Transport and Surface Phenomena for Silicon Epitaxial Growth

シリコンエピタキシャル成長に関わる輸送現象と表面化学反応

Habuka Hitoshi

Transport phenomena, surface chemical processes, dopant concentration profiles and surface roughness of substrate for silicon epitaxial growth are discussed theoretically and experimentally. The objective of this thesis is to develop the models to predict various phenomena relating to the silicon epitaxial wafer. The major part of discussion is based on the calculations of the transport phenomena and the chemical reactions at the surface. At first, the transport phenomena in a pancake reactor and in a single-wafer horizontal reactor are discussed. Secondary, the substrate rotation and the chemical reactions for the epitaxial growth are discussed to describe the growth rate and the film thickness. For further studies, the epitaxial wafer's qualities, the dopant distribution and the surface roughness of silicon substrate, are investigated.

The transport phenomena in a pancake reactor are discussed based on a gas flow visualization technique using a high-sensitivity analogue camera, and numerical calculations. At room temperature and the epitaxial growth temperature of 1423 K, a large recirculation exists in the reactor chamber, in which the gases near the susceptor flow 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.

An evaluation of silicon epitaxial thin-film growth using the SiHCl3-H2 system in a single-wafer horizontal reactor is discussed by solving the transport equations for gas velocity, temperature and concentration of chemical species taking into account of the dependence of gas properties on temperature and composition, assuming a simple Arrhenius-type expression for the chemical reaction of SiHCl3 and H2 on a substrate. Non-Linear increase in the growth rate due to changes in thermal diffusion and diffusion is found to become significant as the SiHCl3 concentration in the reactor increases.

For an enhancement of studies, the effect of substrate rotation on transport of reactive gases and epitaxial growth rate is investigated for a single-wafer horizontal reactor using a model and experiments. The rotating substrate causes a circulating gas flow region above itself, in which an asymmetric and nonuniform SiHCl3 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 good uniformity in the film thickness observed in calculation and measurement is mainly attributed to the averaging effect by integrating the local growth rate along a concentric circle on the substrate surface, and partially by the species concentration distribution change, both of which are caused by the rotating motion of the substrate.

For the discussion of the dependence of the epitaxial growth rate on the source species concentrations, a transport and epitaxy model following Eley-Rideal to describe silicon epitaxial film growth in an SiHCl3-H2 system is developed by numerical calculations and comparison with experiments. The state of the surface during the epitaxial growth is also discussed considering the intermediate species, elementary reactions and rate limiting processes.

The boron concentration profile in silicon epitaxial films grown on a p-type substrate under atmospheric pressure is investigated in two types of epitaxial reactors, a single-wafer horizontal reactor and a pancake reactor. It is concluded thst large amounts of recirculation of gas in an epitaxial reactor should be avoided to obtain an abrupt boron concentration profile.

Since silicon surface after the epitaxial growth must be very smooth and fiat, surface roughness of a silicon wafer heated at 800-1100 °C under atmospheric pressure in hydrogen ambient is studied. AFM images show that the surface heated at 900°C has many small pits which are formed due to the difference in the chemical reaction rates between hydrogen-silicon and hydrogen-silicon dioxide. The behavior of surface roughness with pressure and heating time agrees well with that predicted by the pit formation model in this study.

Electrical engineering [ 540 ]

eng

Copyright(c) by Author

・第2章 H. Habuka, M. Mayusumi, N. Tate and M. Katayama, "Gas Flow and Heat Transfer in a Pancake Chemical Vapor Deposition Reactor", J. Cryst. Growth, 151, 375 (1995). 1995年6月発行 references

・第3章 H. Habuka, M. Katayama, M. Shimada and K. Okuyama, "Numerical Evaluation of Silicon-Thin Film Growth from SiHCl3-H2 Gas Mixture in a Horizontal Chemical Vapor Deposition Reactor", Jpn. J. Appl. Phys., 3 3, 1977 (1994). 1994年4月発行 references

・第4章 H. Habuka, T. Nagoya, M. Katayama, M. Shimada and K. Okuyama, "Modeling of Epitaxial Silicon Thin-Film Growth on a Rotating Substrate in a Horizontal Single-Wafer Reactor", J. Electrochem. Soc., 142, 4272 (1995). 1995年12月発行 references

・第5章 H. Habuka, T. Nagoya, M. Mayusumi, M. Katayama, M. Shimada and K. Okuyama, "Model on Transport Phenomena and Epitaxial Growth of Silicon Thin Film in SiHCI3-H2 System under Atmospheric Pressure", J. Crystal Growth (印刷中). 1996年発行 references

・第5章 羽深等, 片山正健, 島田学, 奥山喜久夫, "輸送現象と表面反応を考慮したSiHCl3-H2系Siエピタキシャル成長の三次元数値解析", 日本結晶成長学会誌, 23(1), 2 (1996). 1996年3月発行 references

・第6章 H. Habuka, M. Mayusumi, H. Tsunoda and M. Katayama, "Effect of Transport Phenomena on Boron Concentration Profiles in Silicon Epitaxial Wafers", J. Electrochem. Soc., 143, 677 (1996). 1996年2月発行 references

・第7章 H. Habuka, H. Tsunoda, M. Mayusumi, N. Tate and M. Katayama, "Roughness of Silicon Surface Heated in Hydrogen Ambient", J. Electrochem. Soc., 142, 3092 (1995). 1995年9月発行 references

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広島大学