Ribbon antenna for versatile operation and efficient RF power coupling
View Patent ↗A plasma processing apparatus and method are disclosed which allows switching between the E and H operation modes and also increase the coupling efficiency of the RF power to the plasma. This apparatus may increase plasma density by a factor of about 1.25-1.65 for a given power output. Simultaneously, due to the high efficiency, the need to cool the antenna may be eliminated. A new antenna geometry which increases the amount of surface area for a given volume is used to take advantage of skin effects associated with RF electric current. In some embodiments, the antenna has a single turn to reduce proximity effects. The antenna may also be embedded in a ferrite material to further optimize its performance.
1. A plasma generation apparatus, comprising: a chamber having a dielectric window; wherein an antenna comprises a ribbon shaded antenna and said antenna abutting said dielectric window, constructed of a material and having a thickness, a width in contact with said dielectric window, and a cross-sectional area defined as a product of said width and said thickness; and a power supply operating at a frequency and in communication with said antenna, wherein said material and said frequency determine a skin depth where most current is carried in said antenna, and wherein a product of said skin depth and said width is greater than 0.001 multiplied by said cross-sectional area of said antenna.
2. The plasma generation apparatus of claim 1 , wherein said product is greater than 0.01 multiplied by said cross-sectional area.
3. The plasma generation apparatus of claim 1 , wherein said product is greater than 0.05 multiplied by said cross-sectional area.
4. The plasma generation apparatus of claim 1 , further comprising a ferrite material, wherein said antenna is disposed between said ferrite material and said dielectric window.
5. The plasma generation apparatus of claim 4 , further comprising a potting material disposed between said antenna and said ferrite material.
6. The plasma generation apparatus of claim 1 , wherein said antenna comprises two substantially parallel portions and two semi-circular ends.
7. The plasma generation apparatus of claim 6 , wherein one of said semi-circular ends comprises a discontinuity, thereby creating two legs of said antenna.
8. The plasma generation apparatus of claim 7 , wherein a first of said legs is in communication with said power supply, and a second of said legs is in communication with a switch, wherein said first leg and second leg are electrically connected in a first position of said switch, and wherein said second leg is electrically connected to a potential different than said first leg in a second position of said switch.
9. The plasma generation apparatus of claim 8 , wherein said switch can be actuated between said first position and said second position while plasma is being generated.
10. The plasma generation apparatus of claim 1 , wherein said antenna comprises only one turn.