Control of Orientation for Polycrystalline Silicon Thin Films Fabricated from Fluorinated Source Gas by Microwave Plasma Enhanced Chemical Vapor Deposition

The structure of polycrystalline silicon films was controlled by selecting deposition conditions, especially gas mixing ratio of H₂/SiF₄, for plasma enhanced chemical vapor deposition on glass at a low temperature of 360°C. Under the H₂/SiF₄ ratio of 10/90 sccms, (111), (220), (311) and (400) diffraction peaks were observed by X-ray diffraction for a 0.5 µm thick film and (400) oriented crystallites grew with film thickness. The sharpness of the Raman peak around 520 cm^-1 and the pseudo-dielectric function measured by an ellipsometer indicated that the crystallites have excellent regularity of the Si–Si bond compared with (220) oriented films and also have small surface roughness, which are preferable features for device applications. The selective growth of (400) oriented grains is thought to partly originate from selective etching due to fluorine related species generated under low hydrogen conditions.