Nucleation Of Silicon Research Articles

Elementary Processes of Organic Thin Film Growth Studied by Modulated Molecular Beam Experiments

Interaction between molecules and surfaces and nucleation processes during organic thin film growth have been studied by modulated molecular beam experiments. After a brief introduction of the background and the experimental technique, we describe the results of our study on the interaction between pentacene and chemically modified SiO2 surfaces. Molecular migration on regularlly-stepped vicinal surfaces of silicon and crystal nucleation controlled by pulsed supply of the molecules are discussed on the basis of the experimental data on phthalocyanine and quinacridone.

Low-Temperature Microcrystalline Silicon Film Deposited by High-Density and Low-Potential Plasma Technique Using Hydrogen Radicals

As a novel direct deposition method of microcrystalline silicon, we have developed the high-density and low-potential plasma-enhanced silane generating chemical vapor deposition (CVD) system. We have studied a two-step deposition process which consists of the silicon nucleation step using atomic hydrogen (radicals) and the microcrystalline growth step using silane plasmas at low temperature. Transmission electron microscopy (TEM) and micro-ultraviolet Raman spectrometry (UV-Raman) analyses reveal that silicon films crystallize with a low defect density starting from the interface between the SiO2 substrate and the film. Furthermore, the electron mobility determined on the basis of the TFT characteristics indicates that this method is highly effective for the direct deposition of microcrystalline silicon.

Molecular dynamics study of homogeneous crystal nucleation in amorphous silicon

We successfully simulated homogeneous crystal nucleation in well-relaxed amorphous silicon by using molecular dynamics. The critical nucleus size evaluated by structural parameters such as potential energy, ring statistics, and bond-angle deviation, amounted to about 30–50 atoms. The shape of nucleus was nearly spherical. The results agree with the experimental data very well.

Solidification mechanisms of unmodified and strontium-modified hypereutectic aluminium–silicon alloys

The effects of strontium on the solidification mode of hypereutectic aluminium–silicon alloys have been studied. Samples were prepared from an aluminium–17 wt% silicon-based alloy and strontium was added at several different concentrations. The development of the microstructure was investigated by cooling curve analysis, interrupted solidification experiments and optical and scanning electron microscopy. It was found that nucleation of primary silicon is suppressed by additions of strontium. The suppressed nucleation results in supersaturation of the liquid prior to nucleation, and an increased growth rate after nucleation. As a result, the silicon crystals become less faceted and more dendritic with increasing strontium additions. Increasing the strontium concentration slightly refined the eutectic spacing and introduced a small amount of fibrous silicon. Electron back-scatter diffraction measurements were performed to determine the crystallographic relation between the primary and eutectic silicon phases. The eutectic silicon in the unmodified alloy does not have any crystallographic relationship with the primary silicon crystals. In contrast, the eutectic silicon crystals in the strontium-modified alloys often share an identical or twin relationship with nearby primary silicon crystals. The incidence of twinning within primary silicon crystals was relatively low and did not appear to increase with strontium additions.

Molecular-dynamics simulations of nucleation and crystallization in supercooled liquid silicon: Temperature-gradient effects

We have investigated atomistic processes of nucleation and crystallization in supercooled liquid silicon (Si) based on molecular-dynamics (MD) simulations using the Tersoff potential. MD cells composed of up to 8192 Si atoms were heated to produce melted Si, and then melted Si was quenched under various supercooled conditions with or without a temperature gradient and the corresponding nucleation processes were visualized. The critical nucleation radius was determined as a function of the amount of supercooling $\ensuremath{\Delta}T$ and it was found to be inversely proportional to $\ensuremath{\Delta}T.$ It was also found, in the case of supercooling under a linear temperature gradient, that nucleation first occurred at the lower-temperature region and then crystallization proceeded toward the high-temperature region with the (111) surface mostly parallel to the temperature gradient.

Modeling extended defect ({311} and dislocation) nucleation and evolution in silicon

End of range (EOR) defects are the most commonly observed defects in ultrashallow junction devices. They nucleate at the amorphous-crystalline interface upon annealing after amorphization due to ion implantation. EOR defects range from small interstitial clusters of a few atoms to {311} defects and dislocation loops. They are extrinsic defects and evolve during annealing. Li and Jones [Appl. Phys. Lett., 73, 3748 (1998)] showed that {311} defects are the source of the projected range dislocation loops. In this article, the same theory is applied to EOR dislocation loops to model the nucleation and evolution of the loops. The model is verified with experimental data and accurately represents the nucleation, growth, and Ostwald ripening stages of dislocation loop evolution. The density and the number of interstitials trapped by dislocation loops are compared with the experimental results for several annealing times and temperatures.

Polycrystalline silicon films by aluminium-induced crystallisation: growth process vs. silicon deposition method

Polycrystalline silicon films were fabricated by aluminium-induced crystallisation (AIC) of aluminium/silicon bi-layer on thermally oxidised Si (t-SiO 2) substrates. The aluminium layer was deposited onto the substrates by electron beam evaporation. Here we investigate if the properties of the silicon precursor film influence the AIC layer exchange process. The silicon layer was deposited by different methods namely plasma enhanced-CVD and DC magnetron sputtering which led to different crystallinity including amorphous and nano(micro)crystalline phases as analysed by Raman spectroscopy. We have investigated the silicon nucleation rate vs. the annealing parameters and the deposited silicon structure. The resulting poly-Si films were analysed by optical and scanning electron microscopy looking to the grain size, presence of Si islands and thermal budget (temperature, time).

Effect of SiCp content on cooling curve characteristics and solidification kinetics of Al-Si/SiCp cast composites

The purpose of this work was to explore the effect of the presence of different quantities of SiCp on the cooling curve characteristics, latent heat released and solidification kinetics, associated with the cooling and solidification of Al-Si/SiCp composites produced by the stir casting process. An increase in SiCp content in A356/SiCp metal matrix composites produces a shortening of the associated cooling curve and an increase in the eutectic growth temperature with respect to the monolithic metal matrix alloy, cooled under the same experimental conditions. The shortening of the cooling curves could be explained as a result of the measured decrease in the amount of latent heat released during solidification. The increase in the maximum eutectic growth temperature is apparently due to the nucleation of eutectic silicon by SiCp and also to the change in the growth kinetics and morphology of the eutectic Si from fibrous to platelike. IJCMR/422

Optimized Parameters for Modeling Oxygen Nucleation in Silicon

Optimized Parameters for Modeling Oxygen Nucleation in Silicon

Nucleation and growth of nanocrystalline silicon studied by TEM, XPS and ESR

Nucleation and growth process of nanocrystalline silicon (nc-Si) formed by radio frequency (RF) sputtering method and subsequently thermal treatment has been studied by using high resolution-transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) methods. Silicon (Si) atoms in amorphous sub-oxide (a-SiO x ) film were coagulated to form nc-Si with diameter of approximately 1.5 nm in the film after annealing at 900 °C. The size and number of nc-Si increased with the increase of the annealing temperature. The average size of nc-Si observed at annealing temperature of 1100 °C was 2.5 nm. We also observed nc-Si with high pressure phase in the annealed sample.

SOI/Bulk Hybrid Wafer Fabrication Process Using Selective Epitaxial Growth (SEG) Technique for High-End SoC Applications

The size of SiN region and the growth condition were investigated for the robust process of selective epitaxial growth for the fabrication of the silicon on insulator (SOI)/bulk hybrid wafer. Silicon nucleation on SiN layer was observed during the selective epitaxial growth process using SiH2Cl2/HCl/H2 mixture at 1000–1100°C. At the center of SiN region, the coverage of SiN region by nucleated silicon increases with the increase of growth rate of epitaxial silicon layer, deposition time and the size of SiN region. At the edge of SiN region, there are nucleation-free regions. Also, silicon nucleation on SiN layer has an incubation time. The incubation time increases with the decrease of the size of SiN region. The incubation time for SiN region which has rectangular shape is longer than that for SiN region of square shape which has the same area. Under the condition which has the same growth rate regardless of the deposition temperature, there is an optimum temperature for suppression of silicon nucleation on SiN layer. These facts mean that the size of the SiN cap layer of SOI region should be decided carefully for the fabrication of SOI/bulk hybrid wafer by the selective epitaxial growth method.

Numerical Studies Of The Dynamics Of Silicon: Relaxation, Nucleation And Energy Landscape

AbstractUsing various simulation techniques, such as molecular dynamics and the activation-relaxation technique, we are slowly developing a consistent picture of the dynamical properties of amorphous silicon. For example, results of an extensive search for the activated events surrounding a single minimum, in a well-relaxed model represented by a modified Stillinger-Weber potential, confirm that barrier height at the transition point, for activated mechanisms, is determined essentially by the binding energy of a single bond and not the details of the mechanism. We will discuss these results in some detail as well as recent simulations of nucleation in liquid and amorphous silicon.

Stress-Induced Nucleation of Microcrystalline Silicon from Amorphous Phase

We have demonstrated that a high intrinsic stress in the hydrogenated amorphous silicon (a-Si:H) phase is essential for microcrystalline silicon (µc-Si:H) nucleation from the amorphous phase at low temperatures (<450°C). In plasma-enhanced chemical vapor deposition at high hydrogen dilution, µc-Si:H nucleation was observed only when compressive stress inside a-Si:H exceeds ∼750 MPa, regardless of deposition temperature. As the result of alternating a-Si:H deposition and H2-plasma treatment, we confirmed that the high compressive stress in a-Si:H originates from H inserted into the a-Si:H network. The high compressive stress in a-Si:H was found to enhance the formation of a SiHn (n=1-2) complex that has been proposed to be a precursor for µc-Si:H nucleation. Based on the above results, we present a broad overview of stress-induced µc-Si:H nucleation from the amorphous phase.

Nucleation and growth behavior of primary silicon in alumina fiber reinforced hypereutectic Al-Si composite

Nucleation and growth behavior of primary silicon in alumina fiber reinforced hypereutectic Al-Si composite

Modeling Dislocation Loop Nucleation and Evolution in Germanium, Arsenic and Boron Implanted Silicon

AbstractA loop nucleation and evolution model in Si+ implanted Silicon was previously introduced [1]. In this study, the model is extended to predict end of range (EOR) and projected range defect nucleation and evolution created by different ion implant species such as Germanium, Arsenic and Boron. The model assumes that all the nucleated loops come from {311} unfaulting and the loop density and average loop radius follow a log normal distribution. The model is verified with the experimental data obtained from literature for Germanium [2], Arsenic [3] and Boron [4] implanted Silicon for different implant doses and energies. Modeling results are in agreement with the experimental results.

Microcrystalline silicon nucleation sites in the sub-surface of hydrogenated amorphous silicon

We have characterized surface structures of hydrogenated amorphous silicon (a-Si:H) by applying infrared attenuated total reflection spectroscopy, in order to investigate the phase transition from a-Si:H to microcrystalline silicon (μc-Si:H). At the onset of μc-Si:H nucleation from the a-Si:H phase, an infrared absorption peak at 1937±5 cm −1 assigned to the SiH n ( n=1–2) complex is detected in a 5-Å thick region of the a-Si:H sub-surface. The SiH n complex concentration within the a-Si:H sub-surface region showed a clear relationship with the μc-Si:H nucleation. We propose that the SiH n complex, formed by insertion of H into a strained Si–Si bond, contributes to the reactions that result in μc-Si:H nucleus formation.

Nucleation and growth of silicon on ceramic substrates by RTCVD at atmospheric pressure

Thin-film solar cells from silicon on insulating substrates (SOI) are a serious option to reduce the cost and silicon production mass. Here we investigated nucleation and growth of silicon on alumina and mullite ceramics in a lamps-heating assisted CVD reactor working at atmospheric pressure with trichlorosilane as a precursor gas. The nucleation density and the structural quality of the deposited Si layers were analyzed as a function of the deposition conditions and the structure and composition of the ceramic substrate. The results were compared with the well-known growth mechanism of silicon on amorphous substrates like SiO 2 . Optimal conditions allowed deposition of 20-30μm thick polycrystalline silicon with grains up 15 μm in size and oriented. These layers are very suitable for solar cells processing.

Real-time spectroscopic ellipsometry studies of the nucleation and grain growth processes in microcrystalline silicon thin films

Real-time spectroscopic ellipsometry (SE) has been applied to investigate the nucleation and grain growth processes in microcrystalline silicon $(\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H})$ thin films deposited by a conventional plasma-enhanced chemical vapor deposition using hydrogen dilution of silane source gas. Real-time SE results revealed the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ nucleation from hydrogenated amorphous silicon $(a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H})$ phase, followed by the coalescence of isolated $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grains exposed on growing surfaces. In the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grain growth process, the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ shows an enhanced surface roughening. The onset of the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grain growth and the coalescence of $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grains were readily characterized by monitoring surface roughness evolution. We found that a $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ nuclei density increases significantly as the hydrogen dilution ratio $R=([{\mathrm{H}}_{2}]/[{\mathrm{SiH}}_{4}])$ increases. In contrast, a film thickness at which most of the surface is covered with the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H},$ gradually reduces with increasing R. The real-time SE results described above showed remarkable agreement with those estimated by transmission electron microscopy and atomic force microscopy. For the $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}/\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ mixed-phase surface formed during the phase transition, however, the SE results showed relatively large errors in the analyses. Such difficulties in the real-time SE analysis for the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ thin film are discussed.

Effect of Strained Si-Si Bonds in Amorphous Silicon Incubation Layer on Microcrystalline Silicon Nucleation

ABSTRACTIn order to investigate microcrystalline silicon (μc-Si:H) nucleation from the hydrogenated amorphous silicon (a-Si:H) phase, we performed a H2-plasma treatment of a-Si:H layers deposited at different temperatures. In the H-treatment experiment, the formation process of an infrared peak at ∼1937 cm-1, assigned to SiHn (n=1∼2) complex, is studied, as the SiHn complex is proposed to be a precursor for the μc-Si:H nucleation. With increasing the a-Si:H deposition temperature, the total amount of the SiHn complex formed by the H treatment increased. Nucleation of μc-Si:H under high H2-dilution conditions showed a clear relationship with the SiHn complex formed by the H treatment. The SiHn complex formation process, in terms of strained Si-Si bond breaking by H, is discussed.

Structure factors of modified liquid Al–Si alloys

The structure factor and the coordination numbers of liquid Al–Si alloys with different Si content have been measured by a high temperature X-ray diffractometer. Radial distribution functions (RDFs), the nearest atomic distance and the coordination numbers of eutectic Al–Si alloys before and after being modified with Sr and Sb were studied. The RDFs of the liquid alloy were decomposed by five Gaussian peaks. The results show that a Si–Si covalent bond exists in the liquid of eutectic and hyper-eutectic alloys. Sr in the liquid Al–Si has a capability to weaken the covalent bonds of Si–Si, suppressing the nucleation of the eutectic silicon phase. On the other hand, Sb in the liquid Al–Si increases the order degree of Si atoms, decreasing the supercooling degree of the nucleation and promoting the nucleation of eutectic silicon.