Energy transfer to a copper surface by low energy noble gas ion bombardment

The energy transferred to a copper surface by bombardment with Xe⁺, Ar⁺, and He⁺ ions with kinetic energies in the range 100–4000 eV has been studied by our group in previous experiments. There were significant experimental uncertainties for that data at energies below about 200 eV. The present investigation overlaps the previous work, extends the energy range to 10 eV, and includes data for Ne⁺. Particular emphasis is placed on the energy range below 200eV. A specially designed ion source was employed in these experiments. A polycrystalline copper film deposited onto a highly sensitive calorimeter was used as the target material. The results show that the Xe⁺ ion deposits more than 97% of its energy over the entire range investigated whereas the lighter ions deposit a decreasing fraction of their energy below about 1 keV. The decrease is largest for the lightest ion (He⁺). In all cases the deposited energy is about or more than 70% of the incident energy. It will be shown that the present results are in agreement with previous measurements for copper and are qualitatively in good agreement with computer calculations using the TRIM.SP code.On leave from: Institut für Schicht- und Ionentechnik, Forschungszentrum Jülich GmbH, W-5170 Jülich, Fed. Rep. Germany     

kinetic energy reflection from polycrystals bombarded with Ar+, Kr+, and Xe+ ions

When the surface of a solid is bombarded with ions a fraction of the primary energy is reemitted by ion reflection and sputtering. The contribution of ion reflection or sputtering to energy reflection is determined by the mass ratio of the bombarding ions to the target atoms.^1,2 In the case of light ions the contribution of reflected ions is dominant. Results for He⁺ and Ne⁺ bombardment were described in a previous paper.³ The present paper deals with results for Ar⁺, Kr⁺, and Xe⁺ bombardment of the same targets as investigated before.³ The energies of the mass selected bombarding ions range from 9 to 16 keV. The measurements were carried out by means of the thermic detector described in a separate paper.⁴ For the given mass ratios most of the reemitted energy is related to sputtering.     

Molecular effects in ion-induced secondary electron spectra

The energy spectra of slow secondary electrons from a copper surface under bombardment with H⁺, H⁺₂, and H⁺₃ ions have been measured at an energy of 200 keV/atom. Distinct molecular effects are revealed in the ratios of the respective distribution curves for molecular ion and proton impact.     

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.     

Die Zerstäubung von Kupfer durch Ne+-, Ar+-, Kr+- und Xe+-Ionen im Energiebereich von 75keV bis 1MeV

Using a 1,3 MeV Van de Graaff-accelerator the sputtering ratioS of polycristalline copper bombarded by normally incident Ne⁺-, Ar⁺-, Kr⁺-, and Xe⁺-ions was measured in the energy range from 75 keV to 1 MeV. In the case of Kr⁺-ions a broad, plateau-like maximum of the sputtering-curveS=f(E) was found at about 100 keV, for Xe⁺-ions a more pronounced maximum at about 125 keV. The results are discussed applying the theories ofGoldman-Simon, Pease, andMartynenko.     

Cesium redeposition artifacts during low energy ToF-SIMS depth profiling

H-terminated Si samples were preloaded with Cs by performing ToF-SIMS depth profiles (250 eV Cs⁺, 15 keV Ga⁺) until the steady state was reached both with and without a bias of +40 V applied to the ion extraction electrode. Xe⁺ depth profiles (350 eV Xe⁺, 15 keV Ga⁺) were obtained inside and around the Cs craters with and without applying the 40 V bias. The results indicate that the maximum of the Cs⁺ signal of the Xe⁺ depth profiles shifts to the surface if no bias is applied, either during the Cs⁺ sputtering or during the Xe⁺ sputtering (i.e., the profiles are broadest with both biases (Cs⁺ and Xe⁺) on and narrowest and closest to the surface if both biases are off). This effect can be explained by the electric field, caused by the bias, deflecting the sputtered low energy Cs⁺ ions back to the surface.     

The effects of ion implantation on the anodic oxidation of silicon

The effects of H⁺, C⁺, N⁺, Ne⁺, Al⁺, P⁺, Cl⁺, Ar⁺, Ga⁺, As⁺, Kr⁺, Sb⁺, Xe⁺, Au⁺ and Tl⁺ ion implantation on the anodic oxidation of Si have been investigated as a function of dose and energy, in the as-implanted stage and after heat treatment at temperatures up to 1050°C. It is speculated that the location, in the formed oxide, of agglomerates containing the dopant, and the influence of these agglomerates on oxygen diffusion in SiO₂ and/or oxygen evaluation at the oxide/solution interface are factors which account for the enhancement/retardation of the anodic oxidation.     

The influence of ion species on ion bombardment induced preferential orientation

Abstract

Vacuum-deposited Cu specimens were implanted with 40 keV Cu⁺, Ni⁺, Ne⁺, Kr⁺ and Xe⁺ ions in an electromagnetic isotope separator. The specimens were investigated for texture by X-ray diffraction techniques on implanted as well as non-implanted areas of the same specimen. It was found that a preponderance of ?110? crystallographic axes parallel to the incident beam develops during irradiation but that the intensity of the effect is dependent on the ion species in an apparently unpredictable way. A previously suggested channelling mechanism for the origin of the effect is discussed in the light of the present findings and it is concluded that modifications to the proposed mechanism is needed to accommodate these results. It is further shown that certain implications of the results presented here could have an important bearing on ion bombardment related phenomena such as ion ranges, sputtering and materials modification by ion implantation.     

On the nature of ion bombardment-induced phase transformations in films of transition metals

Abstract

Electron diffraction studies have been made of polycrystalline Ni films irradiated with well separated beams of ions of different nature, namely ions of inert (He⁺, Ne⁺, Ar⁺, Kr⁺, Xe⁺) and reactive (N⁺ and O⁺) gases. The Ni films were prepared under vacuum conditions (P? 3·10^?6Pa during evaporation) preventing an appreciable contamination of the films with impurities. The samples were irradiated at T? 300 K with ion beams of energies from 10 to 100 keV in the dose range between 5·10¹⁶ cm^?2 and the value leading to sample destruction.

Irradiation with noble gas ions revealed no phase transitions in the Ni films. A similar result was obtained in irradiation of Fe and Cr films with He⁺ ions. The bombardment of Ni films with reactive gas ions does cause changes in the lattice structure of the samples under study, depending on the nature of the bombarding ions. The N⁺ ion bombardment gives rise to the hcp phase with the lattice parameters typical of the Ni₃N compound, and the O⁺ ion bombardment results in the fcc phase with the NiO-type parameter.

The conclusion is drawn on the chemical origin of the phase transformations in the Ni films under ion bombardment. The necessity of revising the concept about the polymorphous nature of phase transformations induced in the films of transition metals by ion bombardment is substantiated.     

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.     

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.     

Combined field ion microscopy and transmission electron microscopy of heavy ion damage in tungsten

Abstract

A field ion microscopy (FIM) and transmission electron microscopy (TEM) investigation of radiation damage in tungsten after heavy ion bombardment has been carried out. Field ion specimens of tungsten were irradiated with 180–230 keV Xe⁺ ions. The irradiation doses were varied between 4 × 10¹¹ and 4 × 10¹² ions/cm². The irradiated specimens were examined in FIM. Experiments combining both TEM and FIM were performed in order to compare the results obtainable by these two methods. The distribution of defects visible by TEM was inhomogeneous. The influence of the imaging field in FIM on the defects visible in TEM is discussed.     

Auger electron emission by ion bombardment of light metals

The energy distribution of secondary electrons ejected from a metallic target upon ion bombardment (Ar⁺, 10 keV) is studied with a 180° magnetic analyser, particularly in the vicinity of the Auger peaks that appear in the electron spectra of the light metals (Li, Be; Na, Mg, Al, Si). A qualitative explanation based on the correlation diagrams which described the evolution of the electronic levels during the collision of two atoms inside the target is proposed to interpret the variation of the Auger peak intensity with the atomic number of the target.     

Theoretical energy distributions of atoms sputtered from elastic collision spikes by monomer and dimer ion bombardment

The energy spectra of atoms sputtered from metal targets by bombardment with heavy monomer and dimer ions have been investigated on the basis of a standard model for elastic collision spikes. In particular we calculated the energy distributions for a Au sample bombarded by 4 keV I⁺ and 8 keV I ₂ ⁺ ions. The results were compared with the recent time of flight measurements performed by de Vries and coworkers. It was shown that the model described accurately most of the experimental observations: the count rates and the relative cascade to spike ratios for both I⁺ and I ₂ ⁺ projectiles, and the energy spectrum for dimer sputtering. The spectrum for monomer bombardment, however, was shifted towards lower energies in comparison to the experimental one. The possible source of this discrepancy is discussed.This work was supported by the Central Research Program CPBP 01.09     

Calculations of the level of primary radiation defects (displacements per atom) taking into account surface sputtering

The results of analytical estimates and computer simulations of the primary radiation damage level in the number of displacements per atom (dpa) in solids are presented and compared, taking into account the material sputtering under ion bombardment. Calculations were performed for the bombardment of carbon-based materials by Ar⁺, Ne⁺, and N⁺ ions with energies of 2?C30 keV, when considerable ion-induced changes in the material??s structure are observed. A comparison shows the close fit of the analytical and computer calculations.     

Experimental and theoretical investigations into the origin of cross-contamination effects observed in a quadrupole-based SIMS instrument

The minimum-detection limits achievable in SIMS analyses are often determined by transport of material from surrounding surfaces to the bombarded sample. This cross-contamination (or memory) effect was studied in great detail, both experimentally and theoretically. The measurements were performed using a quadrupole-based ion microprobe operated at a secondary-ion extraction voltage of less than 200 V (primary ions mostly 8keV O ₂ ⁺ ). It was found that the flux of particles liberated from surrounding surfaces consists of neutrals as well as positive and negative ions. Contaminant species condensing on the bombarded sample could be discriminated from other backsputtered species through differences in their apparent energy spectra and by other means. The apparent concentration due to material deposited on the sample surface was directly proportional to the bombarded area. For an area of 1 mm² the maximum apparent concentration of Si in GaAs amounted to 5 × 10¹⁶atoms/cm³. The rate of contamination decreased strongly with increasing spacing between the bombarded sample and the collector. The intensities of backsputtered ions and neutrals increased strongly with increasing mass of the target atoms (factor of 10 to 50 due to a change from carbon to gold). The effect of the primary ion mass (O ₂ ⁺ , Ne⁺, and Xe⁺) and energy (5–10keV) was comparatively small. During prolonged bombardment of one particular target material, the rate of contamination due to species not contained in the sample decreased exponentially with increasing fluence. In order to explain the experimental results a model is presented in which the backsputtering effect is attributed to bombardment of surrounding walls by high-energy particles reflected or sputtered from the analysed sample. The level of sample contamination is described by a formula which contains only measurable quantities. Cross-contamination efficiencies are worked out in detail using calculated energy spectra of sputtered and reflected particles in combination with the energy dependence of the sputtering yield of the assumed wall material. The experimental findings are shown to be good agreement with the essential predictions of the model.     

Sputtering experiments with silver single crystals and the channeling phenomena

Sputtering yields of monocrystalline silver under irradiation with 7-30 keV Ar⁺, Kr⁺ and Xe⁺ ions, not reported earlier, have been determined. The yield has been found to depend strongly on the orientation of the crystal and mass of the impinging ion. Onderdelinden's model based on Lindhard's theory of Channeling is found to describe satisfactorily, the observed orientation and ion-mass dependence of the yields for the ions of energy ～10 keV or above. The role of the barrier potential approximated in the model in predicting the experimental results is discussed.     

Radiation damage and annealing studies of ion bombarded cobalt

The effects of implantation-induced radiation damage on the thermal oxidation of cobalt have been studied. Bombardment by both Co⁺ self-ions and by Xe⁺ has been studied as a function of ion dose, energy and annealing temperature. A major increase in oxidation was observed for doses of >10¹⁶ Co⁺ cm^–2 in agreement with previous studies on Al. The oxidation behaviour as a function of annealing temperature was markedly different for Co⁺ and Xe⁺ bombarded samples. For Co⁺ bombarded samples, damage anneals rapidly in the temperature range 20–300°C due to thermally assisted repair of point defects and vacancy clusters. However, for Xe⁺ bombardment, it is proposed that the higher annealing temperatures required for damage repair arise due to the stabilisation of three-dimensional vacancy clusters by the oversized Xe atoms. The increase in oxidation after annealing in the temperature range 300–500°C is thought to be due to vacancy release mechanisms which may affect oxide nucleation.     

Self-organized dot patterns on Si surfaces during noble gas ion beam erosion

The erosion of target materials with energetic ions can lead to the formation of patterns on the surface. During low-energy (?2000 eV) noble gas (Ne⁺, Ar⁺, Kr⁺, Xe⁺) ion beam erosion of silicon surfaces dot patterns evolve on the surface. Dot structures form at oblique ion incidence of 75° with respect to surface normal, with simultaneous sample rotation, at room temperature. The lateral ordering of dots increases while the dot size remains constant with ion fluence, leading to very well ordered dot patterns for prolonged sputtering. Depending on ion beam parameters, dot nanostructures have a mean size from 25 nm up to 50 nm, and a mean height up to 15 nm. The formation of dot patterns depends on the ion/target mass ratio and on the ion energy. The temporal evolution and the lateral ordering of these nanostructures is studied using scanning force microscopy (AFM).     

An alternative method for the dechannelling correction in channelling-backscattering experiments

An alternative procedure to evaluate the dechannelling correction for the extraction of disorder depths distributions, particularly for high levels of disorder, in channelling-backscattering studies is described. It involves the use of experimentally determined values of dechannelling and was used for the extraction of damage distributions in a study of disorder generated by 40 keV N⁺, P⁺, As⁺ and Bi⁺ and 20-200 keV Sb⁺ bombardment of (100) GaAs at 40°K. As a result the method appears applicable at least when thermal annealing of disorder is absent. A comparison with various models of small angle scattering is also made.