Microwave plasma electron flood
View Patent ↗A method and apparatus is provided for generating a plasma electron flood using microwave radiation. In one embodiment, a microwave PEF apparatus is configured to generate a magnetic field that rapidly decays over a PEF cavity, resulting in a static magnetic field having a high magnetic field strength near one side (e.g., “bottom”) of the PEF cavity and a low magnetic field strength (e.g., substantially zero) near the opposite side (e.g., “top”) of the PEF comprising an elongated extraction slit. In one particular embodiment, the one or more permanent magnets are located at a position that is spatially opposed to the location of the elongated extraction slit to achieve the rapidly decaying magnetic field. The magnetic field results in an electron cyclotron frequency in a region of the cavity equal to or approximately equal to a microwave radiation frequency so that plasma is generated to diffuse through the extraction apertures.
1. A plasma electron flood system, comprising:
a microwave generation component configured to generate microwave radiation;
a cavity configured to function as both a microwave cavity, substantially resonant at a frequency of the microwave radiation, and as a plasma chamber, wherein the cavity has one or more apertures that allow transmission of microwaves from the microwave generation component to the cavity, one or more extraction apertures in direct contact with an ion implantation system beam line, and an input for a gas; and
a magnetic field generation component comprising one or more permanent magnets arranged in proximity to the cavity and configured to generate a magnetic field that decays rapidly over the cavity from a region of high magnetic field strength to a region of low magnetic field strength in the vicinity of the extraction apertures, wherein the one or more permanent magnets comprise a racetrack shape, which wraps around a perimeter of the cavity as a continuous shape, and that generates the magnetic field configured to form an Electron Cyclotron Resonance (ECR) heating zone extending along a length of the cavity;
wherein the magnetic field results in an electron cyclotron frequency in a region of the cavity that is equal to or approximately equal to the microwave radiation frequency so that a plasma is generated to diffuse through the extraction apertures.
2. The system of claim 1 , wherein the one or more permanent magnets are substantially symmetrically disposed in relation to the extraction apertures so that the magnetic field has a value of substantially zero near the location of the extraction apertures.
3. The system of claim 1 , wherein the one or more permanent magnets are disposed along one or more lower walls of the cavity spatially opposed to the extraction apertures.
4. The system of claim 1 , wherein the magnetic field comprises a single north magnetic pole cusp and a single south magnetic pole cusp extending along the perimeter of the cavity.
5. The system of claim 1 , wherein the cavity comprises a substantially empty housing containing no components other than the gas and the microwave radiation.
6. The system of claim 1 , wherein the cavity comprises a housing that does not contain refractory metals.
7. The system of claim 1 , further comprising a plasma detection component configured to confirm the presence of a plasma by detection of light emitted from the plasma in the cavity or by detection of a microwave field strength in the cavity.
8. The system of claim 1 , wherein the system comprises one or more elements of high permeability material configured to reduce the magnitude of the magnetic field outside of the cavity.
9. A method for generating a microwave plasma electron flood, comprising:
providing a gas to a cavity having one or more extraction apertures in direct communication with an ion implantation system beam line;
generating a magnetic field within the cavity using one or more racetrack shaped permanent magnets configured to wrap around a perimeter of the cavity as a continuous shape that is substantially symmetric in relation to the one or more extraction apertures, wherein the magnetic field decays rapidly over the cavity from a region having a strong magnetic field to a region having a minimal magnetic field in the vicinity of the one or more extraction apertures, and wherein the magnetic field is configured to form an ECR heating zone extending along a length of the one or more extraction apertures so that the magnetic field has a value of zero near the location of the one or more extraction apertures;
generating microwave radiation having a frequency substantially equal to an electron cyclotron frequency in a region of the cavity; and
providing the microwave radiation to the cavity, wherein the cavity has a resonant frequency substantially equal to the frequency of the microwave radiation, and wherein the microwave radiation is absorbed by the gas to form a plasma configured to diffuse through the one or more extraction apertures.
10. The method of claim 9 , wherein the cavity comprises a substantially empty housing containing no components other than the gas and the microwave radiation.
11. The method of claim 10 , wherein the cavity comprises a housing that does not contain refractory metals.
12. The method of claim 11 , further comprising:
detecting the presence of the plasma within the cavity by detecting light emitted from the plasma in the cavity or by detecting a microwave field strength in the cavity.