Ing Hwie Tan

Magnesium plasma immersion ion implantation in a large straight magnetic duct

Magnesium ions were implanted on silicon wafers using a vacuum arc plasma system with a straight 1 m long magnetic duct, 0.22 m in diameter. Good macroparticle filtering was obtained in samples positioned facing the plasma stream and complete filtering was achieved in samples with surfaces parallel to the plasma stream and magnetic field. Deposition is also minimized by placing sample surfaces parallel to the plasma stream. High resolution x-ray diffraction rocking curves of implanted samples show that the changes in lattice constant are due to compressive strain, and the distortion is larger for higher voltages. Without magnetic field the implantation was a few hundred angstroms deep, as expected, but with magnetic field the depth profile was surprisingly extended to over 0.1 μm, a fact for which we do not yet have a convincing explanation, but could be related to radiation enhanced segregation. The presence of a magnetic field increases substantially the retained implantation dose due to the increase in plasma density by two orders of magnitude.

Aluminum Implantation in Kapton® for Space Applications: Magnetic Field Effects on Implantation in Vacuum Arcs

Aluminum was implanted in samples of Kapton®, a polyimide commonly used in spacecrafts, in order to form a protective layer against degradation by atomic oxygen, abundant in space. Implantation was carried out in a vacuum-arc-generated aluminum plasma, with and without the presence of a confining magnetic field. The main effect of the magnetic field is to increase plasma density by two orders of magnitude and, as a result, the dielectric Kapton® sample should charge much faster than in the unmagnetized case. Implantation depths should therefore be larger in the unmagnetized case. Results of X-ray Photoelectron Spectroscopy depth profile analysis, however, showed similiar implantation depths in both cases, with magnetized samples having a slightly deeper and larger mixing layer. Possible mechanisms to explain this result are discussed. Both treatments resulted in an excellent protective layer as demonstrated by samples exposed to oxygen plasmas, adhesion, thermal cycling, transmission and reflectance tests.

Magnetic suppression of secondary electrons in plasma immersion ion implantation

In this work, magnetic suppression of secondary electrons in plasma immersion ion implantation is demonstrated experimentally in a vacuum arc system. Secondary electrons emitted normally to a copper sample surface were detected by a Faraday cup, whose signal exhibited large negative spikes coincident with high voltage pulses when aluminum ions of an unmagnetized plasma were implanted. When a 12.5 mT magnetic field parallel to the sample’s surface is applied, these spikes are not seen, showing that secondary electrons were magnetically suppressed. Another cup, oriented to detect electrons that flow along the field lines, does not exhibit such negative spikes in either unmagnetized or magnetized plasmas, indicating that a virtual cathode was formed by the trapped secondary electrons.

Magnetic field effects on secondary electron emission during ion implantation in a nitrogen plasma

In this work, the magnetic suppression of secondary electrons emitted during nitrogen plasma immersion ion implantation is investigated. Secondary electrons were measured by two Faraday cups with and without the presence of a magnetic field parallel to the target surface. One Faraday cup detects the electrons emerging perpendicularly to the target surface and magnetic field lines, while another cup detects electrons flowing along the field lines. Increase of magnetic field intensity resulted in a decrease of the amount of electrons detected by the perpendicular Faraday cup and in an increase of the electrons detected by the longitudinal one. This shows that secondary electrons were transversally confined by the magnetic field but diffused away from the target ends along the field lines. The secondary electron emission coefficient (γ) was estimated and the results showed that partial suppression (decrease in γ) was achieved when the plasma density was increased by an order of magnitude. We propose an expla...

Polymer Treatment by Plasma Immersion Ion Implantation of Nitrogen for Formation of Diamond-Like Carbon Film

Inst. Nac. de Pesquisas Espaciais Lab. Associado de Plasmas, S. Jose dos Campos 12227-010 SP

Numerical Simulation of the Geometric Factor of a Cylindrical Electrostatic Analyzer to Monitor Electron Precipitation in the South Atlantic Magnetic Anomaly

This paper simulates the performance of a cylindrical electrostatic analyzer specially devised to measure the energy spectra of electrons precipitating in the South Atlantic Magnetic Anomaly (SAMA). Unlike its counterparts built to operate in the auroral region, the dimensions of this analyzer were designed to maximize the geometric factor, and to be the first experiment dedicated to measure the much lower fluxes in the equatorial ionosphere. The geometric factor of the analyzer was calculated based on the numerical simulation of electron trajectories coming from a calibration beam using the package SIMION 8.0. Positive and negative voltages applied to the inner and outer plates were compared to examine the analyzers response, showing small but visible differences. Simulations at the lower and higher ends of the energy spectrum showed similar geometric factors [G] as expected with [G]/Epeak ~ 2.9 × 10-3 (cm2 · sr) and ΔE/Epeak ~ 0.29. These results are in good agreement with semianalytical and empirical estimates. Comparisons with two analyzers designed for measurements in the auroral region showed that the simulated geometric factors are about one order of magnitude larger. Flux estimates based on aeronomic effects over the SAMA indicate that the number of counts should be sufficiently above noise level with the present analyzer design.

Magnesium plasma immersion ion implantation on silicon wafers

Abstract Magnesium ions were implanted by plasma immersion ion implantation on Si wafers. The vacuum arc plasma gun has a straight configuration, and samples were biased from −2 to −8 kV with 20-μs pulses at 700 Hz, with or without a magnetic field of 150 G, with arc currents of 600 A. Three samples were positioned 85 cm away from the anode grid, one sample with its surface facing the plasma stream and perpendicular to B (frontal samples), while the others have surfaces parallel to the plasma stream and the magnetic field (lateral samples). High-resolution X-ray diffraction results showed that implantation occurred, as evidenced by distortion of the rocking curves obtained. Deposition with thickness of the order of 1 μm also occurred, but was considerably thinner for samples positioned parallel to the plasma stream. Lateral samples are also free of macroparticles, as shown by SEM observations. The presence of a magnetic field significantly increases the implanted current and the deposition thickness in frontal samples, since plasma density is increased by two orders of magnitude.