化学气相沉积中影蔽效应对硅薄膜表面形貌和微结构的影响

采用斜入射热丝化学气相沉积技术(OAD-HWCVD),研究了气流入射角度(θ)对氢化非晶硅(a-Si:H)薄膜表面和微结构的影响.实验发现,薄膜厚度为1μm时,均方根粗糙度与tanθ成指数关系;在入射角度为75°时,薄膜表面由自仿射表面转变为mound表面.采用拉曼谱和红外谱表征了硅薄膜的微结构随气流入射角度的变化.在薄膜转变为mound表面生长之前,随入射角度的增加,准局域的影蔽效应使得薄膜中微空洞的数目及尺寸增加,导致薄膜微结构因子升高、致密度下降、薄膜质量变差.在薄膜转变为mound表面生长之后,非局域的影蔽效应导致大尺度的空洞,同时薄膜中以Si-Hn(n 2)形式存在的氢增多.本文以非晶硅薄膜为例,结合标度理论,分析了薄膜生长过程中的表面形貌和微结构与影蔽效应的关系.

Influence of shadowing effect on morphology and microstructure of silicon thin film in chemical vap or dep osition

Influences of gas incident angle (θ) 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 tanθ 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 θ_c(60°< θ_c< 75°). Influences of θ on the microstructural properties of silicon thin films are characterized using Raman scattering and FT-IR measurements. As θ < θ_c, owing to the qusai-local shadowing effect, increasing θ increases the quantity and size of micro-voids, leading to the decrease of film density and quality. For θ > θ_c, the nonlocal shadowing effect causes the formation of large voids or cracks and the proportion of multi-hydride (SiH_n, 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.
Keywords： shadowing effect mounded surface micro-voids surface morphology evolution