R. Cadoret

Mechanisms of silicon monocrystalline growth from SiH4/H2 at reduced pressures

The kinetics of monocrystalline Si deposition on slightly misoriented {111}Si substrates from SiH4 diluted in H2 at reduced pressures is theoretically analysed in terms of a condensation process of Si atoms and SiH4 molecules, taking surface diffusion into account. The possibility of a homogeneous nucleation is considered by applying the classical homogeneous nucleation theory to published experimental results. A growth mechanism limited by diffusion of SiH4 molecules on a surface inhibited by H adsorption is in agreement with the growth rates of monocrystalline Si observed at reduced pressures, when the heated substrate has a surface that is not too large. A condensation of SiH4 molecules explains the homogeneous nucleation.

Thermodynamical and kinetic study of the GaN growth by HVPE under nitrogen

Abstract The growth of GaN by HVPE was analysed by means of a thermodynamical and kinetic study. The thermodynamical constants of the reactions involved in the GaN growth and the partition functions of the molecules used in the kinetic study were calculated. The kinetic coefficients and the activation energies of the reactions were tabulated. Good agreement was obtained between the model and the experimental results. The influence of the reactor geometry and of the parasitic nucleation on the glass walls of the reactor was demonstrated. After analysing the physical phenomena which might take place in the vapour phase, we concluded that the vapour phase was not homogeneous. The reaction of formation of GaCl 3 from HCl and GaCl appears to be incomplete at the GaCl inlet, and almost complete over the substrate. Both effects explain the difficulty of growing GaN layers without extraneous deposit.

Hydrogen and nitrogen ambient effects on epitaxial growth of GaN by hydride vapour phase epitaxy

This study presents the influence of the composition of the carrier gas on the growth of GaN by HVPE. Since no hydrogen is introduced in the vapour phase, the deposition is expected to be controlled by Cl desorption in the form of GaCl 3 , as has been proposed for GaAs. However, our published model predicts much lower growth rates than those observed. We can account for both the observed parasitic deposition and GaN growth rate if we assume that GaCl 3 is not at its equilibrium pressure in the deposition zone and where nucleation takes place on the walls as well as on the substrate. This yields a high rate of parasitic nucleation even though the nominal supersaturation is vanishing small. Very little growth takes place on the substrate where the equilibrium pressure of GaCl 3 is reached. We describe similar experiments performed with a H 2 /N 2 mixture as the carrier gas. In this case, we expect GaN deposition to be controlled by desorption of Cl as HCl, which is known as the H 2 mechanism. It is speculated that the results show the existence of a new growth mechanism.

Chemical vapour deposition of silicon under reduced pressure in a hot-wall reactor: Equilibrium and kinetics

Abstract Silicon chemical vapour deposition (SiH 2 Cl 2 /H 2 system), under reduced pressure conditions, in a hot-wall reactor , is presented. The vapour phase composition is assessed by evaluating two distnct equilbria. The “homogeneous equilibrium”, which assumes that the vapour phase is not in equilibrium with solid silicon, is thought to give an adequate description of the vapour phase in the case of low pressure, high gas velocities, good temperature homogeneity conditions. A comparison with “heterogeneous equilibrium” enables us to calculate the supersaturation so evidencing a highly irreversible growth system. The experimental determination of the growth rate reveals two distinct temperature ranges: below 1000°C, polycrystalline films are usually obtained with a thermally activated growth rate (+40 kcal mole -1 ) and a reaction order, with respect to the predominant species SiCl 2 , close to one; above 1000°C, the films are always monocrystalline and their growth rate exhibits a much lower or even negative activation energy, the reaction order in SiCl 2 remaining about one.

Experimental and theoretical study of InP homoepitaxy by chemical vapour deposition from gaseous indium chloride and hydrogen diluted phosphine

Abstract We are reporting a theoretical and experimental study of InP homoepitaxy by chemical vapour deposition (hydride method) in a near-atmospheric pressure, open flow reactor. We determine the rate limiting reaction as being the chlorine atoms desorption from PInCl adsorbed molecules. The reactions leading to PInCl adsorption are supposed to be in a steady state because their velocities are not infinite compared to the rate limiting reaction velocity. Mass transport processes are taken into account to improve the partial pressure calculations in the gaseous phase above the substrate. The theoretical graphs calculated from those assessments are in good agreement with experiments.

Two-particle surface diffusion-reaction models of vapour-phase epitaxial growth on vicinal surfaces

A generalization of the model of Burton, Cabrera and Frank of step flow epitaxial growth on vicinal surfaces in multi-component systems is presented. In particular, the present model addresses chemical vapour epitaxial growth, where the atomic or molecular species composing the crystal, or growth units, are carried to the substrate inside more complex molecules, or precursors, as well as molecular beam epitaxial growth of compound semiconductors. Surface diffusion, chemical reactions, and incorporation at steps are included in the model, that allows for an analytic computation of the growth rate. Special attention is paid to the delicate problem of boundary conditions at steps in a two-component system.

Direct condensation modelling for a two-particle growth system: application to GaAs grown by hydride vapour phase epitaxy

Abstract A new phenomenological model for the growth of GaAs in the GaCl/AsH 3 /HCl/H 2 vapour phase system is developed. The surface growth kinetics are modelled by taking into account the mechanisms of As and GaCl adsorption and chlorine desorption by H 2 into HCl. Two ad-species AsGaCl and AsGa interact on the surface through a reversible reaction, which is described through a modified two-particle Burton, Cabrera and Frank model. Kinetics data are determined by synthesising experimental and computed results. It is shown that when surface diffusion limitations can be neglected, the growth rate is reduced to a one-particle-like direct condensation expression, weighted by a sticking coefficient which takes into account the desorption frequency of the precursor AsGaCl and its reversible transformation into the crystal particle AsGa. Variations of the growth rate are discussed as a function of the ad-species surface coverage ratios and of the supersaturation of the vapour phase.

Influence of the partial pressure of GaCl3 in the growth process of GaN by HVPE under nitrogen

Abstract This study presents the results of experiments performed in a conventional atmospheric horizontal HVPE reactor. The growth results are analysed with a model based on two desorption mechanisms of chlorine. The kinetic of the epitaxial film growth of GaN on sapphire by hydride vapour phase epitaxy is investigated under a variety of experimental conditions. The growth rate and the parasitical deposit on the quartz walls of the reactor upstream and above the substrate depend on the reactor geometry and on the composition of the vapour phase. The result of the experiment for a zero supersaturation over the substrate is discussed. Theoretical calculations compared with experimental results show the non-homogeneity of the gaseous species and the non-equilibrium of the GaCl 3 in the vapour phase.

Growth of gallium nitride by HVPE

The two mechanisms involved in the growth of (00.1) GaN HVPE have been deduced from the numerous experiments performed on (001) GaAs by the chloride method. They include a desorption of adsorbed Cl as HCl by H2 for the first mechanism and a desorption of two Cl as GaCl3 by GaCl for the second one. Theoretical curves have been computed by taking into account the interactions between the mass transfer, approximated by a simple model, the parasitic GaN deposition and the kinetics. They give a good approximation to the expected and observed growth rate values. A new domain of growth experimentally observed in conditions of expected fast etching by HCl ensures growth rates of 50-60 µm h-1 without parasitic GaN deposit by using a suitable temperature profile. This profile is computed by considering a combined mechanism of Cl desorption by GaCl as GaCl2 and of etching by HCl. The produced GaCl2 has to be supposed to be decomposed fast with respect to the mass transfer velocity. Its formation rate in the vapour phase has to be supposed to be very slow with respect to the reverse reaction. These assumptions are in agreement with the difficulty of observing this species and the well known doubt of its existence.

Mechanism of Si polycrystalline growth on a Si3N4 substrate from SiH4/H2 at reduced pressures

Abstract Si polycrystalline deposition on Si 3 N 4 substrates is theoretically analysed on the basis of the Kashchiev model and nucleation kinetics theories. The experimental results obtained on a heated substrate at reduced pressures are in agreement with a mechnism of heteronucleation, SiH 2 or SiH molecules being the smallest possible stable cluster, the diffusion of SiH 4 molecules on a surface inhibited by H adsorption supplying the Si atoms necessary for the cluster growth. The observation of a superlinear law with respect to SiH 4 appears to be caused by an incomplete condensation of SiH 4 molecules on the surface. The theoretical analysis performed evidences that other effects such as homogeneous decomposition could occur in hot wall reactors at reduced pressures or in cold wall reactors at 1 atm.