Beam Gas Research Articles

Excimer laser ablation of polyimide in a manufacturing facility

High power excimer laser ablation projection tools have been used successfully in IBM manufacturing for about four years. One hundred fifty W XeCL, 300 mJ per pulse and 500 mJ per pulse lasers, running at 500 Hz and 300 Hz, respectively, have been run successfully for over 2 billion pulses. Excimer laser projection ablation tools are very similar to photo-expose tools, and their similarities and differences are explained. The laser and its gas handling, beam delivery, beam homogenization, optics, debris, part handling, and maintenance are discussed.

Production of mixed metal–gas and pure metal ion beams with an electrodeless rf ion source in the low keV regime

Mixed metal–gas or even pure metal ion beams with current densities in the order of 1 mA cm−2 can be generated by electron beam evaporation of metals into the plasma chamber of an rf ion source operated in electron-cyclotron wave resonance. The operation principle of this novel ion beam source is described, and examples for the production of Ag+ and Cu+ beams with varying fractions of Ar+ ions are presented.

Electron-electron scattering probed by a collimated electron beam

The authors compare the effects of current heating, hot-electron injection and lattice temperature on the attenuation of a collimated ballistic electron beam in a two-dimensional electron gas. In the electron gas heating and injection experiments, they use a quantum point contact as a local thermometer. They find that electron-electron scattering is the dominant factor determining the temperature dependence of the collimation signal.

Growth of β-SiC film on Si substrate by surface reaction using hydrocarbon gas and Si molecular beams in ultrahigh vacuum

The growth of β-SiC on Si(111) substrate was performed with a two-step growth method in a molecular-beam epitaxy (MBE) system using a C2H2 gas source and a Si solid source: an initial optimal carbonization process followed by MBE. The properties of SiC film were analyzed with in situ Auger electron spectroscopy, reflection high-energy electron diffraction, and x-ray photoemission spectroscopy and with ex situ Fourier transform infrared and ellipsometry. In the surface carbonization, the reacted surface showed a change from the β-SiC structure to a carbon-absorbed SiC structure with the increase in carbonization time. A carbonization time of 10 min, a substrate temperature of 875 °C, and a growth pressure of 1.6×10−6 Torr were found to be optimal for the surface carbonization. The growth of SiC was conducted at 900 °C for 30 min with a 0.8 Å/s Si beam flux and a 1.6×10−6 Torr of growth pressure and the films obtained showed single crystalline β-SiC. However, thick films obtained with high growth rates showed polycrystalline structures.

Production of high-energy electron beams in moderate and high-pressure gases

The feasibility of producing high-current, high-energy electron beams was studied for the application of nanosecond voltage pulses with amplitudes to 300 kV in accelerating gaps. The pressures of the gap gases (helium and nitrogen) measured from 10−1 torr to atmospheric. Experiments showed that the placement of two barriers in the accelerating gap significantly increased the electron beam current due to an increase in the burn time of the volume discharge under conditions involving significant over-voltage in the electrical field. Electron beams with energies of up to 250 keV and currents up to 260 A were obtained.

Symmetric-charge-transfer cross sections for gadolinium in the energy range 10-1000 eV.

The cross section of symmetric charge transfer between Gd and ${\mathrm{Gd}}^{+}$ as a function of impact energy (velocity) in the range of 10--1000 eV (3.5\ifmmode\times\else\texttimes\fi{}${10}^{5}$--3.5\ifmmode\times\else\texttimes\fi{}${10}^{6}$ cm/sec) was successfully obtained by a crossed-beam technique, which featured a pulsed ion beam produced by laser photoionization in an atomic gas beam. The absolute values and the impact-energy dependence of the cross sections were obtained from the attenuation rate of the primary ions in the atomic gas and the ratio of the detected charge transferred ions to the primary ions, respectively. The cross sections obtained are larger than those of other elements studied in the past, and the impact-velocity--cross-section curve could be fitted with that obtained from the superposition of the resonant and capture-type probabilities resulting in charge transfer, assuming that the capture-type cross section is inversely proportional to the impact velocity.

A theoretical study of laser-induced chemical vapor deposition

Abstract The laser-induced chemical vapor deposition process has been studied using a Monte Carlo procedure. First the action of the laser beam is assumed to induce the gas-phase decomposition of a parent organometallic molecule. It was then assumed that pyrolytic decomposition of adsorbed species can be neglected. The goal of the simulations was to establish the relationship between the morphology of the deposited layer as well as the deposition rate and various characteristics of the system. In particular the dependence on buffer gas pressure, beam intensity and nature (continuous and pulsed) and beam shape were examined. It was found that when a CW beam is used “volcano”-shape deposited layers are obtained due to a competition between the diffusion of parent organometallic molecules back into the irradiated zone and the rate of photodissociation fragments production. In contrast, Gaussian-shape deposited layers were obtained for a pulsed beam. In addition, the deposition rate was found to exhibit a strong dependence on the total pressure in the system.

A theoretical study of laser-induced chemical vapor deposition

The laser-induced chemical vapor deposition process has been studied using a Monte Carlo procedure. First the action of the laser beam is assumed to induce the gas-phase decomposition of a parent organometallic molecule. It was then assumed that pyrolytic decomposition of adsorbed species can be neglected. The goal of the simulations was to establish the relationship between the morphology of the deposited layer as well as the deposition rate and various characteristics of the system. In particular the dependence on buffer gas pressure, beam intensity and nature (continuous and pulsed) and beam shape were examined. It was found that when a CW beam is used “volcano”-shape deposited layers are obtained due to a competition between the diffusion of parent organometallic molecules back into the irradiated zone and the rate of photodissociation fragments production. In contrast, Gaussian-shape deposited layers were obtained for a pulsed beam. In addition, the deposition rate was found to exhibit a strong dependence on the total pressure in the system.

Observations of low-frequency oscillations during relativistic-electron-beam-plasma interactions

During propagation of a relativistic electron beam in hydrogen gas at sub-torr pressures using a foil-less diode, low-frequency oscillations in the megahertz range are observed in the net current wave forms, and continue even after passage of the beam. The novel feature of the experiment is that both beam generation and propagation take place in the same low-pressure regime, and hence the beam parameters are functions of gas pressures. Analysis of the experimental results shows that the low-frequency oscillations result from the resistive-hose instability.

A state selective metastable detector

The design of a simple low-energy metastable detector is described. A time-of-flight technique is used to analyse a metastable nitrogen gas beam and this reveals that the detector may be used to state-select metastable states from the composite beam.

Effects of high temperature surface reactions of aluminium-lithium alloy on the porosity of welded areas

Abstract The purpose of this investigation was to explain and prevent the formation of pores when welding commercial grade aluminium-lithium alloys by tungsten inert gas and electron beam processes. A correlation was shown between the formation of pores and hydrogen contamination of surface layers during solutionizing heat treatment of the alloy. The porosity could be a result of trapping of hydrogen bubbles as the welding bead solidified. Hydrogen contamination is related to the action of water vapour as oxidation occurs during heat treatment in air. Penetration of hydrogen into the material is still disputed. It could result from a mechanism entailing the formation of aluminium oxyhydroxides progressively covered by an oxide film. Hydrogen would be predent in the alloy mainly as lithium hydride.

A study of the propagation of a quasistationary relativistic electron beam in a dense gas. II. Experimental studies

Results obtained from experimental studies of the interaction between a quasistationary electron beam (300 keV, 20 A, 500 μsec, 0.3 cm) and a dense gas are presented. These investigations were carried out in air at atmospheric pressure and, for the purpose of modeling the propagation of a magnetostricted REB, at reduced pressure (3–300 torr). The rarefaction dynamics of a channel heated by the beam are studied and its maximum propagation distances in a dense gas are determined. The results obtained are compared with the theoretical model examined earlier.

The parameters of the plasma channel formed by relativistic electron beams in neutral gases

The results of the measurements of plasma channel conductivity produced by a high current relativistic electron beam (REB) with the following parameters: electron energy E e = 1–1.2 × 10 6 eV, beam current 1–1.5 × 10 4A, pulse duration 60–10 −9 s in gas mixture N 2:O 2 = 4:1 and argon are presented. The results may be employed in a plasmochemistry. For the first time, changes in the radial profile of channel conductivity was followed experimentally during the time of the order of a REB pulse duration.

A study of the propagation of a quasistationary relativistic electron beam in a dense gas. Part I. A physical model of the interaction

A study of the propagation of a quasistationary relativistic electron beam in a dense gas. Part I. A physical model of the interaction

Ion/Neutral Beam Assisted Etching of Semiconductors: Chemical Modifications of the Adsorbed Phase

ABSTRACTThis paper addresses the fundamental aspects of etching semiconductors with inert gas beams in the presence of a suitable precursor gas. In particular, the changes that an energetic bombarding ion/neutral species cause to the surface and sub-surface region of a solid are considered, both in terms of the introduction of damage to the semiconductor and chemical processes that are provoked in the adsorbed states present. The implications for practical etching reactions are then discussed.

High Damage Threshold Optical Films for Excimer Lasers

AbstractHigh damage threshold coating for high energy KrF excimer laser has been developed by the multiple ion beam deposition system, which contains a couple of the ionized cluster beam (ICB) sources and the ionized gas beam source. The damage threshold of low refractive SiO2, high refractive A12O3 and SiO2/A12O3 multilayer coatings is found to be more than 105 shots at 8J/cm2 laser energy. Oxidation is enhanced by ion bombardment during the film growth.The refractive indices of SiO2 and A1203 films were 1.46 and 1.62 at the ion current density of 0.8μA/cm2. The film density of SiOx approaches to the bulk SiO2 of 2.3Og/cm3 with increasing ion current density. The stress-free SiO2 film can be obtained at the ion current density of around 0.5 μA/cm2.

On the use of CsX + cluster ions for major element depth profiling in secondary ion mass spectrometry

The use of Cs bombardment secondary ion mass spectrometry (SIMS) in conjunction with the detection of positively charged Cs-cluster ions, CsX +, is described. This methodology is shown to be useful for the quantitative analysis of matrix-level elements in III–V compounds such as AlGaAs, and atom fractions in mixed Group IV semiconductors such as Si:Ge alloys. The technique obtains this quantitative accuracy while not sacrificing the beneficial characteristics of SIMS such as excellent depth resolution, high dynamic range, and ability to analyze small areas. Data are shown which demonstrate the ability to detect dopant profiles (Zn) while simultaneously obtaining quantitative depth profiles for the major constituents of the sample (AlGaAs). In addition, descriptions are given of this technique's use in quantitative analysis of a sample directly from the CsX + mass spectrum. A mechanism is also put forth which explains the surprising uniformity of sensitivites for elements detected as CsX + cluster ions. The mechanism involves a recombination above the sample surface of the leaving flux of resputtered Cs ions and the leaving sputtered neutral atoms of the sample material. This mechanism separates the ionization process from the sputtering process much like electron gas or electron beam sputtered neutral mass spectrometry (SNMS). The result can be thought of as cesium-ion SNMS.

Experimental study on cold fusion using deuterium gas and deuterium ion beam with palladium

A series of experiments using deuterium gas and low energy deuteron beam with palladium has been designed at Mississippi State University to allow for the observation, if it exists, of cold fusion. Three experiments were performed. One involved the diffusion transient of deuterium gas into palladium. The gas was cooled by liquid nitrogen, and its temperature was permitted to rise to room temperature, changing from near −34°C to 19°C in 75 minutes. A spherical lithium neutron detector, 21 cm from the palladium, gave an audible indication of neutron levels approximately twice the background. A second experiment used a deuterium ion beam (1 kev) which bombarded a palladium target. An average counting rate of 36±6 counts for 2 minutes was measured by a BF3 tube with a paraffin moderator, 50 cm from the target. The background varied from 1–7 counts for each 2 minutes of counting period and averaged 4±2 counts in 2 minutes. A nitrogen ion beam impinging on the same palladium target produced 6 counts for a 2-minute counting period. A third experiment used a hydrogen ion beam first, then a nitrogen ion beam, finally a deuterium ion beam to bombard the same palladium target. These ion beams had energy less than 1 kev, and created neutron counts in the range of background. The palladium specimens were a piece of foil and a tube which used to be the palladium leak in a neutron generator. These preliminary experiments will be repeated, improved, and extended later.

Atoms in flight

The authors describe the use of a time-of-flight technique in the study of gas beam dynamics. The effect of lifetime of excited states, mass of atom or molecule and temperature on the observed speed distribution are discussed.

2-D Simulation for focus of rotating and propagating ion beam in neutral gas

Focusing processes of rotating and propagating proton beams in a neutral hydrogen gas are studied numerically by using a two-dimensional hybrid code. Processes including beam impact ionization, plasma avalanche and field emission are taken into consideration. The plasma formation time depends on the initial gas density and the beam intensity. When 2-Torr neutral gas is filled initially, enough plasma density is created by the rising part of the beam pulse, so that the main pulse is focused and forms a rotating and propagatingbeam configuration.