Surface Of Si Single Crystal Research Articles

Control of ion-flux and ion-energy in direct inductively coupled plasma reactor for interfacial-mixing plasma-enhanced atomic layer deposition

The effects of low-energy (<15 eV) high-flux O2+ ion bombardment on the properties of Al2O3 films deposited on 3D nanostructures by plasma-enhanced atomic layer deposition (PE-ALD) were investigated. High-dose O2+ ion bombardment (>1017 cm−2 cycle−1) during the oxidation steps caused interfacial mixing, and AlSiOx films with abrupt interfaces were formed on Si surfaces. Interfacially mixed AlSiOx films were selectively formed on single-crystal Si, amorphous Si, and degraded SiO2 surfaces, whereas normal ALD Al2O3 films were formed on thermally grown SiO2 surfaces. At the same time, the interfacially mixed AlSiOx films were selectively formed on the horizontal top and bottom faces of the 3D nanostructures, whereas normal ALD Al2O3 films were formed on the vertical sidewalls. The morphology and thickness of the film deposited on the amorphous Si surface were the same as those on the single-crystal Si surface. The interfacially mixed AlSiOx film possessed rough surface morphology and a layered structure of Al-/Si-/Al-rich AlSiOx layers. The low-energy high-flux O2+ ion bombardment condition required for the interfacial-mixing ALD was realized in a direct inductively coupled plasma (ICP) reactor with a self-resonant planar coil, in which high-density plasma was excited near the substrate. The O2+ ion flux was found to be controllable over a wide range through variation in the O2 pressure. The ratio of O2+ ion flux at 0.01 Torr to that at 1 Torr was 289. The steep decrease of the ion flux with increasing pressure was attributed to the decrease of electron density in the upstream plasma for intensifying electron energy loss and the decrease of the ambipolar diffusion coefficient in the downstream plasma. A comparison of electron densities near the substrate and those at the presheath edge calculated from measured positive ion fluxes using the Bohm criterion revealed that negative ions, which significantly affect the positive ion flux, scarcely exist near the substrate. The interfacial-mixing PE-ALD has the potential to realize area-selective and topographically selective depositions, which are key technologies for fabricating next-generation electronic devices with 3D nanostructures. The direct ICP reactor is suitable for realizing selective deposition using the interfacial-mixing ALD.

Pyrolysis of a Low Asphaltene Crude Oil under Idealized in Situ Combustion Conditions

The coke formation is crucial to the crude oil in situ combustion (ISC) process. This study provided some insights through analyzing the influences of temperature and reaction atmosphere on the coke chemical–structural property. Thin coke films were produced on the polished single-crystal Si surface from the Xinjiang crude oil. Their functional groups were compared by Fourier transform infrared spectroscopy (FTIR), while the nanostructures were characterized through Raman spectroscopy, X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) techniques. In addition, the low-temperature oxidation (LTO) coke and the pyrolytic coke reactivities were investigated by thermogravimetric analyses. The results indicated that the main carbon structures in the pyrolytic coke were amorphous. No crystallization phenomena, such as the aromatic ring condensation and the planar stacking, were observed within the characteristic ISC pyrolytic temperature range. Despite the pyrolytic coke yield ...

单晶硅表面金字塔生长过程的实验研究

The texturing process with alkaline solution added a new additive on single-crystal silicon surface was discussed.At different times,alkaline solution added a new additive was used to etch the Si wafers,and samples were scanned by scanning electron microscopy.The results show that there are a few different size pyramids and smooth regions in large-area on the Si surface after etching 10 min;after etching 15 min,the sizes of pyramids become uniform,and the areas of smooth regions will reduce;after etching 20 min,the etched surface is covered with the 2~4 μm of pyramids,and the distribution is more uniformly-densely;after etching 25 min,the sizes of pyramids increase again in the over-etching process.The experiments illustrate that the new additive can effectively reduce the texturing time,make an ideal textured structure,and be applied in industry.

Fabrication, characterization and modeling of single-crystal thin film calorimeter sensors

Thin film based nanocalorimetry is a powerful tool to investigate nanosystems from a thermal point of view. However, nanocalorimetry is usually limited to amorphous or polycrystalline samples. Here we present a device that allows carrying out experiments on monocrystalline silicon. The monocrystalline silicon layer consists of the device layer from a silicon-on-insulator wafer and lies on a low-stress free-standing silicon nitride membrane. We applied a number of characterization techniques to determine the purity and quality of the silicon layer. All these techniques showed that the silicon surface is as pure as a standard silicon wafer and that it is susceptible to standard surface cleaning procedures. Additionally, we present a numerical model of the nanocalorimeter, which highlights that the silicon layer acts as a thermal plate thereby significantly improving thermal uniformity. This nanocalorimeter constitutes a promising device for the study of single-crystal Si surface processes and opens up an exciting new field of research in surface science.

Suppression of Pores Formation on a Surface of p-Si by Laser Radiation

The influence of strongly absorbing N¬2 laser radiation on pores formation on a surface of Si single crystal has been investigated using optical microscope, atomic force microscope and photoluminescence. After irradiation by the laser and subsequent electrochemical etching in HF acid solution morphological changes of the irradiated parts of a surface of Si were not observed. At the same time, pores formation on the non-irradiated parts of Si surface took place. The porous part of the Si surface is characterized by strong photoluminescence in red part of spectra with maximum at 1.88 eV and intensity of photoluminescence increases with current density. Suppression of the pores formation by the laser radiation is explained with inversion of Si type conductivity from p-type to n-type. This fact is explained by Thermogradient effect – generation and redistribution of the intrinsic defects in gradient of temperature. It was shown that the depth of n-Si layer on p-Si substrate depends on intensity of laser radiation and it increases with intensity of laser radiation. The results of the investigation can be used for optical recording and storage of information on surface of semiconductors.

Synthesis of nanostructured SiC films during pulsed photon treatment of Si in a carbon-containing atmosphere

The phase composition, orientation, substructure, and morphology of the films formed during pulsed photon treatment of a single-crystal Si surface by xenon lamp irradiation (λ = 0.2–1.2 µm) and polycrystalline Si films on SiO2-Si in a gaseous atmosphere (C3H8)0.2(C4H10)0.8 are investigated using the methods of transmission electron microscopy, high-energy electron diffraction, atomic force microscopy, and IR-spectroscopy. The irradiation time (the duration of the pulse packet) varied from 1.5 to 2.0 s, which corresponded to variations in the incident’s irradiation energy (Ep) from 215 to 285 J · cm−2. The threshold value of Ep was determined. The films of SiC and Si are characterized by a nanocrystalline substructure and biaxial texture, corresponding to different deviations of grains from parallel epitaxial orientation. The portion of epitaxially oriented grains rising to the film surface is increasing with an increase in Ep and the film thickness. Under the conditions necessary for the formation of a eutectic melt in the near-surface zone, the crystallization yielding the formation of a uniaxial texture takes place. During the synthesis on doped poly-Si films the forming SiC film inherits the texture of the layered substructure of the initial Si’s film blocks.

Crystallography of TiSi 2 (C54) epitaxy on (111) Si and (001) Si surfaces

Following the success in understanding the textures in TiSi 2 (C49) epitaxy on (001) Si surface using the edge-to-edge matching model that was originally developed for predicting the crystallographic features of diffusion-controlled phase transformations in solids, the present work applies this model to understand the in-plane texture in TiSi 2 (C54) thin films on Si single crystal surfaces and to explain why its epitaxial growth is more favoured on (111) Si than on (001) Si. Based on the actual atomic spacing along the matching directions across the interface between the thin films and the substrate, the model predicts most of the experimentally observed orientation relationships (ORs) and that the preferred order among the different systems is C49/(001) Si system > C54/(111) Si system > C49/(111) Si system ≅ C54/(001) Si system. The model has strong potential to be used to develop new thin film materials.

Photopatterning of an Organic Monolayer Formed on a Si Single Crystal Surface via Si–C Covalent Bond by UV Irradiation in an Inert Atmosphere

We demonstrate that photopatterning of an octadecyl monolayer, which was covalently attached to a Si(111) surface via Si–C bond [C18H37–Si(111)], is possible just by irradiating the monolayer surface with UV light (254 nm+185 nm) in an atmospheric Ar environment through Cu microgrid patterns. The grid patterns were successfully transferred to the surface without detectable damage in the non-irradiated region. The patterned monolayer was further used as a template for metal pattern formation by electroless Cu deposition. The organic monolayer effectively worked as an efficient insulating mask for the electroless deposition of Cu, which was selectively deposited on the UV irradiated region. This approach is simple and convenient for fabricating microstructures of various molecules and metals on a Si surface.

Behavior of Hydrogen-Terminated Si(111) Surface in Oxygen-Dissolved NH4F Solution with or without Cu(II) Ions

E-mail: cwlee@korea.ac.krReceived August 2, 2005Key Words : Si(111), Oxygen Am, monium fluoride Cu, (II), STMIn the conjunction with the development of ultra-large-scale integration circuits (ULSI), the skill of the control ofcontaminants in cleansing solutions and also the technologyfor making a flat hydrogen-terminated Si single crystalsurface should be developed in the near future.

Investigation of Surface Damage in Si Exposed to Ar Plasma by Spectroscopic Ellipsometry and Grazing X-Ray Diffraction

Low-damage processes in plasma-surface interactions, particularly lattice deformation and the degree of damage in a single-crystal Si surface exposed to Ar plasma, are investigated by spectroscopic ellipsometry (SE) and grazing X-ray diffraction. The dielectric function spectrum of the damaged Si layer in nano-depth is obtained by use of damage depth estimated by a method based on SE model analysis and confirmed by step etching combined with SE measurement. The third-derivative lineshape of the imaginary part ε2 of the complex-dielectric function provides the damage dependences of interband transition energy and broadening parameter for the E1 (Λ3→Λ1) optical interband transition. The result shows that the surface damage proceeds through lattice expansion and relaxation. The lattice deformation in the damaged surface is also investigated by grazing X-ray diffraction. The X-ray rocking curve around (422)Si is asymmetric and involves small subsidiary curves corresponding to the lattice expansion and relaxation. These observations are in good agreement with the lattice deformation process obtained from the SE analysis.

TEM Observation of Microstructural Change of Silicon Single Crystal Caused by Scratching Tests Using SPM

ABSTRACTIn this study, the microstructural change of the surface of Si single crystal (Si(100)) after the scratching tests under very small loading forces was investigated. At first, line-scratching tests and scanning-scratching tests were carried out using an atomic force/friction force microscope (AFM/FFM). Next, cross-sectional TEM observations of the wear marks which were generated by the scratching tests were carried out. As a result of the TEM observations after the line-scratching tests, it was found that dislocations were observed in the area of less than 100nm thickness from the surface of the wear marks which were formed under the loading forces of more than 5μN. In the case of the loading forces of more than 20μN, an amorphous region was also observed just under the wear marks. As a result of the TEM observations after the scanning-scratching tests, it was found that the introduction of dislocations took place and no amorphous region appeared. It was also found that the several atomic layers at the top surface of the wear marks shifted in parallel to (100).

Cobalt silicide formation inside surface defects of a silicon substrate

The formation process of a CoSi 2 layer after vacuum Co film deposition on an Si single crystal surface was investigated by means of scanning tunneling microscope (STM), SEM and RHEED. The pinholes which cause different kinds of film roughness show marks of melting processes. It is shown that in the limits of the theory of mechanochemical activity the activation energy of the silicide formation is lower inside the defect than in the bulk silicon. Therefore, the exothermic reaction of silicidation starts earlier which leads to a heating of the CoSi product. We calculated the time dependencies of the temperature inside the defect for different areas of its surface using the layer growth diffusion model and proved that the temperature increases up to the melting point at a certain critical area.

Investigation of the Size-Scaling Behavior of Spatially Nonuniform Barrier Height Contacts to Semiconductor Surfaces Using Ordered Nanometer-Scale Nickel Arrays on Silicon Electrodes

Nanosphere lithography has been used to prepare a series of ordered, periodic arrays of low barrier height nanometer-scale n-Si/Ni contacts interspersed among high barrier height n-Si/liquid contacts. To form the arrays, ordered bilayers of close-packed polystyrene spheres were deposited onto (100)-oriented n-type single crystal Si surfaces. The spheres formed a physical mask through which Ni was evaporated to produce regularly spaced and regularly sized Si/Ni contacts. By varying the diameter of the latex spheres from 174 to 1530 nm, geometrically self-similar Si/Ni structures were produced having triangular Si/Ni regions with edge dimensions of 100−800 nm. The resulting Si surfaces were used as electrodes in contact with a methanolic solution of LiClO4 and 1,1‘-dimethylferrocene+/0. The current−voltage and photoresponse properties of these mixed barrier height contacts were strongly dependent on the size of the Ni regions, even though the fraction of the Si surface covered by Ni remained constant. Electrodes formed from large-dimension Si/Ni and Si/electrolyte contacts behaved as expected for two area-weighted Schottky diodes operating independently and in parallel, whereas electrodes having nanoscale Si/Ni regions surrounded by Si/liquid contacts behaved in accord with effective barrier height theories that predict a “pinch-off” effect for mixed barrier height systems of sufficiently small physical dimensions.

Selective-area atomic layer epitaxy growth of ZnO features on soft lithography-patterned substrates

Templated ZnO thin-film growth from the vapor phase is achieved on docosyltrichloro- silane-patterned Si substrates using atomic layer epitaxy (ALE) combined with soft lithography. Patterned hydrophobic self-assembled monolayers (SAMs) are first transferred to single-crystal Si surfaces by hot microcontact printing. Using diethylzinc and water as ALE precursors, crystalline ZnO layers are then grown selectively on the SAM-free surface regions where native hydroxy groups nucleate growth from the vapor phase. High-resolution ZnO patterns with 1.0–40 μm feature sizes are readily achieved, demonstrating that soft lithography combined with ALE is a simple and promising methodology for selective area in situ vapor phase fabrication of patterned oxide thin films.

Formation of conical microstructures upon laser evaporation of solids

The formation and development of the large-scale periodic structures on a single crystal Si surface are studied upon its evaporation by pulsed radiation of a copper vapor laser (wavelength of 510.6 nm, pulse duration of 20 ns). The development of structures occurs at a high number of laser shots (∼104) at laser fluence of 1–2 J/cm2 below optical breakdown in a wide pressure range of surrounding atmosphere from 1 to 105 Pa. The structures are cones with angles of 25, which grow towards the laser beam and protrude above the initial surface for 20–30 μm. It is suggested that the spatial period of the structures (10–20 μm) is determined by the capillary waves period on the molten surface. The X-ray diffractometry reveals that the modified area of the Si substrate has a polycrystalline structure and consists of Si nanoparticles with a size of 40–70 nm, depending on the pressure of surrounding gas. Similar structures are also observed on Ge and Ti.

Chemical structure of dihydride phase on saturated H-chemisorbed Si surfaces

By observing infrared absorption features including dynamic polarizations due to Si–H stretching vibrations, chemical structures were determined on H-chemisorbed single-crystal Si surfaces that were formed in solution. A technique using polarized infrared multiple internal reflections was applied. The absorption features were obtained as a function of surface H density by systematically tilting the orientation of the surfaces from (111) through (113) up to (001). For surface orientations from (111) to (113), narrow absorption peaks, which had been assigned due to the strained vertical dihydride, and (111)-terrace monohydride species were predominantly observed. But, as the surface orientation moved away from (111), narrow peaks with dynamic polarizations in the (1̄10) plane were observed for the first time. Meanwhile, the broad feature with several peaks in the whole Si–H stretching region was detected in the surface-parallel component of dynamic polarization. Because the absorption area for the surface parallel component increased monotonically with the angle, the features were concluded to be localized at the vertical-dihydride step edges along 〈1̄10〉. A complex composed of a strained horizontal dihydride and a strained monohydride provided a temporary explanation. On (001), the peaks caused by the strained vertical dihydride disappeared completely, and the predominant peaks were those observed for the first time on the other surfaces. A major part of the (001) surface was composed of the complex. The microscopic origin for the appearance of such a disordered structure is described.

Comparative studies of Si single crystal surface disorder by using various methods of electromagnetic wave scattering

Silicon surface roughness characterization using electromagnetic wave scattering (from X-ray to infrared range) together with profilometer and AFM measurements are performed. The dependence of relief characterisation accuracy on the wavelength of the used source is analyzed. The comparison of both local (profilometer, AFM) and statistical data (grazing X-ray scattering, optical specular reflectance, multi-angle-of-incidence (MAI)-ellipsometry) is carried out.

Light-Induced Reactions of Porous and Single-Crystal Si Surfaces with Carboxylic Acids

Light-induced reactions of Si surfaces with carboxylic acids to generate Si ester-modified surfaces are studied. The reaction proceeds by photoelectrochemical oxidation of porous or (100)-oriented single-crystal n-type Si in formic, acetic, or trifluoroacetic acid electrolyte solutions. The reaction products at the porous Si surface are identified by Fourier-transform infrared (FTIR) spectroscopy. Derivatization with esters reduces the photoluminescence intensity of porous Si. X-ray photoelectron spectroscopy (XPS) of derivatized single-crystal Si is used to confirm the compositional and bonding information and to demonstrate that the same chemistry occurs at a single-crystal Si surface. A mechanism is proposed in which illumination of reverse-biased Si removes electron density from the Si surface, rendering Si−Si bonds susceptible to nucleophilic attack by carboxylic acid. The reaction has a marked dependence on light intensity and the Si surface can be photopatterned by illumination through a mask during derivatization. Ester-patterned porous Si reacts with CH3(CH2)7(CH3)2SiOCH3, generating an organosilane-patterned Si surface.

IR reflection spectroscopy of hydrogen on single crystal Si surface

IR reflection spectroscopy of hydrogen on single crystal Si surface

Quantitative Characterization of the Fracture Surface of Si Single Crystals by Confocal Microscopy

Experiments are conducted to study the dislocation nucleation conditions at the crack tip in {110}〈110〉 oriented Si single crystals. Specimens with surface cracks are first statically loaded at elevated temperatures for a prolonged period of time to initiate and move dislocations away from the crack tip, then cooled down to room temperature and loaded to fracture to measure the fracture toughness. Fractographic analysis of the fracture surfaces is performed. Distinct wavy patterns on the fracture surface at the initial cleavage crack front are observed, which is attributed to the existence of local mixed mode I/mode III stresses resulting from the inhomogeneous dislocation activity. Confocal microscopy is employed to quantify the fracture surface roughness. The results show that the increase of fracture toughness is directly associated with the increased area of the rough surface, which is characterized by the roughness number or the fractal dimension increment. Our results also demonstrate that dislocation nucleation can occur only at discrete sites. The spacing between these dislocation nucleation sources is of the order of 1 μm. A simple model is developed for the relationship between the fracture toughness and the surface roughness parameters, which is in good agreement with the experimental results.