Beam Current Increases Research Articles

Ion beam induced luminescence of Tb-implanted sapphire

A study has been made of the luminescence during He- or Ar-ion bombardment to Tb-implanted Al 2O 3. Tb-ions of 100 keV were implanted in colorless and transparent single crystal α-Al 2O 3 at a dose of 5 × 10 15 Tb/cm 2 nearly at room temperature. The implanted specimens were annealed in a nitrogen gas atmosphere at 800 for 1 h. The luminescence spectra were measured during 100 keV-Ar or 50 keV-He bombardment of the specimens using a spectrometer with three optical filters and a photomultiplier. The beam current densities ranged from 0.01 to 0.1 μA/cm 2. The spectra emitted by Ar bombardment of Tb-implanted specimens are almost the same as those by He bombardment, except for the peaks corresponding to defects in the sapphire itself. The luminescence has four clear peaks identified as emission due to D-F transitions of the Tb 3+ state, and its color is green due to the strongest peak at 550 nm. Annealing results in the increase of luminescence. He bombardment causes the peaks to be stronger than Ar bombardment. The peak intensity of luminescence rises in proportion as the He-ion beam current density increases. From the results, it is concluded that ion beam induced luminescence of Tb-implanted Al 2O 3 becomes stronger by annealing and He bombardment with a high current.

The Use of a Cold Gas Plasma for the Final Processing of Contamination-Free Tem Specimens

AbstractThe issue of specimen contamination becomes more important at a rate proportional to the use of high-brightness electron source Transmission Electron Microscopes (TMM). The trend in the transmission electron microscopy of materials science specimens is to use higher-voltage microscopes incorporating field emission gun technology [1]. These FEG TEMs combine smaller electron probes with increased beam current, allowing high resolution specimen imaging and enhanced analytical data collection. This is of particular importance for semiconductor specimens which demand fine-probe microanalyis.

Autoneutralization of space charge dominated beams for heavy ion fusion

Several heavy ion beams, each with current in the kiloampere range and particle energy in the gigaelectronvolt range, must be focused onto a millimetre size spot to provide the power required for ignition of high gain, radiation driven targets for inertial confinement fusion. It is difficult to achieve this condition for three reasons: (a) The repulsive space charge forces within individual beams and the mutual space charge repulsion among the beams, which are strongest near the focal spot, prevent multiple beams from focusing onto a small spot. (b) Beam current increases from beam head to tail, so the beam-beam repulsion is time dependent. This prevents multiple beams from being focused onto a small spot throughout the entire pulse. (c) Radiation from the beam heated target photoionizes some beam ions into higher charge states, and these ions are expelled from the beam by the space charge force. To minimize these three effects, it is proposed to place a metallic cylinder in front of the focal spot and to cover the cylinder, at the beam entrance end, with a plastic film of submicron thickness. As the beams pass through the film, the beam space charge force draws electrons from the film to co-move with the beam, `autoneutralizing' the ion beams inside the cylinder. Although the film strips beam ions into higher charge states, particle-in-cell simulations show that autoneutralization is so effective that the residual radial electric field in the neutralized beam is considerably less than that in the unneutralized beam. The application of this scheme thereby results in a great improvement in focusing quality. Beams with higher charge state or lower mass ions, which have the advantages of reducing both the length of the high energy section of induction linacs and the strengths of the final-focusing magnets, can therefore be used

Correlation of Electrical and Physical Properties of SIMOX BOX Affected by Various Implantation Parameters

AbstractThe impact of two implant parameters, namely the implant substrate temperature and implant beam current, on the physical and electrical properties of SIMOX buried oxide are investigated. Three implant substrate temperatures, 540 °C, 590 °C, and 640 °C and three beam current, 45 mA, 55 mA, 65 mA, are investigated. Results from thermal conductivity and surface photovoltage measurements show no apparent differences between samples. Results from interface roughness shows a decreasing trend as the substrate temperature and beam current increases. For the samples with different implant temperatures, the high‐field conduction shows an opposite dependence for top‐interface versus substrate injection. This behavior can be explained by the conservation of silicon in the buried oxide. Correlation of surface photovoltage and high‐field conduction shows weak positive dependency while that of interface roughness and high‐field conduction shows dependency only when the sets of temperature variation and beam current variation are decoupled.

Space charge effects in projection charged particle lithography systems

Charged particle image projection lithography systems have been proposed and are currently under development for design rules of 0.18 μm and below. Although charged particle projection lithography systems do not suffer from diffraction as a limit to spatial resolution as in photolithography, image degradation due to the effects of mutual repulsion of particles in the beam, space charge, will ultimately limit the performance of these systems. Space charge effects increase with increasing beam current. The uncorrectable image blur caused by space charge effectively reduces the dose latitude in projection charged particle lithography and therefore limits the ultimate throughput of such systems. We will describe the effects of space charge in charged particle projection lithography systems using a model we have previously developed. We will compare the predictions of the model with experimental data for an ion projection system and predict the performance of electron and ion beam systems under development. The predictions for image blur caused by space charge are used to calculate the dose latitude as a function of beam current and thus throughput for the SCALPEL(R) electron beam lithography system.

Interaction of ICRF waves with fast particles on TEXTOR

The experiments involving the interaction of radio-frequency heating with fast particles injected by neutral beams on TEXTOR are reviewed. The focus point of the present study is the comparison between experiments and theory. Theory involves the modelling of RF diffusion in velocity space, absorption of radio-frequency waves by non-maxwellian populations, computation of drift trajectories to take trapping and first-orbit losses into account. A more specific theoretical development used in this context is the reconstruction of charge exchange spectroscopy spectra. Three types of experiments are examined. The synergetic increase of beam current drive by radio-frequency power, the large neutron production in third harmonic heating of D beam ions and the control of central fast helium concentration by radio-frequency induced diffusion.

Acceleration of high current heavy ions using a variable energy radio-frequency quadrupole linac and measurement of the input beam emittance

A high current ion beam injection system and a variable energy radio-frequency quadrupole (RFQ) accelerator with an external LC resonance circuit are tested. A four-rod RFQ electrode of 2.3 m length is newly designed to obtain a milliampere class MeV ion beam. To increase accelerated beam current, injected beam emittance into the RFQ is measured and compared with the designed RFQ acceptance. Injected beam emittance tends to increase with the beam current increase. The beam acceleration tests are carried out with a cw rf power supply of 100 kW (10–30 MHz, continuously variable). Results show that the time-averaged beam currents of N+ and Ar2+ are 1.1 mA (0.4 MeV) and 1.03 mA (1.0 MeV), respectively, and that the peak current of these beams is about 5 mA. As representative ion species for fabricating semiconductor devices, P+ and P2+ are accelerated, and the time-averaged beam current of 0.48 mA (0.56 MeV) and 0.28 mA (0.81 MeV) are obtained, respectively. This high current MeV ion implanter has great potential for application to high-dose implantation and high throughput production of semiconductor devices and material surface modifications.

Beam interactions in a focused ion beam system with a liquid metal ion source

Abstract The quality of focused ion beam systems strongly depends on the aberrations of the optical elements and the Coulomb interactions between the beam particles. For a one lens system, with an image distance of 500 mm, it is shown, both experimentally and by simulation that a minimum spotsize of about 100 μm is observed, although the geometrical diameter is only 7.2 μm, including aberration effects. The influence of Coulomb interactions on the current density is also demonstrated: the current density on the target even decreases with increasing beam current.

The process of space current neutralization of intense relativistic electron beam under an externally applied magnetic guide field

The process of space current neutralization of intense relativistic electron beam under an externally applied magnetic guide field is discussed in this paper. Ionization by electron avalanching and by beam electrons impact and recombination is included in the calculation of plasma density buildup, with plasma heating by return current and two- stream instability taken into account. A code to evaluate the process of space current neutralization was set up. The calculations demonstrate that the optimum gas pressure increases as peak beam current increases, and it decreases as the risetime of beam pulse increases.

Investigation of fabrication parameters for the electron-beam-induced deposition of contamination tips used in atomic force microscopy

Electron-beam deposition in a field-emission electron microscope is used to grow high aspect ratio carbon contamination tips suitable for imaging in atomic force microscopy. Tip lengths of up to several microns, tip diameters between 100 and 400 nm and cone half-angles of 3 degrees -50 degrees are achieved with typical radii of curvature between 20 and 40 nm. The influence of the major deposition parameters, i.e. electron energy, beam current, deposition time and working distance, on the growth rate and shape (length, cone angle and cone length) of the tip, are investigated systematically. It is found that increasing beam current leads to a decrease in length growth probably due to enhanced thermal desorption of adsorbates and reduced sticking coefficients. Electron energy mainly determines cone angles and cone length while the variation of working distance only has a small influence on the tip growth. Imaging capabilities of the tips are verified on vertically walled, lithographically fabricated patterns.

Two classes of recombination behavior as studied by the technique of the electron beam induced current: NiSi2 particles and misfit dislocations in Ni contaminated n-type silicon

The recombination activity of well-defined NiSi2 precipitates and of misfit dislocations in Ni contaminated Si samples has been investigated using the technique of the electron-beam-induced current in dependence on sample temperature and beam current. Individual NiSi2 precipitates are found to show a high recombination activity, increasing slightly with temperature and decreasing with increasing beam current. On the other hand, misfit dislocations are nearly inactive at room temperature and increase their activity upon cooling the sample. The experimental findings are discussed in terms of recombination activity controlled by either defect charging or shallow centers.

Direct STEM fabrication and characterization of self‐supporting carbon structures for nanoelectronics

AbstractA quantitative model is proposed to interpret the experimental results concerning the observed anomalous behavior of the thickness of growing self‐supporting carbon‐containing rods: a decrease in the thickness with increasing beam current. The model is based on the surface diffusion of hydrocarbon molecules and takes into account their ionization and desorption from the positively charged end of the growing rod. Possible causes of self‐maintained oscillation instability of the rod growth are discussed. Procedures are recommended to optimize the fabrication of self‐supporting carbon‐containing structures of complicated configurations and to reduce the negative effect of the incident beam electrons during their testing.

Electron beam tracking in a preformed density channel

High-current charged particle beams can be guided by reduced density channels. Such guiding occurs when the distribution of plasma currents in the density channel causes a net attractive force to be exerted on the beam. In particular, a relativistic electron beam (REB) injected parallel to a spatially offset, reduced density channel is pulled toward the channel. The force exerted on the beam is predicted to increase as the beam current increases and as the offset between the beam and the channel increases out to offsets equal to the channel radius. An experiment with a 1 MV, ≊10 kA beam was performed that demonstrates this effect.

Measurement of the Bunch Length on the UVSOR Storage Ring

We have measured the bunch length in single-bunch operation of the UVSOR (Ultraviolet Synchrotron Orbital Radiation) storage ring in a beam current region from 0.1 to 70 mA at energies ranging from 500 to 750 MeV. The momentum compaction factor of the present operation point is determined experimentally from the bunch length and the synchrotron oscillation frequency measured simultaneously at a low beam current. The bunch length increases gradually as the beam current increases, and bunch lengthening is larger when the beam energy is lower. This behavior of bunch lengthening agrees well with a prediction of the potential-well distortion theory. Based on the theory, the effective longitudinal coupling impedance is estimated as a function of bunch length.

Theory of wake-field effects of a relativistic electron beam propagating in a plasma

A theoretical description of the wake-field effects is presented for a relativistic electron beam propagating through a tenuous background plasma. When the electron beam enters the plasma chamber, it expels plasma electrons from its vicinity leaving ions behind. The plasma electrons move out to the charge neutralization radius and oscillate near the radius, producing wake-field effects. In terms of plasma density, beam current, beam current rise time, and a geometrical factor of the system, the theory determines several critically important wake-field quantities, including the oscillation frequency, the wavelength, the radial profile of the induced axial electric field, and its strength. A particle simulation study of the wake-field effects is also carried out by two-dimensional particle-in-cell codes, and the simulation results are compared with the theoretical predictions. The simulation data agree remarkably well with the theoretical values. It is found from the theory and the simulation that the strength of the wake-field effects increases with beam current and plasma density. However, the wake-field strength decreases significantly as the beam current rise time increases.

A high-resolution beam profile measuring system for high-current ion implanters

A high-resolution beam profile measuring system (BPM) has been developed to analyze the correlation between charging damage and the ion beam profile for high-current ion implanters. With the increase of the ion beam current, insulators such as thin oxide layers of VLSI devices are subject to charging damage during ion implantation. To obtain accurate information on the local current density of the ion beam, 125 Faraday cups are placed in the BPM. This system has two measuring modes. One is a topographic mode that can detect the ion beam current density of 12500 sampling points in 30 s. A high-resolution contour map of the current density distribution is displayed on a CRT. The other is a real-time mode in which the current density distribution (125 sampling points) of the ion beam can be monitored every half second on the CRT. In this mode, fine adjustment of the ion beam profile is easily possible by visual control. The charging damage of insulating layers in the TEG (test element group) to the beam profile was investigated using this newly developed BPM. It has been proven that the damage probability increases rapidly above some threshold level of the beam current density. It is confirmed that for high-current implantation a uniform current density distribution of the ion beam is very effective to prevent charging damage. It is concluded that this measuring system is valuable not only for quick analysis of damage phenomena, but also for evaluating machine performance.

Wakefield theory of a relativistic electron beam

A theoretical description of the wakefield effect is presented for a relativistic electron beam propagating through a tenuous background plasma. In terms of plasma density, beam current, beam current risetime and geometrical factor of the system, the theory determines several critically important wakefield quantities, including radial profile of the induced axial electric field and its strength. It is found from the theory and simulation that the strength of the wakefield effects increases with beam current and plasma density. However, the wakefield strength decreases significantly as the beam current risetime increases.

Efficiency dependence on beam current and input power in a cyclotron autoresonance maser amplifier

The efficiency dependence of a cyclotron autoresonance maser (CARM) amplifier on electron beam current and input power is investigated using computer simulations and a theoretical model is presented to explain the findings. For a resonantly tuned CARM, the efficiency is found to initially increase and then decrease with beam current while for an optimally detuned CARM, the efficiency drops with any increase in beam current. If the current is kept constant, the efficiency is also found to drop as the input wave power is increased. Force bunching is found to play an important role in reducing the efficiency at high-beam current, which may make extension to high power through increasing beam current more difficult to achieve.

Experimental study of a high-frequency megawatt gyrotron oscillator

A detailed experimental study of the efficiency and output power of a pulsed gyrotron operating in the TE16,2,1 mode at 148 GHz has been conducted. A peak efficiency of 30% was achieved at 80 kV and 20 A for an output power of 480 kW. The highest output power of 925 kW, corresponding to an efficiency of 19%, was measured at 120 kV and 40 A. Two cavities with different interaction lengths (6.0λ and 4.2λ) were investigated. In both cases, agreement was found between the theoretical and experimental efficiency for beam currents up to 15–20 A. At higher currents, the experimental efficiency saturated between 20% and 25%, well below the 35%– 40% predicted by theory. No increase was obtained for modest positive or negative linear tapering of the cavity magnetic field. Measurements indicate that the beam velocity ratio decreases as beam current increases, partially explaining the reduced efficiency at higher currents. Operation in different azimuthal rotations of the cavity modes was also observed. The measured rotation was found to be consistent with the theoretical coupling between the beam and rf field.

EHT regulation of television circuits

At fifth- and ninth-harmonic tuning the conduction time of the diodes in the flyback transformer of a television receiver is relatively long and the decrease in EHT voltage with increasing beam current is comparatively small. EHT regulation is also dependent on the picture tube and the stray capacitance of the flyback transformer. Some experimental data on these phenomena are given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>