Abstract: A thin film deposition apparatus for use in a semiconductor manufacturing process or the like, is provided to, in particular, deposit a diffusion barrier thin film onto a substrate having a concave portion with a relatively high aspect ratio (hereinafter referred to as a contact hole). In the thin film deposition apparatus, a small surface and point source or a ring-shaped source is employed, evaporation is performed under such a condition that the Knudsen number K.sub.n =.lambda./H (a ratio of a mean free path .lambda. of an evaporation material particle to a distance (H) between the evaporation source and the substrate) becomes 0.1 or more, and a relation of the substrate and the evaporation source is set according to the aspect ratio of the contact hole, resulting in deposition of the thin film with good coverage on a bottom surface of the contact hole.