Process control strategies for the gas phase synthesis of silicon nanoparticles (original) (raw)
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Aerosol Science and Technology, 2009
In this work, a two-dimensional model was developed for silicon nanoparticle synthesis by silane thermal decomposition in a sixway cross laser-driven aerosol reactor. This two-dimensional model incorporates fluid dynamics, laser heating, gas phase and surface phase chemical reactions, and aerosol dynamics, with particle transport and evolution by convection, diffusion, thermophoresis, nucleation, surface growth, coagulation, and coalescence processes. Because of the complexity of the problem at hand, the simulation was carried out via several sub-models. First, the chemically reacting flow inside the reactor was simulated in three dimensions in full geometric detail, but with no aerosol dynamics and with highly simplified chemistry. Second, the reaction zone was simulated using an axisymmetric two-dimensional CFD model, whose boundary conditions were obtained from the first step. Last, a twodimensional aerosol dynamics model was used to study the silicon nanoparticle formation using more complete silane decomposition chemistry, together with the temperature and velocities extracted from the reaction zone CFD simulation. A bivariate model was used to describe the evolution of particle size and morphology. The aggregates were modeled by a moment method, assuming a lognormal distribution in particle volume. This was augmented by a single balance equation for primary particles that assumed locally equal number of primary particles per aggregate and fractal dimension. The model predicted the position and size at which the primary particle size is frozen in, and showed that increasing the peak temperature was a more effective means of improving particle yield than increasing silane concentration or flowrate.
The Journal of Physical Chemistry A, 2004
Thermal decomposition of silane can be used to produce silicon nanoparticles, which have attracted great interest in recent years because of their novel optical and electronic properties. However, these silicon nanoparticles are also an important source of particulate contamination leading to yield loss in conventional semiconductor processing. In both cases, a fundamental knowledge of the reaction kinetics of particle formation is needed to understand and control the nucleation of silicon particles. In this work, detailed kinetic modeling of silicon nanoparticle formation chemistry was carried out using automated reaction mechanism generation. Literature values, linear free-energy relationships (LFERs), and a group additivity approach were incorporated to specify the rate parameters and thermochemical properties of the species in the system. New criteria for terminating the mechanisms generated were also developed and compared, and their suitability for handling an unbounded system was evaluated. Four different reaction conditions were analyzed, and the models predicted that the critical particle sizes were Si 5 for an initial H 2 /SiH 4 molar ratio of 90:10 at 1023 K and Si 4 for the same initial composition at 1200 K. For an initial H 2 /SiH 4 molar ratio of 99:1, the critical particle size was larger than or equal to Si 7 for both temperatures, but it was not possible to determine the exact critical particle size because of limitations in computational resources. Finally, the reaction pathways leading to the formation of nanoparticles up to the critical size were analyzed, and the important species in the pathways were elucidated.
Journal of The Electrochemical Society, 2000
The growth of silicon films via chemical vapor deposition (CVD) is of considerable importance in the microelectronics and photovoltaics industries. This process often involves the thermal decomposition of silane, which is achieved by heating the wafer or rod to be coated to a suitable temperature. A wide range of geometries and conditions are employed. For example, low-pressure chemical vapor deposition (LPCVD), at pressures around 1 Torr (133 Pa), is used with a stagnation-point flow geometry to deposit thin films of silicon in the fabrication of integrated circuits, while cylindrical polysilicon rods are grown on a heated filament using atmospheric-pressure CVD (APCVD).
Multi-scale modelling of silicon nanocrystal synthesis by Low Pressure Chemical Vapor Deposition
Thin Solid Films, 2011
A multi-scale model has been developed in order to represent the nucleation and growth phenomena taking place during silicon nanocrystal (NC) synthesis on SiO 2 substrates by Low Pressure Chemical Vapor Deposition from pure silane SiH 4. Intrinsic sticking coefficients and H 2 desorption kinetic parameters were established by ab initio modelling for the first three stages of silicon chemisorption on SiO 2 sites, i.e. silanol Si-OH bonds and siloxane Si-O-Si bridges. This ab initio study has revealed that silane cannot directly chemisorb on SiO 2 sites, the first silicon chemisorption proceeds from homogeneously born unsaturated species like silylene SiH 2. These kinetic data were implemented into the Computational Fluid Dynamics Fluent code at the industrial reactor scale, by activating its system of surface site control in transient conditions. NC area densities and radii deduced from Fluent calculations were validated by comparison with experimental data. Information about the deposition mechanisms was then obtained. In particular, hydrogen desorption has been identified as the main limiting step of NC nucleation and growth, and the NC growth rate highly increases with run duration due to the autocatalytic nature of deposition.
Journal of Aerosol Science, 2004
A numerical model has been developed to predict gas-phase nucleation, growth, and coagulation of silicon nanoparticles formed during thermal decomposition of silane. A detailed chemical kinetic model of particle nucleation was coupled to an aerosol dynamics model that includes particle growth by surface reactions, coagulation with instantaneous coalescence, and convective transport. Solution of the aerosol general dynamic equation was handled by three approaches: (1) the e cient and reasonably accurate method of moments;
Synthesis of Silicon Nanoclusters by Solid-Gas Reaction
Advanced Materials, 2000
Due to their potential applications in optoelectronic devices, silicon nanoparticles have become the focus of great scientific interest. Efforts to produce nanocrystalline, porous, or amorphous silicon particles have resulted in several different preparation routes to date. CVD methods are the techniques currently used to generate thin films of amorphous Si, where in most cases SiH 4 (often mixed with hydrogen or argon) is decomposed thermally (HOMOCVD) [1] or by electron (plasma enhanced CVD, glow
Synthesis of silicon nanoparticles for hydrogen gas production
Materials Today: Proceedings, 2020
Hydrogen is one of the promising alternative energy sources today. Hydrogen H2 is an ideal fuel with a high calorific value and a non-hazardous combustion product. Large volume of researches in the field of ''hydrogen energy" are carried out. Therefore, this research area attracts more and more attention of researchers from all over the world. In this work the synthesis of silicon nano-and micro particles was carried out in a plasma of radio frequency (RF) discharge in a mixture of monosilane (2%) and argon (98%) at different values of pressure, power and synthesis time. The SEM image and the chemical composition of the samples were obtained, and the particle size distribution was constructed. Also, graphs of the time dependence of particles nucleation at different plasma parameters and the distribution of the diameter and concentration of particles on the synthesis time in the Ar / SiH4 plasma were obtained.
2005
The synthesis of silicon nanocrystals (Si-NC) has attracted a great deal of interest due to their size-dependent optical properties. The appearance of a strong visible photoluminescence (PL) even at room temperature makes this kind of material very interesting for applications in optoelectronics and photonics. In this work, we report on the possibility to control the optical properties of silicon nanostructures by fine tuning of both preparation and processing parameters. Large amount of Si-based nano-powders were prepared by cw CO2 laser pyrolysis of gasphase precursors followed by annealing at different temperatures, in controlled atmosphere. After the heat treatment, the structural and optical analyses revealed the presence of size-controlled optical properties, characterized by the typical Si-NC red-IR emission with lifetime ranging from a hundred of μs to some ms. Next step was the nano-powder dispersion by several methodologies and their incorporation into a silica sol-gel matrix. The realization of a glassy material that preserves the powder luminescence opens the way to a wide range of applications. To this purpose we focused our attention on the study of the influence of the sol-gel processing steps on the optical properties of Si-nano-powders. Moreover, a study of 1.54 micron Er emission sensitizing effect from Si-based nanostructures in sol-gel glasses was performed and is presented here.
Advanced Laser Technologies 2004, 2005
The synthesis of silicon nanocrystals (Si-NC) has attracted a great deal of interest due to their size-dependent optical properties. The appearance of a strong visible photoluminescence (PL) even at room temperature makes this kind of material very interesting for applications in optoelectronics and photonics. In this work, we report on the possibility to control the optical properties of silicon nanostructures by fine tuning of both preparation and processing parameters. Large amount of Si-based nano-powders were prepared by cw CO 2 laser pyrolysis of gasphase precursors followed by annealing at different temperatures, in controlled atmosphere. After the heat treatment, the structural and optical analyses revealed the presence of size-controlled optical properties, characterized by the typical Si-NC red-IR emission with lifetime ranging from a hundred of µs to some ms. Next step was the nano-powder dispersion by several methodologies and their incorporation into a silica sol-gel matrix. The realization of a glassy material that preserves the powder luminescence opens the way to a wide range of applications. To this purpose we focused our attention on the study of the influence of the sol-gel processing steps on the optical properties of Si-nano-powders. Moreover, a study of 1.54 micron Er emission sensitizing effect from Si-based nanostructures in sol-gel glasses was performed and is presented here.