Article

# Fundamental Understanding and Modeling of Reactive Sputtering Processes

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

## Abstract

Reactive sputtering is a commonly used process to fabricate compound thin film coatings on a wide variety of different substrates. The industrial applications request high rate deposition processes. To meet this demand, it is necessary to have very good process control of such processes. The deposition rate is extremely sensitive to the supply of the reactive gas. A too low supply of the reactive gas will cause high rate metallic sputtering, but may give rise to an understoichiometric composition of the deposited film. A too high supply of the reactive gas will allow for stoichiometric composition of the deposited film, but will cause poisoning of the target surface, which may reduce the deposition rate significantly. This behaviour points out that there may exist optimum processing conditions where both high rate and stoichiometric film composition may be obtained.The purpose of this article is to explain how different parameters affect the reactive sputtering process. A simple model for the reactive sputtering process is described. Based on this model, it is possible to predict the processing behaviour for many different ways of carrying out this process. It is also possible to use the results of the modeling work to scale processes from laboratory size to large industrial processes. The focus will be to obtain as simple a model that will still quite correctly describe most experimental findings. Despite some quite crude approximations, we believe that the model presented satisfies this criterion.

## No full-text available

... Non reactive DC sputtering [17,18,28,31]  Low plasma density  Low ionization efficiency  Low deposition rate  Only conductive target materials Non reactive RF sputtering [17,18,28,31,34]  Insulating target material  Dielectric films production with a radio frequency of 13.56 MHz  Deposition rate lower than DC sputtering  Treatment of small areas  High cost for industrial scale Magnetron sputtering  High electron density  High deposition rate  Dense coating production using low pressure Reactive sputtering [11,17,18,28,28,[35][36][37][38]  Insulating and dielectric film deposition  Oxide, nitride, carbide or compound films deposition  Stability problems due to an hysteresis behaviour of the process depending on the reactive gas supply  Poisoning target  Arcing effect occurring by high charges accumulation  Disappearing anode effect Triode sputtering [18,39]  Increase of electrons density and ionization of a DC diode sputtering system  Contamination of the growing film due to the filament erosion in reactive sputtering  Problem of scaling up for industrial application Ion Beam-Assisted Deposition (IBAD) [17,[40][41][42][43][44][45]  Control of the deposition for specific coatings  Slow growth rates  Treatment of small area  Treatment of large area samples thanks to CFUBM (Closed-Field Unbalances Magnetron) ...
... However, the high cost of power supplies limit applications of RF sputtering [31]. Reactive processes showed problems of stability and it was difficult to combine high deposition rate and true stoichiometry of the compound film [18,28,37,38]. ...
... (II- 38) with However, in the mathematics module and PDE interface it is actually defined by: ...
Thesis
Le procédé de pulvérisation cathodique magnétron est un procédé utilisant des plasmas basse pression, très employé pour la synthèse de couches minces dans l’industrie. De nombreuses recherches ont porté sur la compréhension des phénomènes mis en jeu dans le mécanisme de pulvérisation dans le but d’améliorer le procédé. Les simulations numériques associées à des résultats expérimentaux permettent aujourd’hui une meilleure compréhension des phénomènes de la décharge plasma et par conséquent de prédire différente évolution du système afin d’optimiser les conditions opératoires du procédé.L’objectif de cette thèse est de construire un modèle multi-échelles du procédé de pulvérisation cathodique magnétron en couplant une approche fluide avec une approche microscopique basée sur la Dynamique Moléculaire (DM).La première partie étudie la résolution du modèle fluide d’une décharge magnétron DC plane à partir du modèle théorique de Costin, afin de déterminer des paramètres d’entrée pour les simulations de dynamique moléculaire. Les résultats du champ magnétique et du potentiel électrique sont en bon accord avec ceux présentés par Costin. Cependant le calcul du transport des espèces a montré des limitations.La seconde partie s’intéresse à la pulvérisation du titane (Ti) par des ions d’argon (Ar+) pour trois énergies considérées (200, 300 et 400 eV) dans une atmosphère neutre et une atmosphère réactive, ainsi qu’en reproduisant des cibles chaudes (1000 et 2000 K) par des simulations de DM et en combinant avec des simulations Monte Carlo. Les résultats obtenus ont ainsi permis la détermination de taux de pulvérisation du titane et de rétention de l’argon.
... Reactive magnetron sputtering suffers from hysteresis of the process parameters with respect to the supply of the reactive gas [8,9]. This behaviour is a major technological challenge with huge impact on the deposition rate and composition of the deposited material [10]. ...
... Reactive magnetron sputtering can be simulated by a model based on balance equations pioneered by Berg [8]. The approach illustrated in Fig. 1 is, despite all simplifying assumptions, very powerful. ...
... The classical basic "Berg" model of reactive magnetron sputtering with atomic sputtering [8] can be extended to account for metal redeposition at the target surface. Such a model, although time averaged, can describe the main characteristics of reactive HiPIMS. ...
Article
Back-attraction of ionized metal is an important process in reactive high power impulse magnetron sputtering (R-HiPIMS). Here, we discuss the implementation of the metal return in balance type models for reactive magnetron sputtering. We show that the existing description of surface processes needs to be modified to satisfy mass conservation. A new steady-state time-averaged model is presented and used to evaluate the effect of the metal return in R-HiPIMS. The results show that the metal return leads to an increased oxide fraction in the deposited coating in R-HiPIMS. This effect can explain the high rate deposition of stoichiometric compounds deposited in the metal mode of operation that has been observed experimentally.
... PVD-RF sputtered amorphous hydrogenated germanium (a-Ge:H) and a-Si:H single layers as well as a-Si/a-Ge multilayers (MLs) in order to reveal the correlation between the hydrogen content and the structural stability of a-Si/a-Ge multilayers have been studied [12]. In case of the reactive sputtering (RF) process the Berg model [13] serves as a quite general mathematical description. The hydrogen incorporation into silicon during RF sputtering can be interpreted by Berg-modelling based on the fact that the amount of incorporated hydrogen is proportional to the current [14]. ...
... Materials which follow Berg model-like behaviour, and involved in the sputtering process are characterized by the metallic and compound sputtering yields and the sticking coefficient. Sputtering yields are defined as the mean number of metal atoms or compound molecules removed from the target surface per incident ion [13] while sticking coefficient refers to the probability of reaction between the reactive gas molecule and the target surface. Therefore, the simulations can be performed about the outcome of the process. ...
... The basic principle of the Berg model can be defined by stable deposition process in the case of steady state. The Berg model has been built on three different equations describing; (i) the steady state of the target, the reactive gas and the substrate [13]. ...
Article
Full-text available
Incorporated hydrogen and its bonding configuration have an effect on the electrical and structural properties of hydrogenated amorphous silicon (a-Si) thin films. On one hand hydrogenization is known to be very efficient in reducing the density of dangling bonds responsible for deep levels in the bandgap; the technological process that carries out the incorporation of hydrogen improves the device parameters. On the other hand, the H–Si–H bonding configuration may negatively affect the microstructure of the amorphous lattice and promote the creation of voids. In this work the incorporation of hydrogen into radio frequency sputtered amorphous silicon thin films is interpreted by means of Berg-model handling the hydrogen incorporation as a reactive sputtering process involving ionization of molecular hydrogen followed by reactions between elemental target atoms to compound molecules. This approach is suitable for the interpretation of hydrogen incorporation into a-Si films based on the fact that the amount of incorporated hydrogen is proportional to the current. The imaginary and the real part of the dielectric function deduced from spectroscopic ellipsometry are investigated as a function of hydrogen flow. Using the results of spectroscopic ellipsometry and elastic recoil detection analysis presented earlier, as well as the equations of Berg model, the metal and compound sputtering rate and the sticking coefficient between silicon and hydrogen atoms are calculated.
... In this process, the oxygen flow was shown to be one of the most important parameters. 9,10 Simulations of the reactive sputtering growth of transition metal oxide films from metallic targets indicate that the low flow ranges of the oxygen flow rate are generally related to the metallic regime while the high ranges are associated with the poisoned target deposition regime. 9,10 The metallic regime is characterized by low compound formation on the target and low partial pressure of the reactive gas, while in the poisoned regime, the reactive gas partial pressure increases and the target is covered by compounds. ...
... 9,10 Simulations of the reactive sputtering growth of transition metal oxide films from metallic targets indicate that the low flow ranges of the oxygen flow rate are generally related to the metallic regime while the high ranges are associated with the poisoned target deposition regime. 9,10 The metallic regime is characterized by low compound formation on the target and low partial pressure of the reactive gas, while in the poisoned regime, the reactive gas partial pressure increases and the target is covered by compounds. 11 In addition, the oxygen flow used during reactive sputtering deposition has also been related to important structural modifications, including phase changes and texture effects in Y 2 O 3 , TiO 2 , and Al 2 O 3 films. ...
... In order to analyze the specific behavior of the growth rates observed in Fig. 1, let us consider some well-known results about the reactive sputtering processes from metallic targets. 9,16 On these processes, the film growth can be characterized by two types of deposition regimes, defined as metallic and poisoned. 9,16 In the metallic mode, the film growth occurs in zero or low oxygen partial pressures and relatively high deposition rates. ...
Article
The influence of the oxygen gas supply on the stoichiometry, structure, and orientation texture of polycrystalline cobalt oxide films was investigated in this study. The films were grown by direct current reactive magnetron sputtering using a metallic Co target and different O2 inlet flow rates (0.5–5.0 SCCM). The deposition power (80 W), the argon gas flow (40 SCCM), and the total working pressure (0.67 Pa) were kept constant during depositions. The results evidence a strong influence of the oxygen flow over the film’s stoichiometry and structure, where low oxygen flows (<2.0 SCCM) favor the formation of the rock salt CoO phase while higher oxygen flows (>2.5 SCCM) favor the spinel Co3O4 phase formation. The coexistence of monoxide and tetraoxide phases is only observed for the 2.5 SCCM oxygen flow condition. Strain effects related to the oxygen partial pressure are also observed and discussed. Computer simulations of the reactive sputtering growth supported the analysis of the film properties and its correlation to the oxygen partial pressure.
... Although the deposition rates for both DcMS and HiPIMS are not the same, they portrait a similar trend with an increase in Q N 2 . The relationship between the reactive gas and deposition rate is known to be non-linear [34]. Therefore, it is imperative to understand the trend and the influence of the reactive gas flow rate on the deposition rate for DcMS and HiPIMS deposition. ...
... As the Q N 2 increases, the collision between the working gas (Ar) and the reactive gas (N 2 ) gaseous ions increases. The increase in nitrogen ions in the plasma (argon and nitrogen) will result in a lesser sputtering yield [34,35] and a drop in discharge voltage, as noticed from the hysteresis curve. The discharge voltage indicates the energy of the sputtering ion, meaning that the decrease in the discharge voltage will reduce the ion energy and thereby decrease the number of sputtered particles and deposition rate [36]. ...
Article
Full-text available
Understanding the evolution of target composition, hysteresis effect and coatings properties as a function of reactive gas and sputtering techniques in developing new thin film coatings is essential. This research investigation focuses on the influence of reactive nitrogen gas utilized at different flowrate on the hysteresis measurement and properties of TiAlN coatings doped with phosphorous, deposited using direct current magnetron sputtering (DcMS) and high power impulse magnetron sputtering (HiPIMS) techniques. The proportion of nitrogen content required for the transition from metallic to compound region varies with the deposition method as revealed from the hysteresis. The formation of stoichiometric coating was achieved at a lower flow rate of nitrogen in the HiPIMS coating. Dense and columnar structures were noticed in the cross-sectional morphology of the coatings. The XRD diffraction pattern revealed that the preferential orientation of the coatings depends on the nitrogen flow rate and the choice of the deposition techniques. The Raman spectra of the coatings show groups of bands in the acoustic and optical range, with a shift to higher Raman wavelength in the HiPIMS sputtered coatings. The maximum hardness of 28 GPa was found at 6 sccm of nitrogen flowrate of the HiPIMS coating. The optimal corrosion protection resistance for the HiPIMS sputtered coatings was noticed at 8 sccm of nitrogen flowrate. The coefficient of friction of the HiPIMS coating from the scratch test revealed that the CoF decreases with an increase in Nitrogen flowrate until 8 sccm, while the maximum critical load was noticed at 6 sccm.
... After Akiyama [1] demonstrated the large enhancement of the piezoelectric coefficient by doping AlN with scandium, a growing number of studies have been conducted to exploit AlScN in MEMS, with particular interest in RF applications [2][3][4][5][6][7][8]. The augmented d 33 , along with a reduction in the stiffness, enables AlScN-based resonators with a higher electro-mechanical coupling coefficient. This translates to filters with larger bandwidths as compared with their AlN counterparts, while maintaining a similar fabrication flow [9]. ...
... Several Al 0.7 Sc 0.3 N (AlScN) thin films were deposited from a 12" alloy target installed on an Evatec Clusterline-200 PVD module onto 200 mm-Si <100> 20 Ω/sq wafers coated with 20 nm titanium, with 80 nm platinum acting as a bottom electrode layer. Before the AlScN deposition, chamber and target conditioning procedures were performed to improve the base pressure and cleanliness of the target [32,33]. The thin films were deposited starting from a base pressure of 7 × 10 −8 mbar and a chuck temperature set at 300 • C. The wafers sat for 5 min in the hot chuck before a 6 kW pulsed DC was applied for 250 s with 90 sccm of N 2 flow. ...
Article
Full-text available
Sc-doped aluminum nitride is emerging as a new piezoelectric material which can substitute undoped aluminum nitride (AlN) in radio-frequency MEMS applications, thanks to its demonstrated enhancement of the piezoelectric coefficients. Furthermore, the recent demonstration of the ferroelectric-switching capability of the material gives AlScN the possibility to integrate memory functionalities in RF components. However, its high-coercive field and high-leakage currents are limiting its applicability. Residual stress, growth on different substrates, and testing-temperature have already been demonstrated as possible knobs to flatten the energy barrier needed for switching, but no investigation has been reported yet on the whole impact on the dielectric and ferroelectric dynamic behavior of a single process parameter. In this context, we analyze the complete spectrum of variations induced by the applied substrate-RF, from deposition characteristics to dielectric and ferroelectric properties, proving its effect on all of the material attributes. In particular, we demonstrate the possibility of engineering the AlScN lattice cell to properly modify leakage, breakdown, and coercive fields, as well as polarization charge, without altering the crystallinity level, making substrate-RF an effective and efficient fabrication knob to ease the limitations the material is facing.
... Typically, in the transition region between the metallic and compound mode of the target, the process exhibits highly nonlinear and unstable with respect to the flow rate of reactive gas. And it is also difficult to prepare films with the desirable composition and optimal performance by control the flow rate of reactive gas [12][13][14][15]. Moreover, due to the accumulation of charge on the dielectric layer that formed on the target surface, deposition the poor conducting metal oxide films (like VOx) by the DC power supply (DCPS) may suffer from the arcing effect, which not only can destabilize the plasma, disrupt the sputtering process but also can bring some unpredictable deteriorations to the deposited films [13,15,16]. ...
... It is important to note that, once the oxygen was introduced during deposition, the competition between sputtering and formation of the oxide on the target surface will inevitably occur. Especially, the oxide possessing a much lower sputtering yield compare with the metal that cause the deposition rate closely related to the oxide coverage of the target surface [14]. In general, the oxidation of the target surface mainly depends on the amount of the injected oxygen during deposition. ...
Article
In this study, vanadium oxide (VOx) thin films were prepared by reactive pulsed DC magnetron sputtering (PDMS). The influence of pulse frequency (Fp) on the deposition process and properties of VOx films was investigated. The obtained results indicate that with the increase of Fp, which not only can enhance the oxidation of vanadium but also can facilitate the formation of a denser microstructure and smoother surface morphology in the films. More importantly, films with composition from metal-rich to maximum stoichiometry can be accessed by tuning the Fp, without varying any other parameters, especially, the flow rate of reactive gas. And temperature dependent electrical properties of the VOx films can also be tailored via the Fp to fall in the desirable range for microbolometer applications. The impacts of Fp on the reaction between V and O, thin film growth and some dynamic processes occurring during reactive PDMS were analyzed. The corresponding underlying mechanisms were discussed in detail. Our present work may provide a practical and effective way to develop the reactive sputtering towards hysteresis-free, and also paves the way for optimizing the reactive sputtered VOx films with desirable properties via Fp.
... This regime is known as the "transition mode". With increasing the oxygen ratio, the target becomes "complete poisoning" and the deposition rate drop because of the increase of the target coverage which decreases the sputtering yield [10], this stage known as "oxide mode". Bombardment of the growing film during the sputtering process by energetic species such as O -, O 2 is one of the most important parameters governing the thin film phase and the growing film depends on their energy and flux. ...
... ⁄ ⁄ where I A and I R are the intensities of anatase peak and of rutile peak, respectively. Fig. 3: The morphology of ratio (5,10,15,20 and 25) % of O 2 reactive gas. Fig. 4 shows the transmittance of TiO 2 thin films at different oxygen ratio. ...
Article
Full-text available
TiO2 thin films have been prepared using a homemade DC reactive sputtering technique under various ratio of O2 reactive gas. The ratio of O2 reactive gas has been applied with (5, 10, 15, 20 and 25) % of total gas (O2 /Ar+O2). TiO2 thin films have been deposited on microscope glass slides (7101) substrates. The substrate temperature, target-substrate distance, and deposition time have been set at 250 ºC, 25 mm and 3:30 h, respectively. The structural, optical and electrical characteristics of the films have been investigated. The structure of all samples were crystal except the sample of 25% of O2 reactive gas, it was non-crystalline probably because of it may be bombarded by negative ions originated from the sputtering and reactive gases. The thickness of TiO2 thin films of all reactive O2 gas ratios has been reduced from 1013 nm at the ratio 5 % of O2 reactive gas to 633 nm at the ratio 25 % of O2 reactive gas.
... To adjust the structural, morphological, optical and electrical properties of copper oxide films, prepared by different techniques, it's primordial to study the effects of different parameters such as: chemical precursors [10], oxidation time [15], temperature annealing [16], working pressure [17], sputtering power [18] and O 2 flow rate, which is the most important and determining factor [12,14,19]. A specific feature of reactive sputtering, controlled by reactive gas flow rate, is its hysteresis behavior [20]. When the injected reactive gas flow rate is small, most of the reactive gas is combined with a weak proportion of the sputtered metal element, to form compound thin films onto the substrate and the entire inner surface chamber. ...
... Consequently, the film thickness decreased from 1.02 to 0.92 μm. This modification in structure is due to the variation in gas composition [20]. The increase of the O 2 flow rate, and the modification of the films stoichiometry (Fig. 4b), promote the formation of CuO over Cu 2 O. ...
Article
Copper oxide thin films are prepared by radio frequency magnetron sputtering technology. The analysis of the deposited films by X-Ray Diffraction (XRD), spectrometry and electrical resistivity measurements is carried out. The results show that the working pressure and O2 flow rate have a crucial impact on copper oxides films properties. The apparition of the main copper oxides CuO and/or Cu2O phases is affected by the experimental plasma parameters, mainly the O2 flow rate. The presence of multiple peaks on XRD patterns indicates the polycrystalline nature of the deposited films. At higher O2 flow rate, single-phase composed of crystallized CuO is formed. While at lower O2 flow rate the films are two-phase (CuO and Cu2O). The study of the plasma discharge by optical emission spectrometry as function of O2 flow rate, at given pressure and power supply, is essential to find the best operating range to tune the correct stoichiometry and phases, giving therefore the preferred properties for a specific application.
... The oxygen inlet position was around the same as the sample stage. An RF power supply with 13.45 MHz frequency was used to avoid the arcing effect of a DC power supply [29,30]. The transmitter power was 350 W. ...
Article
Full-text available
Citation: Palaniyappan, S.; Trautmann, M.; Mao, Y.; Riesch, J.; Gowda, P.; Rudolph, N.; Coenen, J.W.; Neu, R.; Wagner, G. Yttria-Coated Tungsten Fibers for Use in Tungsten Fiber-Reinforced Composites: A Comparative Study on PVD vs. CVD Routes. Abstract: Tungsten fiber-reinforced tungsten (W f /W) composites are being developed to improve the intrinsic brittleness of tungsten. In these composites, engineered fiber/matrix interfaces are crucial in order to realize toughening mechanisms. For such a purpose, yttria (Y 2 O 3), being one of the suitable interface materials, could be realized through different coating techniques. In this study, the deposition of thin films of yttria on a 150 µm tungsten wire by physical and chemical vapor deposition (PVD and CVD) techniques is comparatively investigated. Although fabrication of yttria is feasible through both CVD and PVD routes, certain coating conditions such as temperature, growth rate, oxidation of W f , etc., decide the qualitative nature of a coating to a particular extent. In the case of PVD, the oxidation of W f is highly reduced compared to the WO 3 formation in high-temperature CVD coating processes. Yttria-coated tungsten fibers are examined comprehensively to characterize their microstructure, phase, and chemical composition using SEM, XRD, and Raman spectroscopy techniques, respectively.
... [117,118,[245][246][247] Sputtering Deposition: Compared with the CVD method, sputtering deposition allows better control of the deposition rate, lowering fabrication complexity by reducing growth parameters and allowing tunability of the h-BN thickness. [248] Sutter et al. [249] used reactive radiofrequency (RF) magnetron sputtering of a B target under ultrahigh-vacuum (UHV) and high-purity Ar/N 2 atmosphere to control this thickness (Figure 14c). At high-temperature conditions on Ru(0001) substrate, up to two-layer high-quality h-BN films can be acquired, shown in Figure 14d. ...
Article
Full-text available
Hexagonal boron nitride (h‐BN) has emerged as a strong candidate for two‐dimensional (2D) material owing to its exciting optoelectrical properties combined with mechanical robustness, thermal stability, and chemical inertness. Super‐thin h‐BN layers have gained significant attention from the scientific community for many applications, including nanoelectronics, photonics, biomedical, anti‐corrosion, and catalysis, among others. This review provides a systematic elaboration of the structural, electrical, mechanical, optical, and thermal properties of h‐BN followed by a comprehensive account of state‐of‐the‐art synthesis strategies for 2D h‐BN, including chemical exfoliation, chemical, and physical vapor deposition, and other methods that have been successfully developed in recent years. It further elaborates a wide variety of processing routes developed for doping, substitution, functionalization, and combination with other materials to form heterostructures. Based on the extraordinary properties and thermal‐mechanical‐chemical stability of 2D h‐BN, various potential applications of these structures are described. h‐BN is one of the most promising inorganic materials of this century with possible applications ranging from aerospace to medicine. It has emerged as an exotic 2D material in the post graphene era, owing to its exciting optoelectrical properties combined with mechanical robustness, thermal stability, and chemical inertness. This review provides an encyclopedic view of the structure, properties, synthesis and applications of h‐BN.
... If the process is feedback controlled, the observed process curve, for example the reactive gas partial pressure as a function of the flow, is S-shaped. The origin of this behaviour can be explained by the interplay between the target and substrate condition which was successfully modelled by Berg et al. [3]. Often, however, not one but two S-shaped curves are observed, one of which corresponds to the path from the metallic to the poisoned state while the other S-shaped curve corresponds to the reverse transition [2,4,5]. ...
Article
When process parameters such as the reactive gas partial pressure or the discharge voltage are studied as a function of the reactive gas flow during reactive magnetron sputtering, the obtained curve has an S-shape. A direct consequence of this behaviour is that process control based on the reactive gas flow exhibits hysteresis. Under specific conditions, it is possible to observe two S-shaped curves: one when the reactive gas pressure is increased, the other during the return to the initial state by decreasing the reactive gas pressure. This behaviour has been described as double hysteresis behaviour. The origin of the double hysteresis behaviour is computationally studied by high-throughput calculations using a previously developed model. The influence of different process and material parameters were evaluated based on newly developed measures to characterize the calculated process curves. This high-throughput analysis reveals that the double hysteresis behaviour is linked to the difference in the removal rate of non-reacted implanted ions during the increase and decrease of the reactive gas pressure. Within the parameter space a region can be defined for which the double hysteresis behaviour is strong. The latter can not only assist further experiments to study this behaviour but also defines conditions to limit its impact. For Al, a discharge current density of approximately 0.025~A/cm ² was found to maximize double hysteresis.
... The substrate temperature during the processes never exceeded 55 • C. Prior to each deposition, the target was sputter cleaned by means of an Ar Plasma for 15 min at 1 Pa. This procedure is necessary to prevent target poisoning and consequent non-reproducible depositions [24]. ...
Article
Full-text available
Biodegradable and bio-derived plastics such as poly(lactic acid) (PLA) are a promising solution to solve the huge environmental and economic issues caused by the enormous consumption of conventional oil-derived polymers, especially in food packaging applications. However, their poor gas barrier properties and high transparency to UV radiation limit their currently commercialization. Therefore, this study is focused on the deposition of tungsten oxide (WOx) thin films on commercial PLA in order to enhance its overall performance. Coatings with different thickness (25, 50 and 100 nm) were deposited by means of radiofrequency (RF) plasma magnetron reactive sputtering. Morphological characterization was carried out with atomic force microscopy (AFM) and scanning electron microscopy (SEM). In order to evaluate surface chemical changes due to plasma treatments, Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis were performed. The PLA/WOx samples demonstrated remarkable improvements both in UV protection and oxygen barrier properties. In particular, light transmittance was reduced by approximately 95% in the UV-B region, 70% in the UV-A region and 50% in the visible region compared to pristine PLA. Regarding oxygen permeation, a reduction of at least 99.9% was achieved. In addition, the PLA/WOx antibacterial properties against Escherichia coli were also investigated, showing a reduction greater than 5 log10 CFU cm−2 after 24 h for the 50 and 100 nm samples. These results demonstrate the potential of WOx thin coating for sustainable food packaging applications.
... The effect of the O 2 % on TiO 2 sputtering rate thus affects the incorporation of the secondary phase in the resulting film. Finally, it is considered that TiO 2 deposition mechanism approaches that propose by Berg and Nyberg 23 . ...
Article
Full-text available
Abstract Recently, there has been growing interest in the incorporation of particles in plasma deposited thin films to creation of multifunctional surfaces. In this work a new hybrid methodology based on the plasma enhanced chemical vapor deposition (PECVD) of hexamethyldisiloxane combined to the reactive sputtering of TiO2 is proposed for the preparation of SiOxCyHz-TiO2 composite films. Specifically, the effect of the proportion of O2 in the plasma environment on the morphology, chemical structure, elemental composition, wettability, thickness and surface roughness, of the films was studied. Agglomerates of TiO2 (16-83 μm) were detected into the organosilicon matrix with the concentration of particulates growing with the percentage of oxygen in the feed. In general, there was elevation in the angle of contact of the surfaces as the oxygen supply increased. Interpretation is proposed in terms of the influence of the oxygen supply on the TiO2 sputtering rate and in the oxidation of plasma species.
... [28] With regard to the r-DCMS preparation process, it is essential to consider the O 2 flow rate and system pumping speed, in addition to the O 2 pressure, as the reactive sputtering process is highly dependent on these parameters. [34,35] There are two distinct operating modes in reactive sputtering: the metal mode and the oxide mode. Transparent WO 3 films are obtained using the oxide mode. ...
Article
... The oxygen inlet position was around the same as the sample stage. An RF power supply with 13.45 MHz frequency was used to avoid the arcing effect of a DC power supply [29,30]. The transmitter power was 350 W. ...
Article
Full-text available
Tungsten fiber-reinforced tungsten (Wf/W) composites are being developed to improve the intrinsic brittleness of tungsten. In these composites, engineered fiber/matrix interfaces are crucial in order to realize toughening mechanisms. For such a purpose, yttria (Y2O3), being one of the suitable interface materials, could be realized through different coating techniques. In this study, the deposition of thin films of yttria on a 150 µm tungsten wire by physical and chemical vapor deposition (PVD and CVD) techniques is comparatively investigated. Although fabrication of yttria is feasible through both CVD and PVD routes, certain coating conditions such as temperature, growth rate, oxidation of Wf, etc., decide the qualitative nature of a coating to a particular extent. In the case of PVD, the oxidation of Wf is highly reduced compared to the WO3 formation in high-temperature CVD coating processes. Yttria-coated tungsten fibers are examined comprehensively to characterize their microstructure, phase, and chemical composition using SEM, XRD, and Raman spectroscopy techniques, respectively.
... Typically in reactive magnetron sputtering discharges, after the introduction of the reactive gas, compound molecules are formed increasing deposition rate, however as more reactive gas is introduced compound molecules are formed on all surfaces in the deposition chamber including the target. The formation of the compound on the target is a product of two competing processes; the sputtering of the particles from the target surface and the formation of compound molecules [34]. To quantify only the effect of reactive gas presence in plasma bulk on the spoke properties an NbN target was utilised and the results were compared to those obtained using Nb target. ...
Article
Plasma in high-power impulse magnetron sputtering discharge, similarly to other discharges ionisation zones predominantly rotating in the E × B direction, called spokes. Many studies utilising E × B field (Hall thrusters, homopolar devices), undergoes self-organisation into the were conducted focussing on the characterisation of their appearance, mode number, rotational velocity, merging and splitting events in different experimental conditions. Nevertheless, only very little research has been conducted in the case of reactive sputtering, where only the general spoke characteristics were evaluated. A dual-image fast camera screening was utilised to capture plasma emission on 3 inch Nb target in a reactive mixture of nitrogen and argon. Spoke characteristics were evaluated while overall pressure and supplied power was kept constant and the content of nitrogen in N2/Ar mixture was varied. The shape, velocity and spoke mode number were significantly affected by the higher content of N2 in the mixture. To distinguish between the effects of the modified target surface state and reactive gas present in the plasma volume on spokes experiments with compound NbN target were also performed. Surprisingly, no real differences of spoke behaviour between Nb and NbN targets were observed.
... At highest Zr content of 26.5 at%, the porous microstructure which more open grain boundaries accompanied with fibrous grain along the coating were indentified. The crosssection pattern were well agreement with Zone T of Thornton's zone model [8]. According to table 1, the thickness increased from 307 to 401 nm as a function of Zr content which increase by increasing the target sputtering current (I zr ) from 300 to 900 mA. ...
Article
Full-text available
In this research, nanostructured chromium zirconium nitride (CrZrN) thin film has been deposited on Si(100) substrates by reactive DC magnetron co-sputtering method without in situ substrate heating and post-deposition annealing. The effects of Zr content on thin film structure and morphology were investigated. The Zr content in the films were varied by applied the sputtering current of Zr target (I zr ) in the range of 300 to 900 mA, whereas the current of Cr target was kept at 300 mA. The crystal structure, microstructure, morphology, thickness, and chemical composition were characterized by glancing angle X-ray diffraction (GA-XRD), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques, respectively. The results showed that the increase of I zr not only increased the deposition rate, but also increased the Zr content of the as-deposited film ranging from 3.9 to 26.5 at%. The as-deposited thin films were formed as a (Cr,Zr)N solid solution, with fcc structure in (111) and (200) plane, where Cr atoms were replaced by Zr atoms in the CrN lattice. The 2θ diffraction peaks were shifted to the lower value as increase of Zr content which was obtained by increased I zr . The nanocrystalline CrZrN structure with crystal sizes smaller than 10 nm structure were calculated for as-deposited thin films. The lattice parameters increased from 4.187 to 4.381 Å, whereas the crystal size decreased from 8.3 to 6.4 nm. The FE-SEM images of all the CrZrN films exhibited compact columnar with dense morphology as a function of Zr content. Moreover, the thickness of the CrZrN thin films was increased of 302 – 421 nm.
... However, these approaches inherently require drastic simplifications of the complex interactions (in particular in case of reactive plasmas) [19]. In addition, establishing an interface model by manually prioritizing and implementing all relevant interactions becomes a tedious task [23,24]. In contrast, machine learning models (e.g., artificial neural networks, ANNs), have been used to generalize complex correlations and create surrogate models in the frame of plasma or gas-phase interactions with surfaces [25][26][27]. ...
Preprint
Simulations of thin film sputter deposition require the separation of the plasma and material transport in the gas-phase from the growth/sputtering processes at the bounding surfaces. Interface models based on analytic expressions or look-up tables inherently restrict this complex interaction to a bare minimum. A machine learning model has recently been shown to overcome this remedy for Ar ions bombarding a Ti-Al composite target. However, the chosen network structure (i.e., a multilayer perceptron) provides approximately 4 million degrees of freedom, which bears the risk of overfitting the relevant dynamics and complicating the model to an unreliable extend. This work proposes a conceptually more sophisticated but parameterwise simplified regression artificial neural network for an extended scenario, considering a variable instead of a single fixed Ti-Al stoichiometry. A convolutional $\beta$-variational autoencoder is trained to reduce the high-dimensional energy-angular distribution of sputtered particles to a latent space representation of only two components. In addition to a primary decoder which is trained to reconstruct the input energy-angular distribution, a secondary decoder is employed to reconstruct the mean energy of incident Ar ions as well as the present Ti-Al composition. The mutual latent space is hence conditioned on these quantities. The trained primary decoder of the variational autoencoder network is subsequently transferred to a regression network, for which only the mapping to the particular latent space has to be learned. While obtaining a competitive performance, the number of degrees of freedom is drastically reduced to 15,111 and 486 parameters for the primary decoder and the remaining regression network, respectively. The underlying methodology is general and can easily be extended to more complex physical descriptions with a minimal amount of data required.
... This finding is impressive as our OES investigation did not show any promising evidence in the spectra of the growing population of sputtering and sputtered plasma species at the latter stages of the gas pulse. The high rate of sputtering observed in these stages might be related to the lesser concentration of reactive gas (O 2 ), which caused the cathode to operate in metallic mode characterized by high sputtering efficiency [25,26]. However, it does not explain why the large species population was not reflected in the OES spectra. ...
Article
This paper presents the effects of a power pulse delay with regard to a gas pulse generated in the Gas Injection Magnetron Sputtering (GIMS) technique. The GIMS technique is a variant of magnetron sputtering, in which the gas pulses control plasma. During the deposition of a coating, the pressure oscillates between the threshold values, initiating and terminating a discharge. In this work, the power pulse was considered as the second parameter of plasma control over the gas pulse. In our opinion, the state of plasma dynamically changes during the gas pulse period, which was studied using optical emission spectroscopy. The largest population of excited atoms of the sputtering gas was detected in the first stage of the gas pulse, while the highest number of ions was observed in the middle stage and the smallest population of plasma constituents in the end stage. The next step of the study involved examining the structure and phase state of the TiO2 coatings deposited when plasma was generated in various stages of the gas pulse. The structure of the coatings strongly depended on the deposition conditions, such as pressure and plasma content. The coatings were characterized by an amorphous structure that crystallized in rutile form under bombardment by energetic plasma species. The depth of crystallization was influenced by the content of plasma in a particular stage of the gas pulse. During the last stages of the gas pulse, very thick coatings were obtained in the deposition process. Moreover, the coatings exhibited metallic features. In such a condition, it can be expected that there will be no sputtering in reactive gas mixture, and the magnetron might operate in the self-sputtering mode. Thus, this work showed that delaying the power pulse with regard to the gas pulse would help to optimize the features of the deposited coating material.
... The deposition rates are generally much higher than that in the RF magnetron processes. However, a different kind of complexity arises associated with the well-known hysteresis behavior of deposition rate dependence on oxygen flow [13,15,[18][19][20][21][22][23][24]. The corresponding problems of controlling the discharge working point and implementation of various stabilization techniques-feedback loops for reactive gas supply-have been extensively discussed in the literature over the past several decades [25,26]. ...
... More information about the hysteresis effect is given in review papers. [163,164] The film growth also depends on the "history" of the sputtering process, as previous depositions will form WS x compounds on the chamber walls which may be resputtered during growth. ...
Thesis
In this thesis, I present the study of artificially generated defects by ion irradiation onthe surface of Transition Metal Dichalcogenides (TMDC), more specifically of tungstendisulphide (WS2) and tungsten diselenide (WSe2) crystals. I also present the structuralanalysis of WS2 films grown by Reactive Magnetron Sputtering (RMS) and compare theobserved structural defects to the artifically generated defects on the bulk crystals Thisthesis is composed of six chapters. In the first chapter, an introduction to the transitionmetal dichalcogenide structure and properties is discussed, followed by a discussion ofprevious studies about the defect generation by ion irradiation. Recent developmentsin the fabrication methods of TMDC thin-films such as reactive magnetron sputteringare also discussed.In chapter 2 I describe in detail the experimental techniques and the analysis methods used to characterize the TMDC materials and in chapter 3 I describe the methodsused for numerical simulation of ion irradiation of TMDCs.In chapter 4, I present my work on the design of the experiments and the calibrationof a ion source which was later used to produce low energy ions to artificially generatedefects on TMDCs surfaces.Chapter 5 I present my characterization results of WS2 films grown by RMS, whichwere grown in Uppsala by the team of Tomas Nyberg.In chapter 6 I present the artificial generation of defects on TMDC surfaces usingthe ion source described in chapter 4. Furthermore, I present the molecular dynamics studies which were performed to have an understanding of the defect productionmechanism in TMDCs by ion irradiation.
... In this Figure, the working points selected to deposit the corresponding cermet materials are also shown. It can be observed that these points fall inside the corresponding hysteresis curves in agreement with the studies conducted on the reactive sputtering process in transition mode [12,13,14]. It is correct to hypothesize that the second requirement was fulfilled because the shape of the hysteresis curve is very narrow and the working point position is constrained in it. ...
... One hour of pre-sputtering within the oxidic regime [15] was used to ensure coverage of all surfaces and a steady-state temperature in the whole chamber. No additional heating of the samples was used; thus, the surface temperature was below 60 • C. Starting from the pure metallic/oxygen-free state, we increased the O 2 flux systematically and later decreased it again to record the hysteresis curve O 2PP vs. O 2 flux. ...
Article
Full-text available
Highly conductive TiO2 films with different Nb doping levels (up to 5 at%) were prepared by reactive DC magnetron sputtering under precise control of the oxygen partial pressure. They were deposited on unheated substrates, covered with a protective Si3N4 layer, and subsequently annealed at 300 °C. The doping efficiency of Nb is greater than 90%. Conductivity is a maximum for a partly oxidized target in the transition range. The best films exhibit a resistivity of 630 µΩ cm and a mobility of 7.6 cm2/Vs combined with a high transparency above 70%. Comparing the behavior of undoped and Nb-containing films, intrinsic limits of the conductivity in the TiO2−x:Nb system could be observed, and a consistent model explaining these findings is presented. The conductivity is limited—by decreasing electron density due to Nb oxidation—by increasing incorporation formation of Nb2O5 clusters as scattering centers with increasing oxygen partial pressure and Nb concentration, by a transition from the crystalline to the amorphous state of the films below a critical oxygen partial pressure.
... Adding a reactive gas to this process further complicates finding a stable process as the reactive gas will create a compound by reacting with the metal on the surface of the target. The fraction of compound present on the target is determined by an equilibrium process between the compound forming rate at a given reactive gas partial pressure and the compound sputter rate removing compound from the target 16,17 . This equilibrium process also gives rise to hysteresis. ...
... The differences observed between the 2 configurations are important since they result in different target erosion and racetrack shape for long-time use of the target. This type of information is also important for any plasma and deposition simulation [25][26][27]. ...
Article
Full-text available
Magnetron sputtering is a widely used physical vapor deposition technique. Reactive sputtering is used for the deposition of, e.g, oxides, nitrides and carbides. In fundamental research, versatility is essential when designing or upgrading a deposition chamber. Furthermore, automated deposition systems are the norm in industrial production, but relatively uncommon in laboratory-scale systems used primarily for fundamental research. Combining automatization and computerized control with the required versatility for fundamental research constitutes a challenge in designing, developing, and upgrading laboratory deposition systems. The present article provides a detailed description of the design of a lab-scale deposition chamber for magnetron sputtering used for the deposition of metallic, oxide, nitride and oxynitride films with automated controls, dc or pulsed bias, and combined with a coil to enhance the plasma density near the substrate. LabVIEW software (provided as Supplementary Information) has been developed for a high degree of computerized or automated control of hardware and processes control and logging of process details.
Article
In this study, CrNx ceramic films were prepared utilizing modulated pulsed power magnetron sputtering (MPP) technique at low deposition temperature, with varying flow rates of the reactive gas, i.e. N2. The influences of N2 flow rate on the density of the plasma surrounding the target sheath, microstructure evolution, mechanical/tribological and anti-corrosion properties of the as-deposited CrNx ceramic films were investigated systematically. Results indicated that the plasma density increased sharply with increasing N2 flow rate in the range of 75 sccm to 175 sccm. Nevertheless, with further increase of N2 flow rate to 200 sccm, the growing trend of ionization slowed down probably due to the insufficiency of the power density. With increasing N2 flow rate, the Cr elemental concentration decreased from 69.7 at.% to 57.5 at.%, and that of N increased from 23.2 at.% to 36.6 at.%. The sub-stoichiometric ratio of the CrN films could be attributed to the relative lower reactive kinetic energy at low deposition temperature. The analyses on the microstructure evolution of CrNx films revealed that with insufficient introduced nitrogen, competitive growth between Cr2N(110), Cr2N(111), Cr(110) phases (note that all crystalline planes indexed here are parallel to the coating surface) were found; and with relative sufficient nitrogen, fcc-CrN phase took over, with preferred orientation of (111). Due to the improvement of density and the fine-grain strengthening mechanism, with 100 sccm N2 flow rate, the hardness of the CrNx films obtained the maximum value of 21.4 GPa. The films deposited at 75 sccm nitrogen showed the highest friction coefficient (i.e. ~0.75), which could be partially attributed to the presence of impurity particles on the film surface. And for the remaining films, the friction coefficient maintained in the range of 0.38–0.52. As for the anti-corrosion properties, the CrNx film deposited at 100 sccm nitrogen showed the lowest corrosion current (i.e. 44.2 nA/cm²), indicating excellent anti-corrosion property.
Article
This study aims towards a systematic reciprocity of the tunable synthesis parameters - partial pressure of N2 gas, ion energy (Ei) and Ti interface in TiN thin film samples deposited using ion beam sputtering at ambient temperature (300 K). At the optimum partial pressure of N2 gas, samples were prepared with or without Ti interface at Ei = 1.0 or 0.5 keV. They were characterized using x-ray reflectivity (XRR) to deduce thickness, roughness and density. The roughness of TiN thin films was found to be below 1 nm, when deposited at the lower Ei of 0.5 keV and when interfaced with a layer of Ti. Under these conditions, the density of TiN sample reaches to 5.80(±0.03) g cm⁻³, a value highest hitherto for any TiN sample. X-ray diffraction and electrical resistivity measurements were performed. It was found that the cumulative effect of the reduction in Ei from 1.0 to 0.5 keV and the addition of Ti interface favors (111) oriented growth leading to dense and smooth TiN films and a substantial reduction in the electrical resistivity. The reduction in Ei has been attributed to the surface kinetics mechanism (simulated using SRIM) where the available energy of the sputtered species ( ) leaving the target at Ei = 0.5 keV is the optimum value favoring the growth of defects free homogeneously distributed films. Secondary ion mass spectroscopy depth profile measurements confirm the uniform distribution of N and Ti across the depth of a sample. The electronic structure of samples was probed using N K-edge and Ti L-edge absorption spectroscopy and the information about the crystal field and spin-orbit splitting confirmed TiN phase formation. In essence, through this work, we demonstrate the role of and Ti interface in achieving highly dense and smooth TiN thin films with low resistivity without the need of a high temperature or substrate biasing during the thin film deposition process.
Article
Multiferroic materials show great academic and technological interest for their role in new generation devices due to the coexistence of magnetic, ferroelectric and elastic ordering. In this article the fabrication of SrRuO3 (SRO) thin films by the RF magnetron ion sputtering technique is presented where the deposition conditions, namely deposit time, substrate temperature and RF power were optimized. The growth of the SRO phase was evaluated using X-ray diffraction. The homogeneity of the films was analysed using energy dispersive X-ray spectroscopy. Film thickness and optical properties were determined by ellipsometry.
Article
PVD-TiMgGdN coatings have been successfully developed by the authors using an industrial DC-magnetron PVD unit. The coatings reveal excellent corrosion protection capabilities for mild steel substrates for at least 800 h in the neutral salt spray test (NSS). MgGd was added to the TiN matrix by using segmented (Seg.) multi-component targets, consisting of segments of pure Ti and of a Mg- 30 wt.-% Gd alloy. The Seg. targets caused an increased defect density due to droplets forming at the gaps between the segments which leads to an unsatisfactory wear performance. To overcome the low mechanical and wear properties by keeping the coatings excellent corrosion performances stable, a TiMgGd target with a specific Ti:Mg:Gd ratio was manufactured by powder metallurgy (PM) technology processed out of pure metal powders. In the present work, the properties of the corrosion and wear performance of DC-PVD-TiMgGdN coatings, which were synthesized onto corrosive mild steel substrates by using a Seg. target and a PM target of comparable Ti:Mg:Gd ratios together with identical deposition parameters, are compared with each other. The coatings were characterized regarding their microstructural, mechanical, physical and corrosion properties. Furthermore, ball on disk wear tests were conducted by reciprocal dry sling SRV III tests. It is shown that the excellent corrosion performance, could significantly be boosted by using the PM TiMgGd sputter target. Moreover, a remarkable increase in wear resistance of the TiMgGdN coatings can be examined by the use of a PM sputter target. It was found that the chemical properties of the TiMgGdN coatings as well as the nitrogen gas flow have a major influence on the mechanical coating properties and on the resulting microstructure, which directly correlates with the corrosion and wear properties.
Article
The flux of negative oxygen ions in a dc reactive magnetron discharge has been measured using a specially developed magnetic-filtering probe. The gridded probe which operates as a retarding field analyzer has a magnetic filter attached to the front entrance to suppress plasma electrons entering the device. As a result, the fluxes of unmagnetized negative ions with energies of higher than ∼10 eV can arrive to an ion collector and contribute to the detected probe current. During the oxide mode of Ti–Ar/O2 magnetron sputtering discharge, the measured negative ion flux is considered to be contributed by the sputtered O⁻ ions generated at the target surface and the plasma O⁻ ions created in the discharge volume. However, in specific discharge conditions, the sputtered ions are likely to dominate in the measured flux signal. As a result, the yield of the sputtered O⁻ ions and associated energy flux can be examined. The magnetic-filtering probe could potentially be employed as a real-time diagnostic tool to monitor the sputtered O⁻ flux as well as the oxide state of the target surface during reactive magnetron sputtering processes.
Thesis
High Power Impulse Magnetron Sputtering technology (HiPIMS) has been developed and considered as an effective method for film preparation. HiPIMS technology allows for much greater flexibility for manipulating film structure and performance, leading to films with unique properties that are often unachievable in the other PVD approaches. However, the underlying plasma mechanism for supporting film growth is currently blurred. Moreover, HiPIMS technology is still stationed in the laboratory, many films with desirable properties have not been explored under HiPIMS framework. In this work, (i) the driven mechanism of high density plasma coherent structure (i.e., spokes) in the HiPIMS discharge and (ii) how the structure and properties of the TaC/a-C:H and HfC/a-C:H films are regulated by HiPIMS were investigated. For the driven mechanism of spokes, based on the dispersion relationship of HiPIMS plasma and the evolution of the coupling between two azimuthal waves, the coupling-induced wave model was proposed. For the TaC/a-C:H and HfC/a-C:H films, the chemical bond states, structure, morphology, mechanical and tribological properties, thermal stability as well as oxidation resistance of the films were investigated. By comparison with DC deposited films, it is demonstrated that HiPIMS technology provides a potential strategy for preparing higher performance TaC/a-C:H and HfC/a-C:H films in terms of hardness, friction coefficient and wear resistance, oxidation resistance and thermal stability by modulating the chemical bonding state and nanocomposite structure of the films through HiPIMS reactive plasma.
Chapter
Volume 22A provides a thorough review of computational modeling and its application in the development of alloys and associated processing techniques. It describes the basic concepts of modeling and simulation and accepted practices in the use of finite elements, computational fluid dynamics, mechanistic and phenomenological modeling, and statistical approaches. It addresses a wide range of processes, including deformation and solidification transformations, recrystallization, grain growth, precipitation, strengthening, and the evolution of microstructure and surface texture. It offers insight on damage evolution processes as well, examining cavitation, fracture, hot tearing, creep, crack growth, and fatigue. It also discusses phase equilibria and phase field modeling, state variable and constitutive modeling, electronic structure modeling, and density functional theory. It explains how use models to simulate and control mechanical properties and minimize defects in specific steels, aluminum, titanium, and superalloys. The volume also includes physical data, mathematical reference information, and a discussion on length scales and relevant effects. For information on the print version of Volume 22A, ISBN 978-1-61503-001-9, follow this link.
Chapter
Doping different materials, especially semiconductors, has been known as a powerful tool for improving properties and finding excellent applications in industry. Applications of doping in semiconductor industry especially in nanoelectronics and nanophotonics is a growing field of research. Lanthanide rare earth (RE) have been extensively used in different types of semiconductors as trace additives with extraordinary photonic, magnetic, photocatalytic, and photovoltaic properties. In this chapter, different types of RE-doped semiconductors will be reviewed and then the common synthetic method and applications of each category will be discussed. It will cover a wide range of doped semiconductors from the conventional Si and III-N materials for photonic applications to TiO2 and ZnO photocatalysts and perovskites for photovoltaic applications. Moreover, different synthetic techniques for each material will be discussed in detail.
Article
In this study, the material properties of reactively sputtered tantalum pentoxide (Ta2O5) thin films were tailored by finely selecting O2 fluxes based on the target voltage-O2 flux curve. The Ta2O5 thin films were applied as solid electrolyte (SE) layers in flexible all-thin-film electrochromic devices (ATF-ECDs) with the device configuration of PET/ITO/NiOX/Ta2O5/WO3/ITO. The material properties including the grain structure, morphology, optical properties and chemical composition of the Ta2O5 thin films were systematically investigated. The flexible ATF-ECD with a Ta2O5 SE layer reactively sputtered at the deflection point performed the highly optical modulation of up to 70% and relatively fast electrical-optical responses as well as better open-circuit memory. The related mechanism was deeply discussed.
Article
Deposition parameters of silicon nitride in reactive direct-current magnetron sputtering were studied in two different chambers in order to establish a characterization protocol assisted by optical emission spectroscopy. Different discharge powers, working pressures and gas proportions (N2:Ar) were used to create characterization curves to identify the optimum conditions for the synthesis of silicon nitride. These curves were used to observe changes in the plasma via emission lines and the supplied electrical parameters (voltage and current). Individual thin films were synthesized using different deposition parameters selected from the previous characterization curves, and their optical properties were characterized via spectroscopic ellipsometry. A correlation between deposition parameters, optical properties, and plasma emission lines was established to optimize silicon nitride deposition.
Article
TiAlN thin films were deposited on Si(100) and AISI 304 austenitic stainless steel substrates at the low deposition temperature below 250℃ by the deep oscillation magnetron sputtering (DOMS), respectively. The peak sputtering power changed from 58.7 kW to 129.9 kW by adjusting the oscillation voltage on-time (τon) / off-time (τoff) ratio with 6 - 12 μs to 30 μs. All TiAlN thin films have a face centered cubic structure with a composition of Ti0.22Al0.28N0.50. With increasing the peak powers, a transit of the columnar morphology in Zone I with the preferred orientation of c-TiAlN(111) to a compact morphology in Zone T with c-TiAlN(200) was characterized. The hardness, residual stress, and H/E and H³/E² ratios of TiAlN thin films increased with the maximal values obtained at the peak power of 90.2 kW, and then slightly decreased. Correspondently, the fracture toughness (KIC) of TiAlN thin films on Si(100) and AISI 304 stainless steel increased firstly from 0.56 MPa∙m1/2 to 1.10 MPa∙m1/2 and from 0.58 MPa∙m1/2 to 1.08 MPa∙m1/2 as the structure from Zone I with c-TiAlN(111) to Zone T with c-TiAlN(200), and then decreased to 0.94 MPa∙m1/2 and 0.71 MPa∙m1/2 at the structure of Zone T with c-TiAlN(200), respectively. The higher KIC values of Ti0.22Al0.28N0.50 thin films in Zone T were achieved on Si(100) and AISI 304 stainless steel at 90.2 kW. The excellent mechanical properties of TiAlN thin films on Si(100) and AISI 304 stainless steel substrates were carried out by using DOMS at the low deposition temperature.
Article
In this work, zinc nitride (Zn3N2) thin film was deposited on glass and silicon substrates by DC reactive magnetron sputtering technique. The structural, optical and electrical properties of Zn3N2 films at various nitrogen gas concentration were investigated. XRD results of the as-deposited films confirm the formation of crystalline cubic anti-bixbyite Zn3N2 structure with a preferred orientation along (400) plane. AFM and SEM have used to study the surface topography and morphology of the deposited film. Raman analysis of the as-grown films show two broad peaks at 265 and 567 cm⁻¹ related to the Raman-active modes in the Zn3N2 compound. The highest optical transmittance of the film was 62% for the film deposited with pure nitrogen and decreased to 1% at 40% N2. There was a blueshift in the absorption edge with increasing the N2 gas concentration. The direct optical band gap of the films ranged from 1.27 to 2.1 eV with increasing N2 gas flow. The I–V characteristics of Zn3N2/p-Si heterojunctions showed rectification characteristics. C–V results showed that the built-in-potential of the heterojunctions was in the range of 0.51–0.82V. A broad responsivity has been observed for all of Zn3N2/p-Si heterojunction photodetectors and the highest spectral responsivity and quantum efficiency of the photodetector are 0.15 A/W and 35% at 600 nm, respectively.
Article
Although several studies have focused on the application of deep-learning techniques in manufacturing processes, the lack of relevant datasets remains a major challenge. Hence, this paper presents a meta-learning approach to resolve the few-shot regression problem encountered in manufacturing applications. The proposed approach is based on data augmentation using conventional regression models and optimization-based meta-learning. The resulting deep neural network can be employed to optimize the reactive-sputtering process used in the fabrication of thin, compounded films of titanium and nitride. The performance of the proposed meta-learning approach is compared to the conventional regression models, including support vector regression, Bayesian ridge regression, and Gaussian process regression, which exhibit state-of-the-art performance for regression over small data sample counts. The proposed meta-learning approach outperformed the baseline regression models when tested by varying the training sample counts from 5 to 40, resulting in a decrease in the root mean square error to 74.6% of that observed in the conventional models to predict the stoichiometric ratio of the film produced during the reactive sputtering process. This is remarkable because regression performed over a small number of data is usually considered unsuitable for deep-learning approaches. Therefore, this approach exhibits considerable potential for usage in different manufacturing applications because of its capability to handle a range of dataset sizes.
Article
In this work, we investigate the effect of anti-site disorder on the half-metallic properties of a Mn 2 FeAl Heusler alloy thin film. The film was grown on TiN-buffered MgO 001 substrates via magnetron sputtering. A detailed structural characterization using X-ray diffraction (XRD) and anomalous XRD showed that the film crystallizes in the partially disordered L 2 1 B structure with 33% disorder between the Mn(B) and Al(D) sites. We measure a positive anisotropic magnetoresistance in the film, which is an indication of non-half metallic behaviour. Our X-ray magnetic circular dichroism sum rules analysis shows that Mn carries the magnetic moment in the film, as predicted, with a positive Fe moment. Experimentally determined moments correspond most closely with those found by density functional calculated ones for the L 2 1 B structure with Mn(B) and Al(D) site disorder, matching the experimental structural analysis. We thus attribute the deviation from half-metallic behaviour to the formation of the L 2 1 B structure, which we support by density functional theory calculations. To realize a half-metallic Mn 2 FeAl film it is important that the inverse Heusler XA structure is stabilized with minimal anti-site atomic disorder.
Article
Full-text available
Abstract This work reports the properties of GaN films grown onto c-Si (100) at relatively low substrate temperature (400°C) by reactive magnetron sputtering. The study depicts the effect of working pressure and RF power on the GaN film structural, vibrational and optical properties characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and spectroscopic ellipsometry. Unusual low pressure deposition condition (0.40 Pa) was achieved by using a separated argon inlet directed to the Ga target surface, resulting in improved crystalline quality of the films. In this condition, the preferential crystalline orientation, the surface morphology and the optical gap of the GaN films show a strong dependence on the RF power applied to the Ga target, where low RF power (30-60 W) was responsible for increasing the c-axis orientation and the optical gap, while higher RF power (75-90 W) decreased the overall crystal quality and increased the surface roughness.
Article
Simulations of thin film sputter deposition require the separation of the plasma and material transport in the gas phase from the growth/sputtering processes at the bounding surfaces (e.g., substrate and target). Interface models based on analytic expressions or look-up tables inherently restrict this complex interaction to a bare minimum. A machine learning model has recently been shown to overcome this remedy for Ar ions bombarding a Ti-Al composite target. However, the chosen network structure (i.e., a multilayer perceptron, MLP) provides approximately 4×106 degrees of freedom, which bears the risk of overfitting the relevant dynamics and complicating the model to an unreliable extent. This work proposes a conceptually more sophisticated but parameterwise simplified regression artificial neural network for an extended scenario, considering a variable instead of a single fixed Ti-Al stoichiometry. A convolutional β-variational autoencoder is trained to reduce the high-dimensional energy-angular distribution of sputtered particles to a low-dimensional latent representation with only two components. In addition to a primary decoder that is trained to reconstruct the input energy-angular distribution, a secondary decoder is employed to reconstruct the mean energy of incident Ar ions as well as the present Ti-Al composition. The mutual latent space is hence conditioned on these quantities. The trained primary decoder of the variational autoencoder network is subsequently transferred to a regression network, for which only the mapping to the particular low-dimensional space has to be learned. While obtaining a competitive performance, the number of degrees of freedom is drastically reduced to 15 111 (0.378% of the MLP) and 486 (0.012% of the MLP) parameters for the primary decoder and the remaining regression network, respectively. The underlying methodology is very general and can easily be extended to more complex physical descriptions (e.g., taking into account dynamical surface properties) with a minimal amount of data required.
Article
In this study, tungsten oxide (WOX) thin films were prepared by reactive magnetron sputtering at different oxygen (O2) fluxes for application in flexible all-thin-film electrochromic devices (ATF-ECDs) with a device configuration of PET/ITO/NiOX/Ta2O5/WOX /ITO. The target voltage vs. O2 flux curve presents two sputtering mode zones, where distinct target voltages reflect the specific target surface states. The WOX thin film deposited at the O2 flux of 4.5 sccm, which sites at the onset point reaching to the maximal target voltage, exhibits amorphous structure, relatively loosen morphology, proper chemical compositions, high light transmittance and best chemical electrochemical properties. The corresponding flexible ATF-ECD performs excellent electrochromic performances with high light modulation of up to 70%, fast response time and the highest coloration efficiencies at both bleaching and coloring steps.
Article
Vanadium oxide is known to be semiconductive and thermochromic with a very selective amount of oxygen in order to form the required monoclinic crystal structure (nonconductive, M phase) at room temperature and transform to a tetragonal phase (conductive, R phase) above 68 °C. In this study, vanadium oxide thin films are deposited by sputtering under different oxygen flow rates to include various amounts of oxygen, which is then followed by rapid thermal annealing to become crystalline with a variety of properties and functions. The properties and functions of annealed vanadium oxide are examined by x-ray diffraction for crystal structures, Raman spectrometer for crystal vibrational modes, four-point probe for electrical resistivity, and UV-Vis-NIR spectrometers for optical properties. All these characterizations help us to determine the range of oxygen supply under which thermochromic VO2 films can form. Results indicate that in our current setup, the lower oxygen (<0.25 SCCM) produces vanadium-rich films, the medium (0.5–1.5 SCCM) results in semiconductive films, and the higher (>2 SCCM) creates insulated oxides. Among the semiconductive films, the one deposited under 1.0 SCCM O2 supply after annealed becomes thermochromic as confirmed by the hysteresis changes of optical transmittance and electrical conductivity under thermal cycles between 25 and 95 °C.
Article
Here, a set of polycrystalline niobium oxide thin films were produced by using reactive sputtering technique on the Ti-6Al-4V alloy surfaces and characterized by OM, SEM/EDX, AFM, DRX/Rietveld refinement, and XPS techniques. CPDP and SVET tests were performed on the coated and uncoated material considering an aggressive medium (NaF and Hank's solution). The results demonstrated the technique used in the present survey was advantageous to produce thin films on the Ti-6Al-4V surfaces. XPS analysis demonstrated that the niobium oxide thin films were composed by Nb2O5/NbO2. Measured and Rietveld refined X-ray diffraction patterns for the Nb-oxide thin film demonstrated the presence of the Nb2O5, NbO2, and NbO crystalline phases. The thin film acts as a barrier layer, suggesting a better corrosion performance when compared to the bare alloy (Ecorr = −111 mVSCE vs −290 mVSCE). The CPDP results demonstrated the current density of the coated Ti-6Al-4V specimen, at the same potential, was lower when compared to the bare alloy. SVET results revealed the coated material displayed low values of current density (~100 μA/cm² for 15 h of immersion time), whilst the bare material (in the range 700–2200 μA/cm² for 1 h of immersion time), suggesting the niobium oxide thin films act as an effective protective barrier against corrosion process evolution over time.
Article
Magnesium zinc oxide (MZO, MgxZn1-xO) is a leading emitter for CdTe-based solar cells due to its transparency and the ability to tune its conduction band offset with the absorber. Devices employing alloyed cadmium selenide telluride (CST, CdSeyTe1-y) absorbers achieved high efficiency (>19%) using MZO deposited by reactive sputtering over a broad composition range (3.68–3.92 eV, x: 0.20–0.35). Minimal differences in implied and measured open circuit voltage indicate that the contacts are well passivated and highly selective across the spectrum of MZO employed. Device performance insensitivity to MZO composition, which is not observed in CdTe devices, is attributed to the formation of an oxygenated interface layer. Se volatility creates a group VI deficiency at the interface that drives O migration from the MZO into the absorber. This introduces conductivity in the emitter not present in its as-deposited state, contributing to the exceptional performance observed. It is shown that the quality of device passivation depends on the oxidation state of the as-deposited MZO such that intelligent control and management of the reactive sputtering process is required.
Article
Full-text available
In this work, a heterojunction TiO2 on Si base has been made by use the D.C magnetron sputtering method with Ti target and oxygen plasma. The film was deposited on Si wafer and then undergone to the annealing process at various annealing temperatures were employed to assess film properties. The capacitance with reverse bias has been measured as a function of bias voltage at frequency 10 kHz, and these measurements have indicated the width of the depletion layer (W) surges with increasing of annealing temperature. The current–voltage characteristic It turned out through the current–voltage graph of TiO2/Si heterojunction the forward current at dark changes with change of applied voltage, in demeanor concordant with recombination-tunneling model. The results have shown that the dark current rises with growth of Ta. Also under illumination condition its clear to show there is a positive correlation relationship between the photocurrent and Ta.
Article
Full-text available
Computer process modeling has become an important tool in the development of new thin‐film processes. Previously, we presented a model that successfully describes the complex behavior of the reactive sputtering of a single‐element target. The model enables one to predict, e.g., the hysteresis effect and the composition of the deposited film. There exists, however, a demand for developing reliable reactive‐sputtering processes for more complicated materials. This calls for an extended reactive‐sputtering model including more than one target element. In this article, we will for the first time present an extension of our previous model now taking the effect of multicomponent targets into consideration. The transition from metallic‐ to compound‐sputtering mode normally occurs at different levels for different single‐element targets. The new extended reactive‐sputtering model predicts the transition from metallic to compound mode during multicomponent reactive sputtering of thin films. The results indicate that under normal operating conditions, only one transition region exists irrespective of the number of target elements involved in the process. This is experimentally verified for the process of reactive cosputtering of Al+Ti in an Ar/O2 atmosphere. We will also point out the complex composition behavior of the reactive‐cosputtering process as compared with reactive sputtering from an alloy target.
Article
We present a new model for process simulation of large area reactive magnetron sputtering. The hybrid model combines "Direct Simulation Monte Carlo" calculations and finite element gas flow calculations in order to adopt Berg's model to real in-line sputter equipment. The model allows for the realistic description of reactive gas pressure gradients due to apertures and shields and for the process kinetics of reactive sputtering. Experimental verification of our simulation results will be shown for the reactive AC magnetron sputtering of SiO2 and ZnO:Al films. Targets operating at high rate in transition mode can be trapped in an inhomogeneous oxidation state leading to deviations of film thickness and composition. For explanation of this effect we introduce a new formalism regarding the relationship between sputter power and ion currents at the target surface. Together with Berg's model, constant sputter power operation rather than constant current operation can now be modeled, yielding a more realistic description for the sputter rate in metallic mode. Furthermore, the new formalism can explain the effect of trapped targets in terms of secondary electron emission coefficients. Hence, this approach is a first step towards incorporation of plasma and magnetron phenomena as well as experimental current-voltage behavior into a heuristic model for real-time speed simulation of in-line sputtering.
Article
Computer simulations of direct current reactive sputtering based on a kinetics model were carried out in this article. It was revealed that, reactive sputtering exhibited steady state transition-free and hysteresis-free behavior, only when the sputtering yield of compound was approximately that of the corresponding metal. By changing the configuration of the sputter system (discharge current, target area, pumping rate), it was possible to get a hysteresis-free reactive sputtering behavior. However, it was too difficult to eliminate the steady states transition by this method. The much lower value of the sputtering yield, as compared with that of the corresponding metal, might be the most important cause of the steady state transition and hysteresis effect.
Article
The model of reactive sputtering of Berg [T. Larsson, C. Nender, and H.‐O. Blom, J. Appl. Phys. 63, 887 (1988)] was extended to include chemical reactions on target and substrate due to an additional reactive gas (etchant). The model explains both the increased deposition rate of the oxides under some conditions and decreased deposition rate under others.
Article
During reactive glow discharge sputtering of copper in an argon/nitrogen plasma, we noticed an abrupt change of the target voltage and the deposition rate when the nitrogen concentration in the plasma exceeds a critical value. To explain this behaviour, the target surface after reactive glow discharge sputtering was examined by x-ray photoelectron spectroscopy (XPS). An experimental arrangement was constructed that allows direct transfer of the glow discharge cathode to the XPS analysis chamber without air exposure. These XPS measurements revealed that several different chemical states of nitrogen are present in the layer that forms on the target surface. The relative concentration of these different states changes when the critical nitrogen concentration in the plasma is exceeded.
Article
To the model of reactive sputtering of Berg {ital et} {ital al}. (S. Berg, H.-O. Blom, T. Larsson, C. Nender, J. Vac. Sci. Technol. A {bold 5}, 202 (1987)) an energy dependent sputtering yield was introduced. Calculated hysteresis curves were in good agreement with measurements.
Article
The present article considers instability phenomena during the sputtering of a single metallic target of titanium in a reactive atmosphere involving argon+oxygen+nitrogen gases. Since the process using two reactive gases is much more complex than one reactive gas, the transition zone of the reactive mode must be defined taking into account oxygen and nitrogen mass flow rates. A two-dimensional representation delimiting boundaries of the instability region and depending on both mass flows is proposed for radio frequency and direct current (dc) polarization of the titanium target. This diagram provides operating conditions favorable to deposit oxy-nitride coatings with a modulated oxygen or nitrogen composition. It is also shown that the supply of one reactive gas affects consumption and behaviors of the other gas as well as its own characteristics. A critical region is then defined in which the process is trapped in reactive mode and can not go back to elemental conditions by changing the mass flow rate of only one reactive gas. Kinetics and pollution of the titanium surface are discussed from measurements of dc potential for various operating points. It is shown that comportments of oxygen and nitrogen towards metallic or poisoned target are interdependent and a surprising evolution of the time of pollution against oxygen and nitrogen introduction is observed. These original results are supported by optical emission spectroscopy experiments. Emission intensities of nitrogen and oxygen species can also be used to monitor the state of pollution of the titanium target and so to control instabilities of the two reactive gases sputtering process. © 1999 American Vacuum Society.
Article
Computer simulation of reactive sputtering was carried out to explain the enhancement of the deposition rate of complete oxide film using reactive gas flow modulation. The model dealt with the preparation of TiO2 film with a titanium target and oxygen in rf reactive sputtering. The computed results showed good agreements with the experimental data obtained in our previous work. The effects of the flow modulation were elucidated with the calculated timewise variations for partial oxygen pressure and target coverage. The effects of modulation patterns were also evaluated using the simulation. © 1996 American Vacuum Society
Article
Reactive sputtering of metal targets in a working gas/reactive gas mixture is a favorable method for the deposition of compound layers like oxides. One basic problem of the reactive sputtering process is the strong dependence of essential process parameters such as the sputtering yield upon the degree of target coverage with compound layers. Via positive feedback effects these dependencies lead to the instability of the process in a range of reactive working points of the so-called transition mode. Often stoichiometric films can only be deposited in this unstable transition mode at high deposition rates. Therefore process stabilization including a control loop for the reactive gas flow is required. In this paper a model of the reactive sputtering process is presented that quantitatively predicts the dependencies of process variables like reactive gas partial pressure, deposition rate and target coverage on the reactive gas flow. Comparison with experimental data for deposition of alumina films shows that the model is in good agreement with the experiments and describes for example the well known hysteresis loop. The novel approach of the model includes the dynamics of the process. It therefore enables us to investigate the stability of the reactive working point and to simulate the operation of a reactive gas control loop in the unstable transition mode. Practical requirements on typical control loops and gas systems like the maximum reaction time of the control devices or the maximum volume of the gas manifold are derived from the simulation.
Article
A theoretical model is presented in order to predict general behaviours and properties of the reactive sputtering process implementing two separated metallic targets in a reactive atmosphere. Taking into account gas kinetic theory, geometrical characteristics of the device and from simple physical and chemical assumptions, the proposed theoretical development is capable of describing evolutions of some process parameters such as reactive gas partial pressure. Some relationships between reactive gas flow rate, gas pressure and sputtering rate coming from each target have been established. Theoretical results determined with this model have been compared with experimental measurements obtained for the titanium–chromium–oxygen system. It is pointed out the proposed model is quite convenient to predict whole behaviours of the multitarget reactive sputtering process. The ‘characteristic function’ has also been calculated leading on some original and interesting theoretical results: a new way to remove totally or to modulate the size and the position of the instability phenomena of the reactive method.
Article
Reactive sputtering process of magnesium target in d.c. planar magnetron discharge using argon and oxygen gases as buffer and reactive gases, respectively, has been investigated. A drastic mode transition between metallic and oxide modes has been observed due to a large difference in the secondary electron emission coefficients of magnesium and magnesium oxide. To describe the experimental results quantitatively, a new reactive sputtering model has been developed. The model is fundamentally based on a simple reactive gas balance model proposed by Berg et al. in 1988, but includes the change in the secondary electron emission coefficient of target. The modified model can deal with the change of plasma properties through the change of ion to electron current ratio at the target, and can quantitatively describe experimental results such as oxygen flow rate dependence of deposition rate and discharge voltage, which were obtained at a constant discharge current.
Article
The reactive sputtering process involving two reactive gases has been investigated. Sputtering titanium in the presence of oxygen and nitrogen in argon was studied by means of optical emission and mass spectrometries. The experiments reveal the mechanism of the mixed target poisoning. Increasing the nitrogen supply in the presence of a constant oxygen supply forces the reactive sputtering system to avalanche from a high-rate metal-sputtering mode to a low-rate compound-sputtering mode at a lower N2-to-Ar ratio as compared with the single reactive gas ArN2 reactive sputtering process. The amount of the oxygen admixture, however, also affects the character of the avalanche and the corresponding hysteresis effect. At a definite level of constant oxygen supply the ArN2 processing behaviour becomes irreversible, successive decreasing of the nitrogen supply to zero in this case is not sufficient to force the process to return back to the high-rate metal-sputtering mode. A “process trapping” effect appears.The coupling effect between the consumption of both reactive gases N2 and O2 during increase and successive decrease of N2 in the presence of a constant O2 supply is reflected in the dependencies of the respective partial pressures. The cause of the observed trapping effect, the shift and the change of the character of the sputtering rate hysteresis curve may be explained in terms of the link between the consumption of the reactive gases and the corresponding target condition. The experimental findings support the theoretical model of the two-gases reactive-sputering process recently presented by the authors.
Article
The electrical, optical, and mechanical properties of a compound film depend strongly on the composition of the film. Therefore, it is interesting to study a wide variety of compositions of many new compound materials. Reactive sputtering is a widely used technique to produce compound thin films. With this technique it is possible to fabricate thin films with different compositions. However, it has not yet, to any great extent, been possible to predict the composition of the sputtered film. In this article we will present a model that enables us to predict both sputtering rate and film composition during reactive sputtering. The results point out that there exists a very simple linear relationship between processing parameters for maintaining constant thin‐film composition in the reactive sputtering process. Based on these results, it is possible for the first time to combine information of both sputtering rate and film composition into the same graphical representation. Access to this new and simple graphical representation may eliminate much of the ‘‘trial and error’’ work that earlier has been associated with the reactive sputtering process.
Article
An experimentally verified useful new model for reactive sputtering is presented. By considering the total system (target erosion, gas injection, chamber wall deposition, reactive gas gettering at all surfaces, etc.) during deposition it is possible to evaluate quite simple relationships between processing parameters. We have expanded earlier treatments to include these phenomena. The model involves that gettering of the reactive gas takes place at the target and at the walls opposite to the target. Arguments are also presented for how the sputtered materials (elemental target atoms and the formed compound) contribute to the formation of the surface composition of the walls opposite to the sputtering electrode. The mass flow of the reactive gas has been chosen as the independent parameter in this presentation. Results for partial pressure and sputter rate are presented. The theoretical values are compared with experimental results from reactive sputtering of TiN. It is also pointed out that the calculated values agree extremely well with results presented in the literature by several other authors.
Article
The reactive sputtering process is very simple to use as long as one wants to deposit fully formed compounds. If, however, an intermediate composition is required it is necessary to use quite advanced process control. Reactive sputtering from an elemental target in argon with the addition of one reactive gas have been extensively studied. Also studies of reactive cosputtering have been reported. The interest for such studies increased dramatically when the high‐temperature superconductive thin films were introduced. In this article we will treat the process of reactive sputtering from an elemental target in argon with the addition of two reactive gases. In such a process, e.g., oxy‐nitride films can be formed. The fundamental reactive sputtering model has been modified to handle two reactive gases. By this new model it is possible to simulate two gases having different reactivity and sticking coefficients to the elemental metal involved. It is possible to predict complex effects in the processing region where the two gases compete to form different compounds. The ‘‘hysteresis effect’’ for this two‐gas reactive sputtering process differs significantly from the hysteresis effect observed in a single gas reactive sputtering process. Poisoning the target by one gas prevents formation on the target of the compound based on the other gas. It should, however, be possible to ‘‘tune’’ the process to deposit any desired composition. A large fraction of these composition intervals occur inside the ‘‘hysteresis’’ region. The simple one‐gas reactive sputtering process operates on a single curve. The two‐gas process will operate on a complex processing surface. Results from computer simulations as well as experiments will be reported in order to explain the physical background to the observed complex behavior.
Article
For a better understanding of the physical and chemical processes underlying the deposition of aluminium nitride and AlNx thin films by reactive magnetron sputtering of aluminium, we compare sputter gas mixtures of argon and nitrogen with mixtures of argon and oxygen. Depending on the flow rates of the reactive gases, their partial pressures are detected by mass spectroscopy and the aluminium densities in the plasma ring are observed by optical emission spectroscopy. The addition of oxygen results in two stable modes, the reactive mode, corresponding to a target surface almost covered by reaction products, and the metallic mode, corresponding to a metallic target surface. Avalanche-like transitions between these two modes lead to hysteresis loops. On the contrary, using nitrogen, the discharges are in a stable state also for partially covered targets. In this case, there is a gradual transition from a metallic target, which is only found at pure argon, to a maximum-covered target. Only small hysteresis effects and no avalanche-like transitions are observed. We conclude that, if sputtering aluminium targets, the addition of oxygen or nitrogen as the reactive gas to argon discharges represents two different model cases of the reactive sputtering process.
Article
In this paper, attention is paid to DC reactive magnetron sputtering and its implications, such as the hysteresis effect and the instability in the reactive gas pressure, differential poisoning of magnetron cathode, as well as the methods which are used to control the process. These methods include: (a) increasing the pumping speed, which requires considerable additional costs; (b) increasing the target-to-substrate distance, which requires larger vacuum chambers (hence, higher costs) and also results in lower deposition rates; (c) obstructing reactive gas flow to the cathode with the resultant reduction of deposition rate and the need for complicated arrangements; (d) pulsed reactive gas flow, which requires an extensive amount of process optimisation and a continuous monitoring and adjustment of the process parameters; (e) plasma emission monitoring; and (f) voltage control, which are inexpensive and have proved to be powerful techniques for monitoring and controlling the reactive sputtering processes, in real time without disturbing the discharge, for the deposition of high-quality films, reproducibly. In addition, arcing and methods to avoid it are reviewed; this includes, arc initiations and their destructive effects (e.g. driving the process to become unstable, reducing the target lifetime and creating defects in the sputtered films), time required for arcs to occur, and finally, methods of avoiding arcs. The latter includes the use of unipolar or bipolar pulsing techniques at frequencies in the range 10–70 kHz.
Article
Aluminium has been d.c. sputtered in a cylindrical chamber into which is leaked argon and oxygen mixtures. The percentage of oxygen, C, was varied from 0–100% while measurements were made of the deposition rate and optical absorption and emission. Above a critical value of C, the deposition rate falls, no ground state aluminium atoms are observed in the discharge and Al2O3 films are deposited. This is due to the formation of an oxide layer on the aluminium, the oxide being sputtered mainly as “molecules”. Similar results are obtained during sputtering of the oxide layer formed on aluminium by exposure to air or oxygen. Atomic adsorption spectroscopy is a sensitive method for determining when this oxide has been removed so that pure aluminium films can be deposited.
Article
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.
Article
By simple arguments as well as results from a recently developed computer simulation model we have found out that for high frequency pulsed DC reactive sputtering the target poisoning does not reflect the periodicity of the pulsed DC power supply. The degree of target poisoning does not change markedly during a single duty cycle. The degree of poisoning essentially exhibits the same continuous time independent behavior as observed for the conventional continuous reactive sputtering process. Furthermore, it is shown that the distribution width of the transit times for sputtered atoms by far exceeds the period time for pulsed DC frequencies higher than 5–10 kHz. This causes a large overlap between sputter eroded material between consecutive pulses during processing resulting in an essentially continuous arrival rate of sputtered atoms to the substrate surface. This implies also that the deposition rate will be constant and will not follow the pulsed sputter erosion variation from the target. These findings show that, with respect to film stoichiometry and homogeneity, the high frequency pulsed DC reactive sputtering process behaves identically as the continuous reactive sputtering process. No chemical reaction effects or gas gettering variations will follow the periodicity of the pulsed DC power supply at high frequencies.