S. Kadlec

Reactive sputtering of TiN films at large substrate to target distances

Abstract The paper is a critical review of the present status of the magnetron ion sputter plating of thin TiN films. Thus different possibilities of extracting high ion current ls from the magnetron discharge to substrates located not only at standard target to substrate distances dS-T of about 50 mm but also at larger distances dS-T are discussed in detail. Special attention is devoted to magnetron sputtering systems with enhanced ionization, to plasma confinement in the magnetron sputtering systems and to the discharge characteristics of an unbalanced magnetron (UM). It is shown that a UM can be operated in the regime of a double-site-sustained discharge (DSSD) and in this case large ls can be extracted to substrates located in large dS-T of about 200 mm and even at high pressures p = 5 Pa. A physical comparison of the conventional magnetron (CM), UM and DSSD is also given. Considerable attention is also devoted to the effect of ion bombardment on properties of TiN films created in the sputtering system using DSSD. It is shown that the microstructure of TiN films seems to be controlled by the combined parameter Ep = e (Upl−Us) νi/νm ∼ eUsis/aD, i.e by the energy delivered per condedering particle, where Upl is the plasma potential, Us is the substrate bias, νi and νm are the fluxes of ions and metal atoms impinging on the substrate, respectively, is is the substrate ion current density, and aD is the deposition rate. At low negative biases |Us⪅50 V, the microstructure of created TiN films strongly depends on is. At low is ⪅ 1 mA cm−2 porous black TiN films and at higher is > 1 mA cm−2 compact, dense, bright golden TiN films are created independently of the distance dS-T. The colour of TiN films prepared in a DSSD, i.e. the brilliance L ∗ = 77–79 , the redness a ∗ = 0.3–0.8 and the yellowness b ∗ = 41–44 , compare well with the colour of the best TiN films prepared by standard ion plating and the cathodic arc processes. It has been shown that with DSSD good quality TiN films can be produced at distance dS-T up to 200 mm. In principle, the distance dS-T can be longer but the magnetic field strength must be sufficient at the substrate to ensure adequate plasma confinement in the space between the target and substrates. The DSSD represents a new qualitative step in magnetron sputter ion plating of thin films and the related sputtering system is also suitable for coating large three-dimensional parts and it is fully competitive with standard commercial deposition devices based on low voltage electron beam (LVEB), triode and arc evaporation.

New results in d.c. reactive magnetron deposition of TiNx films

Abstract This paper deals with d.c. reactive magnetron deposition of non-stoichiometric TiNx films. A decisive influence of the nitrogen flow rate, the substrate temperature and the substrate bias on the properties of TiNx films is demonstrated. The microhardness, the phase and chemical composition, the texture, strains and macrostresses in TiNx films as a function of ON2 are presented in detail. Some results are presented concerning the hysteresis effect in reactive sputtering, the correlation between (i) the maximum microhardness of films, the maximum strains in the films and the strong decrease in preferred orientation of the crystallites and (ii) the change in the sign of the macrostress and the transition of the phase composition from α-Ti(N) to α-TiNx, an extremely high microhardness of TiNx films at x ≈ 0.6 and strong changes in the texture and lattice parameters with changes in the thickness of films prepared under the same conditions. A comparison of TiNx with (Ti, Al, V)Nx films is also given.

Ion-assisted sputtering of TiN films

Abstract Ion bombardment of growing films is one of the possible ways to produce films with specific properties. As yet there are no general rules for the production of these films. The quality of TiN films produced depends on the deposition conditions. A sharp transition from porous, black TiN films to compact, dense, bright gold TiN films is observed at a substrate bias U s of about -40 V. Recent experiments have indicated that the microstructure of TiN films and the transition mentioned above can be controlled by the ion energy delivered to the growing film per deposited particle E p = eU s v i / v m . This paper investigates the transition from porous, soft TiN films with a zone I microstructure to compact, hard TiN films with a zone T microstructure as a function of i s , U s and the deposition rate a D at constant temperature T s = 350 °C and pressure p T = 5 Pa. Correlations between the microhardness HV, the macrostress σ, the microstrain e , the lattice parameters, the intensities of the X-ray reflections and the colour and appearance of the film are discussed. The zone I to zone T transition is observed at E p ≈ 150 eV atom -1 .

Reactive deposition of tin films using an unbalanced magnetron

Summary The paper presents discharge characteristics for a sputtering device operated as a conventional magnetron (CM) or as an unbalanced magnetron (UM). In the UM, with a strong magnetic field of several millitesla reaching the substrates, a double-site-sustained discharge (DSSD) was observed. The UM with the DSSD operation transports a current Is to substrates which is more than 50% of the magnetron current for a wide range of substrate-target distances dS-T up to 150 mm at a pressure pT = 5 Pa and low substrate bias Us = −100 V. Microstructure, composition, crystallographic structure, mechanical properties and colour are reported for TiN films reactively sputtered by the UM at dS-T = 200 mm, pT = 5 Pa, for different Us values between −5 and −100 V and substrate current densities up to 6 mA cm−2. Dense stoichiometric TiN films with a microhardness of 2270 kg mm−2 and critical load Lc = 64 N were obtained at low bias Us = −40 V.

Influence of the pumping speed on the hysteresis effect in the reactive sputtering of thin films

Abstract Detailed analysis of the mutual dependences of the flow rates and partial pressures of inert and reactive gases inside a deposition chamber show that the hysteresis effect occuring during reactive sputtering of thin films can be overcome if the pumping speed of the pumping system is greater than the critical pumping speed. A comparison of the theory with experiment is made for the case of dc reactive magnetron sputtering of TiNx films.

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.

Reactive deposition of hard coatings

Abstract The reactive deposition of thin films is analyzed by means of a microphysical model. This model shows the way in which to (i) eliminate the hysteresis effect and (ii) control the deposition process. Special attention is devoted to physical parameters, such as fluxes of ions v i , metallic particles v m and reactive gas particles v r , the energy of particles bombarding the growing film and the substrate temperature which play a fundamental role in the deposition process, and to deposition systems with enhanced ionization. A correlation between (i) process parameters, (ii) microstructure, texture, phase and chemical composition of films, and (iii) resulting film properties is discussed in detail for Ti−N films. A comparison of arc evaporation and magnetron sputtering is also given. The need for equipment providing independent control of the deposition rate and ion bombardment of films is emphasized.

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.

TIN FILMS GROWN BY REACTIVE MAGNETRON SPUTTERING WITH ENHANCED IONIZATION AT LOW DISCHARGE PRESSURES

Abstract TiN films were produced by reactive magnetron sputtering at a discharge pressure of 0.09 Pa on substrates placed 200 mm away from the magnetron target, using a sputtering system with enhanced ionization by means of multipolar magnetic confinement. The effects on film properties are reported for two ranges of values: an external substrate bias ∪s of from −35 to −150 V, and a floating potential ∪fl of from −24 to −45 V. All films show a dense microstructure, a smooth surface and shiny golden color. The microhardness HV is between 2000 and 2600 kg mm−1, a high critical load of up to Lc = 58 N in scratch tests and the coefficient of friction against a cemented carbide counter ball is between 0.12 and 0.22. The color co-ordinates L ∗ , A ∗ and B ∗ depend on the bias voltage. The brightness L ∗ reaches 78 CIELAB units. The properties of films prepared at ∪s between −60 and −150 V compare well to those of ion-plated films. The films prepared at ‖ ∪s ‖

Growth and properties of hard coatings prepared by physical vapor deposition methods

Abstract Physical vapor deposition (PVD) methods have found widespread application in the deposition of hard coatings. In order to compare potentials and limitations of the PVD methods, a good knowledge of the physical processes of film growth, formation of various film microstructures, and the resulting properties is necessary. Here the latest advances in understanding the effects of physical film growth parameters on the microstructure of growing films are reviewed. Examples of sputtered TiN film microstructures are given. A critical review of the structure zone models is presented. The importance of the homogeneity of both vapor and ion fluxes is also discussed and illustrated with examples. The problems of uniformity of both the film thickness and properties are also discussed. The requirements imposed on surface pretreatment are highlighted.