Increasing Rf Power Research Articles

Light scattering effect of ITO:Zr/AZO films deposited on periodic textured glass surface morphologies for silicon thin film solar cells

Various SF6/Ar plasma-textured periodic glass surface morphologies for high transmittance, haze ratio and low sheet resistance of ITO:Zr films are reported. The SF6/Ar plasma-textured glass surface morphologies were changed from low aspect ratio to high aspect ratio with the increase in RF power from 500 to 600 W. The micro- and nano-size features of textured glass surface morphologies enhanced the haze ratio in visible as well as NIR wavelength region. Micro-size textured features also influenced the sheet resistance and electrical characteristics of ITO:Zr films due to step coverage. The ITO:Zr/AZO bilayer was used as front TCO electrode for p-i-n amorphous silicon thin film solar cells with current density–voltage characteristics as: V oc = 875 mV, FF = 70.90 %, J sc = 11.31 mA/cm2, η = 7.02 %.

Effect of mechanical, barrier and adhesion properties on oxygen plasma surface modified PP

Abstract In this work, the Polypropylene (PP) film was surface modified by Oxygen plasma treatment and the effect of mechanical, barrier and adhesion properties was studied. The PP film was plasma treated with various RF power settings of 7.2 W, 10.2 W and 29.6 W in various time intervals of 60 s, 120 s, 180 s, 240 s and 300 s. To characterize the wettability, the contact angle was measured and the surface energy values were estimated with different test liquids. The generation of oxygen functional groups on the surface of plasma modified PP and the surface change characterization were observed by attenuated total reflection-Fourier transform infrared spectroscope (ATR-FTIR) and they resulted in wettability improvement. The roughness of the PP film and the surface morphology were analyzed by Atomic Force Microscopy (AFM). It was found that the roughness value increased from 1.491 nm to 7.26 nm because of the increase of treatment time and RF power. The PP crystallinity structure of the untreated and treated PP was evaluated by X-ray diffraction analysis (XRD). The bond strength of the untreated and surface modified films were measured by T-peel test method. For the untreated and oxygen plasma treated sample, the mechanical properties like Tensile Strength and the barrier properties like oxygen transmission rate (OTR), Water vapor transmission rate (WVTR) were also calculated. From the results, the tensile strength reduced from 6 MPa to 1.350 MPa because of polypropylene etching and degradation. The OTR increased from 1851.2 to 2248.92 cc/m2/24 h and the Water vapor transmission rate increased from 9.6 to 14.24 g/m2/24 h. Industrial Relevance Plasma technology applied to packaging and printing industry is a dry, environmentally- and worker-friendly method to achieve surface alteration without modifying the bulk properties of different materials. In particular, atmospheric non-thermal plasmas are suited because most are heat sensitive polymers and applicable in continuous process. In the last years plasma technology has become a very active, high growth research field, assuming a great importance among all available material surface modifications in packaging industry.

Vertically aligned Si nanocrystals embedded in amorphous Si matrix prepared by inductively coupled plasma chemical vapor deposition (ICP-CVD)

Abstract Vertically-aligned nanostructured silicon films are deposited at room temperature on p-type silicon wafers and glass substrates by inductively-coupled, plasma-enhanced chemical vapor deposition (ICPCVD). The nanocrystalline phase is achieved by reducing pressure and increasing RF power. The crystalline volume fraction ( X c ) and the size of the nanocrystals increase with decreasing pressure at constant power. Columnar growth of nc-Si:H films is observed by high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The films exhibit cauliflower-like structures with high porosity that leads to slow but uniform oxidation after exposure to air at room temperature. Films deposited at low pressures exhibit photoluminescence (PL) signals that may be deconvoluted into three distinct Gaussian components: 760–810, 920–935, and 990–1000 nm attributable to the quantum confinement and interface defect states. Hydrogen dilution is manifested in significant enhancement of the PL, but it has little effect on the nanocrystal size and X c .

Fluid simulation and experimental validation of plasma radial uniformity in 60 MHz capacitively coupled nitrogen discharges

A two-dimensional self-consistent electrostatic fluid model and the experimental diagnostic method are employed to investigate the plasma radial uniformity in capacitively coupled nitrogen discharges driven at 60 MHz. The effects of the rf power and electrode gap on the spatial profiles of the N2+ ion density and the radial profiles of the ion flux to the lower electrode are demonstrated. It is found in the simulation that with the increase of rf power or the decrease of electrode gap, the electrostatic edge effect becomes remarkable, which gives rise to an increase in the positive ion density at the electrode edge and thus the radial uniformity of plasma becomes worse. Moreover, the radial profiles of the N2+ ion flux to the lower electrode show a similar behavior to that of the ion density. These results are further understood by the calculated axial and radial components of the power deposition, which exhibit pronounced peaks at the electrode edge at high rf power or small electrode gap. In order to validate the simulation results, the radial profiles of the N2+ ion density were measured by a floating double probe. A general qualitative agreement between the experimental and calculated results is achieved.

Experimental diagnostics of plasma radial uniformity and comparisons with computational simulations in capacitive discharges

The plasma density radial profiles in capacitive discharges driven over a wide frequency range (60–220 MHz) are measured by a floating double probe, and the results measured at 60 MHz are compared with those obtained from the electrostatic models, i.e. particle in cell/Monte Carlo collision (PIC/MCC) and the fluid models. It was found that at low pressure the plasma density peaks at the center of the reactor, while it peaks at the electrode edge at high pressure, indicating that the power deposition transitions from ‘non-local’ to ‘local’ with increasing pressure. The plasma radial profiles obtained from the PIC/MCC simulation and fluid model show a qualitative agreement with the experiment at low pressure and high pressure, respectively. This is primarily due to the fact that at low pressure the fluid model substantially under-predicts sheath heating, which, however, is the main electron heating mechanism at low pressure. So the total power into electrons and therefore the plasma density is also under-predicted. In contrast, the PIC/MCC model takes into account these electron collisionless heating effects at low pressure, and thus the plasma density is enhanced in the central region of electrodes. At high pressure, due to local power deposition, both the experiment and fluid simulation show that as rf power increases, a density peak at the electrode edge appears, indicating an enhancement in edge field. Compared with the electrostatic case, at a higher frequency, the plasma density profile is determined by electromagnetic (EM) effects, especially the standing wave effect. To be specific, we found that the standing wave effect exhibits multi-node structure within the electrode at 130 MHz or above, and the wavelength becomes smaller as the excitation frequency increases. At high excitation frequency and high pressure, the rf power is mainly deposited at the electrode periphery due to the fact that the EM waves are strongly damped when they propagate from the discharge edge to the center. In addition, our experimental results show that the standing wave wavelength increases with rf power.

Effect of rf power on the properties of magnetron sputtered CeO2 thin films

Cerium oxide (CeO2) thin films were prepared by rf magnetron sputtering (PVD) technique onto glass substrates at a pressure of 3 × 10−4 mbar of Ar+ atmosphere. The thickness of deposited CeO2 films ranges from 380 to 590 nm. X-ray diffraction studies on the films showed that the films are polycrystalline in nature. The crystallite size (D), dislocation density (δ) and micro-strain (e) were evaluated from XRD patterns. The obtained micro-strain and dislocation density of the films were found to be ~10−3 and ~1016 lines/m2 respectively, along with a marginal increase in crystallite size from ~6 to ~9 nm. The experimental diffraction values of the films agreed with the standard values. The optical properties of cerium oxide films were studied in the wavelength range 325–900 nm. Optical absorption, extinction coefficients, refractive index and optical conductivity were evaluated from optical measurements. The films are found to be highly transparent in visible region and exhibits low reflectance in the ultraviolet region. The optical band gap of the films was found to decrease from 3.53 to 3.45 eV, with the increase of film thickness. The defects were found to increase with the increase of rf power. Emission bands like UV, weak blue, blue, blue–green and green bands were observed from PL spectra of CeO2 thin films. Raman active mode (F2g) of CeO2 thin films was observed at 466 cm−1 and films deposited at higher rf power show increased line width as well as peak intensity in Raman spectra. Rf power induced formations of flower like morphology were observed in SEM images. The surface roughness of CeO2 thin films was increased from 2.9 to 7.7 nm with the increase of rf power as ascertained from AFM images and the results are discussed.

Plasma parameters in 40 MHz Argon discharge

Experimental data related to 40MHz Argon plasma parameters in the RF power and pressure ranges of 25–200W and 0.2–0.5Torr are presented. Electron temperatures are obtained using both double probe and optical spectroscopy methods. Acceptable consistency between results is obtained. Double probe method is also used to obtain the plasma electron density. At any particular pressure value, the effect of increasing RF power seems to be restricted to increasing plasma electron density rather than affecting the plasma electron temperatures. Signature of the Paschen law effect is reflected on the relation between pressure and electron plasma density.

Effect of rf power on the dielectric properties of bismuth magnesium niobium titanium thin films deposited by RF magnetron sputtering

The Bi1.5Mg0.5Nb0.5Ti1.5O7 (BMNT) thin films with cubic pyrochlore structure were prepared on ITO substrates by RF magnetron sputtering. The effect of rf power on the dielectric properties of BMNT thin films were investigated. As the rf power increases, the crystallinity becomes better, the dielectric properties and tunability have an obvious improvement. The BMNT thin film deposited at 250 W exhibited dielectric constant of 105, the tunability of 33, low tangent loss of 0.0035, and the largest FOM of 361.89. The relationship of leakage current and thickness was also studied and a possible explanation was proposed. The excellent dielectric properties make BMNT thin films promising for potential tunable capacitor applications.

Physical properties of rf magnetron sputter deposited NiO:WO3 thin films

The present study describes various physical properties of mixed nickel–tungsten oxide (NiO:WO3) (95:5) thin films prepared on glass substrate by rf magnetron sputtering due to the variation in rf power (100, 150, and 200 W). X-ray diffraction study shows that all the deposited films are amorphous in nature. The maximum transmittance of 97% in the infrared region was observed for the film deposited at 100 W rf power. A systematic reduction in the optical band gap is observed with increasing rf power, which is associated with the rf power induced effect leading to the production of localized states near the band edges of NiO:WO3. The Urbach energy (EU) value was found to increase with rf power, which may be due to the increased defects in the NiO matrix. From the optical study, we have evaluated various parameters such as refractive index, packing density, lattice dielectric constant, ratio between free carrier density and free carrier effective mass, plasma frequency, and dispersion energy parameters, etc. These results are discussed and correlated well with the light of possible mechanisms underlying the phenomena. The compositional purity of the film was confirmed by energy dispersive x-ray analysis (EDAX) and Auger electron spectroscopic (AES) measurements. The Raman spectra of NiO:WO3 films show two peaks corresponding to one-phonon LO mode at 560 cm−1 and two-phonon LO mode at 1100 cm−1 due to the vibrations of Ni–O bonds and a strong peak at 860 cm−1 corresponds to the stretching vibration of W–O pair in the WO6 group. The band edge emission at 369 nm was observed in photoluminescence spectra.

Inductive couple plasma reactive ion etching characteristics of TiO2 thin films

Changes in the inductively coupled plasma reactive ion etching characteristics of TiO2 thin films in response to the addition of HBr, Cl2 and C2F6 to Ar gas were investigated. As the HBr, Cl2 and C2F6 concentration increased, the etch rate increased; however, the etch profile degree of anisotropy followed a different trend. As HBr concentration increased, the greatest anisotropic etch profile was obtained at 100% HBr, while the greatest anisotropic etch profile was obtained at concentrations of 25% when etching was conducted under C2F6 and Cl2. Field emission scanning electron microscopy revealed that 25% C2F6 generated the greatest vertical etch profile; hence, etch parameters were varied at this concentration. The effects of rf power, dc-bias voltage and gas pressure on the etch rate and etch profile were also investigated. The etch rate and degree of anisotropy in the etch profile increased with increasing rf power and dc-bias voltage and decreasing gas pressure. X-ray photoelectron spectroscopy analysis of the films etched under a C2F6/Ar gas mixture revealed the existence of etch byproducts containing F (i.e. TiFx) over the film. CxFy compounds were not detected on the film surface, probably due to contamination with atmospheric carbon.

Structural and photoconductivity properties of silicon carbon thin films

AbstractNanostructured films composed of silicon crystallites dispersed in an hydrogenated amorphous silicon carbon matrix have been deposited by plasma enhanced chemical vapour deposition from silane‐methane mixtures diluted in hydrogen by varying the rf power. Compositional, structural, optical and photoconductivity properties of the films have been investigated. The increase in rf power in the 40‐80 W range enhances the incorporation of carbon and hydrogen in the amorphous matrix and decreases the volume fraction and size of the silicon crystallites leading to an enlargement of the optical band gap from 2.07 to 2.20 eV. Steady state photoconductivity measurements, performed under monochromatic radiations in the visible range, have demonstrated the occurrence of monomolecular recombination kinetics in the samples under illumination and that the mobility‐lifetime product of the free electrons as a function of the optical gap decreases from 1.9 × 10–7 to 2.5 × 10–9 cm2V–1 as in the case of device quality films deposited by silane‐methane mixtures diluted in hydrogen. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dry etching of Co2MnSi magnetic thin films using a CH3OH/Ar based inductively coupled plasma

The inductively coupled plasma etching characteristics of Co2MnSi thin films patterned using a TiN hard mask were investigated by the addition of CH3OH to Ar gas. As the CH3OH concentration increased, the etch rates of Co2MnSi magnetic thin films and TiN hard mask decreased, but the etch profile improved. The effects of rf power, dc-bias voltage and gas pressure on the etch rate and etch profile were also investigated. The etch rate and etch profile degree of anisotropy increased with increasing rf power and dc-bias voltage and decreasing gas pressure. Optical emission spectroscopy analysis revealed that [H], [O], [CO], [OH], [CH3O] and [Ar] species in the CH3OH/Ar plasma played a key role in achieving a good etch profile.

RF Power Effect of Post-Deposition Oxygen Plasma Treatment on HfO2 Gate Dielectrics

The RF power effect of post-deposition O2 plasma treatment on the physical, electrical characteristics, and reliability performance of high-k HfO2 dielectric films were investigated in this study. Increasing RF power in post-deposition O2 plasma treatment results in a stoichiometric HfO2 film, but leading to a thinner interfacial layer with a new Hf-Si bond. Additionally, the electrical performance and reliability of high-k HfO2 dielectric films were related to the RF power in post-deposition O2 plasma treatment. As RF power is less than 50 W, the leakage current density and time-to-breakdown were improved as compared to those of un-treated samples. However, these properties were continuously degraded with an increase of RF power due to plasma damage induced by oxygen active spices in a O2 plasma environment. Therefore, the post-deposition O2 plasma treatment is benefit in the improvement of HfO2 gate dielectric properties, but the plasma power is needed to be well controlled.

Experimental observation of standing wave effect in low-pressure very-high-frequency capacitive discharges

Radial uniformity measurements of plasma density were carried out by using a floating double probe in a cylindrical (21 cm in electrode diameter) capacitive discharge reactor driven over a wide range of frequencies (27–220 MHz). At low rf power, a multiple-node structure of standing wave effect was observed at 130 MHz. The secondary density peak caused by the standing wave effect became pronounced and shifts toward the axis as the driving frequency further to increase, indicative of a much more shortened standing-wave wavelength. With increasing rf power, the secondary density peak shift toward the radial edge, namely, the standing-wave wavelength was increased, in good qualitative agreement with the previous theory and simulation results. At higher pressures and high frequencies, the rf power was primarily deposited at the periphery of the electrode, due to the fact that the waves were strongly damped as they propagated from the discharge edge into the center.

Discrete microfluidics based on aluminum nitride surface acoustic wave devices

To date, most surface acoustic wave (SAW) devices have been made from bulk piezoelectric materials, such as quartz, lithium niobate or lithium tantalite. These bulk materials are brittle, less easily integrated with electronics for control and signal processing, and difficult to realize multiple wave modes or apply complex electrode designs. Using thin film SAWs makes it convenient to integrate microelectronics and multiple sensing or microfluidics techniques into a lab-on-a-chip with low cost and multi-functions on various substrates (silicon, glass or polymer). In the work, aluminum nitride (AlN)-based SAW devices were fabricated and characterized for discrete microfluidic (or droplet based) applications. AlN films with a highly c-axis texture were deposited on silicon substrates using a magnetron sputtering system. The fabricated AlN/Si SAW devices had a Rayleigh wave mode at a frequency of 80.3 MHz (with an electromechanical coupling coefficient k 2 of 0.24 % and phase velocity v p of 5,139 m/s) and a higher-frequency-guided wave mode at 157.3 MHz (with a k 2 value of 0.22 % and v p of 10,067 m/s). Both modes present a large out of band rejection of ~15 dB and were successfully applied for microfluidic manipulation of liquid droplets, including internal streaming, pumping and jetting/nebulization, and their performance differences for microfluidic functions were discussed. A detailed investigation of the influences of droplet size (ranging from 3 to 15 μL) and RF input power (0.25–68 W) on microdroplet behavior has been conducted. Results showed that pumping and jetting velocities were increased with an increase of RF power or a decrease in droplet size.

마그네트론 스퍼터링법으로 증착시킨 TiC 박막의 물리적, 전기적 특성에서 RF 파워의 영향

TiC thin films were deposited on Si wafer by unbalanced magnetron sputtering (UBMS) system with two targets of graphite and titanium. During the TiC sputtering, the RF power was varied from 100 W to 175 W and the physical and electrical properties of TiC films were investigated. The hardness and rms surface roughness of TiC films were improved with increasing RF power and the maximum hardness about 24 GPa and the minimum rms surface roughness about 1.2 nm were obtained. The resistivity of TiC films was decreased with increasing RF power. Consequently, the physical and electrical properties of TiC film wewe improved with increasing RF power.

Understanding the amorphous-to-microcrystalline silicon transition in SiF4/H2/Ar gas mixtures.

We report on the growth of microcrystalline silicon films from the dissociation of SiF4/H2/Ar gas mixtures. For this growth chemistry, the formation of HF molecules provides a clear signature of the amorphous to microcrystalline growth transition. Depositing films from silicon tetrafluoride requires the removal of F produced by SiF4 dissociation, and this removal is promoted by the addition of H2 which strongly reacts with F to form HF molecules. At low H2 flow rates, the films grow amorphous as all the available hydrogen is consumed to form HF. Above a critical flow rate, corresponding to the full removal of F, microcrystalline films are produced as there is an excess of atomic hydrogen in the plasma. A simple yet accurate phenomenological model is proposed to explain the SiF4/H2 plasma chemistry in accordance with experimental data. This model provides some rules of thumb to achieve high deposition rates for microcrystalline silicon, namely, that increased RF power must be balanced by an increased H2 flow rate.

Tuning the work function of graphene by nitrogen plasma treatment with different radio-frequency powers

Graphene prepared by the chemical vapor deposition method was treated with nitrogen plasma under different radio-frequency (rf) power conditions in order to experimentally study the change in the work function. Control of the rf power could change the work function of graphene from 4.91 eV to 4.37 eV. It is shown that the increased rf power may lead to the increased number of graphitic nitrogen, increasing the electron concentration, and shifting the Fermi level to higher energy. The ability to controllably tune the work function of graphene is essential for optimizing the efficiency of optoelectronic and electronic devices.

Tribological and electrical properties of TiO2 thin films for polymer insulator as the dielectric coating of electric railroad

TiO2 thin films were deposited on glass and polymer insulator substrates as self-cleaning coatings. TiO2 films were deposited at various RF powers by the unbalanced RF magnetron sputtering method using a TiO2 ceramic target. We investigated the tribological, structural, and electrical properties of the deposited TiO2 films at various RF powers. The result showed that the hardness and elastic modulus values of the TiO2 films increased with the increase of RF power. The surface roughness and contact angle values also increased with the increase of RF power. Also, the rms leakage currents of the TiO2 films were low for the insulator coating layer. The TiO2 films fabricated in this work are suitable for the protection of polymer insulators because of their low leakage current and good tribological properties.

Highly transparent RF magnetron-sputtered indium tin oxide films for a-Si:H/c-Si heterojunction solar cells amorphous/crystalline silicon

We prepared highly transparent magnetron-sputtered indium tin oxide (ITO) films deposited at various RF powers for a-Si:H(p)/c-Si heterojunction solar cell applications. The surface morphology of ITO films improved in terms of an increase in grain size as the RF power increased. Rapid growth of the (400) plane was observed with increasing RF power, while the (222) plane remain unchanged. The ITO film deposited at 100W showed the lowest resistivity of 3.8×10−4Ωcm and highest visible transmittance of 90.19%. The deposition rate and optical bandgap of ITO films were varied from 20 to 100nm/min and from 3.68 to 3.77eV for RF power from 50 to 250W, respectively. Highly transparent ITO films were utilized as the front anti-reflection layer in heterojunctions with intrinsic thin-layer (HIT) solar cells showed the efficiency of 16.3% for RF power of 100W. The HIT solar cells deposited at RF power of 100W also exhibited higher carrier lifetime and implied voltage.