Plasma Characteristics and Antenna Electrical Characteristics of an Internal Linear Inductively Coupled Plasma Source with a Multi-Polar Magnetic Field

The development of a large-area plasma source with high density plasmas is desired for a variety of plasma processes from microelectronics fabrication to flat panel display device fabrication. In this study, a novel internal-type linear inductive antenna referred to as “double comb-type antenna” was used for a large-area plasma source with the substrate area of 880 mm × 660 mm and the effect of plasma confinement by applying multi-polar magnetic field was investigated. High density plasmas on the order of 3.2 × 10¹¹ cm^?3 which is 50% higher than that obtained for the source without the magnetic field could be obtained at the pressure of 15 mTorr Ar and at the inductive power of 5,000 W with good plasma stability. The plasma uniformity <3% could be also obtained within the substrate area. When SiO₂ film was etched using the double comb-type antenna, the average etch rate of about 2,100 Å/min could be obtained with the etch uniformity of 5.4% on the substrate area using 15 mTorr SF₆, 5,000 W of rf power, and ?34 V of dc-bias voltage. The higher plasma density with an excellent uniformity and a lower rf antenna voltage obtained by the application of the magnetic field are related to the electron confinement in a direction normal to the antenna line.     

Etching Characteristics and Mechanisms of Mo and Al2O3 Thin Films in O2/Cl2/Ar Inductively Coupled Plasmas: Effect of Gas Mixing Ratios

An investigation of etching behaviors for Mo and Al₂O₃ thin films in O₂/Cl₂/Ar inductively coupled plasmas at constant gas pressure (6 mTorr), input power (700 W) and bias power (200 W) was carried out. It was found that an increase in Ar mixing ratio for Cl₂/Ar plasma results in non-monotonic etching rates with the maximums of 160 nm/min at 60 % Ar for Mo and 27 nm/min at 20 % Ar for Al₂O₃. The addition of O₂ in the Cl₂/Ar plasma causes the non-monotonic Mo etching rate (max. 320 nm/min at 40–45 % O₂) while the Al₂O₃ etching rate decreases monotonically. The model-based analysis of etching kinetics allows one to relate the non-monotonic etching rates in Cl₂/Ar plasma to the change in the etching regime from the ion-flux-limited mode (at low Ar mixing ratios) to the neutral-flux-limited mode (for high Ar mixing ratios). In the Cl₂/O₂/Ar plasma, the non-monotonic Mo etching rate is probably due to the change in reaction probability.     

On the LPCVD-Formed SiO2 Etching Mechanism in CF4/Ar/O2 Inductively Coupled Plasmas: Effects of Gas Mixing Ratios and Gas Pressure

An investigation of etching mechanism of low-temperature SiO₂ thin films in CF₄/Ar/O₂ inductively coupled plasmas at constant input power (900 W) and bias power (200 W) was carried out. It was found that that the variations of Ar/O₂ mixing ratio (0–50 %) at constant 50 % CF₄ fraction as well as the change in gas pressure (4–10 mTorr) resulted in non-monotonic SiO₂ etching rates. The zero-dimensional plasma model with Langmuir probe diagnostics data provided the detailed information on formation-decay kinetics for plasma active species. The model-based analysis of etching kinetics showed that these effects were not connected with the non-monotonic change of fluorine atom density (as was found in several works for the binary CF₄/O₂ system), but resulted from the decrease in reaction probability and with the transition from neutral-flux to ion-flux-limited regimes of ion assisted chemical reaction.     

Controlled Fluxes of Silicon Nanoparticles to a Substrate in Pulsed Radio-Frequency Argon–Silane Plasmas

It has been hypothesized that high-energy impact of very small silicon nanoparticles on a substrate may lead to epitaxial growth of silicon films at low substrate temperature. A possible means for producing such energetic nanoparticle fluxes involves pulsing an RF silane-containing plasma, and applying a positive DC bias to the substrate during the afterglow phase of each pulse so as to collect the negatively charged particles generated during the RF power on phase. We here report numerical modeling to provide a preliminary assessment of the feasibility of this scheme. The system modeled is a parallel-plate capacitively-coupled RF argon–silane plasma at pressures around 100 mTorr. Simulation results indicate that it is possible to achieve a periodic steady state in which each pulse delivers a controlled flux of nanoparticles to the biased substrate, that average particle sizes can be kept below 2–3 nm, that impact energies of the negatively-charged nanoparticles that are attracted by the applied bias can be maintained in the ~1 eV/atom range thought to be conducive to epitaxial growth without causing film damage, and that the volume fraction of neutral nanoparticles that deposit by low-velocity diffusion can be kept well below 1 %. The effects of several operating parameters are explored, including RF voltage, pressure, the value of the applied DC bias, and RF power on and off time during each pulse.     

Plasma Characteristics of a Ni–Zn Ferrite Enhanced Internal-Type Inductively Coupled Plasma Source Operated at 2 and 13.56 MHz

Plasma and electrical characteristics of an internal-type inductively coupled plasma source with a Ni–Zn ferrite module installed near the antenna were investigated for different rf power frequencies of 2 and 13.56 MHz. Due to the lower heating of the Ni–Zn ferrite module on the antenna for the operation at 2 MHz compared to the operation at 13.56 MHz, higher plasma density and lower rf rms antenna voltage were resulted for the operation at 2 MHz in addition to more stable plasma characteristics. By the application of 500 W of rf power to the source, a high plasma density of 8 × 10¹¹ cm⁻³ which is about four times higher than that with 13.56 MHz could be obtained at the pressure of 10 mTorr Ar. When photoresist etch uniformity was measured for the operation with 2 MHz by etching photoresist on a 300 mm diameter substrate using 10 mTorr Ar/O₂ (9:1) mixture, the etch uniformity of about 5.5% could be obtained.     

Investigation of the Expansion of an Oxygen Microwave Remote Plasma for the Growth of Functional Oxide Thin Films

The expansion of an oxygen low-pressure microwave plasma was investigated in order to determine the optimal plasma parameters for the growth of functional oxide semiconductors. Langmuir probe measurements show that the electron density (n _e ) increases with the injected power up to a saturation value of 3.0 × 10⁹ cm^?3 determined at 10 mTorr while electron temperature (T _e ) remains constant at a value of 1.5 eV. When pressure is varied, n _e shows a maximum value at a range from 12 to 20 mTorr while T _e decreases monotonously with increasing pressure. In addition, both n _e and T _e decrease with the axial distance from the plasma source. These effects were discussed through the loss mechanisms in the remote plasma. For a pressure of 13 mTorr and at a substrate temperature of 500 °C, plasma enhanced oxidation of pure metallic Ti thin films lead to the formation of a pure TiO₂ anatase phase compared to a mixed phase of TiO₂ and TiO in the absence of plasma activation. For Mn thin films, the exposure to oxygen remote plasma led to the formation of MnO₂ as opposed to obtaining Mn₃O₄ when oxidation is performed in the oxygen gas ambient. Remote plasma processing was thus found to provide selective pathways to control oxidation states, stoichiometry and phase composition of technologically attractive oxide thin films.     

Time growing comparison for ZnO nanorod by using microwave irradiation method

In this study, zinc oxide (ZnO) nanorod were successfully prepared at different growth times (15, 30 and 60 min) using the microwave irradiation method. The ZnO nanorods were simply synthesized at a low temperature (90 °C) with low power microwave assisted heating (about 100 W) and a subsequent ageing process. The synthesized nanorod were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and Ultraviolet–Visible spectroscopy (UV–Vis). The FESEM images showed nanorods with diameter ranging between 50 and 150 nm, and length of 150–550 nm. The XRD results indicate that ZnO nanorods of different time of growth exhibits pure wurtzite structure with lattice parameters of 3.2568 and 5.2125 Å. UV–Vis characterization showed that energy gap decreases with increase in time. The result also shows that growth of ZnO at 60 min produces an energy band gap of 3.15 eV. In general, the results of the study confirm that the microwave irradiation method is a promising low temperature, cheap and fast method for the production of ZnO nanostructures.     

Influence of sputter power on structural and electrical properties of TiO2 films for Al/TiO2/Si gate capacitors

Titanium dioxide (TiO₂) thin films were deposited onto p‐Si substrates held at room temperature by reactive Direct Current (DC) magnetron sputtering at various sputter powers in the range 80–200 W. The as‐deposited TiO₂ films were annealed at a temperature of 1023 K. The post‐annealed films were characterized for crystallographic structure, chemical binding configuration, surface morphology and optical absorption. The electrical and dielectric properties of Al/TiO₂/p‐Si structure were determined from the capacitance–voltage and current–voltage characteristics. X‐ray diffraction studies confirmed that the as‐deposited films were amorphous in nature. After post‐annealing at 1023 K, the films formed at lower powers exhibited anatase phase, where as those deposited at sputter powers > 160 W showed the mixed anatase and rutile phases of TiO₂. The surface morphology of the films varied significantly with the increase of sputter power. The electrical and dielectric properties on the air‐annealed Al/TiO₂/p‐Si structures were studied. The effect of sputter power on the electrical and dielectric characteristics of the structure of Al/TiO₂/p‐Si (metal‐insulator‐semiconductor) was systematically investigated. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparative assessment of the ability of a microwave absorber nanocatalyst in the microwave-assisted biodiesel production process

In this study, a carbon-supported KOH/Ca₁₂Al₁₄O₃₃ nanocomposite was fabricated via the microwave combustion method, in which dextrose was used as a carbon source, and its activity in the microwave-assisted transesterification reaction as a microwave absorption material was assessed. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, Brunauer–Emmett–Teller (BET), field-emission scanning electron microscopy, and energy dispersive X-ray analyses. The results showed that the carbonate and noncarbonate samples had a calcium aluminate (Ca₁₂Al₁₄O₃₃) structure as a support. Different carbon groups were formed during preparation of the carbon-supported KOH/Ca₁₂Al₁₄O₃₃ nanocomposite, which improved its surface area and porosity. Although the samples presented similar basicity, the carbonated nanocomposite exhibited twice as much activity as the KOH/Ca₁₂Al₁₄O₃₃ nanocatalyst for conversion of canola oil to biodiesel in the microwave-assisted transesterification reaction at 270 W microwave power. The nanocomposite with a larger pore size made active sites easily accessible and exhibited higher catalytic ability where the conversion of 98.8% was obtained under the optimized conditions of 270 W microwave power, methanol/oil molar ratio of 15, 4 wt% of the nanocomposite, and 30 min of reaction time. The carbon-supported nanocatalyst can be reused for at least four times with less reduction in activity. Furthermore, the obtained biodiesel showed that it met the standard values (EN 14214 and ASTM D-6751) with respect to the density, kinematic viscosity at 40 °C, acid number, and flash point.     

Quantification of Conversion Degree and Monomer Elution from Dental Composite Using HPLC and Micro-Raman Spectroscopy

The purpose of the study was to analyze the correlation between the quantity of eluted monomers from dental resin-based composite using reverse-phase HPLC and the degree of conversion (DC) using micro-Raman spectroscopy, and to evaluate the influence of the energy of polymerization delivered on the composite material and the applied resin layer thickness on these properties. There was direct proportion in degree of conversion and inverse proportion in monomer elution when the energy of light polymerization was increased from 20 to 40 J cm⁻²; however, further increase in energy density did not influence significantly the DC and the elution of monomers. Investigating the depth of cure significant differences could be measured both in DC and the elution of monomers. 1 mm layer increment up to 3 mm from the top led to 10 % decrease in DC and 30–35 % increase in monomer elution. Further increase in depth from 3 to 4 mm caused 30 % drop in DC and 55 % increase in the amount of leached monomers. The overall result of the findings indicates that direct correlation exists between DC of composite and the elution of unreacted monomers.

     

Plasma Impedance Analysis: A Novel Approach for Investigating a Phase Transition from a-Si:H to nc-Si:H

In the present article we report the transition regime of hydrogenated amorphous (a-Si:H) to nano-crystalline (nc-Si:H) silicon thin films in Silane (SiH₄) plasma using 27.12 MHz assisted plasma enhanced chemical vapor deposition process with the approach of plasma diagnosis. The observed transitions occur within a narrow range of diverse deposition process window and hence plasma diagnosis was vital towards envisaging this variation. Impedance Analyser (V/I probe) was used to monitor plasma characteristics during growth at various process pressure (0.03–0.4 Torr) and applied power (4–20 W). Efforts were made to understand the radicals’ formation and plasma-substrate interaction by evaluating the discharge parameters such as electron density, bulk field, and sheath voltage. From the result of plasma characterizations, highest bulk field (5.7 V/cm) in combination to low sheath voltage (0.1 V) observed on 0.2 Torr pressure at 15 W power which thus provides a clear signature of transition from a-Si:H to nc-Si:H. The structural characterizations also validate the results of observed transition where in particular it was found that the mean crystallite size (4.2 nm) with high crystalline volume fraction (42%) and wider band gap (2.01 eV) with higher hydrogen content (35%) signifies the existing nano-crystalline phase. On account of these results, an empirical relation between plasma impedance and phase angle was established in terms of expansion and contraction of two distinct discharge zones (bulk and sheath) to diagnose the phase transition.     

Etching Characteristics and Mechanisms of TiO<Subscript>2</Subscript> Thin Films in CF<Subscript>4</Subscript> + Ar,Cl<Subscript>2</Subscript> + Ar and HBr + Ar Inductively Coupled Plasmas

The comparative study of etching characteristics and mechanisms for TiO₂ thin films in CF₄ + Ar, Cl₂ + Ar and HBr + Ar inductively coupled plasmas was carried out. The etching rates for TiO₂, Si and photoresist were measured as functions of gas mixing ratios at fixed gas pressure (10 mTorr), input power (800 W) and bias power (300 W). It was found that the maximum TiO₂ etching rate of ~130 nm/min correspond to pure CF₄ plasma while an increase in Ar fraction in a feed gas results in the monotonic non-linear decrease in the TiO₂ etching rates in all three gas mixtures. Plasma diagnostics by Langmuir probes and 0-dimensional (global) plasma modeling supplied the data on the densities of plasma actives specie as well as on particle and energy fluxes to the etched surface. It was concluded that, under the given set of experimental conditions, the TiO₂ etching kinetics in all gas systems correspond to the ion-assisted chemical reaction with a domination of the chemical etching pathway. It was found also that the differences in the absolute TiO₂ etching rates correlate with the energy thresholds for TiO₂ + F, Cl or Br reaction, and the reaction probabilities for F, Cl and Br atoms exhibit the different changes with the ion energy flux according to the volatility of corresponding etching products.     

Study of Internal Linear Inductively Coupled Plasma Source for Ultra Large-Scale Flat Panel Display Processing

An internal-type linear inductive antenna, which is referred to as “double comb-type antenna”, was used as a large-area inductively coupled plasma (ICP) source with a substrate area of 2,300 mm × 2,000 mm. The characteristics of the ICP source were investigated for potential applications to flat panel display (FPD) processing. The source showed higher power transfer efficiency at higher RF power and higher operating pressures. The power transfer efficiency was approximately 88.1% at 9 kW of RF power and a pressure of 20 mTorr Ar. This source showed increasing plasma density and improved plasma uniformity with increasing RF power at a given operating pressure. A plasma density >1.5 × 10¹¹/cm³ and a plasma uniformity of approximately 11% was obtained at 9 kW of RF power and 15 mTor Ar using this internal ICP source, which is applicable to FPD processing.     

Low Cost Compact Nanosecond Pulsed Plasma System for Environmental and Biomedical Applications

Nanosecond pulsed non-thermal atmospheric-pressure plasmas are promising for numerous applications including air and water purification, ozone synthesis, surface sterilization, material processing, and biomedical care. However, the high cost of the nanosecond pulsed power sources has hindered adaptation of the plasma-based technologies for clinical and industrial use. This paper presents a low cost (<100US$) nanosecond pulsed plasma system that consists of a Cockcroft–Walton high voltage charging circuit, a compact nanosecond pulse generator using a spark gap as switch, and a plasma reactor. The nanosecond pulse power source requires only a 12 V DC input, hence is battery operable. Through the optimization of the experimental parameters, pulses with a peak voltage >10 kV, a 3 ns rise time (10 to 90 %), and a 10 ns pulse duration (full width at half maximum) at a pulse repetition rate of up to 500 Hz were achieved in the present study. It has been successfully tested to power three different plasma reactors to form pulsed corona discharges, dielectric barrier discharges, and sliding discharges. The energy efficiency of such a nanosecond pulsed sliding discharge system was assessed in the context of ozone synthesis using air or oxygen as the feed gas, and was found comparable to a previously reported non-thermal plasma system that used commercial high voltage pulsed power sources. This study demonstrated that this low-cost nanosecond pulsed power source can prove to be an energy efficient and simple supply to drive various non-thermal atmospheric-pressure plasma reactors for environmental, medical and other applications.     

Quantification of Conversion Degree and Monomer Elution from Dental Composite Using HPLC and Micro-Raman Spectroscopy

The purpose of the study was to analyze the correlation between the quantity of eluted monomers from dental resin-based composite using reverse-phase HPLC and the degree of conversion (DC) using micro-Raman spectroscopy, and to evaluate the influence of the energy of polymerization delivered on the composite material and the applied resin layer thickness on these properties. There was direct proportion in degree of conversion and inverse proportion in monomer elution when the energy of light polymerization was increased from 20 to 40 J cm^?2; however, further increase in energy density did not influence significantly the DC and the elution of monomers. Investigating the depth of cure significant differences could be measured both in DC and the elution of monomers. 1 mm layer increment up to 3 mm from the top led to 10 % decrease in DC and 30–35 % increase in monomer elution. Further increase in depth from 3 to 4 mm caused 30 % drop in DC and 55 % increase in the amount of leached monomers. The overall result of the findings indicates that direct correlation exists between DC of composite and the elution of unreacted monomers.     

Silver Metallic Nanoparticles with Surface Plasmon Resonance: Synthesis and Characterizations

Silver nanoparticles were synthesized by the reduction of the silver nitrate (AgNO₃) using the latex copolymer in ethanol solution under microwave (MW) heating. The reaction parameters such as silver precursor concentration (from 0.005 to 0.1 g/l) and MW power (200–800 W) significantly affect the formation rate, shape, size and distribution of the silver nanoparticles. A significant reduction of irradiation time was observed when the MW energy is compared to conventional thermal reduction processes. The prepared silver nanoparticles show uniform and stable sizes from 5 to 11 nm, which can be stored at room temperature for approximately 12 months without any visible change. These peculiarities indicate that the latex copolymer is a good stabilizer for the silver nanoparticles. The optical properties, morphology, and crystalline structure of the silver-latex copolymer nanocomposites were characterized by the Ultraviolet–Visible spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The study of the TEM images at high magnifications identified the silver nanoparticles as face-centered cubic (fcc) structure with spherical and hexagonal shapes.     

A new microwave plasma at atmospheric pressure

Plasma at atmospheric pressure can be obtained by surface wave propagation with a surfatron. If the plasma is produced within a quartz tube, it is constricted to a diameter of approx. 1 or 2 mm but its length can attain some tens of centimeters with microwave power as low as 100 W. This plasma is quite uniform along the axis, with a typical electron density of 3 × 10¹⁴ electrons/cm³. Since the excitation and gas temperatures are lower than 4000 K, the plasma is far from local thermodynamic equilibrium. High stability and repeatability is achieved with an argon flow of 0.2–17 l/min. Applications are foreseen in the field of optical spectroscopy and plasma chemistry.     

Analysis and Characterization of Microwave Irradiation–Induced Graft Copolymerization of Methyl Methacrylate onto Delignified Grewia Optiva Fiber

Grafting of methyl methacrylate (MMA) onto delignified Grewia optiva fiber using ascorbic acid/H₂O₂ as an initiator was carried out under microwave irradiation. The effects of varying the microwave power, exposure time, and concentration of initiator and monomer of graft polymerization were studied to obtain maximum grafting percentage (26.54%). The experimental results showed that the optimal conditions for grafting were: exposure time, 10min; microwave power, 110 W; ascorbic acid concentration, 3.74mol/L × 10^?2; H₂O₂ concentration, 0.97mol/L × 10^?1; monomer concentration, 1.87mol/L × 10^?1. The graft copolymers were characterized by Fourier transform-infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA).     

Preparation and characterization of activated carbon from pine cone by microwave-induced ZnCl2 activation and its effects on the adsorption of methylene blue

In this work, activated carbon prepared from pine cone (PCAC) with ZnCl₂ as an activation agent under microwave radiation was investigated. The activation step was performed at the microwave input power of 400 W and radiation time of 5 min. The properties of activated carbon were characterized by N₂ adsorption Brunauer–Emmett–Teller (BET), scanning electron microscopy and Fourier transform infrared spectroscopy. Results showed that the BET surface area, Langmuir surface area, and total pore volume of PCAC were 939, 1,486 m²/g and 0.172 cm³/g, respectively. Adsorption capacity was demonstrated by the iodine numbers. The adsorptive property of PCAC was tested using methylene blue dye. Equilibrium data was best fitted by the Langmuir isotherm model, showing a monolayer adsorption capacity of 60.97 mg/g. The pseudo-first- and pseudo-second-order kinetic models were examined to evaluate the kinetic data, and the rate constants were calculated. Adsorption of the dyes followed pseudo-first order kinetics. Thermodynamic parameters such as free energy, enthalpy and entropy of dye adsorption were obtained.     

Effect of O5+ ion implantation on the electrical and structural properties of Cu nanowires

Ion beam creates changes in the material along their track, not only embody the excellent properties but also tailor new materials. When the ions are implanted into the nanomaterials, they collide with the target atoms and interact through three different phenomena; electron collision, nuclear collision and charge exchange. In the present study, 1 MeV O⁵⁺ ions were implanted in copper nanowires of diameter 80 nm synthesized using template synthesis approach. Electrical and structural properties were recorded using Keithley 2400 series source meter and Rigaku X-ray diffractometer respectively, before and after the implantation. I–V characteristics showed the ohmic behavior with enhancement in conductivity of copper nanowires after implantation. No structural damage in the nanowires was revealed by XRD spectra. The work done can be viewed as a positive aspect of implantation in metallic nanowires especially in 80 nm diameter Cu nanowires and may be utilized to fabricate nanodevices.