Auger electron spectroscopy study of the sputtering effect on platinum silicide surfaces

Modifications of platinum silicides in the composition range between Pt₃Si and PtSi induced by argon ion beams were studied by angle-integrated Auger electron spectroscopy (AES). A platinum surface enrichment, which was stronger at low sputtering energies and in silicon-rich silicides, was found in the 1–5 keV ion energy range. In all silicides sputtering yield ratios Y_Si/Y_Pt of about 2.9 and 2.1 were estimated for the 1 keV and 5 keV steady state regimes respectively. Simultaneous analysis of low and high energy platinum and silicon Auger lines indicated that the platinum enrichment extended over a range of a few tens of ångströms and was slightly higher at the surface than in the subsurface region. The platinum enrichment, its energy dependence and the in-depth graded composition of the altered layer are discussed in terms of silicon preferential sputtering, recoil implantation and surface segregation. Dynamic surface composition changes were also studied, and a model which accounts for the various “shapes” of the transient regimes and their dependence on the height of the steps in the sputtering energy is shown schematically. Shape analysis of the core-valence-valence Auger lines suggests that changes in the chemical bonding in platinum silicides are induced by ion bombardment so that enrichment with platinum results in the formation of compounds which are richer in platinum.     

Ion mixing of the interface between TiNi films and glass substrates

Atomic mixing between TiNi metallic thin films and glass substrates, silica glass and borosilicate glass was induced by argon ion bombardment and investigated by means of Auger electron spectroscopy. 150 keV argon ion bombardment was carried out at room temperature to doses of 5x10¹⁶ and 1x10¹⁷ ions cm^-2. The Auger analysis demonstrated that significant intermixing occured at the TiNi-glass interface after argon ion bombardment and that the degree of atomic mixing varied, depending on the species of the constituent atoms. It was found that the titanium atoms were always transported deeper into the glass substrates than nickel atoms, and silicon atoms diffused into the TiNi overlayer more than oxygen atoms. The light boron atoms in borosilicate glass were found to diffuse least during argon ion bombardment. It was suggested that some metal silicides and oxides were formed in the reacted interface regions. Indentation-fracture tests revealed that the adhesion between the TiNi films and the glass substrates was improved substantially by argon ion mixing. The atomic mixing of each constituent atom was discussed qualitatively using a model of isotropic cascade mixing. The improved adhesion of the interface was thought to result from the interface mixing and the resultant formation of metal silicides and titanium oxides of various valence states in the interface region.     

The fabrication of metal silicide nanodot arrays using localized ion implantation

We propose a process for fabricating nanodot arrays with a pitch size of less than 25?nm. The process consists of localized ion implantation in a metal thin film on a Si wafer using a focused ion beam (FIB), followed by chemical etching. This process utilizes the etching resistivity changes of the ion beam irradiated region that result from metal silicide formation by ion implantation. To control the nanodot diameter, a threshold ion dose model is proposed using the Gaussian distribution of the ion beam intensities. The process is verified by fabricating nanodots with various diameters. The mechanism of etching resistivity is investigated via x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES).     

多能碳离子注入纯铁研究

利用离子注入表面优化技术,在不同温度下,采用多能量叠加方式将碳离子注入纯铁表面;利用XRD和AES等技术分析了表面改性层的相结构以及元素的分布;利用电化学极化法测试了注入样品的抗腐蚀性能.结果表明,573 K时注入的碳离子比373 K时注入的碳离子深;纯铁表面改性层有Fe2C、Fe3C新相生成;离子注入碳提高了纯铁表面抗电化学腐蚀的能力.     

Correlation and autoionization effects in silicide Auger spectra

We measured the Auger CVV lineshape in nickel and chromium silicides and computed the corresponding two-particle spectra. A reasonable agreement between the measured and calculated spectra is obtained if correlation effects are taken into account. The autoionization contribution to the CVV Auger lines in chromium and in chromium silicides was also determined by comparing X-ray-excited spectra with electron-excited spectra and by studying the losses in the absorption edge region.     

9Cr18轴承钢表面不同等离子体浸没离子注入强化处理技术研究

采用不同的等离子体浸没离子注入(PⅢ)工艺在9Cr18轴承钢表面进行了气体、金属、金属加气体的离子注入和碳化钛(TiC)、类金刚石(DLC)薄膜的等离子体浸没离子注入与沉积(PⅢD).对处理后的试样进行了X射线光电子能谱(XPS)、X射线衍射(XRD)、俄歇电子能谱(AES)和拉曼光谱(Raman)分析;测试了处理前后试样的显微硬度、磨痕宽度和摩擦系数.结果表明:处理后试样表面均形成了不同的改性层,且改性层中化学组成和各元素的浓度-深度分布随处理工艺的不同而变化;处理后试样的显微硬度都有较大提高,最大增幅达77.7%;表面摩擦系数由0.8下降到0.16;磨痕宽度减少了23倍;与PⅢ工艺相比,相同参数下,PⅢD处理后的试样表面综合性能更加优异.     

Thin films of rare earth metal silicides

The phase composition, conductance and surface morphology of thin films of silicides of rare earth metals (of the yttrium subgroup) were studied. The silicides were formed by annealing thin film structures of the rare earth metal (Ln) and silicon at 473–673 K for 1–120 min in vacuum. X-ray analysis revealed the formation of crystalline silicide phases of composition LnSi_2-x and of the AlB₂ structural type for all the metals concerned except scandium, gadolinium and lutetium.It was established that the formation of the crystalline silicide phase is determined by the relation between the crystallographic parameters of a rare earth metal hexagonal lattice and silicon; the critical value of the lattice mismatch a is ± 1.3%. The kinetics of formation of a silicide phase were determined by measuring the conductance of thin film structures. A model for the formation of rare earth metal silicides in thin film structures is proposed, which serves as a basis for establishing conditions for the formation of quasi-amorphous, polycrystalline or large-block rare earth metal silicide layers, with a perfect silicide-silicon interface, taking into account the crystallographic orientation and parameter relationship of the substrate and the silicide.     

Diffusion barriers in thin films

Some of the conditions which thin film diffusion barriers should satisfy are enumerated. Various ways to try to meet these conditions are illustrated by means of examples. It is shown that metal films chosen for their mutual immiscibility with the adjoining metals (passive barriers) usually fail as barriers (i.e. are non-barriers) because extended structural defects in the metal film constitute fast diffusion paths. Single-crystal barriers of such metals are effective but not practical. Barriers which are thermodynamically partially stable (partially stable barriers) and those which are fully stable (stable barriers) are discussed. Metal compounds of particular interest for such barriers are suggested. The concept of the sacrificial barrier, which is based on an irreversible loss of barrier material by interfacial reactions with the adjoining metals, is introduced and successful applications are presented. The stabilizing effect of impurities on an otherwise unstable barrier (stuffed barriers), the importance of mechanical stress and the critical influence of the fabrication process of a thin film barrier on its actual performance are described by practical examples. Values of the electrical resistivity for borides, carbides, nitrides and silicides of the early transition metals and values of the coefficient of linear thermal expansion of silicides are compiled for reference purposes.     

Synthesis and properties of some refractory transition metal diboride thin films

Thin films of ZrB₂ and TiB₂ were prepared by r.f. diode sputtering and successfully recrystallized by rapid annealing methods. The properties of the as-deposited and annealed films, which will be described, were evaluated by four-point probe resistivity measurements, Auger electron spectroscopy, Rutherford back- scattering, X-ray diffractometry and transmission and scanning electron microscopy. The resultant annealed thin film resistivities are shown to approach those of the refractory metal silicides; the materials thus appear to be promising candidates for integrated circuit metallization application.     

The diffusion barrier effect of a vanadium layer in the formation of nickel silicides

The formation of nickel silicides and vanadium silicides and the diffusion barrier effect of a vanadium layer in the formation of nickel silicides were studied for annealed metal films deposited on silicon substrates by depth profiling using secondary ion mass spectrometry and X-ray diffraction. Nickel films more than 2500 Å thick react with silicon after annealing at 400 °C for 30 min in a vacuum. A vanadium layer 250 Å thick between nickel and silicon shows a barrier effect in the nickel silicide formation after annealing at 400 °C for 30 min. The barrier effect of a vanadium layer 250 Å thick becomes imperfect after annealing at 500 °C for 30 min.     

Influence of Surface Nanocrystallization on Ti Ion Implantation of Pure Iron

In order to increase the depth or concentration of Ti ion implantation of pure iron, the surface mechanical attrition treatment(SMAT), which can fabricate a nanometer-grained surface layer without porosity and contamination in a pure iron plate, was used before ion implantation. Ti ion was implanted into the SMA treated sample and coarse-grained counterpart by using a metal vapor vacuum arc source implanter. The changing of depth and concentration of Ti was studied in a function of implantation time.By optical microscopy, transmission electron microscopy and X-ray diffraction, the grain size of the nano structured surface was studied. Micro-hardness, friction and wear behavior of nano surface layers were studied. By energy dispersive X-ray spectroscopy and Auger electron spectroscopy, the chemical composition and concentration of Ti ion in the surface implantation layer were studied. Experimental results showed that the concentration of Ti increased dramatically compared with untreated coarsegrained samples, which is attributed to the existence of higher density of defects(supersaturated vacancies, dislocations, non-equilibrium grain boundaries etc.) and compression stress field in the SMA treated nanocrystallined surface layer. The interaction between the defects and the implanted solute atoms leads to the increment of solid solubility. But the implantation depth showed inconspicuous change. It is shown that the ion range is just relevant to the energy and mass of the ion, dose of injection,the mass and density of target material.     

Mo+C双元离子注入65Nb钢表面的研究

利用 MEVVA源引出 Mo离子和 C离子 ,对 65Nb钢进行了不同剂量的离子注入 ,通过硬度测量、XRD、AES等方法研究了注入前后 65Nb钢改性层的性能、成分及相组成的变化。试验发现 Mo+ C双元离子注入 ,可在 65Nb钢注入层形成弥散的 Fe2 Mo C相 ,这是使该种基体钢经离子注入后表面硬度显著提高的重要原因。     

Ion-induced phase formation in metal-silicon systems

By using megaelectronvolt ⁴He ion backscattering techniques and transmission electron microscopy, we have investigated the interactions of ion beams with thin film structures in a number of silicide-forming systems. The mixed layer was found to be an equilibrium compound for near-noble metals and an amorphous phase for refractory metals. Differences in behavior have also been observed in near- noble metal systems. For palladium, the Pd₂Si phase grew with ion dose and remained crystalline up to high dose. For nickel, the compound Ni₂Si was formed initially and became amorphous on prolonged irradiation. All the results indicate the significance of atomic mobility at target temperatures in determining the phase formation and in explaining the sensitivity of the silicides to ion bombardment.     

Effect of Ta2O5/TiO2 thin film on mechanical properties,corrosion and cell behavior of the NiTi alloy implanted with tantalum

The NiTi shape memory alloy has been modified by plasma immersion ion implantation (PIII) with Ta at different incident currents to improve the corrosion resistance and other surface and biological properties. The surface topography, chemical components, mechanical properties, corrosion resistance and cytocompatibility are investigated. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) revealed that Ta implantation led to the formation of compact Ta₂O₅/TiO₂ nano-film on the surface of the NiTi alloy. The results of Auger electron spectroscopy (AES) showed that Ni was suppressed in the superficial surface layer of the modified NiTi alloy samples. The results of nano-indentation illustrated a lower level of nano-hardness and Young's modulus after Ta implantation. Potentiodynamic anodic polarization curves showed that the corrosion resistance of NiTi alloys was enhanced by Ta implantation. Cells reached confluency and a double-layered structure had developed after cultured for three days. The NiTi alloy modified by a moderate incident current possesses a uniform and slippery surface morphology and the largest surface roughness, leading to the best corrosion resistance and the highest cell proliferation rate, respectively.     

Improved temperature stability of Mo/Si multilayers by carbide based diffusion barriers through implantation of low energy CHx ions

To improve the thermal stability of Mo/Si multilayers, a novel method to form carbide based diffusion barriers, produced by the implantation of Si with CH_x⁺ ions, has been developed. The multilayers were grown by e-beam evaporation, while CH_x⁺ ions were implanted at the Mo/Si interfaces, using a Kaufman ion source with a Ne / CH₄ gas mixture. Energies were varied from 300 to 1000 eV. The growth as well as the implantation procedure were monitored by in situ X-ray reflectometry. Auger Electron Spectroscopy was used to characterize the surface composition before and after CH_x⁺ ion implantation. The shift of the Si LVV Auger peak revealed the formation of SiC. Ex situ X-ray reflectometry showed a thermal stability of both the reflectivity and the multilayer period up to 430 K.     

Au/Ni bilayers on n-type silicon: Metallurgical and electrical behaviour

Diffusion effects during the formation of silicides in the Ni-Au-Si system were investigated by means of ⁴He⁺ MeV Rutherford backscattering spectrometry, Auger electron spectroscopy coupled with Ar⁺ ion sputtering and X-ray diffraction as a function of the heat treatment temperature (280–350°C) and time (10–1000 min). Schottky barrier heights were used to identify the type of metal present at the silicon surface. Au/Ni/Si and Ni/Au/Si structures were prepared by electron gun deposition of thin gold and nickel films onto n-type Si〈111〉 single crystals. After thermal treatment only Ni₂Si and NiSi compounds were observed and their formation follows the phase order confirmed by previous investigations on the Ni/Si system, with a growth controlled by a lattice diffusion process. In the Ni/Au/Si〈111〉 structure the diffusion of the silicon through the gold film was detected during the formation of nickel silicide and the kinetics of growth of Ni₂Si and NiSi were similar to those studied in the Ni/Si〈100〉 system. A diffusion of gold towards the Si-NiSi interface was observed during the growth of NiSi in the Au/Ni/Si〈111〉 structure. The Schottky barrier height measurements confirm these findings.     

Improvement of Ta-based thin film barriers on copper by ion implantation of nitrogen and oxygen

Magnetron sputtered polycrystalline Ta and Ta(Si) barriers for copper metallization schemes were modified by nitrogen as well as oxygen high dose ion implantation to improve their thermo-mechanical stability. Ion bombardment changed the initial polycrystalline microstructure to amorphous-like. In contrast to pure Ta, Ta(Si) layers were already amorphous or nanocrystalline after deposition. In this case, the annealing temperature at which formation of a well crystallized structure occurs increased by approximately 100 K as a result of the implantation. In order to demonstrate the improvement in the barrier properties of the implanted Ta films, the intermixing of Ta and Cu at the interface of corresponding layer structures was measured as a function of the annealing temperature by depth profiling using Auger electron spectroscopy (AES). The thermal stability of Ta and Ta(Si) barriers increased from 600 °C/1 h for the non-implanted layers up to 750 °C/1 h after implantation of nitrogen or oxygen.     

Bioimaging of metals and biomolecules in mouse heart by laser ablation inductively coupled plasma mass spectrometry and secondary ion mass spectrometry

Bioimaging mass spectrometric techniques allow direct mapping of metal and biomolecule distributions with high spatial resolution in biological tissue. In this study laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) was used for imaging of transition metals (Fe, Cu, Zn, Mn, and Ti), alkali and alkaline-earth metals (Na, K, Mg, and Ca, respectively), and selected nonmetals (such as C, P, and S) in native cryosections of mouse heart. The metal and nonmetal images clearly illustrated the shape and the anatomy of the samples. Zinc and copper were inhomogeneously distributed with average concentrations of 26 and 11 μg g(-1), respectively. Titanium and manganese were detected at concentrations reaching 1 and 2 μg g(-1), respectively. The highest regional metal concentration of 360 μg g(-1)was observed for iron in blood present in the lumen of the aorta. Secondary ion mass spectrometry (SIMS) as an elemental and biomolecular mass spectrometric technique was employed for imaging of Na, K, and selected biomolecules (e.g., phosphocholine, choline, cholesterol) in adjacent sections. Here, two different bioimaging techniques, LA-ICPMS and SIMS, were combined for the first time, yielding novel information on both elemental and biomolecular distributions.     

Scanning auger microscopy of consolidated Al/Cu2O thermite pellets

The outer and the fractured surfaces of hot-pressed Al/Cu₂O pellets were investigated by scanning Auger microscopy (SAM). The surface images and elemental pictures of aluminum and copper are illustrated. Auger spectra of the outer surface show the existence of carbon, chlorine, oxygen, and sodium as contaminants. Auger mapping of the grains gives a clear picture of the Cu₂O particles and the general continuum of the aluminum. These pictures compare well with scanning electron micrographs taken previously of similar Al/Cu₂O pellets. In-depth elemental profiling by sputter-etching illustrates that carbon, sodium, and chlorine are surface contaminants. The analysis of the fractured surface verified the presence of an interfacial region between the aluminum and the Cu₂O of of at least 100 Å that was caused by the pelletization process at elevated temperatures.     

Thermal oxidation of transition metal silicides

A survey has been made of most publications on the oxidation of transition metal silicide films on either silicon or an SiO₂ substrate.On silicon substrates the general trend is that SiO₂ forms on the sample surface in preference to metal oxides, with the silicide layer being morphologically preserved. Thermodynamics, in terms of heats of formation and ternary phase diagrams, has been used successfully to explain the general absence of metal oxides and also to explain the exceptions to that rule. Kinetics also plays a part in the determination of the reaction products. The growth rate of SiO₂ on silicon substrates obeys the linear-parabolic law. The parabolic rate constant of silicide oxidation is essentially the same as that of silicon oxidation, indicating that the oxide and its diffusivity for the oxidant are the same for silicon and silicides. However, the linear rate constant of silicides exceeds that of silicon, and its value varies with the silicide. The differences among silicides might be attributed to differences in the atomic transport processes within the silicide; the enhancement with respect to silicon has been ascribed to the metallic nature of the silicides.On SiO₂ substrates, the oxidation ultimately leads to the formation of metal oxides as well. Instabilities of structure and loss of material can occur.The properties of the grown SiO₂ are reviewed and directions for further studies are outlined.