Bernas Ion Source Research Articles

Mn2+ doping inside glass substrate utilizing metal ion beam implantation technique

The Korea multi-purpose accelerator complex (KOMAC) has been providing metal ion beam services such as Cr+, Fe+, Co+, Cu+, Mg+ and Ni+ using a modified Bernas ion source for diverse users. In this study, metal ion implantation facilitated by KOMAC has been utilized to implant Mn+ ions into a glass substrate. First, phosphate glass substrate doped with CeBr3 was fabricated following melt-quenching technique and then Mn+ ion beam was irradiated with flounces of 5 × 1016 ions/cm2. The irradiated sample was heat-treated at 400 °C, and characterized by absorption, excitation, and emission spectra. The presence of Mn2+ and the existence of energy transfer from Ce3+ to Mn2+ were explored by characteristic emission and excitation spectra. The emission intensity of Mn2+ was significantly higher when excited by Ce3+ excitation than Mn2+.

Ti+ and Mg+ Ion Beam Extraction from the Modified Bernas Ion Source

The korea multi-purpose accelerator complex (KOMAC) has a metal-ion-beam irradiation facility (150 keV/1 mA) equipped with a Bernas ion source. Metal-ion beams such as Cr+, Fe+, Co+, and Cu+ have been successfully extracted from our facility. Recently, some research groups have requested us to irradiate Ti+ and Mg+ ions into materials. These two kinds of ions have never been provided before. In response to these requests, we carried out the extraction of Ti+ and Mg+ beams at our facility. The vaporization temperatures of TiCl(III) and MgCl(II) under a pressure of 10−4 Torr were less than 300 °C and more than 600 °C, respectively. In this study, optimal extraction conditions for Ti+ and Mg+ ion beams were acquired successfully. To confirm the fluences of the Ti+ and the Mg+ beams, we prepared a silicon wafer sample and a gallium nitride (GaN) sample. Ti+ ions were irradiated with a current density of ∼6 μA/cm2 onto a silicon wafer sample for 90 min, and the dose was 1.68 × 1016 ions/cm2, we measured by using Rutherford backscattering spectrometry (RBS) analysis. Mg+ ions implanted in GaN were confirmed by using secondary ion mass spectroscopy (SIMS). The depth and the concentration of Mg+ ions at the peak were found to be 130 nm and 7.4 × 1019 ions/cm3, respectively. We would expect the newly extracted Ti+ and Mg+ ions to be helpful for research in the fields of material science and condensed matter physics.

Modeling of the charge-state separation at ITEP experimental facility for material science based on a Bernas ion source.

The experiment automation system is supposed to be developed for experimental facility for material science at ITEP, based on a Bernas ion source. The program CAMFT is assumed to be involved into the program of the experiment automation. CAMFT is developed to simulate the intense charged particle bunch motion in the external magnetic fields with arbitrary geometry by means of the accurate solution of the particle motion equation. Program allows the consideration of the bunch intensity up to 10(10) ppb. Preliminary calculations are performed at ITEP supercomputer. The results of the simulation of the beam pre-acceleration and following turn in magnetic field are presented for different initial conditions.

Molecular ion sources for low energy semiconductor ion implantation (invited).

Smaller semiconductors require shallow, low energy ion implantation, resulting space charge effects, which reduced beam currents and production rates. To increase production rates, molecular ions are used. Boron and phosphorous (or arsenic) implantation is needed for P-type and N-type semiconductors, respectively. Carborane, which is the most stable molecular boron ion leaves unacceptable carbon residue on extraction grids. A self-cleaning carborane acid compound (C4H12B10O4) was synthesized and utilized in the ITEP Bernas ion source resulting in large carborane ion output, without carbon residue. Pure gaseous processes are desired to enable rapid switch among ion species. Molecular phosphorous was generated by introducing phosphine in dissociators via 4PH3 = P4 + 6H2; generated molecular phosphorous in a pure gaseous process was then injected into the HCEI Calutron-Bernas ion source, from which P4(+) ion beams were extracted. Results from devices and some additional concepts are described.

Development of the ion source for cluster implantation

Bernas ion source development to meet needs of 100s of electron-volt ion implanters for shallow junction production is in progress in Institute for Theoretical and Experimental Physics. The ion sources provides high intensity ion beam of boron clusters under self-cleaning operation mode. The last progress with ion source operation is presented. The mechanism of self-cleaning procedure is described.

Carborane beam from ITEP Bernas ion source for semiconductor implanters

A joint research and development of steady state intense boron ion sources for hundreds of electron-volt ion implanters has been in progress for the past 5 years. The difficulties of extraction and transportation of low energy boron beams can be solved by implanting clusters of boron atoms. In Institute for Theoretical and Experimental Physics (ITEP) the Bernas ion source successfully generated the beam of decaborane ions. The carborane (C(2)B(10)H(12)) ion beam is more attractive material due to its better thermal stability. The results of carborane ion beam generation are presented. The result of the beam implantation into the silicon wafer is presented as well.

CU+ION EXTRACTION FROM A MODIFIED BERNAS ION SOURCE IN A METAL-ION IMPLANTER

An ion implanter, which can serve as a metal-ion supply, has been constructed and performance tested. Copper ions are generated and extracted from a Bernas ion source with a heating crucible that provides feed gases to sustain the plasma. Sable arc plasmas can be sustained in the ion source for a crucible temperature in excess of 350°C. Stable extraction of the ions is possible for arc currents less than 0.3 A. Arc currents increase with the induced power of a block cathode and the transverse field in the ion source. Cu+ ions in the extracted beam are separated using a dipole magnet. A 20 μA Cu+ ion current can be extracted with a 0.2 A arc current. The ion current can support a dose of 10 16 ions/ cm 2 over an area of 15 cm 2 within a few hours.

The change of atomic distribution and hardness by nitrogen implantation into aluminum alloy

Through many studies of the nitrogen implantation into aluminum alloy, researchers have concluded that AlN (aluminum nitride) formation is the key to hardening the aluminum surface. We implanted nitrogen ions into the Al6061, using an ion implanter which has a modified Bernas ion source. We changed the incident ion energies (25 keV, 50 keV) and fluences (1x10(17)-2x10(18) ions/cm(2)). To measure the depth hardness of implanted samples, we used nanoindentation test. The test results showed that the hardness of the implanted sample increased as the incident ion fluence increased until 1x10(18) ions/cm(2). However, the hardness did not increase at the fluence of 2x10(18) ions/cm(2). Furthermore, another result showed that the hardness was slightly decreased. To see the depth distribution of elements, we used Auger electron spectroscopy (AES) analysis with depth profiling. Through the AES analysis, we observed that the nitrogen atomic ratio did not increase; since the atomic ratio reached its maximum point (50%), the depth profile formed a flat curve in the AES. It is determined by the AlN structure (1:1 combination), that is, by the stoichiometrical rule. The nitrogen atoms diffused to the inner and outer sides rather than made a narrowly ranged accumulation. We observed that the flat curve was lowered downward a little at the fluence of 2x10(18) ions/cm(2). Observing the atomic distribution of oxygen in AES, we could conclude that the lowered curve was due to the recoil implantation of oxygen which had been originally combined with the aluminum surface in the aluminum oxide (Al(2)O(3)) layer. Comparing the AES result and the nanoindention result, we concluded that the recoiled oxygen atoms are not effective on hardening the Al surface. In this study, we observed the tendency to stop increasing the samples' hardness over the ion fluence of 1x10(18) ions/cm(2). We observed the saturation of the atomic ratio by the stoichiometrical rule.

Experimental comparison of time-of-flight mass analysis with magnetic mass analysis

A series of experiments was carried out in which both a magnetic analyzer (mass separator) and a time-of-flight (TOF) spectrometer were used for ion charge/mass spectral analysis of the ion beam formed by a dc Bernas ion source made for semiconductor implantation. The TOF analyzer was a detachable device that provides rapid analysis of charge-to-mass composition of moderate energy ion beams. The magnetic analyzer was a massive device using a 90 degrees -sector bending magnet with radius of the central orbit of 35 cm. Comparison of these two methods for measuring ion beam composition shows good agreement.

ITEP Bernas ion source with additional electron beam

A joint research and development program is underway to develop steady-state intense ion sources for the two energy extremes of MeV and hundreds of eV. For the MeV range the investigations were focused on charge-state enhancement for ions generated by the modified Bernas ion sources. Based on the previously successful ITEP experience with the e-metal vapor vacuum arc ion source [e.g., Batalin et al., Rev. Sci. Instrum. 75, 1900 (2004)], the injection of a high-energy electron beam into the Bernas ion source discharge region is expected to enhance the production of high charge states. Presented here are construction details and studies of electron-beam influence on the enhancement of ion-beam charge states generated by the modified Bernas ion source.

Transport line for beam generated by ITEP Bernas ion source

A joint research and development program is underway to investigate beam transport systems for intense steady-state ion sources for ion implanters. Two energy extremes of MeV and hundreds of eV are investigated using a modified Bernas ion source with an indirectly heated cathode. Results are presented for simulations of electrostatic systems performed to investigate the transportation of ion beams over a wide mass range: boron to decaborane.

Decaborane beam from ITEP Bernas ion source

A joint research and development program is under way to develop steady-state intense ion sources for the two energy extremes of MeV and hundreds of eV. The difficulties of extraction and transportation of low-energy boron beams are investigated using a decaborane compound [I. Yamada, W. L. Brown, J. A. Northby, and M. Sosnowski, Nucl. Instrum. Methods Phys. Res. B 79, 223 (1993)]. Presented here are the results from ITEP experiments using the Bernas ion source with an indirectly heated LaB6 cathode.

Release properties of UC x and molten U targets

The release properties of UC x and molten U thick targets associated with a Nier–Bernas ion source have been studied. Two experimental methods are used to extract the release time. Results are presented and discussed for Kr, Cd, I and Xe.

Development of a long-life ion source for ion-implantation application

The long-life version of a Bernas ion source is developed. It is called a Bernas-type electron active reflection (BEAR) ion source. The ion source has independently potential controlled reflectors, which are isolated from both an arc chamber and a filament. The potential of the reflectors is over 30 V negative with respect to the cathode potential. Because this potential can reflect enough emission electrons from the filament, the plasma production efficiency can be increased. In this method, we can minimize the arc voltage or a filament current compared with a conventional-type Bernas ion source, resulting in the reduction of a tungsten filament. Overall, the decrease in the filament diameter in the BEAR source was experimentally found to be below 50% of the conventional-type Bernas ion source.

Ion sources for implantation application (invited)

A review of the newly developed ion sources for implantation application is presented. These ion sources include Bernas ion source and electron cyclotron resonance (ECR) ion source. They have advantages of source lifetimes and yields of multiply charged ion-beam current. Typical lifetime of Bernas source is 100 h and the ratio of As2+/As+ is about 25% with wide range beam current controllability. Lifetime of the ECR source is more than 150 h and the ratio of As2+/As+ beams is about 50%. The characteristics of these ion sources for the ion implantation system are also presented on actual uses in factories.

Characterization of a Bernas ion source for multiply charged ion implantation

Due to concerns about energy purity and reduced beam current, the use of multiply charged ions to achieve higher effective ion energies with a fixed acceleration potential has not been common for implantation users in the semiconductor industry. Energy purity is compromised primarily by charge exchange in the implanter beamline, caused by neutral gas originating from the ion source extraction aperture. Beam current has been an issue, since traditional implanter ion sources, such as the Freeman source, produce very limited currents of multiply charged species. At low beam currents, the implanter is not economical to use, hence the lack of commercial use of multiply charged ion implantation. Ion sources that address these issues must also meet requirements for adequate source lifetime, simplicity of operation (for computer control) and maintenance, and low cost of ownership. This paper details beam energy purity and usable beam currents for a new medium current Bernas ion source as compared to a standard Freeman ion source. The results show significant performance improvements, while also increasing the ion source lifetime.