RF Induction Research Articles

Reduction of effects of rarefaction in ionized physical vapourdeposition discharges

Ionized physical vapour deposition (IPVD) is of current interest tothe semiconductor industry for the deposition of thin metal films as diffusionbarriers and seed layers in high aspect ratio features. One of the aims ofIPVD is to collimate depositing particle fluxes by ionizing a significantfraction of the incident metal vapour and applying an electric potential biasto the substrate. A system consisting of a dc-powered, 15 cm diameter coppersputter source and a RF induction plasma powered by a single-turn, 36 cmdiameter, loop antenna internal to the vacuum chamber has been examined.Measurements made with a biased quartz crystal microbalance in an argonbackground of 10-90 mTorr demonstrate that, at low magnetron sputteringlevels of 100 W, ionized metal flux fractions (IMFFs) as high as 90% can beobserved. However, further measurements of the IMFFs and plasma densityindicate rarefaction of the background argon gas as the metal flux to theplasma increases. Results are presented from an experimental investigation ofmethods to reduce the gas rarefaction. These include the modulation of themetal flux on the timescale of the process gas residence time and increasingthe target-to-substrate height.

Mixing effect on a nonequilibrium RF induction plasma

An experimental study was conducted to clarify the effect of secondary gas mixing on the thermo-fluid characteristics of a nonequilibrium RF induction plasma. The premixed argon and helium gas was introduced into a reactor to produce a RF induction plasma in a low operating pressure. It is shown that there are large effects of helium gas injection location and guide length on the plasma luminous area, operating limit of stable plasma, concentration and temperature fields of a RF induction plasma. A visualization study was also conducted to correspond to the variation of plasma configurations by premixing with helium gas.

Structural and optical properties of GaN films grown by the direct reaction of Ga and NH 3 in a CVD reactor

GaN films were grown on sapphire using a direct reaction of metallic gallium with ammonia in a conventional RF induction heated chemical-vapor-deposition (CVD) reactor. The crystal and optical qualities of the GaN improved significantly by increasing the distance between the sapphire substrate and Ga source. For thick GaN films grown at a position 3.5 cm away from the Ga source, the FWHM for the (0 0 0 2) peak of the XRD curve was about 684 arcsec which is the best value obtained in this work, and the room-temperature photoluminescence spectrum exhibited a strong band-edge luminescence at 3.414 eV. The correlation of structural and optical properties of the GaN films manifested in deep level yellow luminescence having a close relation to ( 1 0 1 ̄ 0 ) and ( 1 0 1 ̄ 1 ) planes developed during the growth. It was speculated that the emission of YL is mainly due to the formation of deep gap state in the band gap by Ga vacancy and impurities trapped at domain boundary with ( 1 0 1 ̄ 0 ) and ( 1 0 1 ̄ 1 ) atomic facets.

Distributed energy analysis for an integrated radio frequencyinduction plasma system

Electrical and energy balance data were obtained experimentallyfor a 25 kW, 4-5 MHz induction plasma generation system. These are usedfor the validation of the predictions of an integrated mathematical modelof a radio frequency power supply and induction plasma torch system.Results reported for the Tekna PL-35 torch, at different power levels,using argon as the plasma gas are in good agreement with model prediction.The integrated computer simulation model provides means for radio frequencyinduction plasma system optimization and scale-up.

Implantation of low-energy boron ions into silicon from a low-temperature high-density Ar + BF3 plasma

Experiments on low-energy (0.2–0.8 keV) boron implantation into silicon from a low-pressure high-density rf induction discharge plasma were performed. Secondary ion mass spectrometry measurements showed that a boron-implanted layer thickens with ion energy. The creation of an ultrashallow boron-doped silicon layer is a possibility when the accelerating voltage depends on the self-bias potential arising upon applying an rf voltage to the substrate.

On the synthesis and characterization of some new AB 5 type MmNi 4.3Al 0.3Mn 0.4, LaNi 5- xSi x ( x=0.1, 0.3, 0.5) and Mg− x wt% CFMmNi 5−y wt% Si hydrogen storage materials

The viability and feasibility of Hydrogen Energy becoming the clean alternative to Fossil Fuel Energy through replacement of ‘Fossil Fuel’ with ‘Hydrogen’ (the Green Fuel) is inextricably interlinked with development of ‘Hydrogen Storage Systems’. Out of the high pressure gaseous hydrogen, liquid hydrogen, storage in glass microspheres, activated carbon, zeolites, hydrogen rich liquids and solid state hydrides, the last option is of implicit importance. Out of the AB (e.g. FeTi, storage capacity — 1.75 wt%), AB 2 or A 2B (Mg 2Ni — 3.8 wt%), AB 5 (LaNi 5, MmNi 5 — 1.5 wt%) and K 2 PtCl 6 type (Mg 2FeH 6 — 5.2 wt%); the AB 5 type holds potential promise due to easy activation, tolerance to impurities of charging H 2 gas and avid amenability towards material tailoring for improved and better hydrogenation characteristics. We have carried out synthesis, characterization of several of the AB 5 type storage materials. The present paper is aimed at describing and discussing some of our more recent efforts in regard to this. In the present study the hydrogen storage material (MH) has been synthesized through normal casting (Radio Frequency (RF) induction melting) and melt-spinning techniques. The improvements in basic alloys LaNi 5/MmNi 5 have been studied through structural, microstructural and hydrogenation characteristics. The main features revealed by XRD characterizations are the existence of the free Ni and Si together with AB 5 material in melt-spun alloy of LaNi 5- x Si x . These free Ni and Si were found to disappear, giving rise to a singular material after hydrogenation. Also in melt-spun alloy growth has taken place in a direction perpendicular to the c-axis. Melt-spun version was found to be superior over bulk version in regard to kinetics and activation process. For MmNi 4.3Al 0.3Mn 0.4 alloy, melt-spun version has higher storage capacity (1.2 wt%) than bulk version (0.96 wt%). Also the melt-spun version has faster kinetics and improved activation. For example, the kinetics corresponding to the melt-spun version of LaNi 4.7Si 0.3 is 60% faster than the corresponding bulk. Si substitution results in faster kinetics and improved activation. For example, the kinetics of the melt-spun version of LaNi 4.7Si 0.3 is 70% faster than the melt-spun form of MmNi 4.3Al 0.3Mn 0.4. These AB 5-type materials are particularly attractive in relation to MH cathode for high energy density Ni–MH batteries. In addition to the above type AB 5 storage materials, we have also investigated Mg based composites. Of particular interest is the composite material Mg− x wt% CFMmNi 5−y wt% Si ( x=48; y=2). The as-synthesized composite materials have been activated at 500°C under a hydrogen pressure of ∼40 bar and their hydrogen storage capacities and kinetics have been evaluated. It has been found that the composite material corresponding to Mg−48 wt% CFMmNi 5−2 wt% Si has a maximum hydrogen storage capacity of ∼5.0 wt% at ∼400°C. The small metalloid (Si) substitution in the present material in contrast to Mg− x wt% CFMmNi 5 improves the absorption and desorption kinetics. Extensive structural and microstructural studies before and after hydrogenation have been carried out to unravel the details of hydrogenation behaviour. These results will be described and discussed.

The application and status of the radio frequency driven multi-cusp ion source (invited)

The multi-cusp ion source has been operated with 2 and 13.5 MHz in either pulse or cw mode for positive or negative ion beam production. Application of this type of source includes spallation neutron source, ion implantation, ion beam lithography, focused ion beam systems, radioactive ion beam production, and neutron generators. In order to achieve long life and reliable operation, different antenna arrangements have been explored. It is found that several antenna configurations can provide over 100 h of rf induction discharge operations.

2129 多成分モデルによる高周波誘導混合プラズマの熱流動解析

A numerical modelling of RF induction nonequilibrium argon-nitorgen plasma with chemical reactions is conducted at atmospheric pressure using multicomponent model. The thermofluid and concentration fields of chemical species and further plasma parameters are obtained by solving simultaneously the 2D conservations of continuity, momentum, energy and plasma species coupled with the Maxwell's equations. Especially, chemical reactions of dissociation and ionization, thermal nonequilibrium effect and further variable transport properties in the RF induction argon-nitrogen plasma are taken into account in this modelling. It is examined how the thermofluid and diffusion characteristics of plasma species and further plasma parameters in the RF induction plasma are influenced by the injected locations and inlet mass concentrations of premixed argon-nitrogen gas.

非磁性角鋼片の誘導加熱探傷における探傷条件の実験的考察

When the surface of steel billets is heated up by RF induction, the surface defects detour the induced current and then develop the temperature disruption around them. It is the induction heating inspection to detect the surface defects by marking such spots with infrared sensing devices. Authors applied this induction heating inspection to non-magnetic and square billets and optimized the procedures to improve the sensitivity and the accuracy. The results are as follows. (1) The sensors should be placed at the exit of the induction coil to scan the billet surface. (2) The defect detectability is enhanced as the billet travels at the higher speed. (3) The minimum defect depth is 0.5mm to be detected by this system.

Deposition and Characterization of Y3Al5O12 (YAG) Films and Powders by Plasma Spray Synthesis

ABSTRACTYAG powders and coatings were developed for the first time by a novel precursor plasma spraying technique using the radio frequency (RF) induction plasma technique. The XRD of the as -sprayed coating confirms the presence of YAG, H-YAP or O-YAP or a mixture of the above depending on the spray conditions. 27Al MAS NMR of the YAG coating corroborates the x-ray results. TEM studies on the coatings confirm that the coating consists of nano-structured particles. The successful spraying of these complex oxide coatings proves that chemistry of phase formation can be controlled in the plasma, thus opening up new avenues in material synthesis.

Structural and optical characterization of thick gan films grown by the direct reaction of metal Ga and NH3 in CVD reactor

Thick GaN films were grown on sapphire by the direct reaction of metallic Ga and ammonia in a conventional RF induction heated chemical vapor deposition reactor. The crystalline and optical qualities of the thick GaN were evaluated as functions of the distance between sapphire substrate and Ga source and growth temperature. For thick GaN grown at the position of 3.5 cm away from the Ga source, the FWHM for the (0002) peak of X-ray diffraction (XRD) curve was about 684 arcsec. The growth rate of the thick GaN film was about 18 μm/h at this growth condition. The correlation between structural and optical properties of thick GaN films suggested that deep level yellow luminescence (YL) had a close relation with (1010) and (1011) planes developed in the growth. It was speculated that the emission of YL is mainly due to the formation of deep gap state in the band gap by Ga vacancy and impurities trapped at the domain boundary with (1010) and (1011) atomic facets.

202 ガスの注入条件による高周波誘導プラズマ流の高機能化(流体工学)

The main objective of the present study is to clarify the effects of gas injection conditions such as gas mixing and gas injection location on the thermofluid characteristics and on the luminary areas of RF induction plasma flow. The gas temperature distibution shows the drastic variations due to the circulation by Lorentz force, the diffusion of mixed gases and complex flow patterns. On the other hand, the dissociation of N_2 or other secondary mixed gases cause the decrease in the temperature and the luminary area.

炭化チタン粉末のプラズマ酸化反応により生成したＴｉＣ‐ＴｉＯ２複合粉末

TiC-TiO2 composite powders were prepared by in-flight oxidation of titanium carbide powder in RF induction thermal plasmas. Original titanium carbide powder of 20-38μm in particle size was axially injected into the center of argon-oxygen plasma. The powders were partially spheroidized and evaporated through the plasma treatment. X-ray diffraction of plasma-treated powders showed the formation of titanium dioxides, both rutile and anatase phases. The phase content of the plasma-prepared powders strongly depended on the plasma conditions, such as the plasma generating pressure and the oxygen flow rate in plasma generating gas. Especially, the increase of oxygen flow rate in plasma gas gave rise to the increase of heat transfer from plasma to powder particles, exothermic heat of oxidation reaction and cooling rate of plasma, giving the increase of spheroidization ratio, formation ratio of titanium dioxides, and content of anatase phases.

Características de los electrogramas auriculares registrados en las líneas de bloqueo producidas con radiofrecuencia en un modelo experimental

To analyze and quantify atrial electrogram modifications following the induction of linear lesions in the atrial wall using radiofrequency ablation procedures. An epicardial multiple electrode (221 unipolar electrodes) was used in 12 Langendorff perfused rabbit hearts to analyze atrial activation before and after radiofrequency induction of a linear lesion in the left atrial wall. After confirming the existence of conduction blockade in the lesion zone by epicardial mapping and propagation vector analysis, six electrodes each were selected in the lesioned and non-lesioned zones in all experiments, comparing the amplitude, maximum negative slope and morphology of the electrograms in both zones, before (control) and after radiofrequency delivery. Analysis of the reproducibility of the measurements in two consecutive cycles showed a variation of 1 +/- 5% for amplitude (NS) and 1 +/- 9% for maximum negative slope (NS). In the non-damaged zone, amplitude (105 +/- 22%) and slope (92 +/- 16%) (values normalized with respect to those recorded before radiofrequency) did not vary significantly following radiofrequency, and simple electrograms were the most frequent recordings (82 vs 83% in control; NS). Amplitude (19 +/- 7%, p < 0.001) and slope (24 +/- 11%; p < 0.001) decreased significantly in the lesion zone, as did the percentage of simple electrograms (6 vs 86% in control; p < 0,001). In this same zone the morphology could not be determined in 12% of the recordings, while multiple electrograms were obtained in 15% (vs 2% in control; p < 0.01), and the most frequent type corresponded to double electrograms (67 vs 12% in control, p < 0.001), with both components coinciding in time with atrial activation in the zones proximal and distal to the lesion line. Electrograms recorded directly in radiofrequency induce block lines show a significant decrease in amplitude and maximum negative slope. Double electrograms predominate in these recordings, both components of which represent activation on either side of the lesion. In a small proportion of cases simple and multiple electrograms can also be recorded in the block line.

Pulse-Modulated RF Thermal Plasma for Advanced Materials Processing

Thermal plasma has been used for various kinds of materials processing. For further extension of the variable process parameters and the applications of thermal plasma, a time-domain controlled generation was developed of the pulse-modulated RF induction plasma, which has been successfully generated by the present authors, for the first time, with a sufficiently high electric power for the advanced materials processing. At the first stage, the steep overshoot and undershoot of the coil current amplitude of oscillating frequency of 1 MHz were recognized at the time instances of pulse on and off, giving a limited range of stable generation. Two solutions were found for suppressing the magnitude of overshoot and undershoot. One is the introduction of shimmer level, which is a ratio of coil current magnitude between pulse-on and -off periods. The other is that the rise and decay times of RF current was made a little slow in time domain. Consequently, when the Ar-H2 plasma was generated under 750 Torr with a high power level of 17 kW, the low power level went down to about 4 kW, i.e. below 1/4 of the higher level, with which such low power level, the continuous plasma generation was unable to be sustained. The increased difference between the high and lower power levels was large enough to give rise to the non-equilibrium condition in plasma temperature and composition at the instances of pulse on and off. Such unique condition is expected to offer a unique physico-chemical condition for advanced materials processing. The range of well-controlled generation of the pulse-modulated plasma was determined for Ar-H2 plasma with various parameters. It was recognized that the duration of pulse-on and -off times as well as the shimmer current level are the important parameters, which determine the degree of deviation from equilibrated condition in high pressure thermal plasma.

An rf sustained argon and copper plasma for ionized physical vapor deposition of copper

Langmuir probe, optical emission spectroscopy, and biased quartz crystal microbalance measurements were used to investigate an argon and copper plasma used for ionized physical vapor deposition of copper. Copper vapor generated by a magnetron sputter discharge is ionized upon passing through an argon discharge excited by an internal rf induction antenna. Argon plasma characteristics such as electron temperatures Te, plasma densities ne, and plasma and floating potentials Vp and Vf, were studied as a function of argon pressure and rf power. An increase of plasma density versus rf discharge power and argon pressure was observed. The radial profile of plasma density measured by a Langmuir probe reveals a peak ion density at the center of the rf antenna and an increase in the radial ion concentration gradient with argon pressure. The ratios of optical emission intensities from Cu+ ion and Cu neutral lines increase with rf discharge power and argon pressure. The biased quartz crystal microbalance measurements show an increase of both Cu+ ion flux and the ratio of Cu+ ion to Cu neutral fluxes with rf power and argon pressure; however, they also show a decrease of total Cu flux with increasing argon pressure.

Measurement of electron energy distribution function in an argon/copper plasma for ionized physical vapor deposition

The electron energy distribution function (EEDF) has been measured under a variety of conditions in an Ar/Cu plasma for ionized physical vapor deposition. The EEDF is directly measured in a system including a direct-current magnetron sputter source for copper and a radio frequency (rf) induction plasma, using a Langmuir probe with a modulated bias voltage in combination with a lock-in amplifier. The experimental data indicate that at fixed rf ionization power, the electron population in the tail of the EEDF is depleted by the introduction of copper vapor, and the electron average energy decreases slightly. Observed changes in the EEDF are attributed to inelastic collisions with copper atoms, which have lower threshold energies for excitation and ionization as well as larger cross sections as compared to argon, and the resulting reduction in the measured plasma potential.

Compositional modification of boron carbide induced by induction plasma treatment

The in-flight compositional modification of boron carbide powder with a chemical composition of B 5.25C and an average grain size of 22.3 μm was carried out in an Ar–H 2 RF induction plasma. Reactor pressure, powder feed rate and plate power level were taken as the experimental parameters to alter the thermal history of the injected powder particles. The powder was heated to be partially melted and evaporated during the plasma treatment. The carbon content in plasma-treated powders was decreased to 16.2–16.8 wt.% from that of original one, 17.0 wt.%. The formation of free boron, which agreed with the thermodynamic prediction, and the decrease of cell volume of non-stoichiometric boron carbide B x C were shown in plasma-treated powders. The very fine particles coagulated from a vapor phase consisted of carbon and boron carbide.

Vacuum processing technique for development of primary standard blackbodies

Blackbody sources with nearly unity emittance that are in equilibrium with a pure freezing metal such as gold, silver, or copper are used as primary standard sources in the International Temperature Scale of 1990 (ITS-90). Recently, a facility using radio-frequency induction heating for melting and filling the blackbody crucible with the freeze metal under vacuum conditions was developed at the National Institute of Standards and Technology (NIST). The blackbody development under a vacuum environment eliminated the possibility of contamination of the freeze metal during the process. The induction heating, compared to a resistively heated convection oven, provided faster heating of crucible and resulted in shorter turn-around time of about 7 h to manufacture a blackbody. This paper describes the new facility and its application to the development of fixed-point blackbodies.

A custom designed chip to control an implantable stimulator and telemetry system for control of paralyzed muscles.

A custom designed chip has been developed for the control of paralyzed muscles. The system is capable of fulfilling the stimulus and telemetry needs of advanced functional neuromuscular stimulation (FNS) applications requiring multiple channels of stimulation and multiple channels for sensor or biopotential sensing. An inductive radiofrequency link provides power to the implant device as well as 2 way transcutaneous communication. An application specific integrated circuit (ASIC) decodes the commands and provides functional control within the implant, and modular circuitry provides specific implant functions. The ASIC chip provides up to 32 independent channels of stimulation with independent control of stimulus pulse duration, pulse amplitude, interphase delay, recharge phase duration, and pulse interval. It can also control up to 8 independent back telemetry analog channels with independent control of sampling rate and pulse powering parameters (amplitude and duration). The mixed analog digital chip has been fabricated in 1.2 microm n-well CMOS technology.