Intrinsic stress in AIN prepared by dual-ion-beam sputtering

Classified abstracts 65494556 often relates to the m a x i m u m coating thickness which can be deposited without spallation, and this applies to coatings produced by both physical vapour deposition (PVD) and thermal spraying. For plasma-sprayed coatings in particular a heat transfer model is described which predicts the variation in residual stress distribution as a function of coating thickness and deposition rate and the results are compared with experimental observations. The levels of residual stress in plasma-sprayed tungsten have been measured by X-ray and mechanical slitting methods and explanations as to why these methods yield different results given. For PVD tungsten coatings the most important systems parameter is substrate bias since this allows some stress relaxation to occur via its influence on porosity levels in the coating and the consequences this has on residual stress levels is discussed. In P V D tungsten coatings the internal stress was completely relaxed on dissolution of the substrate, accompanied by a decrease in the lattice parameter of the film. D S Rickerby et al, Thin Solid Films, 154, 1987, 125-141. 22 6549. Ultramicrohardness measurements of coated samples Imaging of Vickers imprints for in situ hardness tests of insulating samples in a scanning electron microscope requires a conductive surface layer to avoid charging. The influence of such coatings on the measured hardness and the elimination of this effect by an extrapolation towards zero thickness of the layer are discussed theoretically. The method is checked by the example o f gold-coated silicon. A Wagendristel et al, Thin Solid Films, 154, 1987, 199 206. 22 6550. Adhesion testing by the scratch test method: the influence of intrinsic and extrinsic parameters on the critical load The critical load determined by the scratch test is widely regarded as representative of coating adhesion. Depending on the c o a t i n ~ s u b s t r a t e system to be measured, the critical load can be detected by acoustic emission, and/or by optical or scanning electron microscopy and/or by the variation of the tangential frictional force applied to the sample. It remains, however, difficult to express quantitatively the adherence because the critical load depends on several parameters related to the testing conditions and to the coating-substrate system. Both intrinsic parameters, such as scratching speed, loading rate, diamond tip radius and diamond wear, and extrinsic parameters, such as substrate hardness, coating thickness, substrate and coating roughness, friction coefficient and friction force, are considered in order to improve the interpretation of the critical load results. As well as the experimental relations between critical load and these different parameters, the results of a theoretical approach are also presented. The deformations and stress distributions near the interface caused by the static indentation of a spherical point have been simulated by the finite element analysis. Despite the fact that these calculations have been made in the static mode, they permitted a better understanding of the failures observed in and near the scratches; this represents a justification for the use of a scratch test to characterize the mechanical resistance (adhesion and cohesion) of a coating deposited on a tough substrate. P A Steiumann et al, Thin Solid Films, 154, 1987, 333-349. 22 6551. Adhesion of physically vapor-deposited titanium coatings to beryllium substrates The thrust of this investigation was to examine and identify the bonding mechanism between physically vapor-deposited titanium and a beryllium substrate. A mechanical interlocking model of adhesion was proposed. A n approximation of the adhesive failure stress which was based on classical fracture mechanic principles, is presented. Incorporated into the model was an X-ray diffraction texture characterization of the coating microstructure that was shown to vary with the deposition parameters. Experimental stresses to induce bond failure, in an adherence pull test, were compared with the stress values predicted by the model (which considers a state of plane strain at the coating-substrate interface). Alan F Jankowski, Thin Solid Films, 154, 1987, 183 198. 22 6552. The structure-mechanical property relationship of amorphous silicon monoxide thin films A m o r p h o u s silicon monoxide (SiOx) thin films were produced by Joule heating and electron b o m b a r d m e n t evaporative methods in high vacuum. Real-time force vs. elongation curves were recorded for SiOx films 20(~ 300 n m thick on an instrument known as the nanotensilometer. The

elastic modulus, fracture stress and plastic deformation were determined from hard mode tensile testing. The elastic modulus varied from 53 to 75 G P a independent of film preparation method. N o plastic deformation was detected for successive tensile pulls on a given specimen. Estimates of plastic deformation never exceeded 0.015% strain at the point of fracture. Failure occurred by brittle fracture and fracture stress ranged from 70 to 380 MPa. The film composition determined by Rutherford scattering gave an x value in SiOx within the range 0.9 1.0 for all films independent of evaporation method. The structure of the SiOx was determined to be of an a m o r p h o u s character by electron diffraction and structure imaging using transmission electron microscopy. R W Hoffman J r et ni, Thin Solid Films, 154, 1987, 149-157. 22 6553. The mechanical properties of thin films: a review Methods for the determination of thin film mechanical properties will be reviewed with an emphasis on their strengths and liabilities. Seminal investigations are highlighted which have significantly advanced our understanding of the mechanisms of thin film deformation. New developments in thin film mechanical property testing, as embodied in ultramicrohardness measurements, are covered and the significant improvements in thin film mechanical properties brought about by layered microstructures are discussed. D A Harflwick, Thin Solid Films, 154, 1987, 109-124.

23. I O N A N D P L A S M A ASSISTED F I L M G R O W T H 23 6554. Intrinsic stress in AIN prepared by dual-ion-beam sputtering The intrinsic stress of AIN, prepared by dual-ion-beam sputtering, has been investigated as a function of deposition temperature and nitrogen ion energy. The results show that the stress is compressive over the temperature range 75-700°C with a m a x i m u m value of - 2 8 × 109 dyn cm -2 at 75°C. The stress decreases gradually with increasing deposition temperature up to Td/Tm = 0.33 and then decreases sharply for higher temperatures. These results are similar to those reported for evaporated and r.f. sputtered metal films and appears to be a general result independent of the sign of the stress. The temperature dependence is interpreted in terms of the annealing of a strained layer and grain growth models. The results show that the compressive stress is due to the bombardment of the condensing film by energetic particles. Calculations indicate that the most energetic particles are of the order of 160 eV, originating as neutralized back-reflected argon neutrals. The nitrogen ions from the auxiliary gun do not appear to contribute materially to the intrinsic stress. Evaporation of aluminum, while simultaneously bombarding the film with an independent source, indicates that a saturation stress condition is established above a normalized energy of about 50 eV atom-k H Windischmann, Thin Solid Films, 154, 1987, 15%170. 23 6555. Plasma-processed Ag/P4Sel0 (80 ° deposited) films as a negative resist Lithographic properties of Ag/P4Sel0 (80 ° deposited) films exposed to photons and glow~iischarge hydrogen plasma have been investigated. It has been observed that the etching rate of the exposed film is lower compared to the unexposed one, giving rise to a negative tone behavior of the material. The effect of exposure time on the etching rate and selectivity ratio has been studied. The contrast (7) values obtained for the photoexposed and plasma-exposed negative resists are 2.9 and 5. I, respectively, with a photosensitivity of ~ 10zt photons/cm 2. P K Gupta and K L Chopra, Jappl Phys, 62, 1987, 4303-4305. 23 6556. Preparation of titanium nitride films by reactive ion plating and the influence of discharge current density on the film properties Hard, adhesive and dense titanium nitride coatings were prepared in a triode ion-plating system. This work shows and explains the influence of the discharge current density on the film characteristics. Microstructure, densification, crystalline composition and hardness are functions of the chosen value for the discharge current density. For example, for 0.7 m A cm 2 with a nitrogen pressure of 7.5 × 10 2 Pa and a negative cathode bias o f 2 kV: the phase TizN is the most important quantity and the deposit is the hardest ( ~ 2 5 0 0 kg mm-2). Deposits produced with a density of 0.6 m A cm z contain a predominant a m o u n t o f titanium metal, are porous and have a columnar structure. On coatings produced with 501