PURPOSE: To form a thin film which is not exfoliated by continuously surface treating a substrate and forming a thin film in the same chamber.

CONSTITUTION: Air in a chamber 1 is evacuated, and H2 gas is then fed, for example, through a gas guide pipe 10. A switch 14 is connected with an RF power source 12 side to apply a high frequency voltage between electrodes 9 and 11 to generate an RF electric field, thereby ionizing the H2 gas to diffuse it from the grid of the electrode 9 in the chamber. Simultaneously, the switch 15 is closed to apply a DC voltage between the electrode 4 and 9 to accelerate the ions by the electric field to collide with a substrate 5, thereby causing many defects on the substrate. Thus, after the surface of the substrate 5 is treated, the chamber is sufficiently evacuated, the switch 14 is connected with a power source 8 side, the switch 14 is opened, SiH4 gas is decomposed, for example, as a normal plasma CVD device to accumulate an amorphous silicon.