Conventional Rutherford Backscattering Research Articles

Sputtering Yields of Si Bombarded with 10–540-keV C60 Ions

Sputtering yields of Si have been measured for C60 ions in the energy range from 10 to 540 keV, where the nuclear stopping is dominant, by measuring thickness change of a pre-amorphized layer with conventional Rutherford-backscattering spectroscopy. The measured sputtering yield shows the maximum, which is approximately 600 Si/C60, around 100 keV. Comparing with the sputtering yields for a monatomic ion calculated both based on the linear-collision-cascade theory of Sigmund and using the SRIM2008 code, nonlinear effect on the sputtering yield has been observed. The nonlinear effect depends on the energy of C60 ions: it is very large around the energies where the sputtering yield has the maximum and hardly observed at 10 keV.

Low energy cathodoluminescence analysis of damage build-up in ion irradiated spinel mono- and polycrystals

Abstract In contrast to single crystalline materials a quantitative determination of defect formation in polycrystals is challenging. Here we use low-energy (3 keV) cathodoluminescence (CL) for structural characterization of single and polycrystalline magnesium aluminate spinel (MgAl2O4) exposed to irradiation with 300 keV Ar+ ions at room temperature in a wide fluence range of 1 × 1012–2 × 1016 cm−2. The results for single crystalline materials are also compared with conventional Rutherford Backscattering and Channeling spectrometry (RBS/C). It is demonstrated that damage formation in both single and polycrystalline spinels exhibits a multi-step character where polycrystalline material is more susceptible to ion irradiation. The results also imply that the low-energy CL is more sensitive to low damage levels as compared to RBS/C and it can be efficiently used as a complementary tool showing new perspectives in the damage accumulation studies in single- and polycrystalline materials.

Study of cerium diffusion in undoped lithium-6 enriched glass with Rutherford backscattering spectrometry

Undoped lithium-6 enriched glasses coated with pure cerium (99.9%) with a gold protection layer on top were heated at three different temperatures (500, 550, and 600°C) for varied durations (1, 2, and 4h). Diffusion profiles of cerium in such glasses were obtained with the conventional Rutherford backscattering technique. Through fitting the diffusion profiles with the thin-film solution of Fick’s second law, diffusion coefficients of cerium with different annealing temperatures and durations were solved. Then, the activation energy of cerium for the diffusion process in the studied glasses was found to be 114kJ/mol with the Arrhenius equation.

ToF-MEIS stopping measurements in thin SiC films

Electronic stopping in thin, amorphous, SiC films has been studied by time-of-flight medium energy ion scattering and conventional Rutherford backscattering spectrometry. Amorphous SiC films (8, 21 and 36nm) were prepared by laser ablation using a single crystalline silicon carbide target. Two kinds of substrate films, one with a lower atomic mass (carbon) and one with higher atomic mass (iridium) compared to silicon has been used. Monte Carlo simulations have been used to evaluate electronic stopping from the shift in energy for the signal scattered from Ir with and without SiC. The two kinds of samples are used to illustrate the strength and challenges for ToF-MEIS compared to conventional RBS.

Electrophoretic Deposition of Single Wall Carbon Nanotube Films and Characterization

ABSTRACTElectrophoretic deposition enables the rapid deposition of single wall carbon nanotube films at room temperature. An accurate, reproducible film thickness can be obtained by controlling electric field strength, suspension concentration, and time. To investigate the electrical and mechanical properties of such films, we recorded electric resistance and Young’s modulus using I-V characterization and a nanoindenter, respectively. The measured resistivity of the films varied from 2.14 × 10-3 to 7.66 × 10-3 Ω·cm, and the Young’s modulus was 4.72 to 5.67 GPa, independent of film thickness from 77 to 134 nm. These results indicated that the mechanical and electrical properties of film are comparable with previously reported methods such as layer by layer deposition even though we achieved much higher deposition rates. We also measured the film mass density which is usually unrecorded even though it is an important parameter for MEMS/NEMS device actuation. The film density was found with conventional thickness measurement and Rutherford backscattering spectrometry. It varied from 0.12 to 0.54 g/cm3 as the film thickness increased. This method could be extended to applications of CNT films for flexible electronics or high frequency RF MEMS devices.

Shape, size, and atomic composition analysis of nanostructures in 3D by Rutherford backscattering spectrometry

The emergence of novel micro- and nanofabrication tools lead to the targeted research of highly ordered three-dimensional nanosystems, constructed from regular building blocks like spheres, cylinders, bricks, pyramids, which can be used in a wide range of applications. As a consequence, the exploration of the potential and limits of efficient analytical techniques to characterize structured nanosystems became a significant task. In this work the scope of conventional Rutherford backscattering spectrometry (RBS) analysis is extended to investigate highly ordered periodic nanostructures in three dimensions. Hexagonally arranged spherical and ellipsoidal silica particles, rectangular gold nano-arrays, and embedded structures in Si substrates and silica particles are analyzed. It is shown that the shape of the measured spectra can be correlated with the shape of individual nano-objects through geometrical considerations. The evaluation of the recorded data for different sample tilt angles can be carried out with the Monte-Carlo type 3D simulation model cell concept considering the details of the applied measurement geometry. It is demonstrated that macrobeam 3D-RBS can provide valuable information on the shape, size, spacing, and atomic composition of nanostructured samples as well as on nanoscale atomic transport processes and consequently, it can be utilized as a highly precise, non-destructive characterization tool for nanotechnology.

Three-dimensional view of the shape, size, and atomic composition of ordered nanostructures by Rutherford backscattering spectrometry

Conventional Rutherford backscattering spectrometry (RBS) in combination with Monte Carlo simulations performed on 3D model cells allow the self-consistent determination of the shape, size, and atomic composition of silica particles as model structures, on the submicron scale. Spherical and ellipsoidal particle shapes and the spatial distribution of implanted Ar and Xe in the particles and in the unmasked zones of the underlying substrate is investigated. We demonstrate that both lateral and depth information for ordered nano-objects can be derived from multiple RBS spectrum analysis.

Disordering and dopant behaviour inAu+-ion-irradiated AlN

Single-crystal AlN films on SiC were irradiated at 145 K with 1.0 MeVAu+ ions in a wide range of ion fluences. The accumulation of disorder on both the Al and Nsublattices in AlN has been investigated in situ using conventional Rutherfordbackscattering spectrometry (RBS) and non-RBS along the -axial channelling direction. The results suggest that a disorder saturation stage isattained following an initial disorder increase at doses less than 10 displacements per atom(dpa). A continuously amorphized layer was not formed in AlN for doses up to 208 dpa.Similar disordering behaviour is observed for the Al and N sublattices. The lattice disorderproduced at 145 K is thermally stable at room temperature; further irradiation does notinduce disorder recovery. The microstructures in the irradiated AlN exhibit bothamorphous and crystalline domains at the stage of disorder saturation. The implanted Audoes not show significant redistribution during the ion irradiation or room-temperatureannealing.

Compositional analysis of HfxSiyO1−x−y thin films by medium energy ion scattering (MEIS) analysis

HfxSiyO1−x−y layers with thicknesses of 2 and 10nm were measured by medium energy ion scattering (MEIS) with a toroidal electrostatic analyzer (TEA), in which the yield of MEIS spectra was found to decrease with decreasing energy in contrast to conventional Rutherford backscattering spectrometry (RBS), due to the increase in neutralized particles.The HfxSiyO1−x−y spectra obtained by MEIS were corrected with a ratio of the simulated MEIS yield to measured yield for a virgin Si at each energy. The corrected HfxSiyO1−x−y spectra were analyzed and the compositions for 2 and 10nm thick HfxSiyO1−x−y were obtained by MEIS. An interface layer was found to exist between the Si substrate and the HfxSiyO1−x−y layer.

Interfacial analysis using time-of-flight medium energy backscattering

Time-of-flight medium energy backscattering (TOF-MEBS) is a derivative of conventional Rutherford backscattering (RBS) that uses medium energy ions and a time-of-flight detector resulting in improved surface sensitivity, increased depth resolution, and reduced target damage compared to conventional RBS. In this study, thin dielectric materials and their lower interfaces were analyzed with TOF-MEBS using 270 keV He+ projectiles. Dielectric materials systems studied included Al2O3, SiO2, and ZrO2 on silicon. Film thicknesses ranged from approximately 10 to 200 Å. Data analyses were performed by modeling the ion interactions with material structures and performing a non-linear least squared fit to the backscattering spectra. Simulation fit results were improved up to 40% for alumina and 60% for zirconia samples by including interfacial layers on the order of a few nanometers thick in the material structure models. The significant improvement to fits resulting from the addition of extremely thin interfacial layers demonstrates the technique’s applicability to ultra-thin film characterization.

Characterization of a compact filament-driven multicusp ion source for low energy time-of-flight Rutherford backscattering spectrometry application

Because of the limited pulse height energy resolution of a detector, conventional Rutherford backscattering spectrometry (RBS) requires an energy of the incident α particle to be in the MeV region. At Chiang Mai University we have researched the possibility of utilizing a 280 keV nanosecond pulse of helium ions for RBS applications. We have chosen a compact filament-driven multicusp ion source of 2.6 cm in diameter and 8 cm in length being investigated for the time-of-flight RBS applications. In this article, we present the general ion source performance using helium, nitrogen, and argon for generating the discharge plasma. The general ion source characteristics have been measured and analyzed. The measurements also include the extractable ion current and the ion beam emittance. We have performed beam extraction calculations with a computer simulation code KOBRA. Results of the measurements and calculations will be presented and discussed.

Basic characteristics of the a-SiOC∶H thin films prepared by PE CVD

Hydrogenated amorphous silicon oxycarbide (a-SiOC∶H) thin films were prepared by plasmaenhanced chemical vapor deposition (PE CVD) using an RF helical coupling pulsed-plasma system. Films of the thickness ranging from 210 nm to 1.4 μm were deposited on silicon wafers from vinyltriethoxysilane (VTES) precursor. The thickness of plasma-polymerized films was measured by a Profilometer Talystep using a defined seratch in the layer as deep as the substrate. The deposition rate was observed with respect to the effective power used and the determined dependence could be explained on a basis of the competitive ablation and polymerization mechanisms. Very high deposition rates as far as about 110 nm/min could be reached if proper deposition conditions were tuned. The elemental composition of thin films were studied by conventional and resonant Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA) methods. The Si, C and O bulk content was correlated with the surface one determined from analyses of the photoelectron spectra using X-ray Photoelectron Spectroscopy (XPS).

Fluence loss due to Rutherford backscattering for very low energy ion implantation in silicon

Modern semiconductor device manufacturing process requires ion implantation as low as 0.5 keV. These are source/drain extension implants with high fluences. It is conceivable that the implanted ions cannot be totally retained due to surface sputtering and backscattering. So far the industry has taken a pragmatic route, i.e. implant with enough dopant so that the device reaches certain performance characteristics. Rutherford binary collision model says the stopping power cross-section is inversely proportional to the square of ions energy. This would suggest that the fluence loss from backscattering can be severe when the implant energy is very low. This work is our attempt to verify the theory's validity with such implants. In this work we experiment with boron ions of 250 eV to 5 keV and arsenic ions of 500 eV to 10 keV. With each energy the incident angle of ions to silicon wafers is changed from 0° to 30° and to 60°. A low fluence of 5 × 10 13/cm 2 is used for all the wafers in hope that backscattering effect can be studied without much influence from surface sputtering. Secondary ion mass spectrometry (SIMS) is used to probe for the retained fluence with each implant condition. This paper discusses the retained fluence as a function of species, energy and incident angle of ultra-low energy ions into silicon surface. It is observed that the fluence loss increases at larger tilt angles and the fluence loss due to scattering does not follow the energy dependence as depicted by the conventional Rutherford backscattering theory. At ultra-low energies the surface conditions and surface deposition mechanisms become more important and may compete with the scattering and sputtering processes. We also discuss the difficulties in dealing with such ultra-low energy implants such as the lack of established stopping power models, the issues with ion implantation and SIMS artifacts.

Influence of hydrogen dose and boron doping on the ion cutting of Si

AbstractIon beam techniques were used to study silicon‐on‐insulator (SOI) structures manufactured by the ion cutting process. Silicon wafers and epitaxial Si layers with various doping levels were implanted with H2+ ions at 100 keV prior to wafer bonding. Some wafers were also implanted with B+ ions at 175 keV. The implantation doses varied from 2.5 × 1016 to 5.0 × 1016 cm−2 for H2+ and from 1 × 1013 to 3 × 1015 cm−2 for B+. The thickness of an SOI layer was determined by conventional Rutherford backscattering spectrometry (RBS) and the crystal damage was examined by RBS in channelling mode (RBS/C). The disorder due to implanted hydrogen was found to decrease with increasing boron concentration. The measured thickness of the exfoliated Si layer was 455–460 nm for highly boron‐doped samples and 470–490 nm for the undoped samples. Exfoliation occurred inside the damage zone in all the samples, irrespective of hydrogen dose and boron doping. Our results suggest that the exfoliation depth in Si is associated with the lattice damage generated by the implantation. Copyright © 2003 John Wiley & Sons, Ltd.

Structural characterization of epitaxial Cd 1− xZn xTe semiconductor thin films by ion beam techniques

We report on the structural characterization of ZnTe, CdTe and Cd 1− x Zn x Te epilayers grown on GaAs(1 0 0) by isothermal closed space sublimation epitaxy. A detailed study of the heterostructures based on conventional Rutherford backscattering spectrometry, ion channeling and nuclear reaction analysis allows to determine the thickness, composition, impurities, lateral homogeneity and interface structure of the grown thin films. The growth rates were determined for the extreme composition (ZnTe, CdTe). Stoichiometry and lateral homogeneity were observed in ZnTe and CdTe films. Low carbon contamination homogeneously distributed in the film was present and no oxygen contamination of the samples was observed. The channeling analysis of ZnTe films allowed to evaluate the thickness of the interface damaged region.

Medium energy nuclear microprobe with enhanced sensitivity for semiconductor process analysis

A time of flight (TOF) Rutherford backscattering (RBS) system with a nano-probe line has been designed and installed. A medium energy (100–400 keV) nano-probe with beam pulsing and multiscaling detecting techniques was used to obtain enhanced detecting sensitivity for localized analysis. The multiscaling TOF detecting system has about 5 ns time resolution, corresponding to an energy resolution of 2–5 keV, and an advantage over the conventional RBS measurement system in energy resolution. Total charge exposed by TOF–RBS measurement is 4–5 orders of magnitude less than that by conventional RBS using a solid state detector (SSD).

Thin film interaction between low- k dielectric hydrogen silsesquioxane (HSQ) and Ti barrier layer

The interaction between low- k dielectric hydrogen silsesquioxane (HSQ) and Ti barrier layer has been studied using four-point-probe sheet resistance measurement, X-ray diffraction, conventional Rutherford backscattering spectrometry (RBS), nuclear resonance analysis (NRA), elastic recoil detection (ERD), secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS). The conventional intermetal dielectrics SiO 2 and plasma-enhanced tetraethylorthosilicate (PETEOS) have been studied also for the purpose of comparison with HSQ. In the low temperature regime (300–550°C), a considerable amount of oxygen atoms, from various sources, diffuses into Ti film to form a Ti(O) solid solution, raising the resistivity of Ti significantly and causing the expansion of the Ti lattice. A good correlation between the oxygen composition in the Ti film, the sheet resistance variation of Ti and the change of Ti lattice parameter C 0 have been observed. At the same temperature, there are more oxygen atoms incorporated into the Ti film in Ti/HSQ than those for Ti/PETEOS, suggesting that additional HSQ-related oxygen sources, such as the moisture uptake and the conversion reaction of HSQ, may be attributed to this. In the high temperature regime (550–700°C), HSQ reacts with Ti to form a final TiO/Ti 5Si 3/HSQ stack structure. It is assumed that a few competing reactions occur in this regime. At 550–650°C, HSQ reacts directly with Ti; in the meantime, part of HSQ undergoes conversion reactions, with the reaction products SiO 2 and SiH 4 reacting with Ti to form Ti silicide. At 650–700°C, HSQ is almost completely converted into SiO 2, so the dominant mechanism is Ti reaction with SiO 2. Before HSQ is completely turned into SiO 2, the Ti/HSQ system is more reactive than both Ti/PETEOS and Ti/SiO 2. The initiating temperature for the Ti/HSQ reaction exhibits no obvious Ti thickness dependence.

Influence of target–substrate angle on the elemental concentration of c-axis YBa2Cu3O7−x thin films

The thermalization processes in sputtering suggest a spatial dependence of elemental concentration in the sputter plume. A variety of analysis techniques demonstrate that c-axis films grown at angles which deviate from the standard off-axis geometry produce nominally YBa2Cu3O7−x in the bulk with dramatic changes in the surface morphology and deposition rate. In addition to the common materials characterization techniques of scanning electron microscopy, x-ray diffraction, transport measurements, and conventional Rutherford backscattering spectrometry (RBS), angle-dependent RBS is employed to probe surface inhomogeneities of films grown at target–substrate angles away from the standard off-axis position.

A Study of Substrate Orientation Dependence of the Solid-Phase Epitaxial Growth of Amorphised GaAs

AbstractIn-situ transmission electron microscopy (TEM) has been utilized in conjunction with conventional ex-situ Rutherford backscattering spectrometry and channeling (RBS/C), in-situ time resolved reflectivity (TRR) and ex-situ TEM to study the influence of substrate orientation on the solid-phase epitaxial growth (SPEG) of amorphised GaAs. A thin amorphous layer was produced on semi-insulating (100), (110) and (111) GaAs substrates by ion implantation of 190 and 200 keV Ga and As ions, respectively, to a total dose of 1e14/cm2. During implantation, substrates were maintained at liquid nitrogen temperature. In-situ annealing at ∼260°C was performed in the electron microscope and the data obtained was quantitatively analysed. It has been demonstrated that the non-planarity of the crystalline-amorphous (c/a)-interface was greatest for the (111) substrate orientation and least for the (110) substrate orientation. The roughness was measured in terms of the length of the a/c-interface in given window as a function of depth on a frame captured from the recorded video of the in-situ TEM experiments. The roughness of the c/a-interface was determined by the size of the angle subtended by the microtwins with respect to the interface on ex-situ TEM cross-sectional micrographs. The angle was both calculated and measured and was the largest in the case of (111) plane. The twinned fraction as a function of orientation, was calculated in terms of the disorder measured from the RBS/C and it was greatest for the (111) orientation.

Critical temperature and ion flux dependence of amorphization in GaAs

The formation of amorphous layers in GaAs during ion bombardment at elevated temperatures, where dynamic annealing of radiation-induced defects is substantial, is shown to be extremely sensitive to the implantation temperature. For example, we have found that a temperature change of only 6 °C can change the residual damage from small clusters barely visible by conventional transmission electron microscopy and Rutherford backscattering to a thick amorphous layer. The temperature at which this occurs is strongly dependent upon the ion flux.