Nucleation Of Silicon Research Articles

Two Paths of Oxide Precipitate Nucleation in Silicon

The coherent agglomeration of interstitial oxygen into single-plane and double-plane plates can explain the two peaks in the M-shaped nucleation curves in Czochralski silicon. The density of nucleation sites for the double-plane plates corresponds to the VO2 concentration. Ab initio calculations have shown that the agglomeration of oxygen atoms in single-plane and doubleplane plates is energetically favorable. These plates are under compressive strain. VO2 agglomeration plays only a minor role for modeling the M-shaped nucleation curves because of prior homogenization treatments. It is of much higher impact if as-grown wafers are subjected to nucleation anneals because of the higher vacancy concentration which was frozen in during crystal cooling. This results in higher nucleation rates at higher temperatures. Because the oxygen diffusivity below 700 °C is important for the nucleation rate and many controversial results about the diffusivity in this temperature range were published, we have analyzed the data from literature. We have demonstrated that the effective diffusivity of oxygen at temperatures below 700 °C which corresponds to the quasi equilibrium dimer concentration is very similar to the extrapolation from oxygen diffusivity at high temperature. The high effective diffusivities from out-diffusion and precipitation experiments, and the somewhat lower effective diffusivities from dislocation locking experiments are the result of an ongoing formation of fast diffusing dimers because the equilibrium is disturbed as the result of the strongly increasing difference in the diffusion length between interstitial oxygen and the fast diffusing dimer with decreasing temperature.

Very high growth rate of 4H-SiC epilayers using the chlorinated precursor methyltrichlorosilane (MTS)

The chlorinated precursor methyltrichlorosilane (MTS), CH 3SiCl 3, has been used to grow epitaxial layers of 4H-SiC in a hot wall chemical vapour deposition (CVD) reactor with growth rates higher than 100 μm/h. The addition of chlorinated species to the gas mixture prevents silicon nucleation in the gas phase, thus allowing higher input flows of the precursors resulting in much higher growth rate than that of standard silicon carbide (SiC) epitaxial growth using only silane, SiH 4, and hydrocarbons as precursors. Since MTS contains both silicon and carbon, with the C/Si ratio 1, MTS was used both as single precursor and mixed with silane or ethylene to study the effect of the C/Si and Cl/Si ratios on growth rate, morphology, and doping of the epitaxial layers. When using only MTS as precursor, the growth rate showed a linear dependence on the MTS molar fraction in the reactor. The growth rate dropped for C/Si<1 but was constant for C/Si>1. Further, the growth rate decreased with lower Cl/Si ratio. This study shows that MTS is a promising precursor for homoepitaxial growth of SiC within the concept of chloride-based SiC growth.

Nanocrack nucleation in polycrystalline silicon during grain-boundary sliding

A theoretical model is proposed to describe nanocrack nucleation in polycrystalline silicon. In terms of this model, nanocrack nucleation is stimulated by grain-boundary sliding, which creates sources of local stresses in triple junctions of grain boundaries. The relaxation of these local stresses is the main driving force of nanocrack nucleation near triple junctions in polycrystalline silicon, in which grain-boundary sliding contributes substantially to plastic deformation under cyclic loading at room temperature. The model is used to calculate the critical external stress required for nanocrack nucleation in polycrystalline silicon.

Very high epitaxial growth rate of SiC using MTS as chloride-based precursor

We present results on chloride-based homoepitaxial growth of 4H-SiC in a hot wall CVD reactor. The addition of chlorinated species to the gas mixture prevents silicon nucleation in the gas phase, thus allowing higher input flows of the precursors resulting in much higher growth rate than that of standard SiC epitaxial growth using only silane, SiH 4, and ethylene, C 2H 4, as precursors. We have achieved growth rates higher than 100 μm/h, as compared to 5 μm/h for the standard case. The chlorinated precursor used is methyltrichlorosilane (MTS), CH 3SiCl 3, but since MTS contains both silicon and carbon, with the C/Si ratio 1, we have also added silane or ethylene to optimise the C/Si ratio in order to improve the morphology of the epitaxial layers. We present studies on how the growth rate depends on both the flow of MTS and C/Si ratio. The morphology of the grown epitaxial layer has been investigated using Nomarski microscope and atomic force microscope showing extremely smooth surface and low epi-defect density. The net doping has been determined using capacitance-voltage measurements. Low temperature photoluminescence and high-resolution X-ray diffraction confirm the high quality of the grown epilayers.

Surface nucleation of the (111) plane of excimer laser annealed Si on SiO2 substrates: A molecular dynamics study

We have investigated the nucleation and crystallization processes of molten silicon (Si) on SiO2 substrates by performing molecular dynamics (MD) simulations based on the modified Tersoff potential parameters. A heat flow that leads to a steady fall of the local temperature in the molten Si is achieved by determining the atomic movements with the combination of Langevin and Newton equations. Good agreement is reached between the predictions of temperatures based on the kinetic energies and the velocity distributions of atoms at local regions. The results of simulations revealed that the (111) plane of the Si nuclei formed at the surface was predominantly parallel to the substrate of MD cell. The surface energies of the (100), (110), and (111) planes of Si at 77 K were calculated to be 2.27, 1.52, and 1.20 J∕m2, respectively, and they were in good agreement with the experimental results. The lowest value of surface energy, 1.20 J∕m2, for the (111) plane at 1700 K was obtained under the condition of elastic hard wall. The surface energy anisotropy is expected to be a driving force for the preferential surface nucleation of Si(111) at the surface.

Phase transformations of an alumina membrane and its influence on silicon nucleation during the aluminium induced layer exchange

The aluminium induced layer exchange process is used for growing crystalline Si films on amorphous substrates like glass, which are further epitaxially thickened and can be used for photovoltaic applications. In this work we investigated Al 2O 3 membranes separating the Al and Si layer during the layer exchange by means of high-resolution transmission electron microscopy and studied the influence of the membranes' structure on crystallization of Si. We observed a phase transformation of the membrane from the amorphous state to γ-Al 2O 3 at exchange temperatures at above 450 °C. At higher temperatures this transformations induces cracks into the thin membrane. We further discuss the influence of this phase transformation on the preferential orientation of the growing Si grains.

Effects of oxygen in Ni films on Ni-induced lateral crystallization of amorphous silicon films at various temperatures

Effects of oxygen in Ni films on the Ni-induced lateral crystallization (NILC) of amorphous silicon (a-Si) films at various temperatures have been investigated. It was found that oxygen in Ni films retarded the nucleation of polycrystalline silicon (poly-Si) from a-Si, but had little effect on the growth rate of poly-Si. This is because that needed an incubation period to be reduced to Ni metal for the subsequent mediated crystallization of a-Si.

Nucleation and Growth of Quasicrystalline Silicon Thin Films on Glass Substrate Synthesized by Ceramics Hot Wire Chemical Vapor Deposition

AbstractIn this work, we report on nucleation and growth of silicon thin films on glass substrate with “five-fold” symmetry and “six-fold” symmetry by ceramics hot wire chemical vapor deposition. We observed “confinement of heat and photon” is a powerful approach in developing silicon thin films with novel structure, i.e. quasicrystalline silicon thin films on glass substrate. We found unambiguously that photons emitted from the hot filament influence the nucleation of nanocrystal silicon that produces new type of silicon thin films with “five-fold” symmetry and “six-fold” symmetry.

The growth model and experimental validation of size-controlled nanocrystalline silicon

According to the processes of nucleation and growth of nanocrystalline silicon (nc-Si) with shape changing from sphere-like to disc-like in the a-SiNx/a-Si:H/a-SiNx sandwich structure or a-Si :H/a-SiNx multilayer structure, we have proposed the theoretical model of constrained crystallinzation based on the classical thermodynamics, in which the increase of the interfacial energy between nc-Si and a-SiNx causes the growth of nc-Si to halt, and concludes the critical thickness of a-Si sublayer (34 nm) for constrained crystallization, The model of constrained growth has been validated in a-SiNx/nc-Si/a-SiNx sandwich and nc-Si/a-SiNx multilayer structures formed by laser annealing and thermal annealing.

Pulsed Laser Deposition of Boron Doped Si70Ge30

AbstractThe main objective of this work is to investigate the possibility of combining pulsed laser deposition (PLD) and pulsed laser annealing to realize p-type Si1-xGex thin films suitable for post-processing MEMS on top of standard pre-fabricated driving electronics. The main advantage of this approach is that the substrate is kept at a CMOS backend compatible temperature throughout the deposition and thus the MEMS integration process will have no thermal impact on the underlying electronics. In addition, it is demonstrated that PLD Si1-xGex has good adhesion to SiO2 and accordingly there is no need for a silicon nucleation which is the case for LPCVD and PECVD. Furthermore, this technique is much more economical than CVD as it does don't imply using expensive gas precursors such as germane and silane.

Modeling of Silicon Nanodots Nucleation and Growth Deposited by LPCVD on SiO2 : From Molecule/surface Interactions to Reactor Scale Simulations

ABSTRACTWe present first results combining models at continuum and atomistic (DFT) levels to improve understanding of key mechanisms involved in silicon nanodots (NDs) synthesis on SiO2 by Low Pressure Chemical Vapor Deposition (LPCVD) from silane SiH4. In particular, by simulating an industrial LPCVD reactor using the CFD code Fluent, we find that the deposition time could be increased and then the reproducibility and uniformity of NDs deposition could be improved when highly diluting silane in a carrier gas. A consequence of this high dilution seems to be that the contribution to deposition of unsaturated species such as silylene SiH2 highly increases. This result is important since our first DFT calculations have shown that silicon chemisorption on silanol Si-OH or siloxane Si-O-Si bonds present on SiO2 substrates could only proceed from silylene (and probably from other unsaturated species). The silane saturated molecule could only contribute to NDs growth, i.e. silicon chemisorption on already deposited silicon bonds. Increasing silylene contribution to deposition in highly diluting silane could then also exalt silicon nucleation on SiO2 substrates and then increase NDs density.

Microscopic Mechanisms of Cobalt Disilicide Nucleation in Silicon

The paper presents the results of experimental in-situ observations of cobalt disilicide nucleation in Co+ implanted silicon and ab initio simulations of energies of small cobalt and cobaltvacancy clusters. Based on these results, microscopic nucleation mechanisms of different types of CoSi2 precipitates are discussed.

High growth rate process in a SiC horizontal CVD reactor using HCl

The results of a new epitaxial process using an industrial 6 × 2″ wafer reactor with the introduction of HCl during the growth have been reported. A complete reduction of silicon nucleation in the gas phase has been observed even for high silicon dilution parameters (Si/H 2 > 0.05%) and an increase of the growth rate until about 20 μm/h has been measured. Photoluminescence at room temperature and at 50 K was used for defects quantification and distribution. On these wafers grown using HCl high voltage Schottky diodes have been realized. The diodes were analyzed by current–voltage ( I– V) characteristics.

A novel method for growing polycrystalline Ge layer by using UHVCVD

Poly-Ge grown on SiO 2 substrates by using one-step ultra-high vacuum chemical vapor deposition (UHVCVD) process with thin Si nucleation layers at very low deposition temperature (350 °C) was demonstrated. The results demonstrated that the polycrystalline silicon (poly-Si) nucleation layer is needed for the growth of polycrystalline germanium (poly-Ge) on SiO 2 substrates at low growth temperature. SEM image presents the films with uniform grain size and uniform thickness occurring in the samples. The grain size of poly-Ge is about 100 nm. The Raman shift spectrum and XRD spectrum also identified that films are high quality poly-Ge by using this method.

Influence of the substrate's surface morphology and chemical nature on the nucleation and growth of microcrystalline silicon

Hydrogenated microcrystalline silicon (μc-Si:H) layers about 500 nm thick were deposited in the same run on flat and rough substrates (rms = 60 nm) of various chemical nature. This study reveals that the spatial distribution of the microcrystalline/amorphous phases within the layer depends on the substrate's topography. The influence of the chemical nature of the substrate is shown to be preponderant on the layers nucleation. In particular, this study shows that nucleation density is the highest on plasma enhanced chemical vapor deposited silicon dioxide, whereas it is independent of the substrate's surface topography. Finally, the interpretation of Micro-Raman experiments for the evaluation of the respective volume fractions of amorphous/microcrystalline phases in the layers is discussed in relation with their spatial distribution.

Effects of Epitaxial Layer Growth Parameters on the Defect Density and on the Electrical Characteristics of Schottky Diodes

The effects of the Si/H2 ratio on the growth of the epitaxial layer and on the epitaxial defects was studied in detail. A large increase of the growth rate has been observed with the increase of the silicon flux in the CVD reactor. Close to a Si/H2 ratio of 0.05 % silicon nucleation in the gas phase occurs producing a great amount of silicon particles that precipitate on the wafers. The epitaxial layers grown with a Si/H2 ratio of 0.03% show a low defect density and a low leakage current of the Schottky diodes realized on these wafers. For these diodes the DLTS spectra show thepresence of several peaks at 0.14, 0.75, 1.36 and 1.43 eV. For epitaxial layers grown with higher values of the Si/H2 ratio and then with an higher growth rate, the leakage current of the Schottky diodes increases considerably.

New Achievements on CVD Based Methods for SiC Epitaxial Growth

The results of a new epitaxial process using an industrial 6x2” wafer reactor with the introduction of HCl during the growth have been reported. A complete reduction of silicon nucleation in the gas phase has been observed even for high silicon dilution parameters (Si/H2&gt;0.05) and an increase of the growth rate until about 20 µm/h has been measured. No difference has been observed in terms of defects, doping uniformity (average maximum variation 8%) and thickness uniformity (average maximum variation 1.2 %) with respect to the standard process without HCl.

Robustness of a Selective Epitaxial-Growth Process of Silicon and Its Application to the Fabrication of a High-Quality Hybrid SOI Wafer

Robustness of a selective epitaxial growth of silicon is demonstrated. The process window of selectivity was estimated quantitatively using the Taguchi method and signal-to-noise ratio analysis for the first time. Both the number of the silicon nuclei on the mask layer and the growth rate of silicon on a silicon substrate were investigated as the output parameters of the Taguchi method. One of the most effective process parameters for the suppression of silicon nucleation on the mask layer without retarding the growth rate of silicon is revealed to be the flow rate of SiH/sub 2/Cl/sub 2/. By calculating the number of the silicon nuclei, which could not be detected by an available measurement method, the process window of the selectivity could be determined with which a wafer with selective epitaxial silicon layer having LSI-quality could be fabricated. A high-quality silicon-on-insulator (SOI) wafer that has both an SOI region and bulk-silicon region can be obtained, and a high-quality embedded device could be realized on the SOI wafer.

Control of the nucleation density of Si quantum dots by remote hydrogen plasma treatment

The influence of surface pretreatments by remote hydrogen and/or argon plasma on the silicon nucleation density on thermally grown SiO 2 in the early stages of low pressure chemical vapor deposition (LPCVD) using monosilane (SiH 4) has been studied to control the areal density of Si quantum dots (Si-QDs) on SiO 2. In the remote H 2 (or D 2) plasma treatments prior to SiH 4-LPCVD, the formation of Si OH (Si OD) surface bonds, which act as reactive sites, was confirmed from no changes in the SiO 2 surface microroughness and in the thickness. In fact, by a H 2 plasma pretreatment, the areal density of Si-QDs as high as 7 × 10 10 cm −2 was obtained in the LPCVD condition of the dot density with as low as 6 × 10 8 cm −2 on as-grown SiO 2. By changing the pressure and the substrate temperature in the H 2 plasma pretreatment, the dot density was controlled in the range of 4 × 10 9 to 7 × 10 10 cm −2. Further increase in the dot density and improvement of the dot size uniformity was also demonstrated by the pretreatment of Ar plasma followed by H 2 plasma, presumably because of improved uniformity and integrity in SiO 2 surface coverage with OH bonds just before LPCVD.

Molecular Dynamics Studies of Surface Nucleation and Crystal Growth of Si on SiO2Substrates

AbstractMolecular dynamics (MD) simulations of atomistic processes of nucleation and crystal growth of silicon (Si) on SiO2substrate have been performed using the Tersoff potential based on a combination of Langevin and Newton equations. A new set of potential parameters was used to calculate the interatomic forces of Si and oxygen (O) atoms. It was found that the (111) plane of the Si nuclei formed at the surface was predominantly parallel to the surface of MD cell. The values surface energy for (100), (110), and (111) planes of Si at 77 K were calculated to be 2.27, 1.52, and 1.20 J/m2, respectively. This result suggests that, the nucleation leads to a preferred (111) orientation in the poly-Si thin film at the surface, driven by the lower surface energy.