In this study, diamond films were deposited on the (100) Si substrate using hot filament CVD (HFCVD) process. After deposition, the Si substrate was removed by etching with KOH solution. The morphology and structure of the substrate-side as well as the free surfaces of the diamond film were performed. Results reflect that a better crystallinity of sp(3) diamond phase generated and preferred growth is along I I I I I planes for films deposited at a shorter distance between hot filament and substrate. Comparing the substrate-side surface and top surface of the diamond films, the sp(2) bonded carbon network was formed in the early stage of the deposition process and then transformed to sp(3) bonded diamond as deposition continued. On the substrate-side of the diamond films, unfilled spaces between the particles were observed. The particle sizes at the substrate-side surface are about 3 mu m for the distance of 10 mm and 1.5 mu n for the distance of 15 mm. As distance between the substrate and the hot filament reduces during deposition, both the grain size and the surfaces roughness at the substrate-side surfaces of the diamond films are larger. (c) 2005 Elsevier B.V. All rights reserved.