Typical Ion Energy Research Articles

Helium Ion-Assisted Wet Etching of Silicon Carbide with Extremely Low Roughness for High-Quality Nanofabrication.

Silicon carbide (SiC) is a promising material for a wide range of applications, including mechanical nano-resonators, quantum photonics, and non-linear photonics. However, its chemical inertness poses challenges for etching in terms of resolution and smoothness. Herein, a novel approach known as helium ion-bombardment-enhanced etching (HIBEE) is presented to achieve high-quality SiC etching. The HIBEE technique utilizes a focused helium ion beam with a typical ion energy of 30keV to disrupt the crystal lattices of SiC, thus enabling wet etching using hydrofluoric acids and hydrogen peroxide. The etching mechanism is verified via simulations and characterization. The use of a sub-nanometer beam spot of focused helium ions ensures fabrication resolution, and the resulting etched surface exhibits an extremely low roughness of ≈0.9nm. One of the advantages of the HIBEE technique is that it does not require resist spin-coating and development processes, thus enabling the production of nanostructures on irregular SiC surfaces, such as suspended structures and sidewalls. Additionally, the unique interaction volume of helium ions with substrates enables the one-step fabrication of suspended nanobeam structures directly from bulk substrates. The HIBEE technique is expected to facilitate and accelerate the prototyping of high-quality SiC devices.

Measurements of ion fluxes in extreme ultraviolet-induced plasma of new EUV-beam-line 2 nanolithography research machine and their applications for optical component tests

In modern extreme ultraviolet (EUV) lithography machines, sensitive optical components, such as multilayer mirrors and photomasks, may be affected by plasma interactions. The new 13.5 nm EUV-beam-line 2, designed to provide accelerated tests for next generation lithography, is used to investigate EUV-induced plasma phenomena. First systematic measurements of ion fluxes produced in EUV-induced hydrogen plasma are reported, with operating conditions including 5 and 20 Pa gas pressure, 3 kHz EUV pulse repetition rate, and 4.2 W total EUV beam power produced in a 10–15 ns EUV pulse. Space- and time-resolved distributions of ion fluxes and ion energies were measured using a retarding-field ion energy analyzer mounted next to the EUV beam. Typical ion energies were in the range of 1–8 eV and typical ion fluxes were in the range of 2–8 × 1017 ions m−2 s−1. The obtained ion fluxes are applied in a photomask lifetime test to understand the material effects after an EUV exposure.

UWAVS first mirror after long plasma cleaning: Surface properties and material re-deposition issues

One of the important aspects of the service life of the first and second optical mirrors (FM and SM) in ITER UWAVS diagnostics is to understand the influence of plasma cleaning on materials re-deposition and optical surface quality after multiple cleaning cycles. The capacitively coupled RF 30–60 MHz system is a candidate for the UWAVS mirror cleaning. It generates ion fluxes of tens of electron-volts, sputtering contaminants as well as construction materials. In the present report, we discuss materials re-deposition after cleaning with 30–60 MHz discharges inside the prototype of the front-end vacuum compartment. Typical ion energies were below 100 eV at the RF electrode and 20–30 eV at the grounded wall. Materials sputtered from the FM were deposited at various locations and on the SM. The deposition rates were estimated as 0.05 nm/hour or lower. The experiments showed advantages of Molybdenum as a plasma facing construction material due to lower sputtering. Traces of Fluorine were found, which may indicate cable damage at higher powers. The single-crystal Mo-mirror mock-up was etched at 0.5–1 nm/hr. rate. The mirror reflectivity showed satisfactory results after 60 h of exposure, with 50–60 nm removed. The overall effect on the reflectivity considering full service time is yet to be investigated.

Modification of SRIM-calculated dose and injected ion profiles due to sputtering, injected ion buildup and void swelling

In radiation effects on materials utilizing self-ion irradiations, it is necessary to calculate the local displacement damage level and ion injection profile because of the short distance that self-ions travel in a material and because of the strong variation of displacement rate with depth in a specimen. The most frequently used tool for this is the software package called Stopping and Range of Ions in Matter (SRIM). A SRIM-calculated depth-dependent dose level is usually determined under the implicit assumption that the target does not undergo any significant changes in volume during the process, in particular SRIM ignores the effect of sputtering, injected ions, and void swelling on the redistribution of the dose and injected ion profiles. This approach become increasingly invalid as the ion fluence reaches ever higher levels, especially for low energy ion irradiations. The original surface is not maintained due to sputter-induced erosion, while within the irradiated region of the specimen, injected ions are adding material, and if void swelling is occurring, it is creating empty space. An iterative mathematical treatment of SRIM outputs to produce corrected dose and injected ion profiles based on these phenomenon and without regard to diffusion is presented along with examples of differences between SRIM-calculated values and corrected values over a range of typical ion energies. The intent is to provide the reader with a convenient tool for more accurately calculating dose and injected ion profiles for heavy-ion irradiations.

Interpretation of optical emission in a strongly inhomogeneous PIAD environment

A variety of methods exists for the production of high quality optical coatings. These are for instance magnetron or ion beam sputtering, or thermal evaporation assisted by ion or plasma ion beam sources. The choice of a particular technique is due to the specific demands for tailoring the thin film properties such as homogeneity, refractive index, absorption, mechanical stress, porosity (optical shift), etc.. To allow for economic production of complex multilayer designs, the issue of reproducibility at the highest deposition rate possible has to be faced.The plasma ion assisted deposition (PIAD) has been invented to avoid contamination of the process environment present when gridded ion sources are employed. One example for this approach is the Advanced Plasma Source (APS) which holds a considerable market share in the field of optical coatings. The APS is a hot cathode (LaB6) DC glow discharge with an auxiliary magnetic field, typically operated with argon. A high density (ne ~ 1012 cm-3) and high temperature (Te ~ 20eV) plasma is generated in the source region (V ~ 0.7l) and expands to the chamber (V ~ 103 l) which is held at high vacuum (p ~ 2 • 10-2Pa). The expansion induces a strong drop of the plasma potential Vp which results in an acceleration of the ions towards the substrates. The setup is outlined in figure 1. By varying the discharge voltage (VD=50..150 V), the magnetic field (Bmax=10..40mT) and the gas flux (GAr=2..20 sccm) different characterstics of the plasma ion beam are obtained, where typical ion energies are Ei=50..150 eV. As is described in the references, various probe techniques were adopted to elucidate the mechanisms of plasma beam formation in this particular PIAD setup. In an earlier work the approach of optical emission spectroscopy (OES) has been pursued. This paper contains a description of the diagnostic installation allowing for tomographic reconstruction of the local optical emission near the source exit. With a simple corona model ne and Te could be estimated for an Ar/He mixture. The interpretation of emission close to the APS is hampered by the lack of detailed knowledge of neutral density and temperature in this region.In this extended abstract the preparation of a more elaborate approach using collisional radiative modelling is sketched. The new aspect is the consideration of a global electron energy probability function (EEPF) based on the nonlocal approximation. This concept is useful for reducing the complexity of electron kinetics by coordinate transformation from the 6D phase-space to a 1D total energy space. The analysis of OES data is not merely ment as a proof of principle. The final goal is to interpret the OES data in terms of electron parameters, as a foundation of a control scheme for the APS using non-invasive optical diagnostics. Although global parameters, such as voltages and currents can be maintained accurately, drifts in the plasma parameters which are not measured routinely in the industrial application, may lead to limitations in the reproducibility of the optical coatings. The main reason is suspected to be the alteration of the electrodes of the APS during the PIAD process.

Low-Temperature Deposition of TiN by Plasma-Assisted Atomic Layer Deposition

Titanium nitride () films were deposited by a plasma-assisted atomic layer deposition (PA-ALD) process, based on precursor dosing and remote plasma exposure, at temperatures ranging from 100 to . The plasma, the PA-ALD process, and the resulting material properties were extensively investigated. The plasma was studied by optical emission spectroscopy and Langmuir probe, revealing an ion density of and an electron temperature of just above the substrate. Under floating conditions there is thus a considerable ion flux towards the substrate per ALD cycle with a typical ion energy of . film growth was studied by in situ spectroscopic ellipsometry, revealing self-limiting surface reactions for the complete temperature range. At the growth rate of was found to be significantly lower than the growth rate of at . The stoichiometry of the films varied with the plasma exposure time, while the Cl content was mostly affected by the deposition temperature ( at to at ). Resistivities as low as were obtained at a temperature of , while at a fair resistivity of was reached. These results show that PA-ALD with and plasma is well suited for low-temperature deposition of high-quality films.

Ion emission measurements and mirror erosion studies for extreme ultraviolet lithography

Mirror erosion by high energy ion emission from extreme UV light sources is one of the main factors contributing to EUVL collector mirror reflectivity degradation. We are measuring ion energy distributions at the mirror distance from the plasma utilizing three different ion diagnostics for the case of tin-doped microscopic droplet laser plasmas. Typical ion energy distributions measured by an electrostatic spectrometer are described. From the ion energy distributions, an estimate of mirror erosion is obtained. The effectiveness of electrostatic field mitigation is evaluated for the EUVL source requirement.

Modeling of displacement damage in an ion‐beam‐modified perfluorosulfonate ionomer

AbstractA Monte Carlo simulation has been used to model the effects of medium‐energy ion‐beam modification of Nafion. With typical ion energies of 100–200 keV, the treatment affects the outer 0.5–2‐μm surface layer. An equation has been developed for predicting the expected range of implantation as a function of the ion energy and atomic number. The expected range of displacement damage due to the ion beam can similarly be described over the whole parameter range of interest with a double logarithmic fit. A full characterization of the distributions with their first four statistical moments is also presented. The quantitative description of the profiles obtained is useful for the rational design of an ion‐beam treatment for the preparation of integrally skinned membranes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1343–1350, 2004

Oxide etch behavior in a high-density, low-pressure, inductively coupled C2F6 plasma: Etch rates, selectivity to photoresist, plasma parameters, and CFx radical densities

Silicon dioxide and photoresist substrates were etched in a gaseous electronics conference inductively coupled plasma reference cell using C2F6 feed gas. The power/pressure/bias parameter space of the study generated a plasma which has plasma and ion current densities, plasma potential, ion energy, and etch rate characteristics typical of commercial high density plasma (HDP) etch tools. Absolute number density trends of CF and CF2 were measured using wavelength-modulated infrared spectroscopy in situ with etch rate experiments. For nonreactive surfaces such as Si and photoresist, typical CF and CF2 number densities varied around 4.9×1012 and 4.8×1013 cm−3, respectively. Over an SiO2 surface, these values decreased and evidence of the reaction of CFx radicals with an oxide surface to form COF2 was observed. Source and bias powers were mapped into ion current densities and ion energies, and correlations were made with etch rate, which was in the 0–150 A/s range. Selectivity ranged from 1 to 6. Typical plasma density was 8×1011 cm−3, typical ion current density was 30 mA/cm2, and typical ion energy was 50–160 eV. Both ion current density (source power) and ion energy (bias power) primarily controlled etch rate and selectivity. Transition from net etch to net deposition of fluorocarbon occurred near 30 W bias power. Increasing substrate temperature decreased the polymer growth rate, and increased the etch rate. This data is expected to be important for developing computer simulation plasma models of the HDP oxide etch process.

Angular Distribution of Electron Temperature and Density in a Laser-Ablation Plume

The angular distribution of electron temperature and density in a laser-ablation plume has been studied for the first time. The electron temperature ranges from 0.1 to 0.5 eV and is only weakly dependent on the angle in the low-intensity range studied here. In contrast, the typical ion energy is about 2 orders of magnitude larger, and its angular distribution is more peaked about the target normal. The derived values of the electron density are in agreement with the measured values of ion density.

Thin film processing by biased target ion beam deposition

This paper describes the development of a novel thin film deposition technology, which we call biased target ion beam deposition (BTIBD). BTIBD employs a low energy ion source (<30 eV) directed at a negatively biased target. Because typical ion energies are below the sputter threshold of vacuum construction materials, only those ions arriving at the target acquire sufficient energy to cause sputtering. A second low-energy ion source can be directed at the substrate to provide low energy (<15 eV) bombardment of the growing film. BTIBD is well suited to demanding applications requiring atomically engineered thin films and interfaces because it offers a large range of process pressures, control of adatom energies, and excellent uniformity and repeatability. This paper describes a multi-target, prototype (BTIBT) system, the associated ion sources, and process results on thin Cu films and spin valve structures.

Production of direct fusion neutrons during ultra-intense laser-plasma interaction

The plasma response to a picosecond multi-terawatt laser pulse is characterized by several distinctly different time scales. In the present report we consider the plasma's evolution on the slow time scale typical for excitations of the ionic component. A relativistically strong laser pulse (-) is shown to drive, under proper conditions, mega-ampere ion currents with a typical ion energy of 50-150 keV, which covers the region of the resonance peak in the cross section of D-T fusion and, hence, provides an opportunity to initiate nuclear reactions directly in the laser focus.

Mechanical and Tribological Properties of Zrc/Vc Alloy Films Deposited by Sputtering and Pulsed Laser Deposition

ABSTRACTA study has been conducted on ZrC/VC alloy thin films prepared by both pulsed laser deposition (PLD) and RF magnetron sputtering. The phase formation, wear properties, and hardness of these thin films were examined. An alloy target comprised of 36% VC and 64% ZrC (atomic %) was used to deposit films at 200°, 2000°, and 400° C. The nominal film thickness was 0.6 μm. X-ray diffraction (XRD) analysis revealed these films were solid-solution alloys and showed a preference for (100) orientation for sputter-deposited films and a (110) orientation for laser deposition. More highly oriented films were obtained at elevated temperatures as evidenced by rocking curve measurements on the PLD films. The FWHM of the peaks ranged from 2.2° to 8.3° for films deposited at 400° C and 20° C, respectively.Using time-of-flight quadmpole mass spectrometry (TOFQMS), we performed plume diagnostics to measure particle energies and the thermalization effects of the background gas. In vacuum, typical ion energies ranged from ˜5–100 eV while the neutral atoms had kinetic energies from ˜1–5 eV. Our measurements show that the background gas can be used to selectively thermalize low mass components in the plume. From measured kinetic energies and collision effects of the gas, the changes in crystallographic structure of the alloy with pressure appear to result from collision-induced effects from condensation of the Zr atoms. This ‘heavy’ atom effect may be an important new processing parameter with which to adjust film morphology and crystal texture.

Charge State Distributions of 1 to 7 MeV C and Be Ions Stripped in Thin Foils

The development of ultrasensitive mass spectrometers based on tandem accelerators has lead to a renewed interest in the stripping process of MeV ions and the charge state distributions of the ions emerging from the stripping foil (or the gas stripper). The knowledge of these distributions is of special importance for the optimization of existing facilities for mass spectrometry and for the design of new dedicated machines. The goal was to determine the charge state distributions of Be and C ions passing through thin C-foils at energies between 1.5 and 7 MeV (i.e. for typical ion energies found at the terminal of small tandem accelerators). Both C and Be are of interest in todays efforts of using accelerators as mass spectrometers for rare radioisotopes (/sup 14/C and /sup 10/Be in this case). The determination of the charge state distributions should also give some insight in fractionation effects i.e. effects leading to unequal transmission efficiencies through the spectrometer for different isotopes.

Gas discharge ion source. II. Duopigatron

Ion source performance characteristics consisting of total ion current, ion energy distribution, mass distribution, and ion current density distribution have been measured for several models of a duopigatron. Variations on the duopigatron design involved plasma expansion cup material and dimensions, secondary cathode material, and interelectrode spacings. Of the designs tested, the one with a copper and molybdenum secondary cathode, and a mild steel plasma expansion cup proved to give the best results. The ion current density distribution was peaked at the center of the plasma expansion cup and fell off to 80% of the peak value at the cup wall for a cup 15.2 mm deep. A total ion current of 180 mA consisting of 60%-70% atomic ions was produced with an arc current of 20 A and source pressure of 9.3 Pa. More shallow cups produced a larger beam current and a more sharply peaked ion current density distribution. Typical ion energy distributions were bellshaped curves with a peak 10-20 V below anode potential and with ion energies extending 30-40 V on either side of the peak.

Radiation damage (blistering) in Al, Cu, Si by exposure to a plasma focus discharge

Plates of Al, Cu (polycrystalline) and Si (monocrystal) have been irradiated with beams of D + ions (keV to MeV) and other radiation by exposure to a single discharge of a 5–10-kJ Plasma Focus in deuterium. Scanning electron microscope and elemental X-ray energy dispersive analysis are used for diagnostics. The nonuniformity of the ion beam causes a nonuniform damage with formation of clusters of blisters. A statistical analysis of blister parameters (diameter and skin thickness) is used to investigate the internal structure of a deuteron beam ejected from the plasma. The value K ∼ 10–20 keV is obtained as the typical ion energy for the bulk of the deuterons and an ion energy E ∼ 200–230 keV is typical for individual ion groups (ion strings) forming the high-energy deuteron beam.

Effet du flux instantane sur la formation des cavites dans le nickel irradie aux ions Ni + de 500 keV

In radiation effects on materials utilizing self-ion irradiations, it is necessary to calculate the local displacement damage level and ion injection profile because of the short distance that self-ions travel in a material and because of the strong variation of displacement rate with depth in a specimen. The most frequently used tool for this is the software package called Stopping and Range of Ions in Matter (SRIM). A SRIM-calculated depth-dependent dose level is usually determined under the implicit assumption that the target does not undergo any significant changes in volume during the process, in particular SRIM ignores the effect of sputtering, injected ions, and void swelling on the redistribution of the dose and injected ion profiles. This approach become increasingly invalid as the ion fluence reaches ever higher levels, especially for low energy ion irradiations. The original surface is not maintained due to sputter-induced erosion, while within the irradiated region of the specimen, injected ions are adding material, and if void swelling is occurring, it is creating empty space. An iterative mathematical treatment of SRIM outputs to produce corrected dose and injected ion profiles based on these phenomenon and without regard to diffusion is presented along with examples of differences between SRIM-calculated values and corrected values over a range of typical ion energies. The intent is to provide the reader with a convenient tool for more accurately calculating dose and injected ion profiles for heavy-ion irradiations.

Autoresonant Accelerator Concept

We present a new ion accelerator idea which combines the basic concepts of traveling wave and collective acceleration. The lower cyclotron mode of a relativistic electron beam along a spatially decreasing magnetic field $B$ constitutes the traveling wave, the wave phase velocity varying inversely with $B$. The negative energy character of the wave allows automatic extraction of energy from the electron beam for the acceleration process. Typical ion energy versus current outputs are estimated.

Spectral linewidth limitations set by ion-foil interactions

We show experimentally and theoretically that beam-foil spectral linewidths due to scattering of the ion beam in carbon exciter foils are of the order of 1–2 Å for typical ion energies in the visible spectrum. The empirical relationship θ 2 = 2(m 2/m 1) (ΔE v/E) , θ = rms total scattering angle, m 2 = foil atom mass, m 1 = incident ion mass, ΔE ν = ion energy loss due to nuclear collisi ns in the foil, E = incident ion laboratory energy, fits linewidth data for H, O, Ar, Xe, in the range 0.08–1.5 MeV.