Applied Rf Power Research Articles

Low-temperature deposition of silicon oxide and silicon nitride by reactive magnetron sputtering

In this study, oxide and nitride films were deposited at room temperature through the reaction of silicon sputtered by argon and oxygen ions or argon and nitrogen ions at 250 and 350W with 0.67Pa pressure. It was observed that for both thin films the deposition rates increase with the applied RF power and decrease with the increase of the gas concentration. The Si/O and Si/N ratio were obtained through RBS analyses and for silicon oxide the values changed from 0.42 to 0.57 and for silicon nitride the values changed from 0.4 to 1.03. The dielectric constants were calculated through capacitance–voltage curves with the silicon oxide values varying from 2.4 to 5.5, and silicon nitride values varying from 6.2 to 6.7, which are good options for microelectronic dielectrics.

Solvent-Induced Porosity in Ultrathin Amine Plasma Polymer Coatings

Plasma polymers deposited from n-heptylamine onto silicon wafers have been found to form a porous microstructure when immersed in water and other solvents, with pores of dimensions and densities that vary considerably between coatings deposited under different plasma conditions. This solvent-induced pore formation was found to correlate with the observed percentage of extractable material. With low radio frequency (rf) power inputs, the resultant softer coatings possess considerably more extractable material than coatings deposited at higher applied power levels. The porosity is thus proposed to result from the formation of voids created by the extraction of soluble low-molecular-weight polymeric material, which produces shrinkage stress that the coating, firmly attached to the substrate, cannot relieve by macroscopic contraction. The microscopic contraction of plasma polymer volume creates voids that appear to span the entire film thickness. The effect of aging plasma polymers in air was also investigated. For films deposited at low power it led to reduced extraction of soluble material and different pore morphology, whereas for films deposited at higher rf power levels, the extracted amounts and pore formation were the same for aged coatings. It was also found that the density of surface amine groups was lower for films deposited under the two lowest power settings, in contrast to the commonly held belief that the use of minimal applied rf power aids retention of functional groups. These porous plasma polymer coatings with surface groups suitable for further interfacial chemical immobilization reactions may be useful for various membrane and biotechnology applications.

Plasma characteristics of low-k SiOC(–H) films prepared by using plasma enhanced chemical vapor deposition from DMDMS/O2 precursors

We report in-situ plasma diagnostics during the deposition of low dielectric constant SiOC(–H) thin films on p-Si(100) substrates by using plasma enhanced chemical vapor deposition with dimethyldimethoxysilane (DMDMS, C4H12O2Si) and oxygen gas as precursors. The bulk plasma was characterized by using Langmuir probe and optical emission spectroscopy as a function of radio frequency (rf) power. The electron density and electron temperature were found to increase with increasing rf power. As the applied rf power increases the –CH3 groups present in the DMDMS precursor first dissociated into CH, C and O, without forming CH2 and CH3 radicals and then the CH radical further dissociated into C, Hα, and Hβ related radicals, respectively. The SiO2–C2 and SiO3–C, SiO–C3 and C–C/C–H bonding configurations of the SiOC(–H) film were increased with increasing rf power whereas Si–O2 bond decreased. These bonding structures help to reduce the k value of SiOC(–H) films. The lowest dielectric constant of 2.04 was obtained for the film with an rf power of 700 W.

Robust single-parameter quantized charge pumping

This paper investigates a scheme for quantized charge pumping based on single-parameter modulation. The device was realized in an AlGaAs–GaAs gated nanowire. We find a remarkable robustness of the quantized regime against variations in the driving signal, which increases with applied rf power. This feature, together with its simple configuration, makes this device a potential module for a scalable source of quantized current.

Preparation of Rutile and Anatase Phases Titanium Oxide Film by RF Sputtering

Titanium oxide films were prepared by RF magnetron sputtering onto glass substrates. The effects of RF power and deposition temperature on crystalline structure, morphology and energy gap were investigated, which were analyzed by X-ray diffraction, SEM and UV-Vis spectrometer, respectively. Results show that rutile phase is the favored structure during deposition. Applying RF power in the range of 50-250 W, the amorphous, rutile, and both rutile and anatase phases TiO2 films were obtained in sequence, while the content of anatase is similar in the range of 34-37% although the RF power increases. Increasing the deposition temperature, the anatase phase coexists in the rutile phase in the range of 100-200 degrees C, and the content of anatase increases from 20 to 41% with the deposition temperature. In addition, according to the morphology observation, the granulous surface is found in rutile phase while facetted surface in anatase phase when titanium oxide films deposited at various RF powers and substrate temperatures. The band gap energy of titanium oxide evaluated from (alphahv)1/2 versus energy plots show that the energy gap decreases with RF power increasing.

Diagnostics of N2–Ar plasma mixture excited in a 13.56 MHz hollow cathode discharge system: application to remote plasma treatment of polyamide surface

N2–x% Ar plasma gas mixture, generated in a hollow cathode RF discharge system, has been characterized by both optical emission spectroscopy (OES) and double Langmuir probe, as a function of experimental parameters: total pressure (5–33 Pa), and different fractions of argon (7 ≤ x ≤ 80), at a constant applied RF power of 300 W. N2 dissociation degree has been investigated qualitatively by both the actinometry method and the ratio of the atomic nitrogen line emission intensity at 672.3 nm to the vibrational band (0–0) of the N2 second positive system at 337.1 nm. Both methods showed that the increase in argon fraction enhances the dissociation of N2, with a maximum at x = 50 for the pressure of 5 Pa, although the two methods give two opposite trends as a function of total pressure. Spectroscopic measurements showed that the vibrational temperature of the N2 second positive system increases with both argon fraction and total pressure increase, it lies between 4900 and 12 300 K. Langmuir probe measurements showed that, in the remote zone, the electron temperature falls in the range 1.57–1.75 eV, the density varies between 5 × 109 and 1.4 × 1010 cm−3 and that both the plasma ionization degree and electron temperature increase towards the source. In addition, the process of plasma–polyamide (PA) surface interaction, in the remote plasma zone, has been studied through OES analysis during plasma treatment of PA to monitor the possible emissions due to the polymer etching. An increase in atomic nitrogen line (672.3 nm) intensity is obtained, atomic carbon line (833.52 nm) and the band emission (0–0) from the CN (B 2Σ+–X 2Σ+) violet system were observed. The PA surface modification has been confirmed through the improvement of its hydrophilic character as the water contact angle measured after the plasma treatment significantly decreased.

Nanocrystalline silicon films prepared from silane plasma in RF-PECVD, using heliumdilution without hydrogen: structural and optical characterization

The effect of RF power on the nanocrystallization of a Si:Hnetwork has been studied by PECVD at a substrate temperature of200 °C and a gas pressure of 0.5 Torr, using silane as the source gas and helium as diluent, withoutusing hydrogen. Optical characterization of the films has been done by UV–vis spectroscopy.Structural characterization has been performed by infrared absorption, x-ray diffraction,micro-Raman studies and electron microscopy by HRTEM and FESEM. In general, astructural transformation from the amorphous to nanocrystalline phase accomplished bymetastable helium atoms in the plasma has been identified at a low RF power of 80 W.With an increase in the applied RF power up to 150 W, systematic improvement incrystallinity has been shown as depicted by increased crystalline volume fraction(∼77%), smaller grain size(∼7 nm) reduced bondedhydrogen content (∼8 at.%), enhanced polymerization in the network and gradual widening in the optical gap(∼1.86 eV) obtained at ahigh deposition rate (107 Å min−1), using 1 sccm of silane as the source gas and helium as the only diluent. He dilution of theSiH4 plasma is a well-proven approach to increase the growth rate. However, a nanocrystallinenetwork with high crystalline volume fraction and well-aligned crystallographic latticedistribution, attained in Si:H from a low-power RF plasma at a growth temperature as low as200 °C, and that obtained from purely He dilution, without usingH2, is being reported for the first time. The striking feature comprises that nc-Si:H films ofincreasing crystalline volume fraction, reduced bonded hydrogen content and wider opticalgap are produced with simultaneously increasing deposition rates, which deserves extensivetechnological impact.

Photoluminescence from PP-HMDSO thin films deposited using a remote plasma of 13.56 MHz hollow cathode discharge

Room temperature photoluminescence (PL) from plasma-polymerized hexamethyldisiloxane (PP-HMDSO) thin films deposited on silicon wafers has been investigated as a function of both the applied RF power and the monomer flow rate. Films were deposited in a low pressure–low temperature remote plasma ignited in a 13.56 MHz hollow cathode discharge reactor, using pure HMDSO as a monomer and Ar as a feed gas. The substrate temperature during the deposition was as low as 40 °C and the total pressure was about 0.03 mbar. Optical emission spectroscopy (OES) has been used as in situ tool for monitoring the different chemical species present in the plasma during deposition processes. The deposited PP-HMDSO films showed a strong, broad ‘green/yellow’ PL band. The RF power and the flow rate of the HMDSO monomer are found to have a significant impact on the PL intensity of the deposited film. The changes in the chemical bonding of the film as a function of deposition parameters have been investigated by using the Fourier transform infrared (FTIR) spectroscopic analysis and are related to PL and OES results. The ‘green/yellow’ PL band is ascribed to chemical groups and bonds of silicon, hydrogen and/or oxygen constituting the films, in particular, SiH, SiO bonds and silanol Si–O–H groups.

Optical constants of silicone-like (Si:O x:C y:H z) thin films deposited on quartz using hexamethyldisiloxane in a remote RF hollow cathode discharge plasma

Deposition of amorphous silicone-like (Si:O x :C y :H z ) thin films in a remote RF hollow cathode discharge plasma using hexamethyldisoloxane as monomer and Ar as feed gas has been investigated for films optical constants and plasma diagnostic as a function of RF power (100–300 W) and precursor flow rate (1–10 sccm). Plasma diagnostic has been performed using Optical Emission Spectroscopy (OES). The optical constants (refractive index, extinction coefficient and dielectric constant) have been obtained by reflection/transmission measurements in the range 300–700 nm. It is found that the refractive index increases from 1.92 to 1.97 with increasing power from 100 to 300 W, and from 1.70 to 1.92 with increasing precursor flow rate from 1 to 10 sccm. The optical energy band gap E g and the optical-absorption tail Δ E have been estimated from optical absorption spectra, it is found that E g decreases from 3.28 to 3.14 eV with power increase from 100 to 300 W, and from 3.54 to 3.28 eV with precursor flow rate increase from 1 to 10 sccm. Δ E is found to increase with applied RF power and precursor flow rate increase. The dependence of optical constants on deposition parameters has been correlated to plasma OES.

Barium titanate thin films plasma etch rate as a function of the applied RF power and Ar/CF4 mixture gas mixing ratio

AbstractBaTiO3 (BT) nanocrystalline thin films were plasma etched in the course of several experiments which varied in RF power as well as CF4/(CF4 + Ar) gas‐mixing ratio. The maximum etch rate of approximately 30 nm/min was observed for the maximum power (300 W) and pure Ar plasma atmosphere, which indicates that the process is controlled by the physical mechanism of Ar ion bombardment, while the increasing content of chemically active plasma component (CF4) in the gas mixture slows down barium titanate etch rate. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Determination of the vibrational, rotational and electron temperatures in N2 and Ar–N2 rf discharge

In order to characterize a nonequilibrium molecular plasma from the point of view of translational, vibrational and rotational degrees of freedom and their interaction, the characteristic temperatures of such a plasma were measured in an ICP rf reactor. Both pure nitrogen and argon–nitrogen mixture plasmas were examined for this purpose.The experimental results of rotational (Tr), vibrational (Tv) and electron (Te) temperatures are presented. Vibrational and rotational temperatures were measured as a function of nitrogen content for both E and H modes of ICP discharge using a power range of 45–200 W and pressure range of 2.6–13.3 Pa. Additionally, the pressure dependence of electron temperature in a pure nitrogen discharge was studied. Results show that rotational temperature is ≈370 K for E mode and ≈470 K for H mode and almost does not depend on either the applied rf power or the nitrogen content in the discharge. Vibrational temperature groups in the range 5000–12 000 K increase with applied rf power and constantly decay with an increase of nitrogen content. The measured values and behaviour of electron temperature are comparable with those for the positive column of the dc glow discharge. The results also prove that these three temperatures obey the classical inequality Te > Tv > Tr, as well as clarifying the differences in both vibrational and rotational temperature for different modes of the ICP discharge.

Simulation Study of Stepwise Density Variation with RF Power in a HANBIT Device

One of the peculiar characteristics of the HANBIT discharge is that plasma density varies as stepwise manner on applied RF power and there does not exist stable discharge between the each of steps.We believe that the plasma density is determined as the balance of loss power caused by transport and absorbed power coupled with radio frequency antenna. According to previous simulation concerning RF wave coupling with the plasma, the antenna loading impedance or the plasma resistance is very peaky on the plasma density variation. It implies that the plasma impedance at the density at which the power is balanced is not continuous on applied RF power. Even though the plasma resistance is very sensitive to the plasma conditions of density and external magnetic field and have peaky dependence on plasma conditions, up to now we have used fixed RF matching condition and successfully implemented discharge experiments. To investigate the characteristics of density variation on applied RF power and reason how does the impedance well adjust to separated discharge conditions, we performed self-consistent discharge simulation. The results well explain the behavior of the plasma density on applied RF power and the reason why we can use fixed matching condition for various plasma conditions.

Preparation of carbonaceous thin films by plasma-assisted chemical vapor deposition and their application to energy devices

Preparation of a carbonaceous thin film by plasma-assisted chemical vapor deposition was summarized. First, the resulting carbonaceous thin films were characterized. The resulting carbonaceous thin films were composed of sp2-type carbon and the interlayer spacing (d002) evaluated from X-ray diffraction patterns and the full width at half maximum of the G band in the Raman spectra ascribed the structure of the resulting carbonaceous thin film to a turbostratic structure. The crystallite orientation was depended on the applied rf power based on the transmission electron microscope images. Next, the resulting carbonaceous thin film was used as a negative electrode of lithium-ion batteries. Based on the various electrochemical measurements, it was found that the resulting carbonaceous thin film can be used as a model electrode. The lithium-ion insertion/extraction model was discussed. Finally, the carbonaceous thin film was applied to a coating-layer of metal as a bipolar plate material for polymer electrolyte fuel cells. The improvement in the corrosion property (suppression of metal dissolution) of carbon steel by the carbon-coating was provided by the electroless Ni plating on the carbon steel prior to the carbon-coating.

Surface Reactivity and Energetics of CH Radicals during Plasma Deposition of Hydrogenated Diamondlike Carbon Films

The surface reactivity of CH radicals was measured during plasma deposition of hydrogenated diamondlike carbon (DLC) films using the imaging of radicals interacting with surfaces (IRIS) method. In this technique, spatially resolved laser-induced fluorescence (LIF) is used to determine surface reactivity, R, of plasma species. The measured reactivity of CH is near unity and shows no dependence on the applied rf power (P), argon fraction, substrate temperature, or substrate bias. Kinetic translational temperatures, (T), of CH in the molecular beam were also measured. Modeling of the kinetic data yields ThetaT(CH) values of approximately 2200-2500 K and 1600-1700 K for CH4/Ar plasmas at pressures of 50 and 110 mTorr, respectively, with no clear dependence on the argon fraction (at P = 100 W). The average ThetaT(CH) does, however, change with P, (T) = approximately 2050-9050 K, over the range P = 180-20 W. These results indicate that ThetaT(CH) is associated with the electron temperature in the plasma. The rotational temperature, (R), determined from the CH rotational excitation spectrum is approximately 1450 K with no clear dependence on P or the Ar fraction in the feed. The difference between ThetaT(CH) and ThetaR(CH) can be explained by the different relaxation rates after the dissociation of CH4 by electron impact.

Correlating ion energies and CF2 surface production during fluorocarbon plasma processing of silicon

Ion energy distribution (IED) measurements are reported for ions in the plasma molecular beam source of the imaging of radicals interacting with surfaces (IRIS) apparatus. The IEDs and relative intensities of nascent ions in C3F8 and C4F8 plasma molecular beams were measured using a Hiden PSM003 mass spectrometer mounted on the IRIS main chamber. The IEDs are complex and multimodal, with mean ion energies ranging from 29to92eV. Integrated IEDs provided relative ion intensities as a function of applied rf power and source pressure. Generally, higher applied rf powers and lower source pressures resulted in increased ion intensities and mean ion energies. Most significantly, a comparison to CF2 surface interaction measurements previously made in our laboratories reveals that mean ion energies are directly and linearly correlated to CF2 surface production in these systems.

Improvement of electrical properties of surfactant-templated mesoporous silica thin films by plasma treatment

Surfactant-templated mesoporous silica film draws a great attention due to its superior properties as low-k dielectrics. In this study, electrical properties of the film using Brij-76 surfactant were evaluated after plasma treatment. The selected gases were H 2, O 2, and Ar. X-ray diffraction pattern revealed that mesoporous silica film was highly textured but pore ordering was destroyed when applied rf power and atomic mass of gas increased. Strained Si–O bond near gel pore was reduced and incompletely oxidized Si bond could be controlled after plasma treatment. Optimizing treatment condition can control the structural defects in the wall and as a result, electrical property of the film could be improved. Mesoporous film after H 2 plasma treatment at rf power of 25 W and 100 mTorr showed current density of 3.6 × 10 − 6 A/cm 2 at 1.6 MV/cm. As a conclusion, electrical properties of mesoporous silica film can be improved by plasma treatment through controlling reactivity of gas and ion bombardment effect with low power.

Stabilization of Interchange Modes in Mirror Plasmas by a Nonlinear rf-Plasma Wave Coupling Process

Experimental and theoretical studies are made of the consequences of a nonlinear coupling process between pump rf waves and interchange modes in mirror plasmas. It is demonstrated that the interchange-stable operation window exists depending on the applied rf power and gamma=omega(0)/Omega(i), where omega(0) (Omega(i)) is the angular frequency of the applied rf wave (ion cyclotron frequency). Results are shown that the nonlinear wave coupling process gives rise to the operation window near the resonance (gamma approximately equal to 1), which is elucidated by theoretical analyses combined with full rf wave simulations.

Edge ion heating by launched high harmonic fast waves in the National Spherical Torus Experiment

A new spectroscopic diagnostic on the National Spherical Torus Experiment (NSTX) [J. Spitzer, M. Ono, M. Peng, D. Bashore, T. Bigelow, A. Brooks, J. Chrzanowaki, H. M. Fan, P. Heitzenroeder, T. Jarboe et al., Fusion Technol2. 30, 1337 (1996)] measures the velocity distribution of ions in the plasma edge simultaneously along both poloidal and toroidal views. An anisotropic ion temperature is measured during high power high harmonic fast wave (HHFW) rf heating in helium plasmas, with the poloidal ion temperature roughly twice the toroidal ion temperature. Moreover, the measured spectral distribution suggests that two populations of ions are present and have temperatures of typically 500eV and 50eV with rotation velocities of −50km∕s and −10km∕s, respectively (predominantly perpendicular to the local magnetic field). This bimodal distribution is observed in both the toroidal and poloidal views (for both He+ and C2+ ions), and is well correlated with the period of rf power application to the plasma. The temperature of the hot component is observed to increase with the applied rf power, which was scanned between 0 and 4.3MW. The 30MHz HHFW launched by the NSTX antenna is expected and observed to heat core electrons, but plasma ions do not resonate with the launched wave, which is typically at >10th harmonic of the ion cyclotron frequency in the region of observation. A likely ion heating mechanism is parametric decay of the launched HHFW into an ion Bernstein wave (IBW). The presence of the IBW in NSTX plasmas during HHFW application has been directly confirmed with probe measurements. IBW heating occurs in the perpendicular ion distribution, consistent with the toroidal and poloidal observations. Calculations of IBW propagation indicate that multiple waves could be created in the parametric decay process, and that most of the IBW power would be absorbed in the outer 10–20cm of the plasma, predominantly on fully stripped ions. These predictions are in qualitative agreement with the observations and must be accounted for when calculating the energy budget of the plasma.

Plasma deposition of fluorocarbon thin films from c-C4F8 using pulsed and continuous rf excitation

Fluorocarbon films of varying composition have been deposited from pulsed and continuous plasmas of octafluorocyclobutane (c-C4F8) and c-C4F8/Ar. Continuous plasma deposition rates are a very weak function of applied rf power (may be within experimental error). Pulsed plasma deposition rates are significantly lower than continuous plasma rates at the same average power. The pulsed plasma deposition rates can be attributed almost entirely to the plasma on time during the pulse, but there is a slight dependence on pulse off time. Ar addition affects the deposition rates through a residence time effect, but also affects the deposition chemistry by reducing the degree of C4F8 dissociation, resulting in more fluorinated films. Refractive indices for all films increase approximately linearly with applied rf power, with the pulsed plasma-deposited films falling on the same curve. Carbon 1s x-ray photoelectron spectroscopy shows that the continuous plasma-deposited films become increasingly fluorinated as the rf power is decreased. Pulsed plasma films are more fluorinated than similar average power continuous plasma films: 44% CF2 for 10/50 (400 W on time, 67 W average power) versus 37% for 50 W continuous. Literature and preliminary gas-phase measurements suggest that the C4F8 is not fully dissociated in either plasma system and that larger species in the gas phase may play a significant role in the deposition mechanisms.

Generation of uniform plasmas by crossed internal oscillating current sheets: Key concepts and experimental verification

The results of comprehensive experimental studies of the operation, stability, and plasma parameters of the low-frequency (0.46MHz) inductively coupled plasmas sustained by the internal oscillating rf current are reported. The rf plasma is generated by using a custom-designed configuration of the internal rf coil that comprises two perpendicular sets of eight currents in each direction. Various diagnostic tools, such as magnetic probes, optical emission spectroscopy, and an rf-compensated Langmuir probe were used to investigate the electromagnetic, optical, and global properties of the argon plasma in wide ranges of the applied rf power and gas feedstock pressure. It is found that the uniformity of the electromagnetic field inside the plasma reactor is improved as compared to the conventional sources of inductively coupled plasmas with the external flat coil configuration. A reasonable agreement between the experimental data and computed electromagnetic field topography inside the chamber is reported. The Langmuir probe measurements reveal that the spatial profiles of the electron density, the effective electron temperature, plasma potential, and electron energy distribution/probability functions feature a high degree of the radial and axial uniformity and a weak azimuthal dependence, which is consistent with the earlier theoretical predictions. As the input rf power increases, the azimuthal dependence of the global plasma parameters vanishes. The obtained results demonstrate that by introducing the internal oscillated rf currents one can noticeably improve the uniformity of electromagnetic field topography, rf power deposition, and the plasma density in the reactor.