Sample chip

Abstract

To provide an improved holder for samples analyzed by energy dispersive x-ray spectroscopy (EDS).SOLUTION: A sample holder chip (hereinafter referred to as a sample chip) for releasably holding a sample comprises a cradle comprising beryllium, with a recess for releasably receiving the sample, and a bumper comprising aluminum. Specifically, the invention relates to a sample chip that may be used in a charged particle microscope.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a specimen holder tip (hereinafter referred to as specimen tip) for releasably holding a specimen, the specimen tip comprising a cradle comprising beryllium with a recess for releasably receiving the specimen, and a bumper comprising aluminum. In particular, the present invention relates to a specimen tip that can be used in a charged particle microscope. [Background technology]

[0002] In the field of electron microscopy, various types of optical devices are generally known for producing magnified images of objects, features, or components too small to be seen with the naked eye. Such devices may include transmission electron microscopes (TEMs), scanning electron microscopes (SEMs), and scanning transmission electron microscopes (STEMs). Imaging of a sample is typically achieved by detecting emanations or output radiation from the sample caused by irradiation of the sample with an imaging beam. Such radiation may include secondary electrons, backscattered electrons, x-rays, light (visible light and near-visible light, such as near-IR and near-UV), or any combination thereof. These imaging devices may be part of a “dual beam” system with additional tools that have machining capabilities to modify the sample by removing material, such as by milling or ablation, or adding material, such as by deposition. For example, such a dual beam system may include a focused ion beam (FIB) for machining and an electron microscope for imaging.

[0003] In a process called "energy dispersive X-ray spectroscopy" or "EDS," the energy of the X-rays of the responding electron beam from the sample is measured and plotted on a histogram to form a material-specific spectrum. The measured spectrum can be compared to known spectra of various elements to determine which elements and minerals are present in the sample.

[0004] However, EDS can suffer from certain disadvantages, such as the introduction of spurious peaks from materials present within the instrument, such as the sample holder. Summary of the Invention

[0005] It is therefore an object of the present invention to provide an improved holder for samples analyzed by EDS, which allows a high solid angle towards the EDX detector, provides additional collimation of the EDX detector, allows for high P / B, suppression of spurious peaks generated from the holder / detector surrounding environment, and aims to provide a robust and usable design.

[0006] The present invention addresses this by providing a sample tip for releasably holding a sample, the sample tip comprising: a cradle comprising beryllium and with a recess including an opening or void for releasably receiving a sample; and a bumper including aluminum.

[0007] The specimen tip can preferably be used in a charged particle microscope, in particular a charged particle microscope equipped with an EDX detector.

[0008] The cradle within the sample tip typically comprises a first surface and a second surface that are substantially parallel to one another.

[0009] As used herein, the term "substantially" is intended to mean that the referenced feature has approximately the described feature, but not the exact feature described. For example, substantially parallel is intended to mean that the surfaces are in the same direction but may deviate from being exactly the same distance apart, and substantially circular is intended to mean that the feature may have an approximately circular shape, but not a perfect circle. The referenced feature may deviate from the "exact" feature by about 1.0% to about 0.001%, e.g., about 0.5% to about 0.1%.

[0010] The cradle comprises beryllium. In a preferred aspect of the invention, the cradle can consist essentially of or consist of beryllium.

[0011] For the avoidance of doubt, when the term "comprising" or "comprises" is used herein, it means that the feature being described must contain the recited components, but may optionally contain additional components. When the term "consisting essentially of" or "consists essentially of" is used, it means that the feature being described must contain the recited components, but may contain small amounts (e.g., up to 5% by weight, or up to 1% or 0.1% by weight) of other components, provided that any additional components do not affect the essential properties of the feature. When the term "consisting of" or "consists of" is used, it means that the feature being described must contain only the recited components.

[0012] The cradle may preferably be symmetrical, for example, the cradle may have at least one plane of symmetry.

[0013] The cradle may have at least two curved sides and at least two straight sides, typically the curved sides are opposite each other and the straight sides are opposite each other, i.e. the cradle has two planes of symmetry.

[0014] The cradle can be any shape, but preferably the shape or geometry of the cradle minimizes cradle material in the direct path between the primary generated x-rays and the detector surface.

[0015] It may be preferable for the cradle to have a low profile, particularly when surrounded by the bumper, i.e. the cradle does not extend beyond the upper and / or lower surfaces of the bumper.

[0016] The recess includes an opening or void within the recess. Typically, the opening or void is about 5% to about 20% smaller than the recess, leaving a recessed area of ​​the cradle around the opening or void.

[0017] The recess of the cradle may be positioned on a first surface of the cradle, and the second surface of the cradle may preferably slope from the outer edge of the cradle towards the opening or cavity, or vice versa.

[0018] The recesses may have any shape, but preferably have a substantially circular shape, for example the recesses may have the shape of a circular specimen grid, such as a specimen grid for a charged particle microscope.

[0019] In a preferred embodiment, the recess may have a shape such that a sample grid (such as a sample grid for a charged particle microscope) may fit within the recess.

[0020] As used herein, the term "specimen grid" includes any grid suitable for holding a specimen, such as a half-moon grid or a thin film structure. In particular, specimen grids include any grid that can be used in a charged particle microscope.

[0021] The voids or openings may have the same or different shape as the recesses. Typically, the voids or openings have the same shape as the recesses. For example, the recesses and openings / voids may be substantially circular.

[0022] The specimen tip bumper may comprise, consist essentially of, or consist of aluminum.

[0023] The bumper may releasably connect to the sample holder and / or sample stage on one side, however, in some embodiments it may be necessary for the sample holder and / or sample stage to releasably connect to the cradle.

[0024] Depending on the connection point, the bumper may surround between about 75% and about 100% of the cradle's circumference.

[0025] For example, if the bumper is releasably connected to the sample holder and / or sample stage, the bumper may preferably surround 100% of the cradle.

[0026] However, if the cradle is releasably connected to the sample holder and / or sample stage, the bumper may preferably surround less than 100% of the cradle to allow connection between the cradle and the sample holder and / or sample stage, for example, the bumper may surround about 75% to about 90% of the cradle, e.g., about 75% to about 80% of the cradle.

[0027] As used herein, "surrounding" is intended to mean that the bumper is positioned around the perimeter of the cradle. The bumper may contact the cradle all around, or may contact the cradle only at certain points, as shown in the figures.

[0028] The bumper typically extends to the same location as the cradle.

[0029] Using a Cartesian coordinate system, the specimen tip T (including the bumper and cradle) typically extends in the XY plane.

[0030] The bumper may be of any shape, but preferably has at least two straight sides, for example the bumper may be substantially quadrilateral in shape, such as a square or rectangle.

[0031] The bumper may include first and second surfaces that slope from an outer edge of the bumper toward the cradle.

[0032] The bumper (and therefore the sample tip) has a proximal end and a distal end, the proximal end being the end that can be releasably connected to the sample holder and / or sample stage.

[0033] The cradle may be positioned in the center of the bumper or may be slightly offset, i.e., the cradle may be positioned closer to one side of the bumper. For example, the cradle may be positioned near the side or proximal end of the bumper that releasably connects to the sample holder and / or sample stage.

[0034] Typically, the cradle and bumper are formed independently and then assembled so that the cradle can be removably positioned within the bumper. However, in some situations, it may be necessary to form the cradle and bumper together.

[0035] The sample tip may preferably comprise at least one immobilization element.

[0036] The securing element may include a clamping member movably connected to the bumper or cradle.

[0037] The clamping member is movable between a closed position and an open position, in which the clamping member is positioned so that the sample carrier can be placed in the recess, and in which the clamping member is arranged to directly or indirectly lock the sample carrier in the recess.

[0038] A movable clamping member connected to the holder or cradle allows for improved attachment of the sample carrier with the sample to the sample holder: fast and reliable attachment can be achieved by simply moving the clamping member to the open position, placing the sample carrier in the recess and moving the clamping member again to the closed position.

[0039] Because the clamping members are connected to the holder or cradle, it is relatively easy to move the clamping members between the open and closed positions, and movement of the clamping members provides a reliable method of securely fixing the sample carrier within the sample tip, thereby providing a reliable, safe and fast method of mounting the sample carrier to the sample tip.

[0040] Additionally, the use of movable clamping members offers the possibility of realizing the tip in a very compact manner. A compact design is advantageous, for example, because it allows for tilting the sample. Furthermore, a compact design is useful, for example, for establishing a large aperture angle for EDX analysis.

[0041] Advantageous embodiments are described below.

[0042] The clamping member may be pivotable between the open and closed positions. Pivoting the clamping member allows for a compact structure as well as easy manipulation of the clamping member. It is conceivable that the grid is placed on the horizontal surface of the cradle recess and the movable clamping member holds the grid in place in the closed position. This provides a compact structure that prevents so-called shadowing during TEM investigations.

[0043] The clamping member may comprise a spring element. The spring element may provide the clamping member with a desired clamping force so that the sample carrier is held firmly in place. In a further embodiment, the spring element may be arranged to bias the clamping member towards the closed position. In this way, the clamping member is forced towards the closed position and holds the sample carrier in place by default. Thus, the reliability of the mounting is increased.

[0044] It is contemplated that the clamping member may be actuated by an actuator member, which may be actuated automatically or by a user of the electron microscope, for example.

[0045] An actuator member may be arranged to at least urge the clamp member towards the open position. In combination with a spring element biasing the clamp member towards the closed position, this provides a quick, reliable and easy way of mounting a sample carrier to a sample holder.

[0046] The sample tip may comprise at least one further fixing element, i.e. two, three or four, for fixing the sample carrier in the recess of the holder body. The use of further fixing elements allows for a more secure mounting. It is noted that the fixing element and the further fixing element may differ from each other. For example, the fixing element may be a pivotable clamping member, while the further fixing element may be, for example, a spring element. However, in one embodiment, the fixing element and the further fixing element are substantially similar to each other.

[0047] According to a further aspect of the present invention there is provided a charged particle microscope for inspecting a sample, the charged particle microscope comprising: an optical column including a charged particle source and an illuminator for directing a beam of charged particles emitted from the charged particle source onto a sample; a sample tip according to the present disclosure as defined above for holding a sample grid with said sample therein and positioned downstream of said illuminator; an EDX detector device for detecting X-ray radiation arising from the sample in response to incidence of charged particles emitted by the charged particle source; a control unit for carrying out the operation of the charged particle microscope.

[0048] The present invention also provides a method of inspecting a specimen through a plurality of charged particle beams, the method comprising: providing a charged particle beam; - providing a sample on a sample chip according to the present disclosure as defined above, - directing a beam through a sample; - detecting the energy of the X-rays emitted from the sample. [Brief explanation of the drawings]

[0049] The invention will now be described with reference to the accompanying drawings which show several embodiments of the sample holder described herein. [Figure 1] Schematic of a charged particle microscope. [Figure 2a] 1 is a schematic diagram of one embodiment of a method as disclosed herein. [Figure 2b] 1 is a schematic diagram of one embodiment of a method as disclosed herein. [Figure 3a] Schematic of the specimen chip in top (plan) (FIG. 3a) and front (elevation) (FIG. 3b) views. [Figure 3b] Schematic of the specimen chip in top (plan) (FIG. 3a) and front (elevation) (FIG. 3b) views. [Figure 4] 1 is a schematic diagram of a sample tip connected to a sample holder as disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0050] Figure 1 (not to scale) is a highly schematic depiction of an embodiment of a charged particle microscope M in which a specimen tip as disclosed herein may be used. More specifically, in this case, Figure 1 shows one embodiment of a transmission microscope M that is a TEM / STEM (although, in the context of the present invention, e.g., an SEM, or an ion-based microscope may be equally useful).

[0051] 1, within a vacuum housing 2, an electron source 4 generates a beam B of electrons propagating along an electron-optical axis B' and traversing an electron-optical illuminator 6, which functions to direct / focus the electrons onto a selected portion of a sample S (which may, for example, be (locally) thinned / flattened). A deflector 8 is also depicted, which can be used to (among other things) effect a scanning movement of the beam B.

[0052] The sample S is held on a sample tip T (not shown) mounted on a sample holder H, which can be positioned with multiple degrees of freedom by a positioning device A, which moves a stage A' to which the holder H is (removably) fixed. For example, the sample holder H may be equipped with fingers that can move in the XY plane (see the depicted Cartesian coordinate system), typically moving parallel to Z and tilting about X / Y (so-called alpha-tilt / beta-tilt, respectively). Such movements allow different portions of the sample S to be illuminated / imaged / inspected by the electron beam B traveling along axis B' (Z direction) (and / or allowing a scanning movement to be performed as an alternative to beam scanning). If desired, a cooling device (not depicted, but known to those skilled in the art) can be in intimate thermal contact with the sample holder H, e.g., to keep the sample holder H (and the sample S thereon) at cryogenic temperatures.

[0053] The electron beam B interacts with the sample S in such a way as to cause the sample S to emit various types of "stimulated" radiation, including (for example) secondary electrons, backscattered electrons, x-rays, and optical radiation (cathodoluminescence).

[0054] In the present invention, the X-rays are detected using a detector device 22, an EDX (Energy Dispersive X-ray Spectroscopy) module.

[0055] However, additionally, one can study the electrons that traverse (pass through) the sample S, are emitted / emitted from the sample, and continue to propagate along axis B' (substantially, typically with some deflection / scattering). Such transmitted electron flux enters an imaging system (projection lens) 24, which generally comprises various electrostatic / magnetic lenses, deflectors, collectors (stigmators, etc.). In standard (non-scanning) TEM mode, this imaging system 24 can collect the electron flux onto a phosphor screen 26, which can be retracted / withdrawn (as shown diagrammatically by arrow 26') if desired to move it out of the path of axis B'.

[0056] An image (or Fourier transform diagram) of (a portion of) the sample S is formed on a screen 26 by an imaging system 24, and this image can be viewed through a viewing port 28 located in a suitable part of the wall of the housing 2. The retraction mechanism of the screen 26 can be, for example, mechanical and / or electrical in nature and is not depicted here.

[0057] As an alternative to viewing an image on screen 26, one can instead take advantage of the fact that the focal depth of the electron beam leaving imaging system 24 is generally quite deep (e.g., about 1 meter). As a result, various other types of analytical equipment can be used downstream of screen 26, such as: TEM camera 30. At the position of camera 30, the electron beam can form a still image (or Fourier transform diagram) that can be processed by controller / processor 20 and displayed on a display device (not shown), such as a flat panel display. When not needed, camera 30 can be retracted / recovered (as indicated diagrammatically by arrow 30') so that it is off axis B'. STEM camera 32. The output from camera 32 can be recorded as a function of the (X, Y) scanning position of beam B on sample S, constructing an image that is a "map" of the output from camera 32 as a function of X, Y. Camera 32 differs from the pixel matrix characteristically present in camera 30 in that it may comprise a single pixel, e.g., 20 mm in diameter. Furthermore, camera 32 generally has a higher acquisition rate (e.g., 106 images per second) than camera 30 (e.g., 102 images per second). Again, when not needed, camera 32 can be retracted / retracted (as indicated diagrammatically by arrow 32') so as to be off axis B' (however, such retraction would not be necessary, for example, in the case of a donut-shaped annular dark-field camera 32. In such a camera, a central hole allows the passage of the light beam when the camera is not in use).

[0058] As an alternative to imaging using the cameras 30 or 32, a spectroscopic device 34 can also be implemented, which can be, for example, an EELS module.

[0059] It should be noted that the order / location of items 30, 32, and 34 is not strict and many possible variations are possible. For example, spectroscopic device 34 may be integrated with imaging system 24.

[0060] In the embodiment shown, the microscope M further comprises a retractable X-ray Computed Tomography (CT) module, generally indicated by the reference numeral 40. In computed tomography (also called tomography), a source and a detector (opposing each other) are used to interrogate a sample along different lines of sight so as to obtain transmitted views of the sample from various viewpoints.

[0061] It should be noted that a controller (computer processor) 20 is connected to the various illustrated components via control lines (bus) 20'. This controller 20 may provide various functions such as synchronizing actions, providing set points, processing signals, performing calculations, and displaying messages / information on a display device (not depicted). Of course, the controller 20 (schematically depicted) may be located (partially) inside or outside the housing 2 and may have a unitary or composite structure, as desired.

[0062] Those skilled in the art will understand that the interior of the enclosure 2 need not be maintained at a strict vacuum. For example, in so-called "environmental TEM / STEM," a background atmosphere of a given gas is intentionally introduced / maintained within the enclosure 2. Those skilled in the art will also understand that in practice it may be advantageous to confine the volume of the enclosure 2 so that, if possible, the enclosure 2 essentially encloses the axis B', and the employed electron beam passes through but expands to take the form of a small diameter tube (e.g., about 1 cm in diameter) to house structures such as the source 4, sample holder H, screen 26, camera 30, camera 32, spectrometer 34, etc.

[0063] 2a and 2b show one embodiment of a specimen tip cradle 101 according to the present disclosure, which may be used in a charged particle microscope such as the transmission electron microscope shown in FIG. 1, but is equally applicable to SEM or FIB devices.

[0064] As shown in Figure 2a, the cradle includes a recess 103 in a first surface. The recess comprises a central opening / void 104.

[0065] In FIG. 2 b , the second surface of the cradle 101 is shown tilted towards the opening / void 104 .

[0066] In Figures 2a and 2b, the cradle is shown with two opposing curved edges and a substantially circular recess and opening / void, however, other configurations may be used depending on the circumstances.

[0067] 3a and 3b illustrate one embodiment of the sample tip T.

[0068] In FIG. 3a, the sample chip T is shown in a top (plan) view, with the cradle 101 shown within the bumper 102 and the second surface visible.

[0069] A bumper 102 surrounds the outer edge of the cradle 101 .

[0070] In the embodiment illustrated in Figure 3a, when the cradle and bumper are combined, the chip includes four openings / voids 105 positioned between the cradle 101 and the bumper.

[0071] In FIG. 3b, the specimen tip T is shown in front (elevation) view.

[0072] As shown, the cradle is positioned toward the proximal end of the specimen tip T, with the surface of the bumper 102 sloping toward the cradle.

[0073] FIG. 4 illustrates an embodiment in which a sample tip T is connected at its proximal end to a sample holder H, which is connectable to a stage A′ of a positioning device A as shown in FIG.

[0074] Two fixing elements 106 in the form of spring-based clamping members are shown in Figure 4. Four openings / voids 105 (as shown in Figure 3a) provide space for the spring portions of the clamping members.

[0075] A fixing element 106 is movably connected to the bumper 102, the fixing element (in the form of a spring-based clamping member) being movable between an open position (not shown) and a closed position (shown in FIG. 4).

[0076] In the open position, the fixing element (in the form of a spring-based clamping member) moves away from the recess 103, thereby allowing a sample grid to be placed within the recess 103. In the closed position, the fixing element (in the form of a spring-based clamping member) locks the sample grid within the recess 103.

[0077] As mentioned above, in the embodiment shown, the fixing element is in the form of a spring-based clamping member that is pivotable between an open position and a closed position. By providing a spring element, it is possible to bias the fixing element (in the form of a spring-based clamping member) towards the closed position to hold the sample grid firmly in place when placed inside the recess 103.

Claims

1. 1. A sample tip for releasably holding a sample, said sample tip comprising: a cradle comprising beryllium and with a recess for releasably receiving a sample; a bumper comprising aluminum.

2. The specimen tip of claim 2 , wherein the cradle comprises a first surface and a second surface, the first surface and the second surface being substantially parallel to one another.

3. 3. The sample tip of claim 1, wherein the bumper extends in the same plane as the cradle.

4. The tip according to any one of claims 1 to 3, wherein the tip comprises at least one fixing element for releasably holding the sample.

5. The chip according to any one of claims 1 to 4, wherein the recess is releasably configured to receive a sample grid.

6. The chip of claim 5 , wherein the specimen grid is for a charged particle microscope.

7. The tip of any one of claims 1 to 6, wherein the tip is releasably connected to a sample holder or to a sample stage.

8. The chip of any one of claims 1 to 7, wherein the cradle recess is substantially circular.

9. The chip of any one of claims 1 to 8, wherein the cradle recess comprises a substantially central void.

10. The chip of claim 9 , wherein the void is substantially circular.

11. The chip of any one of claims 1 to 10, wherein the cradle consists essentially of beryllium.

12. The chip of any one of claims 1 to 11, wherein the bumper consists essentially of aluminum.

13. 1. A charged particle microscope for inspecting a sample, comprising: an optical column including a charged particle source and an illuminator for directing a beam of charged particles emitted from said charged particle source onto a sample; a sample tip according to any one of claims 1 to 12 for holding a sample grid with the sample therein and positioned downstream of the illuminator; an EDX detector device for detecting X-ray radiation arising from said sample in response to the incidence of charged particles emitted by said charged particle source; a control unit for carrying out the operation of said charged particle microscope.

14. 1. A method for inspecting a specimen through a plurality of charged particle beams, the method comprising: - providing a charged particle beam; - providing a sample on a sample chip as claimed in claims 1 to 12, - directing the beam through the sample; - detecting the energy of the X-rays emitted from said sample.

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