Masatake Katayama

Model on transport phenomena and epitaxial growth of silicon thin film in SiHCl3H2 system under atmospheric pressure

Abstract A transport and epitaxy model to describe silicon epitaxial film growth in a SiHCl 3 H 2 system under atmospheric pressure is developed by numerical calculations and comparison with experiments. The rate of epitaxial growth is calculated by computing the transport of momentum, heat and chemical species in a reactor incorporating chemical reactions at a substrate surface described by the Eley-Rideal model. The reaction processes determining the growth rate consist of chemisorption of SiHCl 3 and decomposition by H 2 , rate constants of which are evaluated from the model and measured results. The state of the surface during the epitaxial growth is also discussed considering the intermediate species, elementary reactions and rate-limiting processes. The epitaxial growth rate is able to be predicted by the model in this study over wide growth conditions of the species concentrations and the temperatures.

Initial stage of oxidation of hydrogen-terminated Si(100)-2×1 surface

The initial stage of SiO2/Si interface formation on an atomically flat hydrogen-terminated Si(100)-2×1 surface was studied by X-ray photoelectron spectroscopy. The following results were obtained: 1) the initial stage of interface formation does not depend on the initial surface morphology, 2) the interface layer becomes continuous at the oxide film thickness of 0.5 nm, and 3) at thicknesses greater than this the deviation from an atomically flat interface increases with the progress of oxidation, however, an abrupt compositional transition occurs.

Initial stage of oxidation of hydrogen-terminated silicon surfaces

Abstract Structural changes produced by the oxidation of hydrogen-terminated Si(111)-1 × 1 and Si(100)-2 × 1 surfaces at 300°C in dry oxygen under a pressure of 1 Torr were investigated by X-ray photoelectron spectroscopy (XPS) and multiple internal reflection infrared absorption spectroscopy (MIR-IRAS). Following results are obtained from the analysis and simulation of the experimental results: (1) the layer-by-layer oxidation reaction occurs locally at SiO 2 Si (111) interface, while that does not occur at SiO 2 Si (100) interface, however, (2) the oxidation on Si(100) surface proceeds more uniformly in atomic scale than that on Si(111) surface.

Modeling of Epitaxial Silicon Thin‐Film Growth on a Rotating Substrate in a Horizontal Single‐Wafer Reactor

The effect of substrate rotation on transport of reactive gases and epitaxial growth rate is investigated for a horizontal single-wafer reactor using a model and experiments. The governing equations for gas velocity, temperature, and chemical species transport are solved for the SiHCl 2 -H 2 system for Si thin-film preparation. The rotating substrate causes a circulating gas flow region above itself in which an asymmetric and nonuniform SiHCl 3 distribution is formed by thermal diffusion and species consumption due to the surface chemical reaction, even when the growth rate profile on the substrate surface is nearly uniform. The thickness of a thin-film grown at any position is obtained by an integral of the local growth rate along a concentric circle on the substrate surface. The good uniformity in the film thickness observed in calculation and measurement is mainly attributed to the averaging effect by integrating the local growth rate, and partially by the species concentration distribution change, both of which are caused by the rotating motion of the substrate.

Roughness of Silicon Surface Heated in Hydrogen Ambient

Surface roughness of a silicon wafer heated at 800 to 1100°C under atmospheric pressure in hydrogen ambient is studied. Haze of the surface becomes intense as the heating temperature is decreased. However, haze of the surface does not appear when the native oxide film on the silicon surface is completely removed. Atomic force microscopy images show that the surface heated at 900°C has many small pits whose shapes depend on the crystal plane, that is, squares for the (100) plane and triangles for the (111) plane. The pits are formed due to the difference in the chemical reaction rates between hydrogen-silicon and hydrogen-silicon dioxide. Small areas of bare silicon surface caused by the incomplete removal of the native oxide film are etched by hydrogen gas at a faster rate than the native oxide islands. The behavior of surface roughness with pressure and heating time agrees well with that predicted by the pit formation model in this study.

Nonlinear increase in silicon epitaxial growth rate in a SiHCl3H2 system under atmospheric pressure

Abstract The growth rate of Si epitaxial thin film at 1073–1398 K in a SiHCl 3 H 2 system under atmospheric pressure is studied theoretically and experimentally for a horizontal single-wafer reactor using the three-dimensional transport and epitaxy model which can account for both transport phenomena in an entire reactor and surface chemical reactions. The nonlinear increase in silicon epitaxial growth rate with SiHCl 3 concentration at the inlet of the reactor is discussed by investigating the changes in the transport of the chemical species to the substrate surface and the species saturation at the surface by chemisorption which limits the surface chemical reaction rate. An indicator for the rate-limiting factor for transport and reaction is discussed to investigate the saturation of the epitaxial growth rate and is shown to be useful for quantitatively describing the rate-limiting process.

Numerical Evaluation of Silicon-Thin Film Growth from SiHCl3-H2 Gas Mixture in a Horizontal Chemical Vapor Deposition Reactor.

An evaluation of silicon epitaxial thin film growth using the SiHCl3-H2 system in a horizontal chemical vapor deposition (CVD) reactor is discussed. The transport equations for gas velocity, temperature and concentration of chemical species are solved, taking account of the dependence of gas properties on temperature and composition. By comparing the measured and predicted growth rates under atmospheric pressure, the increase in growth rate with temperature and SiHCl3 concentration can be explained by assuming an Arrhenius-type expression for the chemical reaction of SiHCl3 and H2 on a substrate. The calculated growth rate of the Si film increases nonlinearly with SiHCl3 concentration because the flow, temperature, and concentration distributions in the reactor depend on the SiHCl3 concentration. Suppression of the growth rate due to thermal diffusion, which transports SiHCl3 gas away from the hot surface, is found to become significant as the SiHCl3 concentration in the reactor increases.

Valence band edge of ultra-thin silicon oxide near the interface

Abstract The changes in X-ray excited valence band of silicon oxide during progressive oxidation of Si(100) surface in 1 Torr dry oxygen at 600–880°C were studied. The following results are obtained: (1) the energy of top of valence band within the critical distance of 0.9 nm from the SiO 2 /Si interface is different from that of bulk silicon oxide by about 0.2 eV, (2) this critical distance for Si(100) and the amount of change in valence band edge near this critical distance are nearly equal to those for Si(111).

Haze Generation on Silicon Surface Heated in Hydrogen Ambient at Atmospheric Pressure

The change in surface roughness of a silicon wafer with temperature is studied using a dry system composed of quartz parts, a small silicon carbide part, a lamp-heating module, and hydrogen ambient at atmospheric pressure. A large diameter silicon wafer having a large temperature gradient is heated at 850 to 1100°C. Haze appears on the silicon surface and shifts from the higher temperature region to the lower temperature region of the wafer with increasing wafer temperature and finally disappears at temperatures higher than 1000°C. The temperature range in which the haze is generated due to surface pit formation is shown to be 900 to 1000°C. The influence of moisture in the gas phase on haze generation is considered to be very small. The surface pit formation is essentially due to the difference between the etch rates of silicon and silicon dioxide by hydrogen gas.

Gas flow and heat transfer in a pancake chemical vapor deposition reactor

Abstract Gas flow and heat transfer in a pancake reactor for silicon epitaxial film growth are discussed based on a gas flow visualization technique, numerial calculations and a growth rate profile of silicon epitaxial film. In the gas flow visualization, motions of NH4Cl or SiO2 particles are observed using a high-sensitivity analogue camera. The observed gas flow motions are compared with those obtained by three-dimensional calculations of the transport equations of the mass, momentum and energy. At room temperature and the epitaxial growth temperature of 1423 K, a large recirculation in the reactor chamber exists. The gas flow direction near the susceptor at the epitaxial growth temperature is nearly the same as that at room temperature, that is, from the outside toward the center of the susceptor. The profile of the epitaxial film growth rate observed agrees qualitatively with that predicted by visualization and calculations. The gas flow motions near the susceptor in the pancake reactor are parallel to the susceptor, in agreement with that of a horizontal reactor.