RF Plasma Reactor Research Articles

Influence of RF Plasma Reactor Setup on Carboxylated Hydrocarbon Coatings

AbstractFunctional hydrocarbon plasma polymer coatings were investigated using a low pressure RF plasma reactor. The deposition rate was examined for different CO2/C2H4 gas ratios and different power inputs at constant pressure. The CO2/C2H4 ratio can be used to tailor the functionality and the permanence of the plasma polymer coatings which is shown by XPS. The deposition of these plasma polymer coatings was compared in a symmetrical and asymmetrical setup of the reactor and discussed regarding energy input and plasma sheath potential for the varying plasma conditions. Furthermore, the influence of Ar admixture was examined in order to identify sputtering conditions by using an asymmetric Ag electrode. While a drop in the absolute deposition rate can be seen for Ar added in symmetrical conditions, the asymmetrical setup showed no noticeable differences.magnified image

Microcrystalline silicon thin films: A review of physical properties

In this work we present a study of the optical, electrical, electronic and structural properties of Boron doped hydrogenated microcrystalline silicon thin films (μc-Si:H). The films were deposited in an RF plasma reactor using as reactive gas a mixture of silane and diborane, both highly diluted in hydrogen. The Boron concentration in the reactive gas was modified from 0 to 100ppm. The addition of Boron to the silicon films not only moves the Fermi energy level to the center of the gap, but also induces changes in all the physical properties. The Boron effect on structural and morphological properties was studied by X-ray diffraction and atomic force microscopy (AFM); the rugosity and grain size increased with the Boron concentration. The absorption coefficient measured by the constant photocurrent method (CPM) at low photon energies also showed an increase, which can be explained and correlated with an increase in the density of state (DOS) in the gap, due to Boron's bonding. At high temperatures (T>300K) the controlling transport mechanism is thermally activated; the curves conductivity log versus the inverse of temperature gives straight lines. The activation energy, measured from the valence band, decreases with Boron concentration, as expected, passing through a maximum, corresponding this point to the position of Fermi energy of an intrinsic film. At low temperatures (T<300K) the predominant transport mechanism was variable range hopping (VRH). The behavior of the charge hopping under different electrical fields was followed. Results showed that conductivity remained constant in a VRH regime only for a narrow range of electrical field.

Numerical modeling of dust particle configurations in a cylindrical radio-frequency plasma reactor

In the present work, first, plasma phase variables in a cylindrical radio-frequency (rf) plasma reactor are numerically solved using the local field approximation model. Then, equilibrium configurations of a few interacting (sub-)micron-sized dust particles are obtained by integrating the particles equations for their motion and charge, accounting for the various forces acting on each particle in a three-dimensional Lagrangian framework. Direct comparison of the results with experiment demonstrates excellent qualitative agreement. Based on the ion focus phenomenon, a physical model is formulated and proven successful in simulating the vertically aligned structures.

Comparison of composition of ultra-thin silicon oxynitride layers’ fabricated by PECVD and ultrashallow rf plasma ion implantation

In this paper differences in chemical composition of ultra-thin silicon oxynitride layers fabricated in planar rf plasma reactor are studied. The ultra-thin dielectric layers were obtained in the same reactor by two different methods: ultrashallow nitrogen implantation followed by plasma oxidation and plasma enhanced chemical vapour deposition (PECVD). Chemical composition of silicon oxynitride layers was investigated by means of X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The spectroscopic ellipsometry was used to determine both the thickness and refractive index of the obtained layers. The XPS measurements show considerable differences between the composition of the fabricated layers using each of the above mentioned methods. The SIMS analysis confirms XPS results and indicates differences in nitrogen distribution.

Characterisation of SiO xC yH z thin films deposited by low-temperature PECVD

SiO x C y H z thin films were deposited from hexamethyldisiloxane (HMDSO)/O 2 mixtures in a parallel plate, capacitively coupled, RF plasma reactor. Polyethylene terephthalate (PET), Si(1 0 0) wafers and KBr tablets were chosen as substrates. Effect of HMDSO/O 2 ratio, total treatment pressure and power input on the properties of the deposited films were investigated. The structure and bondings were studied by means of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Wettability characteristics of the deposited thin films were investigated by means of water droplet contact angle measurements. Surface morphology was investigated with atomic force microscopy. Barrier properties of the SiO x C y H z thin films were investigated by measuring the water vapour transmission rate of the coated PET substrates. Correlations between the characteristics of the deposited film and their barrier properties were discussed.

Plasma etching of organic material: Combined effects of charged and neutral species

A model organic material, namely the 36-n-alkane hexatriacontane, was etched in a dissymmetrical parallel plate RF plasma reactor and a dual distributed electron cyclotron resonance (DECR) plasma reactor, in different O2-Ar mixtures. A specific attention was paid to the role of the ion bombardment, especially when its effect is combined with the chemically active species created in an oxygen discharge. The discharge was monitored by optical emission spectroscopy (OES). The modifications induced by plasma treatment on the structure of the material were analysed by Fourier transform infrared spectroscopy (FTIR), steric exclusion chromatography (SEC) and composition analysis. We found that the ion bombardment has not only a sputtering effect but also enhances the reaction rate of the chemical species on the layer surface. It appears that plasma treatment leads to cross-linking and recombination with molecules from the room atmosphere.

Synthesis of SiO2 Nanoparticles in RF Plasma Reactors: Effect of Feed Rate and Quench Gas Injection

Nanoparticles of SiO2 have been produced in an inductively coupled thermal plasma reactor. The resulting nanoparticles were characterized based on their morphology and size distribution. Scanning electron microscopy, nitrogen absorption (BET method), laser diffractometry and X-ray diffraction techniques were used to characterize and to measure the equivalent diameter (D(1,0), D(3,2) and D(4,3)) of the resulting nanopowders. The computational fluid dynamics (CFD) software FluentTM 6.1 with the Fine Particle Model (FPMTM) was used to simulate the whole synthesis process. The nanoparticles of SiO2 produced at the exit (filter) and on the reactor wall had primary particles diameter between 10-300 nm while the aggregates were of much larger size, between 1 and 4 micrometers. The simulation predictions were used to gain more insight into the experimental results.

The Monomer Inlet Position Effect on the Fluorocarbon Film Deposited Using RF Plasma

The octafluorotoluene (C7F8) monomer was used to deposit fluorocarbon (a-C:F) film with an aromatic ring structure in an RF plasma reactor. While keeping the argon gas inlet position fixed, the inlet position effect of the C7F8 monomer on the deposited a-C:F film characteristics was investigated. It was found that, when C7F8 entered upstream of the plasma, the deposited film possessed no aromatic structure and the F/C atomic ratio of the film was higher than 1.4. Whereas for film deposited as C7F8 entered from the afterglow region (the so-called 'downstream' process), copious amount of the aromatic structure were preserved and the F/C ratio of the film was lower than 1.0. Higher deposition rate and rougher surface were also found in films deposited in the downstream process. A simplified reaction mechanism is proposed based on these results.

나노 부유 게이트 메모리 소자 응용을 위한 실리콘 나노-바늘 구조에 관한 연구

In this work, nano-needle structures ate formed to solve problem, related to low density of quantum dots for nano floating gate memory. Such structures ate fabricated and electrical properties' of MIS devices fabricated on the nano-structures are studied. Nano floating gate memory based on quantum dot technologies Is a promising candidate for future non-volatile memory devices. Nano-structure is fabricated by reactive ion etching using <TEX>$SF_6$</TEX> and <TEX>$O_2$</TEX> gases in parallel RF plasma reactor. Surface morphology was investigated after etching using scanning electron microscopy Uniform and packed deep nano-needle structure is established under optimized condition. Photoluminescence and capacitance-voltage characteristics were measured in <TEX>$Al/SiO_2/Si$</TEX> with nano-needle structure of silicon. we have demonstrated that the nano-needle structure can be applicable to non-volatile memory device with increased charge storage capacity over planar structures.

Effect of hexafluoropropylene oxide plasma polymer particle coatings on the rheological properties of boron nitride/poly(dimethylsiloxane) composites

This work explores the use of conformal nanoscale plasma coatings on the surface of boron nitride (BN) powders to control the rheological properties of BN/poly(dimethylsiloxane) (PDMS) composites. BN particles are conformally coated with hexafluoropropylene oxide (HFPO) in a tumbling RF-plasma reactor. Following the HFPO plasma treatment, XPS evidence indicates the presence of thin coating on the surface of the particles having a F:C ratio of 1.77. Filled BN/PDMS composites are investigated using oscillatory shear rheometry in the concentration range of 0.09–0.41 vol% ( ϕ). The addition of the plasma treated BN particles to the PDMS matrix reduces the complex viscosity by 40–60% when compared with equally loaded control samples across a broad concentration range. The frequency dependence of the maximum packing fraction ( ϕ m = 0.38 – 0.42 ) is also observed for both treated and untreated particles. The maximum packing fraction does not appear to be significantly affected by the conformal plasma polymer treatment. The investigation has shown that the relative dynamic viscosity of the BN/PDMS can be described by the modified Mooney equation.

Band gap widening of MBE grown InN layers by impurity incorporation

Band gap widening due to impurity contamination such as oxygen (O) incorporation into InN layers has been observed by growth without PBN sealing in the RF-plasma reactor. Furthermore, V/III ratio dependence of the absorption edge of InN layers grown under O-contaminated background has shown a strong correlation with that of the residual carrier concentration. A clearly red-shift of the absorption edge has been also observed for InN layers grown under the simultaneous irradiation of Ga beam. These results strongly indicate that O may be one of the strong candidates of impurity identified as an origin of band gap widening of InN.

Space and time resolved rotational state populations and gas temperatures in an inductively coupled hydrogen RF discharge

Gas temperature is of major importance in plasma based surface treatment, since the surface processes are strongly temperature sensitive. The spatial distribution of reactive species responsible for surface modification is also influenced by the gas temperature. Industrial applications of RF plasma reactors require a high degree of homogeneity of the plasma in contact with the substrate. Reliable measurements of spatially resolved gas temperatures are, therefore, of great importance. The gas temperature can be obtained, e.g. by optical emission spectroscopy (OES). Common methods of OES to obtain gas temperatures from analysis of rotational distributions in excited states do not include the population dynamics influenced by cascading processes from higher electronic states. A model was developed to evaluate this effect on the apparent rotational temperature that is observed. Phase resolved OES confirmed the validity of this model. It was found that cascading leads to higher apparent temperatures, but the deviation (≃25 K) is relatively small and can be ignored in most cases. This analysis is applied to investigate axially and radially resolved temperature profiles in an inductively coupled hydrogen RF discharge.

Reaction Mechanism of Ethylene Oxide at Various Oxygen/Ethylene Oxide Ratios in an RF Cold Plasma Environment

An innovative method was used to simulate ethylene oxide (EO) oxidation in an RF plasma reactor. The objective of this work was to simulate the stable species mole fraction profiles measured in a flowing plasma system at constant temperature and pressure. The mechanism involved participation of 36 species in 140 elementary reactions. Sensitivity analysis was also performed to identify the order of significance of reactions in the mechanism of the model’ s predictions. The results show that the main reactions for EO decomposition changed with a varying O2/EO ratio in the plasma system. That is to say, the most important reaction to the O2/EO ratio of zero was the electron dissociation reaction of EO, C2H4O + e- CH3CHO + e-. While, the most influential reaction for EO decomposition at O2/EO ratio of 5.0 was the formation reaction of HO2, which forms OH radicals, then enhances the decomposition of C2H4O by the reaction, C2H4O + OH = C2H3O + H2O.

ＰＥＣＶＤ成膜装置内での粒子汚染現象に対する操作流量の影響

The effects of gas flow rate on the contamination by dust particles in an RF plasma reactor were studied experimentally. A mixture of tetraethylorthosilicate vapor, oxygen and nitrogen were fed into the reactor to fabricate SiO2 thin film. Dust particles generated in the plasma were visualized by a laser light scattering technique. Particle size was measured by a laser particle counter, and particle deposition for the film was observed by a scanning electron microscope. The dust particles were found to be trapped in a certain region in the reactor. The amount and size of the trapped particles decreased with increasing gas flow rate. The particle contamination on the film surface also decreased with increasing gas flow rate. At a high flow rate, however, dust particles embedded into the film were observed. In addition, high gas flow rate degraded the film uniformity. It is considered from the above results that a proper selection of gas flow rate is important to decrease particulate contamination as much as possible.

On the effect of the substrate pretreatment parameters on the composition and structure of plasma deposited SiO2 thin films

The role of the substrate pretreatment using wet and dry cleaning procedures, on SiO2 thin film adhesion, integrity and composition was investigated. The SiO2 depositions were performed in a 27.12 MHz RF plasma reactor and an interelectrode space of 20 mm. The depositions were carried out on different substrates (magnesium, aluminum and c-Si) and at the low temperature of 100 °C. From the wet cleaning methods the use of 5 % HF aqueous solution was found to significantly improve the SiO2 thin film adhesion in all substrates. Even better results were achieved with the application of H2 plasma pretreatment, indicating that the etching during the plasma pretreatment results to better conditions for the film growth and the surface step coverage, especially on non-uniform and rough substrates.

RF plasma deposition of thin Si xGe yC z:H films using a combination of organometallic source materials

Elements of the IV group of periodic table have been strongly present in the fast development of PECVD techniques for the last two decades at least. As a result, deposition technologies of such materials as a-Si:H, a-C:H, mμ-C:H or DLC have been successfully established. What has followed is an ever growing interest in binary systems of the A x (IV)B y (IV):H kind. One possible way to deposit such systems is to use organosilicon compounds (to deposit Si x C y :H films) or organogermanium compounds (to deposit Ge x C y :H films), as source substances. The present paper reports on a RF plasma deposition of a Si x Ge y C z :H ternary system, using a combination of organosilicon and organogermanium compounds. Thin Si/Ge/C films have been fabricated in a small volume (ca. 2 dm 3) parallel plate RF plasma reactor using, as a source material, a combination of tetramethylsilane (TMS) and tetramethylgermanium (TMG) vapours carried by argon. SEM investigations reveal a continuous compact character of the coatings and their uniform thickness. The elemental composition of the films has been studied using EDX analysis. The results of the analysis show that the elemental composition of the films can be controlled by both the TMG/TMS ratio of the initial mixture and the RF power input. Ellipsometric measurements show good homogeneity of these materials. Chemical bonding in the films has been studied using the FTIR technique. Bandgap calculations have been carried out using ellipsometric data and by applying both the Tauc law and the Moss approach.

Design of functional coatings

Based on the principle of macroscopic kinetics, we present the concept of a standard process to compare different rf plasma reactors. Therefore, the mass deposition rate of pure hexamethyldisiloxane (HMDSO) discharges was chosen, since the plasma polymerization of HMDSO is a radical-dominated process and ion-induced effects can be neglected for a wide parameter range. Two experimental series with pure HMDSO discharges were performed within a symmetrical and a strongly asymmetrical rf plasma reactor. The obtained deposition rates were compared to four experimental series taken out of the literature concerning the deposition rates of plasma polymerized HMDSO coatings. While for each reactor design, the “specific energy” W∕F was found to describe the deposition rates very well, different apparent activation energies Ea were obtained. To bring the data sets into agreement, a new process constant Eadact is introduced taking the width of the active plasma zone dact into account. By this means, functionally gradient SiOC:H films can be designed, e.g., for adhesion, wetting, or barrier improvements. Moreover, processes can be optimized and scaled up.

New Approach for Methane Conversion Using an rf Discharge Reactor. 1. Influences of Operating Conditions on Syngas Production

Traditionally, the process for converting CH4 into syngas (CO and H2) is usually carried out at high temperature with catalysts. In this study, a new approach using a lab-scale radio frequency (rf) plasma reactor is made at room temperature with a single-step process. The major factors that affected the conversion and selectivity were examined by the fractional factorial experimental design method. Experimental results indicated that the higher methane conversion was achieved at either a higher applied power or inlet O2/CH4 molar ratio (R), while the simultaneous higher selectivities of H2 and CO were obtained at a lower R. At [CH4]in = 33.3% and 4000 N/m2, the better operating conditions were at R = 1 with 130 W. The methane conversion equaled 80.1%, and the selectivities of H2 and CO reached 92.6% and 74.0%, respectively, with a H2/CO molar ratio of 2.5.

Influence of artificially accelerated ageing on the adhesive joint of plasma treated polymer materials

An influence of simulated ageing on the adhesive joint of plasma treated polyethylene (PE) and polypropylene (PP) was tested. Plasma surface treatment was performed in the rf-plasma reactor operating at 13,56 MHz. The simulated ageing of prepared specimens for following tensile testing was carried out under conditions given by Volkswagen standard P-VW 1200. Temperature of ageing was regularly oscillating between −40°C and 80°C (relative humidity 80%) for required time. The mechanical tensile properties of adhesive joint were measured according to the standard ISO 527. Surface analysis of treated polymer substrates was characterized by XPS measurement. The observation of surface structure and morphology was obtained using SEM. We used convenient cyanoacrylate adhesive Loctite E 406 for PE and PP joints. Tested adhesive joints were prepared in compliance with the standard ISO 4587.

Development of an electrospray approach to deposit complex molecules on plasma modified surfaces

Two established techniques have been coupled to allow surfaces to be precision engineered. Electrospray ionization to bring large, complex, intact molecular ions into the gas phase has been interfaced with a radio frequency (rf) plasma reactor to treat surfaces making them receptive to the deposition of active biomolecules. The new instrument has been designed and used successfully to deposit a number of high molecular weight molecules including the polysaccharide, sodium hyaluronan (HA), that has an important role in a number of physiological functions. Substrate material is treated using a rf glow discharge plasma chamber, to clean and activate the surface in a controlled manner, then exposed to a beam of multiply charged ions in the gas phase that have been generated using electrospray techniques. The ions are deposited gently onto the substrate and become covalently bound. The molecular integrity and stability of HA surfaces prepared in this way was established using x-ray photoelectron spectroscopy, changes in the observed contact angle, time-of-flight secondary ion mass spectrometry, scanning electron microscopy, and a biological assay–platelet adhesion to the surface.