Radio-frequency antenna unit and plasma processing apparatus
The present invention aims at providing a radio-frequency antenna unit capable of generating a high-density discharge plasma in a vacuum chamber. The radio-frequency antenna unit according to the present invention includes: a radio-frequency antenna through which a radio-frequency electric current can flow; a protective tube made of an insulator provided around the portion of the radio-frequency antenna that is in the vacuum chamber; and a buffer area provided between the radio-frequency antenna and the protective tube. The “buffer area” refers to an area where an acceleration of electrons is suppressed, and it can be formed, for example, with a vacuum or an insulator. Such a configuration can suppress an occurrence of an electric discharge between the antenna and the protective tube, enabling the generation of a high-density discharge plasma in the vacuum chamber.
1. A radio-frequency antenna unit to be used in an apparatus for generating plasma in a vacuum chamber, comprising:
a) a radio-frequency antenna through which a radio-frequency electric current can flow;
b) a protective tube made of an insulator provided around a portion of the radio-frequency antenna that is in the vacuum chamber; and
c) a buffer area provided between the radio-frequency antenna and the protective tube,
wherein a gas seal, in addition to the protective tube, is provided between the buffer area and an inside of the vacuum chamber.
2. The radio-frequency antenna unit according to claim 1 , wherein the buffer area is a vacuum.
3. The radio-frequency antenna unit according to claim 1 , wherein a pressure in the buffer area is at atmospheric pressure.
4. The radio-frequency antenna unit according to claim 1 , wherein the protective tube has a highly resistive coating on a surface of a base tube with a material which is more resistant to the plasma than a material of the base tube.
5. The radio-frequency antenna unit according to claim 4 , wherein the material of the base tube is quartz, and the material of the highly resistive coating is any one of or a mixture of two or more of oxide ceramics, fluoride ceramics, nitride ceramics, carbide ceramics, and silicon.
6. The radio-frequency antenna unit according to claim 1 , wherein the radio-frequency antenna has a highly electrically conductive coating on a surface of a metallic base member with a material which is electrically more conductive than a material of the metallic base member.
7. The radio-frequency antenna unit according to claim 1 , wherein the radio-frequency antenna has a tubular shape for allowing a refrigerant to pass through.
8. The radio-frequency antenna unit according to claim 7 , wherein the radio-frequency antenna has a highly electrically conductive coating on a surface of a tube made of a highly corrosion-resistive metal which is more corrosion-resistive to the refrigerant than copper, the highly electrically conductive coating being made of a metal which is electrically more conductive than the highly corrosion-resistive metal.
9. The radio-frequency antenna unit according to claim 8 , wherein the highly corrosion-resistive metal is stainless steel and the highly conductive coating is made of either gold or platinum.
10. The radio-frequency antenna unit according to claim 1 , wherein the radio-frequency antenna has an open-loop shape.
11. The radio-frequency antenna unit according to claim 10 , comprising an attachment for attaching the open-loop radio-frequency antenna to the vacuum chamber, the attachment being for holding both ends of the open-loop radio-frequency antenna, wherein a communication hole which communicates with the buffer area is provided in the attachment.
12. A plasma processing apparatus having at least one of the radio-frequency antenna units according to claim 1 .