Energy Selective Mass Spectrometer 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.

Chamber with Inverted Electrode Geometry for Measuring and Control of Ion Flux-Energy Distribution Functions

Measurements of ion flux-energy distribution functions at the high sheath potential of the driven electrode in a classical low-pressure asymmetric capacitively coupled plasma are technically difficult as the diagnostic device needs to float with the applied radio frequency voltage. Otherwise, the ion sampling is disturbed by the varying electric field between the grounded device and the driven electrode. To circumvent such distortions, a low-pressure plasma chamber with inverted electrode geometry, where the larger electrode is driven and the smaller electrode is grounded, has been constructed and characterized. Measurements of the ion flux-energy distribution functions with an energy-selective mass spectrometer at the high sheath potential of the grounded electrode are presented for a variety of conditions and ions. The potential for suppressing low-energy ions from resonant charge transfer collisions in the sheath by the dilution of the working gas is demonstrated. Additionally, the setup is supplemented by an inductively coupled plasma that controls the plasma density and consequently the ion flux to the substrate while the radio frequency bias controls the ion energy. At high ion energies, metal ions are detected as a consequence of the ionization of sputtered electrode material. The proposed setup opens a way to study precisely the effects of ion treatment for a variety of substrates such as catalysts, polymers, or thin films.

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.

Properties of secondary particles for the reactive ion beam sputtering of Ti and TiO2 using oxygen ions

The ion beam sputtering of a metallic Ti and a ceramic TiO2 target by bombardment with oxygen ions was investigated systematically. Emphasis was put on the properties of the secondary particles emitted from the target, namely, the angular distribution of the sputtered Ti and the energy distribution of the secondary ions. Ion energies of 0.5, 1.0, and 1.5 keV and incidence angles of 0°, 30°, and 60° were used. The angular distribution of the flux of sputtered Ti particles was determined by measuring the thickness of TiO2 films that were deposited under emission angles in the range between −40° and +80°. An empirical formula was used to describe the angular distribution as a superposition of an isotropic and an anisotropic cosinelike function. Increasing the ion energy or decreasing the ion incidence angle leads to a more isotropic emission of the sputtered Ti particles. The mass and energy distribution of the secondary ions were measured using an energy-selective mass spectrometer. The most prevalent ion species are O+, O2+, Ti+, and TiO+. Ion energy and sputtering geometry, i.e., the combination of an ion incidence angle and an emission angle, were found to have a strong influence on the energy distribution of the secondary ions.

Secondary particle properties for the ion beam sputtering of TiO2 in a reactive oxygen atmosphere

This work deals with the properties of secondary particles, i.e., sputtered target and scattered primary particles, for the ion beam sputtering of TiO2 in a reactive oxygen atmosphere. The angular and energy distributions in dependence on ion beam parameters (ion energy, ion species, or ion mass) and geometrical parameters (ion incidence angle, polar emission angle, or scattering angle) were investigated. The angular distributions of sputtered Ti particles were determined by the collection method, i.e., by growing TiO2 thin films and measuring the thickness, composition, and mass density. The distributions can be described by the superposition of an isotropic and an anisotropic part. The anisotropic part relative to the isotropic part gets more pronounced with decreasing ion energy, increasing ion incidence angle or changing the process gas from Ar to Xe. An energy-selective mass spectrometer was used to measure mass and energy distributions of secondary ions. The most prevalent species were identified to be O+, O2+, Ti+, TiO+, Ar+, and Xe+ ions. The energy distributions of Ti+ and TiO+ ions show a low-energy maximum between 10 eV and 30 eV, followed by an exponential decay. When decreasing the scattering angle, the high-energy tail extends to higher energies. O+, O2+, Ar+, and Xe+ ions show a low-energy maximum between 5 eV and 20 eV, which is followed by a sudden signal drop for scattering angles larger than 90°. For scattering angles smaller than 90°, additional peak(s) at higher energy appear, which are assigned to direct scattering and/or direct sputtering events. The experimental results are compared to calculations based on elastic collision theory and to simulations done with the Monte Carlo code SDTrimSP. The results are also discussed in relation to secondary particle properties for the reactive ion beam sputtering of Ti and to properties of TiO2 thin films grown by reactive ion beam sputter deposition with the same setup and the same parameters. Among others, it was found that sputtering of the TiO2 target exhibits less anisotropy contributions than sputtering of the Ti target.

Reactive ion beam sputtering of Ti: Influence of process parameters on angular and energy distribution of sputtered and backscattered particles

This work focuses on the angular and energy distribution of secondary particles during the ion beam sputtering of a Ti target in a reactive oxygen atmosphere. The influence of ion species, ion energy, and scattering geometry (ion incidence angle and polar emission angle) was investigated systematically. Ion energies of 0.5, 1.0, and 1.5 keV and an ion current of roughly 10 mA were used to sputter deposit TiO2 films from a pure Ti target at an operating pressure of 5.0 × 10−5 and 6.5 × 10−5 mbar and an oxygen partial pressure of 1.0 × 10−5 and 2.5 × 10−5 mbar for sputtering with Ar and Xe ions, respectively. The angular distribution of the flux of sputtered Ti particles was determined by measuring the thickness of TiO2 films. The flux of sputtered Ti particles is described by the superposition of an isotropic and anisotropic part. The isotropic part increases when increasing ion energy, decreasing the incidence angle, or changing the sputtering gas from Xe to Ar. An energy-selective mass spectrometer was used to measure the mass and energy distribution of secondary ions. Several species of sputtered particles were detected, e.g., Ti, TiO, TiO2, Ti2, O, and O2 ions. The most prevalent species are Ti, TiO, and O ions. The energy distribution of the sputtered Ti and TiO ions shows a maximum at an energy between 10 and 30 eV followed by a high-energetic tail proportional to exp(−n·E). Decreasing the scattering angle leads to a decrease in the slope of the high-energetic tail, i.e., it extends to higher energies. The backscattered primary ions (Ar and Xe) and the sputtered atomic O ions show a maximum between 5 and 20 eV, which is followed by a sudden signal drop. For scattering angles less than 90°, additional peaks at higher energy can appear in the energy distribution of Ar, Xe, and O ions. These peaks are related to direct scattering and sputtering events. The experimental results are compared with calculations based on a simple elastic two-particle-interaction theory and with simulations carried out using the Monte Carlo code SDTrimSP.

Advanced Electric Propulsion Diagnostic Tools at IOM

Recently, we have set up an Advanced Electric Propulsion Diagnostic (AEPD) platform [1], which allows for the in-situ measurement of a comprehensive set of thruster performance parameters. The platform utilizes a five-axis-movement system for precise positioning of the thruster with respect to the diagnostic heads. In the first setup (AEPD1) an energy-selective mass spectrometer (ESMS) and a miniaturized Faraday probe for ion beam characterization, a telemicroscope and a triangular laser head for measuring the erosion of mechanical parts, and a pyrometer for surface temperature measurements were integrated. The capabilities of the AEPD1 platform were demonstrated with two electric propulsion thrusters, a gridded ion thruster RIT 22 (Airbus Defence & Space, Germany, [13]) and a Hall effect thruster SPT 100D EM1 (EDB Fakel, Russia, [1,4]), in two different vacuum facilities.

Ion beam sputtering of Ti: Influence of process parameters on angular and energy distribution of sputtered and backscattered particles

In the present study, the influence of ion energy and geometrical parameters onto the angular and energy distribution of secondary particles for sputtering a Ti target with Ar ions is investigated. The angular distribution of the particle flux of the sputtered Ti atoms was determined by the collection method, i.e. by growing Ti films and measuring their thickness. The formal description of the particle flux can be realized by dividing it into an isotropic and an anisotropic part. The experimental data show that increasing the ion energy or decreasing the ion incidence angle lead to an increase of the isotropic part, which is in good agreement with basic sputtering theory. The energy distribution of the secondary ions was measured using an energy-selective mass spectrometer. The energy distribution of the sputtered target ions shows a maximum at an energy between 10eV and 20eV followed by a decay proportional to E−n, which is in principle in accordance with Thompson’s theory, followed by a high energetic tail. When the sum of incidence angle and emission angle is increased, the high-energetic tail expands to higher energies and an additional peak due to direct sputtering events may occur. In the case of backscattered primary Ar ions, a maximum at an energy between 5eV and 10eV appears and, depending on the scattering geometry, an additional broad peak at a higher energy due to direct scattering events is observed. The center energy of the additional structure shifts systematically to higher energies with decreasing scattering angle or increasing ion energy. The experimental results are compared to calculations based on simple elastic two-particle-interaction theory and to simulations done with the Monte Carlo code SDTrimSP. Both confirm in principle the experimental findings.

Ion beam sputtering of germanium – Energy and angular distribution of sputtered and scattered particles

The energy and angular distributions of scattered and sputtered particles produced by ion beam sputtering of a Ge target under variation of geometrical (incidence angle of primary ions and emission angle of secondary particles) and ion parameters (ion species (Ar, Xe) and energy (0.5–1.5keV) are presented.Several sets of Ge thin films are deposited and their thickness is measured by profilometry to determine the angular particle flux distribution of the sputtered particles. The particle flux distributions are of cosine-like shape and tilted in forward direction and the tilt of the maximum position increases with decreasing energy of the primary ions and increasing incidence angle.The energy distributions of the sputtered and the scattered ions are measured with an energy-selective mass spectrometer. The average energy of the sputtered ions increases with increasing incidence angle of the primary ions and with increasing emission angle, but is nearly unaffected by the species of the primary ions and their energy. The energy distribution of the scattered Ar ions reveals high energetic maxima that originate in direct scattering between Ar/Ge and Ar/Ar and which shift with increasing emission angle to higher energies. For Xe ion bombardment, there are only maxima for Xe/Xe scattering observed.All experimental data are compared with Monte Carlo simulations done with the well-known TRIM.SP code.

Ion beam sputtering of Ag – Angular and energetic distributions of sputtered and scattered particles

Ion beam sputter deposition (IBD) provides intrinsic features which influence the properties of the growing film, because ion properties and geometrical process conditions generate different energy and spatial distribution of the sputtered and scattered particles. A vacuum deposition chamber is set up to measure the energy and spatial distribution of secondary particles produced by ion beam sputtering of different target materials under variation of geometrical parameters (incidence angle of primary ions and emission angle of secondary particles) and of primary ion beam parameters (ion species and energies).A representative set of Ag thin films is deposited arranged on a substrate holder equatorial to the Ag target in steps of 10° and characterized concerning their film thickness by profilometry to determine the angular distribution of the sputtered particles. The film thickness distributions show a tilted, cosine-like shape and a shifting of the maximum position depending on the primary particle energy and incidence angle of the primary ions.The energy distributions of sputtered and scattered ions and of sputtered neutrals are measured with an energy-selective mass spectrometer. The average energy of the sputtered ions increases with increasing emission angle and also increases with increasing incidence angle of the primary ions. In contrast, the average energy of the sputtered ions is nearly unaffected by the primary particle energy and particle species. The energy distribution of the scattered Ar ions reveals high energetic maxima which shift with increasing emission angle to higher energies. These maxima are not observed for Xe bombardment. The total energies of sputtered and scattered ions show significant differences between the two bombarding species. The maximum of the energy distribution of sputtered Ag neutrals is used to conclude on the surface binding energy of Ag (2.72eV).All experimental data are compared with Monte Carlo simulations done with the well-known TRIM.SP.

Systematic investigations of low energy Ar ion beam sputtering of Si and Ag

Ion beam sputter deposition (IBD) delivers some intrinsic features influencing the growing film properties, because ion properties and geometrical process conditions generate different energy and spatial distributions of the sputtered and scattered particles. Even though IBD has been used for decades, the full capabilities are not investigated systematically and specifically used yet. Therefore, a systematic and comprehensive analysis of the correlation between the properties of the ion beam, the generated secondary particles and backscattered ions and the deposited films needs to be done.A vacuum deposition chamber has been set up which allows ion beam sputtering of different targets under variation of geometrical parameters (ion incidence angle, position of substrates and analytics in respect to the target) and of ion beam parameters (ion species, ion energy) to perform a systematic and comprehensive analysis of the correlation between the properties of the ion beam, the properties of the sputtered and scattered particles, and the properties of the deposited films. A set of samples was prepared and characterized with respect to selected film properties, such as thickness and surface topography. The experiments indicate a systematic influence of the deposition parameters on the film properties as hypothesized before. Because of this influence, the energy distribution of secondary particles was measured using an energy-selective mass spectrometer. Among others, experiments revealed a high-energetic maximum for backscattered primary ions, which shifts with increasing emission angle to higher energies. Experimental data are compared with Monte Carlo simulations done with the well-known Transport and Range of Ions in Matter, Sputtering version (TRIM.SP) code [J.P. Biersack, W. Eckstein, Appl. Phys. A: Mater. Sci. Process. 34 (1984) 73]. The thicknesses of the films are in good agreement with those calculated from simulated particle fluxes. For the positions of the high-energetic maxima in the energy distribution of the backscattered primary ions, a deviation between simulated and measured data was found, most likely originating in a higher energy loss under experimental conditions than considered in the simulation.

Note: An advanced in situ diagnostic system for characterization of electric propulsion thrusters and ion beam sources

We present an advanced diagnostic system for in situ characterization of electric propulsion thrusters and ion beam sources. The system uses a high-precision five-axis positioning system with a modular setup and the following diagnostic tools: a telemicroscopy head for optical imaging, a triangular laser head for surface profile scanning, a pyrometer for temperature scanning, a Faraday probe for current density mapping, and an energy-selective mass spectrometer for beam characterization (energy and mass distribution, composition). The capabilities of our diagnostic system are demonstrated with a Hall effect thruster SPT-100D EM1.

Wall effects on the chemistry in a pulsed oxygen/silane radiofrequency helicon plasma

A pulsed oxygen/silane radiofrequency (13.56 MHz) plasma is created in a helicon diffusion reactor used for silicon dioxide deposition. An energy selective mass spectrometer is used to measure the time-averaged ion energy distribution function of the four predominant positive ions (H3+, H3O+, SiH3+, and SiOH+) and the positive ion mass spectra during the breakdown phase and the steady-state phase of the pulse. Charging of the silica-covered chamber wall by ∼55 V is observed both for continuous and pulsed excitations. All positive ions with mass greater than 62 (as well as H2O+ and SiOH+) are mostly detected during the plasma breakdown phase. This could result from some physical sputtering of the chamber walls at the beginning of each pulse (when the plasma potential and the ion bombardment energy reach their maximum) or from an increase in the density of heavy radicals during the post-discharge (as a result of the electron density and temperature decrease) which can be ionized during plasma breakdown of the oncoming pulse. During the plasma breakdown an ion bombardment energy of ∼70 V is measured which is larger than the physical sputtering threshold (25 V) of thermally grown SiO2 (P-etch ∼2 Å s−1) in an oxygen plasma. Consequently, for inadequate pulsing conditions, physical sputtering of the soft and porous suboxides (P-etch >30 Å s−1) deposited on the chamber sidewalls will occur, thereby allowing hydrogen-rich radicals and positive ions to reenter the plasma chemistry.

Analysis of relevant plasma parameters for ZnO:Al film deposition based on data from reactive and non-reactive DC magnetron sputtering

ZnO:Al (ZAO) films were prepared by reactive DC/DC dual magnetron sputtering from metallic Zn:Al targets and by non-reactive DC magnetron sputtering from ceramic ZnO:Al 2O 3 targets. The origin of the high resistivity shown by the films at the substrate position facing the erosion area of the target was investigated. By comparison of both sputter modes it could be shown that a nonuniformity in oxygen distribution cannot be its reason. Ion energy distributions measured with an energy selective mass spectrometer system revealed that differences in particle bombardement energies are mainly responsible for the spatial distribution of ZAO film properties. Significant variations in plasma composition between both sputter modes were found: reactive DC sputtering from metallic targets requires at least one order of magnitude more oxygen to produce ZAO films with equally high transmittance and low resistivity. This could be the reason for the differences in the spatial distributions of ZAO film properties DC sputter deposited from ceramic and metallic targets.

Plasma diagnostic of an RF magnetron Ar/N 2 discharge

Physical vapor deposition (PVD) processes are nowadays common in synthesis of hard coatings like cubic boron nitride (cBN). Precise knowledge of plasma characteristics (ion flux, ion energy distribution and plasma composition) is crucial for understanding and controlling cBN thin film growth. This work is devoted to the characterization of an unbalanced RF magnetron Ar/N 2 discharge using a Langmuir probe and an energy selective mass spectrometer. RF power and total pressure were varied from 50 to 300 W and from 0.1 to 0.5 Pa, respectively, for different Ar/N 2 mixtures. Main ionic species are found to be Ar + and N 2 + with a very low fraction of N +. The ion density increases with RF power, pressure and Ar content. The ion energy distribution consists of one single narrow peak with full-width at half-maximum of a few eV. The main neutral species are Ar and N 2. Atomic nitrogen could not be detected by mass spectrometry, indicating a low fraction of this species in the discharge.

Effects of cross field diffusion in a low pressure high density oxygen/silane plasma

A low pressure high density oxygen/silane radio frequency (13.56 MHz) plasma coupled in a helicon reactor used for silicon dioxide deposition is characterized by using an energy selective mass spectrometer situated at the wall of the processing chamber: measurements of positive and negative ion energy distribution functions and mass spectra (1⩽amu⩽150) are obtained for various flow-rate ratios (R=O2/SiH4=1 to 10 but constant total flow rate of 30 sccm), and for a constant radio frequency power and magnetic field of 800 W and 70 G, respectively. Plasma potentials between 35 (R=10) and 60 V (R=1) are measured depending on the silane and oxygen flows showing charging of the silica-covered diffusion chamber wall. The magnitude of the wall charging most likely depends on the effective capacitance formed by the silica layer (which results from months of deposition) and on the inbalance between the positively and negatively charged particles which impinge onto the sidewalls at the discharge initiation until equilibrium of fluxes is reached. This inbalance is a result of the magnetic field configuration generated by the four coils surrounding the reactor and of the subsequent cross-field diffusion of the positively and negatively charged particles to the sidewalls. Maximum wall charging is observed when the silane flow is maximum (R<2), a situation where polymerization is observed in the mass spectrum of the positive ions, and where a minimum density of negative ions (O−, OH−, and H−) are detected close to the walls. Although the polymerization appeared to be a primary candidate for the increase of the plasma potential to ∼60 V, its presence does not significantly change the total positive ion density at equilibrium but is accompanied by a dramatic decrease (two orders of magnitude for the O− ions) in the negative ion density close to the walls when R is increased from 1 to 10. The change in the degree of electronegativity close to the walls affects the global plasma equilibrium and appears as an indirect factor in the magnitude of the wall charging.

Characterisation of an industrial plasma immersion ion implantation reactor with a Langmuir probe and an energy-selective mass spectrometer

Characterisation of an industrial plasma-immersion ion implantation (PIII) reactor developed by the French company Ion Beam Services (IBS) and our laboratory is presented. Nitrogen (N 2) and boron trifluoride (BF 3) plasmas were studied with a Langmuir probe and an energy-selective mass spectrometer. Plasma density between 10 7 and 10 10 cm −3 is obtained in the reactor thanks to an inductively coupled plasma (ICP) source. The measurements have shown that N 2 + (BF 2 +) was the most abundant ion in N 2 (BF 3) plasmas (>80%). The injected power has a great influence on the chemical composition of the plasma: the higher the power, the higher the density is, which induces greater decomposition of the gas molecules. The same effect is observed when the gas pressure increases, but in lower proportions. A time-resolved analysis of pulsed N 2 plasmas is also presented, which shows similar temporal evolution for N + and N 2 + ions. Energetic ions (>40 eV) have been detected at the beginning of the pulse due to energetic electrons, which induce a high plasma potential in the first μs of the discharge.

Ion energy distribution functions and Langmuir probe measurements in low pressure argon discharges

Using an energy selective mass spectrometer, ion energy distribution functions (IEDFs) in a low pressure radio frequency (rf) argon discharge have been measured. This experiment has been done in the diffusion chamber of a helicon source. Two kinds of IEDF have been observed depending on the gas pressure: classical “one-peak” spectra at high pressure (>1 μbar) and “two-peak” spectra at low pressure (<1 μbar). These results have been correlated with the plasma potential and density profiles along the axis of the reactor obtained with a Langmuir probe and the IEDF have been fitted using a simple analytical model. In this way, noncollisional diffusion of energetic ions from the source chamber to the diffusion chamber has been shown.

Nitrogen incorporation and loss during ion nitriding of Al

Ion nitriding of Al has been performed by a nitrogen reactive ion beam using a hot filament ion source. The N incorporation and loss has been determined at a beam energy of 1.6 keV with two ion current densities of 0.1 and 0.2 mA/cm 2, and a substrate temperature of 350 °C. For this purpose, the ion beam has been characterised by an energy selective mass spectrometer, showing solely of N 2 + and N + ions with a composition of about 80% and 20%, respectively. The ion energy distributions of both N 2 + and N + consist of a single narrow peak with a full width at half maximum of about 10 eV. From the beam parameters, N loss due to sputtering and backscattering has been calculated using dynamic binary collision computer simulations. After an initial transient, the stationary partial sputtering yield of N is predicted to be 0.43, while the amount of backscattered N is about 4% of the incident N fluence. The total amount of incorporated N measured by nuclear reaction analysis (NRA) is consistent with the incident N fluence and the N loss obtained from the simulation.

Ion energy distributions in a pulsed, electron beam-generated plasma

In this work, we investigate the ion flux at a grounded electrode located adjacent to a pulsed, argon plasma generated by a high-energy electron beam. The plasmas, produced in 100 mTorr, are characterized by high plasma densities (&amp;gt;1011 cm−3) and low electron temperatures (&amp;lt;1.5 eV). An energy selective mass spectrometer was used to measure temporally resolved ion kinetic-energy distributions at the electrode surface. In addition, ion energy distributions are presented for various electrode locations. The ion energy distributions correlate well with Langmuir probe measurements of the plasma potential.