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Previous theoretical works suggested that superhydrophobicity could be enhanced through partial inhibition of the quantum vacuum modes at the surface of a broadband-absorber metamaterial that acts in the extreme ultraviolet frequency domain. This effect would then compete with the classical Cassie--Baxter interpretation of superhydrophobicity. In this article, we first theoretically establish the expected phenomenological features related to such a kind of "quantum" superhydrophobicity. Then, relying on this theoretical framework, we experimentally study patterned silicon surfaces on which organosilane molecules were grafted with all the coated surfaces having similar characteristic pattern sizes but different profiles. Some of these surfaces can indeed freeze quantum photon modes, while others cannot. While the latter ones allow hydrophobicity, only the former ones allow for superhydrophobicity. We believe that these results lay the groundwork for further complete assessment of superhydrophobicity induced by quantum fluctuations freezing. [ABSTRACT FROM AUTHOR]

The material properties and bonding behavior of silane-based silicon oxide layers deposited by plasma-enhanced chemical vapor deposition were investigated. Fourier transform infrared spectroscopy was employed to determine the chemical composition of the silicon oxide films. The incorporation of hydroxyl (-OH) groups and moisture absorption demonstrates a strong correlation with the storage duration for both as-deposited and annealed silicon oxide films. It is observed that moisture absorption is prevalent in the silane-based silicon oxide film due to its porous nature. The incorporation of -OH groups and moisture absorption in the silicon oxide films increase with the storage time (even in clean-room environments) for both as-deposited and annealed silicon oxide films. Due to silanol condensation and silicon oxidation reactions that take place at the bonding interface and in the bulk silicon, hydrogen (a byproduct of these reactions) is released and diffused towards the bonding interface. The trapped hydrogen forms voids over time. Additionally, the absorbed moisture could evaporate during the post-bond annealing of the bonded wafer pair. As a consequence, defects, such as voids, form at the bonding interface. To address the problem, a thin silicon nitride capping film was deposited on the silicon oxide layer before bonding to serve as a diffusion barrier to prevent moisture absorption and incorporation of -OH groups from the ambient. This process results in defect-free bonded wafers. [ABSTRACT FROM AUTHOR]

Low hydrogen content silicon oxycarbonitride (SiOCN) thin films were grown by plasma-enhanced chemical vapor deposition exploiting hydrogen dilution with silane/methane/nitrous oxide or tetramethylsilane/nitrous oxide precursors. The effects of deposition temperature were compared by investigating the compositional, optical, mechanical, and electrical properties of films grown at 100 °C, 250 °C, and 400 °C at thicknesses ranging from 50nm to 10 µm. The dielectric constant and high breakdown strength of the films remain relatively constant at between 4-5 and 6.8 ±0.2 MV cm-1 to 9.1 ±0.3 MV cm-1, respectively, despite the differences in deposition temperature. Other properties of the films include excellent transparency in the visible regime, high nanoindentation hardness (4 to 12 GPa), and relatively low measured stress on Si (-20 to -300MPa). Overall, the results of this work show that these SiOCN films can be used in a wide variety of applications, including as a dielectric within high voltage capacitors, transparent abrasion-resistant coatings for plastic windows, coatings on flexible substrates, a metal diffusion barrier for low-k dielectrics and polymer films, or within various microelectronic fabrication steps or systems. [ABSTRACT FROM AUTHOR]

Three-dimensional GaN columns recently have attracted a lot of attention as the potential basis for core-shell light emitting diodes for future solid state lighting. In this study, the fundamental insights into growth kinetics and mass transport mechanisms of N-polar GaN columns during selective area metal organic vapor phase epitaxy on patterned SiOx/sapphire templates are systematically investigated using various pitch of apertures, growth time, and silane flow. Species impingement fluxes on the top surface of columns Jtop and on their sidewall Jsw, as well as, the diffusion flux from the substrate Jsub contribute to the growth of the GaN columns. The vertical and lateral growth rates devoted by Jtop, Jsw and Jsub are estimated quantitatively. The diffusion length of species on the SiOx mask surface λsub as well as on the sidewall surfaces of the 3D columns λsw are determined. The influences of silane on the growth kinetics are discussed. A growth model is developed for this selective area metal organic vapor phase epitaxy processing. [ABSTRACT FROM AUTHOR]

To further improve the stability of amorphous/microcrystalline silicon (a-Si:H/μc-Si:H) tandem solar cells, it is important to reduce the thickness of the a-Si:H top cell. This can be achieved by introduction of an intermediate reflector between the a-Si:H top and the μc-Si:H bottom cell which reflects light back into the a-Si:H cell and thus, increases its photocurrent at possibly reduced thickness. Microcrystalline silicon oxide (μc-SiOx:H) is used for this purpose and the trade-off between the material's optical, electrical and structural properties is studied in detail. The material is prepared with plasma enhanced chemical vapor deposition from gas mixtures of silane, carbon dioxide and hydrogen. Phosphorus doping is used to make the material highly conductive n-type. Intermediate reflectors with different optical and electrical properties are then built into tandem solar cells as part of the inner n/p-recombination junction. The quantum efficiency and the reflectance of these solar cells are evaluated to find optical gains and losses due to the intermediate reflector. Suitable intermediate reflectors result in a considerable increase in the top cell current density which allows a reduction of the a-Si:H top cell thickness of about 40% for a tandem cell while keeping the current density of the device constant. [ABSTRACT FROM AUTHOR]

We measure and successfully model the deposition rate (R) of epitaxial Si by hot-wire chemical vapor deposition (HWCVD) onto (100) silicon over a wide range of growth conditions. A deposition rate model based on the fundamentals of gas-filament and gas-substrate interactions is presented; the results are consistent with the observed dependences of R on gas pressure, flow, and filament area. Gas-phase measurements of silane depletion allow calculation of the average radical sticking coefficient from the film deposition rate. Our findings indicate that the epitaxial deposition rate can be increased sufficiently to enable an economical epitaxial film-silicon photovoltaic tech-nology on low-cost foreign substrates. The model can be simply adapted to apply to the HWCVD of amorphous, nanocrystalline, and polycrystalline Si. [ABSTRACT FROM AUTHOR]

One of the main challenges for silicon thin film deposition for solar cell applications is to achieve high rate deposition in order to reduce the manufacturing costs. However, when silane and hydrogen are used as precursor gas in parallel plate plasma-enhanced chemical vapor deposition, high rate deposition is generally synonymous of powdery discharge. In this work, time- and space-resolved light scattering experiments are presented. These were performed in an industrial-type large area reactor with a variable interelectrode distance. Results show that with a standard 25 mm interelectrode distance, the fraction of silane transformed into powder can be as high as 50% and that reducing the interelectrode distance shifts to higher pressure the appearance of powder in the discharge. From a standard 25 mm interelectrode distance to a 10 mm narrow gap reactor, the threshold pressure was increased from 2 to 7 mbars. More generally, it is proposed that the onset of powder formation depends mainly on the product of the interelectrode distance and the gas residence time in the discharge. [ABSTRACT FROM AUTHOR]

In this work, we investigate localized silicon nanowires synthesis in a room temperature-controlled silane filled chamber using submicronic resistors as heating devices. These resistors consist in circuit-connected W wires obtained, on silicon oxide substrates, by focused ion beam induced deposition (FIBID) technology. Our study demonstrates that the morphology of the synthesized nanowires is temperature and time dependent revealing a thermal gradient but also both vapor-liquid-solid and vapor-solid growth effects. Typical silicon nanowires dimensions are a length of 1–2 μm and diameters of 30–40 nm. Structural characterization is performed by high resolution transmission electron microscopy using high energy electron transparent self-supported silicon nitride membranes. Electrical characteristics of FIBID- and self-connected nanowires are obtained. In both cases, they exhibit rectifying behavior. [ABSTRACT FROM AUTHOR]

Si nanowires grown by the vapor-liquid-solid (VLS) mechanism were fabricated using Au-catalyst nanoparticles and silane (SiH4) gas on Si substrates. Au was deposited on the substrate surface both by electron-beam evaporation and Au-colloid deposition. Both kinking defects and vertical nanowire epitaxy on Si <111> substrates were found to be directly related to SiH4 flow rate. A correlation between Au-colloid dilution and the nanowire growth rate was also observed, with the growth rate increasing with increasing concentrations of Au-catalyst particles on the wafer surface. Systematic experiments relating the nanowire growth rate to the proximity of nearest-neighbor Au particles and Au reservoirs were carried out, and the results were found to be in good agreement with a SiH4 reaction model, which associates decomposition to form SiH2 with higher nanowire growth rates. Implications toward the realization of VLS-grown single nanowire transistors are discussed. [ABSTRACT FROM AUTHOR]

Spheroidal inclusions in 4H-SiC homoepitaxial layers deposited by silane-based chemical vapor deposition (CVD) process have been investigated by KOH etching, optical microscopy, and transmission electron microscopy. The inclusions consist of polycrystalline 3C silicon carbide bearing no orientational relationship with the substrate and cause characteristic corrugation of epilayer surface referred to as “arrow” defect. Their origin is interpreted as due to SiC particles deposited on the wafer surface at the initial stages of the CVD process. [ABSTRACT FROM AUTHOR]

Traditionally shear thickening fluid (STF) reinforced with Kevlar has been used to develop flexible armor. At the core of the STF-Kevlar composites is a mixture of polyethylene glycol (PEG) and silica particles. This mixture is often known as STF and is consisted of approximately 45 wt % PEG and 55 wt % silica. During rheological tests, STF shows instantaneous spike in viscosity above a critical shear rate. Fabrication of STF-Kevlar composites requires preparation of STF, dilution with ethanol, and then impregnation with Kevlar. In the current approach, nanoscale silica particles were dispersed directly into a mixture of PEG and ethanol through a sonic cavitation process. Two types of silica nanoparticles were used in the investigation: 30 nm crystalline silica and 7 nm amorphous silica. The admixture was then reinforced with Kevlar fabric to produce flexible armor composites. In the next step, silica particles are functionalized with a silane coupling agent to enhance bonding between silica and PEG. The performance of the resulting armor composites improved significantly. As evidenced by National Institute of Justice spike tests, the energy required for zero-layer penetration (i.e., no penetration) jumped twofold: from 12 to 25 J cm2/g. The source of this improvement has been traced to the formation of siloxane (Si-O-Si) bonds between silica and PEG and superior coating of Kevlar filaments with particles. Fourier transform infrared, x-ray photoemission spectroscopy, and scanning electron microscopy studies were performed to examine chemical bonds, elemental composition, and particle dispersion responsible for such improvement. In summary, our experiments have demonstrated that functionalization of silica particles followed by direct dispersion into PEG resulted in superior Kevlar composites having much higher spike resistance. [ABSTRACT FROM AUTHOR]

Hydrogenated microcrystalline silicon growth by very high frequency plasma-enhanced chemical vapor deposition is investigated in an industrial-type parallel plate R&D KAI™ reactor to study the influence of pressure and silane depletion on material quality. Single junction solar cells with intrinsic layers prepared at high pressures and in high silane depletion conditions exhibit remarkable improvements, reaching 8.2% efficiency. Further analyses show that better cell performances are linked to a significant reduction of the bulk defect density in intrinsic layers. These results can be partly attributed to lower ion bombardment energies due to higher pressures and silane depletion conditions, improving the microcrystalline material quality. Layer amorphization with increasing power density is observed at low pressure and in low silane depletion conditions. A simple model for the average ion energy shows that ion energy estimates are consistent with the amorphization process observed experimentally. Finally, the material quality of a novel regime for high rate deposition is reviewed on the basis of these findings. [ABSTRACT FROM AUTHOR]

Thermally induced (160–300 °C) gas phase grafting of linear alkene molecules (perfluorodecene) was performed on hydrogenated amorphous silicon (a-Si:H) films, either nominally undoped or doped with different boron and phosphorus concentrations. Dense and smooth a-Si:H films were grown using plasma decomposition of silane. Quantitative analysis of in situ x-ray photoelectron spectroscopy indicates the grafting of a single layer of organic molecules. The hydrophobic properties of perfluorodecene-modified surfaces were studied as a function of surface coverage. Annealing experiments in ultrahigh vacuum show the covalent binding and the thermal stability of these immobilized layers up to 370 °C; this temperature corresponds to the Si–C bond cleavage temperature. In contrast with hydrogenated crystalline Si(111):H, no heavy wet chemistry surface preparation is required for thermal grafting of alkene molecules on a-Si:H films. A threshold grafting temperature is observed, with a strong dependence on the doping level which produces a large contrast in the molecular coverage for grafting performed at 230 °C. [ABSTRACT FROM AUTHOR]

Using threshold ionization mass spectrometry, radical densities have been measured at the substrate surface of a radio frequency discharge in silane plus hydrogen vapor. The conditions are 100–300 Pa pressure and a ratio (R) of hydrogen flow/silane flow typical of discharges used to produce large area amorphous (R=20) and microcrystalline (R=40) silicon. For comparison, we include measurements in pure-silane vapor. The neutral radicals observed in the mixed gases are H, SiH3, Si2H2, and Si2H5, with decreasing flux in that order. (Si2H4 is also seen in pure silane and SiH2 for R=20.) The H flux is sufficient for major film etching and restructuring, particularly for R=40. The ion-bombardment species were also measured, establishing that SiyHn+ (y=1–3) ion flux is much larger than the Hn+ (n=1–3) flux. The ion flux provides 15±4% of the total Si flux to the film for R=20 and 37±10% for R=40. This is larger than in pure-silane discharges, and it may be very important to film properties due to the impact energy. [ABSTRACT FROM AUTHOR]

In this study, we investigated the influence of the surface treatment of Al nanoparticles on the electrical properties of linear low density polyethylene composites. Octyl-trimethoxysilane was used as a nonpolar silane coupling agent for the surface treatment of Al nanoparticles. It was found that the incorporation of nonpolar octyl groups onto the surface of Al nanoparticles not only increased the percolation threshold and the resistivity but also improved the dielectric properties as compared to the composites filled with unsurface-treated nanoparticles. The surface treatment makes it possible to easily control the frequency and concentration dependences of dielectric constant and provided an excellent approach able to considerably reduce the dielectric loss of the nanocomposites, which is of great significance from the viewpoint of practical application of the polymer/metal nanocomposites in the electrical and electronic industries. It is concluded that the improved electrical properties could be directly ascribed to the good dispersion and special electrical feature of the surface-treated nanoparticles in the polymer matrix. [ABSTRACT FROM AUTHOR]

Hydrogenated amorphous silicon carbon alloy films of different carbon compositions were prepared by plasma enhanced chemical vapor deposition system using silane and methane with helium dilution and were characterized by structural and optical techniques to understand the microstructural and overall disorder in amorphous semiconductors. The study demonstrates that the increase of the microstructural disorder results in an increase in the overall disorder and the local defect density induced by carbon incorporation seems to dominate the overall defect structure of the network. [ABSTRACT FROM AUTHOR]

A study of the surface passivation of strained InGaAs using vacuum annealing and silane (SiH4) passivation was reported for the first time. X-ray photoelectron spectroscopy reveals the elimination of As–O bond after vacuum annealing and SiH4 surface passivation. Vacuum annealing eliminated poor quality native oxide on InGaAs surface, while a thin silicon interfacial layer was formed by SiH4 treatment, therefore effectively preventing the InGaAs surface from exposure to an oxidizing ambient during high-k dielectric deposition. Transmission electron micrograph confirmed the existence of a thin oxidized silicon layer between high-k dielectric and InGaAs. By incorporating this surface technology during gate stack formation, TaN/HfAlO/InGaAs metal-oxide-semiconductor capacitors demonstrate superior C-V characteristics with negligible frequency dispersion, small hysteresis, and interface state density as low as (3.5×1011)–(5.0×1011) cm-2 eV-1. [ABSTRACT FROM AUTHOR]

Hydrogenated amorphous silicon germanium (a-SiGe:H) alloy films are still under study to improve their incorporation into tandem solar cells. In this paper we have investigated the quality of films deposited in a radio frequency powered plasma enhanced chemical vapor deposition unit. Two series of samples were prepared either from a mixture of silane and germane diluted into hydrogen or from the same mixture to which a small amount of argon was added. The applied rf power at 13.56 MHz was either continuous or modulated by a square wave pulse at a frequency of 1356 kHz. Different films were deposited in the two series controlling the time the plasma was “on.” The ratio of the on time to the total period of the modulation, the duty cycle, was varied between 100% (continuous mode) and 50%. The plasma during deposition as well as structural and optoelectronic properties of the resulting films was studied with several techniques. We found an optimum in the transport properties for a duty cycle of 75%: an ambipolar diffusion length of the order of 100 nm for a material presenting a bandgap of 1.44 eV. To explain this promising result, we present a discussion on the growth mechanisms of such layers linking the structural results to the transport data. [ABSTRACT FROM AUTHOR]

Hydrogenated microcrystalline silicon films (μc-Si:H) deposited at high deposition rates (∼2 nm/s) by means of the very-high-frequency (VHF) deposition technique in the high pressure depletion regime have been integrated into single junction p-i-n solar cells. It is demonstrated that μc-Si:H solar cells can be optimized using a twofold approach. First the bulk properties, deposited under steady-state plasma conditions, are optimized by monitoring the presence of crystalline grain boundaries in μc-Si:H. These hydrogenated crystalline grain boundaries can easily be detected via the crystalline surface hydrides contribution to the narrow high stretching modes by infrared transmission spectroscopy. The crystalline grain boundaries suffer from postdeposition oxidation which results in a reduced red response of the solar cell. The absence of these crystalline surfaces in an as-deposited μc-Si:H matrix reflects the device grade microcrystalline bulk material. Second, the prevention of silane backdiffusion from the background during the initial growth is a necessity to deposit a uniform μc-Si:H phase over the entire film thickness. The initial growth is optimized while preserving the optimized bulk properties deposited under steady-state conditions, using initial profiling of plasma parameters such as the silane flow and the VHF power density. Solar cell devices with efficiency of 8.0% at a μc-Si:H deposition rate of 2.0 nm/s are obtained using the presented approach. [ABSTRACT FROM AUTHOR]

Polycrystalline 3C-SiC thin films are deposited via low pressure chemical vapor deposition from the precursors 1,3-disilabutane (DSB) and dichlorosilane (DCS). Elemental composition, microstructure, surface morphology, and residual stress are characterized as functions of DCS flow rate fraction. Elemental composition varies linearly with DCS fraction, while microstructure changes drastically with slight changes in DCS fraction. Residual stress varies from 1.2 GPa tensile to 240 MPa tensile, and the causes of which are traced to variations in elemental composition and grain size. A model of residual stress accounting for the effects of elemental composition and grain size on intrinsic stress is developed and found to be in reasonable agreement with experimental data. [ABSTRACT FROM AUTHOR]

We have carried out a detailed study on the vapour-liquid-solid growth of silicon nanowires (SiNWs) on (111)-oriented Si substrates using Au as catalytic seed material. Arrays of individual seeds were patterned by electron-beam lithography, followed by Au evaporation and lift-off. SiNWs were grown using diluted silane as precursor gas in a low-pressure chemical vapor deposition system. The silane partial pressure, substrate temperature, and seed diameter were systematically varied to obtain the growth rate of the NWs and the rate of sidewall deposition. Activation energies of 19 kcal/mol for the axial SiNW growth and 29 kcal/mol for the radial deposition on the SiNW surface are derived from the data. SiNW growth at elevated temperatures is accompanied by significant Au surface diffusion, leading to a loss of Au from the tips of the SiNWs that depends on the layout and density of the Au seeds patterned. In contrast to NWs grown from a thin-film-nucleated substrate, the deterministic patterning of identical Au seeds of varying diameters allows accurate measurements of the nucleation yield of the SiNW, which is close to 100%, and analysis of the epitaxial relationship with the substrate. In addition to the vertical and the three 70.5°-inclined <111> epitaxial growth directions, we observe three additional 70.5°-inclined directions, which are rotated by 60°. The 60° rotation is explained by the occurrence of stacking faults in the SiNWs. The overall yield of vertically grown <111> NWs depends sensitively on the partial pressure of the silane and, to a lesser extent, on the growth temperature. At 80 mTorr partial pressure and 470 °C, up to 60% of the SiNWs grow in the vertical <111> direction. In situ doping of SiNWs using arsine resulted in a significant reduction of nucleation and wire growth, whereas doping with trimethylboron and phosphine exhibited no difference in growth and epitaxy compared with undoped samples. [ABSTRACT FROM AUTHOR]

Optical, structural, and electrical characterizations of the Si:H network have been performed during its changes occurred by the increasing H2 dilution to the SiH4 ensemble in hot-wire chemical vapor deposition (HWCVD). A rapid structural transformation from a mostly amorphous phase to comprehensive micro/nanocrystallinity was attained at a relatively low H2 dilution, even at a low substrate temperature, because of the associated abundance of atomic H in HWCVD. However, elevated H2 dilution induces enormous polyhydrogenation and formation of lesser dense network full of voids, mostly around the tiny micro/nanocrystallites. This highly defective grain boundary zone provides high density of electronic trapping centers and contributes significantly to the transport of carriers. The overall electrical transport in the amorphous-micro-nano-crystalline heterogeneous Si:H network has been accounted in the framework of a three-phase model comprised of amorphous and crystalline (micro- and nano-) components while the grain boundary being the third phase, separately contributing to a potential energy barrier in between. The three-phase model to the electrical phenomena of nanocrystalline structures convincingly explains the dual activation energies arising in the electrical conduction with distinguishably different temperature dependent behaviors from that occurs in the conventional amorphous matrix. [ABSTRACT FROM AUTHOR]

An experimental investigation of an instability occurring during dust nanoparticle formation is presented in this paper. The present study has been performed in radio frequency low pressure plasma in an argon-silane mixture. The formation and growth of nanoparticles is followed, thanks to the analysis of the amplitude of the third harmonics (40.68 MHz) of the discharge current and the self-bias voltage (Vdc). In some cases, at the end of the accumulation phase of the nanocrystallites an instability occurs. It seems to be an attachment induced ionization instability as observed in electronegative plasmas. A detailed study of the influence of different operating conditions (injected power, gas temperature, and silane flow rate) on this instability behavior and frequencies is presented. The paper concludes by examining a very particular case of the instability. [ABSTRACT FROM AUTHOR]

The growth of silicon particles has been measured in silane-hydrogen radio-frequency (rf) discharges using a typical hydrogen/silane dilution ratio (20) and the pressure range (1.2–2.2 Torr) used for the production of amorphous and microcrystalline silicon films and devices. By operating brief discharges without gas flow, the particle size is obtained from the afterglow diffusion and the particle density from the scattered-light intensity. These small-reactor data thus provide the expected particle size and density versus location-in a commercial large-area–isothermal-flowing-gas reactor. Particle growth rate is a strong function of pressure, whereas film growth rate is almost independent of pressure. Both growth rates are sensitive to rf voltage, although particle growth is more sensitive. [ABSTRACT FROM AUTHOR]

Powder formation in a 13.56-MHz radio frequency (rf) capacitive glow discharge plasma of silane-argon mixture has been studied by in situ laser light-scattering measurements. The rf power density (Prf) was varied from 18 to 53 mW/cm2. At high Prf the light scattering occurs all along the discharge and extends even beyond the exit end of the electrodes toward the pumping system. With decreasing Prf the maximum intensity of the light scattering decreases and the scattering zone shrinks and moves toward the exit end. With Prf≈20 mW/cm2 a very bright scattering zone only a few centimeters wide appears located at the electrodes outlet. The powders studied by transmission electron microscopy did not show a drastic decrease of their sizes with Prf though clear coagulation of small particles is observed at high Prf. In this paper we have tried to link the laser light-scattering evolution with Prf to various parameters such as the microstructure factor, the deposition rate, the electron mobility×lifetime product, the density of states, and the minority-carriers diffusion length of the films in an attempt to link the effect the evolution of powder formation to the films properties. [ABSTRACT FROM AUTHOR]

An investigation of the effect of the total gas pressure on the deposition of microcrystalline thin films form highly diluted silane in hydrogen discharges was carried out at two different frequencies. The study was performed in conditions of constant power dissipation and constant silane partial pressure in the discharge while using a series of plasma diagnostics as electrical, optical, mass spectrometric, and in situ deposition rate measurements together with a simulator of the gas phase and the surface chemistry of SiH4/H2 discharges. The results show that both the electron density and energy are affected by the change of the total pressure and the frequency. This in turn influences the rate of high energy electron–SiH4 dissociative processes and the total SiH4 consumption, which are favored by the frequency increase for most of the pressures. Furthermore, frequency was found to have the weakest effect on the deposition rate that was enhanced at 27.12 MHz only for the lowest pressure of 1 Torr. On the other hand, the increase of pressure from 1 to 10 Torr has led to an optimum of the deposition rate recorded at 2.5 Torr for both frequencies. This maximum is achieved when the rate of SiH4 dissociation to free radical is rather high; the flux of species is not significantly hindered by the increase of pressure and the secondary gas phase reactions of SiH4 act mainly as an additional source of film precursors. [ABSTRACT FROM AUTHOR]

Boron-doped microcrystalline silicon films have been deposited in a plasma-enhanced chemical vapor deposition system using silane diluted in hydrogen, and diborane (B2H6) as a dopant gas. The temperature dependence of the dark conductivity has been measured from 120 to 420 K in all samples. In the high-temperature range above room temperature, the carrier transport is found to be thermally activated, with a single activation energy that changes with the B2H6 compensation degree. In the low-temperature range (300–120 K), variable range hopping (VRH) was established as a predominant electronic transport mechanism for all samples, with the exception of the sample with a diborane concentration of 12.5 ppm. A model for Mott’s VRH, referred to as the “diffusional model,” which yields a relation between the conductivity and the localized density of gap states, is presented. Using classical equations from the percolation theory and the diffusional model, the density of states near the Fermi level, as well as the hopping parameters, are calculated. A correlation between the hopping parameters for both models is deduced. A numerical factor that improves the value of each parameter is calculated. [ABSTRACT FROM AUTHOR]

A highly stabilized hydrogenated amorphous silicon film was developed using a triode deposition system in which a mesh was installed between cathode and substrate in a plasma-enhanced chemical vapor deposition system. The hydrogen concentrations of the resulting films are very low compared with those of conventional films prepared at the same substrate temperature. It was observed that light-soaking stability of the obtained film is promising, which is confirmed by measuring a neutral spin density as well as an I-V characteristic of a Schottky diode. Reduction of densities of higher silane radicals during film growth is an important factor for controlling degradation. [ABSTRACT FROM AUTHOR]

We have investigated phase separation, silicon nanocrystal (Si NC) formation and optical properties of Si oxide (SiOx, 0

Stable gases produced in SiH4 and H2-SiH4, capacitively coupled rf discharges operated at typical device-production conditions, were investigated by quadrupole mass spectrometry. The production of disilane and trisilane and the depletion of silane and pressure change were measured during consecutive short discharges. Dissociation rate constants and branching ratios for higher-silane production are obtained from the time-dependent densities. The influence of suspended Si particles on stable-gas production is found to be negligible, by changing the duration of individual discharges and thereby the particle densities and sizes. We have also observed pyrolitic decay of disilane and trisilane at 200 °C, although this is negligible under normal reactor conditions. [ABSTRACT FROM AUTHOR]

Silicon nanowires were selectively grown at temperatures below 400 °C by plasma enhanced chemical vapor deposition using silane as the Si source and gold as the catalyst. A detailed growth study is presented using electron microscopy, focused ion beam preparation, and Raman spectroscopy. A radio-frequency plasma significantly increased the growth rate. The Si nanowires show an uncontaminated, crystalline silicon core surrounded by a 2-nm-thick oxide sheath. The as-grown diameters are small enough for the observation of quantum confinement effects. Plasma activation could allow a further decrease in deposition temperature. A growth model for plasma enhanced nanowire growth is discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated silicon particles formed in an inductively coupled plasma (ICP) system and have measured their structural properties by electron microscopy. ICP silane plasmas are shown to be an interesting and versatile source of nanoparticles. Three regimes are mapped out: a regime of no observable particle growth at the lowest pressures, a regime of polydisperse and agglomerated particles at the highest pressures, and a regime yielding highly monodisperse particles at intermediate pressures. Our results suggest that an ICP allows this unique production of monodisperse nanoparticles at high concentrations. The particle size can be controlled from 15 to 200 nm and is determined by the plasma on time. For short plasma times, particle growth appears to be due primarily to coagulation, while in the second phase particle growth is attributed primarily to surface deposition. For H[SUB2] dilutions less than 92%, the growth rate is almost independent of H[SUB2] partial pressure. Transmission electron micrographs, however, indicate that the addition of hydrogen decreases the particle density. At higher dilution ratios, polycrystalline particles are obtained. Under all other conditions the particles are amorphous. [ABSTRACT FROM AUTHOR]

A dusty radio-frequency silane/hydrogen discharge is simulated, with the use of a one-dimensional fluid model. In the model, discharge quantities like the fluxes, densities, and electric field are calculated self consistently. A radius and an initial density profile for the spherical dust particles are given and the charge and the density of the dust are calculated with an iterative method. During the transport of the dust, its charge is kept constant in time. The dust influences the electric field distribution through its charge and the density of the plasma through recombination of positive ions and electrons at its surface. In the model this process gives an extra production of silane radicals, since the growth of dust is not included. Results are presented for situations in which the dust significantly changes the discharge characteristics, both by a strong reduction of the electron density and by altering the electric field by its charge. Simulations for dust with a radius of 2 µm show that the stationary solution of the dust density and the average electric field depend on the total amount of the dust. The presence of dust enhances the deposition rate of amorphous silicon at the electrodes because of the rise in the average electron energy associated with the decrease of the electron density and the constraint of a constant power input. [ABSTRACT FROM AUTHOR]

The role of ions on the growth of microcrystalline silicon films produced by the standard hydrogen dilution of silane in a radio frequency glow discharge is studied through the analysis of the structural properties of thick and think films. Spectroscopic ellipsometry is shown to be a powerful technique to probe their in-depth structure. It allows to evidence a complex morphology consisting of an interface layer, a bulk layer, and a subsurface layer. The ion energy has been tuned by codepositing series of samples on the grounded electrode and on the powered electrode, as functions of pressure and power. On the one hand, reducing the ion energy through the increase of the total pressure and depositing on the grounded electrode, favors the formation of large grains asnd resulst in improved bulk transport properties, but leaves an amorphous interface layer with the substrate. On the other hand, we achieve fully crystallized films on glass substrates under conditions of high energy ion bombardment. We suggest that ion bombardment, and particularly the implantation of hydrogen ions, favors the formation of a porous layer where the nucleation of crystallites takes place. These results are further supported by in situ spectroscopic ellipsometry measurements of the film morphology as a function of the ion energy. [ABSTRACT FROM AUTHOR]

The absolute densities of H atoms produced in catalytic chemical vapor deposition (Cat-CVD or hot-wire CVD) processes were determined by employing two-photon laser-induced fluorescence and vacuum ultraviolet absorption techniques. The H-atom density in the gas phase increases exponentially with increases in the catalyzer temperature in the presence of pure H[sub 2]. When the catalyzer temperature was 2200 K, the absolute density in the presence of 5.6 Pa of H[sub 2] (150 sccm in flow rate) was as high as 1.5×10[sup 14] cm[sup -3] at a point 10 cm from the catalyzer. This density is one or two orders of magnitude higher than those observed in typical plasma-enhanced chemical vapor-deposition processes. The H-atom density decreases sharply with the addition of SiH[sub 4]. When 0.1 Pa of SiH[sub 4] was added, the steady-state density decreased to 7×10[sup 12] cm[sup -3]. This sharp decrease can primarily be ascribed to the loss processes on chamber walls. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A gas phase and surface simulator of highly diluted silane in hydrogen rf discharges used for the deposition of microcrystalline silicon has been developed. The model uses the spatial density distribution of SiH (X [sup 2]Π) radicals measured using laser induced fluorescence and the total silane consumption for estimating the primary electron induced silane dissociation, thus avoiding fluid or statistical approaches commonly used for the prediction of electron impact rate coefficients. A critical analysis is made for the relative importance of all the parameters involved either in the gas phase chemistry or in the surface processes. The model results are compared to experimental data concerning disilane production and film growth rate over a wide range of rf power densities in 2% and 6% SiH[sub 4] in H[sub 2] discharges. The good agreement between experimental and model results allows for the extension of the discussion to the composition of the radical flux reaching the substrate, the relative contribution of each of the radicals to the film growth, and the most probable mechanism of microcrystalls formation under typical conditions of low and high microcrystalline silicon deposition rate. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The influence of frequency in the range from 13.56 to 50 MHz, on the properties of 2% silane in hydrogen 0.5 Torr discharges used for the deposition of microcrystalline silicon thin films, has been investigated. The experiments were carried out under constant power conditions as determined through Fourier transform voltage and current measurements. The increase of frequency leads to a decrease of the rf field, an extension of the bulk, and a marked increase of the electron density and the amount of power consumed by electrons. These changes induce a decrease of the rate of high-energy electron–molecule collision processes (>10.5 eV) at higher frequencies and an enhancement of lower energy processes. Thus, there is a significant increase in the hydrogen flux toward surfaces, which can explain the beneficial effect of frequency to the crystallinity of μc-Si:H thin films. At the same time, SiH[sub 4] electron impact dissociation is enhanced mainly due to the increase of electron density. On the contrary, ionization is not favored by the increase of frequency and the calculated ion flux toward the film surface indicates that the role of ions in a possible enhancement of the surface mobility of the film precursors is minor. The observed increase of the deposition rate is further discussed in terms of the nature of the film precursors and the spatial distribution of their production. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this study, we present a detailed structural characterization by means of transmission electron microscopy and Raman spectroscopy of polymorphous silicon (pm-Si:H) thin films deposited using radio-frequency dust-forming plasmas of SiH[sub 4] diluted in Ar. Square-wave modulation of the plasma and gas temperature was varied to obtain films with different nanostructures. Transmission electron microscopy and electron diffraction have shown the presence of Si crystallites of around 2 nm in the pm-Si:H films, which are related to the nanoparticles formed in the plasma gas phase coming from their different growth stages, named particle nucleation and coagulation. Raman scattering has proved the role of the film nanostructure in the crystallization process induced “in situ” by laser heating. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated the behavior of the absolute density of hydrogen (H) atoms in ultrahigh-frequency (UHF), (500 MHz) silane (SiH[sub 4]) plasma by using a vacuum ultraviolet absorption spectroscopy technique with a microdischarge hollow cathode lamp. In the UHF plasma using SiH[sub 4] highly diluted with hydrogen molecule (H[sub 2]) at a pressure of 20 Pa, an UHF power of 1000 W, and a total flow rate of 200 sccm, the absolute density of H atoms slightly increased from 7.4x10[sup 11] to 7.9x10[sup 11] cm[sup -3] with increasing the SiH[sub 4] flow rate ratios from 0% to 2.5% and then the H atom density decreased at the ratio of 5%. The decrease of the density is due to the increase of the reaction between the H atom and the SiH[sub 4] molecule. The behavior of the absolute density of H atoms was compared with that of the Balmer α(H[sub α]) emission intensity. It was found that the behaviors of the absolute H atom density and the H[sub α] emission intensity were quite different. Moreover, the kinetics of H atom density in SiH[sub 4] plasmas have been clarified on the basis of measured results. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It has been shown that nanocrystalline silicon films can be grown from silane gas without hydrogen dilution by electron-beam excited plasma chemical vapor deposition (EBEP-CVD). A high density of atomic hydrogen, which is derived from the dissociation of silane molecule, is confirmed in the plasma by optical emission spectroscopy. This fact is thought to be a reason for the growth of nanocrystalline silicon films without the introduction of hydrogen gas. Transmission electron spectroscopy reveals that crystallites are not distributed uniformly, but rather form the mosaic-like clusters in an amorphous silicon matrix in the film. Hydrogen gas is introduced into the EBEP-CVD silicon film growth so as to study the effects of the hydrogen gas. The growth rate increases proportionally to the hydrogen flow rate, and it is about 2.5 times greater than when no hydrogen gas is introduced. Also, a decrease in both the hydrogen content and the density of dangling bonds in the film is confirmed. These results imply that the generation of dangling bonds is suppressed by the introduction of hydrogen. The rate constants of dissociation reaction of silane molecules in the EBEP are estimated, and the change in density of radicals in the plasma by introducing hydrogen gas is calculated. A growth model is proposed that assumes the sticking coefficient of SiH[sub 3] precursor radical increases in proportion to atomic hydrogen flux. Using the calculation results and the model, the effects are explained to be due to an increase in the contribution ratio of SiH[sub 3] radicals to the growth, on account of the increase in the introduced hydrogen gas flow rate. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which fabricated nanocrystalline cubic silicon carbide (SiC) films embedded in an amorphous SiC matrix by the hot-filament chemical-vapor deposition techniques using methane and silane as reactance gases. Results and discussion; Conclusion.

Discusses a study that examined the effect of the variation of the dilution level of silane in hydrogen on the microstructure of layers used for the deposition of solar cells. Factors which characterize microcrystalline silicon; Experiments of the study; Results and discussion of the transmission electron microscopy.

Discusses a study which analyzed the rapid particle growth by coagulation of particles in silane plasma reactor. Application of plasma chemical vapor deposition, etching and sputtering in semiconductor manufacturing processes; Analysis of the particle growth; Results and discussion; Conclusions.

Presents information on a study which measured the particle size and number density versus discharge operating time of silane radio frequency discharges. Properties of hydrogenated amorphous silicon photovoltaics or thin-film transistors; Experimental details; Results and discussion; Conclusions.

Highlights a study which analyzed the SiH radicals' interaction with crystalline and amorphous silicon surfaces, in silane containing plasmas. Establishment of the hydrogen concentration on the surface; Details on the usage of the plasma enhanced chemical vapor deposition; Methodology used to conduct the study; Results of the study.

Provides information on an experiment describing some results on particle synthesis in a low-pressure radio-frequency (RF) discharge by using silane and methane as precursors for particle growth. Methodology used to conduct the experiment; Information on single and two-step procedures for particle synthesis; Characterization of the powder obtained in the two-step process; Findings of the experiment.

Describes evidences presented that electron attachment to high-lying electronically excited states of silane have large electron attachment cross sections. Causes of silane's enhanced negative-ion formation; Measurement of electron attachment to thermally excited vibrational states of the ground electronic state of silane; Modeling of silane discharges.

Focuses on a study which investigated the effect of argon dilution on the structure of microcrystalline silicon deposited from silane. Experimental procedures; Results; Conclusions.

Deals with a study which investigated the nucleation and subsequent initial growth processes of particles in radio frequency silane plasmas, using a developed photoemission method. Importance of plasma deposition and etching; Methodology of the study; Results and discussion.

Provides information on a study that examined how the quality of hot wire films made with highly diluted silane depends on the deposition conditions. Methodology of the study; Results and discussion on the study.