Auger Electron Spectroscopy Depth Research Articles

Phenomenological Model of Non-Evaporated Getter for Micro-electromechanical Systems (MEMS) Applications

ABSTRACTThere has been increasing interest in the development and use of micro-electromechanical systems (MEMS) for various applications. Some MEM devices such as gyroscopes, accelerometers and bolometers, must be sealed under vacuum, at pressures below 10 millitorr, for efficient operation. A gas absorbing material (getter) is placed in the packages of these devices, to help maintain vacuum levels over service lives of many years. Heating under vacuum, just prior to sealing the package, activates getter, of this type. This study was undertaken to develop a model that could be used to estimate the quantity of getter needed as well as optimize the activation process subject to process constraints on time and temperature.The material studied was a titanium and zirconium-based alloy (7:3 by weight) non-evaporable getter in the form of strips produced by SAES Getters. The zirconium alloy consisted of zirconium (70.0%), vanadium (24.6%) and iron (5.4%) by weight. The getter was analyzed under different ambient conditions of temperature, time and atmospheric pressure. Auger electron spectroscopy (AES) depth profiling was used to analyze the diffusion depth of the contaminant gases absorbed by the getter material under each condition. The data acquired from the depth profiles were fit to a simple diffusion model. This model is currently being validated, by activating the getter material under various ambient conditions, and measuring pressures and gas compositions inside packages using a residual gas analyzer (RGA). The utility of this model for optimization of getter activation and estimating package vacuum levels over time will be discussed.

Kinetics of the oxidation of GaAs(100) at high pressure: an Auger electron spectroscopy study

Abstract The time evolution of a GaAs(100) ‘epi-ready’ wafer exposed to air at normal conditions of pressure and temperature has been studied by means of Auger electron spectroscopy and argon-ion depth profiling. Our results show that the oxygen signal near the surface evolves during times as long as 5 months. The evolution of the oxygen signal is accompanied by the penetration of an oxidation front as the air exposure increases. This behavior is confirmed by means of different indicators obtained through the study of the low-energy Auger line-shape spectra.

Rolling Contact Testing of Vapor Phase Lubricants—Part III: Surface Analysis©

Infrared microscopy (μ-FTIR), Raman spectroscopy, Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize bearing surfaces lubricated from the vapor phase. Results are presented for surface films generated with a tertiary-butyl phenyl phosphate (TBPP) and a polyphenylether (5P4E). Infrared bands consistent with inorganic poly-phosphates and phosphites were detected in deposition films generated with the TBPP lubricant. Raman shifts consistent with graphite of short range order were detected in films deposited by both lubricants. However, specimens lubricated by the 5P4E had several Raman shifts consistent with Fe2O3 and Fe3O4. Iron oxides were not detected in deposition films generated with the TBPP lubricant. AES depth profiles indicate a predominant mixture of iron and carbon in the TBPP deposition film; whereas, the 5P4E film predominately consists of iron and oxygen. Localized corrosion pitting generated with the TBPP lubricant was analyzed using AES, SEM, and EDS. The results indicate that a modified matrix rich in phosphorus, oxygen and carbon, with a corresponding depletion of iron, transcends to depths of at least 10 microns in the substrate in damaged regions. Lubrication and failure mechanisms of vapor lubricated bearings are proposed based on the results. Presented at the 51st Annual Meeting in Cincinnati, Ohio May 19–23, 1996

Quantitative chemical depth profiles of ZrN/BN multilayers

Multilayers of ZrN/BN have been deposited on Si(100) using a double ion beam sputtering system. The multilayers have been characterized by transmission electron microscopy, Rutherford backscattering spectroscopy and Auger electron spectroscopy (AES) depth profiles in order to get a quantitative analysis of the components and contaminants in the different layers and at their respective interfaces. Factor analysis is used to deconvolute the different chemical states of the components and to identify secondary phases and compounds that determine the quality of the multilayer. Two secondary phases have been observed at the different interfaces: one is associated with the incorporation of oxygen, mainly in the zirconium layer, and leads to the formation of ZrNxOy. In addition we have observed that Ar bombardment during the AES depth profile leads to the formation of ZrBxNy in all the interfaces. © 1998 John Wiley & Sons, Ltd.

Investigation of metallization schemes for high temperature devices based on silicon carbide

The suitability of several metallization schemes for high temperature sensors and devices based on silicon carbide was investigated. Auger electron spectroscopy (AES) depth profiling was used for the detection of possible interface reactions and thermal induced diffusion processes. Changes in the structure of the films under the influence of high temperature were observed by transmission electron microscopy (TEM). The maximum operation temperature for the metallization with aluminum as coverlayer was found at 450 °C. The ability of gold with underlying tungsten nitride as diffusion barrier to work at temperatures above 450 °C was shown.

Assessment of diffusion processes in thin films

Thin spectrally selective solar absorber coatings have to be prevented from degradation caused by the substrate acting as a diffusion source. The effect of an intermediate layer sputtered in between the substrate and the absorber layer was investigated. The samples were tested under high-temperature exposure and under air and vacuum conditions measuring the solar absorptance and the emittance. Auger electron spectroscopy (AES) depth profiling studies were performed in order to investigate the changes of the element concentration caused by the ageing process. The behaviour of the diffusion barrier was examined in a two-layer system. A mathematical model for the grain boundary diffusion was developed and compared with the experimental results.

Laser processing of YBCO thin films on sapphire for microwave applications

Laser ablation has been used to fabricate YBa/sub 2/Cu/sub 3/O/sub 7-x/(YBCO) thin film on sapphire substrates for microwave applications. The Interfaces between the YBCO laser ablated thin films and the r-plane Al/sub 2/O/sub 3/ substrates have been investigated by a transmission electron microscopy (TEM) and an Auger electron spectroscopy (AES) depth profile. The PrBa/sub 2/Cu/sub 3/O7-x (PBCO) buffer layer has been used to prevent the interdiffusion. The interfaces of YBCO/Al/sub 2/O/sub 3/ and YBCO/PBCO/Al/sub 2/O/sub 3/ have been compared. The intermediate diffusion layer in the YBCO film deposited on bare sapphire was visible between the film and the substrate but no diffusion layer between the YBCO/PBCO thin film and the substrate was observed directly by the cross-section image of TEM. The thickness of the diffusion layer on bare sapphire is about 300 /spl Aring/. This result of TEM is consistent with that of AES depth profile. We have fabricated a perturbed superconducting ring resonator on PBCO buffered sapphire for the microwave application. A fundamental resonance peak split was observed in the frequency range of 7.0-8.4 GHz.

Characterization of interfaces of alumina – high alloyed steels by SST and AES depth profiling

Thin alumina films, deposited at 280°C on several high alloyed steels by low pressure metal-organic chemical vapour deposition (LP-MOCVD), were annealed at 0.17 kPa in a nitrogen atmosphere for 2, 4 and 17 h at 600 and 800°C. The effect of the annealing process on the adhesion of the thin alumina films was studied using a scanning scratch tester (SST) and Auger electron spectroscopy (AES). The best adhesion properties were obtained with commercial oxide dispersion strengthened (ODS) high temperature alloys, especially type PM 3030. From the normally high alloyed stainless steels, type AISI-321 showed the best properties. The other stainless steel - alumina combinations showed after a thermal treatment a decrease of the critical load, L c . Using ODS alloys as the substrate resulted in an increased L c . AES-studies revealed that the increased L c can be explained by 1) the presence of sulphur trapping elements, avoiding segregation of sulphur near the interface which could have a detrimental effect on scale adherence, and 2) titanium and carbon enrichment at the interface resulting in a beneficial effect on the adherence between the oxide and the substrate.

A microstructural study on the surface and interface of CdTe/CdS solar cells

The surface and interface properties of CdTe/CdS solar cells, including interfacial mixing, surface and interface geometrical morphology, CdTe grain size and preferential crystal orientation of CdTe layers were studied using Auger electron spectroscopy (AES) depth profiling, atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, optical reflectance (OR) and X-ray diffraction (XRD) techniques. The correlation between the surface and interface properties and CdTe/CdS solar cell performance was also investigated. AES depth profiling was used to analyse the interdiffusion between the CdTe and CdS layers. Atomic force microscopy (AFM) suggests that the interfacial geometrical morphology has a significant influence on the photovoltaic property of CdTe/CdS solar cells. Rough interfaces tend to increase the photovoltaic conversion efficiency of solar cells because of multiple reflections. X-ray diffraction shows that polycrystalline CdTe/CdS solar cells with higher efficiencies appear to be orientated with more (1 1 1) planes of CdTe parallel to the macrosurface, but CdTe single crystals with differently indexed surface planes show almost the same reflection behaviour. Further theoretical and experimental analyses are therefore needed to clarify this observation.

Several Efficiency Influencing Factors In CdTe/CdS Solar Cells

AbstractSeveral efficiency influencing factors in MOCVD-grown CdTe/CdS solar cells, including preferential crystal orientation of CdTe layers, CdTe grain size and surface roughness, interfacial mixing, and surface and interface geometrical morphology, are studied. X-ray diffraction (XRD) shows that polycrystalline CdTe/CdS solar cells with higher efficiencies tend to have more (111) planes of CdTe parallel to the macro-surface. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis reveal the relationship between the grain size/surface roughness and cell efficiency. Secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) depth profiling show that the interfacial geometrical morphology has a significant influence on the efficiency of CdTe/CdS solar cells. Finally it is shown that interfacial mixing reduces the number of interfacial states and recombination centers and the energy loss due to internal reflectance, enhancing the performance of the solar cells.

Pulsed laser deposition of Bi4Ti3O12 thin films and their anomalous imprint characteristics

Using La0.5Sr0.5CoO3(LSCO) or Pt film as a bottom electrode layer, epitaxial Bi4Ti3O12(BTO) thin films were deposited on MgO(001) substrates by pulsed laser deposition. X-ray diffraction patterns showed that the c-axes of BTO films are oriented normal to the substrate surface. Interestingly, an epitaxial Pt/BTO/Pt film showed a strongly preferred polarization state directed towards the top electrode in spite of the symmetric electrode configuration. The inprint state did not change significantly in the pulse test with DC bias. These anomalous behaviors suggest that the imprint characteristic is highly correlated with interfacial states between the electrodes and the BTO films. To understand space charge effects in the metal-ferroelectric contacts, imprint characteristics of the thin film capacitors with various top electrodes were investigated. Auger Electron Spectroscopy(AES) depth profile was measured, to check the possibility of a interdiffusion of the bottom electrode with the BTO layer. Interdiffusion (or reaction) between the BTO and Pt (bottom electrode) seems to be responsible for the strongly preferred polarization.

Formation of Ni/Pt/Au Ohmic Contacts to p-GaN

AbstractWe report a new Ni/Pt/Au (20/30/80 nm) metallization scheme to achieve a low ohmic contacts to p-type GaN with a carrier concentration of 9.4 × 1016 cm-3. A Mg-doped GaN layer (0.5 μm) was grown on (0001) sapphire substrate by metalorganic chemical vapor deposition (MOCVD). All metal thin films were deposited on the p-GaN layer in an electron-beam evaporation system. Samples were annealed by a rapid thermal annealing (RTA) process at a range of temperatures from 300 °C to 850 °C under a flowing Ar atmosphere. A circulartransmission line model (c-TLM) was employed to calculate the specific contact resistance, and current-voltage (I-V) data were measured with HP4155A. The Ni/Pt/Au contacts without the annealing process showed nearly rectifying characteristics. The ohmic contacts were formed on the samples annealed at 500 °C for 30 sec and the I-V data showed a linear behavior. The specific contact resistance was 2.1 × 10-2 Ωcm2. However with increasing the annealing temperature above 600 °C, ohmic contacts were again degraded. Auger electron spectroscopy (AES) depth profiles were used to investigate the interfacial reactions between the trilayer and GaN. AES results suggested that Pt plays a significant role in forming ohmic contact as an acceptor at the interface. Atomic force microscope (AFM) also showed that the samples with good ohmic contact have very smooth surface.

Surface and Interface Properties of InSb Epitaxial Thin Films Grown on Gaas by Low Pressure Metalorganic Chemical Vapor Deposition

AbstractThere is increasing interest in the epitaxial growth of high quality InSb thin films on GaAs substrates for many device applications such as infrared optoelectronics. The large lattice mismatch (14.6%) between InSb and GaAs has meant that both growth techniques and conditions have a large influence on the interface properties and consequently the film quality. A surface science study, by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) together with Nomarski microscopy, on the surface and interface properties of InSb/GaAs by metalorganic chemical vapor deposition is presented. It is found fromthe XPS data that the ambient surface is composed of InSb, In2O3, Sb2O3 and Sb2O5. The interdiffusion phenomena are studied by AES depth profiling; the width of interdiffusion region is determined to be 50±10 nm for all the samples grown at different V/III ratios. This is narrower than the data previously obtained for InSb/GaAs interfaces produced by metalorganic magnetron sputtering. The results also demonstrate that uniform and stoichiometric InSb films have been obtained, and that the reproducibility of the MOCVD technique is excellent.

Ni Removal from Si Wafers by Low-Pressure UV-Chlorine Cleaning

ABSTRACTNi removal from Si wafers by low-pressure UV/Cl2 chemical vapor cleaning (CVC) was investigated at substrate temperatures of 150–200°C. Sub-monolayer Ni coverages were applied to Si(100) by ultrahigh-vacuum physical vapor deposition (UHV-PVD). The Ni surface concentration was reduced to the Auger electron spectroscopy (AES) detection limit by a 2-min UV/Cl2 exposure at 300 mTorr and 200°C. AES depth profiling revealed that Ni was not contained within nor buried beneath the chlorosilyl layer formed by UV/Cl2 CVC. In contrast, Ni was not removed under similar conditions from Si surfaces covered by a thin UV/air oxide layer. These results indicate that Ni removal from Si occurs by a photochemical etching mechanism and not by direct volatilization of NiCl2. Atomic force microscopy (AFM) of Si surfaces after UV/Cl2 CVC indicated that Si etching was limited ˜20 å and that the surface was smooth (RMS roughness = 1.6 å).

Removal of Titanium Oxide Grown on Titanium Nitride and Reduction of VIA Contact Resistance using a Modern Plasma Asher

ABSTRACTIn making multi-level interconnects, a via layer is generally made of a dielectric layer grown on a TiN/AlSiCu/TiN metal stack. The via contact hole to the lower level metal is first etched after metal patterning and intermetal oxide deposition, then the resist mask for via etch is stripped in an oxygen plasma at high temperature before filling the via with tungsten or aluminum. However, during the resist stripping process, the titanium nitride (TiN) is exposed to oxygen radicals and becomes oxidized. This oxidized surface leads to high via resistance and may cause yield loss and poor adhesion of the subsequently deposited metal. Thus, the oxide layer must be removed completely before filling the via hole.Utilizing a modern asher and combining microwave downstream plasma and low damage RIE we have successfully developed an integral process to strip the resist and to remove any oxidized TiN film. This process also gives clean vias that are free of polymer residues from the etching process.Samples were characterized using Auger electron spectroscopy (AES), scanning electron microscopy (SEM), ellipsometry and via resistance measurements. The AES depth profile measurements and ellipsometry show clearly that a titanium oxide has grown onto TiN during the oxygen downstream ashing and is completely removed when adding the RIE step. The electrical measurements show that the resistance of vias cleaned with this two step process in a single tool is comparable to that of vias cleaned with Ar sputtering using a separate tool after the oxygen ashing process.

Diffusion Barrier Reliability with Respect to the Role of Tin Stoichiometry Between Al Metallization and Si Substrate

AbstractIn this study, the relation between interdiffusion in Al/ TiN thin film couples and diffusion barrier stability has been investigated. The TiN diffusion barrier was deposited by reactive sputtering in an Ar-N2 gas mixture. The stoichiometry of TiN was achieved by varying the nitrogen-to-argon ratio in the sputtering gas. Interdiffiusion occurred after annealing for 30 minutes at 475°C and 575°C. Diffusion processes and interfacial reactions with respect to TiN stoichiometry were investigated via Auger Electron Spectroscopy (AES) depth profiling and X-ray diffraction (XRD). The barrier reliability with respect to the stoichiometry changes was established; nitrogen-deficient TiN films result in a high degree of interdiffiusion and decomposition at annealing temperatures of 475°C and 575°C. AI3Ti and AlN intermetallic compounds were formed at the interfaces. The sheet resistance of Al films was measured by four-point probe method. Resistance increases for all the annealed films were due to interdiffusion between Al and TiN. The degree of interdiffusion was analyzed by using AES and XRD.

Combined EPMA and AES depth profiling of a multilayer Ti-Al-O-N coating

In order to compare thin-film electron probe microanalysis (EPMA) and Auger electron spectroscopy (AES) regarding reliability in quantifying chemical compositions of Ti-Al-O-N coatings with depth, a multilayer was prepared on a silicon wafer by using reactive ionized cluster beam deposition technique. Within a total thickness of about 25 nm the composition of the multilayer varied step by step from Ti-Al-O-N at the bottom to Al-O at the top. AES and, as an innovation, EPMA crater edge profiling was applied to measure the composition with depth. For quantification special thin-film EPMA techniques based on Monte Carlo simulations were applied. The chemical binding states of Al and Ti with depth were analysed using a high resolution energy analyser (MAC 3) for the AES investigations working in the direct mode. According to the deposition procedure the concentration profiles of the components varied with depth for both AES and EPMA measurements. AES provided a better depth resolution than EPMA. To get a true calibration of the depth scale an in-situ measurement method like an optical interferometry will be required. Assuming that the relative sensitivity factors are available AES depth profiling delivers concentration profiles with good accuracy. The new EPMA application provided quantitative depth profiles concerning concentration and coverage. For EPMA crater edge profiling the coating needs to be deposited on a foreign substrate because depth distributions of elements being present in both the layer and the substrate cannot be resolved. The combination of AES-depth profiling with EPMA crater edge profiling techniques is a powerful tool to analyse heterostructures quantitatively.

Layer formation on silicon steel by processing in H2/H2O at elevated temperatures

Silicon steel (Fe-3wt%Si), as used for transformers and generators, has been annealed in wet hydrogen at elevated temperatures. The composition, sequence, and thicknesses of the layers found by conversion electron Mossbauer spectroscopy (CEMS) and Auger electron spectroscopy (AES) depth profiling for a 10 minutes anneal in different atmospheres are reported. In the range from 500°C to 720°C we observed carbide formation, indicating that the decarburization is hindered. Above 800°C, the layers consist of fayalite or of fayalite and iron oxides, depending on the oxygen potentialaO. At 843°C, the onset of iron oxide formation was found ataO=0.33.

Protective Zirconia Thin Films on Metal Substrates.

ABSTRACTStabilized Zirconia thin films were deposited by R. F. Magnetron Sputtering onto iron substrates. Deposition parameters such as gas pressure and R. F. voltage were optimized to obtain homogeneous and well adherent protective coatings. The morphology and structure of films before and after thermal treatments were investigated by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Thermogravimetrical Analysis (TGA).Auger Electron Spectroscopy (AES) depth profiling techniques were used to obtain the chemical distribution of the elements in order to study the influence of two important parameters on the adhesion of the ceramic: the presence of a thin layer of native metal oxide and the residual surface roughness after polishing.The effectiveness of coatings to protect the metal substrate against high temperature oxidation in air was evaluated by thermogravimetrical analysis at 773K. The protective action of the ceramic film was well demonstrated.

Near-surface stoichiometry of high temperature superconducting YBaCuO thin films

The surface morphology and near-surface chemical composition of high temperature superconducting Y–Ba–Cu–O thin films have been studied by Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) depth profiling. These films were fabricated on SrTiO3 substrates by RF diode sputter deposition and subsequent furnace annealing in oxygen. The chemical composition at and near the surface of thin films was found to differ from the bulk composition. At about 500 Å below the surface the Y, Ba, and Cu stoichiometry, as determined by AES, gradually approach that of the film interior. These results suggest that, for furnace annealed films, there may exist a minimum deposited Y–Ba–Cu–O film thickness in which superconductivity is possible. It was also found that the calculated copper concentration determined by AES during depth profiling is significantly lower than its actual value.