Silicon nitride films were deposited by helicon plasma enhanced radio frequency (rf) reactive sputtering. This technique was shown to produce films with low hydrogen and oxygen content at very low sputtering-gas pressure, with improved deposition rate compared with conventional rf reactive sputtering. Stoichiometric Si3N4 film with extremely low hydrogen content (<1%) and oxygen content (<1%) was obtained at the Ar/N2 partial pressure ratio of 1.5, and total sputtering-gas pressure of less than 0.1 Pa. The influence of sputtering-gas pressure on the mechanical, chemical, optical and compositional properties of the films was investigated by stress and chemical etch rate measurements, infrared absorption spectroscopy, ultraviolet-visible spectroscopy, and Rutherford backscattering spectrometry (RBS). These studies revealed that when keeping all other deposition conditions the same, reducing the sputtering-gas pressure, can effectively reduce the film contamination of H and O, and increase the film density.

Thin tungsten nitride (WNx) films were produced by reactive dc magnetron sputtering of tungsten in an Ar–N2 gas mixture. The effects of the variation of nitrogen partial pressure on the composition, residual stress, and structural properties of these films as well as the influence of postdeposition annealing have been studied. The films were analyzed in situ by a cantilever beam technique, and ex situ by x-ray photoelectron spectroscopy, electron energy-loss spectroscopy, x-ray diffraction, and transmission electron microscopy (TEM). It was found that at N concentrations below 8 at. %, the films (typical 150 nm in thickness) were essentially bcc α-W. An amorphous phase was observed in the range of about 12–28 at. % N. When N concentrations reached ∼32 at. % or above, a single-phase structure of W2N was formed. Annealing of the as-deposited films resulted in crystallization of the amorphous or an improved crystallinity of the W2N structure, which was related to the N concentration. Stresses of all W and WNx films were compressive. As the N concentration was increased, the stress decreased and reached its lowest value for amorphous samples near 20 at. % N. Past this point, the compression of films rose again. These results can be ascribed to structural changes induced by the pressure-dependent variation in the average energy of particles bombarding the film during deposition. Cross-sectional TEM studies showed that all crystalline WNx films had columnar microstructures. The average column width near stoichiometry of W2N was ∼20±5 nm near the film surface.

The residual stress and structural properties of tungsten thin films prepared by magnetron sputtering as a function of sputtering-gas pressure are reported. The films were analyzed in situ by a cantilever beam technique, and ex situ by x-ray diffraction, cross-sectional transmission electron microscopy (TEM), x-ray photoelectron spectroscopy, electron energy-loss spectrometry, and energy-filtered electron diffraction. It is found that the residual stress, microstructure, and surface morphology are clearly correlated. The film stresses, determined in real time during the film formation, depend strongly on the argon pressure and change from highly compressive to highly tensile in a relatively narrow pressure range of 12–26 mTorr. For pressures exceeding ∼60 mTorr, the stress in the film is nearly zero. It is also found that the nonequilibrium A15 W structure is responsible for the observed tensile stress, whereas the stable bcc W or a mixture of bcc W and A15 W are in compression. Cross-sectional TEM evidence indicates that the compressively stressed films contain a dense microstructure without any columns, while the films having tensile stress have a very columnar microstructure. High sputtering-gas pressure conditions yield dendritic-like film growth, resulting in complete relaxation of the residual tensile stresses. Structural details of the A15 W and amorphous W phases were also investigated at the atomic level using energy-filtered electron diffraction with reduced radial distribution function G(r) analysis. By comparing the experimental and simulated G(r) distributions, the A15 W structure is determined to be composed of ordered and stacking faulted W3W structures and the amorphous W has a disordered structure of W3O. The effect of oxygen in stabilizing the A15 phase found is explained on the basis of structural and thermodynamic stability.

An impulse thermal breakdown model is proposed to understand the breakdown mechanism of Al2O3 thin film based metal-to-metal antifuses. In this model, the electric field dependence as well as the temperature dependence of the electrical conductivity is considered. The I–V characteristic of the antifuses indicated that the conductivity of Al2O3 rose greatly under high field. The threshold breakdown voltage of the antifuses was shown by experiment to be proportional to its insulator thickness and to the square root of the insulator resistivity. When breakdown of the antifuses was carried out by applying constant voltage pulse, the inverse square root of the time to breakdown was shown to be proportional to the amplitude of the pulse. All the experimental results were found to be consistent with the theoretical results of the model. In addition, an antifuse breakdown filament with a diameter of 150 nm was observed by using a scanning electron microscope.

Biomaterials which combine optimum properties of strength and biocompatibility are desirable in improving the long-term performance of implantable medical devices. Our study is aimed at developing technology designed to alter the outer atomic layers of a material to give the desired compatibility with the tissue while retaining the properties of the bulk substratum. Materials used in this study were titanium vanadium alloy (Ti-6Al-4V) and cobalt chromium molybdenum alloy (Co-Cr). Soda lime glass discs and polyethylene terephthalate (PET) acted as controls. A cathode of either Ti-6Al-4V or Co-Cr was used to simultaneously deposit and implant identified substrata. The attachment of human bone-derived cells (HBDC) to various materials was determined using radiolabeling or colorimetric assays. Results show that HBDC adhere preferentially to the unmodified surfaces of Ti-6Al-4V and Ti-6Al-4V on glass compared to the unmodified Co-Cr surfaces and to that of the Co-Cr on glass. Depositing Ti-6Al-4V on Co-Cr gives significantly better attachment of HBDC than when depositing Co-Cr onto Ti-6Al-4V. While cellular attachment to the created surfaces reflects that of the cathodic materials, it is not identical to these materials. Ion deposition/implantation is capable of creating permanent surfaces which reflect the adhesion of source materials not bulk substrata.

A novel antifuse structure with double dielectric layers, AlN(10nm)/ SiN(10nm), is presented in this paper. The SiN and SiO{sub 2} for insulating are deposited by low temperature PECVD. Experimental results show this antifuse has excellent characteristics. Comparing to other antifuses, the thicker insulator layer of this antifuse improves its reliability and also offers a low off-state leakage current while still keeping the breakdown voltage below 15 V. The fabrication process, characteristics of the antifuse and breakdown mechanisms are described and discussed in detail. A low temperature deposition of the insulator layer is important to avoid the interaction between the metal and dielectric layers. It was found that low temperature cathodic arc and PECVD methods are therefore benefit to the reliability of the antifuse. The breakdown link of antifuse was observed under Field Emission Scanning Electron Microscope.

Elastic strain energy under some conditions provides the major contribution to the total energy of a film growing on a substrate from condensing vapour. Polycrystalline films grown with intrinsic stress induced by energetic bombardment are expected to show orientations which minimize total energy. Even for a cubic crystal in a non-hydrostatic stress field the energy is a function of the relative orientation of the stress field and the crystallographic axes. The Gibbs free energy is minimized under constant stress and temperature conditions at thermal equilibrium. In this paper we derive expressions for the Gibbs free energy of a cubic crystal in uniaxial and biaxial stress fields and find the conditions under which it is a minimum. The sign of the expression is the quantity which determines the behaviour of a cubic crystal and if negative, predicts that the [111] direction of the crystal will align with the principal stress of a uniaxial stress field and will lie normal to the plane of principal stresses in a biaxial stress field. Experimental evidence is presented which shows that titanium nitride, TiN, which has a negative value of , obeys these predictions. If is positive, then the [100] direction of the crystal obeys the above rules rather than the [111] direction.

Plasma-assisted chemical vapour deposition (PACVD) has many advantages for the deposition of thin films. The use of ions for the energetic bombardment of the film during growth is an important technique for producing dense structures. This paper discusses recent progress in the understanding of the effects of energetic bombardment on the stress levels and structure of films produced by plasma deposition processes. Diagnostic equipment, such as the in situ ellipsometer, energy selecting mass spectrometer and residual gas analyser, enables the PACVD process to be closely monitored so that conditions at the growth surface can be accurately controlled. New plasma sources, such as the helicon plasma source, give increased ion fluxes. The cathodic arc source is also an intense source of highly ionized plasma which can be used for PACVD. The deposition of rugate optical structures based on SiOxNy can be carried out using a PACVD process in which the refractive index profile is created by the computer control of gas flows. The helicon plasma source is useful for the deposition of SiO2 films and has been adapted for use in an ion plating process for the deposition of cubic phase BN. The deposition of amorphous hydrogenated carbon films by PACVD of acetylene in a cathodic arc has been shown to be possible and demonstrates the effect of using a highly ionized plasma for PACVD.

Thin films of boron nitride (BN) were deposited on glass, silicon and silica substrates in a helicon activated reactive evaporation system. Both the hexagonal (h-BN) and the cubic (c-BN) phases of boron nitride have been grown in the system at different operating conditions. The refractive indices of h-BN and c-BN thin films have been measured at three wavelengths. The films were monitored using in situ ellipsometry giving detailed information on the growth of each film. In situ ellipsometry has generally confirmed a model for c-BN growth based on compressive stress. Control over the formation of both phases of BN has been demonstrated.

An equilibrium thermodynamic analysis of the Gibbs free energy in a non-hydrostatic stress field is applied to the formation of boron nitride thin films. The theory predicts a specific sequence of microstructures from non-oriented hexagonal boron nitride, through oriented hexagonal boron nitride and finally cubic boron nitride. It also predicts a threshold stress for cubic boron nitride formation. These predictions are in agreement with experimental observations reported here and made by others. The synthesis of cubic boron nitride in a new helicon wave plasma source is demonstrated. The operating parameters which produce the cubic phase are determined.

Stoichiometric titanium nitride (TiN) films were deposited at less than 130 °C in a new configuration of the helicon activated reactive evaporation system. An in situ ellipsometer was used to monitor the optical properties of the films during growth. The film stress, lattice parameter, surface roughness, crystallite size, and preferred orientation were investigated as a function of substrate bias and hence ion energy of the incident species. The intrinsic stress dependence on ion energy shows the expected result also shown by a variety of materials and is in good agreement with the theoretical model of Davis [Thin Solid Films 226, 30 (1993)]. The high stress level at −50 V bias is confirmed by measurement of lattice parameter. X-ray-diffraction measurements show that the (111)-preferred orientation normal to the substrate surface correlates strongly with the stress level of the films. By correlating our results with those from a number of other reported studies at higher substrate temperature we conclude that the observed preferred orientation in TiN films can be explained from the viewpoint of the energy minimization principle. Kinetic factors are of less importance except possibly at the highest bombardment energies.

The type and degree of stress in a thin film grown on a substrate is strongly influenced by the energy distribution of the incident species. In the case of material grown from plasmas, the energy distribution is determined by the plasma properties and by substrate bias, For incident species within an energy range, termed the 'hyperthermal' range, strong compressive stress arises in many materials. In this paper, the properties of and preferred orientation effects in TiN films are studied and correlated with the measured stress level. The films were deposited in a new type of plasma process, the helicon assisted evaporation process fitted with in situ ellipsometry, This process enables the preparation of TiN films with stress levels ranging from tensile to highly compressive by adjusting the substrate bias from zero to 300 V negative. The compressive stress shows a maximum at 50 V negative bias and the functional form of the relation is in agreement with a theoretical model, The presence of a (111) preferred orientation normal to the substrate, and low film resistivity correlate with high compressive stress.

There are some advantages of cathodic are deposition techniques over other thin film deposition methods. In this paper we discuss and demonstrate the possibility of applying the cathodic are deposition technology to the production of solar energy conversion devices, particularly solar thermal selective surfaces. We show that cathodic are deposition can be operated in a plasma assisted chemical vapour deposition mode as well as reactive deposition mode to produce metal-dielectric cermet materials. Solar thermal selective surfaces were obtained using this method. The morphology of the surfaces can be varied from rough to smooth by controlling the macroparticles content by means of filtering. Rough but dense films can be deposited, which may have potential for enhancing solar absorption for both solar thermal selective surfaces and solar cells.

The plasma-assisted chemical vapor deposition technique was used to produce thin-film structures with both sinusoidally and stepwise varying refractive-index profiles. The refractive index of the SiOxNy system used in the fabrication was found to be time dependent following a stepwise change in reactant gas flows or initiation of the plasma. This time dependence has been quantified using in situ ellipsometry and was found to have components with exponential and linear dependences. The time dependence of water vapor partial pressure in the system was identified as the cause of the linear dependence. Allowance for the time-dependent effects has improved the agreement between the calculated spectral response and the measured result for a broadband high-reflectance mirror consisting of an arithmetic progression of discrete layers.

Cubic boron nitride (c-BN) is a high quality abrasive material with hardness second only to diamond and with good oxidation and solubility properties. A new ion plating technique using the helicon wave plasma source combined with electron beam evaporation has been developed for the large area, high rate deposition of this material. The apparatus is fitted with a multiwavelength in situ ellipsometer for monitoring growth. The optical properties of both c-BN and h-BN films have been measured in situ and the operating conditions which produce a high growth rate of c-BN have been determined. A simple model for the movement of boron through the system has been developed and compared to experiment.

The silvery reflectance in fish skin is studied using an idealized model of the two optical components, guanine and cytoplasm. A structure in which the thickness of both components are randomized over an interval gives a calculated reflectance in good agreement with the measured reflectance of two species in the family Trichiuridae, including the behaviour in the infrared. Existing ideas based on quarter-wave stacks, either tuned to different wavelengths or with a progression of optical thickness with depth, have been shown to be unsatisfactory. The random or 'chaotic' structure is confirmed by electron microscopy of cross sections of fish skin. The random structure is an example of the phenomenon of optical localization in a biological system.

Compressive biaxial stress fields in thin film boron nitride are shown to provide a means of accessing the region of the phase diagram in which cubic BN (c-BN) is the stable phase. This process differs from high pressure, high temperature synthesis in that c-BN is synthesised from an incoming flux of ions or atoms rather than converted from the hexagonal phase. Experimental evidence is presented that the compressive stress mechanism for c-BN formation is operating during the reactive ion plating deposition process. A well defined threshold stress value is found for the production of c-BN under a wide range of preparation conditions. The microstructure of the films as studied by electron optical methods and the behaviour of the infrared absorption spectrum after stress relief provides further confirmation of the compressive stress mechanism.

Article Atomic Dimensional Influences on Patterns of p-c(n)-T and other Relationships of Palladium Alloy — Hydrogen Systems* was published on February 1, 1989 in the journal Zeitschrift für Physikalische Chemie (volume 163, issue 1).