Determination factor of direction growth in microcrystalline silicon thin film deposition

Abstract

We have proposed the mechanism of the <110> directional growth of microcrystalline silicon (μc-Si) thin films deposited by PECVD (plasma enhanced chemical vapor deposition) from SiH4 and H2 gas mixture, where dimeric radicals act a key role to form bridge nuclei for the ledge formation on the (110) facet. In order to look further into details of the mechanism, we investigated other important factors that influence the growth of μc-Si in <110> direction in terms of their impact on crystallinity with varying deposition temperature. The enhancement of surface diffusion length of radicals is inferred from the enlargement of the crystalline grain size accompanied with the increase of the deposition temperature. The growth in <110> direction is also promoted as the deposition temperature increases. Therefore, it is suggested that the surface diffusion length of radicals is another key factor that governs the crystalline growth in <110> direction. The growth mechanism of μc-Si thin films in <110> direction is discussed in terms of the relation between the surface diffusion length of monomeric radicals depending on the substrate surface temperature and the average space of bridges depending on the density of dimeric radicals on the growing surface.