On chemical kinetics of silicon deposition from silane (III). LPCVD poly silicon formation in the temperature range 900–950 K

LPCVD poly Silicon deposition form silane has been investigated for limited conditions regarding temperature, silane input and pumping speed. It has been found that layer growth is controlled by a chemical reaction of 0.5^th-order in consequence of which growth rate linearly decays along the axis of an open isothermal reactor tube. The slope of that decay is determined not only by the reaction rate constant but also by linear gas velocity within the tube and that part of total substrate surface area that is effectively exposed to silane at each wafer position. In conseqence growth rate decay is the steeper not only the higher temperature will be chosen but also the slower gas velocity is adjusted and the smaller wafers are separated to each other. The kind of how axial layer growth rate distribution is effected by changing wafer spacing is a proof for the heterogeneous reaction mechanism. The silicon forming reaction is characterised by an activation energy of about 52 kcal/mole.     

On chemical kinetics of silicon deposition from silane (IV). In-situ phosphorus doping of LPCVD poly silicon in the temperature range 900–950 K

Highly in-situ phosphorus-doped LPCVD poly silicon deposition from mixtures consisting of silane and phosphine has been investigated for limited conditions regarding temperature, silane input, phosphine-silane ratio and total pressure. Agreeing with the deposition of undoped poly silicon, growth rate linearly decays along the axis of the wafer cage applied for in-situ doped poly silicon. In consequence layer growth should be controlled by a chemical reaction of 0.5^th order. In contrast to undoped poly silicon the slope of axial growth rate decay increases with the distance between wafers increased. This behaviour is a proof for a homogneous chemical reaction mechanism. The silicon forming reaction is characterized by an activation energy of about 25 kcal/mole for PH₃/SiH₄ = 0.003.     

Hydrogenated amorphous silicon produced by laser induced chemical vapor deposition of silane

a-Si:H films deposited by laser induced CVD (LICVD) have been characterized and the growth process modelled. Growth rates are exponentially dependent on gas temperature and film properties follow the equilibrium hydrogen content, exponentially dependent on substrate temperature.     

Equilibrium and kinetics in the chemical vapour deposition of silicon

In the growth of silicon layers on various substrates it appears that the growth rate is not uniquely determined by substrate temperature and input parameters of the gases used. An analysis of this situation is given and essential points in the chain reaction of steps in the growth process will be indicated. Differences in growth rate reported for different experimental situations can be explained on the basis of this analysis where the temperature gradient normal to the growing interface will appear to be of special importance. Some examples are given of resulting surface morphology as a function of growth and etch conditions. Another point of interest in the growth process is the incorporation of dopant which determines the electrical properties of the layers. Here also equilibrium and kinetics show an interplay. For low growth rates there appears to be a good correlation between the concentration of impurities in the solid and the partial pressure of dopant in the gas phase. For growth rates exceeding a critical-value kinetic effects can be expected as those found in liquid phase epitaxy. It appears that an n-type dopant as phosphorus shows this effect. In this case the surface concentration of ionized donors exceeds the bulk concentration of these centres and trapping occurs at higher growth rates.     

Mechanisms of chemical vapor deposition of silicon

The distribution in the silicon epitaxial growth from SiCl₄ and hydrogen are observed in situ by IR absorption spectroscopy. Two methods are used complementarily, one is IR spectroscopy of reactants extracted from the reactor by a fine quartz tube which is not disturbing the reactions, and gives knowledge about the local distribution, the other is direct IR spectroscopy of hot reactants in the reactor which is useful to ascertain the results at the real high temperature situation. The intermediate species are SiHCl₃, SiH₂Cl₂ which is estimated from the induced emission bands at 500 and 570 cm^-1. HCl is a dominant waste product and contributes to reverse reactions. To investigate the reaction, HCl is intentionally injected into the reacting gas. This kind of injection method may also be very effective to analyze the reactions using other reactants such as SiCl₄, SiHCl₃ and SiH₂Cl₂.     

Temperature dependence of doping element incorporation with the chemical vapour deposition of epitaxial silicon (V). Incorporation of arsenic

Based on the knowledge previously obtained with regard to the incorporation of phosphorus as an equilibrium-determined process, theoretical values of the enthalpies of the different possible incorporation equilibria are calculated for the incorporation of arsenic into the growing silicon epitaxial layer. The sublimation enthalpies of elemental arsenic, the formation enthalpy of arsine and the enthalpy of solubility enter into the equation. The results compared to the present experimental data of other authors are discussed.     

Low-temperature deposition of crystalline silicon nitride nanoparticles by hot-wire chemical vapor deposition

The nanocrystalline alpha silicon nitride (α-Si₃N₄) was deposited on a silicon substrate by hot-wire chemical vapor deposition at the substrate temperature of 700 °C under 4 and 40 Torr at the wire temperatures of 1430 and 1730 °C, with a gas mixture of SiH₄ and NH₃. The size and density of crystalline nanoparticles on the substrate increased with increasing wire temperature. With increasing reactor pressure, the crystallinity of α-Si₃N₄ nanoparticles increased, but the deposition rate decreased.     

Heterogeneous kinetics and mass transport in chemical vapour deposition processes: Part II application to silicon epitaxy

The results obtained for the epitaxial deposition of Si from SiC1₄ and H₂ in a rotating disc reactor are described by a single equation in terms of kinetics and transport. The kinetic parameters required to fit the experimental data suggest that the rate determining step for the CVD process is the homogeneous conversion of SiC1₄ to SiHCl₃. The kinetic analysis also shows that the commonly reported activation energy for the overall growth is too low as a result of measurements being made under conditions of combined transport and kinetics. Results of other workers obtained with reactors of very different geometries, when normalised, are in excellent quantitative agreement with both the experimental and theoretical curves found in this work.     

The incorporation of oxygen impurities in semiconductor silicon in chemical vapour deposition

The incorporation of oxygen traces in chemical vapour deposited semiconductor silicon has been calculated for the temperature range of 1200–1500 K in dependence on the excess of hydrogen in the reaction gas. The results obtained correspond to the experimental data. With increasing temperatures of deposition and increasing excess of hydrogen the incorporation of oxygen decreases at a constant concentration of oxygen in the initial state.     

Inelastic light scattering studies of silicon chemical vapor deposition (CVD) systems

Raman and resonance fluorescence spectra, determined by inelastic light scattering measurements, are used to identify molecular species and to measure their concentration gradients on a fine spatial scale throughout a CVD reactor. Raman spectra are also analyzed to give gas temperature and tempetature profiles. The temperature profiles near the leading edge of a horizontal rf heated susceptor in a laminar flow system are adequately described by using Lévêque's solution to an energy balance equation, assuming temperature-independent fluid properties. Raman spectra at room temperature of some of the compounds commonly used as source materials for Si epitaxial growth, SiCl₄, SiCl₃H, SiCl₂H₂ and Si₂Cl₆ indicate that these species are all detectable at the 10–100 ppm level and are distinguishable from each other. Measurements at 500–1300°C of these compounds reveal the presence of a common species, SiCl_x (probably SiCl₂), which exhibits a resonance flourescence spectrum at least 1000 times more intense than typical Raman spectra. SiCl_x density profile measurements above the susceptor indicate a concentration boundary layer thickness of 0.7-0.8 cm for one set of experimental conditions. SiCl_x density measurements as a function of suspector temperature are observed to vary over a range of 4 to 5 orders of magnitude, and are much higher for a SiCl₂H₂ input than for a SiCl₄ input.     

The chemistry and transport phenomena of chemical vapor deposition of silicon from SiCl4

The chemical vapor deposition (CVD) of silicon is among the most important synthesis methods in electronic industry. We developed and applied novel methods of characterization to studies of CVD of Si from SiCl₄. In particular, we studied the chemistry of the Si-Cl-H system as well as transport phenomena, such as the momentum, heat, and mass transport in a horizontal CVD reactor. A flow visualization was used to study the flow dynamics, i.e., the momentum transport in the reactor. The heat transport was studied by measuring temperatures at various points in the reactor as a function of flow-rates and susceptor temperatures. A specially designed movable probe was used for a mass spectrometric sampling in the reactor. In these experiments, we were able to determine quantitatively partial pressures of reactants and products at some desired location in the reactor, thus studying the mass transport during the CVD of Si. The conducted studies of transport phenomena were used to establish a model which can be used to predict the efficiency and uniformity of the deposition.     

Cracking assisted nucleation in chemical vapor deposition of silicon nanoparticles on silicon dioxide

Deposition of sub-monolayer silicon on SiO₂/Si(1 0 0) greatly facilitates nucleation in subsequent thermal chemical vapor deposition (CVD) of silicon nanoparticles. Sub-monolayer seeding is accomplished using silicon atoms generated via disilane decomposition over a hot tungsten filament. The hot-wire process is nonselective towards deposition on silicon and SiO₂, is insensitive to surface temperature below 825 K, and gives controlled coverages well below 1 ML. Thermal CVD of nanoparticles at 1×10⁻⁴ Torr disilane and temperatures ranging from 825 to 925 K was studied over SiO₂/Si(1 0 0) surfaces that had been subjected to predeposition of Si or were bare. Seeding of the SiO₂ surface with as little as 0.01 ML is shown to double the nanoparticle density at 825 K, and densities are increased twenty fold at 875 K after seeding the surface with 30% of a monolayer.     

Doping process control in silicon epitaxy (I). System identification

The transition behaviour of the phosphorus incorporation in silicon epitaxial layers grown in a CVD reactor has been investigated, considering the reactor as a linear control system with u = lg p⁰_PH3 (t) as the input and y = lg N(t) as the output. The response of system to both upward and downward step inputs has been studied experimentally, using SiH₄ and PH₃ sources. The dopant system of a horizontal silicon epitaxial reactor has been identified and a mathematical model relating to the transient behaviour of the system has been found. The parameters of the model have been estimated from layer growth experiments. The step response functions found can be approximated by an exponential function relating to n time constants T, all equal to each other. It was found for the system investigated that the second order model is of sufficient accuracy for the optimal control calculations described in the next part of this series.     

Properties of hydrogenated amorphous silicon prepared by chemical vapor deposition

Properties of hydrogenated amorphous silicon (a-Si:H) prepared by chemical vapor deposition (CVD) are reported and compared to corresponding properties of glow discharge a-Si:H. The CVD material was produced from mixtures of silane, disilane, trisilane and higher polysilanes in hydrogen carrier gas at one atmosphere total pressure, at substrate temperatures from 420 to 530 °C. The photovoltaic properties of our present CVD a-Si:H are somewhat inferior to those of the best glow discharge a-Si:H. However, as discussed below, there are some indications that higher quality CVD a-Si:H may be possible.     

Temperature dependence of doping element incorporation with the chemical vapour deposition of epitaxial silicon (IV). Incorporation of phosphorus in the Si-H-Cl-lP system

The lower temperature dependence of the phosphorus incorporation with the use of phosphine together with chlorosilanes (ΔH = −13 to −15 kcal/ mole) instead of silane (ΔH = −43 kcal/mole) is explained by introducing a special incorporation equilibrium of phosphine bound to the silicon surface. The source materials phosphorus trichloride and phosphorus pentachloride may be incorporated with this equilibrium.     

On the chemical transport of molybdenum dioxide with tellurtetrahalogens (I). The Transport System MoO2/TeBr4

A report is given on the transport behaviour of MoO₂ with TeBr₄. The fundamentals for the calculation of the gaseous phase composition above a solid phase are explained in the system Mo/O/Te/X. The calculated transport behaviour is compared with the experimental results, and the crystal habit of the obtained MoO₂ monocrystals is described.     

A method for determination of size-dependent crystal growth kinetics from batch experiments (I). One-experiment estimation

The method developed for determining size-dependent crystal growth kinetics makes use of the assumption that the linear growth rate is a product of a size-dependent factor and a supersaturation-dependent one. The transformed form of the population balance equation, obtained by means of this assumption, is the basis of the evaluation utilizing measurement data from one seeded batch crystallization experiment, namely the size distributions of the seed and product crystals as well as the supersaturation course. The application of the method is illustrated by evaluating an experiment with potash alum crystals.     

Dependence of doping element incorporation on temperature in the chemical vapour deposition of epitaxial silicon (III). Empirical incorporation characteristic of the Si-P-H system

The shape of the empirical incorporation characteristic of phosphorus in epitaxial silicon, deposited from silane-phosphine-hydrogen mixtures, shows two branches with different incorporation dependences on temperature (incorporation enthalpies). In the lower phosphorus-concentration range (N < 10¹⁸) the experimentally determined value of incorporation enthalpy can be explained as a complex quantity, including the enthalpies of the two phosphorus hydrides PH₃ and PH₂, the latter of which is formed by the partial decomposition of phosphine (PH₃) at deposition temperatures. — In the upper phosphorus-concentration range (N > 10¹⁸) the incorporation equilibrium of the dimeric phosphorus molecules, formed by the nearly complete decomposition of phosphine, is reflected in the incorporation enthalpy of the empirical incorporation characteristic.     

Autodoping during the deposition of epitaxial Silicon layers from the gas phase (I). Autodoping from the gas phase

The doping profile within the autodoping range of epitaxial layers deposited on lowresistance substrates, is considered the result of redistributing a substrate doping fraction through the substrate layer boundary, of incorporating a limited amount of dopants from the gas phase, originating from the preepitaxial process, and the result of incorporating dopants, externally admitted to the gas flow during the deposition. Assuming a special incorporation equilibrium to exist for the gas phase fraction of autodoping an analytic expression is derived, correlating the autodoping profile characteristic to the limited amount of dopants in the gas phase. The extent is discussed, to which the gas phase fraction of autodoping may be influenced by varying the deposition process.