SIMS Spectrometry Technique

Abstract

A method of performing Secondary Ion Mass Spectrometry, comprising: Providing a specimen on a specimen holder; Using an ion beam to irradiate a region of a surface of said specimen, thereby producing ablated specimen material; Collecting ionized constituents of said ablated material in a mass analyzer, and sorting them according to species,
further comprising: Providing a catalytic gas proximal said region of the specimen surface during said irradiation, said gas comprising a component selected from the group comprising perfluoroalkanes and their isomers.

Claims

1. A method of performing Secondary Ion Mass Spectrometry, comprising: using an ion beam to irradiate a region of a surface of a specimen, thereby producing ablated specimen material; collecting ionized constituents of said ablated material in a mass analyzer, and sorting them according to species; and providing a catalytic gas proximal said region of the specimen surface during said irradiation, said gas comprising a component selected from the group comprising perfluoroalkanes and their isomers.

2. A method according to claim 1, wherein an electron transfer reaction is produced between said specimen material and said catalytic gas, thereby producing a relative increase in ionization yield of said ablated material.

3. A method according to claim 1, wherein said catalytic gas comprises C.sub.nF.sub.2n+2, with an alkane length n selected to lie in a range 5-15, more particularly 8-12.

4. A method according to claim 1, wherein said ion beam comprises ions selected from the group comprising Ga and Xe.

5. A method according to claim 1, performed in situ in a Charged Particle Microscope.

6. A Charged Particle Microscope comprising: an ion beam column, for irradiating a region of a surface of a specimen with an ion beam, so as to produce ablated specimen material; a mass analyzer, for collecting ionized constituents of said ablated material and sorting them according to species; a gas injection system, for administering a gas to a vicinity of said region of the specimen surface during said irradiation; a controller, for at least partially controlling operation of said microscope, wherein said controller is configured to control said gas injection system so as to administer a catalytic gas comprising a component selected from the group comprising perfluoroalkanes and their isomers.

7. The charged particle microscope of claim 6, wherein said catalytic gas comprises C.sub.nF.sub.2n+2, with an alkane length n.

8. The charged particle microscope of claim 7, wherein n selected to lie in a range of 5 to 15.

9. The charged particle microscope of claim 7, wherein n selected to lie in a range of 8 to 12.

10. The charged particle microscope of claim 6, wherein said ion beam comprises ions selected from the group comprising Ga and Xe.

11. A method comprising: providing a catalytic gas proximal to a surface of a sample, the catalytic gas comprising a component selected from the group comprising perfluoroalkanes and their isomers; irradiating the surface of the sample with an ion beam; collecting ionized constituents of an ablated material in a mass analyzer, the ablated material generated from the surface of the sample due to the ion beam, wherein the ablated material interacts with the catalytic gas, the catalytic gas increasing a number of ionized species of the ablated material; and sorting the ionized ablated material according to species.

12. The method of claim 11, wherein said catalytic gas comprises C.sub.nF.sub.2n+2, with an alkane length n.

13. The method of claim 12, wherein n selected to lie in a range of 5 to 15.

14. The method of claim 12, wherein n selected to lie in a range of 8 to 12.

15. The method of claim 11, wherein said ion beam comprises ions selected from the group comprising Ga and Xe.

Description

[0025] The invention will now be elucidated in more detail on the basis of an exemplary embodiment and the accompanying schematic drawing, in which:

[0026] FIG. 1 renders a longitudinal cross-sectional elevation view of an embodiment of a dual-beam CPM in which the present invention is implemented.

EMBODIMENT 1

[0027] FIG. 1 is a highly schematic depiction of an embodiment of a dual-beam charged particle microscope (CPM) in which the present invention is implemented; more specifically, it shows an embodiment of a FIB-SEM. The microscope M comprises a particle-optical column 1, which produces a beam 3 of 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 6. 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 6, may, if desired, be biased (floated) to an electrical potential with respect to ground. Also depicted is a vacuum port 5, which may be opened so as to introduce/remove items (components, specimens) to/from the interior of vacuum chamber 5. A microscope M may comprise a plurality of such ports 5, if desired.

[0028] The column 1 (in the present case) comprises an electron source 9 (such as a Schottky gun, for example) and an illuminator 2. This illuminator 2 comprises (inter alia) lenses 11, 13 to focus the electron beam 3 onto the specimen 6, and a deflection unit 15 (to perform beam steering/scanning of the beam 3). 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.

[0029] The detectors 19, 21 are chosen from a variety of possible detector types that can be used to examine different types of stimulated radiation emanating from the specimen 6 in response to irradiation by the (impinging) beam 3. In the apparatus depicted here, the following (non-limiting) detector choices have been made: [0030] Detector 19 is a solid state detector (such as a photodiode) that is used to detect cathodoluminescence emanating from the specimen 6. It could alternatively be an X-ray detector, such as Silicon Drift Detector (SDD) or Silicon Lithium (Si(Li)) detector, for example. [0031] Detector 21 is an electron detector in the form of a Solid State Photomultiplier (SSPM) or evacuated Photomultiplier Tube (PMT) [e.g. Everhart-Thornley detector], for example. This can be used to detect backscattered and/or secondary electrons emanating from the specimen 6.
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.

[0032] By scanning the beam 3 over the specimen 6, stimulated radiationcomprising, for example, X-rays, infrared/visible/ultraviolet light, secondary electrons (SEs) and/or backscattered electrons (BSEs)emanates from the specimen 6. Since such stimulated 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 6, which image is basically a map of said signal as a function of scan-path position on the specimen 6.

[0033] 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.

[0034] In addition to the electron column 1 described above, the microscope M also comprises an ion-optical column 31. This comprises an ion source 39 and an illuminator 32, and these produce/direct an ion beam 33 along an ion-optical axis 33. To facilitate easy access to specimen 6 on holder 7, the ion axis 33 is canted relative to the electron axis 3. As alluded to hereabove, such an ion (FIB) column 31 can, for example, be used to perform processing/machining operations on the specimen 6, such as incising, milling, etching, depositing, etc. Alternatively, the ion column 31 can be used to produce imagery of the specimen 6. It should be noted that ion column 31 may be capable of generating various different species of ion at will, e.g. if ion source 39 is embodied as a so-called NAIS source; accordingly, references to ion beam 33 should not necessarily been seen as specifying a particular species in that beam at any given timein other words, the beam 33 might comprise ion species A for operation A (such as milling) and ion species B for operation B (such as implanting), where species A and B can be selected from a variety of possible options.

[0035] Also illustrated is a Gas Injection System (GIS) 41, which can be used to effect localized injection of gases, such as etching or precursor gases, etc., for the purposes of performing gas-assisted etching (IBIE) or deposition (IBID), for instance. Such gases can be stored/buffered in a reservoir 41, and can be administered through a narrow nozzle 41, so as to emerge in the vicinity of the intersection of axes 3 and 33, for example.

[0036] It should be noted that many refinements and alternatives of such a set-up will be known to the skilled artisan, such as the use of a controlled environment within (a relatively large volume of) the microscope M, e.g. maintaining a background pressure of several mbar (as used in an Environmental SEM or low-pressure SEM).

[0037] In the context of the present invention, the microscope M is further provided with a mass analyzer module 43. If ion beam 33 is directed onto a region of specimen 6, it will cause localized ablation of specimen materialsome of which will be ionized and some (most) of which will be neutral. Ionized constituents of the ablated specimen material can be captured by mass analyzer module 43, which will sort and count them according to mass/charge ratiothus giving qualitative/quantitative information regarding the specimen's (localized) constitution. So as to improve the ionization yield of this specimen ablation process, GIS 41 is used by the preset invention to administer a catalytic gas comprising a component selected from the group comprising perfluoroalkanes and their isomers. As set forth above, the presence of such a fluorine-rich catalytic gas in the vicinity of (the intersection of ion axis 33 with) specimen 6 causes more secondary ions to be produced, via a fluorine-based electron-grabbing process.

[0038] In a specific, non-limiting example, the following parameters can be used: [0039] Gas species: Perfluoro-dodecane, C.sub.10F.sub.22 [0040] Gas pressure: 310.sup.5 bar (background pressure in vacuum chamber 5: ca. 210.sup.6 bar). [0041] Gas temperature: 25 C.