Auger study of preferred sputtering on binary alloy surfaces

Auger Electron Spectroscopy has been used to investigate the preferred sputtering behavior on homogeneous Cu/Ni alloy surfaces. Measurements were made on a range of alloy compositions with Ar⁺ sputter ions of 0.5 to 2 keV energy. A kinetic model has been formulated to describe the time variation of the surface composition during sputtering. Based on this model, we were able to determine the individual sputter yields for Cu and Ni atoms in the alloy and the depth of the surface layer where the composition is altered by sputtering. The sputter yields were found to be relatively independent of the alloy composition but increased almost linearly with energy. The depth of the altered layer was comparable to the Auger sampling depth with its value increasing from 10 Å to more than 20 Å when ion energy increased from 0.5 to 2 keV.     

Sputtering of SiC with low energy He and Ar ions under grazing incidence

The effect of low energy sputtering under grazing incidence upon the surface composition of SiC was investigated by Auger electron spectroscopy. The energy of the sputtering projectiles (He, Ar) varied from 200 to 1500?eV. Peak shifts to the higher energies with increasing argon ion energy were observed for all silicon and carbon Auger transitions. These shifts were explained by enhanced damage of the surface region within the sampling depth of the Auger electrons. The insensitivity of the Auger peak position to the energy of helium ions indicates that the damage state in the surface region does not change with the increasing energy of helium ions. An increase of the carbon concentration with the decrease of the argon energy was observed. The experiments were accompanied by dynamic Monte Carlo simulations by the TRIDYN code.     

Ta2O5/Ta界面分析的新模型

对Ta₂O₅/Ta样品界面区的深度剖面曲线进行了研究。基于离子溅射引起影响层存在的考虑,提出一种解释该曲线的新模型。通过此模型能很好地拟合实验曲线,并反映了溅射过程中的离子混合效应、原子堆积效应及相应的特征参数。样品由阳极氧化法制得,其厚度为500埃。表面分析在PHI-590型扫描俄歇微探针上完成,所有测量均在室温下进行。研究表明:深度剖面曲线并不符合误差函数分布;影响层的厚度为30—50埃,它是进行深度剖面分析时,决定元素俄歇信号强度的第一位重要因素;深度剖面 关键词：     

Formation of Ti and TiN ultra-thin films on Si by ion beam sputter deposition

Ultra-thin titanium and titanium nitride films on silicon substrate were obtained by ion beam sputtering of titanium target in vacuum and nitrogen atmosphere, using argon ions with energy of 5 keV and 15 μA target current. Elemental composition and chemical state of obtained films were investigated by X-ray photoelectron spectroscopy with using Mg-Kα X-ray radiation (photon energy 1253.6 eV). It was shown that it is possible to form both ultra-thin titanium films (sputtering in vacuum) and ultra-thin titanium nitride films (sputtering in nitrogen atmosphere) in the same temperature conditions. Photoelectron spectra of samples surface, obtained in different steps of films synthesis, detailed spectra of photoelectron emission from Si 2p, Ti 2p, N 1s core levels and also X-ray photoelectron spectra of Auger electrons emission are presented.     

AES analysis of nitridation of Si(100) by 2–10 keV N+2 ion beams

Ion beam nitridation of Si(100) as a function of N⁺₂ ion energy in the range of 2–10 keV has been investigated by in-situ Auger electron spectroscopy (AES) analysis and Ar⁺ depth profiling. The AES measurements show that the nitride films formed by 4–10 keV N⁺₂ ion bombardment are relatively uniform and have a composition of near stoichiometric silicon nitride (Si₃N₄), but that formed by 2 keV N⁺₂ ion bombardment is N-rich on the film surface. Formation of the surface N-rich film by 2 keV N⁺₂ ion bombardment can be attributed to radiation-enhanced diffusion of interstitial N atoms and a lower self-sputtering yield. AES depth profile measurements indicate that the thicknesses of nitride films appear to increase with ion energy in the range from 2 to 10 keV and the rate of increase of film thickness is most rapid in the 4–10 keV range. The nitridation reaction process which differs from that of low-energy (< 1 keV) N⁺₂ ion bombardment is explained in terms of ion implantation, physical sputtering, chemical reaction and radiation-enhanced diffusion of interstitial N atoms.     

Ion beam sputtering - the effect of incident ion energy on atomic mixing in subsurface layers

Secondary ion mass spectrometric methods were used to study the effect of incident ion energy on atomic mixing in subsurface layers. A Ta₂O₅ film containing a 50 A ^3lP-rich layer 230 A below the surface was depth profiled for phosphorus using normal incidence 160 primary particles of various energies (1.75 to 18.5 keV). A pronounced energy effect was observed in the widths of 31^P profiles generated by >4 keV ¹⁶O. For 18.5 keV ¹⁶O, the observed profile contained two distinct components-the 31^P-rich layer and the 31^P recoil distribution. This later condition, prevails when the peak of the incident ion damage distribution occurs at a depth which equal or exceeds the distance from the surface to the 31^P-rich layer. The desirable primary ion beam energy for characterizing the true elemental distribution is dictated by the shape and location of the layer to be profited. In most instances, a low energy beam is preferred.     

Mechanisms of oxidation-reduction processes on metal and oxide surfaces under ion bombardment

Surface oxidation occurs if metals are bombarded with low-energy (1–5 keV) ions of a chemically active gas (oxygen) in vacuum. It is ascertained that ion bombardment leads to the generation of lower, intermediate, and higher oxides. The composition and thickness of an oxidized layer depend on the metal reactivity and the dose and energy of oxygen ions. The mechanism underlying the ion-beam oxidation of metal surfaces is proposed. Surface reduction is observed if higher oxides are bombarded with low-energy (1–5 keV) ions of inert gases (argon and helium) in vacuum. It is revealed that ion bombardment not only generates intermediate and higher oxides but sometimes gives rise to surface metallization. The composition and thickness of the reduced layer are determined by the oxide type, the kind of inert gases, and the dose and energy of bombardment. The mechanism describing the ion-beam reduction of higher metal oxide surfaces is proposed.     

The simulation of nanoscale sputter depth profiles using molecular dynamics

The feasibility of using molecular dynamics (MD) for simulation of a nanoscale sputter depth profile experiment is examined for the idealised case of depth profiles of individual atomic layers in a Cu(1 0 0) target. Issues relating to the extraction of depth profile information from MD simulations are discussed in detail. The simulations examine the sputter erosion of static and azimuthally-rotated Cu(1 0 0) targets produced by 3 keV Ar projectiles incident at 25° from the surface. The simulated projectile fluence extends to 5 × 10¹⁵ cm⁻², and the mean value of the sputter depth, z, amounts to 8 Cu(1 0 0) monolayers (ML) or 15 Å. The simulations directly supply progressive layer erosion profiles (curves that depict the extent of sputter erosion of each atomic layer vs. total sputter depth). A fitting method is then used to extract smooth depth profiles for each atomic layer from these predicted erosion profiles. The depth profile characteristics (height, width, shift) for the first 10 layers of the target show a pronounced dependence on layer depth.     

Properties of Cu film and Ti/Cu film on polyimide prepared by ion beam techniques

Cu film and Ti/Cu film on polyimide substrate were prepared by ion implantation and ion beam assisted deposition (IBAD) techniques. Three-dimension white-light interfering profilometer was used to measure thickness of each film. The thickness of the Cu film and Ti/Cu film ranged between 490 nm and 640 nm. The depth profile, surface morphology, roughness, adhesion, nanohardness, and modulus of the Cu and Ti/Cu films were measured by scanning Auger nanoprobe (SAN), atomic force microscopy (AFM), and nanoindenter, respectively. The polyimide substrates irradiated with argon ions were analyzed by scanning electron microscopy (SEM) and AFM. The results suggested that both the Cu film and Ti/Cu film were of good adhesion with polyimide substrate, and ion beam techniques were suitable to prepare thin metal film on polyimide.     

Ion implantation induced by Cu ablation at high laser fluence

High energy laser plasma-produced Cu ions have been implanted in silicon substrates placed at different distances and angles with respect to the normal to the surface of the ablated target. The implanted samples have been produced using the iodine high power Prague Asterix Laser System (PALS) using 438 nm wavelength irradiating in vacuum a Cu target. The high laser pulse energy (up to 230 J) and the short pulse duration (400 ps) produced a non-equilibrium plasma expanding mainly along the normal to the Cu target surface. Time-of-flight (TOF) technique was employed, through an electrostatic ion energy analyzer (IEA) placed along the target normal, in order to measure the ion energy, the ion charge state, the energy distribution and the charge state distribution. Ions had a Boltzmann energy distributions with an energy increasing with the charge state. At a laser fluence of the order of 6 × 10⁶ J/cm², the maximum ion energy was about 600 keV and the maximum charge state was about 27+.In order to investigate the implantation processes, Cu depth profiles have been performed with Rutherford backscattering spectrometry (RBS) of 1.5 MeV helium ions, Auger electron spectroscopy (AES) with 3 keV electron beam and 1 keV Ar sputtering ions in combination with scanning electron microscopy (SEM). Surface analysis results indicate that Cu ions are implanted within the first surface layers and that the ion penetration ranges are in agreement with the ion energy measured with IEA analysis.     

An AES study of surface segregation of AgAu alloys with ion bombardment and annealing

Equilibrium segregation and selective sputtering in the surface of AgAu alloys have been investigated systematically with argon ion bombardment and with annealing by means of AES measurements. Slight enrichment of Ag was observed on the alloy surfaces after the annealing of the alloys at 550°C, while relatively large enrichment of Au was observed on the ion-bombarded surfaces with the use of Au (240 eV) and Ag (300 eV) Auger electrons. With the aid of other Auger electrons with different escape lengths, it was found that the concentration varies with distance from the surface within the sampling depth of the Auger electrons. On the basis of the above facts, the depth profiles were proposed for the annealed and the ion-bombarded surfaces. The uppermost surface layer is enriched more with Ag than the apparent AES observations on both the ion-bombarded and the annealed surfaces. The proposed depth profiles on both the surface layers were compared with previous results by different authors.     

Changes in gold concentration at the surface of a AuCu alloy sputtered at low temperature

A series of depth profiles in Au_0.56Cu_0.44 produced by bombarding at ? 120°C with an argon ion beam of 2 keV energy and current densities of 4, 6, 12 and 24 μA/cm², respectively, are presented. Gold is enriched in the top layer but the concentration rapidly decreases to a minimum at an average depth of about 2 Å, then increases slowly and saturates at about 30 Å. The change in the composition at this point is called a dip. The magnitude of the dip depends on the ion current density, but the depth is nearly independent of it. Segregation and diffusion effects in establishing the surface composition are stressed.     

Stability of ZnO{0 0 0 1} against low energy ion bombardment

The steady-state surface compositions of the polar (O and Zn terminated) faces of ZnO{0 0 0 1} produced by low energy (0.3-2 keV) Ar⁺ ion bombardment were studied by Auger electron spectroscopy and electron energy loss spectroscopy. The alterations produced by the ion bombardment using different ion energies were monitored by calculating the intensity ratios of the low and high energy Zn Auger peaks (59 eV and 994 eV, respectively); Zn and O Auger peaks (59 eV and 510 eV, respectively). Based on the dependence of these ratios on the ion energy and termination of the surface, we could conclude that the stability of the Zn face is higher against the low energy argon ion bombardment-induced compositional changes than that of the O face.     

Quantitative auger electron analysis of homogeneous binary alloys: Chromium in gold

Quantitative Auger electron analysis of Cr/Au alloys with up to 20% Cr has been accomplished. The surface composition of scribed areas were compared to bulk compositions and it was shown that corrections for variation of density, escape depth, and electron backscattering must be included; these corrections change the measured surface Cr concentrations by approximately 15%. Alloy sputter yield ratios have been calculated from surface concentrations after sputtering with Ar or Ne (0.5, 1.0, 1.5, and 2.0 keV). The sputter yield ratio of Cr to Au was 0.5 at 1% Cr (significant preferred sputtering) but was near unity at 20% Cr (no preferred sputtering). The sputter yield ratio was nearly independent of ion species and ion energy. The 2 keV argon ion sputter yields for pure Cr and Au were determined to be 2.0 and 7.9 atoms/ion, respectively. However, the 2 keV argon ion sputter yield for Au in the alloys drops rapidly from 7.9 atoms/ion for pure Au, to 5 atoms/ion at 10–20% Cr. The sputter yield for Cr in alloys (5 atoms/ion) is relatively independent of composition and is 2.5 times higher than the yield of pure Cr. No simple model is known by which pure elements sputter yields could be used to predict alloy sputtering behavior.     

The backscattering factor for systems with a non-uniform surface region: Definition and calculations

It has been recently shown that the backscattering factor (BF) in Auger electron spectroscopy (AES) noticeably depends on the in-depth structure of the surface region. This is a particularly important problem in sputter depth profiling monitored by AES since the signal intensity cannot be described with a single BF value. The BF depends on the removed amount of material and thus varies with sputtering time.In the present work, the definition of the BF is generalized to extend its applicability to systems with an in-depth composition profile. The generalized definition of the BF was applied to the special case of a depth profile, i.e. a buried thin layer. It has been shown that the BF for this case is expressed by the excitation depth distribution function (EXDDF) which is equivalent to the “Phi-Rho-Z” function used in electron probe microanalysis (EPMA). Different algorithms for calculating the BF are discussed. Calculations of the BF for buried layer were performed for the Ag M₄N₄₅N₄₅ Auger transition in a thin layer of silver located at different depths in three matrix materials: Si, Cu, and Au. It was found that, indeed, the BF noticeably varies with the depth of the layer in the analyzed volume, although the extent of this variation depends on the matrix material. For Si, the variation is observed for the lowest primary beam energies considered, i.e., 1 and 2 keV. For Cu, a distinct depth dependence of the BF is visible at 10 keV and lower energies, while for Au, the BF varies with depth even at the highest considered energy, i.e. 30 keV.     

Bombardment-induced segregation of Cu in Pt-Cu alloy observed using different energy Auger line combinations

Pt_0.19Cu_0.81 alloy scraped in situ was bombarded by energetic (0.2–2 keV) argon ions and the surface compositions under steady-state bombardment were determined with different energy Auger line combinations. It is found that the outermost surface is enriched in Cu, but that its concentration rapidly decreases to a minimum at the second layer then increases slowly to the bulk value. This fact strongly suggests the existence of a bombardment-induced Gibbsian segregation even at room temperature.The project was supported by the National Natural Science Foundation of China     

Characterization of oxide layers on amorphous Zr-based alloys by Auger electron spectroscopy with sputter depth profiling

Amorphous Zr-Cu-Ni-Al-[Ti, Nb] ribbons prepared by melt spinning under argon atmosphere were subjected to electrochemical investigations. Passive films developed at potentiostatic anodic polarization in sulphuric acid solution were investigated by Auger electron spectroscopy (AES) and sputter depth profiling.Changes in the shape of the Auger peaks have been analyzed by factor analysis of the spectra obtained during depth profiling. Pronounced changes in shape and position occur for the Zr, Al, and Ti Auger transitions, but not for Cu and Ni. At least three different peak shapes for O(KVV) were found and attributed to different oxygen binding states. The alloy composition has no significant effect on the thickness and composition of the oxide layer.In multi-element alloys preferential sputtering is a common phenomenon. In the steady state of sputtering, a significant depletion in Cu is found. At the oxide/metal interface, a distinct enrichment of copper is found for all alloys and treatments. The degree of this Cu enrichment depends on the pretreatment. It is higher for the electrochemically-passivated samples than for samples with oxide layers grown during melt spinning.     

Strain and defect densities in Si/Si1-xGex heterostructures investigated by ion scattering and X-ray diffraction

MBE-grown Si/Si_1-xGe_x heterostructures on (100) Si have been characterized by Rutherford backscattering spectroscopy (RBS), ion channeling and X-ray diffraction to investigate defect densities and tetragonal lattice distortion. Critical layer thickness and relaxation of strain by formation of misfit dislocations are strongly dependent on the growth temperature. A Si_0.67Ge_0.33 layer with a thickness of 2000 Å is found to be still fully strained at a growth temperature of 450°C, whereas the same layer grown at 550°C shows considerable strain relaxation by dislocations. To obtain better depth resolution than with conventional RBS, medium energy ion scattering (MEIS) experiments have been performed on Si/Ge superlattices with layer thicknesses of 10–40 Å. A position-sensitive toroidal electrostatic analyser was employed to detect the backscattered ions simultaneously over an angular range of 30° with an energy resolution of 1 keV FWHM for 250 keV He ions, corresponding to a depth resolution of about 10 Å.     

Ion beam mixing of Al/Fe binary systems

Ion beam mixing of Al layers on Fe and Fe layers on Al are studied by irradiation with 200 keV Xe⁺-ions at room temperature as a function of the thickness of the top layer and of the ion fluence from 5×10¹⁵ to 7.5×10¹⁶ions/cm². Deconvolution procedures are needed to separate the influence of the ion sputter profiling by AES from the ion beam induced mixing effects. Auger electron spectroscopy data reveal that the mixing induced diffusivity ought to be considered as a function of concentration. The diffusion coefficients are evaluated by the Boltzmann-Matano method. A strong dependence of the diffusion coefficients and also the mixing efficiencies from the ion dose, the depth of the interface and the nuclear energy deposition were observed. Results are discussed in terms of the diffusional and collisional mixing as well as chemical affinity of both Fe and Al.     

GexSi1-x/Si超晶格的俄歇深度剖面分析

用氩离子刻蚀和俄歇电子能谱测量Ge_xSi_1-x/Si应变层超晶格的成分深度分布,得到Ge,Si两种成分随深度的周期性变化,在二次电子象中观察到刻蚀坑边缘的明暗交替的周期性结构。讨论了用俄歇深度剖面分布作超晶格结构分析的特点及其局限性。 关键词：