Reactive Gas Partial Pressure Research Articles

Investigation of zirconium oxynitride thin films deposited by reactive pulsed magnetron sputtering

Zirconium oxynitride films were deposited onto glass and Si (1 0 0) substrates at room temperature by pulsed reactive dc magnetron sputtering of a metallic Zr target in an Ar/O2/N2 atmosphere. The structural, compositional and optical properties of the deposited films were found to depend on the ratio of nitrogen partial pressure to the total reactive gas partial pressure. Morphology investigation by atomic force microscopy showed that most of the zirconium oxynitride coatings have smooth surfaces (average roughness 2.5 nm). X-ray diffraction measurements revealed a change from the monoclinic zirconium oxide phase to the orthorhombic, and then a change to the cubic zirconium nitride phase upon changing the nitrogen content in the films. Optical properties of zirconium oxynitride films were analysed by a spectrophotometer and computer simulations. The calculated refractive index of transparent and semi-transparent films was found to be in the range 2.05–4.73 (at 650 nm). The optical band gap changed from 3.67 to 1.59 eV with changing nitrogen content. This study allows the elaboration process optimization and then the control of the film composition and properties, which is very interesting for a technological transfer.

Effect of O<sub>2</sub> Partial Pressure on Magnetic Properties of Alloys CoFe-Rich Nanocrystalline Thin Films

Alloys of CoFe-rich magnetic films are well known as typical soft magnetic alloys. They are used for many kinds of electric and electronic parts such as magnetic recording heads, transformers and inductors. In order to get superior soft magnetic properties of the CoFe-based nanocrystalline thin films, the effect of O2 partial pressure on magnetic properties of Co-Fe-Hf-O nanocrystalline thin films have been investigated. It is found that the soft magnetic properties and electrical property of these films show a dependence on the partial pressure of reactive gases, which presumably changes the microstructure of the films and related magnetic anisotropy. With optimal conditions, thin film exhibit excellent soft magnetic properties: saturation magnetization (4πMs) of 21 kG, magnetic coercivity (Hc) of 0.18 Oe, anisotropy field (Hk) of 49 Oe, and an electrical property is also shown to be as high as 300 μcm. The combination of high 4πMs and relatively high Hk in these films are believed to be partly responsible for the excellent ultra-high-frequency behavior

Magnetron sputtering process control by medium-frequency power supply parameter

In this paper, the influence of the sputtering technology (reactive gas partial pressure, magnetic field intensity) on the power supply parameters has been investigated. The reactive sputtering of aluminium target in Ar + O 2 atmosphere has been used as an example. The experiments have shown that the formation of the Al 2O 3 layers can be observed by the parameter of the power supply. It allowed estimating the point at which the sputtered material surface was poisoned by the reactive compound i.e. distinguishing magnetron sputtering modes.

Modelling of Magnetron Sputtering of Tungsten Oxide with Reactive Gas Pulsing

Reactive sputtering is one of the most commonly employed processes for the deposition of thin films. However, the range of applications is limited by inherent instabilities, which necessitates the use of a complex feedback control of reactive gas (RG) partial pressure. Recently pulsing of the RG has been suggested as a possible alternative. In this report, the concept of periodically switching the RG flow between two different values is applied to the deposition of tungsten oxide. The trends in the measured time dependent RG pressure and discharge voltage are reproduced by a dynamical model developed for this process. Furthermore, the model predicts the compositional depth profile of the deposited film reasonably well, and in particular helps to understand the formation of the interfaces in the resulting multi-layer film.

Effect of partial pressure of reactive gas on chromium nitride and chromium oxide deposited by arc ion plating

The effects of reactive gas partial pressure on droplet formation, deposition rate and change of preferred orientation of CrN and Cr 2O 3 coatings were studied. For CrN coatings, as nitrogen partial pressure increases, the number and size of droplets increases, the deposition rate initially increases obviously and then slowly, and the preferred orientation of CrN changes from high-index plane to low-index one. For Cr 2O 3 coatings, with the increase of oxygen partial pressure, the number and size of droplets decreases, the deposition rate decreases and the (300) becomes the preferred orientation. These differences are ascribed to the formation of CrN (with a lower melting point) and Cr 2O 3 (with a higher melting point) on the surface of Cr target during the deposition of CrN and Cr 2O 3. Complete coatings CrN or Cr 2O 3 film can be formed when reactive gas partial pressure gets up to 0.1 Pa. The optimized N 2 partial pressure for CrN deposition is about 0.1–0.2 Pa in order to suppress the formation of droplets and the suitable O 2 partial pressure for Cr 2O 3 deposition is approximately 0.1 Pa for the attempt to prevent the peel of the coating.

Process stabilisation for large area reactive MF-sputtering of Al-doped ZnO

A control system for improving the homogeneity of transparent conductive oxide films deposited by reactive magnetron sputtering has been set up for large area in-line coating. The control system monitors operating points along the target axis by measuring the reactive gas partial pressure and a closed loop control of power and gas inlet maintains a user-defined partial pressure distribution. A deviation from set points and switching of local target states into metallic or oxide mode is prevented. As a result, the film properties such as sheet resistance, optical performance and film thickness show an improved homogeneity along the target axis.

Energy-resolved mass spectroscopy studies during the deposition of TiC films by ion plating under different magnetic fields

The energy-resolved mass spectroscopy studies during the discharge in an Ar+C 2H 2 gas mixture in a triode ion-plating system revealed two different working regions. At strong magnetic fields ( I c⩾15 A, B⩾7 mT), the spectra show a high degree of Ti ionisation accompanied by almost complete acetylene dissociation. The main ionised species besides Ar + are Ti +, Ti 2+, H 1 - 3 + , ArH + and 12C +. The intensity of hydrocarbon ions CH 1 - 5 + and C 2 H 1 - 5 + is very low. At weak magnetic fields ( I c<12.5 A, B < 5.8 mT ), the evaporation (and consequently ionisation) of Ti is low, but the plasma is rich in hydrocarbon radicals. The most intense of them is the parent ion C 2 H 2 + followed by C +, CH 3 + and C 2 H 3 + ions. Carefully adjusting the magnetic field, arc current and partial pressure of reactive gases, different plasmas rich in Ti ions or different hydrocarbon ions and even pure carbon ions can be obtained.

Modeling analysis of gradient-index coatings prepared by reactive magnetron sputtering

The formation mechanism of gradient-index coatings by reactive magnetron sputtering is discussed. A practical modeling of gradient-index coatings is propose d, the relationship between refractive index of coatings and pressure of reactiv e gas is established. Next, we discussed the changing rule of partial-pressure o f reactive gas with time requivcd for obtaining a desired refractive index of g radient coatings under specific deposition conditions. A linear coating is tak en as example to illustrate how to get the relationship between partial-pressure of reactive gas and time.

Reactive magnetron sputtering of copper, silver, and gold

Copper, silver, and gold targets were sputtered in various reactive gas mixtures (Ar–N2, Ar–O2, and Ar–CH4) to compare the reactivity of noble metal atoms during the sputtering process. The evolution of the film's growth rate and the variation of the reactive gas partial pressure vs. the reactive gas flow rate were investigated for each kind of metal. The structure of the deposited films was characterised by X-ray diffraction. Electrical resistivity of the coatings was determined at room temperature. The optical band gap of oxides and nitrides films were deduced from UV–visible transmission measurements. The reactive sputtering of copper target leads to the synthesis of Cu3N, Cu2O, Cu4O3, or CuO films. No copper carbide films were deposited. Depending on the methane flow rate, Cu/C films were either nanocomposite coatings (nc-Cu/a-C:H) or amorphous. Silver oxide (Ag2O) films were formed by reactive sputtering of a silver target in Ar–O2 mixtures. On the other hand, the reactive sputtering method did not allow the synthesis of silver nitride nor gold oxide films.

Characterisation of chromium nitride films produced by PVD techniques

Chromium nitride thin films have been deposited on stainless steel substrates by r.f. reactive magnetron sputtering. The influence of process parameters such as substrate bias and partial pressure of reactive gas have been investigated. The characterisation of the coatings was performed by X-ray diffraction (XRD), Raman Spectroscopy (RS) and nano-indentation experiments. These studies allow to analyse the influence of deposition parameters in crystal phases, crystal orientation/texture and crystallite size. The relationship between structural defects and their characteristics with deposition conditions will also be taken into account. The presence of oxygen on the coatings surface, due to atmospheric contamination, is analysed by means of Raman spectroscopy. This optical technique can be used for the characterisation of the surface oxides at different stages of oxidation. The changes observed in Raman spectra can be correlated with process parameters. Coatings produced with an unbiased substrate showed higher tendency to surface oxidation. Increasing the nitrogen partial pressure in the working atmosphere produces changes from a hexagonal Cr 2N to cubic CrN microstructure. The strain in CrN crystals increases with nitrogen content in working atmosphere. When the Cr 2N phase is dominant the hardness has a relative maximum (42.2 GPa), but the highest hardness was obtained for a coating with dominant CrN phase produced with highest nitrogen flow (44.9 GPa).

Modeling the stability of reactive sputtering processes

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.

Stabilization of high-deposition-rate reactive magnetron sputtering of oxides by in situ spectroscopic ellipsometry and plasma diagnostics

A control system for stabilizing the reactive magnetron-sputter process is applied that is based on a combination of a short-term stabilization of the plasma and a long-term stabilization employing an in situ spectroscopic ellipsometer. For the formation of niobium pentoxide, a measurement of the reactive gas partial pressure with a λ-probe measurement was employed. It turns out that the specific deposition rate, i.e., deposition rate divided by the power density, is a suitable control parameter. Compared to the oxide mode, the deposition rate of niobium pentoxide films deposited in the transition mode could be enlarged by a factor of more than 4. The films were grown at different process parameters (oxygen partial pressure, target power, absolute pressure, midfrequency and dc technique) onto unheated substrates. In situ spectroscopic ellipsometry and ex situ spectroscopic ellipsometry at different angles of incidence and scanning electron microscopy investigations were applied to study the optical properties and the morphology of the films.

Kinetics of oxychlorination of magnesium oxide

The kinetics of oxychlorination of MgO by Cl2 + O2 were studied in the temperature range from 850 °C to 1025 °C, using thermogravimetric analysis (TGA). The effects of Cl2/O2 ratio, gas velocity, temperature, and partial pressure of reactive gases on the reaction rate were investigated. The oxychlorination process was characterized by an apparent activation energy of about 214 kJ/mol. The reaction orders with respect to O2, Cl2, and Cl2 + O2 at 950 °C were about −0.37, 0.98, and 0.65, respectively. Data concerning oxychlorination of MgO, Cr2O3, and MgCr2O4 contained in chromite were compared. The effectiveness of using oxychlorination to extract iron oxides contained in magnesia was demonstrated.

Electronic states and mechanical properties in transition metal nitrides

Abstract Thin films of hard materials are of prime importance for wear-resistant, protective and decorative coatings. Besides adhesion, hardness is the most often quoted requirement, even if doubts remain on the experimental determination of the hardness values of thin films, on their theoretical interpretation and on their significance for wear protection. Transition metal interstitial compounds are extensively used because of their broad range of functional properties in the fields of machining, microelectronics, decoration, etc. This article presents a summary of recent relevant results on the structural, mechanical, electronic and optical properties of fcc TiN, VN, CrN, NbN, W2N, hexagonal MoN, and some ternary nitrides in the form of sputtered thin films. The process parameters, e.g. the reactive gas partial pressure and the substrate bias, strongly influence the film properties. The composition and growth parameters influence the morphology, the stress state and other physical properties. The systematic investigation of the electronic density of states in valence and core states of comparable nitrides provides indications of the degree of covalency in the chemical bonding in relation to properties such as cohesive energy and hardness. For example, in molybdenum nitride the low stability of the cubic MoN phase is related to an increase in the charge transfer of Mo d electrons to nitrogen with increasing stoichiometric ratio N/Mo. Ellipsometric measurements of the dielectric function interpreted in relation to details of the band structure measure the variation of the density of conduction electrons. Vacancies and interstitials remove or add a specific number of electrons at the Fermi level. This analysis allows one to differentiate the types of defect at various compositions in, for example, TiNY films, for which the reported hardness values spread over a wide range.

Influence of the target temperature on a reactive sputtering process

Reactive magnetron sputtering often presents an unstable sputtering mode preventing high rate deposition of stoichiometric ceramic films, the origin of which is mainly due to the avalanche-like target poisoning over a critical reactive gas partial pressure. In this paper, the effect of the target temperature is investigated for titanium targets sputtered in Ar–N2 or Ar–O2 reactive discharges. Paradoxically, raising the target temperature yields a stabilisation of the transition sputtering mode close to the elemental sputtering mode. With a discharge current modulated at low frequency, the stabilisation is complete for titanium sputtered in Ar–N2 discharges.

Modelling of reactive sputtering processes involving two separated metallic targets

Abstract 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.

The effects of the process parameters on the electrical and microstructure characteristics of the CrSi thin resistor films: part I

The effects of process parameters, such as target composition, sputtering pressure, reactive gas partial pressure, deposition rate, and anneal temperature, on the electrical and microstructure characteristics of CrSi thin resistor films in very large scale integrated circuits (VLSI) application were investigated in this paper. It was observed that the higher metallic target composition, lower deposition rate, lower nitrogen partial pressure, and higher anneal temperature shift the temperature coefficient of resistance (TCR) to the positive direction. The relationships between TCR and anneal temperature, TCR and nitrogen partial pressure, and TCR and anneal environment were studied. Transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were conducted to explore the microstructure of the films; and the in situ anneal TEM analysis was performed to study the change of the microstructure of the films during anneal. The TEM images show that CrSi films from sputtering have typical cermet film microstructure which consists of darker ‘island’ regions embedded in lighter ‘boundary medium’ regions. When the anneal temperature is lower than 700°C, the microstructure remains largely unchanged as the temperature increases. At 700°C, the diffraction pattern from the pure Ar sputtered sample indicates that a change is occurring at 700°C. No such change was observed in the reactive sputtered sample at the same temperature.

Theoretical Investigations of the Multitarget Reactive Sputtering Process: Application to the Titanium - Chromium - Oxygen System

A theoretical development is proposed in order to predict general behaviours of the reactive sputtering process implementing two metallic targets in a reactive atmosphere. From simple physical assumptions, the proposed model is capable of describing some relationships between most parameters in the whole processing region. Therefore, the evolution of the reactive gas partial pressure and sputtering rate from each target with the reactive gas flow rate have been calculated. Theoretical results have been compared with experimental measurements obtained for the titanium - chromium - oxygen system. It is pointed out that the developed model agrees satisfactorily with practical results regarding reactive gas pressure but does not allow to expect the state and the poisoning chronology of each target.

Computer modeling as a tool to predict deposition rate and film composition in the reactive sputtering process

Reactive sputtering is a widely used technique to deposit oxides, nitrides, etc. A serious drawback of this technique, however, is the drastic decrease in deposition rate that almost always occurs when depositing compound films as compared to depositing pure metal film. In many cases it is possible to overcome this problem by operating the process in the narrow critical processing region between metallic and compound mode sputtering. In this processing region, however, the composition of the deposited compound thin film is extremely sensitive to the processing conditions. It is, therefore, very interesting to investigate the sensitivity of different processing parameters on the overall processing behavior. Computer modeling can be used as a tool to increase the understanding of this complex process. We will show that such results can be used to illustrate the individual effects of the major involved processing parameters. It also serves to assist in the work of process optimization. The relationship between target poisoning, argon current density, deposition rate, reactive gas supply, partial pressure, total pressure, and film composition have been carefully examined. In particular, we will point out a serious limitation that may arise during high rate multielement reactive sputter deposition. The effect of different reactivity of the involved elements may cause that one of the elements during deposition will not be fully oxidized.

Direct current magnetron sputtered W–AlN cermet solar absorber films

W–AlN cermet selective surfaces have been investigated using a special direct current (dc) magnetron sputtering technology. During the deposition of the W–AlN cermet layer, both Al and W targets were run simultaneously in a gas mixture of argon and nitrogen. The total sputtering gas pressure was 1 Pa and the reactive nitrogen gas partial pressure was chosen at 2.5×10−2 Pa, which is beyond the transition point from metal phase to dielectric phase in the deposited material. The ceramic AlN component was deposited by dc reactive sputtering and the metallic W component by dc sputtering due to the excellent nitriding resistance of metallic tungsten. By substrate movement a multi-sublayer system, consisting of alternating W and AlN sublayers, was deposited. This deposited multi-sublayer system can be considered as a macro-homogeneous W–AlN cermet layer with metal volume fraction determined by controlling the thickness of the sublayers. W–AlN cermet selective surfaces with a double cermet layer film structure were deposited. The typical film structure from surface to bottom substrate is an AlN anti-reflection layer on a double W–AlN cermet layer on an Al metal infrared reflection layer. A solar absorptance of 0.92–0.94 with emittance of 0.03–0.05 at room temperature and 0.08–0.10 at 350°C has been achieved for such W–AlN cermet selective surfaces. The W–AlN cermet has excellent thermal stability in vacuum at high operating temperature.