Decomposition Of Silane Research Articles

A-Si:H Films Deposited by Dc-Masd Technique at High Substrate Temperature

AbstractDc-magnetron assisted silane decomposition technique has been tested for deposition of undoped a-Si:H at substrate temperature Ts=300–400°C. In the optimized conditions device-quality a-Si: H films were deposited independently of Ts. A low hydrogen content CH (up to 2 at.°) and microstructure variations are characteristic of the MASD films.

Semi-Insulating Polycrystalline Silicon by Low Pressure Chemical Vapour Deposition from Disilane and Nitrous Oxide

Usually, semi-insulating polycrystalline silicon films SiOx are obtained from the chemical decomposition of silane and nitrous oxide. In this paper we describe the study of semi-insulating polycrystalline silicon (SIPOS) films from disilane and nitrous oxide by low pressure chemical vapour deposition. The kinetics of growth and the variation of oxygen content have been investigated relatively to deposition parameters such as temperature, total pressure and gas flow ratio. The oxygen content is assessed by X-ray photoelectron spectroscopy (XPS) and by differential thickness method. We show that the growth rate is higher for “disilane SIPOS films” than “silane SIPOS films” and we explain this behaviour by the strong difference in growth rate of silylene species. We also show that the inhibition effect of nitrous oxide on the growth rate is very low in the case of SIPOS films obtained with disilane. The electrical resistivity depends on the oxygen content and is ranged between 109 and 1013 Ω· cm.

Direct writing of nanostructures from silane on silicon (111)

Silicon based structures were fabricated using scanning tunneling microscope on a Si(111) surface by the localized decomposition of gaseous silane at pressures of 10−5–10−6 Torr. Continuous wires of width 5 nm could be produced while atomically resolved images of the nearby substrate were obtained. We argue that the fabrication process is effected by field-assisted decomposition of silane on the tip surface, which subsequently migrates to the tunneling region at the tip apex where it field desorbs to the silicon surface.

Influence of the Doping Gas on the Axial Uniformity of the Growth Rate and the Electrical Properties of LPCVD In-Situ Doped Polysilicon Layers

We report in-situ doping of polysilicon grown on glass substrates by a LPCVD process. The growth rate, the resistivity and the dopant concentration of boron in-situ doped polysilicon layers are studied as a function of the deposition pressure and the dopant gas to silane mole ratio. A dependence of the axial uniformity on pressure and B 2 H 6 /SiH 4 mole ratio is put forward, and this effect appears to be very strong especially at high pressure. It is explained by a lowering of the diborane concentration in the gas mixture along the load, because of a different threshold for the thermal decomposition of diborane and silane. It is also put forward that a critical concentration of boron exists above which the growth rate is increasing. Improvements of the horizontal homogeneity are obtained by varying the total gas flow rate.

Growth mechanisms of silicon films produced by laser-induced chemical vapor deposition

We have studied chemical vapor deposition (CVD) of Si from an SiH4 + Ar mixture, using excimer laser beam excitation parallel to a Si substrate. The growth mechanisms were studied by analyzing the effects of the temperature, pressure, laser repetition rate and intensity on the deposition rate and on the film microstructure. In addition, absorption measurements and gas analysis were performed during the deposition. This paper discusses the results of thickness measurements and calculations of the activation energy. A Gaussian-shaped transverse thickness distribution was obtained with a maximum corresponding to the center of the laser beam. This distribution depended on the deposition parameters and was attributed to the diffusion process of the silane decomposition products in the gas phase to the substrate. An Arrhenius plot of the deposition rate vs. the substrate temperature could be divided into two regimes associated with different activation energies. Between 340 and 460 °C, the activation energy is 0.25−0.3 eV, while it is 1.1 eV between 500 and 560 °C. The activation energy in the higher temperature regime is similar to that found for thermal CVD without the use of a laser. However, in the lower temperature regime, the deposition process is mainly laser induced, and the value of the activation energy was attributed to the process of adsorption of the gas species onto the substrate.

A Shock Tube Study of the Thermal Decomposition of Si2H6 Based on Si and SiH2 Measurements

AbstractIn the present investigation the thermal dissociation of disilane (Si2H6) mixed with different additives was measured behind reflected shock waves. Atomic Resonance Absorption Spectroscopy (ARAS) was applied for detecting Si atoms and Ring Dye Laser Absorption Spectroscopy (RDLAS) for detecting SiH2 radicals. Three different series of experiments were performed.In the first group of experiments mixtures of 0.1 to 0.25 ppm Si2H6 diluted in Ar were shock heated to temperatures 2000 K≤T≤3135 K and pressures between 0.8 and 1.4 bar. From the Si‐measurements silane and silylene were found to be the main primary products during disilane decomposition. The SiH2 absorption measurements were carried out at temperatures 1070 K ≤T≤ 1381 K and pressures between 0.35 and 1.3 bar. In these experiments the SiH2 formation was found to be mainly caused by the dissociation reaction Si2H6⇌ SiH4+SiH2 (R1). The rate coefficient k1 was determined by fitting SiH2 profiles calculated based on a simplified reaction mechanism to measured profiles with k1 to be a variable parameter. The value obtained was interpreted based on RRKM calculations. For bath gas concentrations of 3.1 × 10−6≤[M]≤ 4.6 × 10−6 mol cm−3 the rate coefficient k1 can be summarized by the Arrhenius expression k1 = 5.2×1010 exp(‐16850 K/T) s−1. For longer reaction times the SiH2 radicals were consumed due to the reaction SiH2+SiH2 ⇌Si2H2 (R4). The rate coefficient k4 was determined to be k4 = 6.5×1014 cm3 mol−1 s−1 (70%).The second group of experiments was carried out in mixtures with molecular hydrogen as an additive. SiH2measurements were performed in the temperature range 1082 K≤T≤1417 K at pressures 0.24 bar ≤p≤ 1.23 bar by using initial mixtures of 15 to 30 ppm Si2H6 and 5 to 50% H2 diluted in Ar. The aim of this part was to increase the influence of the recombination reaction SiH2 + H2→ SiH4 (R‐2) and to measure the dissociation barrier for the silane decomposition via the equilibrium constant. The data evaluation results in a mean value of E0,2 = 244.1 kJ/mol which is in good agreement to previous investigations.In the last part of this study the influence of silane used as an additive during Si2H6 decomposition was investigated. Initial mixtures of 30 ppm Si2H6 and 300 to 1000 ppm SiH4 diluted in Ar were used under conditions 1060 K ≤ T ≤ 1198 K at pressures between 0.36 and 1.3 bar. From SiH2 concentration measurements an estimation for the rate coefficient of the disproportionation reaction SiH2+SiH4 →H3SiSiH+H2 (R5), k5 = 1.3 × 1013 cm3 mol−1 s−1, was found.

P-doped polycrystalline silicon films obtained at low temperature by hot-wire chemical vapor deposition

P-doped polycrystalline silicon films were deposited over Corning 7059 substrates at a moderate temperature, 330°C, in a hot-wire reactor. The films were obtained from the decomposition of silane and hydrogen (10% SiH 4, 90% H 2) and different amounts of diborane. The structure and morphology of the samples were studied with X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). X-ray diffraction spectra show sharp diffraction peaks corresponding to silicon reflections, and Raman spectra show no evidence of amorphous phases and present a high intensity and narrow peak at 520 cm −1, which is the typical feature of crystalline silicon structure. The efficiency of boron incorporation was studied by secondary ion mass spectrometry (SIMS). The electrical properties of doped samples were also studied.

Silicon Growth Rate Enhancement Using Trisilane in a Laser Direct-Writing Technique

ABSTRACTAn argon-ion laser based direct-writing technique was used to deposit micron-size silicon lines from the decomposition of silane (SiH4) and trisilane (Si3H8) gases. The substrates used were 0.1 μrn polysilicon/1 μ.m silicon dioxide/<100> monosilicon multilayered structures. The vertical silicon deposition rate was investigated as a function of the laser-induced surface temperature and gas pressure. For temperatures ranging between 1000 and 1410 °C, the pressure was varied in the range 5-250 mbar and 0.1-30 mbar for SiH4 and Si3H8, respectively. For both gases, three growth regimes could be distinguished according to precursor pressure. The deposition rates achieved using trisilane are far higher than those obtained with silane in spite of the use of a reduced gas pressure range. For a laser-induced surface temperature of 1300 °C and a precursor pressure of 10 mbar, the deposition rates achieved using SiH4 and Si3H8 are, respectively, 0.42 and 20 μ.m/s, representing an enhancement factor of 50 with the later.

Deposition Efficiency Reducing Reactions in Silicon Deposition from Silane at Low Pressure

AbstractSilane pyrolysis at polysilicon low‐pressure‐deposition conditions is analyzed along the reactor‐tube axis with respect to the existence of competing decomposition reactions leading to the formation of silicon‐containing gaseous byproducts. The presence of such a parallel reaction is indicated by a difference between silane decomposition efficiency ηSiH4 and silicon deposition efficiency ηsi. The rate of such a competing parallel reaction is influenced by the variation of deposition temperature and/or substrate area of silicon deposition. It is drastically accellerated by the presence of phosphine in the gas phase. For the latter case the competing parallel reaction is shown to occur as a homogeneous reaction.

An EELS and EXELFS study of amorphous hydrogenated silicon carbide

A series of thin films of amorphous hydrogenated silicon carbide (a-Si∶C∶H) produced by RF plasma decomposition of propane and silane has been studied by electron energy-loss spectroscopy (EELS) and extended energy-loss fine structure (EXELFS) studies. The composition of the films has been determined by EELS and the nearest neighbour spacings have been determined by EXELFS. These results, along with the energy of the plasmon loss peaks, have been compared with the deposition conditions for each film. The results show that for a large gas ratio (C3H8/(C3H8+SiH4)) the films have a high proportion of carbon and are similar to a-C∶H in structure, whereas those films prepared with Y = 0.4 or 0.5 have nearest neighbour spacings consistent with those for tetrahedrally bonded carbon. The films prepared with lowest Y have nearest neighbour spacings similar to those for amorphous silicon carbide. The results for a-Si∶C∶H have been compared with the results of EELS and EXELFS of CVD diamond films, amorphous carbon and amorphous silicon.

Improved quality a-SiC:H films prepared by photo chemical vapour decomposition of silane and acetylene

Abstract Hydrogenated amorphous and microcrystalline silicon carbon alloy films have been grown by photo-CVD using C2H2 as a source gas of carbon. The hydrogenated amorphous silicon carbon (a-SiC:H) film with a band gap of ~2.0 eV prepared at a very low hydrogen (LD) concentration exhibits better photo-electronic properties compared to that at high hydrogen dilution (HD) having a similar optical gap. Notwithstanding a high deposition rate, the high photosensitivity (∼ 106), the low density of the defect states (∼ 6 × 1016cm−3) and the Urbach energy parameter (72 meV) for the a-SiC:H film prepared at low hydrogen dilution and pressure are impressive. On the other hand, low pressure along with high hydrogen dilution have been found to be conducive to microcrystalline silicon carbon alloy (μc-Si:H) formation. Interestingly, crystallites are of silicon while carbon remains in the amorphous and grain boundary regions.

Deposition Mechanisms of SiO2 in Remote Plasma Chemical Vapor Deposition Analyzed by Spatially Resolved Mass Spectroscopy

The decomposition of silane ( SiH4) with activated neutral oxygen is investigated by spatially resolved quadrupole mass spectroscopy (QMS). SiH4 molecules were found to be decomposed in the vapor phase by collisions with activated neutral oxygen. Generation of hydroxyls (OH, H2O) is discussed in relation to the chemical reactions in the vapor phase and on the substrate surface. The analysis of activation energy in the evolution of hydroxyls from growing surfaces infers that Si–O bonds form on substrate surfaces releasing OH and H2O into the vapor.

Growth kinetics of micrometer-size silicon lines produced by decomposition of silane using a laser direct-writing technique

Polycrystalline Gaussian shape silicon lines as small as 1 μm in width were deposited by pyrolysis of silane (SiH4) on polysilicon/silicon-dioxide/monosilicon substrates. As a heat source, a cw argon-ion laser operating in the 488–514 nm range was used. The growth kinetics and morphology of the silicon lines were investigated at various scanning speeds of the laser spot, laser beam powers, and reactant gas pressures. The scanning speed was varied between 1 and 100 μm/s and the SiH4 pressure was taken in the 5–250 mbar range. From the deposition kinetics, the vertical deposition rate of silicon was calculated. According to the SiH4 pressure and laser output power values, three successive kinetic regimes were observed. At low SiH4 pressures, the deposition rate of Si lines was proportional to the reactant gas pressure. At intermediate SiH4 pressures, the deposition rate was independent of the reactant gas pressure and complied with the Arrhenius law; the apparent activation energy was found to be 25 kcal mol−1. At relatively high SiH4 pressures, the deposition rate increased again with increasing SiH4 pressure. The structure of the deposited lines was analyzed through electron microdiffraction. The morphology of the deposited Si lines, investigated using an optical microscope and an atomic force microscope, was found to be very regular and uniform. The effect of the laser beam on the quality of the interfaces underlying the deposited lines was analyzed by means of a transmission electron microscope. On the basis of the experimental results, a reaction mechanism involving surface decomposition steps of ‘‘cold’’ SiH4 molecules is proposed and discussed in this article.

A novel product pattern in the palladium(II)-catalyzed decomposition of a (1-diazo-2-oxoalkyl)silane

Elimination of dinitrogen from (3,3-dimethyl-l-diazo-2-oxobutyl)-(tert-butyl)dimethylsilane catalyzed by palladium(II) chloride bis(acetonitrile), bis[(η 3-allyl)chloropalladium] or palladium(II) acetate gives the butatriene derivatives (E)- and (Z)-1,4-di[((tert-butyl)dimethylsilyl)oxy]-2,2,7,7-tetramethyl-3,4,5-octatriene, which are the formal dimers of an alkylidene carbene. The siloxyalkene ( tBu)[Me 2( tBu)SiO]CChCl is also formed, with a yield which parallels the amount of catalyst. Similarly, ( tBu)[Me 2( tBu)SiO]C(OAc) is a by product, when the decomposition of the same diazoketone is catalysed by palladium(II) acetate. The structure of the (E) isomer of the bis(siloxy)-3,4,5-octatriene derivative was determined by an X-ray diffraction study.

Structural characteristics of as-deposited and crystallized mixed-phase silicon films

In this work, we report on the structural characteristics of as-deposited and crystallized mixed-phase silicon films prepared by thermal decomposition of silane in a low pressure chemical vapor deposition reactor. Mixed-phase films consist of crystallites embedded in an amorphous matrix. The size of these crystallites depends upon the surface diffusion length, a parameter quantitatively expressing the potential of adsorbed silicon atoms for surface diffusion. The density of the pre-existing crystallites can be related to the maximum density of critical nuclei, which develops during the deposition of the film. Both variables were quantitatively related to the deposition temperature and rate via physical models reflecting the experimental observations. Values for the parameters associated with these models were extracted by fitting the experimental data to the theoretical equations. Our theoretical analysis is the first to relate quantitatively the structural characteristics of as-deposited mixed-phase films to the prevailing deposition conditions. Mixed-phase films can crystallize in a much shorter time than as-deposited amorphous films, due to the combination of the growth of the pre-existing crystallites and the higher nucleation rate of new crystallites within the amorphous matrix of the mixed-phase film. The crystallization time and final grain size of crystallized mixed-phase films were found to decrease with increasing density of pre-existing crystallites. However, we showed that if composite films are deposited, consisting of a mixed-phase layer and an amorphous layer, the grain size after crystallization could be comparable to that of crystallized as-deposited amorphous films, with the crystallization time of such composite films about threefold shorter. The structure of both as-deposited and crystallized single and composite mixed-phase films was found to be identical for films deposited on both oxidized silicon and Corning Code 1735 glass substrates.

Decomposition of Alkoxysilanes on the Surface of a Hot Wire‐Study of the Decomposition Mechanism

The decomposition of alkoxymethylsilanes on a hot Mo wire was investigated within the temperature range of 1300–1600 K and at pressures of 12–90 Pa. Within the temperature range 1400–1600 K a rate law of first order was determined. The activation energy of the decomposition of was estimated to be 74.5 kJ mol−1. The rate constants of the ethoxy silane decomposition decreases with increasing as . From these results and the formed products as ethanol and ethene, a surface‐activated decomposition mechanism is proposed assuming a two‐center reaction of the alkoxy groups with the formed surface on the wire. By esr spectroscopic investigations of condensed radicals the formation of radicals as , and ROO• was confirmed.

In situ UV-visible and Infrared ellipsometry study of the influence of silane dilution on the growth of hydrogenated amorphous silicon

The initial stages of hydrogenated amorphous silicon growth from the RF glow discharge decomposition of pure silane and mixtures of silane with H 2 or He has been studied using UV-visible and infrared ellipsometry. The substrate as well as the gas phase conditions strongly influence the early stages of a-Si:H growth. As compared to pure silane conditions, when using H 2 or He dilution of silane, thicker films must be deposited for SiH bonding to become dominant with respect to SiH 2. Moreover, in the case of high deposition rates from silane-helium mixtures, the SiH 2 band increases with film thickness, indicating that, contrary to low deposition rate conditions, SiH 2 is present in the bulk of the film.

Deposition of device quality a-Si:H films with the hot-wire technique

High quality hydrogenated amorphous silicon (a-Si:H) films have been deposited using thermal decomposition of silane (SiH 4) at a heated tungsten filament. Deposition rates up to 8 Å/s were achieved for device quality material. The stability of the films deposited at substrate temperatures above 400 °C has been observed to be superior to that of device quality glow discharge material. A very low hydrogen content and a small structural disorder (low Urbach energy) of the bulk material can explain this higher stability. Successful phosphine doping was performed and an efficiency of η = 4.3% was achieved for a solar cell with hot wire (HW) deposited i- and n +-layers.

Silicon-hydrogen (Si-H) bond activation on copper: reaction of silane on Cu(111)

The activation and decomposition of silane on Cu(111) have been studied using Fourier transform infrared (FTIR), Auger electron (AES), and temperature-programmed reaction (TPRS) spectroscopies, as well as low-energy electron diffraction (LEED). Silane dissociatively chemisorbs on Cu(111) at 90 K. Cleavage of the Si-H bond yields two structurally distinct adsorbed silyl fragments. Infrared spectroscopy identifies the predominant intermediates formed under these conditions as being adsorbed SiH[sub 2] and SiH species. The relative and absolute concentrations of these intermediates depend sensitively on the surface coverage of both Si and H, which themselves depend upon the silane exposure. SiH[sub 2] is stable over a wide range of coverage up to 180 K, where it then undergoes Si-H bond cleavage to form surface bound SiH. At higher temperatures, bond scission in the Si-H moiety results in the formation of adsorbed silicon atoms and the desorption of dihydrogen in a peak centered at [approximately]330 K. Auger electron spectra show that the amount of silicon deposited on the Cu(111) surface in this way is approximately one-third of the amount deposited on a stable Cu[sub 3]Si surface. This latter surface is readily formed by carrying out the silane exposure at temperatures above 300 K. 39 refs., 15more » figs., 1 tab.« less

In situ ellipsometric study of the influence of powder formation on the initial growth of glow discharge a− Si: H

Even under standard preparation conditions for amorphous hydrogenated silicon ( a− Si: H) by r.f. glow discharge decomposition of silane, powder formation can occur leading to an initial transient behaviour of silane discharges. Phase-modulated real-time in situ ellipsometry is used to study the influence of the discharge behaviour on the initial stage of growth of a− Si: H after ignition and subsequent to intentional discharge interruptions. A clear correlation between the powder-determined time dependences of the discharge parameters pressure and self-bias voltage and of the ellipsometric angles is confirmed. In the discharge regime where this initial transient behaviour due to powder formation is observed, the corresponding Δ - ψ trajectories can be attributed to the initial growth of less dense material. The time-dependent Δ signal of the growing film is found to be very sensitive even to minor discharge perturbations. The influence of controlled temporal variations of preparation parameters on the growing a− Si: H film can be simultaneously monitored by real-time in situ ellipsometry. This offers an opportunity for interface optimization in a− Si: H structures.