Ion Beam Uniformity Research Articles

Multi-filament ion source for uniform ion beam generation

Ion beams are employed in various fields such as semiconductor manufacturing, surface modification and material science. The uniformity of ion beams is crucial in many applications, but conventional ion sources that use a single filament often limit the uniformity and intensity of the ion beam. This paper presents a study that aims to optimize a multi-filament ion source to enhance the uniformity of ion beams. The study includes a detailed explanation of the ion source components and design, methods for measuring ion beam uniformity with its experimental design, followed by results, analysis, discussions and conclusions, completed by suggestions for future research directions. The experimental results demonstrate that the use of a multi-filament ion source improves ion beam uniformity compared to a single-filament ion source. An optimal design for the ion source components and new approaches for improving ion beam uniformity are described. The study’s results provide important information for improving ion beam uniformity and offer a technical basis for providing high-quality products and services in various industries.

Bench tests of a helium ion source for the neutral particle diagnostic system of the ITER tokamak.

Bench tests of a 15 keV helium ion source, which has been developed for the neutral particle diagnostic system of the International Thermonuclear Experimental Reactor (ITER), are described. Being part of the diagnostic system, the ion source will be used to monitor the intactness of carbon stripping foils as well as to check the detection and dispersion systems of the main diagnostic instruments-neutral particle analyzers (NPAs). The ion source produces a wide 5-cm diameter (FWHM) ion beam at a distance of about 50 cm; the ion beam uniformity at a 2-cm area corresponding to the size of the stripping foil is not worse than 10%. The beam current over the area of the stripping foil can be adjusted in the range of 0.1 pA-1 pA. After initial heating, the temporal stability of the ion beam is better than 10%. Pulse height measurements of registered signals show that 15 keV He+ ions can be reliably registered by the NPA detector system. The obtained results allow us to conclude that the developed ion source can provide a reliable check of the NPA system during the diagnostic performance on the ITER tokamak.

A Multi-Pinhole Faraday Cup Device for Measurement of Discrete Charge Distribution of Heavy and Light Ions

A new multi-pinhole Faraday cup (MPFC) device was designed, fabricated and tested to measure ion beam uniformity over a range of centimeters. There are 32 collectors within the device, and each of those is used as an individual Faraday cup to measure a fraction of the beam current. Experimental data show that the device is capable of measuring a charged particles distribution - either in the form of a raster scanned focused beam or a defocused beam.

High homogeneity 25 cm low-energy rf ion source with inherent electron compensation

A 25 cm single-grid low-energy rf ion source with inherent electron compensation is described and characterized. Measurements were carried out using Ar and CF(4) filling gas. The dependence of the ion beam current to the target as well as the current partition between the beam fast and slow ions on the rf discharge pressure for both filling gases is discussed. The unique ability of generation of coinciding ion and electron flows is demonstrated and the measured ion and electron energy distribution functions are presented as well. The developed broad ion beam source is able of providing 0.5-5 mA/cm(2) current density in the low ion energy range of 50-250 eV, with possibility of independent current density and energy control. It is shown that complementing the rf plasma source with a profiling electrode allows for CF(4) ion source operation attaining +/-5% ion beam uniformity over 250 mm in diameter. The presented CF(4) etching test results exhibit the possibility of highly directional anisotropic Si and SiO(2) etching utilizing the developed single grid rf ion source.

Controlling beam halo-chaos via backstepping design

A backstepping control method is proposed for controlling beam halo-chaos in the periodic focusing channels (PFCs) of high-current ion accelerator. The analysis and numerical results show that the method, via adjusting an exterior magnetic field, is effective to control beam halo chaos with five types of initial distribution ion beams, all statistical quantities of the beam halo-chaos are largely reduced, and the uniformity of ion beam is improved. This control method has an important value of application, for the exterior magnetic field can be easily adjusted in the periodical magnetic focusing channels in experiment.

Control of negative ion beam uniformity by using multipower supplies for arc discharge

Multipower supplies for the arc discharge are installed to improve beam uniformity of a large size of the neutral beam injection system in the large helical device (LHD). The plasma tends to shift on the upper side of the arc chamber when the same arc voltage is applied to all filaments. The arc discharge current distribution becomes uniform as a consequence of the individual voltage control, but about 20 V difference of the arc voltage between the top and bottom circuits is required. We have estimated the beam profile from each acceleration grid by comparing the calculation and measurement of the beam profile of Hα and calorimeter. The uniformity of arc discharge has been improved in most regions without the discharge adjustment by a horizontal filament connection. The controllability of the arc discharge distribution of the horizontal filament connection is better than that of the vertical filament connection. The efficiency of the beam production is improved by about 10% in the case of the horizontal filament connection. As a result 3.7 MW of the beam injection has been achieved in the LHD 6th experimental campaign in 2003.

Evaluation of fabrication process for interface-modified ramp-edge junctions

We have examined the parameters in the fabrication process of interface-modified ramp-edge junctions which influence their I c spread. The distribution of ion-beam energy and the uniformity of ion beam for making an amorphous layer and the base-electrode film quality such as the density of outgrowth or particles and the roughness of the ramp surfaces are important factors determining the I c spread. We have found another important factor, that is, the recrystallization energy from a laser plume. By adding proper adjustment of the relative location between substrate and the laser plume, I c spread values of 5.7% and 7.3% have been obtained for arrays of 100 JJ and 1000 JJ, respectively.

Evaluation of fabrication process and barrier structure for interface-modified ramp-edge junctions

For SFQ circuits using high- T c Josephson junctions, it is very important to reduce the I c spread of the junctions. We have studied several causes of the I c spread in interface-modified ramp-edge junctions. First, the relation between the structure and the fabrication process of the barrier has been examined. Reflection high energy electron diffraction pattern observation in the recrystallization process of the interface-modified barrier and transmission electron microscopy observation indicate that several types of barrier structures appear by changing the electron cyclotron resonance ion-bombardment and subsequent annealing conditions. Ion bombardment at a high acceleration voltage of 700 V induces no cubic layer at the interface, while several types of cubic structure can be observed for lower acceleration voltages (300–500 V). Thus, distribution of ion beam energy is one of the important factors determining the I c spread. We also report the importance of other factors including the uniformity of ion beam for making an amorphous layer, and the base-electrode film quality such as the density of outgrowth or particles and the roughness of the ramp surface. By improving these factors in the junction fabrication process, an I c spread of 17% has been obtained for an array of 1000JJs with a relatively small average I c of 0.1 mA, suggesting a possibility of further improvement for junctions with a higher J c.

Simulations of intense pulsed ion beam uniformity in a planar magnetically insulated ion diode

Using the self-consistent, 2-1/2-dimensional particle-in-cell MAGIC code, based upon the explosive emission model, we have simulated the characteristics of the proton flux extracted from a planar magnetically insulated diode with a 200-mm-wide and an 8 mm anode-cathode gap. Results of numerical calculation, e.g., the spatial distributions of the extracted proton current density vs time and the spatial distribution of particles in diode gap are presented at a diode voltage of 300 kV with 40 ns pulse duration and an externally insulating magnetic field of 0–4Bcrit. With the increase of the magnetic field, the uniformity of the extracted proton flux is significantly improved; however, the maximum of the proton current density and one of the proton energy density decrease from 150 to 45 A/cm2 and from 1.0 to 0.3 J/cm2, respectively, when B varied from 0 to 4Bcrit. The effects of the magnetic field on uniformity of the extracted proton flux are discussed in this article.

Design and tests of the new partially ionized beam source

We developed and evaluated a new partially ionized beam (PIB) source to deposit high quality Cu films. The novelty of the PIB source lies in the fact that the crucible and ionization parts are spaced in one cylindrical shell to make its structure compact and to get a uniform beam profile, but their electric circuits are not separated. In this article, we report the characteristics of the PIB source, such as voltage-ampere characteristics of the crucible and ionization parts, Cu+ ion beam uniformity with a change of the ionization currents, and deposition rate.

Response of a DRAM to single-ion tracks of different heavy-ion species and stopping powers

Multiple-bit errors caused by single-ion tracks in a 256-kb DRAM fabricated by a bulk process were observed for different ion species and stopping power values. The results demonstrate the utility of this device for the evaluation of ion-beam uniformity and ion-beam-induced charge collection in IC devices. The data indicate that single-ion-induced charge transport results in multiple-bit error clusters due to lateral diffusion of excess minority carriers (electrons). Charge collection occurred from a depth of up to 35 mu m from te surface of the device. An apparent charge loss was observed for very heavy ions with a high stopping power (Au at 350 MeV).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A broad-beam electron cyclotron resonance ion source for sputtering etching and deposition of material

A broad-beam electron cyclotron resonance ion source for sputtering etching and deposition of material has been designed and constructed. The source uses a 1-kW magnetron at 2.45 GHz and can operate at an argon gas pressure of &amp;lt;0.1 Pa (7.5×10−4 Torr). Plasma ion density of 0.45 to 1×1012 cm−3 and electron temperatures of 7.5 to 11 eV have been obtained. Based on these results and the free fall ion diffusion theory, the calculated ion current density in the source varies from 15 to 30 mA/cm2. The source is also capable of producing a uniform ion beam current density of 0.5 to 1.5 mA/cm2 using an array of grids at an energy range of 100 to 1000 V. The ion beam uniformity varies between ±3% and ±5% across 76–140 mm diameter of the extracted ion beam. Of particular note are the long lifetime and ease of operation.

Enhanced ionization freeman ion source

We developed modifications to a standard Freeman ion source which increased the plasma electron temperature and density by minimum factors of 1.5 and 1.1, respectively. The improvement in these fundamental plasma parameters resulted in a greater than 40% increase in B + currents from boron trifluoride gas and substantial usable beam current increases in B 2+, P 2+, and As 2+. A large increase in triple charge currents was also present in the extracted beam. Ion source lifetime tests were performed at 1 mA scanned B + wafer current with a 125 mm aperture on an Eaton NV-6200 Ion Implanter. Filament lifetime was observed to be in excess of 50 h. Further, erosion was more uniformly distributed along the filament length and tests indicate that the extracted ion beam uniformity was increased along the extraction slit. Therefore, we conclude that our modifications to the standard Freeman ion source also increased discharge uniformity.

Intense ion beam Kα measurements on PBFA-II

Inertial confinement fusion research efforts at Sandia National Laboratories center on generating and focusing high-intensity light ion beams on the Particle Beam Fusion Accelerator PBFA-II. A time-integrating three-frame ion beam spatial monitor was developed for these experiments to determine proton and lithium ion beam uniformity and orbit characteristics by imaging the ion-induced Kα line radiation. The three views of the ion beam are made off axis in three diode quadrants at a 3.8-cm radius. This spatial monitor, in conjunction with other beam diagnostics, allows experimenters to determine the high-voltage focusing characteristics of the ion diode.