Microwave plasma generating device and method for operating same

A microwave plasma generating device, comprising:

• a plasma chamber having chamber walls;
• at least one microwave generating device for generating microwaves disposed outside of said plasma chamber;
• a microwave in-coupling device with which the microwaves are coupled into said plasma chamber, said microwave in-coupling device having an inner conductor leading into said plasma chamber through at least one of said chamber walls of said plasma chamber, an insulating tube enclosing said inner conductor and separating said inner conductor from an interior of said plasma chamber, and at least one outer conductor with at least one outer conductor end leading into said plasma chamber through at least one of said chamber wall, said at least one outer conductor being coaxial to said inner conductor but is not provided over an entire circumference of said inner conductor, said inner conductor and said at least one outer conductor form a microwave line and an outlet of microwaves out of the microwave line in said plasma chamber to generate microwave plasma in said interior of said plasma chamber;
• and
• at least one plasma electrode disposed in said interior of said plasma chamber and electrically insulated from said chamber walls and to which a DC, NF, or HF voltage can be applied, said at least one plasma electrode disposed coaxially to said inner conductor, wherein the microwave plasma is electronically contactable with said at least one plasma electrode so that a function of said at least one outer conductor is transferable at least partly to the microwave plasma, said at least one plasma electrode being tubular-shaped and having tube ends, and one of said tube ends of said at least one plasma electrode, respectively, is provided as an electrical contact to the microwave plasma, a radius of at least one of said tube ends is continuously, gradually, or discontinuously increasing.

A method for generating plasma, which comprises the steps of:

• providing a microwave plasma generating device having a plasma chamber;
• providing at least one microwave generating device disposed outside of the plasma chamber of the microwave plasma generating device, the microwave generating device outputting microwaves being coupled into the plasma chamber by at least one microwave in-coupling device leading through at least one chamber wall into the plasma chamber, the microwave in-coupling device containing an inner conductor leading into the plasma chamber through at least one chamber wall of the plasma chamber, an insulating tube enclosing the inner conductor from an interior of the plasma chamber, and at least one outer conductor having at least one outer conductor end leading into the plasma chamber through the at least one chamber wall and coaxial to the inner conductor but not provided over an entire circumference of the inner conductor, the inner conductor and the at least one outer conductor forming a microwave line and an outlet of microwaves out of the microwave line in the plasma chamber to generate a microwave plasma in the interior of the plasma chamber;
• providing in the interior of the plasma chamber, at least one plasma electrode, being electrically insulated from the chamber wall, to which a DC, NF, or HF voltage is applied, and is disposed coaxially to the inner conductor, the plasma electrode contacting the microwave plasma electrically, wherein a microwave power is transported by the microwave line being used for an ionization of the microwave plasma so that a function of the at least one outer conductor is transferred at least partly to the microwave plasma;
• selecting the at least one plasma electrode from the group consisting of:
• a tubular shaped plasma electrode disposed around the insulating tube being coaxial to the inner conductor and having two plasma electrode elements, each of the plasma electrode elements disposed at one side of the plasma chamber and each ending in an interior of the plasma chamber;
• and
• a single, tubular plasma electrode with a plasma electrode opening formed therein and extending in a longitudinal direction of the tubular plasma electrode;
• and
• adjusting an electrical potential of the microwave plasma by the DC, NF, or HF voltage at the at least one plasma electrode.