Function Of Ion Mass Research Articles

Impact of ion species on ion beam sputtered Ta2O5 layer quality parameters and on corresponding process productivity: A preinvestigation for large-area coatings

The demand for ion beam sputtering-coated substrates is growing. In order to introduce ion beam sputter deposition (IBSD) technology into new fields of application, the deposition area must be further increased. In this context, the ion species applied for the sputtering process is an important parameter. In the present investigation, an industrial scale IBSD process was characterized with respect to productivity and layer quality by varying the ion species. Ar, Kr, or Xe broad ion beams at an ion energy of 1.8 keV were used, and the evaluation was carried out on the basis of Ta2O5 layers. The dielectric films were produced in a reactive process through the sputtering of a metallic Ta target, and their two-dimensional distributions of the coating rate R, the refractive index n(320nm), and the extinction coefficient k(320nm) were determined over a planar area of 0.9 × 1.0 m2 above the target by the collection method. R served as a measure of productivity, while n(320nm) and k(320nm) were quality parameters. Additionally, the layer composition was determined for selected samples on the collector by an electron probe microanalyzer (EPMA). As expected, the different ion-solid interaction mechanisms resulted in significant differences with regard to productivity. Linear scaling of productivity as a function of ion mass was observed. Calculations of the sputtering yield with semiempirical models or SRIM-2013, a binary collision Monte Carlo simulation program, did not confirm the observed linearity. Furthermore, the configuration with the highest productivity, Xe, led to a locally occurring and significant reduction in layer quality, more precisely, an increase of k(320nm). Additionally, the layer compositions determined with EPMA confirmed that ions originating from the ion source were implanted in the thin films during their formation. A detailed evaluation of the angle-resolved energy distributions of the involved particles, simulated with SRIM-2013, was performed. However, the determination of the energies carried away from the target by backscattered ions and sputtered target atoms does not explain the observed degradation mechanism. This concludes that for the realization of future large-area coatings with IBSD, not all relevant mechanisms are yet understood in sufficient detail.

Rotation and instabilities for isotope and mass separation

Rotating plasmas have the potential to offer unique capabilities for isotope and mass separation. Among the various electric and magnetic field configurations offering mass separation capabilities, rotating plasmas produced through static or oscillating fields are shown to be a leading candidate for tackling the unsolved problem of large-scale plasma separation. The successful development and deployment of industrial-scale plasma separation technologies could, among many other applications, provide an innovative path towards advanced sustainable nuclear energy. In this context, the potential and versatility of plasma rotation induced by rotating magnetic fields is uncovered and analysed. Analytical stability diagrams are derived from rotating ion orbits as a function of ion mass. Based on these findings, the basic principles of a rotating field plasma separator are then introduced. In light of these results, challenges associated with this original separation process are underlined, and the main directions for a future research program aimed at this important unsolved problem of applied plasma physics are identified.

Production of amorphous zones in GaAs by the direct impact of energetic heavy ions

The damage produced in GaAs by implantation with low energy heavy ions has been studied as a function of ion mass and implantation temperature (30 and 300 K). The experiments were performed in situ in the microscope-accelerator facility at Argonne National Laboratory. In samples implanted and examined at 30 K, spatially isolated amorphous regions were produced by the direct impact of 50 keV Ar, Kr, and Xe ions. The probability that the impact of an individual ion formed an amorphous zone increased as the ion mass increased from Ar to Kr but not from Kr to Xe. The average dimension of the amorphous zones also increased with ion mass, being greater for the Xe than for the Kr ion implantation. On warming to room temperature, the amorphous zones decreased in size and density as the sample temperature was increased above 200 K. In samples implanted and examined at 300 K, the probability of forming an amorphous zone by direct impact increased as the ion mass increased from Kr to Xe, although the probability was always less than at 30 K. The density of amorphous zones produced at 300 K was similar to that remaining in a sample implanted at 30 K and then warmed to room temperature. With time at 300 K the amorphous zones decreased in size and eventually crystallized completely, leaving no trace of their prior existence.

Mechanism of high density plasma processes for ion-driven etching of materials

We propose a mechanism for ion-driven etching of materials in a high density plasma (>10 11 cm −3) system. An inductively coupled plasma (ICP) reactor was used to model the etch mechanism. Ion density and plasma potential were measured with a Langmuir probe and the self-induced dc bias simultaneously recorded. Power density (i.e. ion flux times ion energy) was found to be the most influential factor for predicting the etch rate of ion-driven materials, like dielectrics and III-nitrides, especially when running in a high density plasma (HDP) mode. Power density is also shown to be a function of ion mass, ion density, ion charge, dc bias and plasma potential. The relation between these plasma parameters and power density can be correlated with process parameters such as ICP source power, rf chuck power, chamber pressure and gas flow rate. This correlation was modeled with the aid of a design of experiment (DOE) simulation. We have demonstrated the use of a power density model to explain the mechanism responsible for HDP etching of SiO 2, which is one example of a high-bond strength material.

Generation of vacancy-type point defects in single collision cascades during swift-ion bombardment of silicon

Silicon samples of n-type have been implanted with low doses (${10}^{7}$-${10}^{10}$${\mathrm{ncm}}^{\mathrm{\ensuremath{-}}2}$) of $^{11}\mathrm{B}$, $^{12}\mathrm{C}$, $^{16}\mathrm{O}$, $^{28}\mathrm{Si}$, $^{74,76}\mathrm{Ge}$, and $^{120}\mathrm{Sn}$ ions using energies between 0.4 and 8.0 MeV. Because of the low doses employed, single-collision cascades prevail, and an analysis of the implanted samples by deep-level transient spectroscopy (DLTS) reveals two dominant point defects of vacancy type, the divacancy (${\mathrm{V}}_{2}$) and the vacancy-oxygen (VO) center. The generation of ${\mathrm{V}}_{2}$ and VO is studied in detail as a function of ion mass, dose, dose rate, sample depth, and sample temperature. Surface-enhanced annihilation of migrating defects is found to play a significant role in depleting the concentration of ${\mathrm{V}}_{2}$ and VO centers in proximity to the surface. The concentration of ${\mathrm{V}}_{2}$ and VO increases linearly with ion dose, but the generation efficiency per incoming ion decreases at high dose rates after displaying a constant value below \ensuremath{\sim}${10}^{8}$${\mathrm{ncm}}^{\mathrm{\ensuremath{-}}2}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. This dose rate effect exhibits a dependence on ion mass, and is qualitatively predicted by computer simulations of the defect reaction kinetics, applying a model where the interaction between individual collision cascades is primarily due to fast-diffusing Si self-interstitials. At dose rates \ensuremath{\leqslant}${10}^{8}$${\mathrm{ncm}}^{\mathrm{\ensuremath{-}}2}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, the generation of ${\mathrm{V}}_{2}$ centers per ion-induced vacancy in the damage peak region is identical, within \ifmmode\pm\else\textpm\fi{}10%, for all the different types of ions studied. However, the ${\mathrm{V}}_{2}$ centers formed by heavy ions are strongly perturbed, as shown by large deviations from a one-to-one relation between the two DLTS peaks associated with the singly and doubly negative charge state of ${\mathrm{V}}_{2}$, and also by a broadening of the two peaks. In contrast to that for ${\mathrm{V}}_{2}$, the generation of VO centers per ion-induced vacancy decreases with increasing ion mass, consistent with the picture that light ions are more effective in generating point defects than heavy ions. At elevated implantation temperatures, gradual relaxation of lattice strain occurs together with recrystallization of disordered zones, promoting the formation of unperturbed ${\mathrm{V}}_{2}$ centers and increasing the generation efficiency of VO centers.

Amorphization of silicon by elevated temperature ion irradiation

Despite extensive study into the amorphization of silicon by ion irradiation, a detailed understanding of the mechanisms associated with the process is still not available. This is especially true in the case of elevated temperature irradiations where increased levels of dynamic annealing can balance defect production. By controlling the irradiating ion flux (defect production rate), the temperature at which an amorphous layer first appears has been determined for a specific fluence of ions, ranging in mass from 12 (C) to 132 amu (Xe), over a matrix of two orders of magnitude in ion flux and 320°C in temperature. The apparent activation energies determined from the data span from 0.7 to 1.7 eV and increase as a function of ion mass and, consequently, temperature. Previously interpreted as representing processes controlling the crystalline-to-amorphous phase transition, these values are discussed in terms of a two-stage nucleation-limited amorphization process. Results are presented which indicate, that, in the regime where dynamic defect annealing is significant, the amorphization process is initially limited by the availability of nucleation sites, supplied by stable extended defect structures produced by defect accumulation and, subsequently, by the supply of simple defects to these sites.

Linear time-of-flight mass spectrometers: Postsource pulse focusing conditions and mass scale

The condition to cancel aberrations that result from initial ion velocities and length of ionization process by postsource pulse focusing in linear time-of-flight mass spectrometers is derived. The ion arrival time distribution as a function of ion mass is given, which permits mass scale calibration. Simple formulas allow calculation of the voltage needed for postsource pulse focusing and the limits of the mass range where the focusing action is felt. The theory is illustrated for a specific instrument case.

Secondary electron resolved mass spectrometry of electrosprayed ions

An important process in mass spectrometric techniques is the registration of analyte ions at appropriate detector surfaces. Although the nature of the ion—surface interaction can introduce bias in the detection process, such biases can also be exploited to yield complementary information about the detected ions. In this paper, results are presented on the secondary electron yield from impacts of electrosprayed macro-molecular ions on an Al 2O 3 surface. The secondary electron yield is parametrized as a function of ion mass and velocity. This information is used to acquire mass information (in contrast to the mass-to-charge ratio information gained in quadrupoles and magnetic sector instruments) from the secondary electron yield measured in the detection part of a mass spectrometer. The primary ions are filtered in a scanning mass-to-charge-ratio filter at the same time as mass information from the secondary electron yield is collected. With this method, peaks caused by certain molecules present at low concentrations can be enhanced, and discrimination against low mass “noise” can be achieved. Also, peaks with the same mass-to-charge ratio but distinctly different masses can be separately identified. Several practical applications are demonstrated, and evidence for gas-phase fragmentation of large poly(ethylene glycols) is presented.

Influence of energy reflected from the target on thin film characteristics

It has been recognized since the 1960’s that bombardment of a growing thin film by energetic particles strongly influences film properties. Particle bombardment has generally been accomplished by accelerating ions into the growing film. However, it has also been recognized since the 1960’s that energetic neutral particles originating at the target also bombard films grown by physical sputtering. It has been frequently suggested that the properties of sputtered films are influenced by bombardment with particles from this source. Nevertheless, a lack of the necessary information has made it difficult to make quantitative (or even semiquantitative) estimates of the magnitude of the energy deposited into the film. A systematic study of the energy reflected from the surface by normally incident, singly charged noble-gas ions on five substrates of different masses has recently been published. These data along with sputter yields from the literature allow estimates to be made which were previously unavailable. The energy reflected from the target is carried away by electrons, sputtered particles, and reflected ions (neutrals). The purpose of this article is to provide basic information which will allow thin film scientists to estimate the influence of various experimental parameters on the amount of energy arriving at the growing film. The energy reflected from the target per sputtered atom will be given as a function of ion mass, target mass, and ion energy. trim.sp Monte Carlo calculations will be used to estimate the ratio of the energy carried away by sputtered atoms to that carried away be reflected ions. Calculations will also be used to estimate the average energy of the sputtered atoms as a function of ion mass, substrate mass, and ion energy. It will be shown how data presented in this article can be used to make estimates for other elements in the periodic table. It will also be shown how this information can be used to guide the adjustment of experimental parameters in sputtering environments so as to control film characteristics.

The role of the ion-solid interaction in ion-beam-induced deposition of gold

Gold films were deposited on quartz-crystal microbalances by decomposing C7H7F6O2Au (dimethyl gold hexafluoroacetylacetonate) with 2–10-keV Xe+, Kr+, Ar+, Ne+, or He+ ion beams. The number of molecules decomposed per incident ion (i.e., the total decomposition yield) was determined as a function of ion mass and energy. The total decomposition yield increases with increasing ion mass and ion energy, and is approximately proportional to the nuclear stopping power. A binary collision model and a thermal spike model are developed that relate the energy deposited by the ion, at the substrate surface, to the total number of molecules decomposed. Both models predict total decomposition yields that are in reasonable agreement with the experimental measurements; however, the variation of total yield with changes in ion mass and energy are best described by the binary collision model. The success of both models demonstrates that the energy deposited into the substrate surface through the ion-solid interaction is responsible for the decomposition of adsorbed molecules.

Ion Beam Induced Damage in Epitaxial TiN Films

Thin epitaxial TiN films have been deposited on MgO(100) substrate by ion plating technique. Both RHEED and XRD analysis indicate crystalline quality of the film. Ion channeling measurements show that the epitaxial TiN films have comparable minimum yield to that of the substrate. The damage produced in the film and the substrate lattice due to ion implantation have been investigated by the measurement of the increase in χ min in the aligned spectrum. The presence of a sharp interface in the RBS and AES spectrum confirmed the absence of any ion induced mixing. The measured minimum yield from RBS-C analysis for 500 keV and 2 MeV Si+, Kr+ and Au+ implanted epitaxial TiN films indicate that the disorder is dependent on damage efficiency which is a function of ion mass and energy.

Influence of Energy Deposited by Energetic Particle Bombardment on thin Film Characteristics

AbstractIt has been recognized since the 1960's that bombardment of a growing thin film by energetic particles strongly influences film properties. Particle bombardment has generally been accomplished by accelerating ions into the growing film. However, it has also been recognized since the 1960's that energetic particles reflected from the target influence the characteristics of films grown by physical sputtering and many experiments have been interpreted on this basis. A systematic study of the energy reflected from the surface by normally incident, singly charged noble-gas ions on five substrates of different masses has recently been published. This data along with sputter yields from the literature allow estimates to be made which were previously unavailable. The energy reflected from the target is carried away by electrons, sputtered particles and reflected ions (neutrals). The purpose of this paper is to provide basic information which will allow thin film scientists to estimate the influence of various experimental parameters on the amount of energy arriving at the growing film. The energy reflected from the target per sputtered atom will be given as a function of ion mass, target mass, and ion energy. TRIM.SP Monte Carlo calculations will be used to estimate the ratio of the energy carried away by sputtered atoms to that carried away by reflected ions. Calculations will also be used to estimate the average energy of the sputtered atoms as a function of ion mass, substrate mass and ion energy. It will be shown how this information can be used to guide the adjustment of experimental parameters in sputtering environments so as to control film characteristics.

Influence of Energy Deposited by Energetic Particle Bombardment on Thin Film Characteristics

ABSTRACTIt has been recognized since the 1960's that bombardment of a growing thin film by energetic particles strongly influences film properties. Particle bombardment has generally been accomplished by accelerating ions into the growing film. However, it has also been recognized since the 1960's that energetic particles reflected from the target influence the characteristics of films grown by physical sputtering and many experiments have been interpreted on this basis. A systematic study of the energy reflected from the surface by normally incident, singly charged noble-gas ions on five substrates of different masses has recently been published. This data along with sputter yields from the literature allow estimates to be made which were previously unavailable. The energy reflected from the target is carried away by electrons, sputtered particles and reflected ions (neutrals). The purpose of this paper is to provide basic information which will allow thin film scientists to estimate the influence of various experimental parameters on the amount of energy arriving at the growing film. The energy reflected from the target per sputtered atom will be given as a function of ion mass, target mass, and ion energy. TRIM.SP Monte Carlo calculations will be used to estimate the ratio of the energy carried away by sputtered atoms to that carried away by reflected ions. Calculations will also be used to estimate the average energy of the sputtered atoms as a function of ion mass, substrate mass and ion energy. It will be shown how this information can be used to guide the adjustment of experimental parameters in sputtering environments so as to control film characteristics.

Highly charged ECR ion sources: Summary and comments (invited)

A review is presented of the historical evolution of the ECR ion source and its application for the production of very highly charged ions. The status of our present understanding of the scaling laws for ion charge state and ion beam current as a function of ion mass, magnetic field strength, and the microwave frequency and power is summarized.

Resonance excitation of ions stored in a quadrupole ion trap. Part 1. A simulation study

Preliminary findings are presented of a simulation study of resonance excitation of gaseous ions stored within a quadrupole ion trap. The ion trap was operated in the common mode wherein a radio-frequency drive potential was applied to the ring electrode while the end-cap electrodes were grounded or held at a small potential. The arrangement chosen for computer simulation of resonance excitation discussed here is that in which an auxiliary potential is applied to both end-cap electrodes such that these electrode potentials are in phase with each other. The effects of resonance excitation are manifested in the following ways: temporal variation of ion kinetic energy; temporal variations of axial and radial displacements from the trap centre; direction of ion ejection; and emergence of new frequency components of ion motion. The extent of resonance excitation has been examined as a function of ion mass, trapping parameters a u and q u , ion initial position and velocity, drive and auxiliary potential phase angles, delayed imposition of auxiliary potential, auxiliary potential amplitude and frequency, and mass of an inert collision gas. Four principal findings are reported. Irradiation of trapped ions at the two fundamental secular frequencies, axial and radial, does not lead exclusively to ejection of ions in the axial and radial directions, respectively: there is clearly a degree of perturbation of ion radial motion upon irradiation at the axial fundamental secular frequency, and vice versa, which can become dominant under certain conditions and lead to a change in direction of ion ejection. Excitation at theoretically predicted secular frequencies other than the fundamental frequencies is virtually negligible, as expected from the magnitudes of the C 2 n coefficients. Strong resonance absorption occurs at a series of frequencies which are not present in the motion of the unexcited ions; these frequencies are designated as new frequencies. The motion of ions subjected to resonance excitation often becomes characterized by additional frequency components which we have designated as induced frequencies.

Partitioning of ion-induced surface and bulk displacements

An analytical method is described to determine the number and partitioning of displacements of surface and bulk atoms by low energy ions incident on a solid. Results are presented for Ge, Si and C (diamond and graphite). For Ge the results are compared with Monte Carlo calculations using the computer code TRIMRC. Good agreement is found in this comparison, thereby verifying the adequacy of several approximations introduced into the formalism. Displacement threshold and surface-to-bulk displacement ratio contours are presented as a function of ion mass and energy based on our analytic calculations. Comparison of these contours with recent experimental results for Si suggests that this approach provides a global framework for understanding and optimizing the effects of low-energy ions on semiconductor expitaxial growth.

Langmuir probe measurements of potential inside a supersonic jet extracted from an inductively coupled plasma

The potential is measured inside a supersonic jet to obtain fundamental information about the extraction process in inductively coupled plasma-mass spectrometry (ICP-MS). The potential in the jet is of positive polarity and varies with sampling position, plasma power, and aerosol gas flow rate in much the same way as both the potential outside in the plasma and the ion kinetic energy. The magnitude of the potential is comparable to the intercept of a plot of mean ion kinetic energy as a function of ion mass. The potential of the probe is affected by both the mass and the concentration of alkali metals in the sample solution, although it is not clear that these changes in potential are directly related to matrix interferences in ICP-MS. A high potential in the jet also tends to be noisy and would be detrimental to the stability of an ICP-MS device.

A critical comparison of reactive etching of materials in microelectronics, fusion and space technologies

Chemical and radiation-enhanced gas-solid etching of materials that are important in microelectronics, fusion and space technologies, are compared and reviewed. Existing evidence suggests that the basic processes that drive spontaneous etching of several etchant-material combinations may be similar: F/Si, H/Si and H/C can be cited as examples. On the other hand, many etchant-material systems appear to involve system-specific processes that should not be generalized: examples are the XeF 2/Si and Cl/Si systems. Experiments show that when chemical etching is the dominant phenomenon, energetic particle or photon bombardment generally enhances etching by thermalized neutral active species. In microelectronic materials etching, investigators have systematically studied etching product yield and product kinetic energy as a function of ion mass, ion energy and angle of incidence; data on temperature dependence of etching are more limited. By contrast, the temperature dependence of etching C and C-composites in fusion technology has been studied extensively, but there is a lack of data on ion mass and angle dependence, and on the kinetic energy of products. There appears to be no comparable data on ion-assisted etching of materials in typical space environments. These fundamental parameters are essential for formulating and testing models of ion-enhanced etching chemistry. The available data are discussed in terms of phenomenological models and calculations that have been developed. It is clear that further work will be required to provide a solid understanding of the phenomena discussed in this review.

Ion mobility influence on stimulated Raman scattering in homogeneous laser-irradiated plasma

1½ D computer simulations have been performed to illustrate the influence of ion dynamics on stimulated Raman scattering in laser irradiated plasmas. A flat density profile has been used. Backward and forward scatter and heated electron distribution have been studied as a function of ion mass and ion temperature. The results show clearly that the lighter the ions, the more inhibited the Raman scatter and associated fast electron production. Futhermore, when ions are cold enough to allow Brillouin scattering release, Raman scatter, as well as associated suprathermal electrons is even more reduced. These observations evidence the complex non-linear coupling of the electron plasma waves driven by the Raman instability and the ion fluctuations which can exist in the plasma.

Thomson spectrometer analysis of collectively accelerated ions

An intense relativistic electron beam (0.5 MeV, 30 kA, 60 ns) was used for the collective acceleration of ions from (1) a localized gas ion source and (2) a localized plasma ion source. The ion energy scaling as a function of ion mass and charge state was found by using a Thomson spectrometer. Peak ion energy depended very weakly on ion mass and was independent of ion charge state. Although the presence of the ion source was necessary for ion acceleration to occur, generally the ion source did not supply the bulk of accelerated ions as many impurity ions were present.