MBE growth and characterization of buried silicon oxide films on Si(100)

Silicon molecular beam epitaxy (Si-MBE) has been used to produce silicon oxide (SiO_x) films by evaporating Si on a heated Si(100) substrate in an ultra high vacuum system with an O₂ pressure of 10⁻⁶ to 10⁻⁴ mbar. Then the SiO_x films were overgrown with pure Si. The influence of the substrate temperature, the O₂ pressure and the Si deposition rate on the oxygen content in the SiO_x films and on the crystalline quality of the Si top-layer was investigated by Rutherford backscattering spectrometry and ion channeling. Epitaxial growth of the Si top-layer was observed up to a maximum concentration of ≈20 at.% oxygen content in the SiO_x film. Cross-sectional transmission electron microscopy shows that the structure of the SiO_x film changes duringa subsequent annealing procedure. Electron energy loss spectrometry proves that amorphous SiO₂ is formed and the development of holes indicates that the density of the as-grown SiO_x film is much lower than that of SiO₂. The specific for the as-grown SiO_x films was determined by I–V measurements.     

The effect of composition on surface morphology, formation mechanism and pinhole generation of cosputtered ytterbium silicide

The surface morphology including pinhole and silicide formation mechanism of codeposited ytterbium silicide films are investigated with various compositions of Yb and Si. Film properties depend on the growth mode of the deposited films. At Si compositions more than half of the stable phase of ytterbium silicide, films have a rough surface with islands of ytterbium silicide formed by the Stranski-Krastanov and Volmer-Weber growth mode. At Si composition below half of the stoichiometic value, films grow in a layer by layer, Frank-van der Merwe mode, with a smooth surface. The transition of the formation mode is due to a trade-off in the dominance of the reaction between the internal atoms in the deposited films or between the deposited films and the substrates. A Si composition of 0.59 provides the smoothest surface with roughness of 1.13 nm in root mean square value and no observed pinholes. Ytterbium silicide films are deposited with a 5% composition tolerance by cosputtering and forming at 450 °C in a conventional furnace.     

Synthesis of Si nanocones using rf microplasma at atmospheric pressure

We report the synthesis of silicon nanocones using the rf microplasma discharge at atmospheric pressure. The products formed underneath the tube electrode on Fe-coated crystalline silicon were constituted mainly of silicon and silicon oxide despite the use of a methane-argon mixture. Carbon nanotubes and silicon nanowires were also formed around the silicon nanocones. The number density and average size of silicon nanocones increased with the plasma exposure time accompanied by the enlargement of their surface distribution. The growth mechanism of silicon nanocones is discussed in terms of the catalytic growth via diffusion of silicon through FeSi_x nanoclusters with nanocrystalline Si particle, and Si oxidation due to the plasma heating.     

Physical model and numerical results of dissociation kinetics of hydrogen-passivated Si/SiO2 interface defects

A simple model of thermal dissociation and recovery of hydrogen-passivated silicon defects at the Si/SiO₂ interface, such as P_b - centers, during vacuum thermal annealing has been suggested. his model considers reactions of hydrogen with defect states at the Si/SiO₂ interface and diffusion of liberated atomic and molecular hydrogen in a silicon dioxide film. The rate constants were calculated in diffusion approximation. A good agreement was obtained between the experimental and numerical simulation results for oxides with different thickness (204–1024 Å), grown, both, (111) and (100) samples and annealed in the temperature range (480–700°C).     

Influence of oxygen partial pressure on the wetting of SiC by a Co–Si alloy

In this investigation the influence of oxygen partial pressure P_O2 on the wetting of SiC by a Co–Si alloy was studied. Wetting experiments were carried out in argon with different oxygen contents (from 5 to 1000 ppm). The relationship between wetting and deoxidation of surfaces (SiC and Co–Si alloy) was investigated. Calculations were performed to evaluate the temperature range over which deoxidation is possible. These calculations are in agreement with the experimental results.     

Growth process from amorphous GaN to polycrystalline GaN on Si (111) substrates

Amorphous GaN (a-GaN) films on Si (111) substrates have been deposited by RF magnetron sputtering with GaN powder target. The growth process from amorphous GaN to polycrystalline GaN is studied by XRD, SEM, PL and Raman. XRD data mean that annealing under flowing ammonia at 850-950 °C for 10 min converts a-GaN into polycrystalline GaN (p-GaN). The growth mechanism can be mostly reaction process through N³⁻ in amorphous GaN replaced by N³⁻ of NH₃. Annealing at 1000 °C, the appearance of GaN nanowires can be understood based on the vapor-liquid-solid (VLS) mechanism. In addition, XRD, PL and Raman measurement results indicate that the quality of GaN films increases with increasing temperature. The tensile stress in the films obtained at 1000 °C is attributable to the expansion mismatch between GaN and Si, with the gallium in the film playing a negligible role.     

Massive Si Phase and Its Growth Mechanism in Al-Si Casting Alloy

Optical microscope and scanning electron microscope were used to observe the microstructure of the AI-11.6%Si and AI-11.6%Si-0.4%Mg alloys and the morphology of the massive silicon particles. It is found that the massive silicon phase, observed in the unfully modified alloys with 0.010%Sr, disappears completely in the alloys fully modified with 0.020%Sr. The serrations and reentrant edges shown in the massive silicon particles with the conventional casting indicate that the TPRE mechanism plays an important role in the growth of the massive silicon phase. The ripples and steps suggest that the "lateral microscopic growth" may be another operating mechanism.     

Heteroepitaxial Growth and Characterization of 3C-SiC Films on Si Substrates Using LPVCVD

3C-SiC films have been deposited on Si (111) substrates by the low-pressure vertical chemical vapor deposition (LPVCVD) with gas mixtures of SiH4, C3Hg and H2- The growth mechanism of SiC films can be obtained through the observations using field emission scanning electron microscope (FESEM). It is found that the growth process varies from surface control to diffusion control when the deposition temperature increases from 1270 to 1350℃. The X-ray diffraction (XRD) patterns show that the SiC films have good crystallinity and strong preferred orientation. The results of the high resolution transmission electron microscopy (HRTEM) image and the transmission electron diffraction (TED) pattern indicate a peculiar superlattice structure of the film. The values of the binding energy in the high resolution X-ray photoelectron spectra (XPS) further confirm the formation of SiC.     

X-ray photoelectron spectroscopy study of the initial growth of transition metal nanoscale films on (100) Si substrates

The initial growth stages of materials non-active to a substrate has been extensively studied for decades, whereas there had been fewer studies on the initial growth of active metals on silicon substrate, despite its technological importance. In this paper the very early growth stages of transition metal (Ti, V and Nb) films deposited by rf sputtering on unheated (100) Si substrate were studied by in situ X-ray photoelectron spectroscopy. The following sequence of the phase composition and the growth mechanism changes during deposition process was revealed. Initially in a submonolayer regime, small 3D TiO₂ islands are formed via reduction of a native silicon oxide layer on a substrate followed by formation of a TiO phase between TiO₂ islands and on their top. After deposition of ca. 2 monolayers a metallic Ti phase appears and later only the metal Ti film grows. The same growth behavior takes place at Nb and V deposition with a difference that in the case of Nb the above changes occur at earlier stages what can be explained by the highest niobium activity to the reduction of silicon oxide in the row V, Nb, Ti.     

Growth of Fe on Si (100) at room temperature and formation of iron silicide

Low-energy electron diffraction (LEED), Auger electron spectroscopy and X-ray photoelectron spectroscopy (XPS) investigations of both the growth of an iron film on silicon (100) at room temperature and the subsequent formation of iron silicide are the subjects of this paper. An in-situ cleaned silicon (100) wafer without carbon or oxygen contamination exhibiting the known 2 × 1 reconstruction in the LEED pattern served as the substrate. Iron was deposited on this reconstructed surface at 300 K. The comparison of theoretical calculations based on three growth mechanisms with XPS data obtained with take-off angles of 0° and 50° clearly demonstrates a layer-by-layer growth of the iron film on silicon (100). At 300 K no formation of iron silicide was observed, although an interaction between iron and silicon could be detected at the interface. The formation of iron silicide was observed at annealing temperatures of 630–730 K. Quantitative XPS analysis yields the presence of FeSi₂, when the thickness is large enough. Neither the iron film on silicon nor the silicide shows any LEED pattern.     

Charge trapping during constant current stress in Hf-doped Ta2O5 films sputtered on nitrided Si

Metal-insulator-silicon structures containing Hf-doped Ta₂O₅ dielectric films sputtered on rapid thermally nitrided Si are shown to have very good reliability properties. Stress-induced leakage currents are low, both at low and at high-fields. It is found that charge trapping during the stress is the dominant wear-out mode for very long stress times of 500 s even for injected current densities J_s as high as 100 mA/cm². Stress curves approach saturation at long stress time, indicating that the trap generation rate is very low, even compared to the observed reduced trapping at pre-existing traps.Applying a trapping kinetics model, two trapping sites with characteristic trapping times τ₁ = 3.2 s and τ₂ = 49 s were determined and attributed to pre-existing defects in the bulk Hf:Ta₂O₅ layer and not in the interfacial SiO_xN_y layer. It was found that both τ₁ and τ₂ do not depend on J_s, which may be explained by the presence of a mechanism of charging the active sites through field activated emission of charge from them.     

Si_3N_4/Si表面Ge生长过程的STM研究

利用STM和LEED分析了Ge在Si3 N4 /Si(111)和Si3 N4 /Si(10 0 )表面生长过程的结构演变。在生长早期 ,Ge在两种衬底表面上都形成高密度的三维纳米团簇 ,这些团簇的大小均在几个纳米范围内 ,并在高温退火时体积增大。当生长继续时 ,Ge的晶体小面开始显现。在晶态的Si3 N4 (0 0 0 1) /Si(111)表面 ,Ge的 (111)晶向的小面生长比其他方向优先。最后在大范围内形成以 (111)方向为主的晶面。相反 ,在非晶的Si3 N4 表面 ,即Si3 N4 /Si(10 0 ) ,Ge晶体的高指数侧面生长较顶面快 ,最终形成金字塔形的岛结构。对这样的表面生长过程进行了探讨并给出了合理的物理解释     

Ordering of Ge islands on Si(001) substrates patterned by nanoindentation

Spatial organization of Ge islands, grown by physical vapor deposition, on prepatterned Si(001) substrates has been investigated. The substrates were patterned prior to Ge deposition by nanoindentation. Characterization of Ge dots is performed by atomic force microscopy and scanning electron microscopy. The nanoindents act as trapping sites, allowing ripening of Ge islands at those locations during subsequent deposition and diffusion of Ge on the surface. The results show that island ordering is intrinsically linked to the nucleation and growth at indented sites and it strongly depends on pattern parameters.     

Growth of Ge nanoparticles on SiO2/Si interfaces during annealing of plasma enhanced chemical vapor deposited thin films

Multilayer germanosilicate (Ge:SiO₂) films have been grown by plasma enhanced chemical vapor deposition. Each Ge:SiO₂ layer is separated by a pure SiO₂ layer. The samples were heat treated at 900 °C for 15 and 45 min. Transmission electron microscopy investigations show precipitation of particles in the layers of highest Ge concentration. Furthermore there is evidence of diffusion between the layers. This paper focuses mainly on observed growth of Ge particles close to the interface, caused by Ge diffusion from the Ge:SiO₂ layer closest to the interface through a pure SiO₂ layer and to the interface. The particles grow as spheres in a direction away from the interface. Particles observed after 15 min anneal time are 4 nm in size and are amorphous, while after 45 min anneal time they are 7 nm in size and have a crystalline diamond type Ge structure.     

硅基GaN外延晶体学位相关系和生长机理研究

采用反应蒸发光地在提高缓冲层的生长温度,通过对Ｓｉ基上ＧａＮ样品缓冲层区域的高分辨透射电镜像（ＨＲＴＥＭ）和界面区域的选区电子衍射（ＳＡＥＤ）分析的基础上,提出了本系统ＧａＮ外延的晶体学位相关系和生长机理。ＧａＮ与Ｓｉ衬底之间存在着下列的晶体学位相关系：ＧａＮ〈０００１〉∥Ｓｉ〈１１１〉,ＧａＮ〈１１２０〉∥Ｓｉ〈１１０〉,ＧａＮ外延生长首先在硅衬底上形成ＧａＮ晶核,生长出ＧａＮ多晶缓冲层,ＧａＮ     

Growth mechanism of primary Ti_5Si_3 phases in special brasses and their effect on wear resistance

In the present work, in-situ Ti₅Si₃ reinforced special brasses were prepared by melt reaction method. The synthesized Ti₅Si₃ phase shows various morphologies in brasses with different Ti₅Si₃ content, and the3 D morphological evolution of primary Ti₅Si₃and its growth mechanism were investigated. The Ti₅Si₃ crystal, which bears D8₈ hexagonal crystal structure, grows along <0001> direction and is revealed by{1010} faces during growth. With the increase of Ti₅Si₃ content in the brasses, the morphology of primary Ti₅Si₃significantly changes from fibers to hexagonal prisms to short-rods with hollow. In addition,the influence of Ti₅Si₃ volume fraction and morphology on the wear behavior of special brass was also revealed. It was substantiated that the wear resistance increases with the increasing volume fraction of Ti₅Si₃, and the corresponding wear mechanism changes from delamination to slight adhesive wear and abrasive wear. However, the friction coefficient shows an abnormal increase when most of the Ti₅Si₃ containing hollows appears in the brass. That is mainly due to the fact that the Ti₅Si₃ is easier to break and fall off resulted by the hollow as a crack source, which makes it unable to resist the plastic deformation of the contact surface during the sliding.     

In situ Fourier transform P-polarized infrared reflection absorption spectroscopic investigation of an interface properties of SiO2/Si(100) deposited using electron cyclotron resonance microwave plasma at room temperature

Amorphous SiO₂ films have been deposited onto the Si substrate, without heating, using sputtering-type electron cyclotron resonance (ECR) microwave plasma. In situ Fourier transform P-polarized infrared reflection absorption spectroscopy (ISFT-PIRRAS) has been used to study the properties of a-SiO₂/Si interface. The results from ISFT-PIRRAS monitoring indicated that the interface stress led to significant distortion in the local structure, which resulted in the broadening of a transverse optical mode (TO₃) located at 1050 cm⁻¹. The interface stress decreased with increased film thickness. In addition, the longitudinal optical phonon mode (LO₃, located at 1223 cm⁻¹) related to TO₃ mode was observed due to Berreman effect [B. Harbecke, Appl. Phys. A: Solids Surf. 38 (1985) 263]. This phonon mode is very sensitive to SiO₂ film thickness, which enables it to be used to detect and characterize ultra thin SiO₂ film. When the film thickness is over 30 nm, a non-linear dependence of the intensity of LO₃ mode on film thickness was observed. However, the TO₃ mode has a near linear dependence on film thickness. Thus, it is more accurate and suitable to detect thick film by monitoring TO₃ mode intensity.     

Growth of 3C-SiC on Si(111) using the four-step non-cooling process

A modified four-step method was applied to grow a 3C-SiC thin film of high quality on the off-axis 1.5° Si(111) substrate in a mixed gas of C₃H₈, SiH₄ and H₂ using low pressure chemical vapor deposition. The modified four-step method adds a diffusion step after the carburization step and removes the cooling from the traditional three-step method (clean, carburization, and growth). The X-ray intensity of the 3C-SiC(111) peak is enhanced from 5 × 10⁴ counts/s (the modified three steps) to 1.1 × 10⁵ counts/s (the modified four steps). The better crystal quality of 3C-SiC is confirmed by the X-ray rocking curves of 3C-SiC(111). 3C-SiC is epitaxially grown on Si(111) supported by the selected area electron diffraction patterns taken at the 3C-SiC/Si(111) interface. Some {111} stacking faults and twins appear inside the 3C-SiC, which may result from the stress induced in the 3C-SiC thin film due to lattice mismatch. The diffusion step plays roles in enhancing the formation of Si-C bonds and in reducing the void density at the 3C-SiC/Si(111) interface.     

Determining adhesion and hermeticity of the interface between encapsulation polymer and insulating layer of micro-sensing chips via a capacitance-voltage technique

The successful application of micro-sensing chips based on ion-sensitive field effect transistor principles depends on preventing the penetration of electrolyte into the interface between the encapsulation polymer and the insulating layer. This study employs a capacitance-voltage (C-V) technique to evaluate the adhesion and hermeticity of the polymer-substrate interface in a liquid environment. Three-layered structures simulating micro-sensing chips were fabricated for the evaluation. Each three-layered structure comprises an upper epoxy layer (with or without a window opening), a middle dielectric layer, and a lower Si wafer substrate. Equivalent circuits were established to explain the C-V characteristics of the three-layered structures. The results show that by applying the C-V technique and using an appropriate equivalent circuit, the adhesion and hermeticity between the encapsulating epoxy layer and the insulating layer can be evaluated.     

Evaluation of thin film adhesion to a compliant substrate by the analysis of progressive buckling in the fragmentation test

The interface toughness of a thin coating/compliant substrate system is estimated based on the evolution of coating buckle patterns in the fragmentation test. The linear density of coating buckles as a function of applied strain is determined experimentally for a SiO_x coating deposited on a polyethylene terephthalate film. A three-dimensional non-linear finite element model is developed to simulate the process of buckle formation in a single narrow coating strip. The elastic energy released during buckling-driven delamination is obtained from the energy balance in the system before and after the buckling event. Both the interface adhesion and the total energy release rate, which includes the plastic dissipation in the substrate during debonding, are evaluated. The apparent interfacial toughness, equal to 15 J/m² at the onset of buckling, is found to increase with strain. This is tentatively explained by the probabilistic features of the buckle accumulation process, reflected also in the random locations of buckles evolving towards a log-normal distribution of buckle spacings at high strains.