Masanori Mayusumi

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.

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.

Surface Imperfection Behavior during the SiH4 Epitaxial Growth Process

The epitaxial wafer is expected to become the industry standard for super large-diameter wafers over 300 mm. The demand for reductions in production cost along with stringent quality improvements are driving diameters upward. The super silicon project has developed an epitaxial process, for 400 mm epitaxial wafers, using SiH 4 gas at a low temperature just under 1000°C. This process promises to decrease contamination, to prevent slip generation, and to improve productivity. Since the epitaxial layer quality is tightly correlated with the growth process, we also characterized the microdefects and microroughness on the surface of epitaxial wafers that were grown with the SiH 4 process. Comparing the results of this experiment with those of a conventional SiHCl 3 process, we conclude that the SiH 4 process presents no problems when applied to super large-diameter epitaxial wafer production.

A Direct Approach for Evaluating the Thermal Condition of a Silicon Substrate under Infrared Rays and Specular Reflectors

A direct approach model using the three-dimensional ray-tracing simulation is developed to evaluate the thermal condition in a rapid thermal processing system composed of tungsten/halogen filament lamps, specular reflectors, and the silicon substrate. The paths of the infrared rays emitted from the tungsten/halogen filament lamps are traced following reflections at the surface of the specular reflectors and the polished surface of the silicon substrate. The relationship between the absorbed ray intensities calculated at the silicon substrate and the measured temperatures of the silicon substrate is expressed by the Stefan-Boltzmann law. The effect of a specular reflector tube installed in the rapid thermal processing system is evaluated based on the temperature profiles and the absorbed ray intensities calculated over the silicon substrate. It is concluded that the temperature profile over the silicon substrate can be predicted using the model developed in this study.

Study of Surface Treatment of Silicon Wafer Using Small Angle Incident X‐Ray Photoelectron Spectroscopy

A small angle incident X-ray photoelectron spectroscopy (XPS) instrument was developed to perform high sensitivity analyses on silicon surfaces by reducing background noise. Silicon surfaces were treated by a new wet cleaning process based on ultra clean technology. Cleaning effectiveness for this process was determined by small angle incident XPS measurements and spectra analyses. At each cleaning step, no elements other than silicon, oxygen, and carbon atoms were detected. The thickness of the SiO 2 film formed during each step was evaluated. Based on the relative O 1s and Si 2p intensities, too much oxygen was found on the surface to attribute only to SiO 2 .

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.

Morphology of Silicon Oxide Film on Silicon Wafer Surface during Its Removal Process in a Hydrogen Ambient

In order to develop the low-temperature silicon epitaxial growth process, the change in the surface morphology of the silicon dioxide film and the silicon surface is studied in a transient state, for the first time, at 1223 K at a pressure of 40–101 kPa in a hydrogen ambient. A very smooth and clear silicon substrate surface is achieved using a uniform silicon dioxide film formed using ozonated ultrapure water and a very low flow rate of hydrogen gas. The surface morphology of the silicon substrate finally becomes smooth and the pit formation is suppressed, although the surface shows a nonuniform island appearance during the removal of the silicon dioxide film. The microroughness of the silicon substrate surface is improved by heating in a hydrogen ambient and by the silicon epitaxial film growth after complete removal of the ozone oxide film.

Effect of Transport Phenomena on Boron Concentration Profiles in Silicon Epitaxial Wafers

The boron concentration profile in silicon epitaxial wafers grown under atmospheric pressure was investigated in two types of epitaxial reactors. Transport phenomena are studied both by numerical calculations or by a gas flow visualization technique. The difference between the measured boron concentration profile and the calculated one using Ficks law was assumed to be due to autodoping. In epitaxial wafers grown at temperatures lower than 1273 K on a p-type substrate in a single-wafer horizontal reactor which has no recirculation of gas, the boron concentration profile changed abruptly at the interface between the epitaxial film and the substrate since the profile is formed only due to solid-state diffusion. In contrast, in a pancake reactor having large recirculation of gas, a gradual change in the boron concentration profile was observed due to autodoping via the gas phase. In conclusion, large amounts of recirculation of gas in an epitaxial reactor should be avoided to obtain an abrupt boron concentration profile.