Annealing of intrinsic stresses in sputtered TiN films: The role of thickness-dependent gradients of point defect density

Morphology, structure and thermal behavior of magnetron sputtered TiN thin films with the thickness in the range 100-2900 nm are characterized. The films are thermally cycled and the relationship between film thickness, defect density and the intrinsic stress relaxation is analyzed. The results indicate that the residual stresses in the as-deposited films and the amount of stress relaxation depend decisively on the specific depth gradient of point defects originating from film evolution during growth. The compressive stresses, representing different driving forces and the amount of stress relaxation decrease, while the onset temperature of stress relaxation increases with increasing film thickness.     

Effect of NbN and ZrN films formed by magnetron sputtering on Ti and porcelain bonding

Niobium nitride (NbN) and zirconium nitride (ZrN) were deposited on Ti substrates by direct-current (DC) reactive magnetron sputtering; the deposited NbN and ZrN films served as intermediate layers of a Ti and porcelain interface. X-ray diffraction (XRD) results proved that the deposited NbN and ZrN films were polycrystalline with a cubic microstructure. The Ti and porcelain bonding strength of the samples in Group Control (27.2 ± 0.75 MPa), Group NbN (43.1 ± 0.59 MPa), and Group ZrN (52.4 ± 0.80 MPa) were measured. The surface roughness in the case of Group Control (1.863 ± 0.10 μm), Group NbN (2.343 ± 0.07 μm), and Group ZrN (2.346 ± 0.10 μm) was also investigated. Statistical analysis showed that both films helped improve the Ti and porcelain bonding strength and increase the surface roughness. Scanning electron microscopy (SEM) results showed that no apparent oxide layer was formed at the Ti and porcelain interface in both Group NbN and Group ZrN. Energy-dispersive X-ray spectroscopy (EDS) results showed that ZrN was more effective in preventing Ti oxidation than was NbN. Overall, the experimental results showed that the deposition of both NbN and ZrN films helps improve the Ti and porcelain bonding strength and that ZrN films are more effective.     

Application of optical transmission interferometry for in-situ structural investigations of titanium dioxide sputter-deposited coatings

Titanium dioxide coatings (from 0.1 to 1.5 μm thick) have been dc sputter-deposited on glass slides from titanium targets in various Ar-O₂ reactive gas mixtures. Deposition rate and optical properties were controlled in-situ by optical transmission interferometry (OTI) with an optical fibre located behind the glass substrate in order to perform a real-time control of transmittance of the growing film. Thus, it is possible to determine in-situ the optical indices (n, k) and the thickness of the as-deposited film by using a simple simulation, developed on Matlab software. The optical properties of the films were investigated in relation to their structure, which depends on the sputtering conditions adopted. In particular, the effects of the sputtering pressure (working pressure and oxygen partial pressure), the discharge power and the substrate location into the reactor are investigated in detail. Films structure is assessed by standard grazing incidence X-ray diffraction (XRD).     

Residual stresses in titanium nitride thin films obtained with step variation of substrate bias voltage during deposition

In this work, a series of depositions of titanium nitride (TiN) films on M2 and D2 steel substrates were conducted in a Triode Magnetron Sputtering chamber. The temperature; gas flow and pressure were kept constant during each run. The substrate bias was either decreased or increased in a sequence of steps. Residual stress measurements were later conducted through the grazing X-ray diffraction method. Different incident angles were used in order to change the penetration depth and to obtain values of residual stress at different film depths. A model described by Dolle was adapted as an attempt to calculate the values of residual stress at each incident angle as a function of the value from each individual layer. Stress results indicated that the decrease in bias voltage during the deposition has produced compressive residual stress gradients through the film thickness. On the other hand, much less pronounced gradients were found in one of the films deposited with increasing bias voltage.     

Modelling of sputtering yield amplification effect in reactive deposition of oxides

Many reactive sputter deposition applications require high deposition rates. The primary limiting parameters in magnetron sputtering are the target power dissipation and sputtering yields of the target elements. In reactive deposition of oxides, the deposition rate is of particular interest due to the low sputtering yield of most commonly used oxides. Traditional high rate techniques rely on a feedback control of the oxygen partial pressure to prevent formation of oxide on the target and hence enable operation in the transition area. An alternative approach, based on target doping, is presented in this paper.By doping the sputtering target with heavy elements, it is possible to substantially enhance the sputtering yield and hence the deposition rate. Simulations of the partial sputtering yield values for aluminium from doped targets sputtered in reactive atmosphere have been carried out. The Monte Carlo based TRIDYN computer code has been used for simulations. The program has been used to find out optimum alloying conditions to obtain maximum partial sputtering yield for deposition of Al₂O₃. Our simulations indicate that the sputtering yield amplification in reactive sputtering may lead to much higher relative deposition rate increase than in a nonreactive case. The highest relative increase may be achieved in the transition region but substantial increase is predicted also in the oxide mode.     

Fabrication and tribological properties of titanium nitride coatings incorporating solid lubricant microreservoirs

The concept of incorporating microscopic reservoirs within a hard coating for the purpose of solid lubricant storage and supply during wear of interacting surfaces has been investigated in this study. A novel method was devised using ceramic beads (1.5-10 μm diameter) as placeholders during the deposition of a TiN coating by reactive sputter deposition. A pin-on-disk wear test was used to test these coatings using graphite and sputter-deposited carbon as the solid lubricant, and an alumina counterface. When tested without any lubricant, the presence of the microreservoirs in the TiN coating appeared to degrade the mechanical integrity of the coating leading to rapid failure. With the graphite lubricant present, the frictional behavior ranged from levels similar to the TiN coating alone, to that of graphite alone. Tests of the TiN coating made using 10 μm beads running against an aluminum counterface showed substantial improvement when the microreservoirs were present. Optical microscopy examination of the wear tracks showed the microreservoirs were generally successful at trapping the graphite lubricant during wear. With a sufficient density and appropriate distribution of the microreservoirs significant improvements in tribological performance can be realized.     

Intrinsic low energy bombardment of titanium chromium oxide thin films prepared by reactive sputtering

Titanium chromium oxide thin films were deposited by a DC reactive magnetron sputtering from separate Ti and Cr metallic targets in a reactive atmosphere. A constant current density J_Ti =150 A m⁻² was used to sputter the titanium target, whereas the current density on the chromium target was systematically changed from J_Cr=0–200 A m⁻². X-Ray diffraction, electron probe microanalysis and atomic force microscopy were used to investigate the effect of an increasing current density of the chromium target on the structural, compositional and morphological parameters of the coatings. A continuous evolution of the Ti_xCr_1−xO_y composition was observed (x=1–0.34 and y=2–1.7), whereas an amorphisation of the material and a maximum of the surface roughness was obtained for J_Cr=50–100 A m⁻². In the same way, energy distribution of the neutral and ionic species impinging on the surface of the growing film were determined by energy-resolved mass spectrometry. Mean energies and the relative fluxes of positive and negative ions were determined from their energy distributions. The behaviour of these species was also affected by the chromium current density especially between J_Cr=50 and 100 A m⁻². Similarities in the changes of the thin films properties and the characteristics of ionic species are discussed, so as to establish some relationships between the plasma parameters and the deposited films.     

X-ray study of tin oxide films obtained by reactive DC sputtering from a metallic tin target in pure oxygen plasma

Tin oxide films deposited on glass substrates were prepared using a metallic tin target in a DC-magnetron sputtering system. Pure oxygen (99.9%) was used as oxidant and plasma gas. The experiments were carried out at a fixed current mode of the power supply and the cathode voltage was measured during 15 min, the first 5 min of pre-sputtering and the last 10 were used for film growth. The deposition was carried out under different conditions of current, oxygen pressure and substrate temperature. The crystalline phases present in the films were identified with an X-ray diffractometer, equipped with a grazing incidence attachment. The angle of incidence was 3°. The preferred orientation degree in the tin oxide films and the relative cassiterite (SnO₂) proportion for each reflection were calculated from the deconvoluted X-ray peaks. It was found that the synthesis conditions have a strong influence over the growth texture and the relative cassiterite proportion over romarchite formation (SnO). To obtain tin oxide films with a high SnO₂ proportion and a high texture in reactive oxygen sputtering, were necessary, relatively high values of substrate temperature, current and oxygen pressure.     

Reactive sputtering of TiOxNy coatings by the reactive gas pulsing process: Part III: The particular case of exponential pulses

A new and original method, namely the reactive gas pulsing process (RGPP), was optimised to deposit titanium oxynitride thin films by dc reactive magnetron sputtering. Pure titanium target was sputtered in a reactive atmosphere composed of argon, nitrogen and oxygen. Argon and nitrogen gases were injected with a constant mass flow rate whereas oxygen was periodically supplied into the sputtering chamber. An exponential signal was generated to the oxygen mass flow meter with a constant pulsing period T = 45 s. During the injection time of the oxygen gas (t_ON time), the exponential shape was systematically modified in order to better control the amount of reactive gas introduced. Duty cycle was also changed and led to an extended alternation of the process between the nitrided and oxidised sputtering mode. Speed of poisoning of the titanium target surface by oxygen was calculated assuming real time measurements of the target potential. It was clearly shown that duty cycle and shape of the exponential signals used during oxygen injection are fundamental pulsing parameters. Both parameters must be taken into account in order to adjust and improve the monitoring of RGPP system for the deposition of titanium oxynitride coatings. Such approach prevents the full poisoning of the target surface by oxygen or nitrogen, and consequently, a wide range of oxynitride compounds can be easily reached.     

AC powered reactive magnetron deposition of indium tin oxide (ITO) films from a metallic target

Transparent highly conductive indium tin oxide (ITO) films for low cost applications were deposited by a reactive dual magnetron sputter process using metallic targets. The magnetrons were equipped with rectangular (130 × 400 mm²) In:Sn targets (90 wt.% In/10 wt.% Sn). A sine wave power supply was used at a frequency of about 70 kHz. All experiments were done in the transition mode at a constant argon flow of 40 sccm and an oxygen flow varied between 35 and 70 sccm. The total pressure was kept constant at 0.4 Pa.The films were deposited onto silicon and float glass substrates which were either moved in an oscillatory manner (dynamic deposition) or fixed in front of the targets (static mode) during deposition. A dynamic deposition rate of about 100 nm × m/min was obtained at an average power of 2 kW/cathode. The film thickness was adjusted to 500 nm. At an optimised Ar/O₂ gas flow ratio of 0.6 we found an electrical resistivity as low as 1.2 × 10^− 3 Ω cm. The refractive index of these films was about 2.05 indicating a dense film structure, while the optical absorption of k = 10^− 2 qualifies these ITO films for many low cost applications. Moreover, the film structure and texture were investigated by XRD methods.Applying a static deposition we have achieved a lower electrical resistivity with a minimum value of 6 × 10^− 4 Ω cm. In this case, the resistivity and the transparency, respectively, were not constant over the substrate but depend on the lateral position in front of the target. To explain this inhomogeneity we have performed spatially resolved deposition rate and Langmuir probe measurements and related their results to film structure and properties. In order to improve the film properties at dynamic deposition the growth conditions have to be homogenised at all substrate positions.     

磁控溅射温度与时间对ZrN薄膜附着力的影响

采用非平衡磁控溅射技术在1Cr18Ni9Ti不锈钢上制备了ZrN薄膜。用SEM、EDS观察并分析了薄膜的表面形貌和成分,用光电轮廓仪测量了膜层厚度。并采用划格法测试不同溅射时间和温度制备的薄膜附着力大小。分析不同溅射时间和温度对薄膜附着力的影响规律。结果表明,通过调节磁控溅射时间和温度可以得到具有一定厚度,成分稳定,结构致密的ZrN薄膜,且溅射时间在1～20 min范围内时间越长薄膜附着力越大,溅射时间超过20 min,附着力趋于稳定;溅射温度在30～90℃范围内温度越高薄膜附着力越大,超过90℃溅射温度继续升高附着力减小。     

High rate reactive magnetron sputtering of ZnO:Al films from rotating metallic targets

Aluminum doped zinc oxide (ZnO:Al) films were reactively sputtered at a high discharge power from dual rotating metallic targets (Zn:Al = 99.5:0.5 wt.%). Deposition conditions like substrate temperature and working points were varied in order to prepare high quality ZnO:Al films. The influences on electrical and optical ZnO:Al thin film properties and surface texture before and after chemical etching in diluted HCl were studied in order to achieve light scattering films as front contact for solar cells. High dynamic deposition rate close to 90 nm m/min and high Hall mobility of up to 47 cm²/Vs were obtained. Transmission of more than 85% in the visible spectral range is obtained for all ZnO:Al films in this study. In addition, the absorption in near infrared region is low due to low doping. Surface texture after etching is usually much rougher than before. However, some films reveal after etching small surface features that are similar to initial surface features. We propose a relationship between initial and post-etched surface textures.     

Reactive sputtering of TiOxNy coatings by the reactive gas pulsing process. Part I: Pattern and period of pulses

Titanium oxynitride thin films were deposited by dc reactive magnetron sputtering. A metallic titanium target was sputtered in argon, nitrogen and oxygen reactive atmosphere. Argon and nitrogen gases were continuously injected into the process whereas oxygen mass flow rate was pulsed during the deposition. By means of a home made pulsing technique, the oxygen gas was introduced using various modulation patterns of the mass flow rate: rectangle, exponential, sine, isosceles triangle, mounting and descending triangles. The period T of the pulse length was systematically changed from 10 to 400 s. Similarly, kinetics and poisoning phenomena of the titanium target by nitrogen and oxygen were investigated from real time measurements of the target potential and total sputtering pressure. Such diagnostics allowed understanding the advantageous role of the reactive gas pulsing process (RGPP) to synthesize titanium oxynitride compounds. Some requirements, especially the shape of the pulses and the period length were established to alternate the process between the oxidised and nitrided sputtering mode. With suitable and reversible operating conditions, the RGPP led to deposit tuneable titanium oxynitride coatings, usually difficult to reach by conventional reactive sputtering.     

Reactive sputtering of TiOxNy coatings by the reactive gas pulsing process: Part II: The role of the duty cycle

The reactive gas pulsing process (RGPP) was used to deposit titanium oxynitride thin films by dc reactive magnetron sputtering. A titanium target was sputtered in a reactive atmosphere composed of Ar + O₂ + N₂. Argon and nitrogen gases were continuously introduced into the sputtering chamber whereas oxygen was injected with a well-controlled pulsing flow rate following a rectangular and periodic signal. A constant pulsing period T = 45 s was used for every deposition and the duty cycle α = t_ON/T was systematically changed from 0 to 100%. The operating conditions were investigated taking into account the poisoning phenomena of the target surface by oxygen and nitrogen. Kinetics of poisoning were followed from measurements of the total sputtering pressure and titanium target potential during the depositions. Deposition rate and optical transmittance of titanium oxynitride coatings were also analysed and correlated with the process parameters. Pulsing the oxygen flow rate with rectangular patterns and using suitable duty cycles, RGPP method allows working according to reversible nitrided-oxidised target conditions and leads to the deposition of a wide range of TiO_xN_y thin films, from metallic TiN to insulating TiO₂ compounds.     

Microstructure modifications of CrN coatings by pulsed bias sputtering

This paper investigates the influence of a combined electron and ion bombardment via asymmetric bipolar pulsed substrate bias on the microstructure and mechanical properties of reactively magnetron-sputtered CrN hard coatings for two different ion-to-atom flux ratios.     

Thermal stability of tungsten nitride films deposited by reactive magnetron sputtering

The studies of thermal stability of nitride coatings are important since their structural, thermal, electrical and optical properties are drastically modified by the oxidation layer formed on the top of these coatings. Tungsten nitride films were deposited from metallic tungsten target using reactive pulsed d. c. magnetron sputtering. The films were annealed in air at different temperatures for 1 h. The structural, electrical resistivity and optical properties of the annealed films were analyzed. Besides the film analysis, powder of tungsten nitride was obtained by scratching the coating from the glass substrates. The oxidation kinetics of the scratched powder was studied using simultaneous thermal gravimetric/deferential thermal analysis measurements. X-ray diffraction patterns revealed that W₂N oxidizes to the two different phases WO₃ and WO_2.92. The oxide diffraction peaks appeared upon annealing at 773 K and the relative intensities increased with annealing temperature. The tungsten nitride was found to oxidize according a parabolic relation between mass gain and oxidation time. The activation energy of oxidation was evaluated by analyzing the Arrhenius relation from the temperature dependence of the weight gain. The obtained value was 1.76 eV. The activation energies of crystallization of the two phases were calculated. The electrical resistivity was found to increase drastically upon oxidation. The optical properties of the films are very sensitive to the oxidation temperature. The optical band gap values for the film oxidized at 773 K and 823 K are 2.71 and 2.58 eV, respectively.     

Use of a theoretical model to investigate RF and DC reactive sputtering of titanium and chromium oxide coatings

An analysis of RF and DC reactive sputtering techniques is presented. The transition between a metal sputtering mode and a compound sputtering mode is usually noticed with a metallic target and an argon+oxygen gas mixture. The so-called hysteresis effect often observed for small amounts of reactive gas is explained in recent models. By considering gas kinetics parameters, it is possible to evaluate quite simple relationships between the main processing parameters. These theoretical calculations enable the prediction and aid the understanding of instability phenomena observed in reactive sputtering. In this paper, the effects of some parameters on the position and size of instability regions are discussed, and the difference between DC and RF reactive deposition is investigated. Simulations and experimental results are compared for the case of titanium and chromium oxide thin films prepared by DC and RF reactive sputtering. The influence of sputtering power on the position of the hysteresis loop is analysed theoretically and experimentally, and the changes observed between the reactive sputtering of titanium and chromium oxide materials are also discussed.     

Fabrication of anatase-type TiO2 films by reactive pulsed laser deposition for photocatalyst application

TiO₂ films having anatase crystal structure were prepared on glass substrates by reactive pulsed laser deposition using a metallic Ti target in an O₂ gas ambient. At a fixed substrate temperature of 400 °C, the crystalline structure, surface morphology, optical properties and photocatalytic activity of the TiO₂ films were greatly affected by the O₂ gas pressure. It was found that nearly pure anatase-phase TiO₂ film can be obtained under an O₂ pressure of 15 Pa, which had smallest grain size among the films deposited under various O₂ gas pressure from 5 to 30 Pa. This film also showed good optical transmittance between the wavelength of 200 and 800 nm and high photocatalytic efficiency on the decomposition of methylene blue in aqueous solution. Discussions were given to explain the experimental phenomena.     

Metallic sputtering growth of high quality anatase phase TiO2 films by inductively coupled plasma assisted DC reactive magnetron sputtering

Anatase phase titanium dioxide (TiO₂) films were deposited on unheated glass substrate by using inductively coupled plasma (ICP) assisted direct current (DC) reactive magnetron sputtering. Oxygen and argon were introduced into the chamber in the vicinity of the substrate and the target, respectively. In order to obtain high deposition rate, all depositions were carried out in the metallic mode of sputtering. X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy were used for the characterization of film structure and UV-VIS spectrophotometer was employed for the analysis of film optical properties. The TiO₂ film grown at an rf power of 500 W and an oxygen partial pressure of 0.20 Pa consists of an essentially complete anatase phase nanocrystallites. This anatase phase TiO₂ film exhibits a high transmittance of 85% in the visible region. The lattice spacing of 0.352 nm and the optical band gap of 3.22 eV of this anatase phase TiO₂ film match with the standard values of the bulk anatase well. Anatase phase TiO₂ films of high quality, in terms of both a high degree of crystallinity and a good oxygen stoichiometry, have been produced in the metallic mode of sputtering at temperature lower than 200 °C.