Electron Spectroscopy Sputter Depth Profiling Research Articles

Interdiffusion in amorphous AlxZr1-x alloys

Interdiffusion in amorphous AlxZr1−x compositionally modulated multilayers was investigated by Auger electron spectroscopy sputter-depth profiling. Microstructural characterisation was performed by X-ray diffraction and cross-sectional transmission electron microscopy. The temperature-dependent chemical diffusion coefficient could be deduced at a series of temperatures in the range of 356 °C to 415 °C and was found to be weakly dependent on composition. The activation enthalpy for the chemical diffusion coefficients is slightly smaller at the composition of the Al-rich am-Al0.62Zr0.38 sublayer (1.6 eV) than at the composition of the Zr-rich am-Al0.27Zr0.73 sublayer (1.8 eV), which is not related to the concentration dependence of the excess free volume but to the smaller atomic size and mass of Al as compared to Zr. The smaller activation enthalpy for interdiffusion in partially crystallised specimens than in entirely amorphous AlxZr1−x multilayers is ascribed to the relatively large excess free volume in the grain boundaries of the nanocrystalline sublayers, as compared to the amorphous phase, at large Al concentrations. On the basis of an evaluation of the role of diffusion-induced stress in amorphous systems, it is shown that stresses induced by interdiffusion relax relatively fast by viscous flow and do not affect the determined diffusion coefficients.

Interdiffusion and stress development in single-crystalline Pd/Ag bilayers

Interdiffusion and stress evolution in single-crystalline Pd/single-crystalline Ag thin films were investigated by Auger electron spectroscopy sputter-depth profiling and in-situ X-ray diffraction, respectively. The concentration-dependent chemical diffusion coefficient, as well as the impurity diffusion coefficient of Ag in Pd could be determined in the low temperature range of 356 °C–455 °C. As a consequence of the similarity of the strong concentration-dependences of the intrinsic diffusion coefficients, the chemical diffusion coefficient varies only over three orders of magnitude over the whole composition range, despite the large difference of six orders of magnitude of the self-diffusion coefficients of Ag in Ag and Pd in Pd. It is shown that the Darken-Manning treatment should be adopted for interpretation of the experimental data; the Nernst-Planck treatment yielded physically unreasonable results. Apart from the development of compressive thermal stress, the development of stress in both sublayers separately could be ascribed to compositional stress (tensile in the Ag sublayer and compressive in the Pd sublayer) and dominant relaxation processes, especially in the Ag sublayer. The effect of these internal stresses on the values determined for the diffusion coefficients is shown to be negligible.

Interdiffusion in epitaxial, single-crystalline Au/Ag thin films studied by Auger electron spectroscopy sputter-depth profiling and positron annihilation

Interdiffusion in epitaxial, single-crystalline Au/Ag bilayered thin films on Si (001) substrates was investigated by Auger electron spectroscopy (AES) sputter-depth profiling and by in-situ positron annihilation Doppler broadening spectroscopy (DBS). By the combination of these techniques identification of the role of vacancy sources and sinks on interdiffusion in the Au/Ag films was possible. It was found that with precise knowledge of the concentration-dependent self-diffusion and impurity diffusion coefficients a distinction between the Darken-Manning treatment and Nernst-Planck treatment can be made, which is not possible on the basis of the determined concentration-depth profiles alone.

Concentration-dependent self-diffusion coefficients in amorphous Si1−xGex solid solutions: An interdiffusion study

Self-diffusion coefficients of Si and Ge in amorphous Si1−xGex (a-Si1−xGex) solid solutions were determined quantitatively in the temperature range of 440 °C – 460 °C by the investigation of interdiffusion in amorphous Si/Si0.52Ge0.48 multilayers using Auger electron spectroscopy sputter-depth profiling. The determined concentration dependent self-diffusion coefficients of Si and Ge in a-Si1−xGex with 0 ≤ x ≤ 0.48 at. % Ge are about ten orders of magnitude larger than in the corresponding crystalline phases, due to the inherent, excess free volume in the amorphous phase. The self-diffusion coefficient of Si (or Ge) in a-Si1−xGex increases in association with a decreasing activation enthalpy with increasing Ge concentration. This concentration dependence has been related to an overall decrease of the average bond strength with increasing Ge concentration.

Influence of oxygen on the formation of cubic boron nitride by r.f. magnetron sputtering

Formation of cubic boron nitride by r.f. magnetron sputtering has been studied with O 2 addition to the common working gas Ar/N 2. The chemical and the phase composition were determined with Auger electron spectroscopy sputter depth profiling and Fourier transform infrared spectroscopy. The result shows that oxygen hinders the formation of cBN in sufficient nitrogen-supply, but facilitates the growth of cBN in insufficient nitrogen-supply. With insufficient nitrogen-supply, there exists an optimal oxygen-supply in the working gas that promoted the establishment of the stoichiometric condition in the growing film. O-concentration in the film increases with oxygen-supply in the working gas. cBN forms only when the oxygen concentration is below 5% and c N/ c B (ratio of concentration of nitrogen atoms and boron atoms) is 1 in the film.

Dependence of depth resolution on primary energy of low‐energy Ar+ Ions (100–1000 eV) in AES sputter depth profiling of GaAs/AlAs superlattice

AbstractThe dependence of the depth resolution on the primary energy of low‐energy Ar+ ions in Auger electron spectroscopy (AES) sputter depth profiling of an ISO reference material GaAs/AlAs superlattice was investigated for the ion incidence angle of 50° from the sample surface normal. The depth resolution was found to improve as the square root of the primary energy of the ions as the primary energy decreased from 1000 to 200 eV. In contrast, a deterioration of the depth resolution was observed at 100 eV, which was induced by the difference in the etching rates between GaAs and AlAs and preferential sputtering. Further investigation of AES sputter depth profiling under irradiation of 100‐eV Ar+ ions at the incident angle of 70° revealed that the difference in the etching rate and preferential sputtering could be suppressed by changing the incident angle from 50° to 70° , leading to a depth resolution of ∼1.3 nm with 100 eV. The present results confirmed that glancing incidence is effective in achieving higher depth resolution from the point of view of the reduction of not only atomic mixing but also the difference in the etching rates and preferential sputtering. Careful attention is required for optimizing conditions of low‐energy ion irradiation in sputter depth profiling using the GaAs/AlAs reference material. Copyright © 2006 John Wiley & Sons, Ltd.

Sulfur incorporation into copper indium diselenide single crystals through annealing in hydrogen sulfide

CuInSe 2 crystals were sulfurized in a H2S–Ar gas mixture at 575 °C. The focus was on the resulting mass transport, in particular, on the interdiffusion of Se and S. Experiments were done for various sulfurization times, and the resulting S distribution was measured by Auger electron spectroscopy sputter depth profiling and analyzed with the Boltzmann-Matano method. A one-dimensional diffusion process had shaped the S distribution in these crystals. The respective diffusion coefficient was on the order of 10−16cm2∕s, and it varied only slightly with the S content in CuIn(Se,S)2.

Preferential sputtering observed in Auger electron spectroscopy sputter depth profiling of AlAs/GaAs superlattice using low‐energy ions

AbstractAuger electron spectroscopy (AES) sputter depth profiling of an ISO reference material of the GaAs/AlAs superlattice was investigated using low‐energy Ar+ ions. Although a high depth resolution of ∼1.0 nm was obtained at the GaAs/AlAs interface under 100 eV Ar+ ion irradiation, deterioration of the depth resolution was observed at the AlAs/GaAs interface. The Auger peak profile revealed that the enrichment of Al due to preferential sputtering occurred during sputter etching of the AlAs layer only under 100 eV Ar+ ion irradiation. In addition, a significant difference in the etching rates between the AlAs and GaAs layers was observed for low‐energy ion irradiation. Deterioration of the depth resolution under 100 eV Ar+ ion irradiation is attributed to the preferential sputtering and the difference in the etching rate. The present results suggest that the effects induced by the preferential sputtering and the significant difference in the etching rate should be taken into account to optimize ion etching conditions using the GaAs/AlAs reference material under low‐energy ion irradiation. Copyright © 2005 John Wiley & Sons, Ltd.

Development of ultrahigh vacuum floating‐type low‐energy ion gun with differential pumping facilities for high‐resolution depth profiling

AbstractAn ultrahigh vacuum floating‐type low‐energy ion gun (UHV‐FLIG) with a differential pumping system was developed. The developed UHV‐FLIG ensured high ion current densities of ∼45 and ∼20 µA cm−2 for Ar+ ions of 300 and 100 eV, respectively, under the UHV condition of the analysis chamber below ∼4 × 10−6 Pa. The application of the developed UHV‐FLIG to Auger electron spectroscopy (AES) sputter depth profiling of a GaAs/AlAs superlattice material revealed that the ultimate high depth resolution of ∼1.0 nm was achieved by sputter etching using 100 eV Ar+ ions. The present results confirmed that lowering the primary energy of Ar+ ions to 100 eV is still significantly effective for achieving higher depth resolution in sputter depth profiling. Copyright © 2005 John Wiley & Sons, Ltd.

Extension of Atomic Mixing, Surface Roughness and Information Depth Model for Auger Electron Spectroscopy Sputter-Depth Profile Using Tilted Cylindrical Mirror Analyzer

An atomic mixing, surface roughness and information depth (MRI) model was extended to describe Auger electron spectroscopy (AES) sputter-depth profiles measured using a cylindrical mirror analyzer (CMA) tilted at oblique angle. The extension was performed by taking into account the effects of the dependence of the information depth of detected Auger electrons on the azimuthal angle of the entrance of the CMA. Al-LVV and Al-KLL depth profiles of a GaAs/AlAs superlattice material were analyzed using the extended MRI model. The present results revealed that the depth profiles calculated by the extended MRI model can be fitted to the experimental ones measured using the tilted CMA under the condition that the thickness of the mixing layer is smaller than the information depth. In contrast, the depth profiles calculated by the conventional MRI model can not trace the experimental ones. The present study confirmed that the extended MRI model is well worthy of application to the analysis of the AES depth profiles obtained using the tilted CMA with low-energy ions of less than a couple of hundreds eV, which is expected to reduce the thickness of the damaged layer.

Surface analytical characterization of SiO2 gradient membrane coatings on gas sensor microarrays

Ion beam assisted deposition is applied to cover a gas sensor microarray of an electronic nose with an ultrathin gas-permeable SiO2 membrane varying in thickness across the array. Auger electron spectroscopy sputter depth profiles and non-Rutherford backscattering spectroscopy were used to study the uniformity of the deposition and the subsequent annealing step. The combination of spectroscopic ellipsometry for the freshly prepared membranes and line scans derived from Auger and angle resolved x-ray photoelectron spectroscopy, respectively, for the baked membrane is presented as a powerful quantification method for the determination of the desired SiO2 membrane thickness profiles.

On the influence of substrate temperature for cubic boron nitride growth

BN-films were deposited on Si(100) substrates with r.f. magnetron sputtering of hBN targets. The chemical and the phase composition were determined with Auger electron spectroscopy sputter depth profiling and with Fourier transform infrared spectroscopy; the film stress was measured with the beam-bending method. Temperature dependent deposition studies for a constant substrate bias of −200 V revealed that cBN was formed at substrate temperatures close to room temperature for appropriate values of the N 2-content in the N 2/Ar working gas. The stress is slightly reduced with increasing substrate temperature, and thicker hBN-sublayers seem to improve the film adherence to the substrate. The commonly observed temperature threshold for cBN growth is very probably required to establish full BN stoichiometry as a condition for cBN formation.

Improved Auger electron spectroscopy sputter depth profiling of W/WNx and WSix layers on Si substrates

We have investigated the effects of sample rotation and ion energy reduction on the quality of ion sputtering assisted Auger electron spectroscopy depth profiling of W/WNx and WSix films on polysilicon substrates. Rotation significantly improves both the depth resolution for W/WNx/Si samples and the sensitivity to oxygen inside the W/WNx film. Rotation does not have any effect on results for WSix/Si interfaces. Atomic force microscopy investigations show that the improved resolution for W/WNx/Si samples is due to reduced roughness of the sputtered surface when the sample is rotated. Reduction of the ion energy from 4 to 1 keV also improves the depth profiles of W/WNx films. The ion energy reduction in the same range leads to larger error in measured elemental concentrations for WSix films due to preferential sputtering. This reduction increases the depth resolution of Auger depth profiles in the case of polycrystalline WSix films, but does not change the depth resolution for amorphous WSix films.

Auger electron spectroscopy sputter depth profiling technique for binary solids

In this work the Auger electron spectroscopy (AES) sputter depth profiling technique for binary solids has been discussed and exemplified by its application to reveal composition profiles generated in Ni 0.7Mo 0.3 by pre-bombardment with Ar +-ions of 1 through 5 keV. Two element-specific, surface-sensitive Auger transitions are employed to monitor the surface composition. The linear correlation between the Auger intensities provides the relative sensitivity factor for the quantification of AES data. A model proposed by Ho and co-workers is reformulated for the conversion of the measured temporal variation of surface concentration C s( t) into the original composition profile C( x). Radiation-enhanced diffusion caused by high-energy ion bombardment turns sputter depth profiling into an underdetermined inverse problem. On the other hand, experiments show that the strong preferential sputtering effect accompanying low-energy sputter may veil the detail of the composition profiles. An intermediate energy between about 100 and 300 eV is found to be optimum for the purpose of sputter depth profiling.

Compositional and structural characterization of temperature-induced solid-state reactions in Al/Ni multilayers

Diffusion controlled solid-state reactions during the annealing of Al/Ni multilayers deposited by rf magnetron sputtering onto silicon substrates have been studied. The samples with an overall atomic concentration of ${\mathrm{Al}}_{0.5}{\mathrm{Ni}}_{0.5}$ consisted of four Ni and four Al sublayers with a double layer thickness of 50.3 nm. The temperature induced compositional and structural changes during the annealing periods of 45 min were determined by Auger electron spectroscopy (AES) sputter depth profiling and x-ray diffraction. Up to 120 \ifmmode^\circ\else\textdegree\fi{}C no intermetallic phase was detected, albeit the AES sputter depth profiles indicated a significant enrichment of Ni in the Al layers. At temperatures around 160 \ifmmode^\circ\else\textdegree\fi{}C these sublayers nucleated completely into the ${\mathrm{Al}}_{3}\mathrm{Ni}$ phase. With a further increase of the annealing temperature the reaction proceeded to the formation of ${\mathrm{Al}}_{3}{\mathrm{Ni}}_{2},$ and finally above 250 \ifmmode^\circ\else\textdegree\fi{}C to a homogeneous layer of bcc ordered AlNi.

Synthesis of silicon carbonitride thin films by means of r.f.-sputtering and ion implantation

Si=C=N layers of various composition were prepared by sequential implantation of 13C and 15N ions into Si 〈111〉 samples and by means of reactive r.f. (radio frequency) magnetron co-sputtering using co-sputter targets consisting of carbon and silicon. The layers were characterized by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) sputter depth profiles. The concentrations were calibrated using non-Rutherford backscattering spectrometry (n-RBS), and the profiles were compared with nuclear reaction analysis (NRA) profiles using the resonant nuclear reactions 13C(p, γ)14N at ERes=1748 eV and 15N(p, αγ)12C at Eres=429 keV, respectively.

Interdiffusion at the Al2O3/Ti interface studied in thin-film structures

The early-stage interfacial reactions between amorphous Al 2 O 3 (a-Al 2 O 3 ) and crystalline α-Ti (c-Ti) thin films were studied in thin-film structures with two different thicknesses. Smooth silicon (111) substrates were covered firstly with a TiN thin-film diffusion barrier and then with a crystalline Ti layer. Finally, amorphous Al 2 O 3 was sputter deposited onto the crystalline Ti layer. The samples were heated in a differential scanning calorimeter with a linear heating rate of 40°C min -1 -from room temperature up to different final temperatures of 350-700°C in an argon atmosphere to activate reactions at the a-Al 2 O 3 /c-Ti interfaces-and then rapidly quenched. The interdiffusion at the a-Al 2 O 3 /c-Ti interface was studied using the rate of change of the reaction width obtained from Auger electron spectroscopy (AES) sputter depth profiles. The beginning of the reaction, which involves the diffusion of oxygen (followed by Al) into the c-Ti thin film, was observed at ∼425°C. The activation energy at the a-Al 2 O 3 /c-Ti interface was found to be 1.6 eV for the oxygen diffusion from the amorphous Al 2 O 3 into the c-Ti thin film between 425°C and 650°C, and 0.9 eV for the Al diffusion between 500°C and 625°C. The new crystalline reaction product is composed of α 2 -Ti 3 Al phase and a solid solution of oxygen in α-Ti. The influence of different sample structures on kinetic quantities is discussed. © 1998 John Wiley & Sons, Ltd.

Method for the study of grain boundary diffusion effects by Auger electron spectroscopy sputter depth profiling

We investigated the effects of grain boundary diffusion (GBD) at elevated temperatures on Auger electron spectroscopy sputter depth profiles of Co-Ag bilayers by using the modified surface accumulation method which is proposed for the first time to our knowledge. The results agree well with our previous ones done by the surface accumulation method. The GBD parameters for Ag in Co along the grain boundaries were found to be as follows: the activation energy and pre-exponential factor for GBD are 0.425±0.025 eV and ∼1×10−7cm2, respectively. These indicate that the modified method is an effective alternative in studying the effects of GBD, and may be applied to complicated systems for which the previous method does not hold.

Temperature induced dissolution of Cr 2O 3 into polycrystalline tantalum

Cr 2O 3 films 1425 Å thick deposited by reactive r.f. magnetron sputtering onto polycrystalline tantalum substrates were annealed in ultrahigh vacuum between 670°C and 750°C. The temperature induced compositional changes were determined by Auger electron spectroscopy (AES) sputter depth profiling without breaking the vacuum. In comparison with an unheated Cr 2O 3/Ta couple the annealing procedure leads to a homogeneous reduction of the oxygen content in the Cr 2O 3, film and an enrichment of chromium in the near-surface region. Based on the concentration depth profiles derived from the AES sputter profiles, the mechanism of oxide dissolution is discussed in detail. It is described by a first-order reaction for which the temperature dependent rate constants have been determined. For the respective activation energy a value of 5.3 eV was found.

Investigations of ion implanted iron silicide layers after annealing and irradiation

200 keV Fe + ions were implanted into silicon at 350°C to investigate the phase formation of α-, β-FeSi 2 and ϵ-FeSi. Doses of 1, 3, 5, and 7 × 10 17 cm −2 were used to produce different silicides. Subsequent annealing of three samples (1, 3, and 7 × 10 17 cm −2) at 1150°C for 30 s leads to phase transitions and changes of the silicide fractions. The sample implanted with 5 × 10 17 cm −2 Fe was irradiated with 3 MeV Si at room temperature, and shows significant changes in the phase composition, too. Conversion electron Mössbauer spectroscopy, Auger electron spectroscopy sputter depth profiling, Rutherford backscattering spectroscopy and X-ray diffraction were used for sample characterization. The results of the different methods, which have different depth sensitivities are combined and compared to each other. The results are discussed with respect to the different processes which take place during implantation, annealing and post irradiation.