Patent ID: 7204921

Claim:
A vacuum apparatus comprising: a vacuum chamber; an RF source; a plasma generator; a detecting device for detecting disappearance of plasma; and first and second variable inductance elements, wherein the first variable inductance element comprises: a first main winding, and a first control winding magnetically coupled to the first main winding, wherein the second variable inductance element comprises: a second main winding, and a second control winding magnetically coupled to the first main winding, wherein the first and second main windings are controlled based on a magnitude of direct current flowing through the first and second control windings respecitvely, wherein the RF source is connected to the plasma generator via the first main winding and the RF source is connected to ground voltage via the second main winding, wherein the plasma generator generates plasma by RF voltage outputted from the RF source, and wherein when the disappearance of plasma is detected by the detecting device, the direct current flowing through the second control winding is decreased in order to increase the inductance of the second main winding larger than its inductance when plasma is maintained, and then, the RF voltage outputted to the plasma generator is increased.