Wide-field charged particle filter

Abstract

An embodiment of a charged particle filter is described that includes a plurality of magnets, each including a sloped surface at an angle relative to a plane defined by a line from the center of the field of view on the detector to the center of the field of view on the platform. In the described embodiment, the sloped surfaces are arranged to form a bore that includes a strongest magnetic field gradient at a first opening in a side of the bore adjacent to the detector.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority from U.S. Patent Application No. 63 / 003,575, filed April 1, 2020, which is hereby incorporated by reference in its entirety for all purposes.

[0002] The present invention is generally directed to a charged particle filter configured to maximize the magnetic field strength within the filter without affecting the field of view. [Background technology]

[0003] In general, charged particle filters (also called "electron traps" or "magnetic deflectors") are widely used in energy dispersive X-ray spectroscopy (EDS) systems to detect X-ray photons emitted from materials exposed to an electron beam. The detected X-ray photons are typically used to characterize the elemental composition of the material. It is also commonly recognized that electron beams also produce backscattered electrons (e.g., charged particles) that produce a signal similar to X-ray photons that cause undesirable background noise in the signal data.

[0004] Exemplary embodiments of the charged particle filter are configured to substantially reduce or prevent charged particles from reaching the detector by generating a magnetic field having a sufficiently high magnetic field strength. Typically, EDS systems are utilized in microscopy applications, such as scanning electron microscopes (SEMs), where a compact form factor of the charged particle filter is highly desirable due to the limited space within the microscope. Examples of charged particle filters for use in microscopy applications are described in U.S. Patent Nos. 9,697,984 and 9,837,242, each of which is incorporated herein by reference in its entirety for all purposes.

[0005] In typical microscopy applications, the compact shape has a small field of view that is compatible with the small scanning areas (e.g., 1 mm x 1 mm) associated with microscopy applications. However, that small field of view is detrimental to its use in other applications, such as electron beam additive manufacturing (EBAM) applications, performed by what are called electron beam melting or electron beam powder bed fusion devices. Typically, EBAM devices include large scanning areas (e.g., 0.2 meters x 0.2 meters). However, simply creating an oversized particle filter with a large opening with a wide field of view would result in insufficient magnetic field strength to effectively prevent the charged particles from reaching the detector. This is particularly problematic for EBAM applications, since the charged particles in EBAM typically have energies of 60 keV, double the usual maximum of 30 keV for SEMs. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, there is a need for a charged particle filter that provides a wide field of view with sufficient magnetic field strength to effectively prevent charged particles from reaching the detector. [Means for solving the problem]

[0007] Systems, methods, and articles of manufacture that address these and other needs are described herein with respect to exemplary, non-limiting implementations. Various alternatives, modifications, and equivalents are possible.

[0008] An embodiment of a charged particle filter is described that includes a plurality of magnets, each including an inclined surface at an angle relative to a plane defined by a line from the center of the field of view on the detector to the center of the field of view on the platform. In the described embodiment, the inclined surfaces are arranged to form a bore that includes a strongest magnetic field gradient at a first opening in a side of the bore adjacent to the detector.

[0009] Depending on the embodiment, the angled surface can be substantially planar or substantially conical, and the radius of the substantially conical surface is relative to the angle, and in some implementations, the angled surface can include an angle in the range of 5 to 45 degrees, and more specifically, an angle of 15.4 degrees.

[0010] Additionally, the bore can have a field of view over the platform defined by a diameter of a second opening in a side of the bore facing the platform. In some cases, the field of view is about 128 mm in diameter. Additionally, the magnetic field gradient can include a range of magnetic field strengths that are about 1000 Gauss to 5000 Gauss.

[0011] Additionally, in some cases, the charged particle filter can include one or more inserts configured to fill spaces between the magnets. Similarly, in some cases, the charged particle filter can include a flux ring with a shape that properly positions the magnets with respect to the tilt angle.

[0012] An embodiment of an electron beam additive manufacturing apparatus is also described that includes an electron beam source configured to generate an electron beam, a platform configured as a support on which the electron beam additive manufacturing apparatus builds a product in response to the electron beam, a detector configured to generate a signal in response to one or more x-ray photons emitted from the product in response to the electron beam, and a charged particle filter configured to deflect one or more charged particles emitted from the product in response to the electron beam away from the detector, the charged particle filter including a plurality of magnets each including an inclined surface at an angle relative to a plane defined by a line from a center of field of view on the detector to a center of field of view on the platform. Further, the inclined surfaces are arranged to form a bore including a strongest magnetic field gradient at a first opening in a side of the bore adjacent the detector.

[0013] Depending on the embodiment, the angled surface can be substantially planar or substantially conical, and the radius of the substantially conical surface is relative to the angle, and in some implementations, the angled surface can include an angle in the range of 5 to 45 degrees, and more specifically, an angle of 15.4 degrees.

[0014] Additionally, the bore can have a field of view over the platform defined by a diameter of a second opening in a side of the bore facing the platform. In some cases, the field of view is about 128 mm in diameter. Additionally, the magnetic field gradient can include a range of magnetic field strengths that are about 1000 Gauss to 5000 Gauss.

[0015] Additionally, in some cases, the charged particle filter can include one or more inserts configured to fill spaces between the magnets. Similarly, in some cases, the charged particle filter can include a flux ring with a shape that properly positions the magnets with respect to the tilt angle.

[0016] The above embodiments and implementations are not necessarily mutually inclusive or exclusive, and may be combined in any manner that is not inconsistent and otherwise possible, regardless of whether they are presented in association with the same or different embodiments or implementations. The description of one embodiment or implementation is not intended to be limiting with respect to other embodiments and / or implementations. Also, any one or more features, steps, operations, or techniques described elsewhere in this specification may be combined with any one or more features, steps, operations, or techniques described in the Summary of the Invention in alternative implementations. Thus, the above embodiments and implementations are illustrative rather than limiting.

[0017] The above and further features will be more clearly understood from the following detailed description when read in conjunction with the accompanying drawings, in which like reference numbers indicate like structures, elements, or method steps, and the leftmost digit of the reference number indicates the number of the figure in which the referenced element first appears (e.g., element 110 first appears in FIG. 1). However, all of these conventions are intended to be exemplary or illustrative rather than limiting. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a functional block diagram of one embodiment of an electron beam additive manufacturing device in communication with a computer. [Diagram 2] 2 is a simplified graphical representation of an embodiment of the electron beam additive manufacturing apparatus of FIG. 1 equipped with a charged particle filter. [Diagram 3] 3 is a simplified graphical representation of an embodiment of the charged particle filter of FIG. 2 having multiple magnets. [Figure 4A] 3 is a simplified graphical representation of an embodiment of the charged particle filter of FIG. 2 in which multiple magnets are arranged to provide a tilt angle. [Figure 4B] 3 is a simplified graphical representation of an embodiment of the charged particle filter of FIG. 2, in which each of the multiple magnets has a shape that includes a tilt angle. [Figure 5A] 3 is a simplified graphical representation of an embodiment of the charged particle filter of FIG. 2 having a flux ring that appropriately positions multiple magnets. [Figure 5B] 3 is a simplified diagram of an embodiment of the charged particle filter of FIG. 2 having a flux ring, the plurality of magnets including a substantially conical surface including an inclined angle within the bore. Like reference numerals refer to corresponding parts throughout the several views of the drawing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] As described in more detail below, the described embodiments of the invention include a charged particle filter that has a wide field of view and provides a magnetic field strength sufficient to effectively prevent charged particles from reaching a detector. More specifically, the charged particle filter is comprised of multiple magnets with inclined faces relative to a plane parallel to the particle movement, with the space between the magnets decreasing from the side of the charged particle filter closest to the charged particle source to the side closest to the detector.

[0020] FIG. 1 illustrates a simplified example of a user 101 that can interact with a computer 110 and an EBAM device 120. An embodiment of the EBAM device 120 can include various commercially available EBAM devices. For example, the EBAM device 120 can include a Q10 electron beam melting device available from Arcam AB (GE Additive). FIG. 1 also illustrates a network connection between the computer 110 and the EBAM device 120, but it will be understood that FIG. 1 is intended to be illustrative and that additional or fewer network connections can be included. Furthermore, network connections between elements can include "direct" transmission of wired or wireless data (e.g., represented by lightning bolts) as well as "indirect" communication via other devices (e.g., switches, routers, controllers, computers, etc.). Thus, the example of FIG. 1 should not be considered limiting.

[0021] Computer 110 may include any type of computing platform, such as a workstation, a personal computer, a tablet, a "smartphone," one or more servers, a compute cluster (local or remote), or other current or future computers or clusters of computers. A computer typically includes known components, such as one or more processors, an operating system, system memory, memory storage devices, input / output controllers, input / output devices, and display devices. It will also be understood that more than one implementation of computer 110 may be used to perform various operations in different embodiments, and thus the representation of computer 110 in FIG. 1 should not be considered limiting.

[0022] In some embodiments, the computer 110 may employ a computer program product comprising a computer usable medium having stored therein control logic (e.g., a computer software program including program code). The control logic, when executed by a processor, causes the processor to perform some or all of the functions described herein. In other embodiments, some functions are implemented primarily in hardware, for example, using a hardware state machine. The implementation of a hardware state machine to perform the functions described herein will be apparent to one of ordinary skill in the art. In the same or other embodiments, the computer 110 may employ an Internet client, which may include a dedicated software application enabled to access remote information over a network. The network may include one or more of various types of networks known to those skilled in the art. For example, the network may include a local or wide area network that may employ what is commonly referred to as the TCP / IP protocol suite to communicate. The network may include a worldwide system of interconnected computer networks commonly referred to as the Internet, or may include various intranet architectures. Those skilled in the art will also appreciate that some users in networked environments may prefer to employ what is commonly referred to as a "firewall" (also referred to as a packet filter, or boundary protection device) to control information traffic entering and leaving their hardware and / or software systems. For example, a firewall may include hardware or software elements, or a combination thereof, and is typically designed to enforce security policies established by a user, such as, for example, a network administrator.

[0023] As described herein, embodiments of the described invention include a charged particle filter having multiple magnets that includes a wide field of view and includes a magnetic field strength sufficient to effectively prevent charged particles from reaching the detector. In the described embodiment, the charged particle filter has a sloped surface at an angle to a plane defined by a line from the center of the field of view on the detector to the center of the field of view on the platform, the sloped surface creating a gradient of magnetic field strength with the strongest magnetic field strength in an area of ​​the charged particle filter close to the detector.

[0024] FIG. 2 provides a simplified illustrative example of an EBAM device 120 that includes a charged particle filter 210 and a detector 220. In some embodiments, the detector 220 may include what is referred to as a silicon drift detector (SDD) or other types of detectors known in the relevant art. Also, in some embodiments, the charged particle filter is disposed within a vacuum chamber 205 that includes a vacuum environment typically used in electron beam additive manufacturing applications. Also, in the same or alternative embodiments, the detector 220 is disposed within an atmospheric chamber 207 that includes an environment substantially similar to the ambient environment outside the EBAM device 120. For example, the charged particle filter 210 and the detector 220 may be disposed in different environments separated by an airtight partition (e.g., a "window") that is transparent to X-ray photons. In some embodiments, it is desirable for the partition to be thin, thereby allowing low energy X-ray photons to pass through, and in some cases supported by additional structure that provides rigidity. Typical partitions used in EDS applications are constructed of polymer-based materials, beryllium (Be), or sodium (Na). However, any type of partition having the desired properties may be used. Also in this example, in a typical electron beam additive manufacturing application, the electron beam 207 originates from directly above the platform 230 (e.g., the electron beam 207 may be substantially perpendicular to the plane of the platform 230, although the electron beam 207 may be directed at angles greater than perpendicular to build products under the directional control of the computer 110). Additionally, the detector 220 and charged particle filter 210 are both positioned on one side of the vacuum chamber 205 with a line of sight to the platform 230, tilted at an angle that depends on the distance from the origin of the electron beam 207, to provide a detector field of view 233 in the region of the platform 230 where the electron beam 207 is used to build products. In many embodiments, the position detector 220 and charged particle filter 210 are limited to the available ports on the vacuum chamber 205.

[0025] 2 also shows a centerline 225 that defines a plane from the center of the field of view on the detector 220 to the center of the field of view on the platform 230. In some embodiments, the centerline 225 defines a distance from the charged particle filter 210 to the platform 230, which is also related to the height distance of the electron beam 207 defined by the distance from the top of the platform 230 (e.g., the support on which the EBAM 120 builds the product) to the top of the vacuum chamber 205. For example, the centerline 225 can include a distance of about 472 mm and the electron beam 207 can include a height distance of about 450 mm. However, it should be understood that the EBAM 120 can include a variety of configurations and dimensions, and thus the dimensions of this example should not be considered limiting.

[0026] 2 further illustrates that the detector field of view 233 is smaller than the maximum field of view 235. In the embodiments described herein, the maximum field of view 235 is defined by the characteristics of the charged particle filter 210, and the detector field of view 233 is defined by the characteristics of one or more other elements, and in some instances, it may be desirable for the detector field of view 233 not to be a limit of the maximum field of view 235. Alternatively, in some applications, it may be desirable for the detector field of view 233 to be substantially the same as the maximum field of view 235. For example, in some embodiments, the detector field of view may include an area with a diameter of about 128 mm, and the maximum field of view may include an area with a diameter of about 316 mm. Also, in some cases, the platform 230 may include an area with a diameter or width of about 200 mm, and the embodiment of the platform 230 is substantially square or rectangular.

[0027] 3 provides a simplified illustrative example of a close-up view of the charged particle filter 210 and detector 220 of FIG. 2. First, FIG. 3 shows an x-ray limiting aperture 305 that selectively limits the number of x-ray photons that impinge on the detector 220. In some embodiments, the x-ray limiting aperture 305 selects x-ray photons from the detector field of view 233 associated with the region being excited by the electron beam 207, thus reducing detection of x-ray photons originating from other parts of the vacuum chamber 205 that may contribute noise to the signal. Importantly, in the described embodiment, the charged particle filter 210 substantially reduces or eliminates detection of charged particles originating from the entire region of the maximum field of view 235 that may be a source of noise in the detected signal.

[0028] In some embodiments, the x-ray limiting aperture 305 can also reduce the number of photons that impinge on the detector 220, which has the advantage of reducing the chance of saturating or damaging elements of the detector 220. It should also be appreciated that some embodiments of the EBAM device 120 allow a user to vary the dimensions of the x-ray limiting aperture 305 to allow for the use of different volumes of the detector field of view 233.

[0029] 3 further shows a plurality of magnets 310, each having a surface inclined at an angle relative to the centerline 225, the inclined surface defining a bore 313 through which the x-ray photons pass. The magnets 310 may include any type of magnet typically used in the art, such as neodymium or other types of magnets having desirable properties. For example, permanent magnets constructed from materials having various grades of SmCo and primarily grades of NdFe may be used.

[0030] In the embodiment of Figure 3, magnet 310 is substantially rectangular with substantially parallel surfaces, and tilt angle 315 is substantially the same as the tilt angle of the surfaces of bore 313. In the example of Figure 3, the tilt angle is approximately 15.4. ° However, tilt angles in the range of 5 to 45 degrees are considered to be within the scope of the present invention.

[0031] In the described embodiment, the position of the magnets 310 defines the region of the maximum field of view 235, and more specifically, a particular portion of the magnets 310 defines the region of the maximum field of view 235 depending on the tilt angle. For example, for a tilt angle of about 15.4° as shown in FIG. 3, the corner of each magnet 310 in the bore 313 at the second opening 317 (e.g., where the x-ray photons and charged particles originate) facing the platform 230 defines the region of the maximum field of view 235. Alternatively, for small tilt angles (e.g., <10°), the corner of each magnet 310 in the bore 313 at the first opening 315 proximate to the detector 220 defines the region of the maximum field of view 235.

[0032] In the example of FIG. 3, the maximum field of view 235 is 36.4°, but the maximum field of view can include a field of view ranging from 10° to 90°. Furthermore, due to the tilt angles of the detector 220 and the charged particle filter 210 (as described above), the centerline 225 interacts with the platform 230 at a platform incidence angle 337, which can include an angle of 72.4°. Also, due to the tilt angles of the detector 220 and the charged particle filter 210, the angles measured from the centerline 225, i.e., angle 333 (e.g., 7.7°) and angle 335 (e.g., 7.1°), are slightly different. Furthermore, one skilled in the art will appreciate that the example of FIG. 3 shows a symmetrical configuration with similar tilt values ​​for both magnets 310 leading to different field of view angles 333 and 335. However, if it is desired that the angles 333 and 335 are similar (or any other value), this can be achieved with magnets 310 having independent tilt configurations including asymmetrical designs (e.g., each magnet 310 has a different tilt angle than the other).

[0033] FIG. 3 also shows the magnetic field 320 including a gradient (e.g., magnetic field strength shown in FIG. 3 by the thickness of the arrow) that is strongest at a first opening 315 on the side of the bore 313 adjacent to the detector 220 and weakest at a second opening 317 on the side of the bore 313 facing the platform 230. In the described embodiment, the spacing between the magnets 310 defines the diameter of the opening 315, or the opening 315 as applied in the particular embodiment. Those skilled in the art will understand that the magnetic field strength is proportional to the strength of the magnets 310 and the distance between them. Also, the magnetic field 320 must include a magnetic field strength sufficient to efficiently deflect the charged particles, but should not be so strong as to affect the electron beam 207 or significantly affect the operation of the detector 220, since charged particles moving within the detector 220 will be affected by the magnetic field 320 if the magnetic field strength is too high. For example, the magnetic field 320 may include a gradient in magnetic field strength in the range of approximately 1000 Gauss to 5000 Gauss (e.g., from the second opening 317 to the first opening 315). However, it should be understood that the strength of the magnetic field depends on various factors, such as the grade of material used in the magnet 310, and thus this example should not be considered limiting.

[0034] FIG. 4A provides a simplified graphical example of a substantially rectangular configuration of magnets 310, in which each embodiment of magnets 310 is tilted to provide a tilt angle, as described above. However, it will be understood that other configurations are also considered to be within the scope of the described invention. One such example is shown in FIG. 4B as magnet 410 including a shape with a tilt angle built into the configuration. For example, magnet 410 does not need to be configured in a specific location within charged particle filter 210. Rather, magnet 410 can be designed to correspond to any location that allows freedom of design of charged particle filter 210. Additionally, as shown in FIG. 4B, magnet 410 is substantially thicker (e.g., wider) at first opening 315 and therefore has a greater magnetic field strength than second opening 317, which has a thinner thickness.

[0035] FIG. 5A illustrates a cross-sectional view (e.g., approximately half) of one embodiment of the charged particle filter 210 including the magnet 310, as described above. FIG. 5A also illustrates a flux ring 503 with a shape that properly positions the magnet 310 at a desired tilt angle. In some embodiments, the flux ring 503 can be constructed of steel or other desired material. For example, the flux ring 503 can be constructed of any suitable ferromagnetically permeable material, which may vary depending on space availability, location to other sensitive items affected by the magnetic field 320, or other factors. In this example, the specific materials include sintered cobalt (250) or mild steel (2,000), although various specialty grades of steel can be used.

[0036] 5A further illustrates an insert 507 that fills the space between the magnets 310 but does not interfere with the bore 313 or the openings 315 and 317. In some embodiments, the charged particle filter 210 may include multiple implementations of the insert 507, which may be constructed of aluminum or other desired materials. For example, the insert 510 should be constructed of a non-magnetic or paramagnetic material. Typically, the material of the insert 510 should include light elements such as aluminum or carbon to minimize the generation of x-rays.

[0037] 5B illustrates a cross-sectional view (e.g., about half) of another embodiment of charged particle filter 210 including magnet 510 including a curved shape of the surface including an oblique angle. In the described embodiment, the magnets form a substantially conical surface with an oblique angle within bore 313. The embodiment shown in FIG. 5B may or may not include an insert element similar to insert 507 described for FIG. 5A, as well as a flux ring 513 having a shape to appropriately position magnet 510.

[0038] While various embodiments and implementations have been described, it should be understood by those skilled in the art that the foregoing are merely illustrative, not limiting, and are presented by way of example only. Many other schemes for distributing functionality among the various functional elements of the illustrated embodiments are possible. The functionality of any element may be performed in various ways in alternative embodiments.

Claims

1. 1. A charged particle filter comprising: a plurality of magnets each including an inclined surface at an angle relative to a plane defined by a line from a center of field of view on the detector to a center of field of view on the platform; The angled surfaces are positioned to form a bore containing a strongest magnetic field gradient at a first opening on a side adjacent the detector.

2. The charged particle filter of claim 1 , wherein the angled surface is substantially planar.

3. The charged particle filter of claim 1 , wherein the angled surface is substantially conical.

4. The charged particle filter of claim 3 , wherein a radius of the substantially conical surface is relative to the angle.

5. The charged particle filter of claim 1 , wherein the inclined surface comprises an angle in the range of 5 to 45 degrees.

6. The charged particle filter of claim 5 , wherein the angled surface comprises an angle of 15.4°.

7. The charged particle filter of claim 1 , wherein the bore has a field of view on the platform defined by a diameter of a second opening of the bore on a side facing the platform.

8. 8. The charged particle filter of claim 7, wherein the field of view is approximately 128 mm in diameter.

9. The charged particle filter of claim 1 , wherein the magnetic field gradient comprises a range of approximately 1000 Gauss to 5000 Gauss.

10. The charged particle filter of claim 1 , further comprising one or more inserts configured to fill spaces between the magnets.

11. 10. The charged particle filter of claim 1 further comprising a flux ring having a shape that properly positions the magnet with respect to a tilt angle.

12. 1. An electron beam additive manufacturing apparatus comprising: an electron beam source configured to generate an electron beam; a platform configured as a support on which the electron beam additive manufacturing device builds a product in response to the electron beam; a detector configured to generate a signal in response to one or more X-ray photons emitted from the article in response to the electron beam; a charged particle filter configured to deflect one or more charged particles emitted from the product in response to the electron beam away from the detector; 1. An electron beam additive manufacturing device, wherein the charged particle filter comprises a plurality of magnets, each including an inclined surface at an angle relative to a plane defined by a line from a center of a field of view on a detector to a center of a field of view on a platform, the inclined surfaces being positioned to form a bore including a strongest magnetic field gradient at a first opening on a side adjacent to the detector.

13. The electron beam additive manufacturing apparatus of claim 12 , wherein the inclined surface is substantially planar.

14. The electron beam additive manufacturing apparatus of claim 12 , wherein the inclined surface is substantially conical.

15. The electron beam additive manufacturing apparatus of claim 14 , wherein a radius of the substantially conical surface is relative to the angle.

16. The electron beam additive manufacturing apparatus of claim 12, wherein the inclined surface comprises an angle in the range of 5 to 45 degrees.

17. 17. The electron beam additive manufacturing apparatus of claim 16, wherein the inclined surface comprises an angle of 15.4 degrees.

18. The electron beam additive manufacturing apparatus of claim 12 , wherein the bore comprises a field of view on the platform defined by a diameter of a second opening of the bore on a side facing the platform.

19. 20. The electron beam additive manufacturing apparatus of claim 18, wherein the field of view is about 128 mm in diameter.

20. The electron beam additive manufacturing apparatus of claim 12, wherein the magnetic field gradient comprises a range of about 1000 Gauss to 5000 Gauss.

21. 13. The electron beam melting apparatus of claim 12, further comprising one or more inserts configured to fill spaces between the magnets.

22. 13. The electron beam melting apparatus of claim 12, further comprising a flux ring including features that properly position the magnets with respect to tilt angle.

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