Hitoshi Habuka

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.

Dielectric behavior and ferroelectric transition of copolymers of vinylidene fluoride and trifluoroethylene

Abstract Dielectric behavior of copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) with VDF contents of 52 to 78 mol % has been investigated over wide frequency and temperature ranges with particular reference to the ferroelectric transition. Some related physical properties such as the dynamic tensile modulus, the thermal expansion, and the enthalpy of transition were also studied. The copolymers exhibited three dielectric relaxations γ, β, and Tt in the increasing order of temperature. The γ process is the local mode relaxation of part of frozen molecular chains below the glass transition. The β relaxation is related with micro-Brownian motions of molecular chain backbone in amorphous regions. The Tt relaxation which is featured with a rather narrow distribution of relaxation times is associated with cooperative motions of molecular chain in crystalline regions in the vicinity of the ferroelectric transition. Dielectric measurements under hydrostatic pressure revealed that the anomalou...

Chemical process of silicon epitaxial growth in a SiHCl3-H2 system

Abstract The chemical process of silicon epitaxial growth in a SiHCl3–H2 system at atmospheric pressure is studied experimentally using a horizontal cold-wall single-wafer reactor and a quadrupole mass spectra analyzer. The dominant chlorosilane species in the gas phase and the dominant overall chemical reaction are experimentally determined to be SiHCl3 gas and SiHCl3+H2→Si+3HCl, respectively. Since the amount of HCl gas produced in the reactor is proportional to the silicon epitaxial growth rate, it is concluded that the dominant chemical process of silicon epitaxial growth in a SiHCl3–H2 system occurs on the silicon substrate surface. The concentrations of SiCl2, SiH2Cl2, SiHCl and SiCl4 gases produced in the gas phase are too low to play a significant role in silicon epitaxial growth.

Dominant Overall Chemical Reaction in a Chlorine Trifluoride-Silicon-Nitrogen System at Atmospheric Pressure

This study evaluates the overall chemical reaction in a chlorine trifluoride–silicon–nitrogen system at atmospheric pressure, based on the observation of the dominant chemical species in the gas phase using a quadrupole mass spectra analyzer coupled with a horizontal cold-wall single-wafer epitaxial reactor. Chlorine trifluoride gas etches the silicon surface, producing two major products, silicon tetrafluoride gas and chlorine gas, at room temperature and 530 K. The production of chlorosilanes was not observed in this study. The results obtained in this study indicate that the dominant overall chemical reaction in a chlorine trifluoride–silicon–nitrogen system is 3Si + 4ClF3 →3SiF4 ↑+ 2Cl2 ↑.

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.

Rate theory of multicomponent adsorption of organic species on silicon wafer surface

For the first time, the time‐dependent change in the concentrations of organic species adsorbed on a silicon wafer surface is modeled using numerical calculations based on rate theory. An equation composed of the adsorption rate from the gas phase to the silicon wafer surface and the desorption rate from the silicon wafer surface is developed accounting for competitive processes in a multicomponent system. This equation can describe and predict the actual increase and decrease in the surface concentrations of propionic acid ester, siloxane (D9), and di(2‐ethylhexyl)phthalate. It is also indicated that the organic species having a large adsorption rate with a small desorption rate remains in significant abundance on the silicon wafer surface for a very long period after cleaning.

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.

Airborne Organic Contamination Behavior on Silicon Wafer Surface

This study theoretically and experimentally evaluates the role of the coexisting organic compounds on the time-dependent airborne organic contamination on a silicon wafer surface in the cleanroom air. The maximum contamination and the ratio of the desorption to the adsorption are independently described from each other, using simple equations consisting only of the surface concentrations of the organic compounds on the silicon wafer surface. These parameters are consistent with the experiment using the silicon plate sampling method. Additionally, the suppression of the increase in the surface concentration of bis(2-ethylhexyl)phthalate theoretically predicted due to the coexisting organic compounds is experimentally observed. The time-dependent behavior of the airborne organic contamination is concluded to occur following the simple rate theory.

Change in Microroughness of a Silicon Surface during In Situ Cleaning Using HF and HCl Gases

The change in microroughness of a silicon substrate surface is studied at each step of an in situ cleaning method performed entirely in a hydrogen ambient at atmospheric pressure, which comprises the removal of native oxide film using hydrogen fluoride gas and the removal of an organic hydrocarbon film using hydrogen chloride gas. The root-mean-square average roughness and the power spectral density show that no surface roughening is caused by this in situ cleaning method. Additionally, it is shown in this study that heat-treatment at 1223 K in a hydrogen ambient at atmospheric pressure can smooth the silicon substrate surface when the surface is bare. The effect of the removal of an organic hydrocarbon film using hydrogen chloride gas on the morphology of the silicon substrate surface is also studied.