Study on the Fundamental Mechanism of Radical Beam Epitaxy

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The objective of this research program is to develop a new epitaxial growth technique for lowering the epitaxial temperature by using a radical beam produced with a dc glow discharge or electron cyclotron resonance (ECR) plasma of a material gas. In order to obtain the fine silicon homoepitaxy at lower temperature and to realize low temperature surface cleaning prior to the epitaxial growth, neutral fragment of SiH_X radicals created by the discharge decomposition of SiH_4 are effused onto a c-Si (100) substrate placed on a ultra-high vacuum chamber. The results are summarized as follows:(1) Silicon epitaxial layers have been grown at temperatures as low as 550 ゜C by using a radical beam produced by the dc glow discharge of 15 % SiH_4 diluted with Ar. (2) When an adequate beam intensity of hydrogen radicals is irradiated on the growing surface, the epitaxial temperature is lowered down to 520 ゜C as a result of in situ removal of oxygen contamination on the surface. In case of irradiating the excess hydrogen radical beam, twin crystal or polycrystalline is formed because the overhydrogenation of surface silicon bonds interrupts the silicon network formation. For a low hydrogen beam intensity, oxygen contamination can not be effectively removed and hence polycrystalline phase appears. (3) SiH_X radical beam irradiation reduce the epitxial temperature to 400 ゜C presumably because ECR plasma effectively creates highly excited SiH_X radicals. (4) Irradiation of a suitable amount of SiH_X radicals from SiH_4 ECR plasma is quite beneficial remove the thin protective oxide formed on the substrate surface. Consequently clean Si surface is obtained at a temperature of 650 ゜C by the radical beam cleaning technique.