PURPOSE: To facilitate forming a thin film continuously and stably for a long forming period by a method wherein a yoke surrounding a magnet which is provided along the circumference of a plasma generating chamber and forms a magnetic field is provided along the circumference of a vacuum waveguide.
CONSTITUTION: A yoke 12 which absorbs flux generated by a magnetic field generating electromagnet 8 provided around a plasma generating chamber 11 and reduces the magnetic field intensity in a vacuum waveguide 10 is provided around the vacuum waveguide 10. The one end of the yoke 12 is so provided as to face the plasma generating chamber 11 and the other end is so provided as to surround the one end of the electromagnet 8 to absorb the flux. With a thin film forming equipment of such constitution, a plasma is not generated in the vacuum wavwguide 10 and, moreover, a steep change of the magnetic field intensity is provided between the vacuum waveguide 10 and the plasma generating chamber 11. Therefore, the plasma is not accelerated toward a microwave introducing window 6. with this constitution, a film of most of the materials can be formed continuously and stably for a long forming period without misting the microwave introducing window 6 regardless of the conductivity of the generated film.