Divergent Magnetic Field Research Articles

Ion Collection by a Hollow Probe in ECR Microwave Plasma under a Divergent Magnetic Field

Ion collection by a hollow probe has been studied in electron cyclotron resonance (ECR) microwave plasma under a divergent magnetic field where an ion beam was accelerated along the plasma axis. The ion current collected by the probe was found to consist of currents proportional to the geometric solid angle from the probe collector caused by the ion beam parallel to the probe axis. The effect of the ion beam energy and its injection angle to the probe has been also discussed.

Deposition of thin films using microwave plasmas: present status and trends

This paper reviews some basic aspects of microwave discharges and properties of the plasma important for thin film processing. It deals with (i) basic methods of generation of isotropie and anisotropie plasmas, (ii) electron cyclotron resonance (ECR) and whistler wave plasma, (iii) generation of a dense and homogeneous magnetoactive plasma in large volumes, (iv) plasma acceleration in a divergent magnetic field, (v) effect of pressure on properties of microwave plasma and (vi) basic microwave plasma reactors for thin film deposition and their classification. Special attention is devoted to microwave plasma enhanced chemical vapour deposition and microwave plasma enhanced low pressure sputtering of thin films. For all deposition devices a crucial problem is plasma generation. It is shown that the best solution is to introduce the plasma produced by whistler wave into the plasma chamber from the side of high magnetic field B ⪢ B ce , where B ce is B which corresponds to ECR. At the end trends of future development of microwave discharges and their applications in industry, namely in submicron microelectronics and surface engineering are clearly formulated.

Transverse ion acceleration and ion conic formation in a divergent-field laboratory plasma

The results of laboratory experiments at the University of California at Irvine are presented in which multidimensional ion velocity distributions in the presence of radio-frequency (RF) waves and a spatially divergent external magnetic field are observed. A plasma volume is subjected to either local or nonlocal electrostatic turbulence, which in turn is responsible for accelerating the ions transverse to the confining magnetic field. The ions flow away from the source of turbulence in a spatially decreasing magnetic field, where the μ ∇B force and magnetic-moment conservation work to distort the heated distribution. Laser-induced-fluorescence (LIF) signals, measured downstream from the plasma source with the aid of optical tomography techniques, reveal substantial ion heating and conic formation.

One-dimensional hybrid modeling and simulation of electron cyclotron resonance discharge

The physical phenomena of the ECR-microwave discharge are numerically studied by a one-dimensional hybrid model of the fluid electrons and particle ions. The present model includes both the ECR heating phenomena and the transport of ions along divergent axial magnetic field lines, microwave is considered as an energy flow attenuated by the thermal electron fluid. Individual ion motion is determined by ambipolar electric field and Monte-Carlo collisions together with the /spl nabla/B force. In the fluid description of electrons, electron motions are coupled to the ions through ambipolarity, and the energy transport is treated with the temperature equation. The simulation results for argon discharges show the two characteristic features of the measurements for the ion energy distribution: the low energy peak as found in energy analyzer measurements, and the high energy bump as found in LIF measurements. Also the strong effect of the distributed ionization on the ion energy distribution is observed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Influence of Local Feature of Electron Cyclotron Resonance Plasma on the Formation of Amorphous Hydrogenated Silicon Films

Amorphous hydrogenated silicon (a-Si:H) film synthesis in an electron cyclotron resonance (ECR) plasma in silane and/or hydrogen diluted gases is studied in correlation with the local feature of the plasma. Experiments are carried out in a divergent magnetic field configuration at a gas pressure of 4 Pa, and the microwave power input is varied up to 500 W. The highest deposition rate is obtained just near the resonance point and the optical gap of the film has the lowest value at this position. The photoconductivity of the films is found to be strongly dependent on the axial distance L between the substrate and the resonance point. The optimum position for the formation of high-quality a-Si:H films is found in the axial direction, and it varies with input microwave power. The distance L which gives the maximum photoconductivity is shifted with input microwave power. For instance, at a microwave power Pµ of about 50 W the highest photoconductivity is obtained at L=6 cm, while at Pµ=100 W, the highest value is obtained at L=8 cm. This feature is attributed to the local behavior of the plasma production and decomposition of radical species near the resonance zone.

Simulation of Ion Trajectories near Submicron-Patterned Surface Including Effects of Local Charging and Ion Drift Velocity toward Wafer

Ion trajectories near a submicron-patterned surface were investigated using numerical simulations including the effects of local charging on the patterned surface and ion drift velocity toward the wafer. The simulation results were also discussed relative to the etched profile characteristics in electron cyclotron resonance (ECR) plasmas with a divergent magnetic field. Since the pattern size was much smaller than the Debye length, charge neutrality was not satisfied on the submicron-patterned surface. The simulated ion trajectories were largely deflected at the inside of the outermost lines of line-and-space patterns. Moreover, the ion trajectory deflection was reduced with increasing ion drift velocity. These simulation results showed a similar tendency as the etching characteristics.

Super-wide electron cyclotron resonance plasma source excited by traveling microwave as an efficient tool for diamondlike carbon film deposition

An electron cyclotron resonance (ECR) plasma source which generates 500-mm-wide plasma has been developed. A divergent magnetic field sufficient for ECR is generated by permanent magnets and a solenoid coil. A 2.45-GHz traveling microwave is supplied through a long slot antenna prepared in the sidewall of the waveguide and excites ECR plasma. This apparatus is applied to the diamondlike carbon (DLC) films deposition and DLC films were deposited in a wide zone 320 mm in width.

Characterization of diamondlike carbon films grown by super-wide electron-cyclotron resonance plasma assisted chemical vapor deposition

An electron-cyclotron resonance plasma source that generates 500 mm wide plasma has been developed. The plasma is generated by a 2.45 GHz traveling microwave which is supplied through a long slot antenna prepared in the waveguide in a divergent magnetic field generated by permanent magnets and a solenoid coil. Diamondlike carbon (DLC) films were deposited in a wide zone 320 mm in width. The breakdown field was 8.4×106 V/cm and permittivity, 3.89. The prepared Al/DLC/Si metal/insulator/semiconductor diode revealed fairly good field effect in its capacitance–voltage curve.

Dependence of the a-Si:H defect density of states on the magnetic field profile of an electron cyclotron resonance microwave plasma

The magnetic field profile of an electron cyclotron resonance microwave plasma was systematically altered to determine subsequent effects on a-Si:H film quality. The mobility gap deep density N D deposition rate and light-to-dark conductivity were determined for the a-Si:H films. By variation of the magnetic field profile N D could be altered by more than an order of magnitude, from 1 × 10 16 to 1 × 10 17 cm −3 at 0.7 mTorr and 1 × 10 16 to 5 × 10 17 cm −3 at 5 mTorr as determined by junction capacitance techniques. Two deposition regimes were found to occur for the conditions of this study. Highly divergent magnetic fields resulted in poor quality a-Si:H, while for magnetic field profiles defining a more highly confined plasma, the a-Si:H was of device quality and relatively independent of the magnetic field configuration. The data is interpreted as a consequence of silane depletion for highly divergent magnetic field profiles.

Motion of ions in an electron cyclotron resonance plasma

The motion of ions emerging from an electron-cyclotron-resonance plasma source has been investigated. Trajectories have been calculated by solving the ion equations of motion in a divergent magnetic field and an electrostatic longitudinal accelerating field which has to be evaluated self-consistently. The trajectory calculations have been combined with a Monte Carlo procedure for choosing the initial ion phase space variables in order to study the propagation of the ion distribution function. It is shown that outside the chamber the spatial profile of this distribution is increasingly broadened with distance from the second magnet due to the diverging magnetic field lines, while at the same time the ions gain energy from the electrostatic field. For an argon plasma a mean ion beam energy of about 16 eV with respect to the plasma source potential results at the target plane in a distance of 60 cm from the source.

Two-dimensional ion velocity distribution functions in electron cyclotron resonance plasma under a divergent magnetic field

Two-dimensional ion velocity distribution functions are measured in electron cyclotron resonance (ECR) argon plasmas under a divergent magnetic field configuration using a directional analyzer. Ions produced in the ECR source grow to a beam in the downstream region inside an allowed angle, while the distribution function is almost isotropic outside the angle. The beam energy corresponds to the potential difference between the ECR source and downstream locations. The ion beam is almost parallel to an applied magnetic field, the beam being deflected along the divergent magnetic field lines. The energy spread and the temperature of the ion beam, and the temperature of the bulk ions are also shown as a function of the distance from the ECR source or of the gas pressure. The validity of the directional analyzer measurements is discussed by considering the motion of an ion in a sheath in front of the analyzer.

Compact electron cyclotron resonance ion source with a permanent magnet

A new compact electron cyclotron resonance ion source that uses a magnetic mirror field and a divergent magnetic field to generate high-density and multicharged ions has been developed. A cylindrical permanent magnet is utilized to produce those magnetic fields. Excited electrons are effectively confined in the mirror field near the exit of the plasma chamber, making it possible to generate high-density and multicharged ions. The generated ions are transported near the center axis and a plasma stream is formed along the divergent magnetic field. A plasma chamber with a diameter 4 cm smaller than the cutoff size (7.2 cm for 2.45 GHz) and a two-layer microwave window are used to fashion the compact structure and to couple microwaves with high-density plasma. The plasma stream is highly directional (plasma stream diameter ∼1.8 cm), and high ion saturation current densities of 18 mA/cm2 (Ar gas) are achieved 12 cm downstream at a low microwave power of 200 W. Moreover, a high Ar2+/(Ar++Ar2+) ratio of above 50% is obtained.

Positron spectromicroscopy with a superconducting magnet

Techniques of positron microscopy have recently been developed for probing solids. Imaging in the prototype positron reemission microscopes was based on electrostatic focussing systems. We are now considering a different design based on a superconducting magnet and a magnetically guided positron beam, in which reemitted positrons or electrons from a sample placed in a strong magnetic field region are magnified by the divergent magnetic field. This technique does not require multiple remoderation of the positrons and should be practical with a benchtop beam. It has excellent energy resolving capability for spectroscopic study of the reemitted particles. We will discuss the possible applications of this setup toward positron reemission spectromicroscopy, as well as positron annihilation-induced Auger electron microscopy. It is also possible to utilize the same method for achieving a magnetically guilded positron microbeam for studying inhomogeneous or small samples.

Electromagnetic particle simulation of electron cyclotron resonance microwave discharge

We present a numerical model to study the electron cyclotron resonance (ECR) microwave discharge using a one-dimensional electromagnetic particle-in-cell Monte Carlo collision method [C. K. Birdsall, IEEE Trans. Plasma Sci. 19, 65 (1991)]. In our model, the electromagnetic wave is polarized circularly and propagates along an external static magnetic field and elastic, excitational, and ionizing electron-neutral collisions and elastic and charge exchange ion-neutral collisions are included. The discharge for helium gas is simulated and the simulation results explain well the physical properties of the ECR discharge which include the energy absorption of electrons through ECR coupling, the propagation of microwave, the transports of the charged particles, and the effect of divergent external magnetic field.

Monte Carlo simulation of electron behavior in an electron cyclotron resonance discharge

Electron behavior in an electron cyclotron resonance microwave discharge maintained by the TM01 mode fields of a cylindrical waveguide has been investigated via a Monte Carlo simulation. Since this discharge has high degree of ionization (≥1%), a self-consistent simulation of the plasma dynamics is achieved through the use of the ponderomotive and grad B (−μ∇∥B) forces. Accumulation of negative charges on the boundary surface sets up a sheath whose influence is also taken into account. The time averaged, spatially dependent electron energy distribution (EED) is computed self-consistently by integrating electron trajectories subjected to the microwave fields, the divergent background magnetic field, the space charge field, and the sheath field, and taking into account electron–electron collisions and collisions with the neutral hydrogen atoms. The EED is characterized by two electron temperatures with the population of the tail increasing for decreasing pressure. At low pressures (∼0.5 mTorr), the sheath potential is on the order of 100 V and decreases with increasing pressure. This observation suggests a pressure range for operation of reactors for diamondlike carbon film deposition.

Behavior of ECR microwave plasma formed in a mirror

Abstract Microwave plasma were produced and studied in a cylindrical chamber with a mirror and divergent magnetic fields. A circular TE 11 mode of 2.45 GHz was introduced into the plasma chamber via a dielectric vacuum window. It was found that microwave breakdowns occurred at sites where the static magnetic field was 875 G. There were two peaks of the plasma density and absorbed microwave power as a function of pressure in the range of 10 −3 −1 Pa. By moving the position of the ECR layer, it was found that the reflected microwave power had periodicity.

Microwave plasma enhanced chemical vapor deposition in magnetic fields below electron cyclotron resonance

Microwave plasmas ( f=2.45 GHz, 200–1000 W) at magnetic fields below electron cyclotron resonance (ECR), Bce = 875 G, were used for room temperature chemical vapor deposition of silicon nitride films. Plasmas were maintained in a nonresonant (with respect to any microwave mode) cavity at magnetic fields of 200–600 G, and were ‘‘extracted’’ with the divergent magnetic field into the process chamber. Silicon wafers of 10–20 cm diameters were positioned at 25 cm downstream in the process chamber. The total gas pressure was 0.7–2 mTorr and silane/nitrogen partial pressure ratio varied from 0.1 to 0.8. The film growth rate was 100–200 Å/min at a microwave power of 100–300 W and was found to be 15%–25% lower than in electron-cyclotron-resonance plasma streams. The index of refraction grew with silane partial pressure and was essentially the same as in ECR plasma films.

ECR Plasma CVD in Different Magnetic Field Configurations

An electron cyclotron resonance (ECR) plasma is produced with a slotted Lisitano coil, and the axial distribution of the plasma parameters is measured in detail for different magnetic field configurations. It is found that the plasma density in uniform magnetic fields axially decreases more slowly than that in divergent magnetic fields. Furthermore, carbon films are formed by ECR plasma chemical vapor deposition (CVD), and the deposition rate obtained in the uniform magnetic fields is found to be larger than that obtained in the divergent magnetic fields.

Dependence of the a-Si:H Defect Density of States on the Magnetic Field Profile of an Electron Cyclotron Resonance Microwave Plasma

ABSTRACTThe magnetic field profile of an electron cyclotron resonance (ECR) microwave plasma was systematically altered to determine subsequent effects on a-Si:H film quality. Films of a-Si:H were deposited at pressures of 0.7 mTorr and 5 mTorr with a H2/SiH4 ratio of approximately three. The mobility gap density of states ND, deposition rate and light to dark conductivity were determined for the a-Si:H films. This data was correlated to the magnetic field profile of the plasma, which was characterized by Langmuir probe measurements of the ion current density. By variation of the magnetic field profile ND could be altered by more than an order of magnitude, from 1×1016 to 1×1017 at 0.7 mTorr and 1×1016 to 5×1017 at 5 mTorr. Two deposition regimes were found to occur for the conditions of this study. Highly divergent magnetic fields resulted in poor quality a-Si:H, while for magnetic field profiles defining a more highly confined plasma, the a-Si:H was of device quality and relatively independent of the magnetic field configuration.

Effect of ion-neutral collisions on plasma flow in the edge region of stellarators

The paper presents a study of the effect of charge exchange and elastic scattering collisions between ions and neutrals on the plasma flow along the divergent magnetic field lines in the divertor region of a stellarator. In the analysis, which is kinetic, an indirect solution to the kinetic equation for the ions is obtained using a Monte Carlo description for the ion dynamics together with the assumption of Boltzmann electrons and quasi-neutrality. Ion-neutral collisions are studied in a three-dimensional velocity space using a Monte Carlo algorithm. The results show that charge exchange and elastic scattering collisions play a significant role in reducing the drop of the electrostatic potential in the divertor chamber below that obtained from collisionless calculations. This, in turn, reduces the electrostatic barrier, which may be useful in retarding the flow of high Z impurity ions from the target plate towards the confined plasma. The calculations for the ion energy distribution suggest that, owing to ion-neutral collisions, most of the impact energy of ions on the divertor plate is gained while they cross the sheath region of the plate.