Influences of gas incident angle () on surface morphology and microstructure of hydrogenated amorphous silicon (a-Si:H) thin films are investigated, which were grown using an oblique angle hot wire chemical vapor deposition (OAD-HWCVD) technique. An exponential relationship between the tan and RMS roughness is observed. The film surface morphology transforms from a self-affine surface into a mounded surface when the incident angle is larger than a critical angle c(60 c 75). Influences of on the microstructural properties of silicon thin films are characterized using Raman scattering and FT-IR measurements. As c, owing to the qusai-local shadowing effect, increasing increases the quantity and size of micro-voids, leading to the decrease of film density and quality. For c, the nonlocal shadowing effect causes the formation of large voids or cracks and the proportion of multi-hydride (SiHn, n 2) increases. Combined with the scaling theory, the relationship between the shadowing effect and the surface morphologies and microstructures of amorphous silicon thin films is discussed.