Study of the growth mechanism of CVD silicon films on silica by X-ray reflectivity, atomic force microscopy and scanning electron microscopy

Abstract
Thin silicon films were made by low pressure chemical vapour deposition from pure silane (SiH₄) on a Si/SiO₂ substrate. They have been studied by X-ray Reflectivity, Atomic Force Microscopy, and Scanning Electron Microscopy, as a function of deposition time. It was observed that the growth starts by the formation of a layer that only partially covers the substrate (thickness < 5 nm). This layer subsequently fully covers the substrate leading to a smooth film that is initially partially covered by a large number of nuclei (height 10 nm, density 120 per square micron). With increasing layer thickness the nuclei density diminishes, the nuclei width increases, and their height becomes smaller. It is suggested that small proportions of the very active radical SiH₂, which is present in the gas phase, play a central role in the first stages of growth. The possibility to obtain complementary information on the surface morphology from X-ray reflectivity and atomic force microscopy data is discussed.