Magnetically enhanced, inductively coupled plasma source for a focused ion beam system
View Patent ↗The present invention provides an inductively coupled, magnetically enhanced ion beam source, suitable to be used in conjunction with probe-forming optics to produce an ion beam without kinetic energy oscillations induced by the source.
1. A method for producing a focused ion beam, comprising the steps of:
applying RF power to an antenna that inductively couples energy to a plasma to induce ionization of the plasma in proximity of the antenna;
providing impedance matching circuitry to adjust the electrical phase shift across the antenna to reduce modulation of the plasma potential;
extracting an ionized beam from a region of extraction in proximity to the antenna; and
applying a focusing mechanism to the ion beam extracted from the region.
2. The method of claim 1 , further comprising the step of providing a magnet in proximity to the region of beam extraction.
3. The method of claim 2 , wherein the magnet is fixed annular magnet.
4. The method of claim 2 , wherein the magnet produces between 200 and 1000 Gauss.
5. The method of claim 1 , wherein the circuitry is adjustable to vary an amount of power transferred to the plasma.
6. The method of claim 1 , wherein the circuitry is adjustable to vary the voltage phase across the antenna.
7. The method of claim 1 , wherein the coil is positioned so that an axis of the antenna substantially coincides with an axis of propagation of the extracted beam.
8. The method of claim 1 , wherein the antenna is positioned to minimize modulation of the plasma potential in the region immediately adjacent to the source exit aperture.
9. A focused ion beam system, comprising:
a vessel enclosing a region of plasma;
an antenna excited by an RF electrical source to induce ionization of the plasma;
circuitry that couples the antenna to the electrical source to substantially reduce RF oscillations in the ionized plasma, and provides adjustment of the electrical phase shift across the antenna to reduce modulation of the plasma potential;
an extraction mechanism to extract the ionized plasma into a beam; and
a focusing mechanism to focus the beam.
10. The system of claim 9 , further comprising a means to dissipate heat generated in the plasma.
11. The system of claim 9 , wherein the antenna comprises a single or multi-turn helical coil oriented to induce high ionization density in the plasma in a region in proximity to the coil.
12. The system of claim 9 , wherein the focusing mechanism focuses the beam for milling and deposition.
13. The system of claim 9 wherein a high ion density in the plasma produces a high beam current without substantial modulation of the plasma potential and hence axial energy spread of extracted ions.
14. A focused ion beam system for milling and deposition, comprising:
a plasma tube comprising an ionizable, non-metallic plasma gas and a source aperture at an end of the tube;
a helical antenna positioned around the plasma tube;
circuitry in a network comprising the antenna and providing adjustment of the electrical phase shift across the antenna to reduce modulation of the plasma potential;
an extractor that enables extraction of the plasma from the source aperture into a beam; and
a focusing mechanism to focus the beam.
15. The system of claim 14 , further comprising a magnet placed in proximity of the source aperture.
16. The system of claim 14 , wherein the focusing mechanism causes a beam of high brightness exceeding 2000 A/cm 2 /sr with an extracted beam energy of 10 keV.
17. The system of claim 14 , wherein the system exhibits an energy spread that is less than 3 eV.
18. The system of claim 14 , wherein the system exhibits an energy spread that is less than 4 eV.
19. The system of claim 14 , further comprising a transformer for coupling the RF source to the plasma.
20. The method of claim 19 , wherein a secondary of the transformer is center-tapped and coupled through a circuit to ground.