Scanning electron microscope

Abstract

A scanning electron microscope (1) comprising a sliding vacuum sealing device (20) between an electron optical imaging system (2) and a sample carrier (10), the sliding vacuum sealing device (20) having a first plate (22) which has a first aperture (24) associated with the electron optical imaging system and bears against a second plate (26) which has a second aperture (28) associated with the sample carrier. The first plate and / or the second plate comprises a groove (40) surrounding the first aperture and / or the second aperture. The scanning electron microscope may comprise a detector (8) movable relative to the electron beam. The scanning electron microscope may comprise a motion control unit for moving the sample carrier along a collision-free path.

Description

[0001] This application is a divisional application, and the invention name of its parent application is "Scanning Electron Microscope", the application date is March 3, 2017, and the application number is 201780027480.2. Field of the Invention

[0002] The present invention relates to the field of scanning electron microscopes. Background Art

[0003] Scanning electron microscopes are known per se. A scanning electron microscope includes an electro-optical imaging system. The electro-optical imaging system may include an electron beam source and an electron detector. The electron beam source provides an electron beam focused onto a sample. Impact of the electron beam causes secondary electrons to be emitted from the surface of the sample. And some electrons from the electron beam are scattered in the forward direction and backscattered. The electron detector detects secondary electrons, scattered electrons, and / or backscattered electrons and generates a signal representative of the amount of electrons detected. The electron beam is moved relative to the sample in order to scan the surface of the sample with the electron beam. Variations in the electron detector signal at each azimuth of the electron beam on the sample provide image information of the sample. Summary of the Invention

[0004] The present invention relates to a scanning electron microscope.

[0005] It is an object of the present invention to provide an improved scanning electron microscope. It is also an object of the present invention to provide at least a useful alternative to known scanning electron microscopes.

[0006] According to a first aspect of the present invention, there is provided a scanning electron microscope including an electro-optical imaging system and a sample carrier, wherein the sample carrier is movable between a loading position for loading a sample and an imaging position for imaging the sample. The scanning electron microscope includes a sliding vacuum seal disposed between the electro-optical imaging system and the sample carrier. The sliding vacuum seal includes a first plate having a first aperture associated with the electro-optical imaging system and bearing against a second plate having a second aperture associated with the sample carrier. The first plate and the second plate are slidably movable relative to each other. The first aperture and the second aperture overlap in the imaging position. The first aperture and the second aperture do not overlap in the loading position. The first plate and / or the second plate includes a groove surrounding the first aperture and / or the second aperture, wherein the groove is arranged for communication with a vacuum system.

[0007] It should be noted that a scanning electron microscope with a sliding vacuum sealing device is known from US2011 / 133083A1. The sliding vacuum sealing device has a first plate which has a first aperture associated with the electron optical imaging system and bears against a second plate which has a second aperture associated with the sample carrier. The first plate and the second plate are slidably movable relative to each other. However, in the sliding vacuum sealing device of US2011 / 133083A1, the first plate and / or the second plate do not include a groove surrounding the first aperture and / or the second aperture, where the groove is arranged to communicate with the vacuum system.

[0008] The first plate and / or the second plate including a groove surrounding the first aperture and / or the second aperture provides the advantage that a vacuum can be applied to the groove, where the groove is arranged to communicate with the vacuum system. Thus, a suction force is effectively provided between the first plate and the second plate. The suction force allows for a firm and / or mechanically rigid abutment of the first plate and the second plate. Especially when the sample carrier is rigidly connected to the second plate and the electron optical imaging system is rigidly connected to the first plate, the mechanically rigid abutment allows for a rigid positioning of the sample relative to the electron optical imaging system. The rigid positioning of the sample allows for high image quality.

[0009] Optionally, the vacuum system is arranged to keep the electron optical imaging system and the sample carrier at a first vacuum level during imaging. The first vacuum level is preferably selected such that it allows the electron beam of the electron optical imaging system to irradiate the sample, as is known in the art.

[0010] Optionally, the vacuum system is arranged to keep the groove at a second vacuum level different from the first vacuum level. Preferably, the second vacuum level is between the first vacuum level and the ambient pressure. Thus, the second vacuum level helps to maintain a good vacuum seal between the first plate and the second plate. Furthermore, keeping the groove at a second vacuum level between the first vacuum level and the ambient pressure improves (e.g., allows for a reduction of) the first vacuum level.

[0011] Optionally, the recess is arranged to surround both the first aperture and the second aperture in both the loading position and the imaging position. This provides the advantage that when moving the sample carrier from the loading position to the imaging position, the recess is not exposed to either the first aperture or the second aperture. Thus, contamination of the recess can be avoided as it is not exposed. Additionally, it may be possible to maintain the vacuum level inside the recess while moving the sample carrier from the loading position to the imaging position. A recess that surrounds the second aperture in the loading position and / or at least a position that is not the imaging position also provides the advantage that the recess can be used as a pre-pump stage for the sample carrier. Applying a vacuum to the recess allows the sample carrier to be pumped down from ambient pressure to (near) the second vacuum level. It should be noted that exposing the imaging system directly to the sample carrier at atmospheric pressure would damage the imaging system, while exposing the recess to the sample carrier at atmospheric pressure would not. After the sample carrier has been pre-pumped through the recess, the imaging system will not be damaged while moving to the imaging area.

[0012] According to a second aspect of the invention, there is provided a scanning electron microscope comprising an electron optical imaging system and a sample carrier, the electron optical imaging system comprising an electron beam source and an electron detector, the sample carrier being located between the electron beam source and the electron detector. The sample carrier is movable relative to the electron beam for moving the sample. The sample carrier may be movable, for example, in a plane orthogonal to the electron beam. The sample carrier may also be arranged such that the sample carried by the sample carrier is movable in a direction parallel to the electron beam. The electron detector is movable relative to the electron beam. The electron detector may be movable in a direction not parallel to the electron beam (e.g., orthogonal to the electron beam).

[0013] The electron detector being movable relative to the electron beam provides the advantage of making the scanning electron microscope more flexible in the mode of detecting secondary electrons and / or (backward) scattered electrons.

[0014] Optionally, the electron detector is arranged to move synchronously with the sample (e.g., with the sample carrier). The electron detector may be arranged to move in the same direction as the sample carrier, e.g., move simultaneously with the sample carrier. The electron detector may be arranged to move the same distance as the sample carrier moves, e.g., move simultaneously with the sample carrier. This provides the advantage that when moving the sample carrier, in order to cause the electron beam to strike different points on the sample, the electron detector also moves. The electron detector may be fixedly connected to the movable sample carrier.

[0015] Optionally, the scanning electron microscope includes a magnetic lens between the sample and the electron detector. Optionally, the scanning electron microscope includes a magnetic lens between the sample carrier and the electron detector. The magnetic lens can be, for example, electromagnetically driven and / or can include permanent magnets. The magnetic lens can be movable relative to the electron beam. The magnetic lens can be movable in a direction not parallel to the electron beam (e.g., orthogonal to the electron beam).

[0016] Optionally, the magnetic lens is arranged to move synchronously with the sample (e.g., with the sample carrier). The magnetic lens can be arranged to move in the same direction as the sample carrier, e.g., move simultaneously with the sample carrier. The magnetic lens can be arranged to move the same distance as the sample carrier, e.g., move simultaneously with the sample carrier. This provides the advantage that when the sample carrier is moved, in order to make the electron beam strike different points on the sample, the magnetic lens also moves. The magnetic lens can be fixedly connected to the movable sample carrier.

[0017] Optionally, the electron detector is positioned in the focal plane of the magnetic lens. Optionally, the electron detector is positioned at the focus of the magnetic lens. Thus, when both the magnetic lens and the electron detector move synchronously with the sample, the electron beam traveling through the sample is deflected by the magnetic lens towards the electron detector. It should be noted that this allows for a simple construction, e.g., the magnetic lens and the electron detector are rigidly connected to the sample carrier, where the position of the electron detector relative to the sample is clear. In the case where the sample is movable relative to the electron detector (which is stationary relative to the electron beam striking the sample), as in prior art scanning electron microscopes, it is more difficult to maintain the mechanical stability and accuracy of the position of the inspected portion in the sample relative to the electron detector.

[0018] Optionally, the bright field region of the electron detector is positioned in the focal plane of the magnetic lens. Optionally, the bright field region of the electron detector is positioned at the focus of the magnetic lens. This provides the advantage that the primary electrons of the electron beam not disturbed by the sample are deflected into the bright field region of the electron detector. Then, the scattered electrons can be deflected to the edge of the electron detector surrounding the bright field region.

[0019] According to a third aspect of the present invention, there is provided a scanning electron microscope including a vacuum chamber and a sample carrier. The vacuum chamber includes internal structures such as an electron optical system, and the sample carrier is for carrying a sample and is movable within the vacuum chamber. The scanning electron microscope includes a motion control unit that includes an input unit arranged to receive user commands related to the movement of the sample carrier. The motion control unit includes a memory that stores a three-dimensional model of the internal structure of the vacuum chamber. The three-dimensional model of the internal structure of the vacuum chamber may include a three-dimensional model of the geometry of the internal structure of the vacuum chamber. The memory stores a three-dimensional model of the sample carrier. The three-dimensional model of the sample carrier may include a three-dimensional model of the geometry of the sample carrier. The motion control unit is arranged to move the sample carrier based on the received user commands and the three-dimensional models of the internal structure and the sample carrier while avoiding collisions between the sample carrier and the internal structure.

[0020] Optionally, the memory further stores a three-dimensional model of the geometry of the sample carried on the sample carrier. The three-dimensional model of the sample may be a three-dimensional model of the geometry of the sample. Then, the motion control unit may be arranged to further move the sample carrier based on the three-dimensional model of the sample while avoiding collisions between the sample, the sample carrier, and the internal structure.

[0021] Optionally, the motion control unit is arranged to determine a collision-free path from the current orientation of the sample carrier to the target orientation of the sample carrier. Sample-based planning algorithms such as probabilistic roadmap (PRM), rapidly-exploring random tree (RRT), or rapidly-exploring dense tree may be used to calculate the collision-free path. However, other algorithms may be used. Optionally, the collision-free path may be smoothed, for example, to reduce vibrations.

[0022] Optionally, the motion control unit is arranged to calculate the minimum distance between, on the one hand, the three-dimensional model of the sample carrier and optionally the sample and, on the other hand, the three-dimensional model of the internal structure. The calculated minimum distance may be used to determine the collision-free path.

[0023] Instead of avoiding collisions between the sample carrier and the internal structure, or in addition thereto, the motion control unit may be arranged to move the sample carrier based on the received user command and a three-dimensional model of the internal structure and the sample carrier and optionally the sample, while maintaining a distance between the sample carrier and the internal structure that is greater than or equal to a predetermined minimum distance. This allows for maintaining a predetermined safety distance. The predetermined minimum distance may have a special purpose when the internal structure is at a different voltage than the sample carrier (e.g., at a high (positive or negative) voltage). For example, the calculated minimum distance may be used to determine a path for maintaining a distance from the internal structure that is at least the predetermined minimum distance when at a different voltage than the sample carrier (e.g., at a high (positive or negative) voltage). Thus, discharges can be avoided.

[0024] Optionally, the motion control unit takes into account a first predetermined minimum distance and a different second predetermined minimum distance. The first minimum distance is maintained with respect to a first type of internal structure, and the second predetermined minimum distance is maintained with respect to a second type of internal structure. The first type of internal structure may be, for example, at a different voltage than the sample carrier (or differs by more than a threshold voltage), while the second type of internal structure is at substantially the same voltage as the sample carrier. Then, the first predetermined minimum distance may be greater than the second predetermined minimum distance.

[0025] Optionally, the motion control unit is arranged to simulate the execution of a user command before executing the user command, wherein the motion control unit is arranged to ignore the user command if the simulation indicates a collision between the sample carrier and / or the sample and the internal structure. Thus, any user command that would result in a collision can be ignored to avoid a collision. It will be appreciated that the motion control unit may be arranged to generate a message for the user that the user command will not be executed. The message may be displayed, for example, on a display device of a scanning electron microscope. Optionally, the motion control unit may determine an alternative route to the route according to the user command that would result in positioning the sample carrier and the sample at a final position according to the user command, the alternative route being collision-free. The motion control unit may be arranged to suggest the alternative route to the user, for example, by displaying a message on the display device. The motion control unit may also be arranged to automatically replace the route according to the user command with the alternative route.

[0026] Optionally, the input unit is arranged to receive data representing the geometry of the sample. For example, it may be possible that the input unit is arranged to receive the measurement results of the sample geometry. The motion control unit may be arranged to determine a three-dimensional model of the sample based on the data representing the geometry of the sample. The scanning electron microscope may include one or more templates for determining the approximate geometry of the sample. The templates may, for example, have cavities with gradually increasing sizes. The template with the smallest cavity mounted on the sample may be understood to represent the geometry of the sample. The cavities may be, for example, cylindrical or hemispherical, although other shapes may be conceivable.

[0027] Optionally, the scanning electron microscope includes an optical camera and a geometry determination unit arranged to determine the geometry of the sample based on at least one image of the sample provided by the optical camera. The optical camera may be arranged to provide a top-plane image of the sample. The top-plane image may be used to determine the perimeter of the sample. The geometry determination unit may be arranged to determine the contour of the sample and identify the pixels that are different in a first image and a second image by obtaining the first image and the second image, wherein in the second image, the sample is rotated by a first angle relative to its position in the first image. The different pixels represent the perimeter of the sample. Alternatively or additionally, the optical camera is arranged to provide a side-view image of the sample. The geometry determination unit may be arranged to determine a three-dimensional model of the sample based on two or more two-dimensional images of the sample. Optionally, the sample carrier includes one or more reference features, such as markers, that appear in the two-dimensional images for the three-dimensional reconstruction of the sample model.

[0028] The present invention also relates to a method for loading a sample into the vacuum chamber of a scanning electron microscope. The method includes providing a sample carrier that is movable between a loading position for loading the sample and an imaging position for imaging the sample. The scanning electron microscope includes a sliding vacuum seal device between the electron optical imaging system and the sample carrier. The sliding vacuum seal device includes a first plate having a first aperture associated with the electron optical imaging system and resting on a second plate having a second aperture associated with the sample carrier. The first plate and the second plate are slidably movable relative to each other. The first aperture and the second aperture overlap in the imaging position. The first aperture and the second aperture do not overlap in the loading position. The first plate and / or the second plate includes a groove surrounding the first and / or the second aperture. The groove is arranged to communicate with the vacuum system. The method includes placing the sample in the sample carrier when the sample carrier is in the loading position. The method may also include applying a vacuum to the groove.

[0029] The present invention also relates to a method for obtaining an electron microscope image of a sample, which includes irradiating the sample with an electron beam from a first side and detecting electrons transmitted through the sample using an electron detector on an opposite second side. The method includes moving the sample through the electron beam and synchronously moving the electron detector with the sample.

[0030] Optionally, the method includes providing a magnetic lens between the sample and the electron detector and synchronously moving the magnetic lens with the sample and the detector.

[0031] The present invention also relates to a method for moving a sample in a vacuum chamber of a scanning electron microscope. The vacuum chamber includes internal structures such as an electron optical imaging system. The method includes positioning the sample on a sample carrier movable within the vacuum chamber. The method includes inputting a user command related to a desired movement of the sample into a motion control unit. The motion control unit includes a memory that stores a three-dimensional model of the internal structure of the vacuum chamber and a three-dimensional model of the sample carrier. The method includes moving the sample carrier by the motion control unit based on the received user command and the three-dimensional models of the internal structure and the sample carrier while avoiding collisions of the sample carrier with the internal structure.

[0032] Optionally, the memory further stores a three-dimensional model of the sample carried on the sample carrier. The method may include further moving the sample carrier by the motion control unit based on the three-dimensional model of the sample while avoiding collisions of the sample, the sample carrier, and the internal structure.

[0033] It will be appreciated that any aspects of the present invention can be combined. It will also be clear that all the features and options mentioned in view of the scanning electron microscope equally apply to the method.

[0034] It will be appreciated that any one or more of the above options can be combined. Description of the Drawings

[0035] Embodiments of the present invention will now be described in detail with reference to the drawings, in which:

[0036] Figure 1A An example of a scanning electron microscope is shown, in which the sample carrier is in a first position;

[0037] Figure 1B An example of a scanning electron microscope is shown, in which the sample carrier is in a second position;

[0038] Figure 1C An example of a scanning electron microscope is shown, in which the sample carrier is in a third position;

[0039] Figure 2A An example of a scanning electron microscope is shown, in which the sample carrier is in a first position;

[0040] Figure 2B An example of a scanning electron microscope is shown, where the sample carrier is in the second position;

[0041] Figure 2C An example of a scanning electron microscope is shown, where the sample carrier is in the third position;

[0042] Figure 3A An example of a scanning electron microscope is shown, where the sample carrier is in the first position;

[0043] Figure 3B An example of a scanning electron microscope is shown, where the sample carrier is in the second position;

[0044] Figure 4A An example of a scanning electron microscope is shown;

[0045] Figure 4B An example of a scanning electron microscope is shown; and

[0046] Figure 4C An example of a scanning electron microscope is shown. Detailed Description

[0047] Figure 1A 、 1B And 1C show an example of a scanning electron microscope 1. The scanning electron microscope 1 includes an electro-optical imaging system 2. In this example, the electro-optical imaging system 2 includes an electron beam source 4 and a magnetic lens 6. The electro-optical imaging system 2 includes an electron detector 8. The scanning electron microscope 1 includes a sample carrier 10. The sample carrier 10 is arranged to carry a sample 12. The electron beam source 4 is arranged to generate an electron beam 14. The magnetic lens 6 focuses the electron beam 14 so as to impinge on the sample 12. A part of the electron beam 14 can pass through the sample 12 without interference. Another part of the electron beam 14 has electrons scattered by the sample 12. The scattered electrons and optionally the non-interfered electron beam 14 are detected by the electron detector 8. The sample carrier 10 is movable relative to the electron beam 14 so that the sample 12 moves relative to the electron beam 14.

[0048] In Figure 1A 、 1B And in the example of 1C, the sample carrier 10 is movable between a loading position 16 for loading the sample and an imaging position 18 for imaging the sample. The scanning electron microscope 1 includes a sliding vacuum sealing device 20 between the electro-optical imaging system 2 and the sample carrier 10. In Figure 1A 、 1BIn FIGS. 1A and 1C, the sliding vacuum seal device 20 includes a first plate 22 having a first aperture 24 associated with the electron optical imaging system 2. In FIG. 1, the sliding vacuum seal device 20 includes a second plate 26 having a second aperture 28 associated with the sample carrier 10. The first plate 22 bears against the second plate 26. The second plate 26 is slidably movable relative to the first plate 22. The contact surfaces of the first plate 22 and the second plate 26 are smooth enough to serve as a vacuum seal.

[0049] When the sample carrier 10 is positioned in the imaging position 18, the first aperture 24 and the second aperture 28 overlap, as shown in Figure 1C FIG. 1C. Thus, the electron beam 14 can pass from the electron beam source 4 through the first aperture 24 and the second aperture 28 and impinge on the sample 12. When the sample carrier 10 is positioned in the loading position 16, the first aperture 24 and the second aperture 28 do not overlap, as shown in Figure 1A FIG. 1A. Thus, the electron beam source 4 and the magnetic lens 6 are sealed by the sliding vacuum seal device 20 from ambient air. Thus, the electron beam source 4 and the magnetic lens 6 can be maintained under vacuum conditions. Additionally, the scanning electron microscope 1 includes a first connector 30 that connects the internal space 32 of the electron optical system 2 to the vacuum system 34. The sample carrier 10 can be open to ambient air in the loading position 16 to load and / or unload the sample 12 onto the sample carrier 10. It will be appreciated that after loading the sample 12, the sample carrier 10 can be closed and also pumped down to vacuum conditions. Additionally, the scanning electron microscope 1 includes a second connector 36 that connects the internal space 38 of the sample carrier 10 to the vacuum system 34, as will be described below.

[0050] In Figure 1A 、 1B FIGS. 1A and 1C, the first plate 22 includes an annular groove 40 surrounding the first aperture 24. The groove 40 is in fluid communication with a third connector 42 connected to the vacuum system 34. As can be seen in Figure 1A 、 1B FIGS. 1A and 1C, the groove 40 surrounds both the first aperture 24 and the second aperture 28 in both the loading position 16 and the imaging position 18. The groove 40 surrounding both the first aperture 24 and the second aperture 28 in both the loading and imaging positions provides the advantage that the apertures 24, 28 do not cross the groove 40 during movement, thus avoiding the risk of mechanically damaging the groove or the apertures. It will be appreciated that it is possible for the groove 40 to surround both the first aperture and the second aperture at least in the imaging position 18. In the loading position, the groove can surround the first aperture 24 rather than the second aperture 28.

[0051] It will be appreciated that alternatively or additionally, the second plate 26 may include a circumferential groove surrounding the second aperture 28. The groove may also be in fluid communication with a connector connected to the vacuum system 34. The groove may also surround both the first aperture 24 and the second aperture 28 in both the loading position 16 and the imaging position 18.

[0052] Regarding Figure 1A 、 1B and the scanning electron microscope 1 described in 1C can be operated as follows.

[0053] Prepare the scanning electron microscope 1 for operation. The sample carrier 10 is positioned in the loading position 16 to receive the sample 12, as shown in Figure 1A . The internal space 32 of the electron optical system 2 is brought to a predetermined first vacuum level by the vacuum system 34. The groove 40 is brought to a predetermined second vacuum level by the vacuum system 34. In this example, the second vacuum level is selected to be different from the first vacuum level. Here, the second vacuum level is selected to be between the first vacuum level and the ambient pressure.

[0054] With the sample carrier 10 in the loading position 16, the sample 12 is positioned in the sample carrier 10. The sample carrier 10 is closed to isolate it from ambient air. In this example, the sample carrier 10 is closed by sliding the second plate 26 to the intermediate position 44, as shown in Figure 1B . In the intermediate position 44, the sample carrier 10 is closed by the first plate 22. In this example, in the intermediate position, the internal space 38 of the sample carrier 10 is evacuated via the second connector 36. In this example, the internal space 38 of the sample carrier 10 is brought to a vacuum level that is at least approximately equal to the first vacuum level in the internal space 32 of the electron optical system 2.

[0055] From the intermediate position 44, the sample carrier is moved to the imaging position 18, as shown in Figure 1C . In the imaging position, the first aperture 24 and the second aperture 28 overlap. Thus, the internal space 38 of the sample carrier 10 is in communication with the internal space 32 of the electron optical system 2. The electron beam source 4 and the magnetic lens 6 are activated to generate an electron beam 14. The electron beam impinges on the sample 12. Both the undisturbed electrons and the forward scattered electrons of the electron beam 14 are detected by the electron detector 8. To provide an image of (a part of) the sample 12, the electron beam 14 is scanned across the surface of the sample 12. The scanned area of the sample 12 can be increased by tilting, i.e., scanning multiple parts of the sample 12 at different positions of the sample 12 relative to the electron beam 14. In this example, the sample 12 is scanned in a plane orthogonal to the electron beam 14 by moving the sample carrier and the second plate 26 along the first plate 22. The sample 12 can be scanned in two orthogonal directions.

[0056] The groove 40 maintained at the second vacuum level provides a suction force that clamps the first plate 22 and the second plate 26 together. Thus, a rigid connection of the sample carrier 10 relative to the electron-optical imaging system 2 can be obtained. This provides good spatial stability of the sample 12 relative to the electron beam 14. It should be noted that when the second plate 26 moves relative to the first plate 22, the suction force may cause a stick-slip effect. In an embodiment, the sample carrier 10 is controlled to always approach the target position from the same direction in order to avoid a hysteresis effect in positioning. For example, when moving in two orthogonal directions X and Y in a plane orthogonal to the electron beam 14, the sample carrier 10 can be controlled to always approach the target position in the positive X direction and in the positive Y direction.

[0057] Figure 2A 、 2B and 2C show examples of the scanning electron microscope 1 similar to the examples shown in Figure 1A 、 1B and 1C. The same reference numerals refer to the same features. In the examples of Figure 2A 、 2B and 2C, the groove 40 extends around the first aperture 24. In this example, at the imaging position 18, the groove 40 extends around the first aperture 24 and the second aperture 28. In this example, at the loading position 16, the groove 40 extends around the first aperture 24 rather than around the second aperture 28.

[0058] It should be noted that in this example, the second connector 36 is not necessary. Instead, in the intermediate position 44, as shown in Figure 2B , the internal space 38 of the sample carrier 10 can be evacuated via the third connector 42.

[0059] Figure 3A and 3B show examples of the scanning electron microscope 1. Similarly as described with respect to Figure 1A 、 1B 、1C、2A、2B and 2C, the scanning electron microscope 1 includes an electron-optical imaging system 2. In this example, the electron-optical imaging system 2 includes an electron beam source 4 and a magnetic lens 6. The electron-optical imaging system 2 includes an electron detector 8. The scanning electron microscope 1 includes a sample carrier 10. The sample carrier 10 is arranged to carry a sample 12. The electron beam source 4 is arranged to generate an electron beam 14. The magnetic lens 6 focuses the electron beam 14 so as to impinge on the sample 12. A portion of the electron beam 14 can pass through the sample 12 without interference. Electrons of another portion of the electron beam 14 are scattered by the sample 12. The forward-scattered electrons and optionally the non-interfered electron beam 14 are detected by the electron detector 8. The sample carrier 10 is movable relative to the electron beam 14 so as to move the sample 12 relative to the electron beam 14.

[0060] In Figure 3A and 3B example, the scanning electron microscope 1 includes a second magnetic lens 46. The second magnetic lens 46 is positioned between the sample 12 and the electron detector 8. The electron detector 8 is positioned in the focal plane of the second magnetic lens 46. In this example, the second magnetic lens 46 is rigidly connected to the sample carrier 10. Thus, the position of the second magnetic lens 46 relative to the sample 12 is clear. In this example, the electron detector 8 is rigidly connected to the sample carrier 10. Thus, the position of the electron detector 8 relative to the sample 12 is clear.

[0061] The sample carrier 10 is movable relative to the electron beam 14. In this example, the sample carrier is movable in a plane orthogonal to the electron beam. The sample carrier 10 can be, for example, a movable part of a sample stage. As explained with respect to Figure 1A 、 1B and 1C or Figure 2A 、 2B and 2C, the sample carrier can also be movable. Since the second magnetic lens 46 is rigidly connected to the sample carrier, the second magnetic lens 46 moves synchronously with the sample carrier 10. Since the electron detector 8 is rigidly connected to the sample carrier, the electron detector moves synchronously with the sample carrier 10. Since the electron detector 8 is positioned in the focal point of the second magnetic lens 46, the electron beam 14' traveling through the sample 12 will be deflected by the second magnetic lens 46 towards the focal point, i.e., towards the electron detector 8. This can be seen, for example, in Figure 2B in.

[0062] In Figure 3A and 3B example, the electron detector 8 includes a central bright field region 50 and a dark field region 52 surrounding the bright field region. The bright field region 50 of the electron detector 8 is positioned in the focal plane of the second magnetic lens 46. Thus, the undisturbed electron beam 14' is deflected towards the bright field region 50. The forward scattered electrons are deflected towards the dark field region 52.

[0063] Figure 4A 、 4B and 4C illustrate examples of the scanning electron microscope 1. Similarly as with respect to Figure 1A 、 1B, as described by 1C, 2A, 2B, 2C, 3A and 3B, the scanning electron microscope 1 includes an electron optical imaging system 2. In this example, the electron optical imaging system 2 includes an electron beam source 4 and a magnetic lens 6. The electron optical imaging system 2 includes an electron detector 8. The scanning electron microscope 1 includes a sample carrier 10. The sample carrier 10 is arranged to carry a sample 12. The electron beam source 4 is arranged to generate an electron beam 14. The magnetic lens 6 focuses the electron beam 14 so as to impinge on the sample 12. A portion of the electron beam 14 can pass through the sample 12 without interference. Electrons of another portion of the electron beam 14 are scattered by the sample 12. The forward scattered electrons and optionally the non-interfered electron beam 14 are detected by the electron detector 8. However, there can also be other detectors, for example, a backscattered electron detector (BSD), a secondary electron detector (SE), an energy dispersive X-ray detector (EDX), a detector for sample current, a cathodoluminescence detector (CL), an Auger detector, an optical camera, etc. The sample carrier 10 is movable relative to the electron beam 14 to move the sample 12 relative to the electron beam 14.

[0064] The scanning electron microscope 1 includes a vacuum chamber 54. The vacuum chamber 54 includes internal structures such as the electron optical imaging system 2. The sample carrier 10 is movable within the vacuum chamber 54. A movement system 55 is provided for moving the sample carrier 10. The movement system 55 can include guides and actuators known in the art. The movement system can be arranged to move the sample carrier along one or more axes and / or to rotate the sample carrier about one or more axes. The movement system can be arranged to move the sample carrier in six degrees of freedom. The movement system 55 can be arranged to move the sample carrier in two directions in a plane orthogonal to the electron beam 14. The movement system 55 can be arranged to move the sample carrier 10 in a direction parallel to the electron beam. The movement system can be arranged to tilt the sample carrier in one or two directions relative to the electron beam. The movement system can be arranged to rotate the sample about an axis parallel to the electron beam.

[0065] The scanning electron microscope includes a motion control unit 56. The motion control unit 56 is arranged to control a movement system 55 for moving a sample carrier 10. The motion control unit 56 includes an input unit 58 which is arranged to receive user commands related to the movement of the sample carrier 10. The input unit 58 may include a keyboard, a pointer device, a touch screen, a voice activation unit, and the like. The motion control unit 56 includes a memory 60. In this example, the memory 60 stores a three-dimensional model of the internal structure of the vacuum chamber 54. The three-dimensional model of the internal structure may include a three-dimensional model of the geometric structure of the internal structure of the vacuum chamber 54. The three-dimensional model of the internal structure may further include a three-dimensional model of the inner wall of the vacuum chamber 54. In this example, the memory 60 further stores a three-dimensional model of the sample carrier 10. The three-dimensional model of the sample carrier may include a three-dimensional model of the geometric structure of the sample carrier 10.

[0066] As described with respect to Figure 4A , 4B and 4C, the scanning electron microscope 1 can be operated as follows.

[0067] Position the sample carrier 10 carrying the sample 12 at a first position inside the vacuum chamber 54. The electron beam 14 can impinge on the sample 12. The user can input a user command related to the desired movement of the sample carrier 10 into the input unit 58. In this example, the user command relates to the absolute position, such as coordinates, of the desired second orientation of the sample carrier 10. It is also possible that the user command relates to the relative position of the desired second orientation of the sample carrier 10, for example, the desired displacement of the sample carrier 10, such as 0.125 mm in a predetermined direction. Based on the current position of the sample carrier 10 at the first position and the desired orientation of the sample carrier 10 at the second orientation, the motion control unit 56 calculates the path to be traveled by the sample carrier from the first position to the second position. When calculating the path, the motion control unit 56 uses the three-dimensional model of the internal structure and the three-dimensional model of the sample carrier 10 to calculate a collision-free path for the sample carrier 10 and the internal structure. In this example, the motion control unit 56 uses a sample-based planning. The sample-based planning algorithm can be, for example, a probabilistic roadmap (PRM), or a rapidly-exploring random tree (RRT), or a rapidly-exploring dense tree. However, other algorithms can be used. Optionally, the collision-free path can be smoothed, for example, to reduce vibrations of the sample carrier 10. Once the collision-free path has been determined, the motion control unit 56 controls the movement system 55 to move the sample carrier 10 along the collision-free path.

[0068] Note that, when determining a possible path, a collision can be determined if, at at least one position along the path, the three-dimensional model of the sample carrier contacts or intersects with the three-dimensional model of the internal structure. It will be appreciated that a safety margin can also be used, where a collision is considered to be a distance less than a pre-determined safety distance. In this case, if, at at least one position along the path, the minimum distance between the three-dimensional model of the sample carrier 10 and the three-dimensional model of the internal structure is less than the pre-determined safety distance, the motion control unit determines that the path includes a collision.

[0069] It will be appreciated that the mobile system 55 is embodied as a sample stage. Alternatively, the sample carrier 10 can be a movable part of the sample stage. When the sample carrier 10 moves, various parts of the sample stage can move at different rates or strokes. It will be appreciated that the memory can also store the three-dimensional model of the sample stage. When calculating the path, the motion control unit 56 can also use the three-dimensional model of the sample stage to calculate a path without collision between the sample stage and the internal structure. More generally, when calculating the path, the motion control unit 56 can also use the three-dimensional model of the mobile system to calculate a path without collision between the sample carrier, the mobile system and the internal structure.

[0070] In one mode, the memory 60 further stores the three-dimensional model of the sample 12 carried on the sample carrier 10. The three-dimensional model of the sample can include the three-dimensional model of the geometric structure of the sample 12. The motion control unit 56 can use the three-dimensional model of the sample 12 when calculating the path to be traveled by the sample carrier 10 from a first position to a second position, so as to avoid collisions between the sample 12, the sample carrier 10, optionally the mobile system 55 and the internal structure.

[0071] The motion control unit 56 controls the sample carrier 10 to move from the first position to the second position along the calculated collision-free path.

[0072] In this example, the motion control unit 56 is arranged to simulate the execution of a user command before executing the user command. The simulation includes calculating a path from the current position to an updated position of the sample carrier 10 according to the user command. If the path calculated in the simulation indicates a collision between on the one hand the sample carrier 10 (and optionally the sample 12 and / or the movement system 55) and on the other hand the internal structure, the motion control unit avoids implementing the user command. Thus, the motion control unit 56 is arranged to ignore the user command if the simulation indicates a collision. This prevents a collision or a risk of collision if a safety margin is observed. The motion control unit 56 can be arranged to generate a message for the user that the user command cannot, should not or will not be implemented. The message can be displayed, for example, on the display device 59 of the scanning electron microscope. The motion control unit 56 can be configured to determine an alternative path instead of the path according to the user command, which would position the sample carrier 10 at the final position according to the user command, and the alternative path is collision-free. The motion control unit 56 can be arranged to suggest the alternative path to the user, for example, by displaying a message on the display device 59. The motion control unit 56 can also be arranged to automatically replace the path according to the user command with the alternative path. The motion control unit 56 can generate a message indicating the use of the alternative path. The motion control unit 56 can be arranged to indicate the alternative path, for example, overlapping with the microscope image, at the display device 59.

[0073] In Figure 4A , 4B and 4C example, the input unit 58 is arranged to receive data representing the geometry of the sample 12. It is possible that the geometry of the sample is known. Then, the data can include a three-dimensional model of the geometry of the sample. Alternatively, the data representing the geometry of the sample can indicate the geometry of the sample.

[0074] In Figure 4A example, the scanning electron microscope 1 includes a plurality of templates 62 for determining an approximate geometry of the sample 12. In this example, each template includes a cavity having a predetermined size. Here, the cavity is a cylinder with different diameters and / or heights. However, alternative shapes can be used, such as hemispheres, rhombuses, cubes, cones, etc. The user can mount one or more of the templates 62 on the sample 12 on the sample carrier 10 to select the template 62 with the smallest cavity mounted on the sample 12. An indication of the selected template 62, for example, a code or a number, can be provided to the input unit 58. Thereby, the scanning electron microscope 1 can determine an approximate geometry of the sample 12.

[0075] In Figure 4BIn the example, the scanning electron microscope 1 includes an optical camera 64 and a geometric structure determination unit 66. The geometric structure determination unit 66 is arranged to determine the geometric structure of the sample 12 based on at least one image of the sample 12 provided by the optical camera 64. The optical camera 64 is positioned to provide a top plane image of the sample 12.

[0076] Here, the geometric structure determination unit 66 determines the perimeter of the sample 12. The optical camera 64 obtains a first image of the sample 12 in a top view. Next, the sample is rotated through a predetermined angle about an axis substantially parallel to the optical axis of the camera 64. Then, the optical camera 64 obtains a second image of the sample 12 in a top view. The geometric structure determination unit 66 compares the first image with the second image. In this example, the geometric structure determination unit compares the intensity of each pixel in the first image with the intensity of the corresponding pixel in the second image. Pixels for which the intensity difference between the first image and the second image exceeds a predetermined threshold level are determined to indicate the contour of the sample 12. The geometric structure determination unit 66 determines the approximate geometric structure of the sample based on the determined contour. It will be appreciated that the height of the sample can be determined as a predetermined height or as a function of the contour dimensions, for example, a predetermined percentage of the maximum diameter of the top plane contour of the sample.

[0077] In Figure 4C the example, the optical camera 68 is arranged to provide a side view image of the sample 12. The optical camera 68 obtains a first image of the sample 12 in a side view. Next, the sample is rotated through a predetermined angle about an axis substantially orthogonal to the optical axis of the camera 68. Then, the optical camera 68 obtains a second image of the sample 12 in a side view. The geometric structure determination unit 66 determines a three-dimensional model of the sample 12 based on the first image and the second image. Optionally, the optical camera 68 can obtain additional images of the sample at different rotational positions for use by the geometric structure determination unit 66. The geometric structure determination unit 66 can use techniques for reconstructing a three-dimensional model based on two or more two-dimensional images known in the art. In Figure 4C the example, the sample carrier 10 includes a marker 70. The marker 70 is positioned within the field of view of the optical camera 68. Thus, the marker 70 appears in the two-dimensional image obtained by the camera 68. The marker can be used in the three-dimensional reconstruction of the model of the sample based on the two-dimensional image.

[0078] It will be appreciated that Figure 4C the camera 68 of Figure 4B can also be combined with

[0079] the camera 64 of

[0079] Then, the camera 64 can provide information about the contour of the sample 12, while the camera 68 can provide information about the height of the sample.

[0079] In this document, the present invention is described with reference to specific examples of embodiments of the invention. However, it will be apparent that various modifications and changes can be made therein without departing from the essence of the invention. For the purpose of clear and concise description, features are described herein as part of the same or separate embodiments, however, alternative embodiments having combinations of some or all of the features described in these separate embodiments are also contemplated.

[0080] It will be appreciated that the scanning electron microscopes described with respect to Figure 3A , 3B , 4A, 4B and 4C may also include a sliding vacuum seal arrangement, for example, as described with respect to Figure 1A , 1B , 1C, 2A, 2B and 2C.

[0081] It will be appreciated that the scanning electron microscopes described with respect to Figure 1A , 1B , 1C, 2A, 2B, 2C, 4A, 4B and 4C may also include a second magnetic lens and / or an electron detector that is synchronously movable with the sample carrier, for example, as described with respect to Figure 3A and 3B .

[0082] It will be appreciated that the scanning electron microscopes described with respect to Figure 1A , 1B , 1C, 2A, 2B, 2C, 3A and 3B may also include a motion control unit, for example, as described with respect to Figure 4A , 4B and 4C.

[0083] In the examples of Figure 4A , 4B and 4C, the motion control unit is arranged to avoid collisions. It will be appreciated that it is also possible for the motion control unit to be arranged to maintain a distance between the sample carrier and the internal structure that is greater than or equal to a predetermined minimum distance. This can provide a predetermined safety margin. For example, the calculated minimum distance can be used to determine a path for maintaining a distance from the internal structure at least the predetermined minimum distance at a different voltage from the sample carrier (e.g., at a high (positive or negative) voltage). Thus, discharges between the sample carrier and / or the sample and the corresponding internal structure can be avoided.

[0084] It will be appreciated that the motion control unit and the geometry determination unit may be embodied as dedicated electronic circuits, possibly including software code portions. The motion control unit and the geometry determination unit may also be embodied as software code portions executed on a programmable device such as a computer, a tablet device or a smart phone, and as software code portions stored, for example, in the memory of a programmable device such as a computer, a tablet device or a smart phone.

[0085] Although embodiments of the invention described with reference to the drawings include computer devices and processes implemented in computer devices, the invention also extends to computer programs, particularly computer programs on or in a carrier suitable for putting the invention into practice. The program may be in the form of source code or object code, or in any other form suitable for use in an implementation of a process according to the invention. The carrier may be any entity or device capable of carrying the program.

[0086] For example, the carrier may include a storage medium such as a ROM (e.g., a CD ROM or a semiconductor ROM), or a magnetic recording medium (e.g., a floppy disk or a hard disk). In addition, the carrier may be a transmissible carrier such as an electrical or optical signal that may be transmitted via a cable or an optical fiber cable or by radio or other means (e.g., via the Internet or the cloud).

[0087] When the program is embodied in a signal that can be directly transmitted via a cable or other device or means, the carrier may consist of such a cable or other device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being suitable for implementing the relevant process or for use in implementing the relevant process.

[0088] However, other modifications, variations and alternatives are also possible. The description of the specification, the drawings and the examples should accordingly be considered in an illustrative rather than a restrictive sense.

[0089] For the purposes of clear and concise description, features are described herein as parts of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of some or all of the described features. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of other features or steps than those listed in the claims.

[0090] Furthermore, the words "a" and "an" should not be construed as limited to "only one", but are used to mean "at least one", and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A scanning electron microscope, comprising: an electron optical imaging system including an electron beam source and an electron detector, a sample carrier located between the electron beam source and the electron detector, the sample carrier being movable relative to the electron beam for moving a sample, and wherein the electron detector is movable relative to the electron beam, wherein the electron detector is arranged to move synchronously with the sample carrier, wherein the electron detector is fixedly connected to the movable sample carrier, a magnetic lens included between the sample and the electron detector, wherein the magnetic lens is movable relative to the electron beam, wherein the magnetic lens is arranged to move synchronously with the sample carrier, and wherein the magnetic lens is fixedly connected to the movable sample carrier, wherein the sample carrier is movable between a loading position for loading a sample and an imaging position for imaging the sample, wherein the scanning electron microscope includes a sliding vacuum seal between the electron optical imaging system and the sample carrier, wherein the sliding vacuum seal includes a first plate having a first aperture associated with the electron optical imaging system and resting on a second plate having a second aperture associated with the sample carrier, the first plate and the second plate being slidably movable relative to each other, the first aperture and the second aperture overlapping in the imaging position and not overlapping in the loading position, wherein the first plate and / or the second plate includes a groove surrounding the first aperture and / or the second aperture, the groove being arranged to communicate with a vacuum system.

2. The scanning electron microscope according to claim 1, wherein the electron detector is positioned in the focal plane of the magnetic lens.

3. The scanning electron microscope according to claim 2, wherein the bright field region of the electron detector is positioned in the focal plane of the magnetic lens.

4. The scanning electron microscope according to any one of claims 1-3, comprising: a vacuum chamber including an internal structure, wherein the sample carrier is movable within the vacuum chamber, and a motion control unit including an input unit arranged to receive user commands related to the movement of the sample carrier, the motion control unit including a memory storing a three-dimensional model of the internal structure of the vacuum chamber and a three-dimensional model of the sample carrier, wherein the motion control unit is arranged to move the sample stage based on the received user commands and the three-dimensional models of the internal structure and the sample carrier while avoiding collisions between the sample carrier and the internal structure.

5. The scanning electron microscope according to claim 4, wherein the internal structure is an electron beam source.

6. A method for obtaining an electron microscope image of a sample by a scanning electron microscope including an electron optical imaging system, the electron optical imaging system including an electron beam source and an electron detector, the method comprising: Provided is a sample carrier, which is disposed between the electron beam source and the electron detector, and the sample carrier is movable relative to the electron beam for moving the sample, and wherein the electron detector is movable relative to the electron beam, wherein the electron detector is arranged to move synchronously with the sample carrier, wherein the electron detector is fixedly connected to the movable sample carrier, a magnetic lens, which is included between the sample and the electron detector, wherein the magnetic lens is movable relative to the electron beam, wherein the magnetic lens is arranged to move synchronously with the sample carrier, wherein the magnetic lens is fixedly connected to the movable sample carrier, wherein the sample carrier is movable between a loading position for loading the sample and an imaging position for imaging the sample, wherein the scanning electron microscope includes a sliding vacuum seal disposed between the electron optical imaging system and the sample carrier, wherein the sliding vacuum seal includes a first plate having a first aperture associated with the electron optical imaging system and resting against a second plate having a second aperture associated with the sample carrier, the first plate and the second plate being slidably movable relative to each other, the first aperture and the second aperture overlapping in the imaging position and the first aperture and the second aperture not overlapping in the loading position, wherein the first plate and / or the second plate includes a groove surrounding the first aperture and / or the second aperture, and the groove is arranged to communicate with a vacuum system, irradiating the sample from a first side with an electron beam and detecting electrons transmitted through the sample using an electron detector on an opposite second side, moving the sample through the electron beam and moving the electron detector synchronously with the sample, including providing a magnetic lens between the sample and the electron detector and moving the magnetic lens synchronously with the sample and the detector.

7. A computer program product, comprising a computer program, characterized in that the computer program, when executed by a processor, implements the steps of the method according to claim 6.

8. A computer-readable medium, on which computer instructions are stored, characterized in that the computer instructions, when executed by a processor, implement the steps of the method according to claim 6.

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