Decomposition Of Silane Research Articles

Time-dependent gas phase kinetics in a hydrogen diluted silane plasma

The gas phase kinetics in a high-pressure hydrogen diluted silane plasma has been studied at time scales of 10−2–6×102 s. The time-resolved gas phase composition shows the following kinetics at different time scales: silane decomposition and polysilane generation in ≲2×10−1 s, nanoparticle formation and plasma density reduction in 10−1–100 s, polysilane accumulation in 100–102 s, and silane depletion and electrode heating in ≳101 s. Disilane radicals are implied to be the dominant film precursors in addition to silyl radicals.

Induction Delay Times and Detonation Cell Size Prediction of Hydrogen-Nitrous Oxide-Diluent Mixtures

Silane-nitrous oxide mixtures are widely used in some industries such as semiconductor manufacturing. Since the decomposition of silane is faster than that of N2O and involves the formation of H2, the H2-N2O system might be an important sub-system of the silane oxidation mechanism. The induction delay times of this system have been widely studied in the low pressure range. Aim of the present study is to investigate the high-pressure behaviour of H2-N2O-Ar. Induction delays behind reflected shock waves have been measured between 1300–1860 K, at the pressure of 910±50 kPa for mixtures with equivalence ratios of 0.5, 1, and 2. It has been shown that equivalence ratio variations have no effect on induction delays. The modeling of delays has been improved by including an excited OH* kinetic sub-mechanism. Finally, various techniques of detonation cell size prediction have been evaluated in comparison with available experimental data.

Effect of Nitrogen on the Stability of Silicon Nanocrystals Produced by Decomposition of Alkyl Silanes

Si nanocrystals 1−10 nm in size highly resistant to oxidation were prepared by thermal (680 °C) or gold-induced (450−600 °C) decomposition of tetramethylsilane and tetraethylsilane using trioctylamine as an initial solvent. Transmission electron microscopy analysis of samples obtained in the presence of gold showed that Si nanocrystals form via solid-phase epitaxial attachment of Si to the gold crystal lattice. The results of computational modeling performed using first principles density functional theory calculations show that the enhanced stability of nanocrystals to oxidation is due to the presence of N or N-containing groups on the surface of nanocrystals.

High quality passivation for heterojunction solar cells by hydrogenated amorphous silicon suboxide films

In this letter, we report on our investigations of hydrogenated amorphous silicon suboxides (a-SiOx:H) used as a high quality passivation scheme for heterojunction solar cells. The a-SiOx:H films were deposited using high frequency (70MHz) plasma enhanced chemical vapor deposition by decomposition of carbon dioxide, hydrogen, and silane at a substrate temperature of around 155°C. High effective lifetimes of outstanding 4ms on 1Ωcm n-type float-zone material and a surface recombination velocity of ⩽2.6cm∕s have been repeatedly obtained. Optical analysis revealed a distinct decrease of blue light absorption in the a-SiOx:H films compared to commonly used intrinsic amorphous silicon passivation used in heterojunction cells.

Investigation of the emitter band gap widening of heterojunction solar cells by use of hydrogenated amorphous carbon silicon alloys

The hydrogenated amorphous carbon-silicon alloys [a-SixC1−x(n):Hy] and [a-Six(n):Hy] layers were investigated in order to prove the feasibility to widen the optical band gap in emitters of the heterojunction solar cells. The alloys were fabricated by decomposition of silane (SiH4), phosphine (PH3), methane (CH4), and hydrogen (H2), using a plasma enhanced chemical vapor deposition. Particularly, we focused on the incorporation of hydrogen and carbon within the resulting [a-SixC1−x(n):Hy] and [a-Six(n):Hy] films, which later form the emitter. The corresponding local vibrational modes of Si−Hx, C−H, and the corresponding network have been analyzed by μ-Raman spectroscopy. The addition of carbon degrades the photoelectronic properties in the emitter layer. This deterioration can be minimized by H dilution. The resulting optical band gap EG as well as the thickness of the emitter were determined by spectroscopic ellipsometry. It was confirmed that the band gap EG can be tailored by using an appropriate gas mixture during the decomposition. Furthermore, we analyzed the I−V characteristics of the prepared heterojunction solar cells. A trade-off between the electrical defects density and the optical losses induced an improvement of the I−V characteristics with increasing carbon and hydrogen concentration in the feedstock during the deposition.

In Situ Mass Spectrometry for Chemical Identification in SiC Epitaxial Deposition

A quadrupole mass spectrometer unit was utilized to accurately detect the chemical species present inside a SiC CVD reactor growth chamber before, during, and after epitaxial deposition. The in-situ mass spectrometer has been able to confirm the presence of silane (SiH4) and propane (C3H8) decomposition products (eg. Si and CH4) that were predicted from chemical modelling, and give insight into specific reaction kinetics. Additionally, the mass spectrometer has positively detected trace amounts of oxygen, which has helped to identify process weaknesses and possible sources of vacuum leaks.

A novel method for suppressing silicidation of tungsten catalyzer during silane decomposition in Cat-CVD

Growth of tungsten silicide (WSi x ) on tungsten (W) catalyzer surface is investigated by monitoring resistance change of heated W wire in silane (SiH 4) atmosphere. To know a method suppressing the silicide formation, the effect of carbonization of W surface is also studied. Resistance change of heated W, observed in initial stage just after SiH 4 introduction, is brought about increase in power consumption due to decomposition of SiH 4. This power consumption can be drastically reduced when W surface is carbonized. Therefore, carbonization of tungsten surface is effective to stabilize the catalyzer temperature and to suppress W silicidation.

Hot Ta filament resistance in-situ monitoring under silane containing atmosphere

Monitoring of the electrical resistance of the Ta catalyst during the hot wire chemical vapor deposition (HWCVD) of thin silicon films gives information about filament condition. Using Ta filaments for silane decomposition not only the well known strong changes at the cold ends, but also changes of the central part of the filament were observed. Three different phenomena can be distinguished: silicide (stoichiometric Ta X Si Y alloys) growth on the filament surfaces, diffusion of Si into the Ta filament and thick silicon deposits (TSD) formation on the filament surface. The formation of different tantalum silicides on the surface as well as the in-diffusion of silicon increase the filament resistance, while the TSDs form additional electrical current channels and that result in a decrease of the filament resistance. Thus, the filament resistance behaviour during ageing is the result of the competition between these two processes.

Radical species involved in hotwire (catalytic) deposition of hydrogenated amorphous silicon

Threshold ionization mass spectroscopy is used to measure the radicals that cause deposition of hydrogenated amorphous silicon by “hotwire” (HW), or “catalytic,” chemical vapor deposition. We provide the probability of silane (SiH 4) decomposition on the HW, and of Si and H release from the HW. The depositing radicals, and H atoms, are measured versus conditions to obtain their radical-silane reaction rates and contributions to film growth. A 0.01–3 Pa range of silane pressures and 1400–2400 K range of HW temperatures were studied, encompassing optimum device production conditions. Si 2H 2 is the primary depositing radical under optimum conditions, accompanied by a few percent of Si atoms and a lot of H-atom reactions. Negligible SiH n radical production is observed and only a small flux of disilane is produced, but at the higher pressures some Si 3H n is observed. A Si–SiH 4 reaction rate coefficient of 1.65 ⁎ 10 − 11 cm 3/s and a H + SiH 4 reaction rate coefficient of 5 ⁎ 10 − 14 cm 3/s are measured.

Computational Fluid Dynamics (CFD) Modeling of a Laser-Driven Aerosol Reactor

Here we present a detailed 3-dimensional computational fluid dynamics (3D CFD) model of a laser-driven (photothermal) reactor system used in our laboratory to produce nanoparticles of silicon and other materials. This model includes detailed descriptions of the fluid flow, heat and mass transfer, and chemical reactions leading to silane decomposition in the gas phase. Eight chemical reactions and eight chemical species were included in the reacting flow simulation. The overall characteristics of the photothermal reactor system were captured. Temperature and velocity profiles along the axis of the reactor were extracted from the simulations and used with a simple 1D aerosol dynamics model to predict particle size, concentration and size distribution.

Computational Modeling of Silicon Nanoparticle Formation

Particulate contamination formed by reactions of silicon- hydrogen species within silicon chemical vapor deposition processes is an important source of yield loss. On the other hand, intentional synthesis of silicon nanoparticles is of great interest because of the unique properties of nanostructured silicon. Thus, fundamental understanding of the various interconnected mechanisms involved in the particulate formation, such as gas phase and gas-surface phase kinetics and particle size/morphology evolution through nucleation, growth, coagulation and coalescence, is of great value in optimizing these processes. The first part of this work provides a framework for using gas phase kinetic mechanisms produced via automated mechanism generation software for the simulation of silicon nanoparticle formation. The second part focuses on developing a 1.5 dimensional aerosol model for the reaction zone of a laser driven aerosol reactor, which fully couples the silane decomposition chemistry, aerosol dynamics, and the fluid velocity/temperature field. The effects of operating conditions on particle product characteristics were investigated.

Crystalline Silicon Surface Passivation by Pecv-Deposited Hydrogenated Amorphous Silicon Oxide Films [a-SiOx:H

AbstractIn the research field of crystalline silicon (c-Si) solar cells, electronic surface passivation has been recognized as a crucial step to achieve high conversion efficiencies. The main issue of this article is to analyze the surface passivation properties of both, n-type and p-type crystalline silicon wafers by hydrogenated amorphous silicon sub oxide [a-SiOx:H] films the for use in hetero-junction (a-Si/c-Si) solar cells. A window layer is obtained with a certain fraction of oxygen in the a-SiOx:H layers.The a-SiOx:H films were deposited by decomposition of silane, carbon dioxide and hydrogen as source gases using plasma enhanced chemical vapor deposition (PECVD). Films with varying deposition parameters such as gas flow ratio (oxygen fraction) and plasma frequency (13.56, 70.0 and 110.0 MHz) are compared.To determine the passivation quality of the a-SiOx:H films, microwave-detected photo conductance decay (µ-PCD) provides a contactless measurement of the effective recombination lifetime of free carriers. The film compositions and also the changes in the microscopic structure of the amorphous network upon thermal annealing are studied using Raman spectroscopy and optical profiling techniques.The Raman spectra reveal the generation of Si-(OH)x and Si-O-Si bonds after thermal annealing in the layers, leading to a higher effective lifetime, as it reduces the defect absorption of the sub oxides.For n-type FZ material, lifetime values as high as 1650 µs are obtained, resulting in a surface recombination velocity Seff < 9.5 cm/s.

Silicon epilayers grown by chemical vapor deposition from high-purity silane

Structurally perfect, high-purity silicon epilayers up to 20 μm in thickness, with a carrier concentration n = 1012 cm−3 are grown through thermal decomposition of silane. Experimental evidence is presented that the concentration of “electrically active” impurities in high-purity silane can be evaluated from the electrical parameters of Si epilayers grown from it.

Directed growth of horizontal silicon nanowires by laser induced decomposition of silane

We present an original method to force the horizontal growth of silicon nanowires by laser assisted chemical vapor deposition of silane. The Ar+ laser beam, tightly focused on the absorbing sample, induces a local thermal horizontal gradient over the laser spot area, which determines the growth direction of the nanowires (NWs). The reaction of formation of Si NWs occurs via the vapor-liquid-solid process, when gold particles are spread on the surface to catalyze the reaction. The effect of laser power (i.e., of laser induced local temperature) and silane pressure on the morphology of the nanowires is presented.

Quantum size effect of valence band plasmon energies in Si and SnOx nanoparticles

Spherical Si and SnOx nanoparticles in the size range between 3 and 30nm have been synthesized by microwave induced decomposition of silane and gas phase condensation, respectively. They are deposited on thin metal films and investigated by electron microscopy, Auger electron, and electron energy loss spectroscopy. An analysis of the surface composition and stoichiometry reveals that the Si particles are covered with a native oxide of less than 1nm. The energy loss spectra show features corresponding to electronic excitations in the nanoparticles due to valence band plasmons, interband transitions, and core-level ionizations. The plasmon energies are found to increase with decreasing particle diameter d as d−1.17 for Si and d−0.83 for SnOx. These energy shifts are related to the change of the dielectric band gap energy of the semiconductor due to quantum size effects.

Printed nanoparticulate composites for silicon thick-film electronics

Abstract The production of active semiconductor thick-film components typically involves the deposition of precursor materials and subsequent thermal processing to produce a massive semiconductor layer. In this paper, we present electronic materials, based on nanoparticulate silicon, to produce the active semiconducting layer, which can simply be printed onto low-temperature substrates such as paper. Particular emphasis will be given to the structure, morphology, and composition of the nanoparticles, which are produced by either gas-phase decomposition of silane or mechanical attrition of bulk silicon. Of further importance are the electrical characteristics of the composite materials, in which the active semiconductor is formed from an interconnecting backbone of silicon particles. These will be discussed for example structures, including junction field effect transistors (FETs), insulated-gate FETs, and photodiodes.

Controlling growth and field emission properties of silicon nanotube arrays by multistep template replication and chemical vapor deposition

A multistep template replication route was employed to fabricate highly ordered silicon nanotube (SiNT) arrays, in which annular nanochannel membranes were produced first, and then silicon was deposited into the annular nanochannels by pyrolytic decomposition of silane. Electron microscopy revealed that these SiNTs are highly crystalline and the wall thicknesses can be controlled by the spaces of the annular nanochannel. Field emission characterization showed that the turn-on field and threshold field for the SiNT arrays are about 5.1V∕μm and 7.3V∕μm, respectively. These results represent one of the lowest fields ever reported for Si field emission materials at technologically useful current densities.

High-rate deposition of microcrystalline silicon with an expanding thermal plasma

Hydrogenated microcrystalline silicon has been deposited at elevated deposition rates using an expanding thermal plasma for the decomposition of the precursor gas silane (SiH 4). An extensive survey of the influence of the deposition parameters on the optical, electrical, and structural material properties is carried out. X-ray diffraction and Raman spectroscopy reveal the transition from amorphous to microcrystalline deposition conditions. Reflection-transmission measurements are used to determine the thickness, the refractive index, and the absorption coefficient. Scanning electron microscopy analyses show columnar growth and infrared absorption shows varying oxygen content. It is demonstrated that the best material is obtained when a pure hydrogen plasma, instead of a mixture of Ar and H 2, is used and the precursor gas (SiH 4) is injected into the plasma at about 55 mm above the growing film. The best material properties are obtained when the SiH 4 flow is adjusted such that the material is near the transition of microcrystalline to amorphous silicon. For these conditions the dark and photoconductivities are approximately 10 − 8 S/cm and 10 − 6 S/cm, respectively. The first attempts of the incorporation of this material in solar cells are presented. It is concluded that the expanding thermal plasma is well suited for the deposition of microcrystalline silicon and growth rates up to 3.7 nm/s have been obtained. However, further optimization of the structural and opto-electronic properties is still necessary.

The influence of filament material on radical production in hot wire chemical vapor deposition of a-Si:H

The choice of filament material has an influence on the decomposition of silane during the hot wire chemical vapor deposition of amorphous and microcrystalline silicon films. In this paper, the Si radicals produced from W, Re, Mo and Ta filament materials are probed by laser-based single photon ionization as a function of hot wire temperature. The apparent activation energy of the Si radical production in the surface reaction regime from Ta (140–180 kcal/mol) and Mo (120–160 kcal/mol) are found to be close to the corresponding Si thermal desorption energies from these surfaces, suggesting that the Si production is controlled by the desorption process from the bare metal. On the other hand, the Si activation energies from W and Re (60 kcal/mol) are lower than the related desorption energies, suggesting silicon desorption from a silicon layer formed on the surfaces. Kinetic modeling supports this desorption mechanism. In addition to the Si radical study, the corresponding film deposition is detected in situ by multiple internal reflection infrared spectroscopy, from which growth rates are estimated. The results show similar activation energies for both the growth rate and Si formation from the various filaments, implying that Si radical production and subsequent film growth are dominated by the same elementary reactions at low pressure.

Study of the poly/epi kinetic ratio in SiH 4 based chemistry for new CMOS architectures

In this work, we studied the effect of the deposition temperature, partial pressure and crystallite texture on the poly/epi growth rate ratio by decomposition of silane. Deposition was performed by rapid thermal chemical vapor deposition (RTCVD) in the temperature range 590< T<720 °C and in the silane partial pressure range 0.14< P<1.7 Torr. For monocrystalline silicon, we have observed that growth rate is proportional to the silane partial pressure. On the other hand, we have shown that for “polysilicon” the growth rate ratio slightly increases with partial pressure, like the amorphous content. For a fixed temperature, we found that amorphous content is related to the silane partial pressure and that the growth rate ratio is strongly dependent on the polycrystal roughness. It results in a non-monotonous trend of growth rate ratio versus silane partial pressure. From our experiments, we have obtained growth rate ratio varying from 1.2 to 2.5.