Auger Electron Spectroscopy Depth Profiling Research Articles

Atomic layer deposition of HfNx films and improving the film performance by annealing under NH3 atmosphere

Flowchart illustrating how the films are deposited (a) without and (b) with cleaning step, and Auger electron spectroscopy depth profile of 15 nm HfNx deposited with precleaning step, before annealing (c) and after 900 °C annealing at NH3 atmosphere.

Corrosion resistance of tungsten carbide-rich coating layers produced by noble gas ion mixing

Tungsten carbide (WC) belongs to the class of protective coatings due to its good mechanical properties and corrosion resistance. Herein WC-rich coating layers have been produced by irradiating C/W multilayers with noble gases at room temperature. The in-depth concentration distributions after ion irradiation have been measured by Auger electron spectroscopy depth profiling. The corrosion resistance of the formed layers has been tested in 3.5 wt% NaCl solution. It has been shown that the growth of the WC-rich layer started at the interfaces and with increasing fluence the separately growing layers coalesced. With the coalescence of the layers the corrosion resistance of the system suddenly increased. To describe this phenomenon the term effective areal density has been introduced. If the effective areal densities of WC were lower and higher than 550 (1/nm2) and 1200 (1/nm2), the corrosion current densities were 0.5 and 0.08 (µA/cm2), resp. The in-depth distribution of the WC-rich layer and thus the corrosion resistance could be tailored by varying the projectiles, fluences, energies and initial layer structure. The maximum corrosion resistance found was better than that of stainless steel and WC cermet. The effective areal densities could be predicted by TRIDYN simulations allowing the design of corrosion resistive coatings.

Quantification of Ag/Ni Auger electron spectroscopy depth profiles upon preferential sputtering with non-stationary roughness

The measured Auger electron spectroscopy (AES) depth profiles of the as-deposited Ag/Ni multilayers demonstrate a strong preferential sputtering effect. In the framework of the Mixing-Roughness-Information depth (MRI) model, the influence of preferential sputtering on the “measured” depth profile is quantitatively evaluated. The mass conservation upon AES preferential sputtering is verified and applied to obtain the true layer thickness from the measured depth profiling data (i.e. intensity or composition as a function of sputtering time). Meanwhile the influences of preferential sputtering and non-stationary roughness effects on the depth resolution are also quantitatively evaluated. Based on the developed model, the measured AES depth profiles of the Ag/Ni multilayers as-deposited and annealed at different temperatures are fitted and the interdiffusion coefficients are obtained accordingly.

Design and production of tungsten-carbide rich coating layers

Ion beam induced mixing (IBM) can be used for making protecting coating layers at room temperature. We have studied the production of tungsten-carbide, having high strength and low friction, by IBM since this material is also a candidate for protective coatings. WC rich layers have been produced by irradiating C/W multilayer of various structures (with individual layer thicknesses from 10 to 20 nm) by noble gases using medium energy projectiles. The resulting alterations of the samples have been measured by Auger electron spectroscopy (AES) depth-profiling. TRIDYN simulations, with some parametrization, were applied to determine the elemental in-depth distribution after IBM; the compound formation was calculated by a simple model. The calculated and measured depth profiles were compared and excellent agreement has been found for a rich dataset differing in layer structures, projectiles, ion fluences and energies. The good agreement in a wide parameter range validates our procedure and allows the design of the WC-rich layers and also enables the significant decrease of the experimental work.

Evaluation of AES depth profiles with serious artefacts in C/W multilayers

Ion beam mixing was applied to produce tungsten carbide nano-layers in C/W nano-multilayer structures, which was studied by Auger electron spectroscopy depth profiling. The destructive AES depth profiling caused serious artefacts such as tungsten-carbide production at the interfaces, even when choosing the optimal sputter removal conditions. Here we show that ion mixing due to the AES depth profiling could be described by TRIDYN simulation, and compound formation could be also estimated by introducing a simple model. Thus, despite the serious artefact production the original pristine depth distribution could be reconstructed. This evaluation method has been checked on C/W layer systems containing tungsten-carbide enrichment in the interface region (due to high energy ion beam mixing); the true in-depth distribution could be reconstructed. It has been found also that with increasing carbide formation the artefact production decreases allowing the use the AES depth profiling without reconstruction.

Effect of SC-1 Cleaning to Prevent Al Diffusion for Ti Schottky Barrier Diode

We report the effect of Standard Clean-1 (SC-1) cleaning to remove residual Ti layers after silicidation to prevent Al diffusion into Si wafer for Ti Schottky barrier diodes (Ti-SBD). Regardless of SC-1 cleaning, the presence of oxygen atoms is confirmed by Auger electron spectroscopy (AES) depth profile analysis between Al and Ti-silicide layers. Al atoms at the interface of Ti-silicide and Si wafer are detected, when the SC-1 cleaning is not conducted after rapid thermal annealing. On the other hand, Al atoms are not found at the interface of Ti-SBD after executing SC-1 cleaning. Al diffusion into the interface between Ti-silicide and Si wafer may be caused by thermal stress at the Ti-silicide layer. The difference of the thermal expansion coefficients of Ti and Ti-silicide gives rise to thermal stress at the interface during the Al layer deposition and sintering processes. Although a longer sintering time is conducted for Ti-SBD, the Al atoms do not diffuse into the surface of the Si wafer. Therefore, the removal of the Ti layer by the SC-1 cleaning can prevent Al diffusion for Ti-SBD.

Improvement of thermal stability of Ta-N film in Cu metallization by a Zr-Si interlayer

Ta-N (10 nm)/Zr (20 nm) film was grown on n-type (100) silicon wafer at various substrate temperatures in a rf magnetron sputtering system, followed by in situ deposition of Cu. The Cu/Ta-N/Zr/Si samples were subjected to thermal annealing up to 800 ℃ under the protection of pure nitrogen gas. In order to investigate the effect of insertion of a thin Zr layer under Ta-N film on Ta-N diffusion barrier performance in Cu metallization, Cu/Ta-N/Zr/Si contact system was characterized by X-ray diffraction (XRD), four-point probe (FPP) measurement, scanning electron microscopy (SEM), and Auger electron spectroscopy (AES) depth profile. The results reveal that the microstructure of Ta-N films deposited on Zr is amorphous at different substrate temperatures. The barrier breakdown temperature of Ta-N/Zr film is about 100°C higher than that of Ta-N. It can effectively prevent the diffusion of Cu after annealed at 800°C. The improvement of diffusion barrier performance may be due to the production of Zr-Si layer with low contact resistivity after annealed at 800°C.

Se diffusion in CdTe thin films for photovoltaics

Manipulating CdSeTe bandgrading to enhance photocurrent and carrier lifetime is an essential part of high-performance CdTe photovoltaics (PVs). In this work, we examine Se diffusion kinetics in single-crystal and polycrystalline CdTe during deposition, thermal annealing, and CdCl2 treatments. Se distributions are determined by dynamic secondary-ion-mass spectroscopy and Auger electron spectroscopy depth profiling and coupled with electron backscatter diffraction images of the crystalline structure. Effective bulk and grain boundary diffusion coefficients are determined by analytical models and discussed in the context of processing and film morphology. Se is found to diffuse in CdTe at much higher rates during CdCl2 treatments than with thermal processing alone. GB diffusion also occurs at a significantly faster rate than bulk diffusion. As a result of these two effects, the near interface bulk and GB Se diffusion during CdCl2 treatments dominates the bandgrading profiles in CdTe PVs.

Thermally-induced phase transitions in Pt/Tb/Fe trilayers

Structural phase formation induced by thermally-activated diffusion processes and intermixing of layered structures is a promising reaction pathway for the synthesis of unexpected (metastable) thin film materials. Furthermore, the sequence of structural phase transitions during annealing can substantially differ from those predicted by corresponding bulk phase diagrams due to the underlying grain boundary diffusion mechanisms as well as surface and interface effects. In this study, phase transitions in Pt/Tb/Fe trilayers occurring during post-annealing up to 620°C were investigated by various techniques including x-ray diffraction, transmission electron microscopy, secondary neutral mass spectrometry, Auger electron spectroscopy depth profiling, and magnetic properties measurements. At an annealing temperature of 215°C pronounced Pt and Tb diffusion intermixing is observed leading to the formation of the binary Pt2Tb phase. Further annealing up to 280 °C is accompanied by the appearance of the chemically disordered A1-FePt phase and significant Tb segregation to the outer surface forming an oxide layer. The chemically ordered L10-FePt phase starts to form in parallel to the disappearance of the Pt2Tb phase at 450°C. The final phase product at 620°C is characterized by the coexistence of two remaining phases, L10-FePt and TbO2. Structural phase transitions have a significant impact on the films magnetic properties – heat treatment leads to an enhancement of the coercive field. This fact is associated with the formation of the hard magnetic L10-FePt phase, which might be accompanied by grain isolation induced by partially Tb/Tb-O grain boundary filling.

Improved High-Temperature Oxidation Properties for Mn-Containing Beta-Gamma TiAl with W Addition

TiAl-based alloys containing relatively high Mn (e.g., Ti–42Al–5Mn (in at.%)) possess excellent hot workability and cost-effective advantages, but may also have poor oxidation resistance at high temperature. Hence, additional attention needs to be paid on the oxidation resistance of these alloys. In this study, a Mn-containing γ-TiAl-based alloy with the composition of Ti–42Al–5Mn has been chosen, and the oxidation behavior of this alloy with different W additions under thermal cycling conditions at 800 °C was investigated. The morphology and the composition distribution of the oxide scale were analyzed by means of scanning electron microscopy equipped with energy-dispersive spectroscopy, X-ray diffractometry and X-ray photoelectron spectroscopy. Auger electron spectroscopy depth profiling was used to investigate the effect of W on the initial stage of oxidation. It shows that the addition of 1 (at.%) W can significantly reduce the oxidation mass gain, and the oxidation reaction rate constant is decreased by an order of magnitude. The adherence of oxide scale is greatly enhanced with no spallation observed in Ti–42Al–5Mn–(0.8, 1)W after 100-h cyclic oxidation. Tungsten promotes the selective oxidation of Al and formation of a denser oxide scale which prevents the inward diffusion of oxygen; in this way, high-temperature oxidation resistance of the alloy is improved.

Characterisation of oxide layers on technical copper based on visible hyperspectral imaging

The detection and characterisation of oxide layers on metallic copper samples plays an important role for power electronic modules in the automotive industry. However, since precise identification of oxide layers by visual inspection is difficult and time consuming due to inhomogeneous colour distribution, a reliable and efficient method for estimating their thickness is needed. In this study, hyperspectral imaging in the visible wavelength range (425–725 nm) is proposed as an in-line inspection method for analysing oxide layers in real-time during processing of copper components such as printed circuit boards in the automotive industry. For implementation in the production line a partial least square regression (PLSR) model was developed with a calibration set of n = 12 with about 13,000 spectra per sample to determine the oxide layer thickness on top of the technical copper surfaces. The model shows a good prediction performance in the range of 0–30 nm compared to Auger electron spectroscopy depth profiles as a reference method. The root mean square error (RMSE) is 1.75 nm for calibration and 2.70 nm for full cross-validation. Applied to an external dataset of four new samples with about 13,000 spectra per sample the model provides an RMSE of 1.84 nm for prediction and demonstrates the robustness of the model during real-time processing. The results of this study prove the ability and usefulness of the proposed method to estimate the thickness of oxide layers on technical copper. Hence, the application of hyperspectral imaging for the industrial process control of electronic devices is very promising.

Evaluation of sputtering induced surface roughness development of Ni/Cu multilayers thin films by Time-of-Flight Secondary Ion Mass Spectrometry depth profiling with different energies O2+ ion bombardment

As a follow up on a previous paper on the quantitative evaluation of sputtering induced surface roughness and its influence on Auger electron spectroscopy depth profiling of polycrystalline Ni/Cu multilayers thin films, the ion sputtering induced surface roughness of these multilayered Ni/Cu polycrystalline thin films under low energy (0.5, 1.0 and 2.0 keV) O2+ ion bombardment and 1.0 keV Cs+ ion sputtering were investigated with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Atomic Force Microscopy (AFM). The lowest energy (0.5 keV) O2+ ion sputtering gave the best depth resolution for the different energy ion sputtering. Furthermore the 1.0 keV Cs+ ion sputtering led to a better resolution than the O2+ ion sputtering. The ToF-SIMS depth resolution was also better than the AES depth profiling with a 2.0 keV Ar+ ion sputtering. The Mixing-Roughness-Information depth (MRI) model used for fitting of the ToF-SIMS depth profiles accounts for the broadening upon experimental depth profiling owing to the effects of atomic mixing, surface roughness and information depth. The MRI fitted roughness parameters obtained from the ToF-SIMS depth profiling are in good agreement with the root-mean-square roughness obtained from the AFM topography scans of the crater bottom. Ion sputtering induced roughness and depth resolution during ToF-SIMS depth profiling of Ni/Cu multilayers were quantitatively evaluated according to the MRI fitting parameters.

Characterization of Oxide Layers on Technical Copper Material Using Ultraviolet Visible (UV-Vis) Spectroscopy as a Rapid On-Line Analysis Tool.

An ultraviolet visible (UV-Vis) spectroscopy method was developed that can quantitatively characterize a technical copper surface to determine oxide layers and organic impurities. The oxide layers were produced by a heating step at 175 ℃ for four different times (range = 1-10 min). Partial least squares (PLS) regression was used to establish a relation between the UV-Vis spectra and film thickness measurements using Auger electron spectroscopy depth profiles. The validation accuracy of the regression is in the range of approximately 2.3 nm. The prediction model allowed obtaining an estimation of the oxide layer thickness with an absolute error of 2.9 nm. Alternatively, already known methods cannot be used because of the high roughness of the technical copper surfaces. An integrating sphere is used to measure the diffuse reflectance of these surfaces, providing an average over all angles of illumination and observation.

Diffusion Behavior and Wear Mechanism of WC/Co Tools when Machining of Titanium Alloy

In this paper, fine-grain WC/Co tools were utilized in dry turning of the Ti-6Al-4V alloy. The wear modes of the cutting tools at different cutting speeds were analyzed. The diffusion behavior between the cutting tool and the workpiece was studied in detail based on the Auger electron spectroscopy (AES) depth profile technology. The diffusion wear mechanism was revealed. The results showed that the diffusion layer formed at the interface between the cutting tool and the adhering material. The diffusion ability of C was the strongest, followed by W, the weakest was Co in all the elements of the cutting tool. The chemical reactions took place close to the adhering material, forming the reaction layer. As a diffusion barrier, it was possible to limit the elements diffusion from the cutting tool to the adhering material, decrease the changes in the cutting tool composition and damages. The diffusion layer, which was weakened by diffusion, was worn off and taken away by the fast flowing chip during the cutting process, causing the diffusion wear characterized by a smooth crater formation on the tool surface.

Design of Corrosion Resistive SiC Nanolayers.

Recently, we have shown that the protecting layer of nanosize can be produced by means of ion beam mixing (IBM) of a Si/C multilayer system. The corrosion resistance of the layer correlated with the SiC amount and distribution, determined by Auger electron spectroscopy depth profiling. It has also been shown that the IBM of the Si/C system can be well described by TRIDYN simulation. By combining these two findings, it is possible to design protective layers for various arrangements of layer structure and irradiation conditions. Three different multilayer structures (with individual layer thicknesses falling in the range of 10-20 nm) have been irradiated by Ar+ and Xe+ ions at room temperature in the energy and fluence ranges of 40-120 keV and 0.25 × 1016 to 6 × 1016 ion/cm2, respectively. The carbon and silicon depth distributions have been calculated by TRIDYN simulation. From these profiles applying a simple rule for compound formation, the SiC in-depth distributions were calculated. The resulting corrosion resistance has been measured by potentiodynamic corrosion test in 4 M KOH solution. Excellent correlation between these results and the in-depth distribution (calculated by TRIDYN simulation) of SiC has been found. Thus, the design of a protective SiC coatings operating in harsh environments is possible by applying fast and cheap simulation techniques.

Extremely Thermal Stable Ni/W/TaSi<sub>2</sub>/Pt Simultaneous Ohmic Contacts to n-Type and p-Type 4H-SiC

Studying the ohmic contacts formed on ion-implanted SiC layers is fundamental to understand and to predict the behavior of practical devices. Ohmic contacts to n- (1×1019 cm−3) and p-type (1×1020 cm−3) ion-implanted 4H-SiC using Ni/W/TaSi2/Pt were investigated. No degradation of the specific contact resistance nor a minute change of the surface morphologies was observed after 300 h of 500 oC thermal treatment in air. From auger electron spectroscopy (AES) depth profiles, it was found that the oxidation of the protective platinum silicide overlayer significantly slowed down further migration of oxygen to the SiC interface. In addition, Pt and W played the role of mutual blocking, which guarantees the stability of the contact. This research suggests that the contacts are very promising for applications in harsh environments, where the simultaneously completed both on n-and p-type stability ohmic contacts is crucial.

Gold-Tin Solder Wetting Behavior for Package Lid Seals

This study examined the cause of nonwetted regions of the gold (Au) finish on iron-nickel (Fe–Ni) alloy lids that seal ceramic packages using the 80Au-20Sn solder (wt %, abbreviated Au–Sn) and their impact on the final lid-to-ceramic frame solder joint. The Auger electron spectroscopy (AES) surface and depth profile techniques identified surface and through-thickness contaminants in the Au metallization layer. In one case, the AES analysis identified background levels of carbon (C) contamination on the surface; however, the depth profile detected Fe and Ni contaminants that originated from the plating process. The Fe and Ni could impede the completion of wetting and spreading to the edge of the Au metallization. The Au layer of lids not exposed to a Au–Sn solder reflow step had significant surface and through-thickness C contamination. Inorganic contaminants were absent. Subsequent simulated reflow processes removed the C contamination from the Au layer without driving Ni diffusion from the underlying solderable layer. An Au metallization having negligible C contamination developed elevated C levels after exposure to a simulated reflow process due to C contamination diffusing into it from the underlying Ni layer. However, the second reflow step removed that contamination from the Au layer, thereby allowing the metallization to support the formation of lid-to-ceramic frame Au–Sn joints without risk to their mechanical strength or hermeticity.

Application of linear least squares to the analysis of Auger electron spectroscopy depth profiles of plutonium oxides

Application of the linear least squares (LLS) methodology allows for quantitative determination of variation in material composition with depth. LLS fits were applied to decompose and enhance the interpretation of spectra obtained by Auger electron spectroscopy during depth profiles of oxidized plutonium surfaces. By means of the LLS algorithm, chemical state assignments of the Pu P1VV/O45VV, O KLL, and C KLL Auger transitions were determined and the existence of a subsurface oxycarbide layer was identified, with confirmation of the oxide and metal components provided from comparison to previous measurements of standard samples.

Direct formation of graphene on dielectric substrate: Controlling the location of graphene formation adopting carbon diffusion barrier

The authors report a method to form multilayered graphene directly on top of a dielectric SiO2/Si substrate by the solid-phase crystallization of amorphous carbon (a-C) using Ni as a catalyst and Ti as a carbon diffusion barrier layer; the layer sequence is Ti/Ni/a-C/SiO2/Si. During annealing, carbon diffuses through Ni and forms TiC at the Ti/Ni interface, blocking further carbon diffusion to the Ti layer. During cooling, the remnant carbon in the Ni layer precipitates out at the Ni/SiO2 interface, forming multilayers of graphene. Then, both Ti and Ni are etched away using Radio Corporation of America standard cleaning (SC-I) and FeCl3-based wet etching. The graphene layers formed on top of the dielectric substrate can be utilized without further transfer methods. The best-quality of graphene is formed at 600 °C with the Raman signal D- to G-peak intensity ratio of 0.29. Auger electron spectroscopy depth profiles and sequential etching tests with SC-I and FeCl3-based etchant confirms that the Ti layer is transformed to TiOxCy or TiC layer, which may reduce the carbon diffusion flux through this layer, as expected.

Sputtered PdO Decorated TiO2 Sensing Layer for a Hydrogen Gas Sensor

We report a sputtered PdO decorated TiO2 sensing layer by radiofrequency (RF) sputtering methods and demonstrated gas sensing performance for H2 gas. We prepared sputtered anatase TiO2 sensing films with 200 nm thickness and deposited a Pd layer on top of the TiO2 films with a thickness ranging from 3 nm to 13 nm. Using an in situ TiO2/Pd multilayer annealing process at 550°C for 1 hour, we observed that Pd turns into PdO by Auger electron spectroscopy (AES) depth profile and confirmed decorated PdO on TiO2 sensing layer from scanning electron microscope (SEM) and atomic-force microscope (AFM). We also observed a positive sensing signal for 3, 4.5, and 6.5 nm PdO decorated TiO2 sensor while we observed negative output signal for a 13.5 nm PdO decorated one. Using a microheater platform, we acquired fast response time as ~11 sec and sensitivity as 6 μV/ppm for 3 nm PdO under 33 mW power.