of the viability of using a standard XRD study to make a simplistic estimate of the behavior of the X-ray elastic constants and also the state of residual stress and the strain distribution in films made by physical vapor deposition. Values of the residual stress are derived, but it is shown that the orientation factor dependence of the lattice parameters deviates very strongly from theory. This is discussed in terms of plastic deformation and cracking in the films. It is concluded that this approach to estimating residual stress cannot be used without great care being exercised in the interpretation of the XRD data as considered in terms of e.g. the Nelson-Riley and orientation factor extrapolations.

Residual stress in physically vapor deposited films: A study of deviations from elastic behavior

Abstract The residual stress in films made by plasma-enhanced physical vapor deposition is generally very high, of the order of 1% of the shear modulus. The present work is a report of a study of the lattice parameter and the residual stress as measured by X-ray diffraction (XRD) methods on different crystal planes. ZrN films are studied on stainless steel substrate; these films are considered typical of group IVB nitride films and were used as a model system of practical significance. Deviations from simple behavior after a heat treatment are found on the (111) and (200) families of planes but not on high index planes. The deviations are discussed in terms of plastic deformation, shear stresses and microcracking on these planes which are the primary and secondary slip systems respectively. The residual stress in the substrate is low, in contrast to what would be expected from the high stress in the film. The XRD data appear to indicate that the effect of this stress is absorbed, at least in part, by plastic deformation on the (200) planes of the stainless steel substrate; unfortunately the present experimental arrangement did not permit the (111) primary slip plane to be studied.

Structural analysis of tin films by Seemann-Bohlin X-ray diffraction

Abstract The accuracy of the Seemann-Bohlin method has been improved by usinginternal standards and a new calibration function. Experimental results illustrated by four typical examples show that the stress and stress-free lattice parameter values determined by this method are crystallographically averaged quantities convenient for an overall characterization of lattice distortions. Combination of the method with the Bragg-Brentano technique and with sample annealing or substrate dissolution can be used for the separation of particular structural effects on the properties of TiN hard films.

On picostructural models of physically vapor-deposited films of titanium nitride

Abstract The atomistic models of Knotek et al. and of Goldfarb et al. explaining the intrinsic stresses in physically vapor-deposited films by an ion-peening mechanism are tested against X-ray diffraction data from magnetron-sputtered TiN films deposited at different ion current densities. It was found that both models fail to explain the observed data completely. Using additional microstructural information from electron micrographs, new models are presented to account for lattice distortions observed in both the tensile and the compressively stressed films. These models assume the existence of oriented lattice defects. Further experiments which could reveal the actual role of argon entrapment and an origin of intrinsic lattice distortions are suggested.

Lattice vacancies in TiN and HfN films: A study by positron annihilation☆

Abstract Films of the group IVB nitrides can have expanded lattices which are restored by tempering, reflecting the presence of a high concentration of defects. This positron annihilation study is a first attempt to obtain a qualitative understanding of the lattice relaxation on an atomic scale. The spectra measured before and after tempering were resolved into three components, showing more than one type of defect to be present. The major contribution is attributed to the trapping of positrons in vacancies. The results of all samples taken together support the proposal that the dominant mechanism is the migration of interstitial atoms into lattice vacancies. The nature of the defects leading to the longer-lived positron states, possibly voids and/or dislocations, is still uncertain.

Residual stress and strain distribution anomalies in TiN films deposited by physical vapor deposition

Abstract The residual stress, lattice parameters and strain-broadening of diffraction peaks have been studied in a series of TiN films deposited on a C3 cemented carbide substrate by reactive magnetron sputtering. The substrate bias voltage and the sputter target input power were varied. It was found that complex residual stress situations could exist where, for example, (220) planes could exhibit high compressive and shear stress, (422) planes, simple low tensile stress and (333)–(511) planes, simple low compressive stress conditions within a given film. The observed residual stress behavioral patterns fell into three groups depending upon the deposition conditions. In addition, the lattice parameters and peak broadening showed positive or negative deviations from the average values of the remaining planes, specific within each behavioral pattern range. It is thought that these effects are associated with the dramatic increases in the defect and stacking fault population found with increasing bias, and with the ultramicrocracking on (220) planes, which have been reported in the literature from transmission electron microscopy studies of TiN films made by physical vapor deposition methods.