Method for the in situ preparation of microscopic specimens

A method relates to the in situ preparation of a microscopic specimen is carried out using a particle beam device, which includes a particle beam column for producing a focused beam of charged particles, a specimen receptacle for receiving a specimen block, and a detector for detecting interaction products of the interaction between particle beam and specimen material. The method includes: providing a specimen block having an exposed structure that comprises a specimen region of interest; producing a bending edge in the exposed structure by the action of the particle beam such that at least some of the exposed structure is shaped in the direction of the incident particle beam; and moving the specimen receptacle, in which the specimen block is received, so that a specimen region, which is enclosed by the shaped structure, is observable and/or processable in the particle beam device.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit under 35 U.S.C. § 119 to German Application No. 10 2017 212 020.7, filed Jul. 13, 2017, the entire contents of which are hereby incorporated by reference.

FIELD

The disclosure relates to a method for the in situ preparation of specimens for an examination by electron microscopy, wherein the specimens are obtained from a specimen block. The electron microscopy specimen is shaped, and observed and/or processed, in a particle beam device by the action of a beam of charged particles.

BACKGROUND

Electron microscopy specimens (also referred to in short as microscopy specimens below) have dimensions that lie in the sub-millimeter range, i.e., in the range of a few micrometers (μm) or nanometers (nm). Usually, these specimens are examined in an electron microscope (scanning electron microscope or transmission electron microscope, TEM) or in an ion microscope or in other devices with a similar resolution.

Such specimens may have different configurations. An example of an often-used microscopic specimen is a TEM lamella, which is involved for transmission electron microscopy. TEM lamellas are so thin that, at least in portions, they are transmissive to electrons. Therefore, the electron-transparent specimen regions can be passed by electrons within the scope of the examination in the transmission electron microscope (TEM) such that transmitted electrons can be detected and used for image production purposes.

So that TEM lamellas contain the specimen region of interest (ROI), they are, in general, be prepared from the full specimen material, i.e., from a specimen block. The TEM lamella is severed and removed from the specimen block by way of a so-called lift out so that it is then examined in a different device, preferably a TEM.

In general, a distinction is made in the microscopic specimen preparation between ex situ methods and in situ methods, depending on the type of lift out.

In the case of an ex situ lift out, a specimen region of interest, which is still situated in the specimen block, is initially thinned using a focused ion beam (FIB) in an FIB device. That is to say, material is ablated with the ion beam until the specimen has the desired lamella thickness and said specimen is present as an electron-transparent lamella. Then, the ion beam is used to cut the side edges of the TEM lamella free such that the TEM lamella is largely exposed. In the next step, the entire specimen block, together with the TEM lamella, is removed from the FIB device and transferred into a light microscope. There, a glass tip is fastened to the TEM lamella with the aid of a micromanipulator. The TEM lamella can now be detached from the specimen block and transferred to a TEM grid or any other suitable specimen holder via the micromanipulator. The TEM grid with the TEM lamella is then transferred into the TEM for further examination.

In the case of the in situ lift out, the region of the future TEM lamella is initially freely prepared with the ion beam in broad brushes. The TEM lamella is released from the specimen block via a micromanipulator, which is attached to the FIB device, held in the specimen chamber of the FIB device and thinned to the desired lamella thickness by way of the ion beam. Finally, the TEM lamella is placed on a TEM grid or the like and fastened where desired, and it thus can be transferred from the FIB device into the TEM.

In the ex situ lift out, the specimen block is therefore situated outside of the FIB device when

the microscopic specimen is severed from the specimen block, whereas this occurs within the FIB device in the in situ methods. What is common to both methods is that special manipulation tools such as micromanipulators, micro grippers or needles are involved.
Some methods additionally involve apparatuses for introducing process gases such that substances can be deposited in a targeted manner, said substances allowing the prepared microscopic specimen to be fastened to a glass tip or a metal needle, for example. Moreover, the user should have a certain amount of experience of handling the tools and experimental skill in order to successfully prepare the specimens within a justifiable amount of time.

Therefore, in many applications in electron microscopy and ion microscopy, it would be advantageous to be able to release selected small structures or specimen regions in a contactless manner from the specimen block from which they are obtained in order to thus make said small structures or specimen regions accessible to the further examination or processing.

Various methods of TEM lamella preparation are known. Thus, different types of FIB lift out techniques (ex situ and in situ) have been described for the defect analysis of wafers (Giannuzzi et al., 2002; Giannuzzi & Stevie, 1999).

Additionally, improved methods for the in situ lift out of TEM specimens with the aid of a two-beam device (Langford & Rogers, 2007; Tomus & Ng, 2013) are known.

EP1998356 A2 describes a method for an in situ STEM specimen preparation via an SEM-FIB combination device, which makes do without a flip stage.

Moreover, a method for the three-dimensional nano fabrication of thermoplastic polymers via FIB has been described.

Langford et al. (2000) disclose a cantilever technique for the TEM lamella production, in which the specimen block is removed from the FIB device in order to sever the prepared cantilever from the specimen block by the application of force.

Moreover, methods have been described for shaping microscopically small structures with micro and nano tools (so-called “nano forging”).

SUMMARY

The disclosure provides methods with which microscopic specimens can be shaped in a contactless manner and can be made accessible to further examinations. Moreover, the disclosure relates to the transfer of microscopic specimens by way of contactless shaping.

In one general aspect, the disclosure provides a method for in situ preparation of a microscopic specimen, carried out with the aid of a particle beam device including: a particle beam column for producing a focused beam of charged particles; a specimen receptacle for receiving a specimen block; and a detector for detecting interaction products of the interaction between particle beam and specimen material. The method includes: a) providing a specimen block having a structure that is exposed and that includes a specimen region of interest (ROI); b) producing a bending edge in the exposed structure by the action of the particle beam such that at least some of the exposed structure is shaped in the direction of the incident particle beam; and c) moving the specimen receptacle, in which the specimen block is received, in such a way that a specimen region, which is enclosed by the shaped structure, is observable and/or processable in the particle beam device.

In another general aspect, the disclosure provides a method for transferring a microscopic specimen, carried out with the aid of a particle beam device including: a particle beam column for producing a focused beam of charged particles; a specimen receptacle for receiving a specimen block; a detector for detecting interaction products of the interaction between particle beam and specimen material; and a displaceable transfer apparatus for receiving the microscopic specimen. The method includes: a) providing a specimen block having a structure that is exposed and that includes the specimen to be prepared; b) positioning the transfer apparatus; c) producing a bending edge in the exposed structure by the action of the particle beam such that at least some of the exposed structure is shaped in the direction of the incident particle beam, wherein the shaped structure is moved into the vicinity of the transfer apparatus; d) fastening the structure to the transfer apparatus; and e) severing the structure from the specimen block.

The present disclosure further relates to a computer program product which prompts a particle-optical apparatus to carry out a method according to the disclosure.

Moreover, the disclosure provides microscopic bending objects that have a plurality of bending edges and that are obtainable from one of the disclosed methods.

In a general aspect, the disclosure provides a microscopic specimen having a plurality of bending edges, obtainable according to a method disclosed herein.

Sometimes, microscopic specimens are prepared from the full specimen material, i.e., from a specimen block. Using the method according to the disclosure, a selected specimen region can be exposed from the specimen block in the particle beam device—i.e., in situ—, with the specimen region remaining connected to the specimen block. This is brought about by virtue of the specimen region being embodied as a cantilever that is folded out of the plane of the surface of the specimen block in a contactless manner. In this context, contactless means that the specimen region to be shaped does not come into direct contact with a shaping tool and it is not connected indirectly to such a tool either (for example, by depositing material or by accumulations on account of electric charges or other forces, such as van der Waals' forces, for example).

As a result of the contactless shaping, the microscopic specimen is deformed plastically—i.e., permanently. The deformation is possibly caused by electric charges and/or thermal effects, which trigger internal tensions. The specimen region of interest, which is situated in or at the cantilever-shaped structure, becomes accessible to further examinations or the further processing in the particle beam device by the shaping. An advantage of this method is that there is no need for holding tools such as a micromanipulator or glass needle. Moreover, preparation and observation or processing can be carried out in the same particle-optical device, and so the transfer between different devices, which is used in the known methods, can be dispensed with.

The method according to the disclosure is carried out in a particle-optical apparatus. This can be an ion beam microscope or a multi beam microscope (i.e., a combination device that includes at least two particle beam devices). By way of example, the apparatus can be embodied as a two-beam microscope (i.e., a combination device including an ion beam microscope and an electron beam microscope) or as an electron beam microscope with a gas injection system. It is also conceivable for the method to be carried out using a combination device, which includes an ion beam microscope and a light microscope. The particle beam device also can include an x-ray apparatus.

Using the method according to the disclosure, it is possible, for example, to produce TEM lamellas. TEM lamellas are ultra-thin specimens that are suitable for the examination in the transmission electron microscope since the lamellas are transparent to electrons, at least at points. This means that the specimen material of the TEM lamella can be traversed by electrons of an electron beam produced in the TEM. As a rule, TEM lamellas substantially have the form of a flat cuboid, the length and width of which are usually several micrometers (μm). The thickness (lamella thickness) of the cuboid is usually less than one hundred nanometers (nm), and so the lamella is electron- transmissive.

However, other specimen forms can also be prepared using the method according to the disclosure, said specimen forms having the form of a cylinder, a pyramid or a cone, for example. Such specimen forms are usually used for x-ray tomography or electron tomography.

Moreover, using a special embodiment of the method according to the disclosure, it is possible to transfer a microscopic specimen from the specimen block onto a transfer apparatus. By way of example, the transfer apparatus can be embodied as a micromanipulator needle or as a specimen holder.

Further, an embodiment of the disclosed method renders it possible to prepare electron- transparent specimens in situ and analyze these using a STEM (scanning transmission electron microscopy) detector.

According to further embodiment, it is possible to examine and image particles that lie on the surface of a specimen block. To this end, the particles are embedded in an applied coating. Subsequently, the deposition layer is shaped such that the particles fixed therein are lifted out of the plane of the specimen surface and able to be analyzed in the particle beam device.

Moreover, microscopic bending objects can be designed by contactless shaping using the method according to the disclosure. This occurs by virtue of cantilever-shaped structures being shaped by the action of a particle beam. Here, it is possible for the microscopic specimen produced to have two or more bending edges. Moreover, this allows different, three-dimensional microscopic bending objects to be produced.

EXEMPLARY EMBODIMENTS

FIG. 1shows a flowchart of the method according to the disclosure, which is carried out in a particle beam device. A specimen block with an exposed structure is provided in step S1. To this end, the specimen block is advantageously held by a specimen receptacle in the specimen chamber of the particle beam device.

Various methods are conceivable for producing a specimen block with an exposed structure. After a region of interest (ROI) has initially been identified and its position in the specimen block has been determined, specimen material surrounding this region is removed. The material ablation can be carried out in many different ways, for example by virtue of so-called trenches being ablated using the ion beam (so-called milling) or by virtue of the material being ablated in a step-shaped manner. It is also conceivable to bring about the material ablation by electron-beam-induced etching. To this end, etching gas is guided into the vicinity of the specimen surface while the electron beam is directed onto the specimen site to be processed. Specimen material is removed by the interaction of etching gas and electron beam. The introduction of the etching gas and the irradiation with the electron beam is preferably performed simultaneously in order to obtain a higher etching rate and be able to process a specific specimen region in a targeted manner. Moreover, however, it is also conceivable to produce a suitable specimen block with an exposed structure by mechanical processing (by cutting with a microtome or ultra- microtome, for example), by laser processing or by other methods.

In any case, the region of interest (ROI) is exposed to such an extent that it is situated in or at a cantilever-shaped structure, which is referred to as an exposed structure. Thus, the exposed structure includes the specimen region which should be examined in more detail and which should be prepared as a microscopic specimen. The method steps described below are carried out using a specimen block that has been prepared in this way.

A bending edge is produced in step S2by the action of a beam of charged particles. By way of example, the particle beam can be a beam of focused ions. The ion beam is guided over the exposed structure such that specimen material is ablated by milling and a bending edge arises. Alternatively, it is also conceivable for the beam to be an electron beam and the bending edge to be produced by electron-beam-induced etching. The exposed structure is shaped along the bending edge as a result of notching the bending edge, and so the exposed structure is moved into another spatial position.

Usually, the bending edge arises by virtue of specimen material being ablated along a straight line via the particle beam. The bending edge is produced in the exposed region of the cantilever. As a result, the exposed structure is bent along the bending edge such that the structure is moved out of the original plane into a plane that is arranged at an angle with respect to the original plane. Only so much material is ablated when the bending edge is produced that the shaping occurs without, however, the exposed structure being severed from the specimen block.

The disclosure is based on the surprising discovery that the observed shaping behavior of the microscopic specimen can be used for specimen preparation and for contactless specimen transfer. The inventors have determined that the proposed method can be carried out with exposed structures whose cantilever has a cross-sectional thickness in the range from several ten nanometers to several micrometers. By way of example, it is conceivable for the method according to the disclosure to be carried out with a typical TEM lamella with an area of 20 μm×2 μm and a thickness of approximately 1 μm, wherein the cross-sectional thickness of the cantilever, in which the bending edge is produced, can be between 0.1 μm and 2 μm.

The exposed structure is shaped by producing the bending edge in the direction toward the incident particle beam. The user can stop the shaping process by virtue of stopping the action of the particle beam. However, the shaping process can also be continued again if the particle beam acts on the bending edge again. Then, the exposed structure is shaped further in the direction of the incident particle beam. In this way, the user can determine the extent of the shaping.

In step S3, the specimen receptacle, on which the specimen block is received, is moved. This is preferably carried out by rotating the specimen receptacle together with the specimen block about an axis that extends parallel to the specimen surface. As a result, the region of interest, which of course is situated in or at the shaped structure, can be examined further in the particle beam device without having to sever the exposed structure from the specimen block to this end. Likewise, the specimen block need not be removed from the particle beam device. Since the exposed structure has been moved out of the body of the specimen block, the specimen region of interest is now accessible from outside of the specimen block and observable and/or processable in the particle beam device.

Optionally, the method can be carried out with the additional step S4, in which a specimen region in the shaped structure is observed and/or processed with the aid of the particle beam device. This can occur in situ, i.e., without a transfer of the specimen from the particle beam microscope into another apparatus being involved. By way of example, regions of the shaped structure can be imaged with the aid of a detector, which can be included by the particle beam device, wherein the interaction products of the interaction between particle beam and specimen material are detected and an image is produced. Here, the detector can be embodied as a secondary electron detector, as a backscattered electron detector, as an EBSD (electron backscatter diffraction) detector, as a cathodoluminescence detector, as an x-ray detector or as any other suitable detector. Moreover, it is possible to process the shaped structure in situ, for example by irradiation with a particle beam, i.e., ablate material locally or areally or deposit material.

In a particularly advantageous embodiment, the form of the bending edge is stabilized by depositing material. To this end, material (e.g., a Pt-containing layer) is applied to the bending edge by an introduction of process gas and—where desired—an activation by electron and/or ion beam irradiation. As a result, the trench that arose when milling the bending edge is filled, while the two areas adjoining the bending edge are connected to one another.

FIG. 2Ashows cross-section of an exemplary specimen block26, which includes an exposed structure25. This is understood to be a structure in the form of a cantilever that only abuts, or is connected to, the specimen block at one side. It is particularly advantageous if the cantilever-shaped structure includes a specimen region of interest, i.e., that specimen region that should be examined in more detail.

In the present example, the cantilever has the form of a cuboid. This means that the exposed structure25has six boundary surfaces in this case, of which five are exposed, i.e., do not have an areal contact with the specimen block26. The cantilever is only connected to the material of the specimen block26at one boundary surface or along one cuboid edge.

It is also conceivable for the exposed structure to initially have the form of a bridge, which still abuts the specimen block at two boundary surfaces or two edges. By ion beam milling or etching a separating line extending predominantly transversely to the longitudinal direction of the bridge, it is possible to divide the bridge-shaped structure into two cantilevers, via which it is then possible to carry out the method according to the disclosure. It is also conceivable for the cut angle not to be arranged exactly transversely (90°) to the longitudinal direction of the exposed structure but instead assume a different angle between 0 and 90°.

Furthermore, it is possible for the exposed structure to be embodied as a conductor track of an electronic component. By way of example, the exposed structure can be embodied in such a way that it can subsequently serve as a capacitor or as a micro-switch.

However, the method is not restricted to cuboid, exposed structures. In principle, it is conceivable also to shape other structures, such as, e.g., cylindrical or conical structures, or any other form that is only connected to the specimen block at one edge. This is helpful, in particular, when producing three-dimensional objects by the method according to the disclosure. It is also conceivable for assembled forms to be produced using the described method: By way of example, the exposed structure can be embodied as a cuboid, connected to which there is a cylindrical specimen region that includes the point of interest.

The specimen block26illustrated inFIG. 2Ais held by a specimen receptacle (not illustrated), which is situated in the specimen chamber of a particle beam device. The particle beam device includes a particle-optical column21, which has an optical axis22.

During operation, charged particles are produced in the particle-optical column21, said particles being accelerated and steered onto the specimen block26as a focused particle beam23. In the process, the charged particles substantially move along the optical axis22. The particle-optical column21has an observation and processing plane24, which extends substantially perpendicular to the optical axis22. This is advantageous in that the particle beam is incident on the specimen surface at an angle γ of approximately 90°. However, it is also conceivable for the angle γ, at which the particles are incident on the specimen, to deviate from 90° and equal less than 90° and more than 0°, for example, preferably 80° or 70°. Advantageously, a first boundary surface of the exposed structure25lies in the observation and processing plane24, and so processing of the exposed structure25is made simpler.

In the method according to the disclosure, the focused particle beam23is now steered onto the first boundary surface of the exposed structure25in such a way that a bending edge28is produced. By way of example, this is implemented by virtue of the particle beam23being guided over the first boundary surface along a processing line280such that specimen material is ablated along this line280. As a result, a bending edge28arises and the exposed structure25is shaped in the direction of the incident particle beam23. This means that, after shaping, the first boundary surface of the structure25no longer lies in the observation and processing plane24but instead assumes an angle β in relation to the observation and processing plane24that deviates from zero.

The exposed structure is only shaped for as long as the particle beam acts on the bending edge. By deactivating or deflecting (so-called blanking) the particle beam, the shaping is also stopped. This renders it possible to halt the shaping process once the desired extent of shaping has been achieved. Thus, the user can predetermine the desired extent of the shaping of the exposed structure25and shape the exposed structure in a targeted manner by stopping the action of the particle beam and, where desired, allowing the particle beam to act again.

In other words: The user can determine the angle β that the shaped exposed structure27adopts in relation to the observation and processing plane24.

At most, the angle β can assume the value of the angle γ, at which the particle beam23used for the shaping is incident on the specimen surface. This means that the exposed structure can, at most, be shaped up to the incident particle beam. However, the angle β achievable overall can be increased by displacing the specimen block and/or tilting the specimen block (i.e., by moving the specimen receptacle) and repeated reshaping.

In principle, the specimen region of interest can extend in a plane parallel to the first boundary surface of the specimen block (areal section) or in a plane that extends perpendicular to the first boundary surface (cross section).

The example ofFIG. 2Ashows a specimen that was carved out as an areal section. For a further examination or further processing, the particle beam should be incident on the surface of the shaped structure27in approximately perpendicular fashion; i.e., the particle beam29should extend in the plane of the drawing as illustrated inFIG. 2B. To this end, the specimen receptacle with the specimen block can be displaced and/or rotated appropriately.

FIGS. 3A-3Cillustrate how a cross section specimen is prepared. This is of particular interest to specimens that should be examined via STEM or TEM.

The cross section specimen allows lifting a specimen detail32of interest, which is buried in the interior of the specimen block31, out of the volume of the specimen block31and making said specimen detail accessible to a further examination in the particle beam device. Here, the specimen detail32is initially identified in the interior of the specimen block31and an exposed structure33which includes the specimen detail32is prepared. A focused particle beam34is used to produce a bending edge35in the boundary surface36which lies in the focal plane of the particle beam34, the specimen detail32rotating about said bending edge in the direction of the incident particle beam34during the shaping.

In the process, the exposed structure33is moved beyond the plane of the boundary surface36of the specimen block such that the specimen detail32is likewise moved beyond the plane of the boundary surface36and it is now possible to examine and/or process said specimen detail with the particle beam device. In the example ofFIGS. 3A-3C, the areal extent of the specimen detail32of interest is mainly in a plane that extends perpendicular to the first boundary surface36, i.e. perpendicular to the specimen surface. This means that the region of interest32represents a cross section of the specimen block, as is often the case in TEM lamellas, too.

In a particularly advantageous embodiment, the exposed structure33includes the specimen region which should be prepared as a TEM lamella and which is therefore embodied as a very flat cuboid. It is advantageous, during the subsequent examination or processing, if the particle beam is incident perpendicular onto the surface of the specimen detail32, i.e., if the particle beam extends perpendicular to the plane of the drawing. To this end, the specimen receptacle with the specimen block can be displaced and/or rotated appropriately.

FIGS. 3D and 3Eelucidate that the disclosed method also can be used to prepare tomography specimens for x-ray or electron tomography.

Reference signs31,33,35and36in this case have the same meaning as described inFIGS. 3A-3C. In order to prepare microscopic tomography specimens, the specimen detail of interest is prepared in such a way that it include a cylindrical structure37(FIG. 3D), which is connected to the cantilever-shaped exposed structure33. Alternatively, the specimen detail of interest can also include a conical structure38(FIG. 3E). In any case, the exposed structure33is shaped by the described method such that the region to be examined by tomography is flapped out of the interior of the specimen block31and consequently accessible from outside of the specimen block31. As a result, the tomography specimen is prepared in such a way that it can be processed and/or examined further in situ or can be transferred into another apparatus. What is advantageous in the case of preparing tomography specimens using the method according to the disclosure is that a cylindrical or conical structure (which is also referred to as a “pillar”) is obtained, which can be penetrated from different sides for the purposes of a further examination without holding tools or a transfer into another apparatus being involved.

It is also conceivable to produce an adjustable capacitor using the method according to the disclosure. To this end, a specimen block including two cantilevers, which extend in parallel and which are embodied as conductor tracks, is provided. Said cantilevers each have a plate-shaped projection, said projections being able to serve as capacitor plates. The capacitance of the capacitor is determined by the distance of the two capacitor plates from one another and by the size of the effective area of the capacitive plates. The effective area is understood to be that area of a capacitor plate that interacts with the associated, oppositely charged capacitor plate (counter plate) in order to obtain the capacitor effect. By shaping at least one cantilever with a capacitor plate, the position of the capacitor plate is modified in relation to the counter plate, and so the size of the effective area is modified. In this way, the capacitance of the capacitor is modifiable, and so the capacitor effect is adjustable. Alternatively, the capacitor can also have such an embodiment that the first capacitor plate is embodied as a cantilever while the second capacitor plate is formed by a wall surface of the specimen block.

In another embodiment, the capacitor is embodied as a cylindrical capacitor, i.e., in the form of two electrically conductive, concentric cylinder jackets. Here, the inner cylinder jacket is embodied as an exposed conductor track and connected to a cantilever. By producing a bending edge in the cantilever, it is possible to modify the position of the inner cylinder jacket, and so the length of the capacitor—and hence its capacitance—is modifiable. Consequently, this cylinder capacitor is also adjustable.

An electric micro-switch can be produced and operated with another embodiment of the method. Here, switching is brought about by a bending edge being introduced into a cantilever-shaped structure according to the disclosure in order to shape the structure such that the current flow via the switch is interrupted.

The entire exposed structure25,33or only part of the exposed structure25,33is shaped, depending on where the bending edge28,35is produced along the longitudinal axis of the cantilever. Advantageously, the bending edge28,35should extend near the support of the cantilever in order to shape the exposed structure25,33as a whole. Moreover, it was found to be advantageous if the bending edge28,35extends more or less perpendicular to the longitudinal axis of the exposed structure25,33. Preferably, the position and the profile of the bending edge are selected in such a way that the exposed structure25,33does not contact the specimen block26,31during shaping.

FIGS. 4A-4Dshows, in an exemplary manner, another special configuration of the method according to the disclosure, in which the intention is to prepare a specimen block41which has particles48that should be examined in more detail situated on the surface thereof. By way of example, specimen block41includes silicon.

A coating42, which includes platinum, for example, is applied onto the specimen block41via ion beam deposition (FIG. 4A) This coating42covers a layer of the silicon- containing specimen material situated therebelow and acts as a protective layer for the covered specimen region. The particles48lying on the specimen surface are embedded into the coating material. However, producing the coating is not restricted to depositing a platinum-containing layer. Rather, the coating can be effected by depositing other metals (e.g., tungsten) or by depositing carbon or other suitable substances. As an alternative to ion beam deposition, use can also be made of gas-assisted electron beam deposition.

The coating42is now prepared to be free (FIG. 4B) by virtue of being undercut in etching. This can be brought about via ion beam etching using xenon difluoride (XeF2). Since XeF2is able to etch the specimen material even without the influence of the ion beam, the silicon under the platinum deposition is removed; i.e., the coating42remains freestanding and forms a bridge-like structure over the ablated region43.

Now, the bridge-like coating42is cut with the aid of the ion beam (FIG. 4C). As shown in this example, this may be effected more or less centrally, and so two cantilevers of approximately the same size arise as exposed structures44by way of the severing cut45.

Then, the coating42is processed along a processing line by the particle beam such that small amounts of material are ablated and a bending edge47arises, at which the structure44is shaped (FIG. 4D). Therefore, the position of the processing line (and hence that of the bending edge47) can be selected as desired within the exposed region. By way of example, a gallium ion beam with an acceleration voltage of 30 kV and a beam current of 50 pA can be used to produce the bending edge47.

As a consequence of shaping, the exposed coating42folds in the direction of the incident ion beam, and so the deposition layer42with the particles48contained therein rotates about the bending edge47and said deposition layer is lifted out of the processing plane, and hence out of the plane of the specimen surface.

Here, too, shaping is effected slowly and it can be interrupted by deactivating or pivoting away (so-called “blanking”) the ion beam. Shaping can be continued at a later time. As a result, the angle which the shaped structure adopts in relation to the observation plane of the particle beam device can be determined by the user. The maximum angle is restricted by the profile of the optical axis of the particle beam device; i.e., the deposition can be shaped at most so far that the structure reaches the trajectory of the incident ion beam.

The described shaping is repeated at the second cantilever, and so the specimen form shown inFIG. 4darises.

FIG. 5shows the electron-microscopic image of a specimen block51that was prepared using the method according to the disclosure. The specimen block51contains silicon and was etched using XeF2in order to produce two exposed, gold-containing structures52. The exposed structures52were shaped by producing bending edges53.

FIGS. 6A-6Cschematically shows the production of a microscopic, three-dimensional bending object. Initially, a specimen block61, which may include silicon, for example, is provided, an initial structure62having been deposited thereon. By way of example, this can be brought about by gas-induced ion beam deposition (e.g., of platinum-containing layers) or gas-assisted electron beam deposition.

Then, the initial structure62is undercut in etching, for example with XeF2, in order to expose the initial structure62. XeF2is able to etch silicon even without the influence of activating radiation, and so material can be ablated even at positions that cannot be irradiated directly by the particle beam. Four exposed cantilever structures63arise in this way in the present example. A bending edge64is produced at each of the exposed structures63by the action of the particle beam, and so the structures63are shaped. Hence, a three-dimensional object65, which has a plurality of bending edges64, arises.

FIGS. 7A and 7Bschematically show a further embodiment of the method according to the disclosure. In the specimen block71there is an exposed structure72, which has a first bending edge73. The structure72has been shaped along the first bending edge73using the method according to the disclosure. The shaped structure can now be shaped another time. A second bending edge74is produced by the action of the particle beam, and so the shaped structure72now has two bending edges73,74.

FIGS. 8A and 8Billustrate a further, particularly advantageous configuration of the method in which a microscopic specimen is prepared in situ by the method according to the disclosure and the shaped exposed structure is examined using a STEM detector. A STEM (Scanning Transmission Electronic Microscopy) detector detects electrons that have passed through a specimen that is electron transparent at least at points, and it is usually attached to a scanning electron microscope or an SEM-FIB combination device.

It is particularly advantageous if this embodiment of the method is carried out using a two-beam device which includes a STEM detector88. Such a two-beam device includes an electron beam column81and an ion beam column83. Both columns81,83each have an optical axis82,84, said axes adopting an angle α in relation to one another since the columns are arranged inclined with respect to one another. By way of example, the absolute value of the angle α can be 54°. However, it is also conceivable for the magnitude of the angle α to adopt a value in the range between 0° and 90° or between 10° and 90°. It can be particularly advantageous if the angle α adopts a value in the range from 40° to 80° or in the range from 45° to 70° or in the range from 50° to 60°, for example 52° or 55°.

A specimen block85with an exposed structure is received on the specimen receptacle86, which is arranged at a specimen stage89. The specimen receptacle86has a displaceable and rotatable (tiltable) embodiment. The axis of rotation of the specimen receptacle86extends perpendicular to a plane spanned by the optical axis82of the electron beam column and the optical axis84of the ion beam column. That is to say that the axis of rotation of the specimen receptacle86extends perpendicular to the plane of the drawing in the example ofFIGS. 8A and 8B. Usually, the axis of rotation is also referred to as a tilt axis of the specimen receptacle86. By way of a rotation about this tilt axis, the specimen receptacle86can adopt different angles in relation to the optical axes82,84. Moreover, it can be advantageous if the specimen receptacle86is arranged in rotational fashion in relation to the specimen stage860and consequently able to adopt different angles in relation to the base of the specimen stage860.

Initially, the specimen receptacle is rotated in such a way that a first boundary surface89of the exposed structure extends substantially perpendicular to the optical axis84of the ion beam column83. This means that the first boundary surface89is arranged in the focal plane of the ion beam column83. This arrangement is advantageous in that the specimen block85can be processed by the ion beam and, at the same time, observed with the aid of the electron beam and a detector for detecting products of the interaction between electrons and specimen material.

When carrying out an observation using the STEM detector, it is advantageous if the specimen has a lamella-like form. A lamella is understood to mean a flat cuboid, the length and width extent of which is usually only a few micrometers (μm). The thickness (lamella thickness) of the cuboid should be selected to be such that the lamella is transmissive for electrons, and so the thickness is usually less than one hundred nanometers (nm).

The lamella is prepared in such a way that it is freed at the two sides, at the one end side and at the sides facing the specimen block. That is to say, the lamella (which represents the exposed structure) is only still connected to the specimen block at the second end side.

Now, a bending edge is produced in the exposed structure using the ion beam. Advantageously, the bending edge is produced in the, or at the, second end face that is still connected to the specimen block by virtue of specimen material being removed along a line. This leads to the exposed structure being shaped and bent out of the focal plane of the ion beam in the direction toward the ion beam. Should the region of interest of the lamella not be electron transparent yet or not be sufficiently electron transparent, this region can now be thinned with the ion beam until the region is sufficiently thin.

Then, the specimen receptacle86with the specimen block85is rotated and—should this be desired—modified in terms of its spatial position such that the shaped exposed structure87is positioned perpendicular to the optical axis82of the electron beam column81.

The specimen region of interest in the shaped structure87is now penetrated by electrons from the electron beam column81. In relation to the propagation direction of the electrons, the STEM detector88is arranged downstream of the specimen, and so the interaction products that arose when the specimen was penetrated can be detected by the STEM detector88. Advantageously, the STEM detector88is configured in such a way that it can be inserted into the specimen chamber for use and can be retracted therefrom again after use.

Advantageously, the various embodiments of the method according to the disclosure can be carried out with a two-beam device (FIB-SEM combination device) with the gas injection system, which is illustrated inFIG. 9. The two-beam device91includes two particle beam columns, namely an electron beam column93for producing an electron beam and an ion beam column108for producing an ion beam. Both particle beams are directed to the processing location on the specimen103, which advantageously is situated at the coincidence point of both particle beams. The specimen103is received in a specimen receptacle104and situated in the specimen chamber92of the two-beam device, in which vacuum conditions are prevalent.

Advantageously, the specimen receptacle104is embodied as a five-axis specimen stage. This means that the specimen receptacle104can be displaced in the x-, y- and z-direction—i.e., in three mutually perpendicular spatial directions—and can be rotated about a tilt axis and an axis of rotation. The rotation about the tilt axis, which extends perpendicular to a plane spanned by the optical axes96,107(i.e., perpendicular to the plane of the drawing), renders it possible to allow the surface of the specimen, which is intended to be irradiated by charged particles, to adopt different adjustable angles in relation to the optical axes96,107.

During operation, primary electrons are produced in the electron source94, said primary electrons being accelerated along the optical axis96of the electron beam column93, focused by the lens-element systems95,97and trimmed by at least one aperture stop98. Moreover, the electron beam column93includes a deflection system99, via which the primary electron beam can be guided over the specimen103in a raster-type manner. Furthermore, the FIB-SEM combination device91includes at least one detector100for detecting interaction products of the interaction between particle beam and specimen103.

Moreover, the two-beam device91includes an ion beam column108with an ion source109, a deflection system106and a focusing lens element105. The ions produced in the ion source109are accelerated along the optical axis107of the ion beam column108and focused such that the ions are incident on the specimen103in focus and can be used to ablate material from the specimen103and/or image the specimen.

It is advantageous if the particle beam device moreover has a gas injection system (GIS)102. The latter usually includes a reservoir for a process gas which can be supplied in a controlled fashion to the specimen103via a line that ends near the processing location. The process gas can be embodied as a precursor gas. The precursor gas is initially activated by the ion beam or the electron beam and thus converted into a reactive form that is able to ablate specimen material or deposit material at the specimen. By way of example, a precursor gas of xenon difluoride (XeF2) can be supplied, which is converted into the reactive xenon difluoride by activation such that the specimen material is etched. The processing progress of the specimen can be simultaneously or successively observed with the aid of the electron beam column93and a connected detector100.

Moreover, the particle beam device91includes an evaluation and control unit101. The evaluation and control unit101can carry out a sequence of control commands, which are included in a computer program product. By carrying out the control commands, the particle beam device is prompted to carry out the method according to the disclosure.

In a special embodiment, which is illustrated inFIGS. 10A-D, the method can be used for the sparing transfer of a prepared specimen onto a manipulator needle1001or a specimen carrier. To this end, the particle beam device includes a displaceable transfer apparatus, which advantageously includes a micromanipulator, which has a manipulator needle1001or a similar tool for receiving the specimen. The exposed, i.e., cantilever- shaped, specimen1003is shaped as described above by the action of the particle beam1002(FIG. 10A). In the process, the exposed structure and, therewith, the specimen region of interest1005move in the direction of the manipulator needle1001until the exposed structure contacts the manipulator needle1001. This is advantageous in that the user notices when the specimen material in fact abuts the manipulator needle1001, specifically when the shaping movement is stopped on account of the resistance of the micromanipulator needle1001(FIG. 10B). The force exerted on the specimen material in the process is very low, and so there is no damage. By contrast, specimens are often damaged in conventional methods by the movement of the manipulator needle. Subsequently, the shaped structure is fastened to the manipulator needle1001(FIG. 10C). By way of example, this can be effected by a gas-assisted deposition of platinum-containing layers with the ion or electron beam (FIG. 10C). To this end, a precursor substance is applied to the manipulator needle1002and the specimen material1003, for example with the aid of a hollow needle1006, and converted into material that is deposited with the aid of the particle beam1002. Then, the exposed structure103is severed from the specimen block1004(FIG. 10D) such that the specimen region of interest1005can now be moved into any position by displacing the manipulator needle1001.

By way of example, the specimen transferred in this manner can be a TEM lamella, a microscopic tomography specimen or the conductor track of an electronic component. Advantageously, the employed particle beam device includes an ion beam column for producing a focused ion beam. It is particularly advantageous if the particle beam device is embodied as a multi-beam device, which includes an ion column for producing a focused ion beam and an electron column for producing a focused electron beam. It is also conceivable for the particle beam device to include a gas injection system for introducing etching gas such that the structure can be processed via gas-assisted etching or that coatings can be deposited.

It is also conceivable for a specimen region of interest to be transferred onto a specimen carrier, for example a glass tip or a micromanipulator needle, with the aid of the method according to the disclosure. To this end, a specimen carrier is introduced into the specimen chamber via a micromanipulator and held above the structure prepared to be free, which includes the specimen region of interest. By shaping the exposed structure according to the disclosure, the structure is moved in the direction of the specimen carrier until the structure abuts the specimen carrier and fastened to the specimen carrier by way of a gas-assisted deposition of platinum-containing layers, for example. Then, the specimen carrier can be brought into another position together with the specimen region of interest, or it can be transferred into another apparatus. It can be particularly advantageous if the specimen carrier has a cutout and the exposed structure is shaped in such a way that the region of interest is positioned in the cutout.

The methods described for transferring the specimen are advantageous in that the user can notice with some certainty when the specimen abuts on the micromanipulator needle or the specimen carrier, specifically when the resistance of the needle or of the specimen carrier stops the shaping movement. Moreover, only small forces act on the specimen such that the risk of damaging the specimen is minimized, and therefore this method is suitable for very sensitive specimens, too.

LIST OF REFERENCE SIGNS

S1Step: Providing a specimen block

S2Step: Producing a bending edge

S3Step: Moving the specimen receptacle

S4: Step: Observing and/or processing the shaped structure

24Observation and processing plane

27Shaped exposed structure

29Particle beam for the further examination

32Specimen detail of interest

46Shaped exposed structure

72Shaped exposed structure

81Electron beam column

82Optical axis of the electron beam column

83Ion beam column

84Optical axis of the ion beam column

87Shaped exposed structure

89First boundary surface

91Particle beam device

93Electron beam column

95First condenser lens element system

96Optical axis of the electron beam column

97Second condenser lens element system

101Control and deflection unit

102Gas injection system

105Focusing lens element

107Optical axis of the ion beam column

108Ion beam column

1005Specimen region of interest (ROI)