Si 3 H 8 Based Epitaxy of Biaxially Stressed Silicon Films Doped with Carbon and Arsenic for Cmos Applications
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Si3H8 BASED EPITAXY OF BIAXIALLY STRESSED SILICON FILMS DOPED WITH CARBON AND ARSENIC FOR CMOS APPLICATIONS M. Bauer*, S. Zollner#, N. D. Theodore#, M. Canonico#, P. Tomasini*, B.-Y. Nguyen#, C. Arena* *ASM America Inc., 3440 East University Drive, 85034 Phoenix, Arizona, USA #Freescale Semiconductor, Inc., 2100 East Elliot Road, 85284 Tempe, Arizona, USA
ABSTRACT. Arsenic doped Si:C films were grown epitaxially using Silcore® (Si3H8), methylsilane and arsine as source gases with growth rates up to 90 nm/min at 550ºC. We observed a strong dependence of C and As incorporation on growth rate, caused by a growth rate dependent surface segregation behavior of C and As. High-resolution x-ray diffraction measurements of the epi layers reveal a perpendicular lattice constant as low as 5.323 Å. This corresponds to a biaxial stress of more than 2 GPa. Grazing exit (224) x-ray diffraction reciprocal space maps show the full tetragonal strain expected from the C content, suggesting that no relaxation of the films has occurred. Spectroscopic ellipsometry (SE) spectra were acquired in the 0.74 to 6.6 eV photon energy range. For intrinsic Si:C alloys, the E1 critical point shows the expected blueshift due to the alloying. For Si:C:As, a strong broadening of the E1 and E2 transitions exists, due to scattering of Bloch electrons in the crystal by As atoms. Additionally, free carrier effects lead to a decrease (increase) of the real (imaginary) part of the dielectric function in the near-infrared, consistent with a free carrier concentration in excess of 5×1020 cm-3. Transmission electron microscopy (TEM) of As doped Si:C films confirmed single-crystal epitaxial growth. INTRODUCTION Interest in Si1-yCy alloys stems from its complementary nature to the Si1-xGex system. Since epitaxial Si1-yCy films are under tensile strain, one can produce type II band alignment without the need for a thick relaxed Si1-xGex buffer layer. However, epitaxial growth of C containing random alloys is challenging due to the large mismatch between diamond and silicon lattices, low solubility of C in Si, and the tendency of Si1-yCy to precipitate. For device applications, a desirable goal is a material in which C is incorporated into silicon substitutional sites. Substitutional C concentration determines electronic properties including band offsets. Non-substitutional C may influence the presence of deep levels in the band gap. A common strategy is to kinetically stabilize the C atoms on substitutional lattice sites using non-equilibrium growth conditions. This approach enables control of the movement of the C species on the growing surface, so that the atoms have just enough energy for substitutional incorporation into the lattice. Additional energy would lead to chemical reactions resulting in formation of undesirable Silicon carbide. It is well known in molecular beam epitaxy (MBE) how to suppress C segregation in order to maximize substitutional C incorporation, i.e., by using low temperatures and high growth rates [1-5]. Chemical vapor deposit
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