Secondary Ion Mass Spectrometry Depth Profiling Research Articles

Ge nanocrystals in lanthanide-based Lu2O3 high-k dielectric for nonvolatile memory applications

Ge nanocrystals embedded in lanthanide-based high-k dielectric (amorphous Lu2O3 in this work) were formed using pulsed laser deposition followed by rapid thermal annealing in N2 ambient. The formation and evolution of the Ge nanocrystals have been studied using transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) in conjunction with depth profiling, and secondary ion mass spectroscopy (SIMS) analysis. Plan-view TEM images indicated that the formation of nanocrystals was first initiated during the deposition process. The annealing treatment significantly enhanced the nucleation of Ge nanocrystals, resulting in a high areal density of 7×1011cm−2 Ge nanocrystals with a mean size of about 6nm in diameter in the amorphous Lu2O3 matrix. XPS depth profile analysis revealed that Ge nanocrystals were predominantly formed from the precipitation of Ge nuclei from the oxide phase. A low annealing temperature of 400°C was sufficient to dissociate the GeO2 and GeOx leading to the formation of Ge nanocrystals. An accumulation of Ge species close to the upper Ge∕Lu2O3 interface was observed from XPS and SIMS depth profile analysis. Different charge storage behaviors observed from the memory capacitor devices before and after annealing could be correlated to the changes in structure and composition of the film. The memory capacitor device fabricated from the annealed sample showed efficient charge storage effect under a low operation voltage without significant initial charge decay.

Factors influencing charge capacity of vanadium pentoxide thin films during lithium ion intercalation/deintercalation cycles

The intercalation of vanadium pentoxide by lithium ions leads to a change in optical properties, a process that is of value in thin-film electrochromic devices. In this study, films of V2O5, deposited on indium tin oxide (ITO) glass coupons by a sol-gel process, were challenged by increasing numbers of charge-discharge cycles ranging from 72 to 589 full cycles. The samples were characterized by x-ray photoelectron spectroscopy (XPS) and then examined in the deintercalated state by time-of-flight secondary ion mass spectroscopy (SIMS). XPS enabled measurement of the thickness and composition of the solid-electrolyte interface and provided evidence of the residual V4+ concentration within the top few nanometers of the surface. The SIMS profile gave direct information on the thickness of the films and on the thickness loss caused by rinsing the samples after the electrochemical exposure. Determination, by SIMS, of the concentration of lithium ions has enabled a correction to be made for the amount of inactive material within the electrochemically active region of the film. The SIMS depth profiles for lithium in the four samples are similar, with a marked buildup of Li at the interface with the ITO. This interphase zone had a thickness of ∼27nm and was electrochemically inactive, enabling a further correction to be made. Thus, by means of the XPS and the SIMS results the chemistry and thickness of the films could be fully characterized. The remaining inconsistency between capacity (between 35% and 100% of the anticipated charge) and number of cycles is ascribed to edge effects arising from the method used for production of the coupons.

Spatial determination of gold catalyst residue used in the production of ZnO nanowires by SIMS depth profiling analysis

AbstractIn this paper we demonstrate how secondary ion mass spectrometry (SIMS) can be applied to ZnO nanowire structures for gold catalyst residue determination. Gold plays a significant role in determining the structural properties of such nanowires, with the location of the gold after growth being a strong indicator of the growth mechanism. For the material investigated here, we find that the gold remains at the substrate–nanowire interface. This was not anticipated as the usual growth mechanism associated with catalyst growth is of a vapour–liquid–solid (VLS) type. The results presented here favour a vapour–solid (VS) growth mechanism instead. Copyright © 2007 John Wiley & Sons, Ltd.

Ultrashallow depth profiling using SIMS and ion scattering spectroscopy

AbstractThe accuracy of ultrashallow depth profiling was studied by secondary ion mass spectrometry (SIMS) and high‐resolution Rutherford backscattering spectroscopy (HRBS) to obtain reliable depth profiles of ultrathin gate dielectrics and ultrashallow dopant profiles, and to provide important information for the modeling and process control of advanced complimentary metal‐oxide semiconductor (CMOS) design. An ultrathin Si3N4/SiO2 stacked layer (2.5 nm) and ultrashallow arsenic implantation distributions (3 keV, 1 × 1015 cm−2) were used to explore the accuracy of near‐surface depth profiles measured by low‐energy O2+ and Cs+ bombardment (0.25 and 0.5 keV) at oblique incidence. The SIMS depth profiles were compared with those by HRBS. Comparison between HRBS and SIMS nitrogen profiles in the stacked layer suggested that SIMS depth profiling with O2+ at low energy (0.25 keV) and an impact angle of 78° provides accurate profiles. For the As+‐implanted Si, the HRBS depth profiles clearly showed redistribution in the near‐surface region. In contrast, those by the conventional SIMS measurement using Cs+ primary ions at oblique incidence were distorted at depths less than 5 nm. The distortion resulted from a long transient caused by the native oxide. To reduce the transient behavior and to obtain more accurate depth profiles in the near‐surface region, the use of O2+ primary ions was found to be effective, and 0.25 keV O2+ at normal incidence provided a more reliable result than Cs+ in the near‐surface region. Copyright © 2007 John Wiley & Sons, Ltd.

Geochemical variations in late-stage growth of volcanic phenocrysts revealed by SIMS depth-profiling

In the petrologic and geochemical study of volcanic rocks, microlites have become an important tool with which to determine magma decompression rate and ascent path prior to eruption. However, studies in experimental petrology and kinetic modeling indicate that growth of pre-existing phenocrysts will occur over a much wider range of decompression-induced undercoolings than microlite nucleation. Consequently, we have developed a method using secondary ion mass spectrometry (SIMS) depth profiling to measure geochemical trends recorded during the final stage of phenocryst growth. To test and demonstrate the new method, we examined explosive and effusive eruptive products collected from Soufrière Hills volcano, Montserrat. Plagioclase feldspar crystals were removed from clasts of pyroclastic deposits. Phenocrysts were individually selected on the basis of euhedral morphology and a relatively homogeneous distribution of surface contamination, such as volcanic glass. Crystals were cleaned, embedded in In, and analyzed by SIMS in depth-profiling mode. We used an O 2+ primary ion beam, which provides a faster sputtering rate than the typically utilized O - primary beam. A normal-incidence electron gun is used for charge compensation. Ten isotopes were examined over 2-10 h periods and the resulting crater depth was determined. Data show variable trends in An, K, and Fe that we interpret to represent late-stage physical variations within the magma prior to eruption. The continuous chronology of geochemical data obtained from the SIMS analyses presented here provide information with unprecedented (~0.1 μm) resolution, allowing researchers to determine physical conduit conditions during magma ascent from the chamber to eruption at the surface

The Use of SIMS and SEM for the Characterization of Individual Particles with a Matrix Originating from a Nuclear Weapon

The application of scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS) for characterization of mixed plutonium and uranium particles from nuclear weapons material is presented. The particles originated from the so-called Thule accident in Greenland in 1968. Morphological properties have been studied by SEM and two groups were identified: a "popcorn" structure and a spongy structure. The same technique, coupled with an energy-dispersive X-ray (EDX) spectrometer, showed a heterogeneous composition of Pu and U in the surface layers of the particles. The SIMS depth profiles revealed a varying isotopic composition indicating a heterogeneous mixture of Pu and U in the original nuclear weapons material itself. The depth distributions agree with synchrotron-radiation-based mu-XRF (X-ray fluorescence microprobe) measurements on the particle (Eriksson, M., Wegryzynek, D., Simon, R., & Chinea-Cano, E., in prep.) when a SIMS relative sensitivity factor for Pu to U of 6 is assumed. Different SIMS identified isotopic ratio groups are presented, and the influence of interferences in the Pu and U mass range are estimated. The study found that the materials are a mixture of highly enriched 235U (235U:238U ratio from 0.96 to 1.4) and so-called weapons grade Pu (240Pu:239Pu ratio from 0.028 to 0.059) and confirms earlier work reported in the literature.

Effect of heating on the behaviors of hydrogen in C-TiC films with auger electron spectroscopy and secondary ion mass spectroscopy analyses

C-TiC films with a content of 75% TiC were prepared with magnetron sputtering deposition followed by Ar + ion bombardment. Effect of heating on the behaviors of hydrogen in C-TiC films before and after heating was studied with Auger Electron Spectroscopy and Secondary Ion Mass Spectroscopy (SIMS) analyses. SIMS depth profiles of hydrogen after H + ion implantation and thermal treatment show different hydrogen concentrations in C-TiC coatings and stainless steel. SIMS measurements show the existence of TiH, TiH 2, CH 3, CH 4, C 2H 2 bonds in the films after H + ion irradiation and the changes in the Ti LMM, Ti LMV and C KLL Auger line shape reveal that they have a good hydrogen retention ability after heating up to the temperature 393 K. All the results show that C-TiC coatings can be used as a hydrogen retainer or hydrogen permeable barrier on stainless steel to protect it from hydrogen brittleness.

Ion mass interferences and matrix effects on SIMS depth profiling of thin Ti/Si multilayer films induced by hydrogen, carbon and oxygen contaminations

Secondary ion mass spectrometry (SIMS) with argon beam has been used to determine the depth profile of ultra-thin Ti/Si multilayer system deposited on crystalline silicon wafers by laser ablation of titanium and silicon targets. The redistribution of elements in the structure has been studied after subsequent high temperature (HT)-treatment, what leads to uniform metastable phase of the composite films. The data obtained by positive atomic ion detection generated from sample before HT process show anomalous behavior of titanium distribution. We discuss the influence of contaminations on the results and attribute apparent Ti + signal in Ti/Si-based films to numerous ion mass interferences and matrix effects present during sputtering of the multilayers. The negative SIMS analysis in conjunction with detection of sputtered TiO 2 − and Si 2 − molecular species is proposed for depth profiling of Ti/Si to avoid artifacts in Ti and Si profiling, respectively, caused by the presence of contaminations in the multilayers.

Redistribution of arsenic during the reaction of nickel thin films with silicon at relatively high temperature: Role of agglomeration

The redistribution of As during the solid state reaction of nickel thin films with a n-doped (1 0 0) Si substrate has been analysed by secondary ion mass spectrometry (SIMS), X-ray reflectivity (XRR) and sheet resistance measurements. Heat treatment between 400 °C and 650 °C leads to the formation of the monosilicide (NiSi) and to very different SIMS depth profiles of As. The role of the agglomeration of NiSi on the SIMS measurements of As redistribution and particularly on As concentration at NiSi/Si interface is shown.

Spectroscopic evaluation of the structural and compositional properties of GaN xAs 1− x superlattices grown by molecular beam epitaxy

GaN x As 1− x multiple-quantum-well (MQW) samples ( x ≤ 0.025) grown by molecular beam epitaxy have been studied by photoluminescence (PL) spectroscopy, high-resolution X-ray diffraction (HR-XRD), secondary-ion mass spectrometry (SIMS) and ultra-high-resolution infrared local-vibrational-mode (IR LVM) spectroscopy in order to determine their compositional and structural properties. Compositional data from PL spectroscopy and HR-XRD, derived using simple models of the superlattice structure, show good agreement. SIMS depth profiles show that the wells are triangular, and are wider and shallower than predicted, with nitrogen present in the barrier layers. A comparison between SIMS and HR-XRD suggests the presence of interstitial nitrogen for samples with the highest nominal concentrations. By contrast, IR LVM measurements demonstrate that substitutional nitrogen incorporates linearly with increasing nitrogen fraction.

Surface roughening and erosion rate change at low energy SIMS depth profiling of silicon during oblique [formula omitted] bombardment

Surface roughening of boron δ -doped Si samples under low energy (0.5 keV/ O 2 + , 44 ° and 54 ° , and 1.0 keV/ O 2 + , 48 ° ) O 2 + bombardment at oblique incidence with and without oxygen flooding was studied with atomic force microscopy (AFM) and secondary ion mass spectrometry (SIMS). The erosion rate, the surface topography and the depth resolution as a function of depth have been measured. Changes in secondary ion yields have been correlated with changes in surface topography. It is found that the surface roughness depends on impact energy and incidence angle without flooding. The roughness decreases with decreasing impact energy. For the same energy (0.5 keV/ O 2 + ), the wavelength increases slightly with increasing angle of incidence and the roughness increases with increasing angle of incidence. With flooding, the roughness can be efficiently avoided. The best conditions to avoid roughness when analysing ultra shallow profiles with our magnetic sector instrument is 0.5 keV/ O 2 + , 44 ° with flooding. A procedure for the depth calibration of the profiles revealed that surface roughness causes an erosion rate change as measured using the shift of the position of the measured B peaks with and without flooding. The consequences of the roughness in terms of depth resolution of the profiles are analysed with and without flooding. Moreover, we show that the value of the Gaussian broadening parameter of the depth resolution function is closely related to the final dispersion of the heights in the crater bottom.

SIMS depth profiling of rubber-tyre cord bonding layers prepared using 64Zn depleted ZnO

Zinc oxide and copper/zinc sulphide layers are formed during vulcanisation and moulding of rubber to brass-coated steel tyre reinforcing cords. Previous studies have described how zinc diffuses through the rubber–brass interface to form zinc sulphide, and combines with oxygen to create zinc oxide during dezincification. The zinc is usually assumed to originate in the brass of the tyre cord, however, zinc oxide is also present in the rubber formulation. We reveal how zinc from these sources is distributed within the interfacial bonding layers, before and after heat and humidity ageing. Zinc oxide produced using 64Zn-isotope depleted zinc was mixed in the rubber formulation in place of the natural ZnO and the zinc isotope ratios within the interfacial layers were followed by secondary ion mass spectroscopy (SIMS) depth profiling. Variations in the relative ratios of the zinc isotopes during depth profiling were measured for unaged, heat-aged and humidity-aged wire samples and in each case a relatively large proportion of the zinc incorporated into the interfacial layer as zinc sulphide was shown to have originated from ZnO in the rubber compound.

Alternative method of using an electron beam for charge compensation during ultralow energy secondary-ion-mass spectroscopy experiments

Secondary-ion-mass spectroscopy (SIMS) analysis of insulators using positive primary beams is routinely performed by compensating the induced charge with a coincident electron beam. In the case of SIMS depth profiling, the established method consists of focusing an electron beam into the SIMS crater with a current well in excess of that of the primary ion beam. In this article we used both caesium and oxygen beams to bombard float glass, and intrinsic and doped diamond samples while varying the electron beam current and the area bombarded by electrons. We have studied how the electron beam to primary ion current density ratio modifies the charging conditions. We demonstrate that, for certain insulating and highly resistive materials, defocusing of the electron beam so as to cover the whole of the sample surface and part of the sample holder is extremely effective. It is also observed that the defocused electron beam works efficiently for an electron to primary ion current density ratio less than 1. We attribute this to the enhancement of surface conductivity through the creation of carriers in the conduction band, and observe similar effects when irradiating the surface with a laser diode. The ability to use a defocused electron beam will significantly aid profiling of insulating and highly resistive materials where alignment of the coincident electron and ion beams is problematic. Defocusing of the electron beam also offers the possible advantage of reducing or eliminating localized electron beam damage of certain material surfaces prior to and during profiling.

SIMS characterisation of superconductive MgB 2 layers prepared by ion implantation and pulsed plasma treatment

Thin films of magnesium diboride (MgB 2), an intermetallic compound, possessing superconductive properties, were analysed by secondary ion mass spectrometry (SIMS). The samples were prepared using a new two-step technique of ion implantation followed by plasma treatment. Two kinds of structures were obtained when boron and magnesium were used as targets. Eighty kiloelectronvolt magnesium ions were implanted into boron samples and 100 keV boron ions into magnesium strips. Plasma treatment was performed using hydrogen and argon 1 μs plasma pulses of fluence 2–5 J/cm 2. Magnetic moment and electrical conductivity measurements confirmed superconducting properties of the obtained layers. SIMS depth profiling was performed using 5 keV Ar + ion beam (06-350E Physical Electronics) and quadrupole mass spectrometry (QMA 410 Balzers). Sensitivity factors for boron and magnesium were obtained based on SIMS analyses of bulk reference samples MgB 2, B and Mg. Obtained results allow modifying technology parameters of thin film MgB 2 synthesis.

Depth profiling using C 60+ SIMS—Deposition and topography development during bombardment of silicon

A C 60 + primary ion source has been coupled to an ion microscope secondary ion mass spectrometry (SIMS) instrument to examine sputtering of silicon with an emphasis on possible application of C 60 + depth profiling for high depth resolution SIMS analysis of silicon semiconductor materials. Unexpectedly, C 60 + SIMS depth profiling of silicon was found to be complicated by the deposition of an amorphous carbon layer which buries the silicon substrate. Sputtering of the silicon was observed only at the highest accessible beam energies (14.5 keV impact) or by using oxygen backfilling. C 60 + SIMS depth profiling of As delta-doped test samples at 14.5 keV demonstrated a substantial (factor of 5) degradation in depth resolution compared to Cs + SIMS depth profiling. This degradation is thought to result from the formation of an unusual platelet-like grain structure on the SIMS crater bottoms. Other unusual topographical features were also observed on silicon substrates after high primary ion dose C 60 + bombardment.

Correlation between silicon‐nitride film stress and composition: XPS and SIMS analyses

AbstractThe characteristics of silicon‐nitride films deposited with plasma‐enhanced chemical vapour deposition (PECVD) can vary not only in composition, but also in terms of physical properties. An important parameter in the fabrication of micro‐electro‐mechanical systems (MEMS) devices is the control and tailoring of the film stress. In fact, silicon‐nitride film stress can vary from tensile (up to 800 MPa) to compressive (−500 MPa), depending on the PECVD deposition conditions (e.g. plasma pressure, plasma frequency and power).In this work, we have investigated the role of frequency mixing on the resulting film structure and stress. The layers were prepared with a commercial PECVD deposition chamber, keeping all deposition parameters constant except the ratio between low (380 kHz) and high (13.56 MHz) frequency. Film stress values were compared with compositional and chemical data from X‐ray photoemission spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) measurements. These two techniques are complementary.The comparison between quantified SIMS depth profiles and the XPS HF etch‐back method shows a good agreement in nitrogen profile behaviour. In addition, XPS analyses have provided a suitable chemical characterisation of the different growth processes.We demonstrate that this analytical approach is really effective for the physico‐chemical characterisation of PECVD grown silicon nitride. Copyright © 2006 John Wiley & Sons, Ltd.

Characterization of Wear and Surface Reaction Layer Formation on Aerospace Bearing Steel M50 and a Nitrogen-alloyed Stainless Steel

Abstract The formation of reaction layers on surfaces in mechanical contact is strongly affected by the tribological loading conditions, the materials used, the lubricant and the service temperature. An appropriate balance between reactivity of material and lubricant in tribological systems decreases wear and friction and increases the durability. The goal of this paper is to compare the reaction layer formation on a standard aerospace bearing steel AMS 6491 (M50) with that on a high strength stainless steel grade AMS 5898 exhibiting a nominal chemical compositions of 0.82C-4.1Cr-1V-4.2Mo (wt. %) and 0.3C-0.4N-15.2Cr-1Mo (wt. %), respectively. As lubricant jet engine oil Mobil Jet II has been used. Rolling contact fatigue (contact pressure: 6 GPa) and ball-on-disk tests (contact pressure: 1.6 GPa, sliding speed 10 cm/s) at room temperature and at 150°C were employed to study the effect of extreme loading conditions and temperature dependence of the reaction layer formation. The contact areas were inspected by means of optical profilometry, scanning electron microscopy (SEM), and secondary ion mass spectrometry (SIMS) in order to determine type, thickness, homogeneity, and distribution of the reaction layers in the contact zone. The main result of the study is that the reaction layer formation is significantly less on the stainless steel grade compared with M50. SIMS depth profiles were determined in order to explain the differences in the wear characteristics of the two materials. The reaction layers are mainly built up of PXOY molecules, which might be phosphates resulting from the tricresyl phosphate (TCP) lubricant additive. The role of the chemical reaction of the steel and TCP regarding the layer formation will be discussed.

Formation of precipitates in heavily boron doped 4H-SiC

Secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) are utilized to study precipitation and the solubility of B in 4H-SiC epitaxial layers super saturated with B. Heat treatments are performed in Ar atmosphere in an rf-heated furnace at temperatures between 1700 and 2000 °C. SIMS ion images, and TEM micrographs reveal the formation of two types of precipitates where the larger, more thermally stable one is suggested to be B 4 C. The boron solubility is determined from SIMS depth profiles and is shown to follow the Arrhenius expression: 7.1 × 10 22 exp(−1.4 eV/ k B T ) cm −3 over the studied temperature range.

SIMS depth profiling of CdTe-based solar cells grown on sapphire substrates

CdTe/CdS/TCO solar cell structures were grown on sapphire substrates especially to investigate the impurity distributions in them. The study was performed using quantitative secondary ion mass spectrometry (SIMS) depth profiling, from the CdTe back surface through to the TCO layer. The species investigated were F, Br, Na, Si, Sn, In, O, Cl, S and Te, and for the purpose of comparison, some of the structures were investigated in their as-grown state. It has been shown that while Si concentration profiles are similar to those for structures grown on glass, Na was more than one order of magnitude lower when sapphire was used as substrate instead of glass. This demonstrates that Na diffused from the glass substrate. Moreover, the overall Na concentration in structures with and without CdCl 2 treatment showed that Na also originated from the CdCl 2, which is in accordance with our recently reported studies of impurities in CdCl 2. The concentration of Br was found to be at least 10 times higher in the etched structures compared to the un-etched ones, especially near the CdTe surface where there was a clearly resolved diffusion profile. In the CdTe active layer, the concentration of F was about 4 × 10 15 cm − 3 with a relatively flat level but with surface segregation following heat treatment. Finally, the potential diffusion of Sn and In from the sputtered SnO 2/ITO:F TCO layer into the CdTe active layer was investigated. It was found that there was no measurable diffusion of Sn from the SnO 2 layer into CdTe. Moreover, the SnO 2 layer played an important role in preventing the diffusion of In from the In-containing TCO layer.

Oxygen Pipe Diffusion in Sapphire Basal Dislocation

The oxygen self-diffusion behavior in deformed sapphire single crystals (α-Al2O3 sapphire) with a high density of unidirectional basal dislocations was examined in the temperature range of 1424-1636°C using 18O isotopes and secondary ion mass spectrometry-depth profiling techniques. The pipe and lattice diffusion kinetics were best described by r2Dp=4.6×10-20 exp (-4.8[eV]/kT) [m4/s] and Dl=2.9×10-1 exp (-5.5[eV]/kT) [m2/s], respectively. Both the magnitude of pre-exponential factor and activation energy for oxygen pipe diffusion were in good agreement with that of indirect measurements of pipe diffusion deduced from the annihilation of dislocation dipoles. The measured bulk diffusion coefficient is also in good agreement with previously reported data having activation energies ranged between 5.5-6.1 eV.