CHARGED-PARTICLE MICROSCOPE WITH EXCHANGEABLE POLE PIECE EXTENDING ELEMENT

Abstract

A charged-particle microscope having a vacuum chamber comprises a specimen holder, a particle-optical column, a detector and an exchangeable column extending element. The specimen holder is for holding a specimen. The particle-optical column is for producing and directing a beam of charged particles along an axis so as to irradiate the specimen. The column has a terminal pole piece at an extremity facing the specimen holder. The detector is for detecting a flux of radiation emanating from the specimen in response to irradiation by the beam. The exchangeable column extending element is magnetically mounted on the pole piece in a space between the pole piece and the specimen holder. Methods of using the microscope are also disclosed.

Claims

1. A charged-particle microscope having a vacuum chamber comprising: a specimen holder for holding a specimen; a particle-optical column for producing and directing a beam of charged particles along an axis so as to irradiate the specimen, the column having a terminal pole piece at an extremity facing the specimen holder; a detector for detecting a flux of radiation emanating from the specimen in response to irradiation by the beam; and an exchangeable column extending element magnetically mounted on the pole piece in a space between the pole piece and the specimen holder.

2. A microscope according to claim 1, wherein: a receiving face of the pole piece is provided with a first mechanical aligning feature; and a mating face of the extending element is provided with a second mechanical aligning feature; wherein the first and second mechanical aligning features engage with each other so as to cause the extending element to be held in a pre-defined position on the pole piece.

3. A microscope according to claim 2, wherein the pre-defined position is substantially centered on the axis.

4. A microscope according to claim 2, wherein: the receiving face is provided with a first set of utilities interconnects; the mating face is provided with a second, corresponding set of utilities interconnects; wherein when the mechanical aligning features are engaged, the first and second sets of utilities interconnects are coupled to one another, so as to allow transfer of utilities between the pole piece and the extending element.

5. A microscope according to claim 1, wherein an interface between the pole piece and the extending element forms a, vacuum seal.

6. A microscope according to claim 1, wherein the extending element comprises material that is not permanently magnetic, and is held in place on the pole piece by a magnetic field emanating from the pole piece.

7. A microscope according to claim 1, wherein the extending element comprises an electromagnetic member that can be activated to effect the magnetic mounting.

8. A microscope according to claim 1, further comprising: an in situ library for storing a variety of different extending elements; an exchanger mechanism for de-mounting a first extending element from the pole piece and storing the first extending element in the library; and retrieving a second extending element from the library and mounting the second extending element on the pole piece.

9. A microscope according to claim 8, wherein the specimen holder comprises at least part of the exchanger mechanism.

10. A microscope according to claim 1, wherein the microscope is a dual-beam microscope comprising: an electron-optical column, for producing an electron beam and directing the electron beam so as to irradiate the specimen; and an ion-optical column for producing an ion beam and directing the ion beam so as to irradiate the specimen, wherein the extending element is mounted on at least one of the particle-optical columns.

11. A microscope according to claim 1, wherein the extending element is configured to alter a profile of an electromagnetic field emerging from the particle-optical column toward the specimen.

12. A microscope according to claim 1, wherein the extending element is configured to produce at least one effect selected from the group comprising: at least partially shielding an interior space of the particle-optical column from an environment exterior to the column; positioning an active electrical device proximal the specimen, which device is configured to interact with at least one of the beam and the specimen; or positioning a metallic target on the axis, to act as an X-ray source when impinged upon by the beam.

13. A method of using a charged-particle microscope, comprising: providing a specimen on a specimen holder; using a particle-optical column to produce and direct a beam of charged particles along an axis so as to irradiate the specimen, the column having a terminal pole piece at an extremity facing the specimen holder; using a detector, for detecting a flux of radiation emanating from the specimen in response to irradiation by the beam; and magnetically mounting an exchangeable column extending element on the pole piece in a space between the pole piece and the specimen holder prior to irradiating the specimen.

14. A method according to claim 13, wherein an exchanger mechanism is used to retrieve the extending element from an in situ library for storing a variety of different extending elements and to mount a retrieved extending element on the pole piece.

15. A method according to claim 14, wherein during a use session of the microscope on a particular specimen, the exchanger mechanism is used to perform one or more exchanges of the extending element for one or more other extending elements stored in the library.

16. A charged-particle microscope having a vacuum chamber comprising: a specimen holder for holding a specimen; a particle-optical column for producing and directing a beam of charged particles along an axis so as to irradiate the specimen, the column having a terminal pole piece at an extremity facing the specimen holder; and an exchangeable column extending element magnetically mounted on the pole piece in a space between the pole piece and the specimen holder.

17. A microscope according to claim 16, wherein: a receiving face of the pole piece is provided with a first mechanical aligning feature; and a mating face of the extending element is provided with a, second mechanical aligning feature; wherein the first and second mechanical aligning features engage with each other so as to cause the extending element to be held in a pre-defined position on the pole piece.

18. A microscope according to claim 17, wherein the pre-defined position is substantially centered on the axis.

19. A microscope according to claim 17, wherein: the receiving face is provided with a first set of utilities interconnects; the mating face is provided with a second, corresponding set of utilities interconnects; wherein when the mechanical aligning features are engaged, the first and second sets of utilities interconnects are coupled to one another, so as to allow transfer of utilities between the pole piece and the extending element.

20. A microscope according to claim 17, wherein the extending element comprises an electromagnetic member that can be activated to effect the magnetic mounting.

Description

[0074] The invention will now be elucidated in more detail on the basis of exemplary embodiments and the accompanying schematic drawings, in which:

[0075] FIG. 1A renders a longitudinal cross-sectional view of an embodiment of a CPM in which the present invention is implemented.

[0076] FIG. 1B renders a magnified view of a portion of the subject of FIG. 1A, and depicts a particular embodiment of a column extending element according to the present invention.

[0077] FIG. 1C renders a magnified view of a different portion of the subject of FIG. 1A, and depicts a particular embodiment of another column extending element according to the present invention.

[0078] FIG. 2 shows an alternative embodimentto that shown in FIG. 1Bof a column extending element according to the present invention.

[0079] FIG. 3 illustrates a different embodiment of a column extending element according to the present invention.

[0080] FIG. 4 illustrates another embodiment of a column extending element according to the present invention.

[0081] FIG. 5 illustrates yet another embodiment of a column extending element according to the present invention.

[0082] In the Figures, where pertinent, corresponding parts may be indicated using corresponding reference symbols.

EMBODIMENT 1

[0083] FIG. 1A is a highly schematic depiction of an embodiment of a CPM in which the present invention is implemented; more specifically, it shows an embodiment of a microscope M, which, in this case, is a FIB-SEM (though, in the context of the current invention, it could just as validly be a SEM, (S)TEM, or ion-based microscope, for example). The microscope M comprises a particle-optical column (illuminator) 1, which produces a beam 3 of input charged particles (in this case, an electron beam) that propagates along a particle-optical axis 3. The column 1 is mounted on a vacuum chamber 5, which comprises a specimen holder 7 and associated actuator(s) 7 for holding/positioning a specimen S. The vacuum chamber 5 is evacuated using vacuum pumps (not depicted). With the aid of voltage supply 17, the specimen holder 7, or at least the specimen S, may, if desired, be biased (floated) to an electrical potential with respect to ground. The column 1 (in the present case) comprises an electron source 9 (such as a Schottky gun, for example), lenses 11, 13 to focus the electron beam 3 onto the specimen S, and a deflection unit 15 (to perform beam steering/scanning of the beam 3). The column 1 has a terminal pole piece 1 at an extremity facing said specimen holder 7. The microscope M further comprises a controller/computer processing apparatus 25 for controlling inter alia the deflection unit 15, lenses 11, 13 and detectors 19, 21, and displaying information gathered from the detectors 19, 21 on a display unit 27.

[0084] The detectors 19, 21 are chosen from a variety of possible detector types that can be used to examine different types of emergent radiation emanating from the specimen S in response to irradiation by the input beam 3. In the apparatus depicted here, the following (non-limiting) detector choices have been made: [0085] Detector 19 is a solid state detector (such as a photodiode) that is used to detect cathodoluminescence emanating from the specimen S. It could alternatively be an X-ray detector, such as Silicon Drift Detector (SDD) or Silicon Lithium (Si(Li)) detector, for example. [0086] Detector 21 is an electron detector in the form of a Solid State Photomultiplier (SSPM) or evacuated Photomultiplier Tube (PMT), for example. This can be used to detect backscattered and/or secondary electrons emanating from the specimen S.
The skilled artisan will understand that many different types of detector can be chosen in a set-up such as that depicted, including, for example, an annular/segmented detector. By scanning the input beam 3 over the specimen S, emergent radiationcomprising, for example, X-rays, infrared/visible/ultraviolet light, secondary electrons (SEs) and/or backscattered electrons (BSEs)emanates from the specimen S. Since such emergent radiation is position-sensitive (due to said scanning motion), the information obtained from the detectors 19, 21 will also be position-dependent. This fact allows (for instance) the signal from detector 21 to be used to produce a BSE image of (part of) the specimen S, which image is basically a map of said signal as a function of scan-path position on the specimen S.
The signals from the detectors 19, 21 pass along control lines (buses) 25, are processed by the controller 25, and displayed on display unit 27. Such processing may include operations such as combining, integrating, subtracting, false colouring, edge enhancing, and other processing known to the skilled artisan. In addition, automated recognition processes (e.g. as used for particle analysis) may be included in such processing.

[0087] In addition to the electron column 1 described above, the microscope M also comprises an ion-optical column 31. In analogy to the electron column 1, the ion column 31 comprises an ion source 39 (such as a Knudsen cell, for example) and imaging optics 32, and these produce/direct an ion beam 33 along an ion-optical axis 33. The column 31 has a terminal pole piece (electrode) 31 at an extremity facing said specimen holder 7. To facilitate easy axis to specimen S on holder 7, the ion axis 33 is canted relative to the electron axis 3. As hereabove described, such an ion (FIB) column 31 can be used to perform processing/machining operations on the specimen S, such as incising, milling, etching, depositing, etc.

[0088] As here depicted, the CPM M makes use of a manipulator arm A, which can be actuated in various degrees of freedom by actuator system A, and can (if desired) be used to assist in transferring specimens to/from the specimen holder 7, e.g. as in the case of a so-called TEM lamella excised from the specimen S using ion beam 33.

Alternatively/supplementally, this manipulator arm A (or another one like it) can be used in the specific context of the present invention, to assist in mounting/swapping/demounting of extending elements 41 (see below).

[0089] It should be noted that many refinements and alternatives of such a set-up will be known to the skilled artisan, including, for instance, the use of a, controlled environment at the specimen S, e.g. maintaining a pressure of several mbar (as used in an Environmental SEM or low-pressure SEM) or by admitting gases, such as etching or precursor gases, etc.

[0090] In accordance with the current invention, at least one of the pole pieces 1/31 is provided with an exchangeable column extending element 41, which is magnetically mounted on said pole piece 1731 so as to face (specimen S on) specimen holder 7. This extending element 41 can have a variety of forms/functionalities (see above), and will be described in more detail below. In the current embodiment, said magnetic mounting is achieved by: [0091] Embodying at least an upper portion of extending element 41 (facing pole piece 1) to comprise ferromagnetic material; [0092] Exploiting pole piece 1 as an electromagnet which, when energized, will firmly hold extending element 41 in place.

[0093] As here depicted, the microscope M also comprises an in situ library 43 for storing a variety of different extending elements 41. In this particular embodiment, this library 43 comprises a tray 45 on which various extending elements 41 are arranged in respective parking locations, and this tray 45 is attached to/co-moved with specimen holder 7; however, this does not have to be the case, and the library 43 might instead take the form of a rack or carrousel, for example, and/or not be connected to the holder 7. In order to swap/exchange a stored extending element 41 for a deployed extending element 41, one can, for example, proceed as follows: [0094] Use the manipulator arm A to de-mount extending element 41 from pole piece 1/31; move it to a vacant parking location on tray 45 and deposit it thereon; pick up a different extending element 41 from tray 45, move it to pole piece 1/31 and mount it thereon; and/or [0095] Move tray 45 so as to position a vacant parking location along axis 3/33 of pole piece 1/31; disable the magnetic coupling between deployed extending element 41 and pole piece 1/31, causing extending element 41 to be released from pole piece 1/31 and set down on said parking location; move tray 45 so as to position parked extending element 41 along axis 3/33 of pole piece 1/31; activate said magnetic coupling, so as to cause extending element 41 to be sucked up from its parking location and adhered to pole piece 1/31.

[0096] Turning now to FIG. 1B, this renders a magnified view of a portion of the subject of FIG. 1A, and depicts a particular embodiment of a column extending element 41 according to the present invention. More particularly, the Figure shows (tapering) pole piece 1, which has a circumferential recess 1a on a receiving side facing specimen S and centered on beam axis 3. The column extending element 41 is a hollow cone having walls comprised of ferromagnetic material (such as Permalloy) with a circumferential protrusion/lip 41a on a mating side thereof, and this is dimensioned so as to sit into (engage/mate with) said recess 1a, thereby auto-aligning/centering the extending element 41 on axis 3. The ferromagnetic walls of element 41 are magnetically attracted to the pole piece 1 when the particle-optical column 1 is energized, thereby firmly clamping/mounting the extending element 41 to the pole piece 1. The effect of the extending element 41 is to lower a main particle-optical plane of column 1moving it from an initial level P to a shifted level Pand thereby effectively increase the column's focal length. Concurrently, imaging aberrations are reduced and resolution is enhanced. See example (a)(i) above.

[0097] FIG. 1C, shows an alternative/supplemental situation to that depicted in FIG. 1B, in that an inventive extending element 41 is magnetically mounted to ion column 31 as opposed to electron column 1. The extending element 41 is a tapered hollow cone, whose walls comprise a nested set of three electrodes 411, 413 and 415 (which may, for example, respectively be at low potential/ground, high potential and low potential/ground). When the extending element 41 is engaged with pole piece 31, these electrodes 411, 413, 415 mate with corresponding electrodes 311, 313, 315 in pole piece 31, thus forming electrical interconnects between the pole piece 31 and the extending element 41. These various electrodes may, for example, comprise a metal such as titanium. To effect the magnetic mounting in this case, note that: [0098] The pole piece 31 is provided with an annular yoke 317 of ferromagnetic material, which is centered on axis 33 and has a U-shaped cross-section at the end of a given radius. Within this yoke 317, an annular electrical coil 319 is arranged. [0099] The extending element 41 is provided with a cooperating flange 417 of ferromagnetic material, which is positioned and dimensioned so as to engage with yoke 317 and close it (converting the aforementioned cross-section from U to O) when the extending element is mated with pole piece 31 (by insertion in the direction of arrow 421). [0100] An electrical current passed through coil 319 will magnetize the yoke portions 317, 417, clamping them to one another. The closed magnetic circuit formed by closed mated yoke portions 317, 417 will prevent magnetic field lines from coil 319 from interfering with an ion beam travelling along axis 33.
As in FIG. 1B, the effect of the arrangement in FIG. 1C is to lower a main particle-optical plane of column 31 and thereby effectively increase the column's focal length. This, in turn, creates an ion beam that is focused into a smaller spot. See example (a)(iv) above

EMBODIMENT 2

[0101] FIG. 2 renders a magnified view of a portion of the subject of FIG. 1A, and depicts a different embodiment of a column extending element 41 to that shown in FIG. 1B. More particularly, the Figure shows (tapering) pole piece 1, within which is located a booster tube 1. As in FIG. 1B, the element 41 has (on an upper/mating side thereof) a circumferential protrusion/lip 41a that engages in an auto-aligning manner with a circumferential recess 1a on (a lower/receiving side of) pole piece 1. In this particular instance, the extending element 41 has the following structure: [0102] An upper collar 42 of ferromagnetic material (such as Permalloy); [0103] A lower plate 46 of ferromagnetic material; [0104] An interposed spacer 44 of non-ferromagnetic material.
The upper collar 42 is magnetically attracted to the pole piece 1 when the particle-optical column 1 is energized, thereby firmly clamping/mounting the extending element 41 to the pole piece 1. At the same time, the presence of the non-magnetic spacer 46 will force magnetic field lines passing from collar 42 to plate 46 to exit the element 41 at the location of the spacer 44, thereby creating a non-immersion magnetic lens just above the specimen S. See example (a)(iii) above.

EMBODIMENT 3

[0105] FIG. 3 illustrates a different embodiment of a column extending element 41 according to the present invention, which in this case is a holder for an X-ray tomography (micro-CT/nano-CT) target T. Once again, the element 41 has a ferromagnetic collar 42 that engages with pole piece 1 in an auto-aligning manner. Attached to collar 42 is an arm 48 that holds a metallic target T upon axis 3. An electron beam travelling along axis 3 will impinge upon target T, causing a flux X of X-rays to be produced. The specimen holder 7 has been modified (by incorporation of stand 7) to hold a specimen S in the flux X, which passes through specimen S and falls upon X-ray detector 19. In this way, the CPM M can be used to perform X-ray tomography on a specimen S, which may be a mineralogical, crystallographic, semiconductor or biological sample, for instance. See example (d) above.

EMBODIMENT 4

[0106] FIG. 4 illustrates another embodiment of a column extending element 41 according to the present invention, which in this case is an adapter used to create a rudimentary STEM/TSEM. Once again, the element 41 has a ferromagnetic collar 42 that engages with pole piece 1 in an auto-aligning manner. Below 42, a bay 410 (vacant space) has been created into which specimen holder 7 can be inserted, so as to position specimen S on axis 3. Below this bay 410 is a counterpole 412 (comprising ferromagnetic material) on which is mounted a STEM camera 414. See example (c)(iii) above.

EMBODIMENT 5

[0107] FIG. 5 illustrates yet another embodiment of a column extending element according to the present invention, which in this case is a shielding element. Within ferromagnetic collar 42, a shielding plate 416 has been mounted, with a small aperture 418 centered on axis 3. Such a construction can, for example: [0108] Shield/protect internal elements of the electron column 1 from debris produced during specimen modification (e.g. high-throughput FIB milling) using the ion column 31 (see FIG. 1A); [0109] Act as an atmospheric gas barrier, to help maintain the inside of column 1 at a high vacuum level when the microscope M is used in environmental/low-pressure mode (with gas in the vicinity of specimen S). See example (b) above.

[0110] In view of the many possible embodiments to which the disclosed principles may be applied, it should be recognized that the illustrated embodiments are only preferred examples and should not be taken as limiting the scope of protection. Rather, the scope of protection is defined by the following claims.