Applied Rf Power Research Articles

Electrochemical Properties of Graphitized Carbonaceous Thin Films Prepared by PACVD

Graphitized carbonaceous thin-film electrodes were prepared by plasma-assisted chemical vapor deposition (PACVD). X-ray diffraction and Raman spectroscopy showed that while the bulk of the film was highly crystallized, its surface was less crystallized, indicating that this surface-modified graphitized thin-film electrode was obtained by a single process. The structures of the surface and bulk of the thin film are influenced by applied radio frequency (rf) powers: the crystallinity of the surface increased with increasing applied rf power, while the crystallinity of the interior bulk decreased with increasing applied rf power. The electrochemical properties of the obtained films were studied in electrolyte consisting of propylene carbonate or ethylene carbonate and diethyl carbonate (1:1 by volume) containing 1 mol by cyclic voltammetry and ac impedance spectroscopy. Because the crystallinity of the surface is low, nearly identical electrochemical properties were seen regardless of the electrolytes used, although the bulk structure is highly graphitized. AC impedance spectroscopy showed that charge transfer resistance decreased with decreasing applied rf power, which suggests that highly graphitized carbonaceous thin films with a less-crystallized surface should be ideal electrodes for the fabrication of thin-film batteries. © 2004 The Electrochemical Society. All rights reserved.

Characterization of a capacitively coupled RF plasma for SiO2 deposition: numerical and experimental results

A fluid model including an electron beam of hot electrons is presented and used to describe the transport of charged particles in a 13.56-MHz O2 plasma. An increase in the electron density when the RF power increases is observed from Langmuir probe measurements. The calculated evolution of the electron number density shows a reasonable agreement if the secondary emission coefficient is chosen equal to 10−4 on a steel (316L) electrode. The values of the plasma potential increase with increasing RF power from 30 to 35 V at 0.5–0.6 Torr, in the range 100–300 W. Surprisingly, the electron temperature decreases with increasing applied RF power. No clear explanation for this behavior is available yet.

Creation of SiOF films with SiF4/O2 plasmas: From gas-surface interactions to film formation

Fluorinated SiO2 (SiOF) films have been studied because of their relatively low dielectric constant and their potential as a replacement for SiO2 in the microelectronics industry. Despite the intense scrutiny, many of the details of the mechanisms for SiOF film deposition remain unclear. Here, we examined the macroscopic and molecular level chemistry of SiOF film deposition using SiF4/O2 plasmas. In the film formation studies, the plasma parameters of SiF4 fraction in the feed gases, F, defined as SiF4/(SiF4+O2), and applied rf power (P) were examined as well as the effects of ion bombardment and substrate temperature on film deposition. Fluorine incorporation in the film increases with both F and P. Film-deposition rate also increases with P, whereas its dependence on F is more complex. Ion bombardment decreases the film deposition rate and affects film composition significantly. On the molecular level, we examined the surface reactivity of SiF and SiF2 during SiOF film deposition using the imaging of radicals interacting with surfaces technique. SiF2 shows significant surface production during film deposition. The scattering coefficient S varies from 1.63±0.07 to 2.01±0.07. In contrast, SiF shows high surface reactivity R (defined as 1−S for S⩽1), which varies from 0.96±0.13 to 0.73±0.09, depending on plasma parameters. The surface interactions of SiF and SiF2, along with plasma gas-phase composition, were correlated with film characteristics to reveal possible film-deposition mechanisms.

InN films deposited by rf reactive sputtering in pure nitrogen gas

We have investigated the effect of deposition conditions on the crystal structure and optical properties of InN films deposited by reactive sputtering in pure nitrogen gas. InN films have been deposited onto glass, (0 0 0 1) sapphire and (1 1 1) Si substrates by rf reactive puttering of pure In target. The nitrogen gas pressure, substrate temperature and applied rf power were varied in the range of 0.5–1.3 Pa, RT∼600°C and 20–55 W, respectively. All deposited films had a wurtzite structure with strong 〈0 0 0 1〉 preferred orientation. In the case of the glass substrate, the full-width at half-maximum of InN 0 0 0 2 peak became large with increasing applied rf power and/or nitrogen gas pressure. The angular dispersion of the c -axis of films deposited onto sapphire increases with increasing substrate temperature. This behavior was similar to that of the films on glass substrates. The angular dispersion of the c -axis of films deposited on (1 1 1) Si at temperatures between 200° and 450°C was smaller than those films grown on the others. This may suggest the existence of some interactions between the growing InN film and (1 1 1) Si substrate.

Polymer-Like C:H Thin Film Coating of Nanopowders in Capacitively Coupled RF Discharge

Nanopowders of amorphous SiO2, with typical particle sizes of 30–80 nm, were treated under the non-equilibrium plasma conditions, created by a capacitively coupled (CC) RF discharge formed in pure methane or ethane. The plasma gas flow rate varied between 0.02 and 0.06 slpm, with reactor pressures between 1000 and 5000 Pa, and applied RF power inputs between 700 and 1500 W. The plasma properties were monitored through measurements of the rotational temperature, as derived from the C2 5160 A Swan band and N2 second positive 3577 A band, and the atomic hydrogen excitation temperature, from the Hβ Hγ and Hδ lines during the powder treatment process. The compositions of the gases that passed through the plasma were analyzed by mass spectrometry. In spite of the evidence for the presence of CnH2n+2 and CnH2n (n=1–3) species and acetylene in the discharge, the homogeneous formation of soot was not observed. At the same time, the introduced nanoparticles were observed to act as centers for the inception and growth of C:H thin coatings in the form of a polymer-like hydrocarbon layers, of thickness between <5 and 30 nm. The results of TEM, IR spectroscopy, thermo-gravimetric and precision calorimetric analysis performed on the treated powders provide evidence to the formation of an amorphous, high density C:H matrix on the particles' surfaces.

InN films deposited by rf reactive sputtering in pure nitrogen gas

We have investigated the effect of deposition conditions on the crystal structure and optical properties of InN films deposited by reactive sputtering in pure nitrogen gas. InN films have been deposited onto glass, (0 0 0 1) sapphire and (1 1 1) Si substrates by rf reactive puttering of pure In target. The nitrogen gas pressure, substrate temperature and applied rf power were varied in the range of 0.5–1.3 Pa, RT∼600°C and 20–55 W, respectively. All deposited films had a wurtzite structure with strong 〈0 0 0 1〉 preferred orientation. In the case of the glass substrate, the full-width at half-maximum of InN 0 0 0 2 peak became large with increasing applied rf power and/or nitrogen gas pressure. The angular dispersion of the c-axis of films deposited onto sapphire increases with increasing substrate temperature. This behavior was similar to that of the films on glass substrates. The angular dispersion of the c-axis of films deposited on (1 1 1) Si at temperatures between 200° and 450°C was smaller than those films grown on the others. This may suggest the existence of some interactions between the growing InN film and (1 1 1) Si substrate.

RF MEMS Switches With Enhanced Power-Handling Capabilities

This paper reports on the experimental and theoretical characterization of RF microelectromechanical systems (MEMS) switches for high-power applications. First, we investigate the problem of self-actuation due to high RF power and we demonstrate switches that do not self-actuate or catastrophically fail with a measured RF power of up to 5.5 W. Second, the problem of switch stiction to the down state as a function of the applied RF power is also theoretically and experimentally studied. Finally, a novel switch design with a top electrode is introduced and its advantages related to RF power-handling capabilities are presented. By applying this technology, we demonstrate hot-switching measurements with a maximum power of 0.8 W. Our results, backed by theory and measurements, illustrate that careful design can significantly improve the power-handling capabilities of RF MEMS switches.

Inductively coupled plasma chemistry examinations with visible acousto-optic tunable filter hyperspectral imaging

Inductively coupled plasma optical emission spectrometry (ICP-OES) is widely used in trace-metal analysis. However, the behavior of this hot, ionized gas and effects on analyte excitation and ionization is not fully understood. To obtain sufficient information on the characteristics of plasma, two previous approaches, Abel inversion and tomography, have been used. Major drawbacks of these approaches include complex optical and data manipulation systems, significant amounts of time required for data collection, and long-term plasma drift and flicker. Initial examinations of an approach to alleviate many of these problems are presented. A hyperspectral imaging (HSI) system using an acousto-optic tunable filter (AOTF) as a wavelength selection device and a charge coupled device (CCD) camera as a detector is described. In these studies, the behavior of a visible paratellurite AOTF is presented. Six elements that yield intense emission lines in the visible wavelength region were examined. With in-house written software, plasma image background correction was achieved in a rapid fashion. Plasma chemistry was studied while varying plasma conditions including the applied rf power, nebulizer sample carrier gas flow, and liquid sample delivery rate. Results indicate that correlations between elemental excitation and ionization energies and the enhancements on emission intensities could be clearly discerned. It is demonstrated that the AOTF-HSI system has the potential to be a powerful tool for plasma chemistry research.

Au/SiO2 Nanosystems by XPS

Au/SiO2 nanocomposites were prepared by rf-sputtering of gold on amorphous silica substrates. Deposition experiments were carried out in Ar plasmas at temperatures as low as 60 °C. Particular attention was devoted to the combined influence of the applied rf power and total pressure on the chemico-physical properties of the final nanosystems. In particular, low pressures (&amp;lt;0.2 mbar) and high rf powers (&amp;gt;20 W) resulted in a higher sputtering yield, allowing the deposition of continuous gold films on silica. Conversely, decreased sputtering yields (at higher pressures and lower powers) enabled the preparation of discontinuous Au/SiO2 nanosystems. A thorough investigation of the structure-properties relationships was attained by means of a multi-technique characterization. In particular, laser reflection interferometry (LRI) was employed for an in situ monitoring of growth processes, while glancing-incidence x-ray diffraction (GIXRD) and transmission electron microscopy (TEM) provided valuable information on the system nanostructure. Moreover, x-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy, and atomic force microscopy (AFM) were used to investigate the chemical composition, optical properties, and surface morphology, respectively. This study is dedicated to an XPS investigation of the principal core levels (Au, Si, O) of Au/SiO2 nanosystems. In particular, detailed scans for the Au 4f, Si 2s, O 1s, and C 1s regions and related data for a gold film on silica and a discontinuous Au/SiO2 specimen are presented and discussed.

Study of Ag/SiO2 Nanosystems by XPS

Silica-supported silver nanocomposites were synthesized by rf sputtering of Ag from Ar plasmas. Depositions were performed on amorphous silica substrates at temperatures as low as 60 °C. As a general rule, a careful choice of the synthesis conditions allowed the obtainment of Ag/SiO2 nanosystems with well-tailored chemico-physical properties. In fact, a proper combination of the applied rf power and total pressure resulted in a fine tailoring of the nanosystem structure and morphology, enabling the preparation of both cluster/island-like systems or continuous thin films. A detailed characterization of the obtained specimens was attained by the combined use of several analytical techniques. While laser reflection interferometry (LRI) was employed for an in situ real-time investigation of growth dynamics, glancing-incidence x-ray diffraction (GIXRD), and transmission electron microscopy (TEM) provided useful information on the system nanostructure. Furthermore, x-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy, and atomic force microscopy (AFM) were used to investigate the chemical composition, optical properties, and surface morphology, respectively. This work has been focused on the XPS characterization of two representative Ag/SiO2 specimens. In particular, detailed scans for the Ag 3d, Ag MVV, Si 2s, O 1s, and C 1s regions and related data for a silver thin film on silica and a discontinuous Ag/SiO2 specimen are presented and discussed.

Deodorization of Dimethyl Sulfide Using a Discharge Approach at Room Temperature

The traditional technologies for odor removal of thiol usually create either secondary pollution for scrubbing, adsorption, and absorption processes, or sulfur (S) poisoning for catalytic incineration. This study applied a laboratory-scale radio-frequency plasma reactor to destructive percentage-grade concentrations of odorous dimethyl sulfide (CH3SCH3, or DMS). Odor was diminished effectively via reforming DMS into mainly carbon disulfide (CS2) or sulfur dioxide (SO2). The removal efficiencies of DMS elevated significantly with a lower feeding concentration of DMS or a higher applied rf power. A greater inlet oxygen (O2)/DMS molar ratio slightly improved the removal efficiency. In an O2-free environment, DMS was converted primarily to CS2, methane (CH4), acetylene (C2H2), ethylene (C2H4), and hydrogen (H2), with traces of hydrogen sulfide (H2S), methyl mercaptan (CH3SH), and dimethyl disulfide. In an O2-containing environment, the species detected were SO2, CS2, carbonyl sulfide, carbon dioxide (CO2), CH4, C2H4, C2H2, H2, formal-dehyde, and methanol. Differences in yield of products were functions of the amounts of added O2 and the applied power. This study provided useful information for gaining insight into the reaction pathways for the DMS dissociation and the formation of products in the plasmolysis and conversion processes.

Radio-frequency-driven near atmospheric pressure microplasma in a hollow slot electrode configuration

We report hollow electrode geometries that support near atmospheric (89 kPa) microdischarges in Ar and Ar–air mixtures when excited at 13.56 MHz with rf voltages of 50–230 V. The slot dimensions are 200 μm wide by 400–600 μm deep and 3–35 cm in length. Optical emission along the slot length is uniform in intensity at applied rf power levels up to 10 W/cm of slot length under the experimental conditions described herein. When metal electrodes are employed, we can draw 0.18 A/cm of self-bias dc current into the rf-driven plasma. Measurements of the electrode self-bias dc voltage level indicate operation in both negative as well as positive self-bias discharge modes. The latter mode, to our knowledge, has not been reported previously in rf microdischarges at near atmospheric pressures.

Probe diagnostics of the RF barrier-torch discharge at atmospheric pressure

Abstract Accurate control of plasma microparameters at the position of the substrate is crucial factor in applications of the barrier-torch plasma source for technological purposes. We present measurements of the electron temperature T e in the RF barrier-torch discharge by means of the planar RF-compensated Langmuir probe. The probe was mounted at the substrate position. The error caused by collisions of charged particles with neutrals in the space-charge sheath around the probe (collision probe working regime) at atmospheric pressure is discussed. In order to minimize this error the single probe technique was used to acquire the probe data, which were then recalculated to get the double probe characteristic. From this the electron temperature T e has been obtained in usual manner. The T e was measured at the position of the substrate in the single- and multi-torch barrier atmospheric plasma-jet systems. Using He as a working gas T e was found to be in the interval T e =2.7–6 eV depending on the applied RF power and system configuration. The neutral gas temperature has been measured by optical diagnostics and found to be 400–800 K. The plasma of the RF barrier-torch discharge is therefore strongly non-isothermal even at such high operation pressure.

Ionic densities and ionization fractions of sputtered titanium in radio frequency magnetron sputtering

Ionic densities of sputtered titanium (Ti) in rf magnetron sputtering were measured using an optical absorption method. Measurements of ionic densities of sputtered Ti were made by varying pressure of Ar gas, applied rf power and distance from the target. The densities of Ti atoms were measured using an atomic absorption method for deriving ionization fraction of sputtered Ti. At the rf power of 200 W, ionic densities of Ti were found to be lower than 1.0×1010 cm−3 indicating that ionization fractions were of the order of several percentages at Ar pressures lower than the pressure of several Pascals that is used in conventional sputtering. The ionic density increased with increasing pressure and reached a maximum value of 4.8×1010 cm−3 at the Ar pressure of 21 Pa for z=15 mm where z is axial distance with origin at the Ti target surface. Also, both ionic and atomic densities of sputtered Ti increased monotonically with increasing rf power resulting in an almost constant value of ionization fraction at the Ar pressure of 7 Pa. Probe measurements indicated that fractions of Ti ion were around 30%–40% of the total ionic density which at pressures higher than several Pa was mainly made up of Ar ion. The ionization rate of electron impact for Ti and Ar is discussed based on measurements made by the authors.

Investigation of the RF plasma jet system for deposition of LiCoO x thin films

The RF plasma jet system was investigated as a source for the sputtered deposition of LiCoO x thin films. As preliminary results of experiments, LiCoO x films with hexagonal high temperature structure were deposited. The RF hollow cathode in the shape of the cylindrical nozzle was sintered from powder of LiCoO 2. This hollow cathode was reactively sputtered in Ar+O 2. Plasma jet parameters were investigated during the sputtering process by a Langmuir probe system in the position of the substrate. The electron energy distribution function (EEDF) deviated from the Maxwellian distribution mainly in the energetic range below 5 eV. For higher energies above this value, the EEDF could be approximated with a Maxwellian fit in the limited interval of energies. Obtained electron concentrations were in the range n e=10 9–6×10 10 cm −3 and were strongly dependent on the magnitude of the applied RF power P RF. Electron temperature T eh describing only the limited energy part of EEDF was calculated from this Maxwellian fit and the dependence of T eh on P RF is discussed. Besides XRD, deposited films were investigated by electron microprobe system, scanning electron microscopy and cyclic voltammetry.

Reactive Species in RF Plasma Sputtering Deposition of Nanocrystalline Calcium Phosphate Bio-Active Films

Optical emission of reactive plasma species during the synthesis of functionally graded calcium phosphate-based bioactive films has been investigated. The coatings have been deposited on Ti-6Al-4V orthopedic alloy by co-sputtering of hydroxyapatite (HA) and titanium targets in reactive plasmas of Ar + H2O gas mixtures. The species, responsible for the Ca-P-Ti film growth have been non-intrusively monitored in situ by a high-resolution optical emission spectroscopy (OES). It is revealed that the optical emission originating from CaO species dominates throughout the deposition process. The intensities of CaO, PO and CaPO species are strongly affected by variations of the operating pressure, applied RF power, and DC substrate bias. The optical emission intensity (OEI) of reaction species can efficiently be controlled by addition of H2O reactant.

Deposition of plasma polymerized perfluoromethylene-dominated films showing oil-repellency

Plasma polymerized fluorocarbon films were deposited onto polyethylene (PE) substrates to increase oil-repellency of PE. Depositions were performed using the monomer, 1H,1H,2H-perfluoro-1-dodecene in a parallel-plate, radio frequency (rf) reactor, with variable continuous-wave power ranging from 2 to 160 W. The film deposition rate and morphology were strongly dependent on the applied rf power. Most importantly, the chemical structure of the deposited films was also altered, resulting in changes in contact angles of various liquids and the surface energy. Films deposited at low power were composed mainly of perfluoromethylene (CF2) species (up to 67.2%), as shown by x-ray photoelectron spectroscopy (XPS). With an increase in rf power, CF2 content in the film decreased as further fragmentation of the monomer occurred. For each deposition at varying rf powers, even at powers as low as 2 W, the C=C and C–H bonds in the monomer were dissociated by the plasma and not incorporated into the films, as shown by Fourier transform infrared spectroscopy. Oil-repellency, as shown by increased contact angles of hydrocarbon liquids, was found to increase as the amount of CF2 species increased in the film structure. A low critical surface energy (2.7 mJ/m2) was calculated for the film deposited with only 2 W of rf power. Adhesion of the plasma-polymerized films to the PE was also evaluated and found to be poor for films with a high concentration of CF2 species, where cohesive failure within the film occurred. However, adhesion increased as a function of rf power, where the film structure showed more cross-linking. There was a compromise between producing a film with high oleophobicity (oil-repellency) while maintaining adhesion of the film to PE, as some disruption of the CF2 chains in the films was necessary for cohesion through cross-linking.

Velocity Distributions of SiF and SiF2 in an SiF4 Plasma Molecular Beam

Our imaging of radicals interacting with surfaces (IRIS) technique has been used to measure the velocity distributions of SiF and SiF2 molecules in an effusive SiF4 plasma molecular beam as a function of applied rf power. Modeling the kinetic data yields the corresponding translational temperatures ϑT. The translational temperatures of both SiF and SiF2 increase with radio frequency (rf) power, from 571 ± 180 K at 80 W to 869 ± 54 K at 200 W for SiF, and from 427 ± 65 K at 80 W to 557 ± 31 K at 200 W for SiF2. These differences in ϑT for SiF and SiF2 indicate that the SiF4 plasma is not in full thermal equilibrium. Possible mechanisms for the trend of increasing ϑT with rf power are discussed by correlating SiF and SiF2 velocities with relative gas-phase densities. In addition, the effects of ϑT on the surface scatter coefficients for each molecule have also been addressed.

Hollow Electrode Enhanced RF Glow Plasma Generation and its Application to the Fast Deposition of Microcrystalline Silicon Films

AbstractA hollow electrode enhanced RF glow plasma excitation technique has been newly developed. In this technique, the reactor is divided into a capacitively-coupled RF glow discharge space and a processing space by the counter electrode, which includes a hollow structure and is placed between a RF electrode and the substrate. After introducing hydrogen gas into the chamber and applying RF power to the electrode, high intensity plasma emission is observed near and inside the hollow structure attached to the counter electrode. By using hollow RF electrode excitation in addition to the hollow counter electrode technique, it is found that plasma emission is further enhanced. The application of these discharge types for semiconductor processing is studied in the case of plasma enhanced chemical vapor deposition (PECVD) of hydrogenated microcrystalline silicon thin films. High crystallinity, photo-sensitivity and a maximum deposition rate of 4.9nm/s can all be achieved at a plasma excitation frequency of 13.56MHz and a temperature of 300°C. Properties of these plasmas are investigated by observing the plasma emission pattern and optical emission spectrum analysis. It is found that, using additional hollow RF electrode discharge, faster processing of device grade hydrogenated microcrystalline silicon thin films can be achieved under lower RF power compared to hollow counter electrode technique alone.

Characterization of damage in reactive ion etched ZnTe

Reactive ion etching of ZnTe has been carried out at various applied rf powers and CH4/H2 concentrations. The damage induced during dry etching is characterized by low-temperature photominescence (PL) measurements. It is observed that the PL intensity of the free excitons decreases with increasing applied rf power, which is ascribed to the increase of the surface damage by ion bombardment. The amount of the surface damage can be reduced by adding more CH4 in the gas mixture due to the effect of chemical etching.