Uwe Beck

Determination of mechanical film properties of a bilayer system due to elastic indentation measurements with a spherical indenter

Abstract A recently developed theoretical model represents the generalization of the indentation of a sphere into an infinite homogeneous halfspace to the problem of a Hertzian load acting on a halfspace covered with one or more films having different elastic properties. The model allows the analytical calculation of the complete elastic stress field and the deformations within the films and the substrate. Some results of the model shall be confirmed by nanoindentation experiments using an UMIS-2000 nanoindenter into Si3N4/SiO2 and SiO2/ Si3N4 double layers on BK7 glass and Si(100) single crystal. The materials used allow accurate measurements due to their homogeneous, amorphous structure as well as low surface and interface roughness. After the determination of the instrument compliance and the real, depth dependent indenter radius the measured load–depth data are compared with calculated results. It is shown that measurement results can be correctly interpreted by the model. The onset of plastic deformation is investigated for the same samples by multiple partial unloading experiments with a 4-μm radius diamond sphere. The critical load at which a first deviation from a wholly elastic response occurs is used for a stress calculation with the model. The mechanical behavior of the different film combinations is interpreted by means of the von Mises comparison stress. The measured results, together with the analytical modeling, allow an optimization of the thickness and modulus of the individual layers to get a maximum mechanical stability.

Evaluation of optical properties of decorative coatings by spectroscopic ellipsometry

Abstract Some of the hard coatings ( e.g. TiN, TiCN, TiCN, TiAlCN) occur in different colours. Using goniospectroscopy in the visible wavelength range colours are deduced by measuring the spectral reflectance factor R λ . This factor depends on both the samples and the white reference as well as on the geometry of illumination and measurement. It is very difficult or even impossible to distinguish colours according to their origin and to relate them to bulk material composition, thin film coatings and interference layers by means of goniospectroscopy as unpolarized light is used. By using polarized light in spectroscopic ellipsometry these difficulties could be overcome as there is no reference to white and the geometric influences of illumination and measurement are negligible, but on the contrary the visual impression is not correctly described. From the measurement of the relative amplitude ratio tan Ψ and the relative phase shift cos Δ it is possible to calculate either the parallel and normal components R p and R s of the reflectivity R or the complex refractive index N = n + i k as well as the dielectric function e = e 1 + i e 2 which are strongly related to the electronic structure of the material used. It is shown that in this way it is possible to describe optical properties more physically, to separate interference effects and to detect changes in stoichiometry.

Decorative hard coatings: new layer systems without allergy risk

Abstract Combinations of physically vapour deposited (PVD) coatings and electroplated layers are widely used for decorative applications. The electroplated layer beneath the PVD coating acts as a diffusion barrier. Conventionally electroplated barrier layers make use of nickel which has to be replaced in allergy-free systems by for example Ni/NiPd and CuSn(Zn). The PVD coating has to meet a variety of requirements: attractive colour, high wear resistance and good corrosion resistance. Within the scope of the search for new colours a number of nitrides of binary IVa metal-based alloys such as (Ti,V)N, (Zr,V)N, (Zr,Al)N, (Zr,Cr)N, (Zr,Y)N were deposited by reactive magnetron sputtering. To describe the colour the CIE L ∗ a ∗ b ∗ system was used. Spectroscopic ellipsometry (SE) was introduced to determine material related parameters. In general, both the stoichiometry and the structure can influence the colour of a coating. The correlation between colour, stoichiometry and structure was determined by surface analytical methods (glow discharge optical spectroscopy, Auger electron spectroscopy, X-ray diffraction). Proper selection of process parameters (target composition, N 2 flow rate, etc.) results in coatings with colours exceeding the conventional spectrum of decorative coatings. As an example of structural and stoichiometric influences on colour, ZrN and (Zr,Y)N coatings are discussed.

Decorative optical coatings

Abstract The paper gives a survey of current research on decorative coatings. In the first part the main deposition techniques as well as characterization techniques are discussed. The paper is restricted to decorative physically vapor deposited hard coatings with electrochemically deposited barrier coatings. The influence of stoichiometry, structure, and surface roughness on the colour of physically vapor deposited hard coatings is reviewed. In the last decades, a number of different coating deposition techniques have been developed. The demand for environmental compatibility of low cost large-scale production techniques has resulted in the development of combinations of physical vapor deposition and electroplating. Coating systems have been developed using NiPd and CuSn(Zn) instead of Ni electroplated coatings as interlayers, strongly reducing the allergy risk. New industrial applications demonstrate the increasing economic importance of decorative hard coatings.

Decorative hard coatings: advances in optical characterization techniques

Abstract Transition metal compounds are finding increasing use in decorative coatings, combining intense colour, high wear resistance and good corrosion resistance. From the decorative point of view, colour and gloss are the most important features. The physiological colour impression is well described by the CIE-L∗a∗b colour space. Integrating sphere measurement (ISM) and goniospectroscopy (GS) derive colours from a measurement of the spectral reflectance factor Rλ relative to a white reference. Spectroscopic ellipsometry (SE) is a reference-free technique for measuring amplitude ratios and phase changes of polarized light upon specular reflectance. ISMs of (Zr,Y)N coatings are presented, which show considerable yellow and red values at intermediate lightnesses. The effect of the surface roughness is discussed for TiN coatings. The angular dependence of L∗a∗b∗ and the behaviour of Rλ are shown by means of GS for these TiN coatings in off-specular directions. These results of ISM and GS are compared with the SE data. The high sensitivity of SE to changes in stoichiometry as well as the capability of separating additional interference effects are demonstrated for (Zr,Cr)N and (Zr,Zl)N coatings. However, it is shown especially in the case of rough surfaces that each technique is helpful in distinguishing features of physical and physiological interest.

Multilayer reference coatings for depth profile standards

Depth profiles of layer systems consisting of different film materials and having different thicknesses are of great practical importance. Multilayer reference coatings of conducting (Ti/Al) and non-conducting (SiO2/Si3N4) material are analyzed with Auger electron spectroscopy (AES) and glow discharge optical emission spectroscopy (GDOES) depth profiling. Deposition techniques, physical vapor deposition for Ti/Al layers and plasma-enhanced chemical vapor deposition for SiO2/Si3N4 layers, as well as measurement and testing procedures for the determination of layer thickness such as optical and mechanical stylus and spectroscopie ellipsometry are discussed. GDOES depth profiles in direct current (d.c.) and radio frequency (r.f.) mode are related to measurements of crater profiles and compared with line scans and depth profiles performed by AES. It is shown that such multilayer reference systems are appropriate for calibration of depth profiles, i.e. the definition and the evaluation of the depth resolution at the interface, the determination of sputter rates both for d.c.- and r.f.-GDOES and AES, the optimization of the conditions of analysis, and the quantification of analysis itself.

Structure and properties of decorative rare-earth hexaboride coatings

Abstract Hexaborides of the rare-earth elements are considered for applications as wear- and corrosion-resistant hard coatings for decoration of consumer products such as eye-glass frames and wristwatch casings. After a review of physical vapour deposition (PVD) methods used for the deposition of rare-earth hexaborides, a survey of studies is given that extends the range of suitable decorative coating materials. Within the scope of the search for new colours, the interdependence between deposition conditions, microstructure and mechanical and optical properties of boride coatings based on LaB6, CeB6, SmB6 and YB6 is presented and discussed. As a result of the strong directionally of covalent boron—boron bonds, hexaboride coatings show an increasing tendency to amorphous film growth with decreasing metallic radius of the rare-earth metal. Mechanical as well as optical properties are strongly influenced by the crystallographic structure of the hexaboride phase. The most pronounced visual colour impression is observed for LaB6-based coatings corresponding to a dark violet colour. Proper selection of process parameters for these coatings may widen the conventional spectrum of decorative coatings.

Round Robin exercise: Coated materials for glow discharge spectroscopy

A Round Robin (RR) exercise on selected coated materials has been carried out with the aim of finding the optimal conditions for the analysis of nitride layers with GD-OES. Such pre-normative work is necessary for the evaluation of parallel development of the production of nitride layers as certified reference materials (CRMs). Two types of samples, Ti–N layer and V–N layer, respectively, with chemical compositions close to stoichiometry and a thickness of ∼3 μm, deposited on a steel substrate, have been provided to the RR participants. Additionally, another type of sample, a (100 nm CrNi/100 nm Cu) multilayer (ML) stack deposited on silicon wafer has also been included in the RR. This sample can be used as a CRM for checking GD spectrometer conditions and it has been proved helpful in further development of GDS instrumentation and methodology. The RR exercise has been performed in the frame of the EC Thematic Network on Glow Discharge Spectroscopy for Spectrochemical Analysis (‘GDS-Net’).

Availability of layered certified reference materials for industrial application of glow discharge spectrometric depth profiling

Owing primarily to speed, low cost and ease of use relative to competing surface analysis techniques, glow discharge spectrometry (GDS) has become an economically important depth profiling method for certain niche industries in Europe and Japan. For the industrial application of this method, layered certified reference materials (CRMs) are needed to ensure accuracy, as well as comparability between individual users. A survey of existing CRMs has been conducted to evaluate the availability of layered CRMs with appropriate characteristics. No materials with the desirable characteristics necessary for efficient implementation were found. These results indicate a need for the production of new layered CRMs. The survey was conducted by an advisory group assembled as part of the activities of the Glow Discharge Spectrometry Subcommittee (ISO TC201/SC8) associated with the ISO Technical Committee on Surface Chemical Analysis (ISO TC201).

Metrological characterization of nanometer film thickness standards for XRR and ellipsometry applications

Two types of film thickness standards have been developed, manufactured and investigated - for X-ray reflectometry (XRR), X-ray fluorescence analysis (XRR), electron probe microanalysis (EMPA) on the one hand, and ellipsometry on the other. Metrological characterisation of both specific kinds of material measures and investigation results achieved are reported. The standards for XRR, XRF, EMPA consist of quarts substrate coated with Pt resp. a C-Ni-C-layer-system with a nominal metal layers thickness of 10 nm alternatively 50 nm. An established process for manufacture of X-ray mirrors was used for coating. XRR proved to be the dominant investigation method. Apart from film thickness characteristics like film thickness variances, interdiffusion between substrate and film have been analysed. In conclusion it can be estimated that the expanded measurement uncertainty of the film thickness for XRR applications is less than 0.5 nm. The standards for calibration of ellipsometer used for film thickness determination consist of an Si-substrate and an SiO2-film. They are provided with an additional topographic structure making a topographic film thickness determination (approximately) possible. The nominal values of film thicknesses are between 6 nm and 900 nm. Film thickness determinations were effected by XRR, Scanning Force Microscopy in combination with Transmission Electron Microscopy as well as various ellipsometrical techniques. The consistency of results found by different measurement techniques is discussed.