Si Substrate Surface Research Articles

Crystal growth of ZnO on Si(1 1 1) by metalorganic vapor phase epitaxy

This paper reports the novel growth procedure for ZnO films on Si substrates by metalorganic vapor phase epitaxy. This can lead to conductive and inexpensive substrates for ZnO, which have been obstructed by the difficulty of growing ZnO films on Si due to easy oxidation of Si substrate surface with an oxygen source. Our proposal is based on the following three step growth, that is, (i) the growth of initial nucleation layer, (ii) the successive growth of recovery layer, and (iii) the growth of main layer. As a result, the three step growth is found to be a promising procedure to grow ZnO films on Si substrates with smooth surface. The increase of VI/II ratio for the main layer growth is also effective for further improvement of the surface morphology.

Deposition and Characterization of Ultra-Smooth Nanocrystalline Diamond Films Using a Graphite-Grid Assisted Hot Filament CVD Method

Nanocrystalline diamond films (NDFs) were deposited on mirror-polished silicon (100) substrates using a graphite-grid assisted hot filament chemical vapor deposition (HFCVD) technique. The evidence of nanocrystallinity, smoothness and purity was obtained by characterizing the sample with various advanced analyses. A graphite-grid was used as the DC electrode, which was pre-coated by diamond films and could emit electron when a negative bias was applied to the under electrode. The results show that the film consists of nanocrystalline diamond grains with sizes of about 7-15nm. The Raman spectroscopy, XRD pattern, HR-TEM image and SAED pattern of the films indicate the presence of nanocrystalline diamond. Surface roughness is measured as Ra<20nm by the profilometry scans. A large quantity of electrons emission from the graphite-grid and positive ions bombardment to the graphite-grid results in an enormous enhancement of the generation of diamond nuclei. Density of a diamond nuclei as high as 1010~1011/cm2 can be attained with this method. NDFs can be deposited on mirror-polished Si substrate surfaces without damaging surface pretreatment for nucleation enhancement. These ultra-smooth films will display excellent performances, which make them the best candidates for semiconductor and MEMS applications.

Quantitative TEM characterizations of La/B 4C and Mo/B 4C ultrathin multilayer gratings by the geometric phase method

Artificially fabricated multilayers that exploit the effect of Bragg diffraction at long wavelengths are used as X-ray optical components. Periodic ultrathin bilayer stacks of, alternatingly, a metallic reflection layer and a non-metallic spacer layer prepared as μm-scaled surface grating promise particularly high performance in applications as X-ray filters for high-resolution spectroscopy. Such gratings can be prepared by multilayer deposition onto Si(0 0 1) gratings or by coating flat Si(0 1 1) substrate surfaces with a multilayer, followed by subsequent etching of a grating structure. The structural quality of ultrathin multilayer gratings of both types has been characterized quantitatively combining TEM bright-field imaging of specimen cross-sections and applying a geometric phase method. The geometric phase method has been originally developed for the analysis of local displacement fields from HREM images and allows to obtain the relevant structure parameters. The application of this method to the characterization of Mo/B 4C and La/B 4C multilayer systems shows that the functionally decisive structure parameters, such as layer perfection, layer periodicity, and layer orientation, can be obtained with high precision from evaluation of TEM bright-field images. The essential role of such data analyses for a quantitative characterization of multilayer systems and for optimising the layer deposition techniques in the fabrication of X-ray optical layer systems will be demonstrated and discussed.

Growth of GaN nanowires on Si substrate using Ni catalyst in vertical chemical vapor deposition reactor

GaN nanowires were successfully grown on Ni-coated Si substrate by direct reaction of gallium with ammonia gas in a home-made vertical tubular chemical vapor deposition reactor. The growth of GaN nanowires was uniformly observed across the Si substrate surface, but the density and average diameter of the nanowires varied along the position of the substrate surface. At the position of 5 cm above Ga source surface, the growth of GaN crystal grains was observed with few nanowires. The length of the nanowires reached several micrometers. The clear lattice fringes in HRTEM image revealed the growth of good quality hexagonal single-crystal GaN nanowires. Photoluminescence of the GaN nanowires showed a strong band edge emission at the energy position of ∼3.4 eV with negligible deep level yellow emission. Field emission characteristics of the GaN nanowires showed that the turn-on field of GaN nanowires was ∼7.4 V/um with a field enhancing factor Βof ∼555. The catalytic growth mechanism of the GaN nanowires was discussed on the basis of experimental results in this work.

Chemical vapour deposition of oriented diamond nanocrystallites by a bias-enhancednucleation method

A microwave plasma chemical vapour deposition (MPCVD) system hasbeen used to deposit nanometre-sized single-crystalline diamonds on1 × 1 cm2 Si(100) substrates. The distribution of deposited diamonds has good uniformity over thewhole Si substrate surface by using a dome-shaped Mo anode which allows the applicationof bias-enhanced nucleation. The morphology and crystallinity of the deposits on Si werecharacterized by scanning electron microscopy (SEM) and transmission electron microscopy(TEM) with electron diffraction and lattice images. SEM and TEM observations show thatoriented diamond nuclei as single crystals with facets can form on self-formed Si conesthrough epitaxial SiC within a short bias period. After a longer bias time, it has beenobserved that polycrystalline diamonds formed as a result of secondary nucleation.

Spherical carbon particle growth in a methane plasma

There is strong evidence that the spherical carbon particles composed of graphite carbon onions of ca. 10nm are grown to micron size under the conditions of a heated Si (100) substrate surface exposed to irradiation by a CH4∕Ar plasma. Furthermore, it is described that these carbon particles of micron size are spherically grown in the plasma and then fall to the substrate surface.

Post-annealing temperature dependence of infrared absorption enhancement of polymer on evaporated silver films

Infrared absorption spectra were measured at normal incidence of radiation for polymers on post-annealed silver films of 4–10 nm mass thicknesses that had been deposited in ultra high vacuum onto Si substrate surfaces. Results show that the polymer absorption intensity depends on the annealing temperature and the silver mass thickness. Results clarified that no simple relation existed, such as a negative correlation between reflectivity and the infrared absorption enhancement, even when the mass thickness was made constant and the silver particles' size and shape were changed. For infrared absorption intensity to become large, particles must be positioned discretely, but if the distance between particles is too large, absorption intensity decreases. Moreover, results verified that optimal thin-film morphology was different according to the wavelength region.

Electric‐Field‐Guided Growth of Carbon Nanotubes during DC Plasma‐Enhanced CVD

AbstractCarbon nanotubes (CNTs) have been grown aligned with the directions of electric fields in a DC plasma‐enhanced (DC PE) CVD process. The CNTs can be grown at various predefined angles with respect to the substrate. It is shown that the local electric field, even at the very surface of the substrates, can be inclined. The strength of the electric field inside the plasma sheath is estimated and the electric‐field directions near the surface of Si substrate where the CNTs grow are modeled. By control of the directions of these electric fields, several novel CNT morphologies are demonstrated, which could be useful for various applications.

Cross-sectional Transmission Electron Microscopy of Interface Structure of β-FeSi2/Si(100) Prepared by Ion Beam Sputter Deposition

The effect of a silicon substrate surface pretreatment on epitaxial iron silicide film formation on a Si(100) substrate with ion beam sputter deposition (IBSD) was investigated. In this study, two surface pretreatment methods namely, thermal etching (TE) and sputter etching (SE) with subsequent thermal annealing, were employed. The interface structure between a β-FeSi2 film and a Si substrate was analyzed by cross-sectional observation using a transmission electron microscope (XTEM). High-resolution XTEM images showed that the lattice of the Si substrate is an almost perfect crystal immediately after the TE treatment. However, the TE treatment results in an undulated interface, and the deposited silicide contained coalesced β-FeSi2 islands. On the other hand, the dislocations and stacking faults produced by radiation damage were observed near the Si substrate surface for the SE treatment. Even though this treatment produced defects, the interface of the SE-treated epitaxial β-FeSi2(100) film had a smooth interface after the deposition at 973 K. It can be concluded that a moderate disorder of the silicon substrate surface treated by SE may well enhance the mixing of Fe and Si atoms for the epitaxial growth of β-FeSi2.

Fabrication and magnetic properties of nanopatterned FePt media

A method for fabricating nanopatterned media has been investigated. A monolayer of regularly distributed Ni nanoparticles of uniform diameter (∼5nm) fabricated on the surface of a polyimide-coated Si substrate using metal film-polyamic acid interactions was utilized as a protruding template to deposit an array of FePt phase. A FePt film (5 nm thick) was sputtered onto this template with or without an underlayer of either 5-nm-thick MgO or CoO and analyzed before and after annealing. It was observed that while the FePt films sputtered on flat Si substrates with underlayers exhibited low Hc of only about 1 kOe after the L10 conversion, the FePt samples deposited onto protruding Ni nanoparticle templates showed a significant increase in Hc to ∼8.1kOe. The FePt sample with CoO underlayer exhibited a possibly strong perpendicular magnetic anisotropy. The intergranular exchange coupling of the samples was also investigated by using ΔM method.

Laser synthesis of nanostructures based on transition metal oxides

Abstract Nanostructures based on iron oxides in the form of thin films were synthesized while laser chemical vapor deposition (LCVD) of elements from iron carbonyl vapors (Fe(CO) 5 ) under the action of Ar + laser radiation ( λ L = 488 nm) on the Si substrate surface with power density about 10 2 W/cm 2 and vapor pressure 666 Pa. Analysis of surface morphology and relief of the deposited films was carried out with scanning electron microscopy (SEM) and atomic force microscopy (AFM). This analysis demonstrated their cluster structure with average size no more than 100 nm. It was found out that the thicker the deposited film, the larger sizes of clusters with more oxides of higher oxidized phases were formed. The film thickness ( d ) was 10 and 28 nm. The deposited films exhibited semiconductor properties in the range 170–340 K which were stipulated by oxide content with different oxidized phases. The width of the band gap E g depends on oxide content in the deposited film and was varied in the range 0.30–0.64 eV at an electrical field of 1.6 × 10 3 V/m. The band gap E g was varied in the range 0.46–0.58 eV at an electrical field of 45 V/m. The band gap which is stipulated by impurities in iron oxides E i was varied in the range 0.009–0.026 eV at an electrical field of 1.6 × 10 3 V/m and was varied in the range 0–0.16 eV at an electrical field 45 V/m. These narrow band gap semiconductor thin films displayed of the quantum dimensional effect.

Thinning Technology for Lithium Niobate Wafer by Surface Activated Bonding and Chemical Mechanical Polishing

A lithium niobate (LiNbO3) hybrid wafer was developed by a combination of wafer bonding and chemical mechanical polishing. In this study, various plasma ambients were applied to activate the surface of LiNbO3 and Si substrate to bond the wafers at room temperature. After the surface activated bonding process, the LiNbO3 substrate was lapped by chemical mechanical polishing. The thickness of the 10 cm diameter LiNbO3 substrate can be decreased from 400 to 10 µm without generating serious cracks. Under the optimum lapping parameters, a 1.5 nm surface roughness of the LiNbO3 film can be obtained.

In Situ Real-Time Infrared Spectroscopy Study of Formation of Porous Anodic Alumina on Si

We have investigated in situ and in real-time the formation process of anodic porous alumina on silicon using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). We have collected IR absorption spectra of the interface between a porous alumina film and a Si substrate to elucidate the chemical processes involved in the porous-alumina formation. On the basis of the detailed analysis of IRAS spectra together with the variation of the anodic current density, we demonstrate that the chemical process at the alumina–Si interface proceeds as follows: As the pore reaches the alumina–Si interfacial region, inhomogeneous etching takes place. It produces small holes or cracks in the “barrier layer” at the bottom of the alumina pore, and through those holes or cracks the electrolyte pours into the vicinity of the Si substrate surface to form nanodots. With further anodization, oxidation of the Si substrate surface occurs and finally peels the porous alumina film off the Si substrate. IRAS data are consistent with the results of observation by a field emission scanning electron microscope. The present results show that MIR-IRAS is a powerful tool for in situ monitoring chemical processes at semiconductor–solution interfaces.

First-principles study of acetylene and ethylene adsorption onβ−SiC(001)−(2×1)

Structural and electronic properties of acetylene and ethylene adsorbed on the Si-terminated $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{SiC}\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface are investigated by ab initio calculations based on density functional theory. A host of conceivable adsorption geometries with half-monolayer and monolayer coverages are considered. The resulting optimal adsorption configurations are quite intriguing in that they differ qualitatively from those of the related and well-studied adsorption systems of acetylene and ethylene on $\mathrm{Si}(001)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$. At the $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{SiC}\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface, acetylene is found to preferentially adsorb for both coverages in a rotated bridge site forming four $\ensuremath{\sigma}$ bonds with Si substrate surface atoms. In this site, the molecule is located in the middle between four neighboring Si surface layer atoms and is oriented perpendicular to the original Si dimers of the clean surface. For ethylene adsorption, a cross dimer site is favored in which the molecule is bonded by two $\ensuremath{\sigma}$ bonds to two surface layer Si atoms of neighboring Si dimers. The ethylene monolayer forms a $c(2\ifmmode\times\else\texttimes\fi{}2)$ configuration. This cross dimer structure is favored by about $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ per molecule with respect to ethylene adsorption in on top positions above Si dimers. This is noteworthy, since for ethylene adsorption on the $\mathrm{Si}(001)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface, the on top site is most favorable. Interestingly, when ethylene adsorbs dissociatively on $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{SiC}\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ this leads to an even larger adsorption energy giving rise to dihydride structures with $1\ifmmode\times\else\texttimes\fi{}1$ or $c(2\ifmmode\times\else\texttimes\fi{}2)$ unit cells for monolayer or half-monolayer coverages, respectively. We present, as well, surface band structures and charge densities for a few adsorption configurations and discuss them in relation to the electronic properties of the clean $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{SiC}\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface and of acetylene and ethylene molecules.

GaN nanorod assemblies on self-implanted (1 1 1) Si substrates

Periodic arrays of GaN nanostructures are fabricated by MBE growth on self-implanted (1 1 1) Si substrates. Nanocapillary condensation is found to be an effective catalytic process fostering the formation of epitaxially aligned GaN nanorods in company with the thin film matrix. Changes of Si substrate surface morphology prior to deposition as a result of ion bombardments are responsible for the enhanced nanorod growth. This is attributed to the nanocapillary condensation of Ga droplets that serve as a medium to the vapor–liquid–solid growth of nanorods out of its supporting matrix.

Surface modification of Si(111) substrate by iron ion implantation: Growth of a thin β-FeSi2 layer

The processes in the synthesis of a thin layer of the semiconducting iron silicide (β-FeSi2) on the surface of a single-crystal Si(111) substrate by implantation of 195 keV Fe ions with a dose of 8×1017cm−2 are investigated. Using Rutherford backscattering spectrometry, x-ray diffraction and cross-sectional transmission electron microscopy, the structure and the phase composition of the synthesized layers are studied. The infrared transmittance spectra show the absorption at 310cm−1 as an indication of the initial nucleation of β-FeSi2 precipitates during the implantation of iron into silicon substrate.

Iron filled carbon nanotubes grown on substrates with thin metal layers and their magnetic properties

The thermal decomposition of ferrocene combined with a catalyst-assisted structuring of a Si-substrate surface is a favourable way to produce Fe-filled carbon nanotubes in good quality and in high yields. In this work we have studied the growth of such aligned filled nanotubes on iron and cobalt pre-coated Si-substrates and their dependence on the deposition time. The nanotube diameter depends on the used catalyst metal on the substrate surface. Magnetization measurements were carried out perpendicular (along tube axis) and parallel to the substrate and show excellent coercivities, a strong uniaxial anisotropy (ratios of H c,per/ H c,par up to 6) and high saturation magnetization moments per substrate square. The magnetic behavior has been also interpreted as a function of deposition time and of the catalyst metal on the substrate. These investigations were complemented by X-ray diffraction, which revealed a majority fraction of α-Fe and a small amount of Fe 3C.

Development of the Cleaning Method Using High-Speed Shear Flow of Ultrapure Water (2nd Report)

We notified that Cu concentration on the Si substrate surface could be reduced to less than 2.4×109atoms/cm2 by the cleaning method using high-speed shear flow of ultrapure water. But the mechanism of Cu removal in this cleaning method was not clarified. In this study, we have attempted the clarification of Cu removal mechanism by the observation and analysis of the Si substrate surface after the cleaning using high-speed shear flow of ultrapure water and SPM (sulfuric acid-hydrogen peroxide mixture) cleaning. In consequence, we showed that a lot of bosses were not observed on the Si substrate surface contaminated by Cu after the cleaning using high-speed shear flow of ultrapure water though after SPM cleaning. And we supposed the reasons about removing Cu from Si substrate and not forming a lot of bosses on the Si substrate surface by Pourbaix diagram for Cu-H2O system.

Study on nucleation and dynamic scaling of morphological evolution of ZnO film deposition by reactive magnetron sputtering

Atomic force microscopy has been applied to study the morphological evolution o f ZnO film on Si(100) and Si(111) substrates with a native oxide layer. With dyn amic scaling of the film morphology at different growth stages, the nucleation a nd growth behavior have been studied for ZnO films deposited by radio-frequency reactive magnetron sputtering. It is found that ZnO film has three nucleation st ages, namely the stages of initial nucleation, low-rate nucleation, and seconda ry nucleation. The growth exponents of the three stages are β1=1.04 ，β2=0.25±0.01 and β3=0.74 for ZnO film on Si(100) and β1=0.51，β2=0.08±0.02 and β3=0.63 for ZnO f ilm on Si(111), respectively. In the initial nucleation stage, the intrinsic def ects on Si substrates may be responsible for the surface roughening and the dens ity of surface defects determines the nucleation density of ZnO films. The growt h behavior of ZnO film is dominated by the diffusion effect and oriented growth mechanism, as well as the coarsening mechanism induced by the lattice mismatch s tress. In the low-rate nucleation stage, few new ZnO islands are detected and t he films are roughened slowly in morphology. The deposition rate plays a role of controlling the morphological evolution and the lattice mismatch stress may be released in this stage. The secondary nucleation of ZnO films may result from th e bombardment of energetic ions or atoms on the surface of Si substrates. In the secondary nucleation stage, shadowing effect may influence the roughening of Z nO films. In the stage of steady growth, ZnO films have a roughness value much l ower than the ones in nucleation stages and grow in the form of columnar grains.

Study of Cleaning Method for Si Substrate Using High-Speed Shear Flow of Ultrapure Water

Since organic contaminants, which adhere on the silicon substrate surface, have an adverse impact on the quality of the gate oxide films, it is very highly required for the current semiconductor fabrication processes to take them off the surface before producing the films. Therefore, some kinds of cleaning method for silicon substrate, such as SPM (Sulfuric acid-hydrogen Peroxide Mixture) cleaning, ozone water cleaning and ultraviolet exposure cleaning, have applied to remove organic contaminants from the substrate surface. But these cleaning methods exert a bad influence of the global environment and spend high cost for the semiconductor fabrication. On the contrary, we have developed the new cleaning method for the silicon substrate using the high-speed shear flow of only ultrapure water and composed the new cleaning system. In the result of cleaning the silicon substrata surface contaminated by dioctyl phthalate at 1×1015atoms/cm2, we demonstrated that DOP(dioctyl phthalate) concentration on the substrate reduced at the level of 1013atoms/cm2 using our cleaning system. Moreover, we showed that our cleaning method possessed oxidizing property to Si substrate surface and supposed that DOP removal mechanism from Si substrate surface and this oxidizing property were related.