keV O2 Research Articles

Interaction of molecular oxygen ions with copper surface: features of the energy spectra of sputtered and backscattered ions

An experimental study on the energy spectra of ions emitted from the surface of a polycrystalline Cu target under the bombardment by 2 keV O2+ molecular ions was carried out. Sputtered atomic ions Cu+ and O+ were prevailed among the positively charged secondary ions, and among the negative ions, in addition to sputtered ions Cu-, CuO2-, O-, and O2-, intense elastically and inelastically backscattered O-, and O2+ ions were revealed. Keywords: energy spectra, ion sputtering, backscattered ions, charge exchange.

Взаимодействие молекулярных ионов кислорода с поверхностью меди: особенности энергетических спектров распыленных и обратнорассеянных ионов

An experimental study on the energy spectra of ions emitted from the surface of a polycrystalline Cu target under the bombardment by 2 keV O2+ molecular ions was carried out. Sputtered atomic ions Cu+ and O+ were prevailed among the positively charged secondary ions, and among the negative ions, in addition to sputtered ions Cu-, CuO2-, O-, and O2-, intense elastically and inelastically backscattered O- and O2+ ions were revealed.

ToF-SIMS Depth Profiling of Metal, Metal Oxide, and Alloy Multilayers in Atmospheres of H2, C2H2, CO, and O2.

The influence of the flooding gas during ToF-SIMS depth profiling was studied to reduce the matrix effect and improve the quality of the depth profiles. The profiles were measured on three multilayered samples prepared by PVD. They were composed of metal, metal oxide, and alloy layers. Dual-beam depth profiling was performed with 1 keV Cs+ and 1 keV O2+ sputter beams and analyzed with a Bi+ primary beam. The novelty of this work was the application of H2, C2H2, CO, and O2 atmospheres during SIMS depth profiling. Negative cluster secondary ions, formed from sputtered metals/metal oxides and the flooding gases, were analyzed. A systematic comparison and evaluation of the ToF-SIMS depth profiles were performed regarding the matrix effect, ionization probability, chemical sensitivity, sputtering rate, and depth resolution. We found that depth profiling in the C2H2, CO, and O2 atmospheres has some advantages over UHV depth profiling, but it still lacks some of the information needed for an unambiguous determination of multilayered structures. The ToF-SIMS depth profiles were significantly improved during H2 flooding in terms of matrix-effect reduction. The structures of all the samples were clearly resolved while measuring the intensity of the MnHm–, MnOm–, MnOmH–, and Mn– cluster secondary ions. A further decrease in the matrix effect was obtained by normalization of the measured signals. The use of H2 is proposed for the depth profiling of metal/metal oxide multilayers and alloys.

High Mass Resolution Multireflection Time-of-Flight Secondary Ion Mass Spectrometer.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is popular because of its advantages of parallel m/z detection and less damage for unknown or rare samples compared to sector field instruments. However, the mass resolving power of conventional TOF-SIMS is limited by its relatively large energy spread and primary ion pulse width. In this work, a high mass resolution multireflection time-of-flight secondary ion mass spectrometer (MR-TOF-SIMS) was designed and constructed. Compared with conventional TOF-SIMS, the ion flight path of the MR-TOF-SIMS was extended from meters to subkilometers, and the mass resolving power reached to 87000 after an 80 cycles flight. A pair of symmetrically arranged ion orthogonal injection/ejection deflectors, which could eliminate the influence of fringing field and remove ions with a large energy spread, were proposed to further improve the mass resolving power in fewer flight cycles. A zircon standard sample sputtered by a 10 keV O2- beam was used to demonstrate the performance of the MR-TOF-SIMS instrument. As a result, the mass resolving power was up to 30000 only after 22 flight cycles. The 92Zr+ peak was significantly separated from the mass interference peaks of 91ZrH+, 90ZrH2+, 13CC6H7+, and C7H8+. The mass accuracies of Zr ions and their hydrides were better than 1.2 ppm. An ion transmission efficiency over 40% was achieved after 115 cycles.

Evaluation of sputtering induced surface roughness development of Ni/Cu multilayers thin films by Time-of-Flight Secondary Ion Mass Spectrometry depth profiling with different energies O2+ ion bombardment

As a follow up on a previous paper on the quantitative evaluation of sputtering induced surface roughness and its influence on Auger electron spectroscopy depth profiling of polycrystalline Ni/Cu multilayers thin films, the ion sputtering induced surface roughness of these multilayered Ni/Cu polycrystalline thin films under low energy (0.5, 1.0 and 2.0 keV) O2+ ion bombardment and 1.0 keV Cs+ ion sputtering were investigated with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Atomic Force Microscopy (AFM). The lowest energy (0.5 keV) O2+ ion sputtering gave the best depth resolution for the different energy ion sputtering. Furthermore the 1.0 keV Cs+ ion sputtering led to a better resolution than the O2+ ion sputtering. The ToF-SIMS depth resolution was also better than the AES depth profiling with a 2.0 keV Ar+ ion sputtering. The Mixing-Roughness-Information depth (MRI) model used for fitting of the ToF-SIMS depth profiles accounts for the broadening upon experimental depth profiling owing to the effects of atomic mixing, surface roughness and information depth. The MRI fitted roughness parameters obtained from the ToF-SIMS depth profiling are in good agreement with the root-mean-square roughness obtained from the AFM topography scans of the crater bottom. Ion sputtering induced roughness and depth resolution during ToF-SIMS depth profiling of Ni/Cu multilayers were quantitatively evaluated according to the MRI fitting parameters.

An effect of measurement conditions on the depth resolution for low‐energy dual‐beam depth profiling using TOF‐SIMS

An effect of measurement conditions on the depth resolution was investigated for dual‐beam time of flight‐secondary ion mass spectrometry depth profiling of delta‐doped‐boron multi‐layers in silicon with a low‐energy sputter ion (200 eV – 2 keV O2+) and with a high‐energy primary ion (30 keV Bi+). The depth resolution was evaluated by the intensity ratio of the first peak and the subsequent valley in B+ depth profile for each measurement condition. In the case of sputtering with the low energy of 250 eV, the depth resolution was found to be affected by the damage with the high‐energy primary ion (Bi+) and was found to be correlated to the ratio of current density of sputter ion to primary ion. From the depth profiles of implanted Bi+ primary ion remaining at the analysis area, it was proposed that the influence of high‐energy primary ion to the depth resolution can be explained with a damage accumulation model. Copyright © 2013 John Wiley & Sons, Ltd.

Low energy ion beam smoothening of artificially synthesized single crystal diamond chips with initial surface roughness of 0.08–0.4 nm rms

High quality ultra- smooth single crystal diamond chips are used as molds for nano-imprints, mirrors for X-ray free-electron lasers, and so on. Conventional mechanical process using lap plate of fine diamond powder cannot be applied in thinning down of diamond materials to the order of 10μm. Therefore we applied ion beam machining for the smoothening of the surface of artificially synthesized single crystal diamond chips (100) with the initial surface roughness of 0.08–0.4nm rms. We found that by 1.0keV Ar+ ion beam at a normal angle of ion incidence, the processed surface became ultra-smooth with the surface roughness of 0.10nm rms and waviness of 0.12nm rms. However, the speed of processing by Ar+ ion beam was low. In order to increase the speed, 0.5keV O2+/O+ beam was applied for the smoothening of the diamond surface at normal incidence angle. In this method, we successfully obtained ultra-smooth surface with a surface roughness of 0.10nm rms at a much higher processing rate. We also observed that in ion beam machining, a rough surface becomes smooth and smooth surface becomes rough and both trends tend to saturate towards a roughness level at a particular dose. To understand this contrasting phenomenon, we conducted power spectral density (PSD) profile analysis of the un-processed and processed surfaces, and studied the roughening and smoothening mechanisms taking place on the diamond chip surface during its ion beam machining.

Multilayer thin-film coatings based on chromium nitride and aluminum nitride: Comparative depth profiling by secondary ion mass spectrometry and glow-discharge optical emission spectrometry

Round-robin characterization is reported on the sputter depth profiling of CrN/AlN multilayer thin-film coatings on nickel alloy by secondary ion mass spectrometry (SIMS) and glow-discharge optical emission spectrometry (GD-OES). It is demonstrated that a CAMECA SIMS 4550 Depth Profiler operated with 3 keV O2+ primary ions provides the best depth resolution and sensitivity. The key factor is sample rotation, which suppresses the negative influence of the surface topography (initial and ion-induced) on the depth profile characteristics.

Ultralow energy boron implants in silicon characterization by nonoxidizing secondary ion mass spectrometry analysis and soft x-ray grazing incidence x-ray fluorescence techniques

Boron ultralow energy (0.2–3 keV) high dose (1×1015 cm−2) implants in single crystalline Si (100) were characterized by secondary ion mass spectrometry using an ultralow energy (0.35–0.5 keV) O2+ ion primary beam and collecting positive secondary ions. In particular, the not fully oxidizing approaches (primary beam oblique incidence and ultrahigh vacuum analysis atmosphere) were investigated because they are expected to provide better accuracy on the profile shape, especially in the region between the surface and the native oxide/substrate interface. The main drawback represented by an early formation of roughness on the crater bottom has been overcome by combining the ion sputtering with the rotation of the sample during the analysis. The reduced formation of roughness ensures more stable sputtering conditions and a more stable erosion rate with a more accurate depth calibration. The measured dose values were then cross-checked comparing them with results of soft x-ray synchrotron radiation grazing incidence x-ray fluorescence.

Upper critical field and Raman spectra of MgB2 thin films irradiated with low energy oxygen ion

The structure, upper critical field, and Raman spectrum of epitaxial MgB2 thin films irradiated by 300 keV O2+ ions have been investigated. Lattice parameter c expands after irradiation. There is a significant increase in upper critical field in the moderately irradiated films, while the critical temperature is reduced slightly. The values of critical field at zero temperature exhibit a maximum for samples with a moderate irradiation level for the applied magnetic field both perpendicular and parallel to the film surface. The temperature dependence of the anisotropy parameter, which is defined as the ratio of the upper critical field with the field parallel to the film surface and perpendicular to the film surface, reveals that oxygen ion irradiation mainly affects the σ band at a low irradiation level. With increasing irradiation level, π band scattering is strongly enhanced, and finally both bands are in the dirty limit. A broad peak centered around 570 cm−1 is observed in the Raman spectrum of the unirradiated films, and the peak position has a visible redshift in the irradiated samples. In particular, high-frequency spectral structures appear and become dominant, while the E2g broad band diminishes gradually with increasing irradiation fluence. The results are discussed by considering the disorder-induced change in carrier scattering within and between the σ and π bands and a violation of the Raman selection rules due to oxygen ion irradiation.

Enhancement of critical current density and flux pinning in oxygen ion-irradiatedMgB2 thin films

The effects of 300 keV O2+ ion irradiation on the temperature and magnetic field dependence of the critical current density(JC) in highquality epitaxial MgB2 thin films have been studied. Upon irradiation, the critical temperatureTC drops gradually and ultimately to less than 2 K and the residual resistivity increases from about 1 to125 µΩ cm with increasing doses. At a moderate radiation level of1 × 1013 cm−2,JC isenhanced and its performance in magnetic fields is significantly improved over a certain range of fields appliedalong the c-axis. The scaling behavior of reduced pinning force with reduced field reveals that the fluxpinning mechanism evolves from grain-boundary-like pinning in the pristine and lightlyirradiated films, to point-like pinning in moderately irradiated films, and again tograin-boundary-like pinning in heavily irradiated films. It is then concluded that point-likepinning centers, which can be modified by the damage level, have been introduced afteroxygen ion irradiation.

Role of initial surface roughness on ion induced surface morphology

We report here the influence of initial surface roughness on the development of ion induced Si surface morphology. Surfaces of different initial roughness have been generated chemically and bombarded by 16.7keV O2+ ions at an oblique angle. It is observed that surface roughness enhances the initial perturbation, which aids to form the ion induced regular nanostructures at an ion fluence typically one to two orders of magnitude less than that are required to produce the same structures on an initially flat surface. This observation also explores the role of initial surface perturbation on the initiation of curvature dependent sputtering.

Ultrashallow depth profiling using SIMS and ion scattering spectroscopy

AbstractThe accuracy of ultrashallow depth profiling was studied by secondary ion mass spectrometry (SIMS) and high‐resolution Rutherford backscattering spectroscopy (HRBS) to obtain reliable depth profiles of ultrathin gate dielectrics and ultrashallow dopant profiles, and to provide important information for the modeling and process control of advanced complimentary metal‐oxide semiconductor (CMOS) design. An ultrathin Si3N4/SiO2 stacked layer (2.5 nm) and ultrashallow arsenic implantation distributions (3 keV, 1 × 1015 cm−2) were used to explore the accuracy of near‐surface depth profiles measured by low‐energy O2+ and Cs+ bombardment (0.25 and 0.5 keV) at oblique incidence. The SIMS depth profiles were compared with those by HRBS. Comparison between HRBS and SIMS nitrogen profiles in the stacked layer suggested that SIMS depth profiling with O2+ at low energy (0.25 keV) and an impact angle of 78° provides accurate profiles. For the As+‐implanted Si, the HRBS depth profiles clearly showed redistribution in the near‐surface region. In contrast, those by the conventional SIMS measurement using Cs+ primary ions at oblique incidence were distorted at depths less than 5 nm. The distortion resulted from a long transient caused by the native oxide. To reduce the transient behavior and to obtain more accurate depth profiles in the near‐surface region, the use of O2+ primary ions was found to be effective, and 0.25 keV O2+ at normal incidence provided a more reliable result than Cs+ in the near‐surface region. Copyright © 2007 John Wiley & Sons, Ltd.

The initial sputtering of Cu(1 0 0) by 1 keV O2 projectiles

Molecular dynamics simulations of the sputter erosion of a Cu(100) crystal by 1keV O2 projectiles up to a nominal fluence of 1.7×1015 O2 molecules cm−2 are reported for both normal and oblique projectile incidence. O–Cu attractive interactions have been described in the simulations using a many-body Gupta potential that was fitted to ab initio structural and energy predictions for O–Cu clusters. The simulations predict that implanted oxygen atoms segregate from octahedral sites in the bulk to hollow sites at the surface, and that the sputter yield of the target is enhanced by a factor of two due to the efficient formation of CunO clusters. The predicted yields of CunO clusters display a non-monotonic abundance distribution, with a maximum at n=2–3, in contrast to the monotonic, power-law abundance distribution predicted for Cun clusters.

In situ XPS and SIMS analysis of O2+ beam‐induced silicon oxidation

AbstractThe chemical composition variation of silicon under 4 keV O2+ ion beam bombardment at different incident angles was studied by in situ small‐area XPS. The changes in secondary ion profile (30Si+, 44SiO+, 56Si2+, 60SiO2+) during oxygen ion beam bombardment also have been monitored. We present a direct correlation of the changes in secondary ion depth profile with surface composition during sputtering. Evolution of the secondary ion profile obtained from SIMS shows similar trends with variation of oxygen concentration in the crater surface measured by XPS. It is shown that when the oxygen ion beam incidence angle is < 40° silicon dioxide is the dominant species on the crater surface and the matrix ion species ratio (MISR) value for 44SiO+/56Si2+ is higher than for 30Si+/56Si2+. For incidence angles of >40°, the formation of sub‐oxide is favoured and thus the MISR value for 44SiO+/56Si2+ is lower than for 30Si+/56Si2. At 40° bombardment there are similar amounts of SiO2 and sub‐oxides present on the crater surface and the MISR values for 44SiO+/56Si2+ and 30Si+/56Si2+ are also similar. Copyright © 2004 John Wiley & Sons, Ltd.

Investigation of boron penetration through decoupled plasma nitrided gate oxide using backside secondary ion mass spectrometry depth profiling

High drive-in temperature during dopant activation of p+-poly metal-oxide-semiconductor field effect transistors causes boron penetration through the thin gate oxide, which degrades the device performance. Conventional secondary ion mass spectrometry (SIMS) depth profiling is unable to accurately analyze boron penetration under rapid thermal annealing conditions due to ion knock-on and mixing effects. With the development of backside SIMS depth profiling technique using SOI wafers [Yeo et al., Surf. Interface Anal. 33, 373 (2002); Runsheim et al., J. Vac. Sci. Technol. B 20, 448 (2002)], quantification of the amount of boron penetration becomes possible. In this article, boron penetration through decoupled plasma nitridation silicon dioxide was studied by performing both front and backside depth profiling using 0.5 keV O2+ with oxygen flooding and 2 keV Cs+ primary ions at oblique incidence in a Cameca IMS-6f SIMS instrument.

Evaluation of the silicon capping technique in SIMS

AbstractThe effectiveness of the silicon capping technique in ultrashallow secondary ion mass spectrometry using 1 keV O2+ at 56° incidence angle is investigated. It is shown that a capping layer of at least 20 nm is needed to ensure a steady‐state erosion rate when profiling the doped region. The matrix intensity is very sensitive to the presence of native oxide, and enhancement is evident for oxides as thin as one monolayer. The oxygen enhancement is further influenced by the high dopant concentration on the sputter surface. The present results favour the model that relates the surface spike present during depth profiling to the sputtering of native oxide. Copyright © 2002 John Wiley & Sons, Ltd.

Optimal low‐energy SIMS conditions for characterizing ZrO2/Si interfaces

AbstractDevelopment of high‐K gate dielectric materials has placed a stringent demand for inspection tools with ultrahigh depth resolving power and detection sensitivity. Low‐energy SIMS is potentially the technique of choice provided that the analytical related artifacts are well understood and efficiently suppressed. In this work we profiled superficial and buried metal–organic chemical vapour deposited ZrO2 films and investigated the artifacts involved in SIMS profiling at various beam conditions. It was demonstrated that O2+ beams at near‐normal incidence yielded extremely broad Zr down‐slopes in Si, an artifact likely due to a pronounced preferential sputtering of Si when the instantaneous surface reached the ZrO2/Si interfaces. Suppression of this artifact can be realized by probing O2+ beams at oblique incidence, favorably at 60° for a 1 keV O2+. Nevertheless, the normal‐incidence O2+ beam remained optimal for characterizing the up‐slope of Zr at the polycrystalline Si (polySi)/ZrO2 interface, owing to the minimized matrix effects and suppressed surface roughness. For profiling a gate stack (polySi/ZrO2/Si) at oblique incidences, the high depth resolution of low‐energy SIMS was hindered by the pronounced roughness in poly‐Si. This can be remedied by ion beam smoothing of the poly‐Si prior to SIMS profiling. Using the optimal SIMS conditions, we profiled poly‐Si/ZrO2/Si wafers with and without dopant activation anneal. The SIMS data revealed significant reactions between ZrO2 and Si upon thermal anneal at 1025°C for 10 s. Copyright © 2002 John Wiley & Sons, Ltd.

SIMS backside depth profiling of ultrashallow implants using silicon‐on‐insulator substrates

AbstractWe report the use of secondary ion mass spectrometry (SIMS) backside depth profiling for ultrashallow implants using silicon‐on‐insulator (SOI) wafers for substrate thinning. The SOI layer, after removal of the buried oxide layer, provides a smooth and flat surface for high‐resolution SIMS depth profiling from the backside. The dopant distribution of 0.5 keV boron implants (5 × 1014 atoms cm−2) was studied by performing both front and backside depth profiling using 0.5–5 keV O2+ primary ions at oblique incidence in a Cameca IMS‐6f SIMS instrument, with and without sample rotation. The backside depth profiles give significant improvement in depth resolution compared with conventional frontside SIMS depth profiling. Copyright © 2002 John Wiley & Sons, Ltd.

Flux dependence of oxygen-beam-induced ripple growth on silicon

The influence of flux on the growth of ripples on Si(111) under bombardment of oblique, 1 keV O2+ beams was investigated. We found that a low flux leads to a significantly higher ripple growth rate per ion than a high flux. This effect is attributed to a reduction in the viscous flow of the amorphized material. At low fluxes, the viscous flow is reduced because there is more thermal annealing of the radiation damage. Current models of surface roughening remain valid if the flux dependence of the viscous flow is taken into account.