Broad-beam Ion Source Research Articles

Characterization of an RF-excited broad beam ion source operated with a mixture of CHF3 and O2

The composition and ion energy distributions of the main ion species of an ion beam were recorded and analyzed. The RF-type broad beam ion source was operated with a mixture of CHF3 and O2. A plasma bridge neutralizer operating with Ar was employed for ion beam neutralization. The data were collected with an energy-selective mass spectrometer (ESMS). The mass spectrum showed numerous ion species, beginning with ionized molecules, dissociation products of the process gases and products from reactions with background gas and the plasma discharge vessel, and the extraction system. For a quantification of the ion beam composition, the mass dependent transmission functions for two ESMS were determined. The ion energy distributions show that, in comparison to operation with inert gases, there are additional slower ions present. These ions can be related to dissociation processes outside of the ion beam source. As a result of their typically lower etching yield, these slower ions affect the etching behavior.

Characterization of a broad beam ion source converted into a high intensity deuterium beam

Avalanche Energy is developing deuterium ion beams for the Orbitron fusion device. For these and similar projects, modification of off-the-shelf high current ion sources enables affordable and rapidly accessible alternatives to custom-built systems. We have successfully operated the Veeco MARK I broad beam source on deuterium to create multi-keV energy ions. Directing this beam through a small aperture required carefully designed optics. Once a narrower beam was created, a faraday cup was used to measure the beam current and profile while a Thomson Parabola was developed to help understand the beam species and energy composition.

Low-energy ion beam erosion of Si with simultaneous co-deposition of metallic surfactants: Experimental and simulated data

Ion beam erosion of Si under co-deposition circumstances supports the formation of surface patterns on the nano- and micrometer scale. To evaluate the effect of surfactant sputtering within a setup relevant for ultra precision surface finishing, this work is presented. We present data for samples prepared with Ar ion beam erosion, at low ion energy. Al, Cu, steel, Cr, Ni, Mo, Ti, Ta, Zn and Si were chosen as co-deposition material. Simultaneous irradiation of the co-deposition material and the Si samples were performed with a broad beam ion source. The structuring and pattern formation are discussed with SEM and AFM measurements. It was shown that the evolution of structures on the substrate is induced by the silicide-forming metals. This corresponds with a higher surface roughness. Whereas the non-silicide-forming metals did not show patterning, and accordingly, lower surface roughness. Measurements regarding the Si removal rate showed, that it depends on the co-deposition material. Supporting simulation data proposed that the effect of the co-deposition material on the Si removal is determined by the combination of sputtering and scattering properties of the co-deposition material. The ratio of scattered Ar ions to sputtered metal particles describes the effect on the removal change. For metals which tend to higher scattering, the removal is enhanced. This applies for most of the metals with higher atomic number. Whereas the metals with lower atomic number favor self-sputtering, which results in an decreased Si removal.

Improving broad-beam ion etching equipment through innovative ion optics design

Ion beam etching (IBE) is a crucial technique used for the manufacturing of nanostructures, including blazed gratings and slanted gratings. In the overall design of a complete IBE system, the ion optics play an important role. To achieve a high-performance broad-beam ion source, the design of the ion optics presents greater challenges. In this study, a full-particle three-dimensional model was utilized to calculate the extraction of the ion beam from the discharge plasma, with the presentation of the influence of ion optics parameters on beam current. To enhance the beam current of broad-beam equipment, a novel approach to the design of the ion optics with chamfered apertures was proposed, followed by an investigation into the influence of chamfering parameters on the ion optics. The research provides a significant theoretical basis and a wide range of possibilities for the design and performance improvement of IBE ion optics.

Characterization of a broad beam Kaufman-type ion source operated with CHF3 and O2

Process stability and reproducibility are essential for highly precise manufacturing with reactive ion beam etching (RIBE) in optics industry. Therefore, the ion beam source characteristic must be well known. For this study, a Kaufman-type broad beam ion source operated with CHF3 and O2 is characterized with energy selective mass spectrometry and Faraday measurements. These results are compared with etching experiments on SiO2, Si, and AZ®1505 photo resist. The influence of the source setup and process conditions on ion beam composition, ion energy distribution, and the etch selectivity are discussed. It was found that etch selectivity applying different ion beam currents at a fixed feed gas composition correlate with resulting ion beam composition. Due to a change in ion beam composition, selectivity also changes with the total volumetric mass flow of the feed gas at a fixed ion beam current and constant mixing ratio of CHF3 and O2.

Erratum: “Characterization of an RF excited broad beam ion source operating with inert gases” [J. Appl. Phys. 129, 223305 (2021)

Erratum: “Characterization of an RF excited broad beam ion source operating with inert gases” [J. Appl. Phys. 129, 223305 (2021)

Comparative analysis of different charged particles emerging from a broad beam ion source

In this research, the ion-source is modified to produce differently charged particles; that could be successfully used in a variety of applications. The different parameters affecting the particles; neutral charge, electron, and positive ion emerging from a broad beam cold cathode ion source are studied using argon and nitrogen gases. The neutral and the electron current are measured using a simple technique. It is found that the neutral particles and the electrons depend on the positive ion current, gas pressure, and gas type. Also, the ratio of the neutral to the positive charge is increased by increasing the gas pressure and its reach to 1.2 at pressure 4 × 10-4 mbar in case of argon and reach to 1.45 at pressure 5 × 10-4mbar in case of nitrogen gas. Also; it is found that the ratio of the electron to the positive charge is inversely proportional to the gas pressure in the case of argon gas. But in the case of the nitrogen gas it is found that this ratio is directly proportional and reaches 2.1 at pressure 5 × 10-4mbar.

Characterization of an RF excited broad beam ion source operating with inert gases

Ion current density distributions, mass spectra, and ion energy distribution functions (IEDFs) for the use of Ar and mixtures of Ar/He and Ar/Ne in an RF broad beam ion source have been measured as a function of the extracted ion beam current and the applied RF-power. For the measurements, an array of Faraday probes and an energy-selective mass spectrometer have been used. Regardless of the gases or gas mixtures used, a broadening of the ion current density profile is measured at constant grid voltages with increasing RF-power. The IEDFs of all species are also dependent on the applied RF-power and show a bimodal shape with an increasing energy shift for a higher RF-power. The data show a significant contribution of charge exchange processes after the ions left the ion beam source. Besides ions of the process gas, additional species of ions originating from the erosion processes of the ion beam source, can be found in the mass spectrum. The measurements show that the operating conditions of the ion source have a significant influence on the beam properties and thus can also affect the results of ultraprecise ion beam-assisted processes.

ION BEAM IRRADIATION EFFECTS ON SURFACE MORPHOLOGY AND OPTICAL PROPERTIES OF ZnO/PVA COMPOSITES

Polymer nanocomposites composed of zinc oxide nanoparticles (ZnO NPs)-doped polyvinyl alcohol (PVA) polymer matrix have been synthesized using solvent casting preparation method. The ZnO/PVA polymer nanocomposite films are irradiated with different argon ion beam fluences using broad-beam ion source. The prepared films are characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and UV–visible spectroscopy. The XRD shows that ZnO NPs are successfully formed on PVA polymer and the mean size of ZnO NPs is 31.2[Formula: see text]nm. The FTIR peaks indicate that ZnO NPs are attached to the polymer chains, whereas the SEM analysis shows that ZnO NPs are homogeneously dispersed into the PVA polymer surface. The optical bandgap, band tail width and number of carbon atoms in cluster are obtained and discussed using UV–visible spectroscopy. The transmittance is shown with low transmittance intensity in the UV region with the addition of ZnO NPs and ion beam irradiation. The optical bandgap [Formula: see text] showed significant decrease from 5.25[Formula: see text]eV for pristine PVA to 3.10[Formula: see text]eV by adding ZnO and from 3.10[Formula: see text]eV for un-irradiated ZnO/PVA to 2.98[Formula: see text]eV after being irradiated by [Formula: see text][Formula: see text]cm[Formula: see text]. The number of carbon atoms in cluster [Formula: see text] is increased by ZnO addition, whereas the Urbach energy [Formula: see text] is decreased. These results confirmed that there are significant modifications in PVA polymer, and the produced flexible ZnO/PVA is a good polymer nanocomposite film for technological applications.

In situ XRD measurements to explore phase formation in the near surface region

Though X-ray diffraction (XRD) is a well-established technique—yet still continuously evolving—for characterization of thin films and diffusion layers, there are two inherent limitations due to the underlying physical principles leading to the diffraction: (i) all data are a weighted integral across the information depth and (ii) X-ray amorphous or nanocrystalline phases are very difficult to be detected. The purpose of this Perspective is to show how a straightforward combination of in situ XRD with depth profiling using a laboratory experiment in combination with a low-energy broad-beam ion source may allow us to overcome these limitations for functional surfaces. Whereas time-resolved investigations of diffusion and phase formation during ion implantation using reactive species are well established, using ion beam sputtering with nonreactive species for depth profiling of the phase composition during the measurements is a rather recent development. While employing analysis of differential spectra leads to a depth resolution below the information depth, ongoing in situ sputtering will lead to information obtained from layers deeper than the information depth. Keeping track of the total diffraction intensity permits the identification of phases without reflections in the XRD measurements, i.e., they appear to be amorphous, and their depth distribution. Selected examples drawn mainly from investigations of the nitriding kinetics of austenitic stainless steel will be used to demonstrate the potential and possible limitations of this method.

Characterization and optimization of low-energy broad-beam ion source

In this work, a cold-cathode ion source was modified to produce a broad beam that could be successfully used in a variety of applications. The ion source features gave reliable, long-term, maintenance-free operation. The ion source was surrounded by a magnetic field to produce uniform plasma in limited volume at low gas pressures (10−3 torr). The output ion beam current was up to 700 μA, and the diameter of the cold cathode was broad (∼25 mm). The stainless steel cathode disk and the cylindrical anode were separated by a Teflon flange. The fabrication of the source was simple, and a stable discharge medium was obtained by adjusting the operating conditions, such as discharge voltage, magnetic field intensity and argon (Ar) gas pressure. Also, the output ion beam was measured at different acceleration voltages. Moreover, the ion beam profile is characterized at different magnetic field intensities.

Development of a Radio Frequency Coupled Broad Beam Ion Source for Material Processing

The development of a radio frequency (RF) broad beam ion sources for generating a high brightness ion beams for material processing is presented. The source was able to deliver ion beams from 100 eV up to 2000 eV and with beam currents 100 µA up to 25 mA. The beams divergence do not exceed 7 degrees when using nominally flat grids. The current of ions extracted from a plasma source depends on the plasma parameters particularly the electron number density and electron temperature of the plasma. The Optical Emission Spectroscopy (OES) is employed to determine the plasma electron density and temperature. The effects of argon filling pressures and RF power on electron temperature and density plasma parameters are investigated. The electron density of Ar plasma is between 4x1011 cm-3 and 7x1012 cm-3 whereas electron temperatures 0.6 - 5 eV at pressures from 5x10-4 - 8.5 x10-3 mbar over the RF powers deposited within the plasma from 25 W to 200 W. The ion source is installed on a homemade accelerating tube. The beam optics is extensively studied with space charge compensation by TRANSPORT code. A solenoid magnet located between the ion source and the accelerating tube is used to focus and get the beam divergence under control. The performance of the accelerating facility is reported and applications for material modification is examined.

Characterization of the Ion Beam Current Density of the RF Ion Source with Flat and Convex Extraction Systems

The characterization of ion beam current density distribution and beam uniformity is crucial for improving broad-beam ion source technologies. The design of the broad ion beam extraction system directly affects these two parameters, therefore, depending on the application, the design and geometry of the source is changed. In this study, the effect of the presence or the absence of a neutralization process on the ion beam density was investigated. Also, the effect of the probe bias on the ion beam current measurement was evaluated. Eventually, using a flat probe, the ion beam profiles obtained from the extraction system of the ion source (Model RFIS 60, ACECR, Iran) were measured at energies from 300 eV to 1000 eV and compared in terms of current and uniformity of the ion beam in the absence of the neutralizer. In these experiments, screen and accelerator grids with different geometries (flat and convex grids) were used for comparison purposes. According to the obtained results, the flat grids generate a higher current density while the convex grids generate a more uniform beam. Therefore, each of these grid geometries can be suitable depending on the desired application.

Ion mass and energy selective hyperthermal ion-beam assisted deposition setup.

For the synthesis of high-quality thin films, ion-beam assisted deposition (IBAD) is a frequently used technique providing precise control over several substantial film properties. IBAD typically relies on the use of a broad-beam ion source. Such ion sources suffer from the limitation that they deliver a blend of ions with different ion masses, each of them possessing a certain distribution of kinetic energy. In this paper, a compact experimental setup is presented that enables the separate control of ion mass and ion kinetic energy in the region of hyperthermal energies (few 1 eV - few 100 eV). This ion energy region is of increasing interest not only for ion-assisted film growth but also for the wide field of preparative mass spectrometry. The setup consists of a constricted glow-discharge plasma beam source and a tailor-made, compact quadrupole system equipped with entry and exit ion optics. It is demonstrated that the separation of monoatomic and polyatomic nitrogen ions (N+ and N2+) is accomplished. For both ion species, the kinetic energy is shown to be selectable in the region of hyperthermal energies. At the sample position, ion current densities are found to be in the order of 1 μA/cm2 and the full width at half maximum of the ion beam profile is in the order of 10 mm. Thus, the requirements for homogeneous deposition processes in sufficiently short periods of time are fulfilled. Finally, employing the described setup, for the first time in practice epitaxial GaN films were deposited. This opens up the opportunity to fundamentally study the influence of the simultaneous irradiation with hyperthermal ions on the thin film growth in IBAD processes and to increase the flexibility of the technique.

Modernization of high-power (5 kW) broad ion beam source

In the course of the long-term performance (during 5 years) of a high-power source of gas ions (25 keV, 0.2 A, 600 cm2) with a plasma emitter based on cold cathode discharge, the character and rate of key constructive elements faults were determined, which allowed to calculate the inter-repair time, complexity and cost of the repair. The peculiarities of the gas-discharge system and the ion beam forming system limiting the effectiveness of ion beam treatment were revealed as well. Conditions favorable for the decrease in the discharge voltage by 50–200 V and igniting voltage up to 1.5-2 times are determined. The possibilities of lowering the minimal flow of working gas are demonstrated. The design of the discharge system with reduced sputtering rate of local areas of the hollow cathode is offered. The changes added to ion source design aimed to enhance the lifetime of the plasma chamber that is exposed to cyclic heating by the back electron beam leading to the development of through cracks, and to enlarge the rupture life of glow discharge hollow cathode by optimizing its configuration and the conditions of discharge ignition and burning, are described. The upgraded design of a multislit ion-optical system with enhanced performance ensures uniform surface distribution of ion fluence.

Modifying the Ni-MoS2Contact Interface Using a Broad-Beam Ion Source

Charge transport at the contacts is a dominant factor in determining the performance of devices using 2D MoS2. Using a low-energy beam of Ar ions, the interface between Ni and MoS2 was modified to improve the performance in 2D field-effect transistors (FETs). This broad-beam ion source is integrated into an ultrahigh vacuum, physical vapor deposition system that allowed for in situ modification of the MoS2 immediately prior to Ni contact deposition. The contact resistance decreased leading to a corresponding and highly reproducible boost in the on-current by up to four times. Spectroscopic analysis of the ion beam-modified MoS2 suggests that there are generated defects, which supply dangling bonds that improve carrier injection between the Ni metal contact and MoS2. This approach for modifying the Ni-MoS2 interface opens a promising new path for reducing the impact of contacts on MoS2 FET performance.

Complete coating of metal rings by ion beam sputtering of a W-shaped concave target with a broad-beam ion source

Ion beam sputter coating with the substrate at ambient temperature or water-cooled is a well-known process for coating temperature-sensitive substrates with films of high quality, despite the low process temperature. However, ion beam based methods suffer from an intrinsic drawback, the so-called line-of-sight restriction. Since a directed beam of the material to be deposited is used, only that part of a sample that is “seen” by the particle source is properly treated. This renders coating of 3-dimensional objects with ion beam methods difficult. Particularly challenging is to completely coat such objects from all sides. A typical example are rings. When they are to be treated with ion beam techniques, sophisticated manipulation of substrate or ion beam or even both is required. Despite these problems, under certain circumstances it is nevertheless possible to apply ion beam techniques for treating/coating 3-D objects. When ion beam sputter coating is used, the sputter target, i.e. the source of the material to be deposited, is usually flat. With such a sputter target, a ring can hardly be coated uniformly. However, when the sputter target is formed according to the substrate shape, here as a concave/convex double-cone, a very effective coating can be achieved. This is demonstrated by coating rings for corrosion protection.

Profile etching for prefiguring X-ray mirrors.

A method to pre-shape mirror substrates through etching with a broad-beam ion source and a contoured mask is presented. A 100 mm-long elliptical cylinder substrate was obtained from a super-polished flat Si substrate with a 48 nm root-mean-square (r.m.s.) figure error and a 1.5 Å r.m.s. roughness after one profile-etching process at a beam voltage of 600 V without iteration. A follow-up profile coating can be used to achieve a final mirror. Profile etching and profile coating combined provide an economic way to make X-ray optics, such as nested Kirkpatrick-Baez mirrors.

Instrument for spatially resolved simultaneous measurements of forces and currents in particle beams

The article presents a device for spatially resolved and simultaneous measurements of forces and currents in particle beams, especially in beams composed of ions and neutral atoms. The forces are exerted by the impinging beam particles on a plane circular conductive target plate of 20 mm diameter mounted on a pendulum with electromagnetic force compensation. The force measurement in the micronewton range is achieved by electromagnetic compensation by means of static Helmholtz coils and permanent magnets attached to the pendulum. Exemplary measurements are performed in the 1.2 keV beam of a broad beam ion source. The simultaneous measurements of forces and currents onto the same target are compared with each other and with Faraday cup measurements.

Distribution of ion current density on a rotating spherical cap substrate during ion-assisted deposition

The uniformity of ion density is critical for applications relying on the ion assisted deposition technique for the fabrication of the high quality thin films. The authors propose and describe here a method allowing one to calculate the ion density distribution on spherical substrate holders under stationary and rotating conditions for different positions of the ion source. The ion beam shape was approximated by a cosn function, and the ion current density was represented by a function inversely proportional to the distance from the ion source in accordance with our experimental results. As an example, a calculation of the current density distribution on the spherical cap substrate was performed for a broad beam ion source operated with an anode current of 3 A. The authors propose an approach for process optimization with respect to the ion source position and its inclination, in terms of uniformity and absolute value of the ion current density.