Constant Ar Flow Research Articles

Influence of O2 flow rate on the characteristics of TiO2 thin films deposited by RF reactive sputtering

Titanium dioxide (TiO2) thin films were prepared by radio-frequency (13.56 MHz) reactive sputtering onto glass substrate with different oxygen flow rates while maintaining a constant Ar flow rate. The structural and optical properties of these films were studied with variation in O2 flow rate. X-ray diffraction (XRD) analysis of these films reveals the presence of anatase and rutile phases. The lattice parameters and crystallite size were evaluated from XRD patterns. The optical properties of these films were correlated with their morphological nature. Field emission scanning electron microscopy (FESEM) results show a dense granular morphology and the particle size is found to decrease with increase in oxygen flow rate. The average optical transmittance was observed to be 96% for all the films. The room temperature photoluminescence (PL) spectroscopy revealed a blue shift of the near band edge emission as the oxygen flow rate is increased and defect related emissions is shifted towards red region.

Effect of O2 flow rate on the characteristics of ZnO thin films deposited by RF reactive magnetron sputtering

ABSTRACTZnO thin films were deposited on glass substrates by radio-frequency (RF) reactive sputtering under different O2 flow rates, with constant Ar flow rate (50sccm). The dependence of O2 flow rate on structural and optical properties of deposited ZnO films were studied comprehensively. From X-ray diffraction (XRD) data, the microstructural parameters such as lattice constant, average crystallite size and stress were estimated and correlated with the morphology and optical properties of the deposited ZnO films. Field emission scanning electron microscopy (FESEM) results reveal that, the deposited ZnO thin films have spherical shaped crystallites and their size decreases with increasing O2 flow rate. The optical properties were studied by UV-Vis transmission and photoluminescence (PL) spectroscopy. The room temperature PL study shows a near band edge emission (NBE), which exhibits a blue shift from 393 nm to 378 nm with increase in O2 flow rate, and defect related emission peaks in the visible region.

The correlation of γ-irradiation, particle size and their effects on physical properties of AgInSe2 nanostructure thin films

In this work the effect of γ-irradiation on the optical and electrical properties of near stoichiometric AgInSe2 nanostructure thin films have been characterized. The XRD pattern of ingot AgInSe2 powder prepared by solid state reaction showed tetragonal polycrystalline single-phase structure. The thin films of thickness 75nm were prepared by inert gas condensation (IGC) technique at using constant Ar flow and substrate temperature of 300K.Thin films were exposed to annealing process at 473K for 2h in vacuum of 10−2Torr. The amorphous and tetragonal nanocrystalline structures were detected for as-deposited and annealed films respectively by grazing incident in-plane X-ray diffraction (GIIXD) technique. The structure and average particle size of annealed irradiated films by different γ-doses from 0 to 4Mrad were determined using high resolution transmission electron microscope (HRTEM). Optical transmission, reflection and absorption spectra were studied for both annealed unirradiated and irradiated films. Two optical transitions for each annealed unirradiated and film exposed to γ-irradiation doses from 0 to 4Mrad were observed. The evaluated Eg1 due to 1st transition have decreased from 1.52 to 1.44eV and Eg2 due to 2nd transition have decreased from 2.83 to 2.30eV as the particle size increased from 7.3 to 9.5nm by raising the irradiation dose up to 1Mrad. The behavior of d.c. electrical conductivity with temperature that measured under vacuum was examined for all films under investigation. The evaluated activation energies due to irradiation doses are ranging from 0.58 to 0.68eV.

Surface modifications on as-grown boron doped CVD diamond films induced by the B2O3–ethanol–Ar system

The surface termination of as-grown microcrystalline (MCD) and nanocrystalline (NCD) boron-doped diamond films was assessed by X-ray photoelectron spectroscopy (XPS) and water contact angle techniques. The diamond coatings were grown on mirror-polished silicon nitride ceramic substrates using the hot-filament chemical vapor deposition (HFCVD) technique. The boron doping source, boron oxide (B2O3) diluted in ethanol, was dragged by a constant Ar flow at different CH4/H2 gas ratios and system pressures. The electrical resistivity of these semiconducting diamond films was obtained and their surfaces were further characterized by scanning electron microscopy (SEM) and Raman spectroscopy.The results have shown that the increasing total pressure particularly affects the crystal size of the boron doped MCD samples by enhancing diamond renucleation due to the higher residence time of Ar. Also, both as-grown MCD and NCD surface types were found to be inherently hydrophobic, with contact angles ~90°C, but retain significant amounts of oxygen bonded to carbon atoms mainly as C–O–C and C=O terminations. Such partial diamond surface oxidation is the result of a very unique stable gas mixture containing hydrogen, carbon and oxygen, when boron oxide and ethanol are added to methane during the CVD process.

On the formation of nanocomposite TiC/a-C:H coatings by the method of the magnetron sputtering of Ti in an electron-beam activated Ar/C2H2 mixture

Composite TiC/a-C:H coatings with a thickness of 5 μm are produced by the reactive magnetron sputtering of titanium in an Ar/C2H2 gas mixture, which was additionally irradiated by a wide electron beam with an energy of 100 eV and an electric current of up to 1 A. The composition of the coatings is controlled by changing the C2H2 flow rate in the range from 1 to 16 mL/min under a constant Ar flow rate (40 mL/min) and magnetron current (2 A, 10 μs, 50 kHz). X-ray diffraction (XRD) investigations and high resolution transmission electron microscopy (HRTEM) methods confirm the formation of nanostructured coatings with a thickness of 4 to 9 nm. The hardness of the coatings nonmonotonically depends on the acetylene-flow rate. A maximum microhardness of 30 GPa is obtained when the atomic concentration of titanium in the coating determined by the Auger spectroscopy method is close to 38%. It is established that the electron-beam irradiation of a gas mixture during the deposition of coatings promotes the accelerated decomposition of acetylene and leads to a multiple (from 10 to 2 mL/min) decrease in the C2H2 flow rate, at which the maximum microhardness of coatings is reached.

Effect of hydrogen addition on the residual stress of B–C–N films with cubic boron nitride phase prepared by r.f. magnetron sputtering of a B4C target

The effect of hydrogen on the compressive residual stress of B–C–N films composed of amorphous B4C, hexagonal boron nitride (hBN), and cubic boron nitride (cBN) phases has been investigated. The films were basically deposited on silicon (100) substrates by sputtering of a B4C target with a gas mixture of Ar (25sccm), N2 (5sccm), and H2 (0–5sccm) at a chamber pressure of 0.27Pa. To improve the adhesive strength of the films, a compositional gradient B–C–N buffer layer, which was prepared by step-wise deposition with an increasing nitrogen flow rate from 0sccm to 4.5sccm in Ar/N2 mixed gas with a constant Ar flow rate of 25sccm, was adopted before the nucleation stage of the cBN phase. Up to 5sccm hydrogen was added to the Ar/N2 reactive gas after the deposition of the B4C layer with pure Ar gas. For all deposition conditions, hBN and cBN phases were observed to form in the B–C–N films. The cBN fraction in these films remained around 65%, irrespective of the amount of hydrogen added. However, the compressive stress of the B–C–N films was observed to rapidly decrease from 9.5GPa to 4.2GPa, with increasing the hydrogen flow from 0sccm up to 5sccm. The stress reduction is discussed in terms of the relation between the penetration probabilities of hydrogen and argon ions into the films, which was the main origin of the compressive residual stress of the compositional gradient B–C–N layer with hBN structure.

Synthesis and tailoring of GaN nanocrystals at room temperature by RF magnetron sputtering

We report here the synthesis of hexagonal GaN nanocrystals on p-silicon substrates by Radio-Frequency (RF) magnetron sputtering without substrate heating or by post-deposition annealing treatment. GaN nanocrystals are synthesized and tailored as a function of RF power at constant Ar and N2 flow rates (working pressure). The observed reduction in grain sizes as a function of RF power has been correlated with an increase in compressive strain. The effect of RF power on crystallite orientation has been determined by diffraction intensities using the degree of c-axis orientation. Atomic force microscopy shows uniform lateral nanocrystal sizes with spherical in shape by insignificant difference in Root-Mean-Square (RMS) roughness values for all the deposited thin films. Transmission electron microscope and field emission-scanning electron microscope studies have been performed to understand the surface morphologies and grain sizes. Thus, tailoring the size of the nanocrystals has been discussed by correlating RF powers, working pressures and cathode voltages on lattice vibrations.

Analysis of gaseous reaction products of wet chemical silicon etching by conventional direct current glow discharge optical emission spectrometry (DC-GD-OES)

Major parts of the mechanism of the wet chemical etching of Si using mixtures of nitric and hydrofluoric acid are still in question. One of them is the issue about the formation of H and its relevance in the oxidation of Si. In the present work H evolution during acid etching of Si was estimated as a function of the HF/HNO3 mixing ratio and the temperature. A commercial GD-OES instrument with an unchanged Grimm type glow discharge chamber was used to determine the amount of formed H. A small fraction of the reaction gases, originated by etching of Si in a PTFE apparatus under Ar atmosphere, was fed by a constant Ar flow via a drying column into the discharge chamber. The gases were excited by the plasma of a continuously DC sputtered Fe sample. Numerous elements like Si, N, O, H, and even B from the B-doped Si were detected. However, only the H emissions at 121.5 nm and 656.3 nm were used for the estimation of the released H. The obtained results show that H is preferentially generated in HNO3-poor etch solutions (HNO3 < 40% (v/v)). In the range from −10 to 35 °C the temperature of the etch solution shows a negligible influence on the H generation, but affects the amount of nitrous gases. This indicates that particularly in HNO3-poor etch solutions the oxidation of Si proceeds to a considerable extent via the formation of H parallel to the already known pathway via the reduction of HNO3.

Correlation of plasma characteristics to etch rate and via sidewall angle in a deep reactive ion etch system using Langmuir probe and optical emission spectroscopy

A Langmuir probe and optical emission spectroscopy were used in a deep reactive ion etch system to correlate plasma parameters (atomic fluorine and argon emission, electron density, ion density, and electron average energy) with the etch rate and via sidewall angle. All data were obtained for coil powers ranging from 200 to 800 W, platen powers ranging from 7 to 16 W, and pressure ranging from 3.8 to 62 mTorr with constant SF6 and Ar flow rates of 112 and 18 SCCM (SCCM denotes cubic centimeter per minute at STP), respectively. Results indicate that there is a correlation with etch rate for all plasma parameters except for argon emission. For argon emission, the etch rate exhibits a double-valued relation where the etch rate can either increase or decrease with increasing argon emission intensity due to changes in pressure which affect the energy coupling efficiency. As expected, the etch rate increases for measured increases in fluorine emission, electron density, and ion density. The etch rate, however, decreases with increasing average electron energy due to collision processes. In contrast, no correlation is observed between any of the measured plasma parameters with sidewall angle. The last result is consistent with the idea that sidewall angle is primarily controlled by the passivation cycle as opposed to the etching cycle, where all the authors’ data were obtained.

Spatial characterization of pressure-based plasma regimes in a radiofrequency glow discharge by using optical emission spectroscopy

A new experimental set-up has been developed in order to perform spatially resolved measurements of the optical emission in a radiofrequency glow discharge (rf-GD). The emitted radiation is not only detected through an end-on window (as usually done in commercial GD-OES instruments), but the emission along the plasma plume is also measured axially-resolved by side-on measurements. The GD source is a modified Grimm-type source and follows a previous configuration designed for analytical applications in glow discharge coupled to mass spectrometry (GD-MS) instruments. Depending on the argon flow rate and pressure, and for a pure copper sample, two different plasma regimes have been observed and characterized by analyzing the spatial distribution of different excited species present in the plasma. Keeping a constant Ar flow rate, pressures higher than a certain value lead to enhanced Cu (analyte) emission (green regime) while at lower pressures a violet plasma is observed. In the violet regime, the spatial extension of Cu and Ar excited species along the plasma axis is found to be broader.

Deposition and Characterization of Hard Coatings in the Material System V–Al–N by Reactive Magnetron Sputter Deposition

AbstractBinary and ternary hard coatings in the system V–Al–N were deposited with varying substrate bias at substrate temperatures around 350 °C by reactive d.c. and r.f. magnetron sputtering in an Ar/N2 gas mixture from a V and/or Al target. For each experiment, Si (100) and polished 1.2379 steel substrates were placed on the rotating substrate table. VN coatings were deposited at a constant Ar flow of 250 sccm, while the bias voltage was varied between −80 and −200 V. The influence of this variation on the mechanical properties hardness and reduced elastic modulus was examined by microindentation and the critical load of failure by scratch test, friction coefficient was determined by ball‐on‐disc tribometer tests. For the deposition of AlN and VAlN coatings bias voltage, Ar/N ratio and the total pressure were varied. The chemical composition of the obtained coatings was determined by electron microprobe analysis and the crystal structure of the films was characterized by X‐ray diffraction.

An Iron Catalytic Probe for Determination of the O-atom Density in an Ar/O2 Afterglow

An iron fiber optics catalytic probe has been constructed and applied for the real-time measuring of the O-atom density in an Ar/O2 afterglow. The recombination coefficient for the heterogeneous surface recombination of O atoms on the oxidized iron foil was measured at different temperatures between 400 and 950 K. The coefficient was found to be constant in the entire range of experimental conditions and had a value of 0.41 ± 0.12. The iron fiber optics catalytic probe has an advantage over the classical nickel fiber optics catalytic probe: the probe signal is higher for the iron probe due to a higher recombination coefficient thus causing an easier real-time monitoring of the O-atom density. The O-atom density was measured in an afterglow of microwave plasma created at different discharge powers up to 300 W, at a constant Ar flow rate of 1000 sccm/min and at different oxygen flow rates between 50 and 300 sccm/min. The O-atom density was found to be dependent on oxygen flow. At low oxygen flow rates up to 100 sccm/min, a saturation of the O-atom density was obtained at a certain discharge power, while at high oxygen flow rate the O-atom density kept increasing with the increasing power. The results were explained by gas phase and surface phenomena.

Improved Etched Surface Morphology in Electron Cyclotron Resonance-Reactive Ion Etching of GaN by Cyclic Injection of CH4/H2/Ar and O2 with Constant Ar Flow

Electron cyclotron resonance reactive ion etching (ECR-RIE) conditions for GaN using CH4/H2/Ar are investigated. GaN can be etched even with continuous etching using CH4/H2/Ar when Ar gas of a higher flow rate is introduced, but only rough etched surfaces are obtained. A cyclic injection method using CH4/H2/Ar etching gas and O2 ashing with constant Ar flow is introduced for GaN etching for the first time, and a rather high etch rate and very smooth etched surfaces are successfully obtained. The cyclic injection of CH4/H2 and O2 prevents deposition of carbon polymers by oxygen plasma, and constant Ar flow removes the surface oxidized layer formed during the O2 ashing by Ar+ ion etching. Under the optimized etching condition, an etch rate of 34 nm/min and a good morphology of etched surfaces (rms of less than 1.0 nm) are obtained.

Characterization of hydrogen plasma with a fiber optics catalytic probe

The most important parameter in reactive hydrogen plasma is the density of neutral hydrogen atoms. The density can be measured by different means including a variety of optical emission and absorption spectroscopy methods, titration and catalytic probes. Recently, it was shown that catalytic probes have some advantages over the other methods. The main advantage is the ability for real time measurement of the atom density. A catalytic probe was used to measure the H density in an afterglow of a plasma reactor. Plasma was created in a mixture of argon and hydrogen. At a constant H2 and Ar flow rates, the H density was found to increase with increasing power. At a low concentration of hydrogen in the gas mixture, saturation in the H density was observed. The lower the hydrogen concentration the lower the power at which the saturation was observed. At high hydrogen concentrations, no H saturation was observed. The results were explained with collision phenomena in ionized gases and heterogeneous recombination of H atoms on surfaces.

Influence of O 2 flow rate on the structural properties of MgO films deposited by dual magnetron sputtering

MgO films were deposited by a mid frequency dual magnetron reactive sputtering system composed of two identical magnetrons and powered by a sinusoidal generator. Atomic force microscopy, scanning electron microscopy, X-ray diffraction, and a diode discharge device were used to characterize surface morphology, crystalline structure, and secondary electron emission ( γ) coefficient of the films, respectively. The influence of O 2 flow rate with a constant Ar flow rate of 120 sccm on the structure and properties of the films was systematically studied. As the O 2 flow rate is increased from 5 to 14 sccm, the intensity ratio of the (111) to (200) peak of cubic MgO phase increases significantly, leading to a change of the film texture from a combined (100) and (111) preferred orientation to a highly (111) preferred orientation. The (111) peak center shifts to a larger angle, and the full width at half maximum of the (111) peak decreases greatly, indicating a considerable decrease of defect density in the films. The increases in the relative intensity of the (111) peak and the decrease in the defect density in the films contribute to a remarkable increase in the γ coefficient of the films. Furthermore increase of O 2 flow rate results in no significant change in the crystalline structures and the γ coefficient of the MgO films.

Electron Cyclotron Resonance-Reactive Ion Etching of III-V Semiconductors by Cyclic Injection of CH4/H2/Ar and O2 with Constant Ar Flow

Electron cyclotron resonance-reactive ion etching (ECR-RIE) is very useful for fabricating semiconductor photonic devices and integrated circuits (PICs). The mixture gas of CH4/H2 is used for etching III-V semiconductors, but the carbon polymer film deposited on the surface during the etching process presents some problems. Thus, the polymer film must be ashed off using an O2 plasma. We introduced the cyclic injection of CH4/H2/Ar and O2 to ECR-RIE, and demonstrated that it was very useful for etching of InP. However, compound semiconductors containing Al (e.g., AlGaAs and InAlAs) react with oxygen and an alumina layer is formed, which cannot be etched by CH4/H2 etching. Therefore, we used a new cyclic etching process with constant Ar flow in the chamber to remove this alumina layer by Ar ion etching, and obtained good results for etching rate and surface morphology for the compound semiconductors containing Al. We also proposed a suitable combination of three cyclic etching procedures (continuous etching, cyclic etching without constant Ar flow and cyclic etching with constant Ar flow) for etching the multilayer heterostructure of III-V semiconductors including InP and/or compound semiconductors containing Al.

Room Temperature Deposition of Silicon Oxynitride Films with Low Stress Using Sputtering-Type Electron Cyclotron Resonance Plasmas

AbstractSilicon oxynitride (SiOxNy) films with low stress were deposited successfully at room temperature using sputtering-type electron cyclotron resonance (ECR) plasmas. Films were deposited for a wide range of flow rate ratio of O2 to N2 at a constant Ar flow rate. Film properties were verified by characterizations of refractive index (ellipsometry), structural properties (Fourier transform infrared and Auger electron spectroscopy), intrinsic stress, and barrier strength of water penetration (thermal desorption spectroscopy). A near-stoichiometric SiOxNy (x = 1.44 and y = 0.41) film with low stress could be formed at the optimum deposition condition, under which the SiOxNy film had a refractive index of 1.54. The results of thermal desorption spectroscopy measurements showed that the SiOx Ny film had a higher barrier against moisture penetration relative to deposited SiOx and SiNy films. The SiOxNy film was directly deposited on the organic EL device and the applicability was shown clearly. These results indicate that this SiOxNy film deposited using a sputtering-type ECR plasma has the potential to be utilized as a passivation layer of organic EL devices, which are required to be formed at low temperature.

In situ FT-IR reflective absorption spectroscopy for characterization of SiO 2 thin films deposited using sputtering-type electron cyclotron resonance microwave plasma

Plasma conditions for depositing high quality SiO 2 thin films using a sputtering-type ECR (electron cyclotron resonance) method have been investigated. Film properties have been studied as a function of an oxygen flow rate, F O 2 , in the range 2–8 sccm with a constant Ar flow rate of 16 sccm. Dielectric breakdown characteristics have been investigated by ramp I- V measurements, indicating that the film prepared with F O 2 = 8 sccm to the thickness of 412 Å have a good dielectric breakdown field of 8–10 MV/cm. The deposited films were characterized in terms of refractive index and IR (infra-red) properties using FT-IRRAS (Fourier transform infrared reflective absorption spectroscopy) and ellipsometry. The refractive index of films deposited with more than F O 2 = 3 sccm is close to 1.46 which indicates that the films prepared in this range are approximately stoichiometric. In addition, quantitative analysis of the dominant IR (infra-red) mode shows that the peak frequency and FWHM (full width at half-maximum) of a TO (transverse optical phonon) mode for films prepared with more than F O 2 = 6 sccm are comparable with thermally grown SiO 2, i.e. v = 1075 cm −1 and FWHM = 70 cm −1. These observations indicate the optimum operating condition of the sputtering-type ECR apparatus, at which it can produce high quality films for MOS (metal-oxide semiconductor) device manufacture without the need for substrate heating.

A study of film growth and tribological characterization of nanostructured C-N/TiN X multilayer coatings

Coatings of C-N/TiN X composite multilayers, where X ≤ 1 in the nanometer range, have been deposited in a reactive sputtering system with side-by-side cathodes of titanium and carbon. Coatings were deposited on samples of tungsten carbide, and high-speed steel on a substrate holder rotating with variable speed from 2 to 28 rpm. Sputtering was performed in nitrogen/argon with a constant Ar flow of 25 sccm. The individual bilayer thicknesses were derived from the deposition rate and the rotation speed. Power for the Ti and C cathodes was kept constant at 1200 W. Deposition parameters were selected from curves showing total sputtering pressure and the voltages of the Ti and C sputtering cathodes versus the nitrogen gas flow. The acoustic emission scratch test developed for coating-adhesion measurements was used as a coarse test for coating evaluation. Particularly, the acoustic emission signal will be discussed and the friction coefficient for sliding against a Si 3N 4 ball in a ball-on-disk tribometer was measured, and showed a strong dependence on the deposition parameters.

Low-temperature deposition of high-quality silicon dioxide films by sputtering-type electron cyclotron resonance plasma

High-quality silicon dioxide films have been deposited at 130 °C by a sputtering technique using an electron cyclotron resonance microwave plasma. Film properties have been studied as a function of O2 flow rate in the range of 2–8 sccm with a constant Ar flow rate of 8 sccm when other plasma conditions were a microwave power of 700 W, and a radio frequency power of 700 W supplied to a target for sputtering. Dielectric breakdown characteristics have been investigated by ramp current–voltage measurements. Films deposited with an O2 flow rate of 5.3 sccm have a dielectric breakdown field of 10 MV/cm, which is close to that of thermally grown silicon dioxide film. The deposition rate was as high as 23 nm/min. Structural properties of films have also been characterized by ellipsometry and infrared absorption spectroscopy, showing that films with O2 flow rates above 4 sccm have near-stoichiometric composition.