Anisotropic carrier transport in preferentially oriented polycrystalline silicon films fabricated by very-high-frequency plasma enhanced chemical vapor deposition using fluorinated source gas

Abstract Structural and transport anisotropy of low temperature polycrystalline silicon (poly-Si) were studied. Poly-Si films with (2 2 0) preferential orientation were fabricated by very-high-frequency chemical vapor deposition from SiF 4 and H 2 mixtures. The crystallite size perpendicular to the film surface increased and orientation fluctuation decreased with increasing growth temperature ( T s ) as inferred using X-ray diffraction. This indicated that a columnar structure was developed with increasing T s . The 150°C T s films had smaller grain sizes perpendicular to the film surface and no transport anisotropy was observed. The films fabricated at T s > 200°C had larger grains perpendicular to the film surface. The conductivity perpendicular to the film surface was five times larger than parallel. This transport anisotropy originates from an anisotropic grain structure. In addition, ac conductivity analysis detected the presence of a thin conductive layer on the film surface resulting from impurity in-diffusion.