Preferential Sputtering Effects Research Articles

Quantification of preferential sputtering and contamination overlayer effects in AES sputter profiling

AbstractA model calculation is presented for the quantitative evaluation of AES sputtering profiles of thin layers in the case of preferential sputtering and a contamination overlayer. The model is based on the statistical contribution to depth resolution, the escape depth effect correction and the preferential sputtering model of Ho et al. (1976). Applications to measured AES sputtering profiles of the anodic oxides Ta2O5 and Nb2O5 allow the determination of the thickness and the oxygen content of the contamination overlayer.

The depth resolution of sputter profiling

Depth profiles of impurity markers and overlayers obtained by sputter-sectioning techniques such as secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy (AES) are modeled by a diffusion theory incorporating atomic mixing and preferential sputtering effects. The model explains very well the broadening and shifts frequently observed in experimental depth profiles.

Characterization of a high depth‐resolution tantalum pentoxide sputter profiling reference material

AbstractA major use of surface analysis instruments concerns composition depth profiling. In many instances poor depth resolution is obtained, one cause of which is poor ion beam alignment and uniformity. To enable instrument users to optimise instrument settings and know (1) the instrument contribution to depth resolution and (2) the ion etch rate, tantalum pentoxide reference materials have been developed with thicknesses of 30 nm and 100 nm and interface widths, measured by AES, of 1.5 and 1.7 nm respectively. The effects of argon ion beam energy, electron beam current density, sputtering geometry and gas purity effects on etch rate and interface width are measured and interpreted in terms of basic parameters, showing that the material is a well‐behaved model system that is robust and easily used. The precise shape of the interface and preferential sputtering effects are also analysed.

The reactive sputtering of tantalum oxide: Compositional uniformity, phases, and transport mechanisms

Reactive sputtering has been investigated by a number of workers, but no clear, generalized picture of the method or the phenomena involved has emerged. It is shown that the variation observed in the partial pressure of O2 during both reactive and nonreactive Ta depositions is a sensitive measure of reactive surface activity in the plasma. A detailed examination of the O2 behavior is made as the degree of activity of either target or substrate is systematically changed. A correlation is made between observed O2 partial pressure variations and resulting compositional variations of the collected films using Auger electron spectroscopy, Auger sputter profiling, and transmission electron microscopy. Most importantly, we describe the reactive sputtering of Ta in O2 in terms of two inverse reactions at two reactive surfaces; a dissociative reaction proceeds at the target while its inverse proceeds at the substrate. A generalized process in which a metal oxide dissociates to a less-stable suboxide at the target, transfers to the substrate as the suboxide, and recombines to form the original target compound, is suggested for the reactive sputtering of any metal oxide which exhibits preferential sputtering effects.

Analysis of the auger electron line shape to determine the composition of CuNi alloys

AbstractThe quantitative analysis of alloys by Auger electron spectroscopy combined with ion beam sputtering becomes difficult when the Auger line shape depends on composition, when individual peaks overlap or when the composition is changed by preferential sputtering during ion bombardment. As an example, it is shown how these difficulties can be managed in the case of CuNi alloys. Variations of the peak shape in the alloy have been found to be a consequence of a linear superposition of the overlapping peaks of the pure elements. Therefore, the composition can be determined by a peak fitting procedure. The peak‐to‐peak amplitudes, on the other hand, are more complicated functions of the composition. It is shown how a concept including several sensitivity factors for the overlapping peaks can be used in order to determine the composition from the peak‐to‐peak amplitudes. The effects of preferential sputtering which produce an altered layer enriched in Ni can be corrected by an empirical sputtering correction factor. From these results the principal shape of the concentration profile within the altered layer has been estimated.

Stoichiometric Disturbance in InP Measured During Ion Implantation Process

ABSTRACTTo measure the sputtered ions during implantation a specially designed UHV-target chamber with a SIMS apparatus was set up. Quantitative analysis are possible with an Auger spectrometer. Disturbances in the stoichiometry in InP are measured during implantation of Sn. The enrichment of the doped surface of InP with the lighter component phoshorus will be discussed in consideration of preferential sputtering and recoil effects during implantation. Measured depth profiles of Sn in InP will be compared with calculated distributions on condition that sputtering takes place. The sputtering yield of InP bombarded by 120 keV Sn+ is 17±5.

DETERMINATION OF THE ATOMIC CONCENTRATION RATIO ON InP (100) CLEAN SURFACES BY X-RAY PHOTOELECTRON SPECTROSCOPY

The atomic concentration ratio of In to P on InP(100) surfaces has been determined to an accuracy of 20% by measuring the In 3d5/2 and P 2p XPS intensities and using the corresponding atomic sensitivity factor values previously derived by the authors. The experimental results show that there exists a preferential sputtering effect for the argon ion bombardment. The In to P concentration ratio reaches a value of 2.2 at 1 keV ion beam energy and increases monotonically with the ion energy. After annealing the sample at approximate 300℃ in ultra high vacuum for 30 minutes, the In to P ratio at the surface decreases to 1.2 which is quite closed to the value of bulk stoichiometric ratio. It can be deduced from the angular dependence of the XPS intensities and the chemical shift of In 3d5/2 binding energy that after the heat treatment, the In-P chemical bonds which were broken by the ion bombarding could reconnect, and the surface atomic arrangement was thus led to become an ordered structure with an outmost atomic layer rich in In.

Composition analysis of some metal alloys using Auger electron spectroscopy

Composition analysis of some metal alloys, based on quantitative Auger electron spectroscopy, is presented and the effects of preferential sputtering are discussed. It is shown that a simplified model can yield quite satisfactory composition results if certain experimental conditions are fulfilled.

Sputter-induced surface composition changes in alloys

Radiation-induced redistribution of alloying elements in the near-surface region of dilute binary alloys during low-energy Ar + ion sputtering was calculated using a kinetic model that includes the effects of radiation-induced segregation and preferential sputtering. Changes in the alloy surface composition were calculated as functions of sputtering time, temperature, ion flux and initial alloy composition for Ni-based model alloys. In the temperature range 200–850°C, radiation-induced segregation is dominant initially and the surface is enriched with or depleted of solutes whose fluxes are coupled predominantly to interstitial or vacancy fluxes, respectively. As the bombardment time increases, the effects of preferential sputtering become dominant and the surface composition approaches a steady-state value determined by the sputtering coefficients of the alloy components. Below 200 and above 850°C, the surface composition is altered by preferential sputtering because radiation-induced segregation is insignificant. The time required to achieve steady state increases with increasing temperature and decreasing ion flux. The present calculations may be of importance in the areas of sputter depth-profiling, sputter etching, and plasma contamination in fusion reactors.

Effects of radiation-induced segregation and preferential sputtering on the sputtering rate of alloys

Changes in the surface composition and in the sputtering rate of binary alloys were calculated using a kinetic model that includes the effects of radiation-induced segregation and preferential sputtering. Numerical solutions were obtained for two dilute Ni-based model alloys, Ni-Cu and Ni-No, under 5-keV Ar + ion bombardment as functions of sputtering time, temperature, and intial alloy composition. In the temperature range 200 – 850°C, the sputtering rate is initially affected by strong radiation-induced segregation. As the bombardment time increases, preferential sputtering becomes dominant; the surface composition and hence, the sputtering rate, approach the steady-state values determined entirely by the sputtering coefficients of the alloy components. Below 200 and above 850°C, the sputtering rate is controlled by preferential sputtering only because radiation-induced segregation is insignificant in these temperature regimes.

Preferential sputtering in oxides as metals and revealed by x-ray photoelectron spectroscopy

The surface film on an oxidized multicomponent alloy usually contains a number of metallic and oxidized phases. During depth-profile analysis, such metal and oxide phases can be differentiated by x-ray photoelectron spectroscopy (XPS), provided the surface oxides are sufficiently stable to withstand ion bombardment without decomposition. A quantitative analysis of the surface composition, however, is not possible without taking account of the effects of preferential sputtering of some phases. We have investigated the effects of 3-keV argon ion bombardment on the composition of oxide-free surfaces of iron–nickel and iron–nickel–chromium alloys. In addition, the effect of ion bombardment on metal–metal oxide surfaces has been studied using composite preparations of metal particles, 10–50 μm diameter, in an oxide matrix. Quantitative XPS measurements of the sputtered alloy surfaces, using photoelectrons of 1.0–2.0 nm mean free path, do not reveal any significant change in the steady-state compositions (i.e., ≳10%) compared with the bulk compositions. In the composite metal–oxide mixtures studied, depletion of the metallic phase is significant in some cases and must be taken into consideration in a quantitative depth profile.

Auger and X-ray photoelectron spectroscopy studies of preferential sputtering in Y 2O 3-doped ZrO 2 films

Auger and X-ray photoelectron spectroscopies have been used to investigate preferential sputtering effects in stabilized cubic 8 mole ??? Y 2O 3-doped ZrO 2 films. The results show that oxygen is preferentially removed by Ar + ion bombardment while the relative Y to Zr concentrations remain essentially constant. At 900 eV, the ratio of the oxygen to zirconium sputtering yields was found to be ≈90% of the value observed at 2000 eV. The XPS spectra showed a decrease in the binding energy of the metal 3d peaks with an associated peak broadening toward lower energies.

Simple model for surface composition changes of alloys and compounds by'ion bombardment

Abstract Surface composition change of binary alloys and compounds is calculated in a first approximation by considering preferential sputtering and knock-on effect. It is shown that this produces an ion energy dependence term in the equation of the composition change at low energy.

Search for preferential sputtering in Ag/Au alloys

Sputtering yields from AgxAu1−x alloys were obtained by 20Ne+ ion scattering spectroscopy in order to detect preferential sputtering effects. Selective sputtering and concomitant enrichment of the sputtered surface was not observed, implying that the ion yield does not change with alloy composition. (AIP)

Sputtering in Thin Film Analysis Methods

Sputtering by ion bombardment plays an increasingly important role in various recently developed surface analysis methods. Even in those techniques which are based on X-ray or electron beam stimulation in situ sputtering is used for sample cleaning or microsectioning. In quantitative studies the important question arises in how far the ion bombardment changes the composition of the sample surface. The rather limited experimental data on “preferential sputtering” which have been collected so far seem to suggest that major composition changes are more an exception than the rule, but each case needs to be checked separately because no general guidelines have been established so far. A number of cases will be discussed in which it becomes orders of magnitude more difficult to sputter one atom species from another than from its own. Preferential sputtering effects become in general more pronounced at lower ion energy. Some suggestions for future studies will be outlined.

Properties of thin piezoelectric films

The Monte-Carlo-based “high dose” programt-dyn has been used to simulate bias sputter deposition processes.t-dyn follows the collision cascades caused by energetic ions in a solid. The changes in the target caused by each collision sequence are stored and the target composition modified accordingly for the next incoming ion. The program also allows the addition of five different non-energetic atomic fluxes to the surface. Calculations of the continuous deposition and resputtering make it possible to simulate the substrate-film interface formation as well as the build-up of a coating on the substrate surface.In this presentation we focus on some phenomena which occur during bias sputter deposition in the limit where the resputtering rate is close to the arrival rate of the deposition species. We shall present simulation studies that illustrate that substrate-dependent preferential sputtering effects frequently appear during film-substrate interface formation. The resputtering yield of the deposition species from the interface may differ by an order of magnitude for different substrates. This effect is so pronounced that for identical processing conditions it is possible to obtain zero net film growth at certain substrates but substantial net film growth at other substrate materials.It is well known that because of preferential resputtering the film composition obtained during bias sputter deposition from an binary alloy target may differ significantly from the target composition. What is less known, however, is that for very thin coatings the resulting film composition may also depend on the underlying substrate. We shall describe how the substrate-dependent resputtering rate effect also may explain this substrate “memory” effect in film composition during bias sputter deposition of binary alloys.