Electron Spectroscopy Depth Profile Analysis Research Articles

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.

Effects of Al2O3 gate insulator on the instability of amorphous indium-gallium zinc oxide thin film transistors

This study analyzes bottom-gated amorphous indium-gallium zinc oxide (a-IGZO) thin film transistors (TFTs) with different gate insulators of Si3N4 and Si3N4/Al2O3. The aim is to investigate the effect of Al2O3 on the instability of IGZO TFTs with respect to native point defects. Although the DC properties of Si3N4/Al2O3 devices are inferior to those of Si3N4 devices, the bias stress-induced hump is not observed in Si3N4/Al2O3 devices. From calculations of the oxygen exchange kinetics between the insulator and IGZO, it appears that more oxygen atoms diffuse from Al2O3 to the IGZO than from the Si3N4. This oxygen diffusion is confirmed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Auger electron spectroscopy depth-profiling analysis. In addition, more oxygen interstitials with fewer zinc interstitials are detected at the IGZO interface with Al2O3. From the results, it can be concluded that the distribution of native defects in Al2O3 devices reduces the instability of IGZO TFTs.

Luminescent properties of pulsed laser deposition (PLD) thin films of SrGa2S4:Ce3+

The influence of different substrate temperatures on the morphological and optical properties of SrGa2S4:Ce3+ thin films prepared by the pulsed reactive cross laser ablation (PRCLA) technique has been investigated for application in flat panel displays. Auger electron spectroscopy (AES) depth profile analyses on the films were performed in order to measure the stoichiometric distributions of the deposited material as a function of depth. A depletion of S was obtained for the 600°C substrate temperature sample. AES coupled with a cathodoluminescence (CL) spectroscopy system and X-ray photoelectron spectroscopy (XPS) was employed to measure the CL intensity and the CL intensity degradation as well as the surface chemical changes during and after exposure to 2keV prolonged electron irradiation. The effect of different pressures on the degradation characteristics of the SrGa2S4:Ce3+ thin films ablated at 400°C and 600°C substrate temperatures was also investigated. The rate of degradation was observed to be slower in vacuum compared to oxygen. CL emission of Ce3+ was observed for the 400°C sample and both the emissions of the 600°C sample showed a red shift of about 32–33nm, due to a change in the chemical composition and therefore a change in the crystal field. XPS results obtained for the film prepared at 600°C substrate temperature suggest that a change in elemental bonding occurred during the degradation process.

In-situ monitoring and control of hydrogenated amorphous silicon–germanium band-gap profiling during plasma deposition process

In-situ germanium content monitoring and its characteristics in SiH4/GeH4/H2 plasmas was studied during hydrogenated amorphous silicon–germanium (a-SiGe:H) film depositions. Since an appropriate band-gap profiling in a-SiGe:H deposition is very important to achieve high efficiency solar cell, the accurate monitoring and control of Ge contents are required. In this work, we found the spectral intensity ratio of silicon atom (288.2 nm) and germanium atom (303.9 nm) emission has strong relation with Ge content in plasmas. In typical, band-gap energy of films was decreased with the increasing of gas flow ratio GeH4/SiH4. However, at different total flow rate of GeH4, the band-gap was different for same gas flow ratio cases because the Ge content in plasmas was changed due to the changes of electron temperature by hydrogen dilution. On the other hand, the emission intensity ratio Ge/Si detected the band-gap variation. Using this method, therefore, we measured and control Ge/Si to make a U-shape band-gap profile which was proved by an ellipsometer and Auger electron spectroscopy depth profile analysis.

The effects of UV radiation on SiC(O)N/SiOC(− H) thin films grown on Si substrates using plasma-enhanced atomic layer deposition

Multilayer Cu/SiC(O)N/dense SiOC(−H)/porous SiOC(−H)/p-Si(100) thin-film stacks were fabricated. A 200-nm-thick porous SiOC(−H) film was deposited on an Si substrate using plasma-enhanced chemical vapor deposition. Subsequently, a 60-nm-thick dense SiOC(−H) film followed by a 20-nm-thick SiC(O)N film was deposited using plasma-enhanced atomic layer deposition. These multilayer films were then irradiated with ultraviolet (UV) light at 400°C for various times in the range 5 to 20min to improve their structural, mechanical, and electrical properties. The effects of the UV radiation on the interfacial bonding configurations and the mechanical properties of the interface between the SiC(O)N etch stop layer and the porous low-k SiOC(−H) film were investigated. The elemental concentrations of Si, C, N, and O were determined at the SiC(O)N/SiOC(−H) interfaces using Auger electron spectroscopy depth-profile analysis, and the electrical properties of the Cu/SiC(O)N/SiOC(−H)/Si metal-insulator-semiconductor structures were investigated using capacitance–voltage and current–voltage profiling. Based on our experimental results, UV exposure for 5 to 10min is optimal for improving the characteristics of Cu/SiC(O)N/SiOC(−H)/Si multilayered films.

CrN–Ag nanocomposite coatings: Control of lubricant transport by diffusion barriers

1-μm-thick self-lubricating CrN–Ag composite coatings containing 16at.% Ag were deposited on Si substrates by reactive co-sputtering at Ts=400°C, and were covered with CrN cap layers with a columnar microstructure and a thickness d=0–1000nm. Vacuum annealing at Ta=500 and 600°C for 1h causes Ag transport to the sample surface and the formation of Ag surface grains. Quantitative scanning electron microscopy and energy dispersive spectroscopy analyses show that increasing d from 0 to 10 to 100nm for Ta=500°C leads to a decrease in the areal density of Ag surface grains from 0.86 to 0.45 to 0.04μm−2, while their lateral size remains constant at 360±60nm. However, increasing Ta to 600°C causes a doubling of the Ag grain size, and a 4–30 times larger overall Ag transport. These results are explained by kinetic barriers for Ag diffusion through the porous cap layer with a porosity that decreases with increasing d, resulting in an effective activation barrier for Ag transport that increases from 0.78eV in the absence of a cap layer to 0.89eV for d=10nm and 1.07eV for d=30nm. Auger electron spectroscopy depth profile analyses of annealed layers reveal no detectable Ag within the CrN cap layer and a uniform depletion of the Ag reservoir throughout the composite coating thickness, indicating unhindered Ag transport within the composite. The overall results show that a CrN diffusion barrier cap layer is an effective approach to control Ag lubricant transport to the surface of CrN–Ag composite coatings.

Effect of catalyst for nickel films for NiSi formation with improved interface roughness

Iodine is an effective catalyst to obtain homogeneous and smooth metal films with good interface properties. We adopted an iodine catalyst during the nickel film deposition by using atomic layer deposition (ALD) with bis(1-dimethylamino-2-methyl-2-butoxide)nickel [Ni(dmamb) 2] precursor and hydrogen reactant gas. The effect of iodine catalyst to nickel nucleation process was studied. The deposited films were silicided by rapid thermal process (RTP) which was performed by varying temperature from 400 °C to 900 °C in nitrogen ambient. The crystalline properties of nickel and nickel silicide films were examined by X-ray diffractometer (XRD) with various deposition temperatures. The interface properties and the surface morphology of nickel silicide films were studied by using Auger electron spectroscopy (AES) depth profile analyses and scanning electron microscopy (SEM). The experimental results showed that the iodine-catalyzed silicide film, which have a clean and smooth interface, exhibit lower resistivity, and lower leakage current density compared to that of non iodine-catalyzed films in implemented n +/p junction diode.

Effect of alkaline cleaning and activation on aluminum alloy 7075-T6

The effect of alkaline cleaning and activation on the composition and thickness of the oxide layer on aluminum alloy 7075-T6 was studied. E–pH diagrams were developed to predict the effect of alkaline cleaning and activation solutions on the stability of the oxide surface layers. The thickness of the native oxide layer was determined to be ∼30 nm by Auger electron spectroscopy depth profiling analysis. The outer ∼20 nm was rich in magnesium while the remaining ∼10 nm was rich in aluminum. Cleaning in a 9.1 pH alkaline solution was found to remove the magnesium-rich layer and leave behind an aluminum-rich oxide layer ∼10 nm thick. Activation in alkaline solutions of NaOH (pH > 12.9) or Na 2CO 3 (pH > 11.5) produced an oxide that was ∼20 to 60 nm thick and rich in magnesium. Alkaline cleaning and activation altered the oxide composition and thickness making it possible for deposition of thicker cerium-based conversion coatings (∼100 to 250 nm) compared to only alkaline cleaning (∼30 nm), with application of one spray cycle of deposition solution.

Anomalous atomic transport in driven systems: Ion-sputtering induced enhanced intermixing and cratering in Pt/Ti

Probing the anomalous nanoscale intermixing using molecular dynamics (MD) simulations in the Pt/Ti bilayer we reveal the enhancement of the interfacial atomic transport. It is shown that the Pt atoms undergo anomalous atomic transport across the interface of Pt/Ti with surprisingly high rates. In particular, the low-energy (0.5 keV) ion-sputtering induced transient enhanced intermixing has been studied by MD simulations. Ab initio density functional calculations have been used to check and reparametrize the employed heteronuclear interatomic potential. The transient enhanced intermixing behavior explains the long diffusity tail in the concentration profile obtained by Auger electron spectroscopy depth profiling analysis in Pt/Ti bilayer (reported in Ref. P. Sule, M. Menyhard, L. Kotis, J. Labar, J.F. Egelhoff Jr., J. Appl. Phys. 101 (2007) 043502). Moreover, we point out that atomic mass-anisotropy has no effect on interdiffusion in the nanoscale hence other (unknown) factors are responsible for the anomalous interface broadening. The mean-square of atomic displacements scales superlinearly in Pt/Ti, while show sublinear scaling behavior in Ti/Pt. The exponent of a fitted power-law expression is 1.65 in Pt/Ti which suggests the anomalous character of intermixing. Anomalously long (ballistic) atomic jumps of Pt atoms across the interface are seen also only in Pt/Ti. Moreover, the robust Pt atomic injection into the Ti bulk takes place together with an enhanced surface cratering in Pt/Ti. No such behavior is seen for Ti/Pt. These surprising atomistic features could be the signature of an anomalous driven process not reported yet for bulk systems.

Borate Volatility from SOFC Sealing Glasses

The volatility of borate species from glasses developed for solid oxide fuel cell seals was studied using thermodynamic calculations and compared with experimental results. Vapor pressure diagrams were used to identify the most volatile compounds under a range of expected operational conditions, e.g. oxidizing and reducing atmospheres with water vapor, at temperatures in the range of 700°–1000°C. The species with the highest vapor pressures were BO2(g) under dry conditions and B3H3O6(g) under wet, reducing conditions. The depletion of boron from glass surfaces to depths beyond 100 nm was characterized using Auger electron spectroscopy depth profile analysis. Weight loss experiments were conducted on several different glass compositions. The cumulative weight loss from a glass with 20 mol% B2O3 (“glass #59”) was about 10 times greater than from a glass with 2 mol% B2O3 (“glass #27”), under the same conditions. The activation energy for volatilization from glass #59 was 371±86 kJ/mol and was 272±65 kJ/mol for “glass #27.” The cumulative weight loss of each composition in forming gas with 30% water vapor was greater than in dry air at 800°C. Volatile species were collected in a water trap, and these results confirmed predictions about the effect of atmosphere and B2O3 content on volatilization behavior.

Structural investigation of direct current magnetron sputtered Ti/NiV/Ag layers on n +Si substrate

Direct current sputtered Ti/NiV/Ag thin film metallization scheme on n +Si substrate was studied to reveal the nature of interface structure and adhesion related mechanisms. Ti/NiV/Ag scheme is usually applied when solderable backside contact is required. When thermal annealing of this sputtered metallic stack is performed below 550 °C, delamination frequently occurs. By energy dispersive X-ray spectroscopy analysis the delaminating interface was found to be between Si and Ti layer. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) depth profile analyses through metallic stack/Si substrate on samples exhibiting poor adhesion showed that a very thin amorphous Ti–Si phase was grown at Ti/Si interface when annealed at 400 °C. The XPS analyses of peeled layer and the surface of remained Si substrate after adhesion failure show that the delamination occurs between Si-substrate and amorphous Ti–Si layer. No contamination at Ti/Si interface was found as a possible origin for adhesion degradation. AES depth profiling of samples having good adhesion and annealed at 550 °C, revealed the formation of Ti-silicide and Ni-silicide at metal layers/Si interface, which in combination with Ni–Ti compound formed above this interface promote the adhesion.

Interfacial Structure of Ta 2O 5/Si Film and Photoactivity

Tantalum oxide (Ta 2O 5) thin film photocatalysts were prepared on single crystal Si(110) substrates via sol-gel and spin coating methods. Ta 2O 5 crystallinity was improved, and the crystal size became larger with the increase of heat-treating temperature. The interface diffusion and reaction of the film were studied by using Auger electron spectroscopy (AES) depth profile and line shape analysis. Diffusion was dominant at the interface layer when the calcination temperature was below 700 °C. When the temperature reached 800 °C, both interface diffusion and reaction occurred. The photocatalytic activity was studied using aqueous salicylic acid as a degradation probe molecule under UV-light irradiation. It was found that Ta 2O 5/Si film showed a photocatalytic activity similar to that of TiO 2/Si film.

Intermixing in Cu/Co: Molecular Dynamics Simulations and Auger Electron Spectroscopy Depth Profiling

The ion-bombardment induced evolution of intermixing is studied by molecular dynamics simulations and by Auger electron spectroscopy depth profiling analysis (AESD) in Cu/Co multilayer. It has been shown that from AESD we can derive the low-energy mixing rate and which can be compared with the simulated values obtained by molecular dynamics (MD) simulations. The overall agreement is reasonably good hence MD can hopefuly be used to estimate the rate of intermixing in various interface systems.

Growth and Auger electron spectroscopy characterization of donut-shaped ZnO nanostructures

Zinc oxide (ZnO) nanodonuts have been obtained by vapor phase transport process utilizing a mixture of ZnO, graphite and erbium oxide powder as the evaporation source. ZnO nanodonuts prepared under various thermal processes indicate that ZnO nanodonuts start forming during the initial thermal ramp up stage. A subsequent holding of the growth temperature at 1000 °C causes the nanodonut to evolve into perfectly donut-shaped nanostructure. Additional deposition of ZnO on top of the nanodonut during the holding of the furnace temperature at 1000 °C result in partially filled nanodonuts or hemispherical nanostructures, or donuts that are completely buried beneath ZnO film. Auger electron spectroscopy depth profile analysis indicates that the deposited ZnO film is stoichiometric, whereas the nanodonuts and the completely filled hemispherical nanostructures are porous and are oxygen deficient. The volume density of the nanodonut is estimated to be 20% that of the background ZnO film.

Asymmetric transient enhanced intermixing in Pt/Ti

The ion-sputtering induced intermixing is studied by Monte Carlo transport of ions in matter (TRIM), molecular-dynamics (MD) simulations, and Auger electron spectroscopy depth profiling (AES-DP) analysis in Pt/Ti/Si substrate (Pt/Ti) and Ta/Ti/Pt/Si substrate (Ti/Pt) multilayers. Experimental evidence is found for the asymmetry of intermixing in Pt/Ti, and in Ti/Pt. In Ti/Pt we obtain a much weaker interdiffusion (broadening at the interface) than in Pt/Ti. The unexpected enhancement of the interdiffusion of the Pt atoms into the Ti substrate has also been demonstrated by simulations. We are able to capture the essential features of intermixing using TRIM and MD simulations for ion-beam sputtering and find reasonable values for interface broadening which can be compared with the experimental measurements. We explain the asymmetry of IM by the possible occurrence of transient enhanced diffusion in Pt/Ti which manifests in the exponential high diffusity tail of the AES concentration profile.

Plasma immersion ion implantation in arc and glow discharge plasmas submitted to low magnetic fields

The influence of low magnetic fields ( B ≤ 130 G) on the plasma parameters of a DC nitrogen glow discharge is investigated with a double Langmuir probe. The discharge was optimized for maximum plasma density for different values of a magnetic field, and a condition was found in which density was enhanced by an order of magnitude. In this condition partial suppression of secondary electron emission was obtained during ion implantation experiments. Silicon samples implanted in this optimum density condition showed larger retained dose and penetration depth compared with samples treated in non-magnetized plasmas as shown by Auger electron spectroscopy depth profile analysis. These results were compared with previous similar experiments in much denser magnetized vacuum arc plasmas, in which total suppression of secondary electrons (SE) was obtained, corroborating the theory that the maintenance of a virtual cathode for SE suppression is favored by higher plasma density. Silicon samples implanted in magnetized magnesium plasmas exhibited much larger doses (as expected) and penetration depths (not so obvious) than the ones treated in non-magnetized plasmas. The deeper ion penetration obtained in magnetized gaseous and vacuum arc plasmas indicates that an enhanced diffusion may be taking place induced by the large ion bombardment in dense plasmas.

Front and back side Auger electron spectroscopy depth profile analysis to verify an interfacial reaction at the HfN∕SiO[sub 2] interface

Sputter-induced artifacts can create the appearance of an interfacial reaction between Hf-based films and the underlying SiO2 in sputter depth profiles. A combination of front and back side Auger electron spectroscopy depth profile analysis is used to distinguish between a native interfacial reaction at the interface between HfN and SiO2 and a potential sputtering artifact. Experimental results show that a native reaction occurs; however, the extent of the reaction may be over-represented in the front side profile due to a sputter artifact component.

Manufacture, microstructure and mechanical properties of CrWN and CrN/WN nanolayered coatings

Chromium nitride and tungsten nitride coatings were fabricated in sequence to form a CrN/WN nanolayered coating by rf reactive magnetron sputtering technique with a dual-gun system. The CrWN coating was also manufactured for comparison. The bilayer period of the nanolayered CrN/WN coating were controlled at 10 and 24 nm. Periodic feature of elemental distribution of the nanolayered coatings was revealed by the Auger electron spectroscopy depth profiling analysis. The phase identification results indicated that the composite CrWN coating was composed of CrN phase with solid-solution of W, while CrN and amorphous/nanocrystalline WN and W 2N phases was observed in the nanolayered CrN/WN coatings. The CrN/WN nanolayered microstructure was evaluated by scanning and transmission electron microscopy. Nanoindentation technique was employed to evaluate the mechanical properties, including hardness and Young's modulus. The nanolayered CrN/WN coatings exhibited a high hardness around 30 GPa, which was superior to that of the CrWN coating. The nanolayered structure with confined grains of the nitrides in the nano range was beneficial to the enhancement of the mechanical performance for the multilayer coating.

Corrosion behaviour of Zr-based bulk glass-forming alloys containing Nb or Ti

Cylindrical bulk samples of Zr–Cu–Al–Ni–X (X=Nb, Ti up to 5 at.%) alloys with 3 mm diameter were prepared by copper mould casting. The microstructure of the samples was characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The corrosion properties of the Nb- and Ti-containing alloys were studied in comparison to those of the bulk glass-forming Zr 55Cu 30Al 10Ni 5 alloy in aqueous electrolytes at 298 K. It was found that in 0.1 M Na 2SO 4 electrolyte with pH=8, the corrosion resistance of these new alloys is comparable to that of the quaternary alloy. However, in 0.01 M NaCl solution, the pitting susceptibility of the Nb- or Ti-containing bulk alloys is significantly lower. Auger electron spectroscopy depth profile analysis (AES) was applied to passivated sample surfaces in order to study the role of alloying elements for corrosion protection. Nb-containing amorphous alloys with higher Zr content than that of the Zr 55Cu 30Al 10Ni 5 reference alloy form comparatively thinner passive films which are more enriched in copper and nickel species close to the interface oxide/alloy and which provide a lower protective effect.

Swift heavy ion-induced recrysallization of silicon-on-insulator (SOI) structures

Buried Si 3N 4–Si interfaces and overlayer in silicon-on-insulator (SOI) structures were improved by irradiation with 100 MeV 107Ag after the synthesis of buried silicon nitride layers by high dose nitrogen ion-implantation. Auger electron spectroscopy (AES) depth profile analysis illustrates that the MeV heavy ions irradiation in the SOI structure, modifies the distribution of nitrogen that results in better stoichiometry of the buried silicon nitride layers and abrupt Si 3N 4–Si interfaces. Electron spin resonance (ESR) technique shows the improvement in the crystalline structure of the Si over layer. Current–voltage and high frequency capacitance–voltage ( C– V) characteristics were studied, and electrical breakdown measurements were performed on metal nitride silicon (MNS) structures fabricated after removing the Si over layer in the SOI structure. In the ion-beam irradiated SOI specimens, buried silicon nitride layer show a high breakdown field strength of 4.5–6.5 MV/cm as compared to that of 3.0–3.9 MV/cm in the unirradiated one. The C– V analysis of the MNS capacitors reveals that the buried Si 3N 4–Si substrate interface exhibits a better quality with reduced fixed insulator charge and interface state densities after the ion-beam irradiation. Mid-gap interface state density at the buried Si 3N 4–Si substrate interface was as low as 1.0×10 11 cm −2 V −2 after the ion-beam irradiation, which is comparable to that of silicon nitride films deposited on silicon (Si) by the conventional low pressure chemical vapor deposition technique. The role of MeV ion-beam irradiation in improving the properties of SOI structures has been discussed on the basis of various models.