Probing buried interfaces on Ge-based metal gate/high-k stacks by hard X-ray photoelectron spectroscopy

In this contribution, we present results of a non-destructive in-depth analysis of concentration of chemical components at buried interfaces on Ge-based CMOS by means of hard X-ray photoelectron spectroscopy (HAXPES) and low angle X-ray reflectivity (XRR). Two samples composed of a Ge/Si/SiO₂/HfO₂/TiN stack, with layer and interlayer thicknesses of 2500, 0.9, 0.5, 4.9, 3.4 nm and 2500, 0.7, 1, 5.8, 3 nm have been studied. The use of electrons with kinetic energies from few eV up to 15 keV enables to tune the information depth being able to analyze the desired interface in a non-destructive way. XRR enables the determination of the exact layer thickness and density. The results suggest that the Si interlayer prevents the Ge oxidation. Depth profiles of the electronic structure have been obtained for both samples by following the evolution of the photoemission signal from the Hf 2p_3/2 core level as a function of the photoelectron kinetic energy. The depth profile of the electronic structure reveals the presence of a chemical shift of the Hf 2p_3/2 core level, which is related to an interfacial bonding state. Our results demonstrate the excellent capability of HAXPES to study buried interfaces in a non-destructive way.     

A universal algorithm for calculating the backscattering factor in Auger-electron spectroscopy

We describe a universal Monte Carlo algorithm that can be used for the efficient calculation of backscattering factors (BFs) for quantitative Auger-electron spectroscopy (AES). This algorithm makes use of the continuous slowing-down approximation and the electron stopping power instead of simulation of individual inelastic-scattering events. This approach is attractive because it can be applied to any material with an empirical formula for the stopping power, available data for differential elastic-scattering cross sections, and an empirical formula for inner-shell ionization cross sections. We report BFs for the Si KL₂₃L₂₃, Cu L₃M₄₅M₄₅, Ag M₅N₄₅N₄₅, and Au M₅N₆₇N₆₇ Auger transitions in the corresponding elemental solids. These BFs were calculated for normal incidence of the primary beam, primary energies from near threshold for ionization of the relevant core levels to 20 keV, and Auger-electron emission angles of 10°, 60°, and 80°. We found satisfactory agreement between these BFs and values obtained from a more accurate algorithm in which individual inelastic-scattering events were simulated. Percentage deviations between BFs from the two algorithms were <2% for Au, <5% for Ag, <7% for Cu, and <10% for Si for primary energies likely to be used in practical AES. These deviations arise mainly from our use of stopping powers from the empirical formula rather than more reliable values calculated from experimental optical data.     

Fabrication and analysis of buried iron silicide microstructures using a focused low energy electron beam

We fabricated iron and iron silicide microstructures on an Si(1 0 0) clean surface via electron beam induced process of Fe(CO)₅ multilayer and subsequent annealing. The fabricated microstructures were in situ analyzed by Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). We successfully analyzed the coverage and chemical states of the artificial deposited iron structure area-selectively by AES. The artificial iron structure was fabricated after heating to above 350 K to desorb residual Fe(CO)₅ species. The artificial structure was observed even after 1190 K annealing by SEM, but AES measurements showed it to be covered by Si atoms. We concluded that the buried iron silicide microstructure was formed by the present process.     

AES, LEED and PYS investigation of Au deposits on InSe/Si(1 1 1) substrate

Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED) and Photoelectron Yield Spectroscopy (PYS) measurements have been used to monitor the interaction of gold (Au) deposits on InSe/Si(1 1 1) substrate. Au has been sequentially deposed under ultra-high vacuum onto 40 Å-thick film of layered semiconductor InSe which is epitaxially grown by molecular beam epitaxy (MBE) on a Si(1 1 1)1 × 1-H substrate and kept at room temperature. Au coverage varies from 0.5 monolayer to 20 monolayers (ML) (in terms of InSe atomic surface plane: 1 ML = 7.2 1014 at/cm²) which is corresponding to 1.30 Å of Au-metal. The Au/InSe/Si(1 1 1) system was characterized as function of Au deposit, we noticed an interaction at room temperature starts as an apparent intercalation process until 5 ML. Beyond this dose Au islands begin to form on the sample surface without interaction with InSe substrate, thus the interface is far from to be a simple junction Au-InSe.     

An AES study of surface segregation of AgAu alloys with ion bombardment and annealing

Equilibrium segregation and selective sputtering in the surface of AgAu alloys have been investigated systematically with argon ion bombardment and with annealing by means of AES measurements. Slight enrichment of Ag was observed on the alloy surfaces after the annealing of the alloys at 550°C, while relatively large enrichment of Au was observed on the ion-bombarded surfaces with the use of Au (240 eV) and Ag (300 eV) Auger electrons. With the aid of other Auger electrons with different escape lengths, it was found that the concentration varies with distance from the surface within the sampling depth of the Auger electrons. On the basis of the above facts, the depth profiles were proposed for the annealed and the ion-bombarded surfaces. The uppermost surface layer is enriched more with Ag than the apparent AES observations on both the ion-bombarded and the annealed surfaces. The proposed depth profiles on both the surface layers were compared with previous results by different authors.     

Growth of fullerene on Ag and hydrogen-passivated Si substrates: Effect of electron beam exposure on growth modes

We have used Auger electron spectroscopy (AES) to investigate the effect of electron beam exposure on growth modes of fullerene (C₆₀) on substrates like Ag and hydrogen-passivated Si(1 1 1). The electron beam comprises of 3.4 keV electrons, which are used in the AES study. To investigate the effect, Auger signal (AS) vs. deposition time (t) measurements were conducted in a sequential mode, i.e., alternating deposition of C₆₀ and analysis using the electron beam. Duration of AES data collection after each deposition was the duration of exposure to electron beam in this experiment. For the growth study of C₆₀ on Ag, three AS-t plots were recorded for three different durations of exposure to electron beam. Changes in the AS-t plot, depending on the duration of exposure to the electron beam, reflect the electron beam-induced damage. Electron beam-induced damages of C₆₀ produce carbon materials of different densities and consequently transmission coefficient (α) of Auger electron through this material changes. In order to fit the AES (AS vs. t) data a model has been used which simultaneously provides the growth mode and the transmission coefficient. Observation of an increasing transmission coefficient with the increasing duration of exposure to the electron beam from α=0.34 to 0.60 indicates the change of the nature of the carbon material due to the partial damage of C₆₀.     

AES analysis of nitridation of Si(100) by 2–10 keV N+2 ion beams

Ion beam nitridation of Si(100) as a function of N⁺₂ ion energy in the range of 2–10 keV has been investigated by in-situ Auger electron spectroscopy (AES) analysis and Ar⁺ depth profiling. The AES measurements show that the nitride films formed by 4–10 keV N⁺₂ ion bombardment are relatively uniform and have a composition of near stoichiometric silicon nitride (Si₃N₄), but that formed by 2 keV N⁺₂ ion bombardment is N-rich on the film surface. Formation of the surface N-rich film by 2 keV N⁺₂ ion bombardment can be attributed to radiation-enhanced diffusion of interstitial N atoms and a lower self-sputtering yield. AES depth profile measurements indicate that the thicknesses of nitride films appear to increase with ion energy in the range from 2 to 10 keV and the rate of increase of film thickness is most rapid in the 4–10 keV range. The nitridation reaction process which differs from that of low-energy (< 1 keV) N⁺₂ ion bombardment is explained in terms of ion implantation, physical sputtering, chemical reaction and radiation-enhanced diffusion of interstitial N atoms.     

Auger electron spectroscopy investigation of sputter induced altered layers in SiC by low energy sputter depth profiling and factor analysis

The thickness of the altered layer created by ion bombardment of the 6H–SiC single crystal was determined by means of Auger electron spectroscopy (AES) depth profiling in conjunction with factor analysis. After pre-bombardment of the surface by argon ions with energies 1, 2 and 4 keV until the steady state, the depth profiles of the induced altered layers were recorded by sputtering with low energy argon ions of 300 eV. Since the position and shape of the carbon Auger peak depend on the perfection of the crystalline structure, they were used for depth profile evaluation by factor analysis. In this way the depth profiles of the damaged surface region could be estimated in dependence on the ion energy. As a result, the thickness of the altered layer of SiC bombarded with 1, 2 and 4 keV Ar ions using an incident angle of 80° as well as the corresponding argon implantation profile could be measured.     

Origins of interdiffusion, crystallization and layer exchange in crystalline Al/amorphous Si layer systems

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/a-Si and a-Si/Al bilayers was studied upon annealing at low temperatures between 165 and 250 °C, by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Upon annealing the inward diffusion of Si along grain boundaries in Al takes place, followed by crystallization of this diffused Si. Continuous annealing leads to (more or less) layer exchange in both types of bilayers. The change in bulk energy of the Al phase (release of macrostress and microstrain, increase of grain size) promotes the occurrence of layer exchange, whereas changes in surface and interface energies counteract the layer exchange.     

GexSi1-x/Si超晶格的俄歇深度剖面分析

用氩离子刻蚀和俄歇电子能谱测量Ge_xSi_1-x/Si应变层超晶格的成分深度分布,得到Ge,Si两种成分随深度的周期性变化,在二次电子象中观察到刻蚀坑边缘的明暗交替的周期性结构。讨论了用俄歇深度剖面分布作超晶格结构分析的特点及其局限性。 关键词：     

CEMS study of silicon implanted iron

Thin layers of iron-rich Fe-Si alloys were formed by silicon implantation into iron at room temperature with different energies (100, 200, and 300 keV) and ion doses (2 × 10¹⁷ to 1×10¹⁸ cm^–2). The produced layers were investigated by⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS) to identify the phases formed by the ion implantation. Auger electron spectroscopy (AES) was used to measure the concentration depth profiles of the implanted silicon. Depending on the implantation parameters different disordered Fe-Si structures were detected. At low doses only magnetic phases were formed while at high doses a non-magnetic phase with a hitherto unknown structure appeared. Annealing of the samples resulted first in the formation of a D0₃-like short-range order and a slow decrease of the non-magnetic phase, and subsequently in the migration of Si out of the investigated depth range.     

Plasma processing of the Si(0 0 1) surface for tuning SPR of Au/Si-based plasmonic nanostructures

Au nanoclusters have been deposited on Si(0 0 1) surfaces by sputtering of a metallic Au target using an Ar plasma. Different wet and dry treatments of the Si(0 0 1) surface, including dipping in HF solution and exposure to H₂ and N₂ plasmas, have been applied and the effects of these treatments on the Au nanoparticles/Si interface, the Au nanoclusters aspect ratio and the surface plasmon resonance (SPR) energy and amplitude are investigated exploiting spectroscopic ellipsometry and atomic force microscopy. It is found that the Au nanoclusters aspect ratio depends on the extent of the Au-Si intermixing. The thicker the Au-Si interface layer, the larger the Au nanoparticles aspect ratio and the red-shift of the SPR peak. Furthermore, SiO₂ and the H₂ plasma treatment inhibit the Si-Au intermixing, while HF-dipping and the N₂ plasma treatment favour Au-Si intermixing, yielding silicide formation which increases the Si wetting by Au.     

离子注入形成SOI结构的界面及埋层的俄歇能谱研究

本文中研究了O⁺(200keV,1.8×10¹⁸/cm²)和N⁺(190keV,1.8×10¹⁸/cm²)注入Si形成SOI(Silicon on Insulator)结构的界面及埋层的化学组成。俄歇能谱的测量和研究结果表明:注O⁺的SOI结构在经1300℃,5h退火后,其表层Si和氧化硅埋层的界面存在一个不饱和氧化硅状态,氧化硅埋层是由SiO₂相和这不饱和氧化硅态组成,而且氧化硅埋层和体硅界面不同于表层Si和氧化硅埋层界面;注N⁺的SOI结构在经1200℃,2h退火后,其氮化硅埋层中存在一个富N的疏松夹层,表层Si和氮化硅埋层界面与氮化硅埋层和体硅界面性质亦不同。这些结果与红外吸收和透射电子显微镜及离子背散射谱的分析结果相一致。还对两种SOI结构界面与埋层的不同特征的原因进行了分析讨论。 关键词：     

Ta/Ni/Ta multilayered ohmic contacts on n-type SiC

The interface formation, electrical properties and the surface morphology of multilayered Ta/Ni/Ta/SiC contacts were reported in this study. It was found that the conducting behavior of the contacts so fabricated is much dependent on the metal layer thickness and the subsequent annealing temperature. Auger electron spectroscopy (AES) and X-ray diffraction analyses revealed that Ni₂Si and TaC formed as a result of the annealing. The Ni atoms diffused downward to metal/SiC interface and converted into Ni₂Si layer in adjacent to the SiC substrate. The released carbon atoms reacted with Ta atoms to form TaC layer. Ohmic contacts with specific contact resistivity as low as 3 × 10⁻⁴ Ω cm² have been achieved after thermal annealing. The formation of carbon vacancies at the Ni₂Si/SiC interface, probably created by dissociation of SiC and formation of TaC during thermal annealing, should be responsible for the ohmic formation of the annealed Ta/Ni/Ta contacts. The addition of Ta into the Ni metallization scheme to n-SiC restricted the accumulation of carbon atoms left behind during Ni₂Si formation, improving the electrical and microstructure properties.     

Metallic thin film depth measurements by X-ray microanalysis

In this study, a low-cost technique, energy dispersive spectroscopy (EDS), was used to explore the application of X-ray microanalysis in depth determination of metallic films. Al, Ni and Au films with varied thicknesses from 50 to 400 nm were deposited on silicon (Si) substrates by magnetron sputtering. Electron beam energies ranging from 4 to 30 keV were applied while other parameters were kept constant to determine the electron beam energy required to penetrate the films. The effect of the atomic number of the metallic films on the penetration capability of the electron beam was investigated. Based on the experimental results, mathematical models for Al, Ni and Au films were established and the interaction volume was simulated using a Monte Carlo program. The simulations are in good agreement with the experimental results. Al/Ni/Au multilayers were also studied.     

Thermal stability of W2B and W2B5 contacts on ZnO

Rectifying contact formation on n-type bulk single crystal ZnO using novel W₂B or W₂B₅ metallization schemes was studied using current-voltage, scanning electron microscopy and Auger electron spectroscopy (AES) measurements. When a single Au overlayer was used to reduce the metal sheet resistance, the contacts were ohmic for all annealing conditions due to outdiffusion of Zn through the metal. By sharp contrast, when a bilayer of Pt/Au was used on top of the boride layers, rectifying contacts with barrier heights of ∼0.4 eV for W₂B were obtained. The highest barrier height of 0.66 eV was achieved for W₂B₅ annealed at 600 °C, although at this condition the contact showed a reacted appearance and AES showed almost complete intermixing of the metallization.     

Effect of implantation energy and dose on low-dose SIMOX structures

In order to form silicon (Si)-on-insulator (SOI) layers with various thicknesses, oxygen implantation with doses between 1.0×10¹⁷/cm² and 6.0×10¹⁷/cm² and at energies between 40 and 240 keV has been carried out into 300 mm diameter (100)Si wafers at a temperature of 560 °C. After implantation, Si wafers are annealed in dry Ar mixed with 1% O₂ at a temperature of 1350 °C for 4 h. The quality of buried oxide (BOX) layers and the microstructure in implanted layers before and after annealing is characterized by transmission electron microscopy. The results reveal that the appreciable number of threading dislocations (TDs) is generated in SOI layers implanted at energies above 200 keV under the optimum dose-energy conditions for the continuous BOX layer formation. Whereas, in the case of discontinuous BOX layers, the TD generation is observed in samples implanted at energies above 120 keV. The generation of TDs is discussed with the emphasis on the effect of implantation energy. PACS 61.72Ff; 61.72Lk     

Evaluation of the barrier capability of Zr-Si films with different substrate temperature for Cu metallization

Barrier capability of Zr-Si diffusion barriers in Cu metallization has been investigated. Amorphous Zr-Si diffusion barriers were deposited on the Si substrates by RF reactive magnetron sputtering under various substrate temperatures. An increase in substrate temperature results in a slightly decreased deposition rate together with an increase in mass density. An increase in substrate temperature also results in grain growth as deduced from field emission scanning electron microscopy (FE-SEM) micrographs. X-ray diffraction (XRD) spectra and Auger electron spectroscopy (AES) depth profiles for Cu/Zr-Si(RT)/Si and Cu/Zr-Si(300 °C)/Si samples subjected to anneal at various temperatures show that the thermal stability was strongly correlated with the deposition temperature (consequently different density and chemical composition etc.) of the Zr-Si barrier layers. ZrSi(300 °C) with higher mass density make the Cu/Zr-Si(300 °C)/Si sample more stable. The appearance of Cu₃Si in the Cu/Zr-Si/Si sample is attributed to the failure mechanism which may be associated with the diffusion of Cu and Si via the grain boundaries of the Zr-Si barriers.     

Formation of ultrathin nanocomposite SiO2:nc-Au structures by Pulsed Laser Deposition

A method for the formation of Au nanocrystal (nc) arrays embedded in an ultrathin SiO₂ layer in one vacuum cycle is proposed. The method is based on the co-deposition in vacuum of ∼1 nm thick uniform Si-Au amorphous layer at a specific composition ratio by Pulsed Laser Deposition on the pre-oxidized Si(1 0 0) substrate, followed by its oxidation in the glow discharge oxygen plasma at room temperature, resulting in the precipitation of Au ncs at the bottom interface and/or at the surface of the forming SiO₂ layer. The capping SiO₂ layer is formed by the glow discharge plasma oxidation of further deposited ultrathin Si layer. Au ncs 2-5 nm in size and with the separation of ∼3-20 nm from each other segregate during the oxidation of Au-Si mixture as evidenced by transmission electron microscopy (TEM). The evolution of Au and Si chemical state upon each step of the SiO₂:nc-Au nanocomposite structure formation is monitored in situ by X-ray photoelectron spectroscopy (XPS). The metrology of nanocomposite SiO₂:nc-Au structures describing the space distribution of Au ncs as a function of Au/Si ratio is presented.     

Effect of oxygen exposure on the magnetic properties of ultrathin Co/Si(1 1 1)-7×7 films

Effect of oxygen exposure on the magnetic properties of ultrathin Co/Si(1 1 1)-7×7 films have been studied. In ultrahigh vacuum environment, Auger electron spectroscopy (AES) analysis shows that no oxygen adsorption occurs on Si(1 1 1)-7×7 surface and Co-Si compound interfaces. As the thickness of Co films increases above 5 monolayers (ML), pure cobalt islands form on the surface and the amount of oxygen on the surface layers increases with increasing the oxygen exposure time. From the results of slight chemical shift and depth profiling measurements, the oxygen is weakly adsorbed on the topmost layer of 15 ML Co/Si(1 1 1) films. The adsorbed oxygen influences the electronic density of states of Co and leads to the changes of the magnetic properties. The appearance of the O/Co interface could modify the stress anisotropy, as a result, the coercivity of ultrathin Co/Si(1 1 1) films are enhanced. As an example for 15 ML Co/Si(1 1 1), the coercivity increases from 140 to 360 Oe with 5000 Langmuir of oxygen exposure.