Pyrolysis Of Silane Research Articles

Light scattering diagnostics of silicon particle growth in CO 2 laser-driven reactions

laser-induced pyrolysis of silane in a flow reactor, based on scattering of He-Ne laser light by a particulate in the reaction flame. The scattering and extinction measurements have been used to measure nucleation and growth kinetics of silicon powders within the reaction zone. The experience gained by this technique allowed synthesis of silicon particles with a wide size range.

Silicon Particle Formation in Pyrolysis of Silane and Disilane

AbstractSilane and disilane diluted in argon and hydrogen mixtures were pyrolyzed behind incident shock waves at temperatures ranging from 900 to 2000 K, pressures from 0.2 to 0.7 atm, and total concentration from 3 × 1016 to 1 × 1017 silicon atoms per cm3. Formation of silicon particles was monitored by the attenuation of laser beams of two different wavelengths, thereby determining particle size, number density, and fractional yield. The conversion of silane and disilane into silicon particles exhibited a pronounced maximum at about 1150 K, which was found to be affected by reaction pressure, initial reactant concentration, and addition of hydrogen. Selected silicon particle samples were examined by electron diffraction, transmission electron microscopy, and secondary ion mass spectrometry. The results indicated that the produced particles were spherical, ranging from 100 to 400 Å in diameter, loosely agglomerated, and contained about 15% hydrogen on an atomic basis. A detailed chemical kinetic model was developed that describes gas‐phase pyrolysis of the parent molecule and homogeneous nucleation of silicon particles by 117 elementary reactions of 42 chemical species, and coagulation of the forming particles and their growth by gas‐surface deposition reactions with a method of moments. The model predictions were found to be extremely sensitive to the values of optical constants assigned to the silicon particle material.

Microcrystalline structure of poly-Si films prepared by cathode-type r.f. glow discharge

X-ray diffraction (XRD) and spectroscopic ellipsometry measurements have been performed to study the crystalline structure of polycrystalline silicon films deposited by cathode-type r.f. glow discharge. Ratios of XRD peak intensities are used to describe the degree of crystallinity of samples. For ellipsometric data analysis, a multilayer structure model is used based on the effective medium approximation. It is found that the crystalline fractions of the deposited films increase with the increase of power density and substrate temperature. The film compositions of as-deposited samples are compared with those of annealed samples and films prepared by thermal pyrolysis of silane. The crystallinity estimated from the ellipsometric measurements compares well with that obtained from XRD measurements.

The Critical Transition between Phase Formation Modes in the Pyrolysis of Silane

A jump-wise transition between two different kinetic modes of phase formation in the course of silane pyrolysis has been found experimentally. In one mode the solid phase is formed as an aerosol, in the other as a film; the phenomenon can be reproduced by mathematical analysis of a model mechanism.

Analysis of Hydrogen in Aerosol Particles of a‐Si: H Forming during the Pyrolysis of Silane

AbstractThe hydrogen content in aerosol particles of a‐Si: H, forming during pyrolysis of silane, is studied by means of the methods of hydrogen evolution and IR spectroscopy. The conclusion is drawn that the evolution peaks at 650,730, and 750 to 850 K correspond to hydrogen present in the dihydride groups of polysilane chains, the monohydride groups of the clustered phase, and the monohydride groups of the dilute phase, respectively. In the IR spectra the monohydride groups of the clustered phase cause absorption near 2000 cm‐−1 and the monohydride groups of the dilute phase near 2100 cm‐−1. Under low silane conversion the main fraction of hydrogen is contained in (SiH2)n, under conversion more than 50% in monohydride groups.

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.

X‐ray induced AES study of the effect of chemically bound hydrogen on the oxidation kinetics of an Si3N4 powder

AbstractSilicon nitride powders manufactured by the pyrolysis of silane and ammonia were found to contain chemically bound hydrogen. Most of this hydrogen could be removed by vacuum annealing at 1000°C. In the present study, x‐ray‐induced AES has been used to determine the oxidation kinetics for vacuum‐annealed Si3N4 powders that were heated in air at temperatures between 850 and 975°C. The average oxide thickness on the surface of the powder particles for each temperature and oxidation time was calculated from the ratio of the SiO2 to Si3N4 Si KLL peak intensities. The results are compared with those for the as‐manufactured powder, which contained the hydrogen impurity. For both annealed and unannealed powder, the oxidation rate was linear within the temperature range 850–1000°C. Within this temperature range, the oxidation rate was significantly higher for the vacuum‐annealed Si3N4 powder.

Homogeneous gas-phase nucleation in silane pyrolysis

Dilute and particle free mixtures of silane in the range of 100 ppm to 10% by volume in different carrier gases were decomposed thermally in a tube reactor. The onset of homogeneous nucleation was determined as a function of temperature and silane concentration for each carrier gas using a CNC with a detection limit of ca 0.01 μm. The gaseous decomposition by-products, disilane, trisilane and hydrogen were measured simultaneously using gas-phase chromatography. The onset of gas-phase nucleation was found to be inversely proportional to the temperature and influenced by the nature of the carrier gas. In inert gases, no chemical reaction took place between the decomposition products of silane and the carrier gas. In hydrogen, equilibrium displacement with the primary decomposition product (SiH 2) lead to a retardation of particle formation. Thus, the temperatures of onset of gas-phase nucleation was higher for mixtures in hydrogen than for mixtures in inert gases.

Silicon Nitride Ceramic Matrix for CMCs from Silane Derived Si Powders and Preceramic Polymers

ABSTRACTSi powders synthesized by the laser pyrolysis of silane can be nitrided at 1200–1250°C, producing an improved reaction bonded silicon nitride. This RBSN is a potential matrix for composites since it can be formed at temperatures which do not degrade the strengths of commercially available amorphous ceramic fibers. However, the density of the RBSN matrix has been limited to about 75% using the silane-derived Si powder. Combining Si powders and preceramic polymers offers an approach for increasing the density and mechanical properties of the reaction-formed Si3N4matrix. The incorporation of polysilazanes inhibited the nitridation at 1250°C, but samples could be effectively nitrided at 1400°C. These higher nitriding temperatures are compatible with SCS-6 and other lowoxygen, crystalline SiC fibers which can be used as reinforcements for ceramic composites.

Kinetics of homogeneous decomposition of silane

The kinetics of homogeneous decomposition of silane in a low-pressure reactor for polysilicon film deposition is investigated. The process is found to proceed as a first-order reaction and its rate depends exponentially on the residence time of silane in the system. A kinetic equation is derived and the activation energy is determined to be ≈ 43 kcal/mol. A mathematical model of the polysilicon film growth in a LPCVD reactor is developed, taking into account the simultaneous gas-phase and surface-catalytic pyrolysis of silane. Its analysis reveals that the relative share of the homogeneous reaction in the overall process grows with the increase in temperature and pressure in the system, leading to a substantial degradation of the layer thickness uniformity. The results obtained contribute to the more precise and fuller prediction and optimization of the process of thermal decomposition of silane.

Estimation of Arrhenius parameters for the 1,1 elimination of hydrogen from disilane and the role of chemically activated disilane in silane pyrolysis

Arrhenius parameters for the 1,1 H 2 elimination from disilane are estimated. Chemically activated disilane should play a significant role in the high-temperature pyrolysis of silanes, such as the shock tube dissociation of SiH 4 and the atmospberic pressure silicon CVD from a SiH 4 source. Estimates for ΔH o f,298 (H 3 SiSiH) are also made that are consistent with those Arrhenius parameters.

Improved model of silicon epitaxial growth by VPE

Abstract An improved model for simulating the growth of epitaxial silicon in the vapour phase by pyrolysis of silane (SiH4) in a horizontal reactor at atmospheric pressure has been developed. The model takes into account the variation of reactant concentration and the thickness of the boundary layer with distance inside the reactor. Using the above conditions, an expression for the growth rate of the epi-layer has been derived as a function of temperature, flow rate, mole fraction, position of wafer, etc. A comparison between the theoretically predicted values and experimental results shows satisfactory agreement.

Two‐Dimensional Modeling of Low Pressure Chemical Vapor Deposition Hot Wall Tubular Reactors: I . Hypotheses, Methods, and First Results

A new two‐dimensional model taking into account hydrodynamics and mass transport with chemical reactions has been developed. The system of partial differential equations has been solved by finite differences procedures and a Gauss‐Seidel algorithm. The case of pure polysilicon deposition is first described, taking into account the chemical species produced by silane pyrolysis, i.e., disilane and silylene. The concentration profiles of , , , and in the gas phase have been calculated and the contributions of these different species to the silicon deposit have been evaluated: more than 90% of the silicon deposition results from the direct silane contribution and less than 10% from silylene. The small over‐thicknesses numerically observed at the wafer's periphery result from the silylene contribution.

On Chemical Kinetics of Silicon Deposition from Silane (V) The Effect of Hydrogen Formation

AbstractIn consequence of hydrogen formation during silane pyrolysis total gas volume increases, when the reaction proceeds at constant total pressure. Any mole of silane decomposed produces two moles of hydrogen. In the present paper expressions are derived for 1st and 0.5th reaction order describing axial growth rate distribution of the isothermally proceeding reaction for the condition of constant total pressure. Those theoretically expected distributions are compared with results obtained by way of experiment on the one hand and those theoretically expected for the condition of constant gas volume on the other. It is concluded that the experimental results discussed rather agree with constant gas volume than with constant total pressure conditions. So, a compensating increase of total pressure along the tube axis might be supposed.

Deposition of Doped Polysilicon Films by Plasma‐Enhanced Chemical Vapor Deposition from AsH3 / SiH4 or B 2 H 6 / SiH4 Mixtures

Polycrystalline silicon thin films prepared by the pyrolysis of silane with the assistance of a plasma have been investigated. The films were deposited in an experimental CVD reactor at a deposition pressure of 6 mtorr, and over the temperature range of 500° to 800°C. The foremost characteristic of the plasma was the enhancement of the growth rate of the film. A thirtyfold increase in growth rate was observed in films deposited at 600°C by plasma enhancement over similar films deposited thermally. The films deposited below 600°C were amorphous. The glow‐discharge was also seen to favor the nucleation of <220> islands in the polysilicon film, but had no effect on the electrical properties of the film. In situ doped n‐type polysilicon films were deposited by plasma enhancement from mixtures. The growth rate of the latter films was found to be weakly sensitive to the arsine dilution in silane. For p‐type depositions from mixtures, the plasma promoted the decomposition of the reactant gas, resulting in a growth rate enhancement. The texture of the doped polysilicon films deposited with plasma enhancement was insensitive to dopant dilution in the reactant gas. Moreover, the conductivities of the n‐ and p‐type doped films were successfully modulated by over six orders of magnitude when the dopant dilution in the reactant gas was increased from 0 to 500 ppm. Finally, a segregation of the dopant atoms from the gas phase to the solid phase was observed for both p‐ and n‐type dopants.

Modelling of epitaxial growth rate of silicon by vapour phase epitaxy

A growth model based on chemical kinetics for vapour phase epitaxy of silicon by pyrolysis of silane (SiH 4) in a horizontal rectangular reactor at atmospheric pressure has been developed. The model incorporates the dependence of growth rate on various physical and geometrical parameters such as temperature, flow rate, mole fraction, position and angle of tilt. The model has been tested against such experimental data as are available in the literature and satisfactory agreement has been observed. An interesting feature of the model is that it predicts the growth rate to be fairly independent of the position of the susceptor within the reactor when the angle of tilt is 1.5°. The model has been coded in a simple computer program.

On chemical kinetics of silicon deposition from silane (II). Comparing 1st- and 0.5th-reaction order

AbstractTheoretical expressions for silicon layer deposition from silane pyrolysis within an open isothermal reactor tube has been derived for 0.5th order of chemical reaction with restricting the discussion to homogeneous gas reaction, and compared to the analogous expressions of chemical reaction characterized by 1st order relationship. Both kinds of theoretical equations give results free from contradictions when applied to experimentally based data of silane consumption on the one hand and silicon deposition distribution on the other, at least, with respect to those data published by Puga. First order reaction is characterized by an activation energy of ΔEaSi = 34 – 39 kcal/mole, and 0.5th order reaction by ΔEaSi = 23 – 26 kcal/mole. Chemical reaction of 0.5th order is to be preferred rather than 1st order.

In‐situ doping of LPCVD poly silicon (II). Temperature influence

AbstractPoly silicon deposition by pyrolysis of silane under low pressure conditions has been investigated with respect to the influence of temperature when simultaneously in‐situ doping of the deposited layer takes place.The growth rate of poly silicon is retarded in the presence of phosphine provided that a certain lower PH3/SiH4‐ratio has been exceeded. It has been shown how that lower ratio depends on temperature.Increasing PH3/SiH4‐ratio not only slows down layer growth rate but also the apparent activation energy of the layer forming reaction. An empirical equation describing the temperature dependence of that activation energy has been derived. Phosphine adsorption has been discussed as a cause of both layer growth rate and activation energy reduction. Additionally, incorporation of phosphorus during layer growth has been investigated with respect to the total amount and the electrically active concentration, the latter measured after a postdeposition anneal at 1000 °C.

Growth Kinetics of Polycrystalline Silicon from Silane by Thermal Chemical Vapor Deposition Method

The growth rates of polycrystalline silicon by thermal chemical vapor deposition from silane diluted in hydrogen and helium were measured in higher temperature range of 973–1173 K at 1 atm using a rod reactor with a double tube. The experimental conditions and the reactor configuration were carefully determined so that mass transfer at the surface of a substrate might not be dominant in the overall growth rate. Deposition mainly occurred from heterogeneous silane pyrolysis, for ambient hydrogen reduced homogeneous silane pyrolysis. A general partial differential equation model was derived, in which both surface reaction and mass transfer near the rod were considered. The distributions of silane concentration, temperature, and gas velocity in the reactor were calculated by the finite difference method, yielding the growth rate profile on the surface of the silicon rod in an axial direction. The rate constant of polycrystalline silicon deposition was estimated from curve fitting of the simulated growth rate profile and the experimental one by use of the nonlinear least squares method. A rate formula was determined in the temperature range 1073–1173 K and with the mole fraction of silane up to 2% in hydrogen atmosphere, assuming a chemical reaction mechanism on the growing surface by taking account of the reaction of hydrogen gas with adsorbed species.

Impact of Various Polysilicon Deposition Process on Thin Gate-Oxide Properties in Submicron CMOS Technology

AbstractThe dielectric quality (defect density, Do and breakdown strength, Fbd) of 150Å SiO2 gate oxide (GOX) films grown by conventional or stacked oxidation scheme are discussed from the leakage measurements of polysilicon capacitors on test structure simulating our submicron CMOS process. Various polysilicon (poly) deposition processes from silane pyrolysis (570°C -620°C) were used by the low pressure chemical vapor deposition (LPCVD) technique. Both in situ and ex situ poly doping by phosphorus (P) were used to ascertain their impact on the GOX properties. The substructural characteristics of the poly/SiO2 and SiO2/Si interfaces generated by various combinations of GOX and poly deposition processes were done by the high resolution TEM lattice fringe technique under phase contrast mode.