To provide a thin film deposition method, and a semi-conductor device manufacturing method by which a capacitor insulating film having a uniform film thickness fixed in composition ratio is deposited in the state of covering an inner wall of a trench formed in a substrate by an atomic layer vapor deposition method.

In the thin film depositing method and the semi-conductor device manufacturing method, a trench capacitor, in which at least a capacitor insulating film 14 and an upper electrode are laminated successively from a lower layer, is provided on the inner wall of the trench 13 formed in the substrate 11, and the capacitor insulating film 14 is deposited in the state of covering the inner wall of the trench 13 by the atomic layer vapor deposition method. In the step of depositing the capacitor insulating film 14, gaseous hydrogen is used for the carrier gas of a source gas for forming the atomic layer.