Anisotropic angular distribution of sputtered atoms

The sputtering yield angular distributions have been calculated on the basis of the ion energy dependence of total sputtering yields for Ni and Mo targets bombarded by low-energy Hg⁺ ions. The calculated curves show excellent agreement with the corresponding Wehner's experimental results of sputtering yield angular distributions. This fact clearly demonstrates the intrinsic relation between the ion energy dependence of total sputtering yields and the sputtering yield angular distribution. This intrinsic relation had been ignored in Yamamura's papers [Yamamura, Y. (1982). Theory of sputtering and comparison to experimental data, Nucl. Instr. and Meth., 194, 515–522; Yamamura, Y. (1981). Contribution of anisotropic velocity distribution of recoil atoms to sputtering yields and angular distributions of sputtered atoms, Rad. Eff., 55, 49–55.] due to some obvious mistakes.     

Determination of the negative ion yield of copper sputtered by cesium ions

Abstract

This paper describes the determination of secondary ion yields for negative ions obtained by bombardment of copper by cesium ions. Stable and reproducible surface conditions are reached by high rate sodium deposition simultaneously with sputtering. An optimum thickness of sodium corresponding to about one monolayer is found. Total negative ion yields K ^? _Σ are measured by a double modulation technique. Individual negative ion yields K ^? _i are then found by mass spectrometrically determining the various negative ion intensities, the sum of which relates linearly to K ^? _Σ. This method is based on the assumption of an equal angular and energy distribution of all sputtered negative ions. Data are given for K^? _Σ and K ^? _Cu and K^? _O. The dependence of K ^? _i on primary ion energy (500 to 2500 eV) is similar to ordinary sputtering which points to the same basic mechanism in both cases.     

Sputtering yields for light ions as a function of angle of incidence

The sputtering yield of Ni, Mo, and Au have been measured at oblique angles of incidence for H⁺-, D⁺-, and⁴He⁺-ion irradiation in the energy region from 1 to 8 keV. The yields were determined from the weight loss of the targets. For Ni and Mo the dependence of the sputtering yield on the angle of incidence was found to be much stronger for H⁺- and D⁺-ion than for⁴He⁺-ion irradiation. In all cases the maximum in the yield was found at angles of incidence ϑ≧80°, where ϑ is the angle measured from the surface normal. Furthermore the ratio of the maximum yield to the yeild at normal incidence increases with increasing surface binding energy of the target material as well as with increasing ion energy in the energy region inveestigated. The results are discussed qualitatively in view of a model for the sputtering mechanism for light ions.     

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.     

聚变α粒子对第一壁辐照损伤的蒙特-卡罗研究(Ⅱ)——溅射

本文应用蒙特-卡罗方法研究聚变α粒子对不锈钢第一壁的溅射损伤。首先,计算单种元素Fe,Cr,Ni的溅射产额随入射能量的变化,并与实验结果比较,以确定计算中所用到的一些重要参数,如原子位移能等。在此基础上计算聚变α粒子对不锈钢(Fe_0.73Cr_0.18Ni_0.09)的部分(和总)溅射产额,溅射粒子的能谱、角分布和源深度分布,以及上述各量与α粒子入射角的关系。结果表明,在考虑入射α粒子随能量及入射角的分布后,其平均总溅射产额为0.375。由于1     

Carbon sputtering yield measurements at grazing incidence

In this investigation, carbon sputtering yields were measured experimentally at varying angles of incidence under Xe⁺ bombardment. The measurements were obtained by etching a coated quartz crystal microbalance (QCM) with a low energy ion beam. The material properties of the carbon targets were characterized with a scanning electron microscope (SEM) and Raman spectroscopy. C sputtering yields measured under Ar⁺ and Xe⁺ bombardment at normal incidence displayed satisfactory agreement with previously published data over an energy range of 200 eV-1 keV. For Xe⁺ ions, the dependence of the yields on angle of incidence θ was determined for 0° ≤ θ ≤ 80°. Over this range, an increase in C sputtering yield by a factor of 4.8 was observed, with the peak in yield occurring at 70°. This is a much higher variation compared to Xe⁺ → Mo yields under similar conditions, a difference that may be attributed to higher scattering of the incident particles transverse to the beam direction than in the case of Xe⁺ → C. In addition, the variation of the yields with θ was not strongly energy dependent. Trapping of Xe in the surface was observed, in contrast to observations using the QCM technique with metallic target materials. Finally, target surface roughness was characterized using atomic force microscope measurements to distinguish between the effects of local and overall angle of incidence of the target.     

Sputtering of A 3 B 5 materials (GaP, GaAs, GaSb, InP, and InSb) by 2-to 14-keV N 2 + ions

Investigations of the general characteristics and distinctive features of sputtering of A ³ B ⁵ materials (GaP, GaAs, GaSb, InP and InSb) under bombardment with N ₂ ⁺ ions have been carried out. From the experimental data, dependences of the sputtering yield of these materials on the incidence angle and ion energy have been obtained and the surface relief patterns produced by target etching have been studied. It has been shown that the dependence on energy of the sputtering yield for GaP, GaAs, and InP can be adequately described by the Haffa-Switkovski formula for binary materials and Yudin’s approximation for elemental targets. Sputtering of GaSb and InSb proceeds in the surface layer recrystallization mode, and the sputtering yield agrees with calculations based on Onderlinden’s model. From a comparison of the experimental and calculated dependences, the surface bonding energies have been determined.     

The influence of implanted xenon on the sputtering yield of silicon

Following implantation labeling with either 200 or 270 keV Xe⁺ the sputtering yield of silicon bombarded with 20 keV Xe⁺ has been determined in situ by means of the backscattering technique (Y = 3.0 ± 0.3 (atoms/ion)). Yield enhancement by up to 60% was observed in cases where the implantation-induced xenon concentrations exceeded the saturation concentration during sputtering. The effect is attributed to (i) an increase in energy deposition at the surface introduced by pronounced xenon loading of the target and (ii) lowering of the surface binding energy. As a consequence the energy dependence of the xenon sputtering yield of silicon is expected to be strongly affected by the energy dependence of the xenon saturation concentration in silicon. Available experimental data support this idea.     

Systematic investigation of the reactive ion beam sputter deposition process of SiO<Subscript>2</Subscript>

Ion beam sputter deposition (IBSD) is an established physical vapour deposition technique that offers the opportunity to tailor the properties of film-forming particles and, consequently, film properties. This is because of two reasons: (i) ion generation and acceleration (ion source), sputtering (target) and film deposition (substrate) are locally separated. (ii) The angular and energy distribution of sputtered target atoms and scattered primary particles depend on ion incidence angle, ion energy, and ion species. Ion beam sputtering of a Si target in a reactive oxygen atmosphere was used to grow SiO₂ films on silicon substrates. The sputtering geometry, ion energy and ion species were varied systematically and their influence on film properties was investigated. The SiO₂ films are amorphous. The growth rate increases with increasing ion energy and ion incidence angle. Thickness, index of refraction, stoichiometry, mass density and surface roughness show a strong correlation with the sputtering geometry. A considerable amount of primary inert gas particles is found in the deposited films. The primary ion species also has an impact on the film properties, whereas the influence of the ion energy is rather small.     

Sputter yields in diamond bombarded by ultra low energy ions

Artificial diamond is an ideal material for high power, high voltage electronic devices, and for engineering use in extreme environments. Diamond process development requires parallel development in characterization techniques such as ultra low energy SIMS (uleSIMS), especially in the ability to depth profile for impurities and dopants at high depth resolution.As a contribution to the background knowledge required, we have measured the sputter yields of single crystal high pressure high temperature (HPHT) diamond using O₂⁺, Cs⁺ and Ar⁺ primary ions in the energy range 300 eV to 2 keV. We compare these with yields for silicon and GaAs. We show that the erosion rates with oxygen are ∼10 times what would be expected from ballistic processes and essentially energy independent in the measured range. This result agrees with the anomalously high sputter yield observed in the ion etching context. Conversely, positive ion yields for elements such as boron are very low in comparison with silicon. This points to a reactive ion etching process liberating CO or CO₂ rather than sputtering as the principal erosion process.This is both problematic and beneficial for SIMS analysis. Oxygen can be used to reach buried structures in diamond efficiently, and the effects of the near-normal incidence beam are planarizing as they are in silicon. Conversely, since positive ion yields are low, alternative probes or strategies must be found for high sensitivity profiling of electropositive elements.     

On the energy spectra of secondary ions emitted from silicon and graphite single crystals

Secondary ion emission from silicon and graphite single crystals bombarded by argon ions with energies E ₀ varied from 1 to 10 keV at various angles of incidence α has been studied. The evolution of the energy spectra of C⁺ and Si⁺ secondary ions has been traced in which the positions of maxima (E _max) shift toward higher secondary-ion energies E ₁ with increasing polar emission angle θ (measured from the normal to the sample surface). The opposite trend has been observed for ions emitted from single crystals heated to several hundred degrees Centigrade; the E _max values initially remain unchanged and then shift toward lower energies E ₁ with increasing angle θ. It is established that the magnitude and position of a peak in the energy spectrum of secondary C⁺ ions is virtually independent of E ₀, angle α, and the surface relief of the sample (in the E ₀ and α intervals studied). Unusual oscillating energy distributions are discussed, which have been observed for secondary ions emitted from silicon (111) and layered graphite (0001) faces. Numerical simulations of secondary ion sputtering and charge exchange have been performed. A comparison of the measured and calculated data for graphite crystals has shown that C⁺ ions are formed as a result of charge exchange between secondary ions and bombarding Ar⁺ ions, which takes place both outside and inside the target. This substantially differs from the ion sputtering process in metals and must be taken into account when analyzing secondary ion emission mechanisms and in practical applications of secondary-ion mass spectrometry.     

Sputtering of compound semiconductor surfaces. I. Ion-solid interactions and sputtering yields

Several phenomena occur on the surface of a solid when being bombarded by energetic ions. A short general review is given of the major ion-solid interactions on compound semiconductor surfaces. An in-depth discussion is presented of the total sputtering yields of component semiconductors. For this discussion, GaAs is assumed to be the prototype compound semiconductor because most experimental measurements exist for GaAs. To exclude any chemical effects in the sputter yields, only the total sputtering yield data for argon ion bombardment of GaAs are compared with the predictions of the major sputtering theories, with particular attention to the Sigmund theory for linear cascade sputtering. Different proposals of each of the parameters in this theory are presented and compared with the GaAs data. These parameters are the surface binding energy, the nuclear stopping power, and the factor α, which represents the fraction of energy available for sputtering. Use of the different parameters results in a large variation in the predictions. Topics also considered are the angle dependence of the sputtering yields, sputter threshold energy, and channeling effects in the sputter yields of compound semiconductors. Spike sputtering effects are evident in the sputtering yields of GaAs by krypton and xenon ions.     

Artifacts in the sputtering of inorganics by C60

In the present study, the basic issues in C₆₀ⁿ⁺ sputtering are studied using silicon, gold and platinum samples. Sputtering yields are measured for energies in the range of 5-30 keV, by sputtering micrometre sized craters on the surface of flat clean samples and measuring their volumes using atomic force microscopy (AFM). Net deposition of carbon occurs for all three materials at 5 keV, and is not specific to silicon which forms a carbide. The threshold energy for net sputtering is dependent on the sputtering yield and the stopping power of the substrate. Away from the threshold, the sputtering yields agree well with Sigmund and Claussen's thermal spike model after allowance for the sputtering of the deposited carbon atoms. AFM images show the formation of unusual surface topography around the transition region between sputtering and deposition. Analysis of the bottom of a crater using imaging SIMS shows a significant enhancement of carbon clusters as well as various silicon-carbon groups, indicating the importance of carbon deposition and implantation in a gradual mixed layer formed from sputtering. The thickness of this interface layer is shown to be approximately 5 nm.     

Sodium halide sputtering by H+, He+, Ar+ ions

Sputtering experiments were performed with 70 to 300 keV H⁺, He⁺ and Ar⁺ ions impinging on KC1, KBr and Kl. The alkali halide samples are prepared as polycrystalline layers of about 2500 Å thickness, deposited on carbon-aluminium backings. During the ion bombardment the targets are kept at elevated temperatures between 50 and 300°C, in order to study the temperature dependence of sputtering. During the irradiation the removal of halogen and sodium is simultaneously observed by Rutherford backscattering.

The present results are (i) preferential sputtering of the halogen atoms, (ii) temperature dependent sputtering yields with 0.2 eV activation energy, (iii) sputtering yields proportional to the electronic stopping power, rather than the nuclear stopping power, and (iv) sputtering yields orders of magnitude higher than estimated by elastic collision cascade theories. These findings can be interpreted by a Pooley process with subsequent migration of the interstitial halogen atom to the surface.     

Study on the orientation of silver films by ion-beam assisted deposition

Low energy ion beam assisted deposition (IBAD) was employed to prepare Ag films on Mo/Si (100) substrate. It was found that Ag films deposited by sputtering method without ion beam bombardment were preferred (111) orientation. When the depositing film was simultaneously bombardment by Ar⁺ beam perpendicular to the film surface at ion/atom arrival ratio of 0.18, the prepared films exhibited weak (111) and (200) mixed orientations. When the direction of Ar⁺ beam was off-normal direction of the film surface, Ag films showed highly preferred (111) orientation. Monte Carlo method was used to calculate the sputtering yields of Ar⁺ ions at various incident and azimuth angles. The effects of channeling and surface free energy on the crystallographic orientation of Ag films were discussed.     

Vacancy-type defect distributions near argon sputtered Al(100) surface studied by variable-energy positrons and molecular dynamics simulations

A beam of variable-energy positrons, whose back-diffusion probability is measured as a function of positron implantation energy, is applied to studies of depth distribution of sputtering damage in aluminum. The defects are produced by argon ion bombardment of an Al(110) surface in ultra-high vacuum. We have varied the Ar⁺ energy, incident angle and dose, as well as sputtering and annealing temperatures. The extracted defect profiles have typically a narrow peak at the surface with a width of 10–20 A and a broader tail extending down to 50–100 Å. The shape of the defect profile varies only slightly with the sputtering energy and angle. Defect production at less than 1 keV Ar⁺ energies is typically 1–5 vacancies per incident ion. The defect profiles become fluence-independent at about 2 × 10¹⁶ Ar⁺ cm⁻². The defect density at the outer atomic layers saturates at high argon fluences to a few at%, depending on sputtering conditions. The sputtering temperature (below or above the vacancy migration stage at 250 K) has little effect on vacancy profiles. Defects anneal out gradually between 100 °C and 400 °C. Sputtering damage was also evaluated with the molecular dynamics technique. The shape and depth scale of the simulated collision cascades are in agreement with the experimentally extracted quantities.     

Anisotropic energy distribution of sputtered atoms induced by low energy heavy ion bombardment

The theory of anisotropic sputtering published in Phys. Rev. B 71(2), 026101 (2005) and Radiat. Effects Defects Solids 159(5), 301 (2004) has been modified and used to calculate the sputtering yield energy distributions for copper, tungsten, and aluminum targets bombarded by low-energy argon ion. As usual, the electronic stopping is ignored in the analysis. The present theory (modified Sigmund’s theory) has been shown to fit the corresponding experimental results of sputtering yield energy distributions well, except for the cases where the larger ion incident angle and larger sputtering emission angles were considered. The larger discrepancy between the present theory and the experimental result in the latter cases is probably due to the influence of direct recoil atoms on the energy spectrum. Compared with Falcone’s analytical theory, the present theory can reproduce much better experimental results of sputtering phenomena. The fact clearly demonstrates the intrinsic relation between the ion–energy dependence of the total sputtering yield and the sputtering yield energy distribution and suggests the great importance of momentum deposited on the target surface in the physical sputtering     

The effect of incident angle on the C60 bombardment of molecular solids

The effect of incident angle on the quality of SIMS molecular depth profiling using C₆₀⁺ was investigated. Cholesterol films of ∼300 nm thickness on Si were employed as a model and were eroded using 40 keV C₆₀⁺ at an incident angle of 40° and 73° with respect to the surface normal. The erosion process was characterized by determining at each angle the relative amount of chemical damage, the total sputtering yield of cholesterol molecules, and the interface width between the film and the Si substrate. The results show that there is less molecule damage at an angle of incidence of 73° and that the total sputtering yield is largest at an angle of incidence of 40°. The measurements suggest reduced damage is not necessarily dependent upon enhanced yields and that depositing the incident energy nearer the surface by using glancing angles is most important. The interface width parameter supports this idea by indicating that at the 73° incident angle, C₆₀⁺ produces a smaller altered layer depth. Overall, the results show that 73° incidence is the better angle for molecular depth profiling using 40 keV C₆₀⁺.     

Point-defect properties of,and sputtering events in,the {001} surfaces of Ni3Al. II. Sputtering events at and near surfaces

Atomic recoil events at and near {001} surfaces of Ni₃Al due to elastic collisions between electrons and atoms have been simulated by molecular dynamics to obtain the sputtering threshold energy as a function of atomic species, recoil direction and atomic layer of the primary recoil atom. The minimum sputtering energy occurs for adatoms and is 3.5 and 4.5?eV for Al and Ni adatoms on the Ni–Al surface (denoted ‘M’), respectively, and 4.5?eV for both species on the pure Ni surface (denoted ‘N’). For atoms within the surface plane, the minimum sputtering energy is 6.0?eV for Al and Ni atoms in the M plane and for Ni atoms in the N surface. The sputtering threshold energy increases with increasing angle, θ, between the recoil direction and surface normal, and is almost independent of azimuthal angle, ?, if θ<60°; it varies strongly with ? when θ>60°, with a maximum at ??=?45° due to ?{110}? close-packed atomic chains in the surface. The sputtering threshold energy increases significantly for subsurface recoils, except for those that generate efficient energy transfer to a surface atom by a replacement collision sequence. The implications of the results for the prediction of the mass loss due to sputtering during microanalysis in a FEG STEM are discussed.     

Ion sputtering rates of W-, Ti- and Cr-carbides studied at different Ar ion incidence angles

To study the ion sputtering rates of W-, Ti- and Cr-carbides, trilayer structures comprising C-graphite (59 nm)/WC (50 nm)/W (38 nm), C-graphite (56 nm)/TiC (40 nm)/Ti (34 nm) and C-graphite (46 nm)/C₃C₂ (60 nm)/Cr (69 nm) with a tolerance ±2% were sputter deposited onto smooth silicon substrates. Their precise structural and compositional characterization by transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) revealed that the WC and Cr₃C₂ layers were amorphous, while the TiC layer had a polycrystalline structure. The ion sputtering rates of all three carbides, amorphous carbon and polycrystalline Cr, Ti and W layers were determined by means of Auger electron spectroscopy depth profiling as a function of the angle of incidence of two symmetrically inclined 1 keV Ar⁺ ion beams in the range between 22° and 82°. The sputtering rates were calculated from the known thicknesses of the layers and the sputtering times necessary to remove the individual layers. It was found that the sputtering rates of carbides, C-graphite and metals were strongly angle dependent. For the carbides in the range between 36° and 62° the highest ion sputtering rate was found for Cr₃C₂ and the lowest for TiC, while the values of the sputtering rates for WC were intermediate. The normalized sputtering yields calculated from the experimentally obtained data for all three carbides followed the trend of theoretical results obtained by calculation of the transport of ions in solids by the SRIM code. The sputtering yields are also presented in terms of atoms/ion. Our experimental data for two ion incidence angles of 22° and 49° and reported values of other authors for C-graphite and metals are mainly inside the estimated error of about ±20%. The influence of the ion-induced surface topography on the measured sputtering yields was estimated from the atomic force microscope (AFM) measurements at the intermediate points of the corresponding layers on the crater walls formed during depth profiling.