LOW-TEMPERATURE IONIZATION OF METASTABLE ATOMS EMITTED BY AN INDUCTIVELY COUPLED PLASMA ION SOURCE

Abstract

The present disclosure combines inductively coupled plasma (ICP) ion-source technology together with laser-cooling and photoionization techniques to create a new ion source that has improved performance.

Claims

1. An ion source system, comprising: a. an inductively coupled plasma (ICP) source, wherein metastable atoms and ions are generated within a plasma vessel; b. a first mode and a second mode for producing an ion beam from the metastable atoms and the ions generated in the plasma vessel; c. wherein the first mode further comprises 1. metastable atoms emitted from the plasma vessel; 2. one or more beams of laser radiation configured to excite the emitted metastable atoms to form ions; 3. charged particle optics configured to accelerate the emitted or extracted ions to form the ion beam; d. wherein the second mode further comprises 1. ions emitted or extracted from the plasma vessel; 2. charged particle optics configured to accelerate the emitted or extracted ions to form the ion beam. e. charged particle optics configured to condition the ion beam for use in focused ion beam instrumentation.

2. The system of claim 1, further comprising one of more beams of laser radiation configured to cool or compress the metastable atoms emitted from the plasma vessel.

3. The system of claim 2, further comprising a magnetic field applied in the vicinity of the one of more beams of laser radiation configured to cool or compress the metastable atoms emitted from the plasma vessel.

4. The system of claim 1, further comprising one or more beams of laser radiation applied to the metastable atoms contained inside the plasma vessel.

5. The system of claim 4, further comprising a magnetic field inside the plasma vessel configured to mediate the interaction of the metastable atoms and the one of more beams of laser radiation applied to the metastable atoms contained inside the plasma vessel.

6. The system in claim 1, wherein the beams of laser radiation excite a resonant ionization process in the electric field

7. The system in claim 1, wherein the beams or laser radiation excite the metastable atoms to Rydberg states that subsequently ionize in the electric field.

8. The system in claim 1, further comprising the introduction of an additional gas species to the plasma vessel to enhance the production of metastable atoms.

9. An ion source system comprising: f. an inductively coupled plasma (ICP) source, wherein metastable atoms and ions are generated within a plasma vessel; g. one or more beams of laser radiation configured to cool or compress the metastable atoms contained inside the plasma vessel; h. ions emitted or extracted from the plasma vessel; i. charged particle optics configured to accelerate the emitted or extracted ions to form the ion beam.

10. The system of claim 9, further comprising a magnetic field inside the plasma vessel configured to mediate the interaction of the metastable atoms and the one of more beams of laser radiation applied to the metastable atoms contained inside the plasma vessel.

11.-19. (canceled)

20. An ion source comprising: j. an inductively coupled plasma (ICP) source comprising: 1. a plasma discharge vessel containing a gas and having a gas inlet and a plasma outlet; 2. an antenna adjacent said discharge vessel and configured to receive an RF current; 3. a plurality of electrodes arranged adjacent said plasma outlet; k. a laser cooling and photoionization stage, comprising: 1. a metastable atom inlet configured to receive a beam of metastable atoms from said inductively coupled plasma source; 2. a first set of laser emitters each configured to direct a laser beam into said beam of metastable atoms to cool and/or condense said beam of metastable atoms; 3. a second set of laser emitters each configured to direct a laser beam into said beam of metastable atoms to photoionize a population of said metastable atoms to produce a population of ions; 4. a plurality of electrodes arranged adjacent said beam of metastable atoms configured to produce an electric field that converts said population of ions into an ion beam;

21. An ion source according to claim 20, further comprising a plurality of laser emitters each configured to direct a laser beam into said plasma discharge vessel.

22. An ion source according to claim 20, further comprising a plurality of permanent magnets configured to produce a magnetic field inside said plasma discharge vessel.

23. An ion source according to claim 20, further comprising a plurality of current-carrying wires configured to produce a magnetic field inside said plasma discharge vessel.

24. An ion source according to claim 20, further comprising a plurality of permanent magnets configured to produce a magnetic field in the vicinity of said beam of metastable atoms.

25. An ion source according to claim 20, further comprising a plurality of current-carrying wires configured to produce a magnetic field in the vicinity of said beam of metastable atoms.

26. An ion source according to claim 20, wherein the second set of laser emitters is configured to excite a resonant photoionization process in said electric field

27. An ion source according to claim 20, wherein the second set of laser emitters is configured to excite said metastable atoms to a Rydberg state that subsequently ionizes in said electric field

28. An ion source according to claim 20, further comprising a second gas contained in the plasma discharge vessel.

29.-37. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] FIG. 1 is a schematic showing primary features of an ion source according to an embodiment of the invention.

DETAILED DESCRIPTION

[0075] A system and method are described for creation of ions utilizing an inductively coupled plasma as well as laser-cooling and photoionization laser beams.

[0076] An inductively coupled plasma ion source [100] in which a gas of metastable atoms [101] and ions are produced inside a plasma discharge vessel [102] through collisional excitation with plasma electrons. The plasma electrons are typically excited via a RF current applied to an antenna [103]. During Normal Mode operation, one or more electrodes [104-107] near the discharge vessel may be biased with selected voltages to produce, tune, or suppress a beam of ions from ions produced in the discharge vessel. The discharge vessel may be made from a transparent dielectric material.

[0077] A second gas species (other than the one from which ions are produced) may be optionally introduced to the plasma vessel [102]. It is known in the art that addition of a second gas to the plasma vessel may enhance the production or properties of metastable atoms emitted from the plasma vessel; the introduced gas may alter the mean number, density, or temperature of said metastable atoms.

[0078] In a departure from prior art, one or more beams of laser radiation [108, 109, 110] may be transmitted through the discharge vessel [102], configured radially or axially or at any other orientation. These beams may optionally be used during either Normal Mode or during Cold Ion Mode according to various laser cooling and trapping techniques to shape or increase the phase space density of the beam of metastable atoms [111] emitted from the plasma vessel.

[0079] In another embodiment, used in Normal Mode operation, the beams of laser radiation [108, 109,110] are configured to instead alter the velocity or spatial distribution of metastable atoms within the plasma vessel. The generation of ions in an ICP often results from the ionization a metastable atoms; by cooling or compressing the metastable atoms in the ICP, the distribution of ions emitted from the discharge vessel [102] may have an enhanced brightness.

[0080] Additionally, a laser-cooling and photoionization stage [120] may be configured to receive the beam of metastable atoms [111] from the inductively coupled plasma ion source [100] (FIG. 1 shows an embodiment where electrodes 104-107 are biased to suppress the emission of ions from the ICP). Stage 102 is central to the operation of the ion source in Cold-Ion Mode. Stage 102 is positioned to receive the beam of metastable atoms effusively emitted from the discharge vessel [102]. One or more beams of laser radiation [121, 122] may then be applied to the beam of metastable atoms [111] in order to cool, compress laterally, deflect, or in general apply forces or manipulate the internal state of the atoms in the beam.

[0081] A magnetic field [129] may also be introduced in the [120] region to mediate the interaction between the laser beams and the metastable atoms. In addition, a magnetic field that varies in space may optionally be used directly to apply a conservative force-field to the atoms in the beam; for example a magnetic field with a gradient in a given direction will deflect the beam along that axis, while a field with a radial gradient would focus or defocus the metastable atom beam.

[0082] To create ions [131], one or more beams of laser radiation [123, 124] may be applied to the beam of metastable atoms [111] and configured to ionize the atoms. Configured here means tuning the beam's shape, intensity, frequency to optimize brightness and minimize the energy spread of the ion source. The ionization may be performed in a number of ways including resonant photoionization, non-resonant photoionization, and excitation to a Rydberg state that subsequently ionizes in an electric field that may differ from the field where the excitation occurred, see, e.g., U.S. Pat. No. 10,020,156 B2.

[0083] To accelerate the ions [131] created from the photoionized metastable atoms, one or more electrodes [125-128] may be configured spatially and have bias voltages applied to them to create an electric field in the region containing the ions.

[0084] The electrodes [125-128] may also be configured to provide a specific electric field (including zero field) necessary to facilitate the photoionization or Rydberg excitation process. Furthermore, the electrodes may be configured to provide more than one electric field or an electric field gradient as needed to facilitate ionization, as in the case of Rydberg excitation, or in shaping the ion beam for integration into a focused ion beam system's probe-forming optics.

[0085] The combined set of electrodes [104-107,125-128], as well as the coils or magnets producing static magnetic fields [129] compose the set of Charged Particle Optics in the system. Charged Particle Optics is defined herein to mean the set of physical objects controlling the acceleration of charged particles in their vicinity. Charged Particle Optics include, but are not limited to sets of conductive materials to which voltages are applied to create electric fields, e.g. electrodes, sets of current-carrying wires, or permanent magnets which generate magnetic fields.

REFERENCES

[0086] 1. U.S. Pat. No. 8,829,468 B2; MAGNETICALLY ENHANCED, INDUCTIVELY COUPLED PLASMA SOURCE FOR A FOCUSED ION BEAM SYSTEM [0087] 2. P. Chabert, N. Braithwaite. Physics of Radio Frequency Plasmas. Cambridge University Press (2011). ISBN 978-0-521-76300-4 [0088] 3. U.S. Pat. No. 10,020,156 B2; RESONANT ENHANCEMENT OF PHOTOIONIZATION OF GASEOUS ATOMS [0089] 4. Y Hayashi et al. 2009 J. Phys. D: Appl. Phys. 42 145206. DOI 10.1088/0022-3727/42/14/145206