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

Structural and transport anisotropy of low temperature polycrystalline sili con (poly-Si) were studied. Poly-Si films with (220) preferential orientati on were fabricated by very-high-frequency chemical vapor deposition from Si F4 and H-2 mixtures. The crystallite size perpendicular to the film surface increased and orientation fluctuation decreased with increasing growth tem perature (T-s) as inferred using X-ray diffraction. This indicated that a c olumnar structure was developed with increasing T-s. The 150 degrees C T-s films had smaller grain sizes perpendicular to the film surface and no tran sport anisotropy was observed. The films fabricated at T-s, > 200 degrees C had larger grains perpendicular to the film surface. The conductivity perp endicular to the film surface was five times larger than parallel. This tra nsport anisotropy originates from an anisotropic grain structure. In additi on, ac conductivity analysis detected the presence of a thin conductive lay er on the film surface resulting from impurity in-diffusion. (C) 2000 Elsev ier Science B.V. All rights reserved.