Wide Field Charged Particle Filter

Abstract

The present invention describes an embodiment of a charged particle filter that includes a plurality of magnets, each of the plurality of magnets having a surface that is angled with respect 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 angled surfaces are positioned to form a hole that includes a magnetic field gradient that is strongest at a first pore on the side of the hole that is closer to the detector.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of priority of U.S. Patent Application No. 63 / 003,575, filed Apr. 1, 2020, which is incorporated herein by reference in its entirety for all purposes. Technical Field

[0003] The present invention generally relates to a charged particle filter configured to maximize the field strength within the filter without compromising the field of view. Background Art

[0004] It is generally understood that charged particle filters (sometimes also referred to as "electron traps" or "magnetic deflectors") are widely used in conjunction with energy dispersive X-ray spectroscopy (EDS) systems that detect X-ray photons emitted from materials exposed to an electron beam. The detected X-ray photons are generally used to characterize the elemental composition of the material. It is also generally understood that the electron beam generates backscattered electrons (e.g., charged particles) that produce signals similar to X-ray photons, thereby introducing unwanted background noise in the signal data.

[0005] Typical embodiments of charged particle filters are configured to substantially reduce or prevent charged particles from reaching the detector by generating a magnetic field having a field strength that is high enough. Generally, EDS systems are used in microscopy applications, such as in scanning electron microscopes (SEM), where due to the limited space within the microscope, a compact geometry of the charged particle filter is highly desirable. Examples of charged particle filters for microscopy applications are described in U.S. Pat. Nos. 9,697,984 and 9,837,242, each of which is hereby incorporated herein by reference in its entirety for all purposes.

[0006] In typical microscopy applications, the compact geometry includes a small field of view compatible with the small scan area (e.g., 1 mm×1 mm) associated with the microscopy application. However, such a small field of view is disadvantageous for use with other applications, e.g., in electron beam additive manufacturing (EBAM) applications implemented by so-called electron beam melting instruments or electron beam powder bed fusion instruments. EBAM instruments generally include a large scan area (e.g., 0.2 m×0.2 m). However, simply creating an oversized particle filter with a large field of view and large pores will not have sufficient submission strength to effectively prevent charged particles from reaching the detector. This is particularly problematic for EBAM applications because the charged particles in EBAM typically have an energy of 60 keV, which is twice the normal maximum of 30 keV in SEM.

[0007] Accordingly, there is a need for a charged particle filter having a wide field of view and sufficient field strength to effectively prevent charged particles from reaching the detector. Summary of the Invention

[0008] Systems, methods, and products are described herein for illustrative, non - limiting, embodiments to address these and other needs. Various alternatives, modifications, and equivalents are possible.

[0009] Embodiments of a charged particle filter are described that include a plurality of magnets, each of the plurality of magnets having a surface that is angularly inclined 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 embodiments, the inclined surface is positioned to form a hole that includes a magnetic field gradient that is strongest at a first aperture on the side of the hole that is closer to the detector.

[0010] According to an embodiment, the inclined surface can be substantially planar or substantially conical, where the radius of the substantially conical surface is related to the angle. Additionally, in some embodiments, the inclined surface includes an angle in the range of 5 - 45°, and more specifically can include an angle of 15.4°.

[0011] Furthermore, the hole can have a field of view on the platform that is defined by the diameter of a second aperture on the side of the hole that faces the platform. In some cases, the diameter of the field of view is about 128 mm. Additionally, the magnetic field gradient can include a magnetic field strength range of about 1000 Gauss - 5000 Gauss.

[0012] Additionally, in some cases, the charged particle filter can include one or more inserts configured to fill the space between the magnets. Similarly, in some cases, the charged particle filter can include a flux ring having a geometry that positions the magnets correctly for the inclination angle.

[0013] Embodiments of an electron beam additive manufacturing apparatus are also described that include: 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 that are released from the product in response to the electron beam; and a charged particle filter configured to deflect one or more charged particles released from the product in response to the electron beam away from the detector, where the charged particle filter includes a plurality of magnets, each of the plurality of magnets including a surface that is angularly inclined 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. Furthermore, the inclined surface is positioned to form a hole that includes a magnetic field gradient that is strongest at a first aperture on the side of the hole that is closer to the detector.

[0014] According to an embodiment, the inclined surface can be substantially planar or substantially conical, where the radius of the substantially conical surface is related to the angle. Additionally, in some embodiments, the inclined surface includes an angle in the range of 5 - 45°, and more specifically can include an angle of 15.4°.

[0015] In addition, the aperture can have a field of view on the platform, which is defined by the diameter of a second porosity on the side of the aperture facing the platform. In some cases, the diameter of the field of view is about 128 mm. Additionally, the magnetic field gradient can include a magnetic field strength range of about 1000 Gauss - 5000 Gauss.

[0016] Further, in some cases, the charged particle filter can include one or more inserts configured to fill the space between the magnets. Similarly, in some cases, the charged particle filter can include a magnetic flux ring having a geometry that positions the magnets correctly for the tilt angle.

[0017] The above - described examples and embodiments are not necessarily inclusive or exclusive of each other, and the examples and embodiments can be combined in any non - conflicting manner and with any other possibilities, regardless of whether they are presented in combination with the same or different examples or embodiments. The description of one example or embodiment is not intended to be restrictive with respect to other examples and / or embodiments. Additionally, in alternative embodiments, any one or more of the functions, steps, operations, or techniques described elsewhere in this specification can be combined with any one or more of the functions, steps, operations, or techniques described in the present disclosure. Accordingly, the above - described examples and embodiments are illustrative rather than restrictive. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and additional features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. In the drawings, the same reference numerals indicate the same structures, elements, or method steps, and the left - most digit of the reference numeral indicates the figure number in which the reference element first appears (e.g., element 110 first appears in Figure 1 ). However, all of these conventions are intended to be exemplary or illustrative, and not restrictive.

[0019] Figure 1 is a functional block diagram of an embodiment of an electron beam additive manufacturing instrument in communication with a computer;

[0020] Figure 2 is Figure 1 a simplified graphical representation of an embodiment of an electron beam additive manufacturing instrument having a charged particle filter;

[0021] Figure 3 is Figure 2Simplified graphical representation of an embodiment of a charged particle filter having multiple magnets;

[0022] Figure 4A is Figure 2 Simplified graphical representation of an embodiment of a charged particle filter having multiple magnets arranged to provide an angle of inclination;

[0023] Figure 4B is Figure 2 Simplified graphical representation of an embodiment of a charged particle filter, wherein each of the multiple magnets has a geometry that includes an angle of inclination;

[0024] Figure 5A is Figure 2 Simplified graphical representation of an embodiment of a charged particle filter having flux rings with the multiple magnets correctly positioned; and

[0025] Figure 5B is a charged particle filter having flux rings Figure 2 Simplified graphical representation of an embodiment of a charged particle filter, and the multiple magnets include a substantially conical surface that includes an angle of inclination within a bore.

[0026] Throughout several views of the drawings, like reference numerals refer to corresponding parts. Detailed Description

[0027] As will be described in more detail below, embodiments of the described invention include a charged particle filter that has a wide field of view and includes sufficient field strength to effectively prevent charged particles from reaching a detector. More specifically, the charged particle filter is configured with multiple magnets that have an inclined surface relative to a plane parallel to the particle travel, wherein the space between the magnets decreases from the side of the charged particle filter closest to the charged particle source to the side closest to the detector.

[0028] Figure 1 A simplified illustrative example of a user 101 capable of interacting with a computer 110 and an EBAM instrument 120 is provided. Embodiments of the EBAM instrument 120 may include a variety of commercially available EBAM instruments. For example, the EBAM instrument 120 may include a Q10 electron beam melting instrument available from Arcam AB (GE Additive). Figure 1 A network connection between the computer 110 and the EBAM instrument 120 is also shown. However, it should be understood that Figure 1For purposes of example, and may include additional or fewer network connections. In addition, network connections between components may include "direct" wired or wireless data transmission (e.g., represented by lightning bolts in the figures) and "indirect" communication via other devices (e.g., switches, routers, controllers, computers, etc.). Thus, the Figure 1 instances of should not be considered limiting.

[0029] Computer 110 may include any type of computing platform, such as a workstation, personal computer, tablet computer, "smartphone", one or more servers, a computing cluster (local or remote), or any other current or future computer or computer cluster. A computer typically includes well-known components such as one or more processors, an operating system, system memory, memory storage devices, an input-output controller, input-output devices, and a display device. It should also be understood that more than one implementation of computer 110 may be used to perform various operations in different embodiments, and thus Figure 1 the representation of computer 110 in should not be considered limiting.

[0030] In some embodiments, computer 110 may employ a computer program product including computer-usable media having control logic (e.g., a computer software program including program code) stored therein. 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, such as a hardware state machine. Implementing a hardware state machine to perform the functions described herein will be apparent to those skilled in the relevant art. And in the same or other embodiments, computer 110 may use an Internet client, which may include a specialized software application enabled to access remote information over a network. The network may include one or more of many different types of networks well known to those of ordinary skill in the art. For example, the network may include a local area network or a wide area network that communicates using a protocol commonly referred to as the TCP / IP protocol suite. The network may include the worldwide system of interconnected computer networks commonly referred to as the Internet, or may also include various intranet architectures. Those of ordinary skill in the relevant art will also understand that some users in a networked environment may prefer to use a so-called "firewall" (sometimes also referred to as a packet filter or border protection device) to control information traffic to and from 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 placed in position by a user (such as, for example, a network administrator, etc.).

[0031] As described herein, embodiments of the described invention include a charged particle filter having a plurality of magnets, which includes a wide field of view and includes sufficient field strength to effectively prevent charged particles from reaching a detector. In the described embodiments, the charged particle filter has a surface that is angularly inclined 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, wherein the inclined surface creates a field strength gradient, wherein the field strength is strongest in the region where the charged particle filter is closest to the detector.

[0032] Figure 2 A simplified illustrative example of an EBAM instrument 120 including a charged particle filter 210 and a detector 220 is provided. In some embodiments, the detector 220 may include a so-called silicon drift detector (SDD), or other types of detectors known in the prior art. Additionally, in some embodiments, the charged particle filter is positioned within a vacuum chamber 205, which includes a vacuum environment commonly used for electron beam additive manufacturing applications. Additionally, in the same or alternative embodiments, the detector 220 is positioned within an atmospheric chamber 207, which includes an environment that is substantially similar to the surrounding environment external to the EBAM instrument 120. For example, the charged particle filter 210 and the detector 220 may be positioned in different environments separated by an airtight partition (e.g., a “window”) that is transmissive to X-ray photons. In some embodiments, it is desirable for the partition to be thin to allow low-energy X-ray photons to pass through, and in some cases is supported by additional structures to provide rigidity. A typical partition used in EDS applications may be composed of a polymer-based material, beryllium (Be), or sodium (Na). However, any type of partition having the desired characteristics may be used. Additionally, in this example, in a typical electron beam additive manufacturing application, the electron beam 207 originates directly above the platform 230 (e.g., the electron beam 207 may be substantially perpendicular to the plane of the platform 230; however, it should be understood that the electron beam 207 constructs the product under the direction control of the computer 110 and may be oriented at an angle greater than vertical). Further, both the detector 220 and the charged particle filter 210 are positioned on one side of the vacuum chamber 205, with a direct line of sight to the platform 230, and both are inclined at an angle that depends on the distance from the origin location of the electron beam 207 to provide a detector field of view 233 to the region of the platform 230 where the electron beam 207 is used to construct the product. In many embodiments, the location of the detector 220 and the charged particle filter 210 is limited to the available ports on the vacuum chamber 205.

[0033] Figure 2Also shown is 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 the distance between the charged particle filter 210 and the platform 230, which is also related to the height distance of the electron beam 207, which is the distance between the top of the platform 230 (e.g., the support on which the EBAM 120 builds the product) and the top of the vacuum chamber 205. For example, the centerline 225 may include a distance of about 472 mm and the electron beam 207 may include a height distance of about 450 mm. However, it should be understood that the EBAM 120 may include a variety of configurations and sizes, so the dimensions in this example should not be considered limiting.

[0034] In addition, Figure 2 it is shown 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, where in some cases, it may be desirable for the detector field of view 233 not to be at the 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. Additionally, in some cases, the platform 230 may include an area with a diameter or width of about 200 mm, where embodiments of the platform 230 are substantially square or rectangular.

[0035] Figure 3 There is provided Figure 2 a simplified illustrative example of an enlarged view of the charged particle filter 210 and the detector 220. First, Figure 3 shown is an X-ray limiting aperture 305 that selectively limits the number of X-ray photons impinging 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 area excited by the electron beam 207, thereby reducing the detection of X-ray photons from other parts of the vacuum chamber 205 that may cause noise in the signal. Importantly, in the embodiments described, the charged particle filter 210 substantially reduces or eliminates the detection of charged particles from the entire area of the maximum field of view 235, which may be a source of noise in the detected signal.

[0036] In some embodiments, the X-ray limiting aperture 305 may also reduce the number of photons striking the detector 220, which has the benefit of reducing the likelihood of saturating or damaging the components of the detector 220. Additionally, it should be understood that some embodiments of the EBAM instrument 120 may allow the user to vary the size of the X-ray limiting aperture 305, such that different volumes of the detector field of view 233 can be utilized.

[0037] Figure 3 A plurality of magnets 310 are further shown, each having a surface that is angularly inclined relative to the centerline 225, where the inclined surface defines an aperture 313 through which X-ray photons pass. The magnets 310 may comprise any type of magnet commonly used in the art, such as neodymium or other types of magnets having the desired properties. For example, permanent magnets composed of materials having various grades of SmCo and a predominant grade of NdFe may be employed.

[0038] In Figure 3 the embodiment of, the magnet 310 is substantially rectangular with substantially parallel surfaces, where the angle of inclination 315 is substantially the same as the angle of inclination of the surface of the aperture 313. In Figure 3 the example of, the angle of inclination is equal to approximately 15.4°, however, angles of inclination within the range of 5 - 45° are considered to be within the scope of the present invention.

[0039] In the described embodiments, the position of the magnet 310 defines the region of the maximum field of view 235, and more specifically, a particular portion of the magnet 310 defines the region of the maximum field of view 235 according to the degree of the angle of inclination. For example, for an angle of inclination of approximately 15.4° as Figure 3 shown, each magnet 310 within the aperture 313 defines the region of the maximum field of view 235 at the corner (e.g., where X-ray photons and charged particles originate) at the second aperture 317 facing the platform 230. Alternatively, for small angles of inclination (e.g., < 10°), each magnet 310 within the aperture 313 defines the region of the maximum field of view 235 at the corner at the first aperture 315 near the detector 220.

[0040] In Figure 3 the example of, the maximum field of view 235 is 36.4°, however, the maximum field of view may encompass fields of view within the range of 10 - 90°. Additionally, due to the angles of inclination of the detector 220 and the charged particle filter 210 (as described above), the centerline 225 interacts with the platform 230 at a platform incident angle 337, which may encompass an angle of 72.4°. Further, due to the angles of inclination of the detector 220 and the charged particle filter 210, the angles measured from the centerline 225, namely angle 333 (e.g., 7.7°) and angle 335 (e.g., 7.1°), are slightly different. Additionally, those of ordinary skill in the art will understand that Figure 3The example of shows a symmetric configuration with similar slope values for the two magnets 310, which results in different field of view angles 333 and 335. However, if it is desired that angles 333 and 335 be similar (or any other value), this can be achieved by means of magnets 310 independently having an inclined configuration including an asymmetric design (e.g., each magnet 310 has a different inclination angle from the others).

[0041] Figure 3 Also shown is a magnetic field 320 including a gradient that is strongest at a first pore 315 on the side of the aperture 313 near the detector 220 and weakest at a second pore 317 on the side of the aperture 313 facing the platform 230 (e.g., as indicated by the thickness of the arrows in the Figure 3 magnetic field strength shown). In the described embodiment, the spacing between the magnets 310 defines the pore 315, or in certain embodiments, it defines the diameter of the applied pore 315. Those of ordinary skill in the art will understand that the magnetic field strength is proportional to the strength of the magnets 310 and the distance between them. Additionally, the magnetic field 320 must contain sufficient field strength to effectively deflect charged particles. However, the field strength should not be so strong that it affects the electron beam 207 or significantly affects the operation of the detector 220, because if the field strength is too high, the charged particles migrating inside the detector 220 may be affected by the magnetic field 320. For example, the magnetic field 320 may include a magnetic field strength gradient in the range of about 1000 Gauss - 5000 Gauss (e.g., from the second pore 317 to the first pore 315). However, it should be understood that the field strength depends on various factors, such as the grade of the material used for the magnets 310, and thus the examples should not be considered restrictive.

[0042] Figure 4A A simplified graphical example of a substantially rectangular configuration of the magnets 310 is provided, where each embodiment of the magnets 310 is inclined to provide an inclination angle, as described above. However, it should be understood that other configurations are also considered within the scope of the described invention. One such example is shown in Figure 4B as the magnet 410, which includes a geometry having an inclination angle incorporated into the configuration. For example, the magnet 410 does not need to be configured in a specific position within the charged particle filter 210. Instead, the magnet 410 can be designed to fit into any position, thereby allowing freedom in the design of the charged particles 210. Additionally, as shown in Figure 4B , the magnet 410 is substantially thicker (e.g., wider) at the first pore 315 and thus has a greater magnetic field strength compared to at the second pore 317 where it has a smaller thickness.

[0043] Figure 5A A cross - sectional view (e.g., about half) of an embodiment of the charged particle filter 210 including the magnets 310 as described above is shown. Figure 5AThe flux ring 503 is also shown, which includes a geometry for correctly positioning the magnet 310 for the desired tilt angle. In some embodiments, the flux ring 503 may be constructed of steel or other desired materials. For example, the flux ring 503 may be constructed of any suitable ferromagnetic permeable material, which may vary depending on spatial availability, the location of other sensitive items affected by the magnetic field 320, or other factors. In this example, the specific material may include sintered cobalt (250) or mild steel (2,000), but various special grades of steel may be used.

[0044] In addition, Figure 5A An insert 507 is shown that fills the space between the magnets 310 but does not interfere with the insertion of the holes 313 or the pores 315 and 317. In some embodiments, the charged particle filter 210 may include various embodiments 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. Generally, the material used for the insert 510 should include light elements to minimize X-ray generation, such as aluminum or carbon.

[0045] Figure 5B A cross-sectional view (e.g., approximately half) of another embodiment of the charged particle filter 210 including a magnet 510 is shown, the magnet including a curved geometry of a surface including a tilt angle. In the described embodiment, a plurality of magnets form a substantially conical surface with a tilt angle in the hole 313. Figure 5B The illustrated embodiment may or may not include an insert element similar to the insert 507 described for Figure 5A and a flux ring 513 having a geometry for correctly positioning the magnet 510.

[0046] Various embodiments and implementations have been described. It should be apparent to those skilled in the relevant art that the foregoing is illustrative only and not restrictive, and has been presented by way of example only. Many other schemes for distributing functions among the various functional elements of the illustrated embodiments are possible. The function of any element may be implemented in various ways in alternative embodiments.

Claims

1. A charged particle filter, comprising: a plurality of magnets, each including a surface that is angularly inclined relative to a centerline from the center of the field of view on the detector to the center of the field of view on the platform, wherein the inclined surface is positioned to form a hole including a magnetic field gradient that is strongest at a first pore on the side of the hole closer to the detector and weakest at a second pore on the side of the hole facing the platform, and wherein the spacing between the magnets decreases from the side of the charged particle filter closest to the platform to the side closest to the detector.

2. The charged particle filter according to claim 1, wherein: the inclined surface is substantially planar.

3. The charged particle filter according to claim 1, wherein: the inclined surface is substantially conical.

4. The charged particle filter according to claim 3, wherein: the radius of the substantially conical surface is related to the angle.

5. The charged particle filter according to claim 1, wherein: the inclined surface includes an angle in the range of 5 to 45°.

6. The charged particle filter according to claim 5, wherein: the inclined surface includes an angle of 15.4°.

7. The charged particle filter according to claim 1, wherein: the hole includes a field of view on the platform, the field of view being defined by the diameter of the second pore on the side of the hole facing the platform.

8. The charged particle filter according to claim 7, wherein: the diameter of the field of view is about 128 mm.

9. The charged particle filter according to claim 1, wherein: the magnetic field gradient includes a magnetic field change of about 1000 gauss to 5000 gauss.

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

11. The charged particle filter according to claim 1, further comprising: a flux ring including a geometry for correctly positioning the magnets for the tilt angle.

12. 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 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 that are released from the product in response to the electron beam; and a charged particle filter configured to deflect one or more charged particles released from the product in response to the electron beam away from the detector, wherein the charged particle filter includes a plurality of magnets, each of the plurality of magnets including a surface that is angularly inclined relative to a centerline from the center of the field of view on the detector to the center of the field of view on the platform, wherein the inclined surface is positioned to form a hole including a magnetic field gradient that is strongest at a first pore on the side of the hole closer to the detector and weakest at a second pore on the side of the hole facing the platform, and Wherein, the spacing between the magnets decreases from the side of the charged particle filter closest to the platform to the side closest to the detector.

13. The electron beam additive manufacturing apparatus according to claim 12, wherein: The inclined surface is substantially planar.

14. The electron beam additive manufacturing apparatus according to claim 12, wherein: The inclined surface is substantially conical.

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

16. The electron beam additive manufacturing apparatus according to claim 12, wherein: The inclined surface includes an angle in the range of 5 to 45°.

17. The electron beam additive manufacturing apparatus according to claim 16, wherein: The inclined surface includes an angle of 15.4°.

18. The electron beam additive manufacturing apparatus according to claim 12, wherein: The hole includes a field of view on the platform, and the field of view is defined by the diameter of the second porosity on the side of the hole facing the platform.

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

20. The electron beam additive manufacturing apparatus according to claim 12, wherein: The magnetic field gradient includes a magnetic field change of about 1000 gauss to 5000 gauss.

21. The electron beam additive manufacturing apparatus according to claim 12, further comprising: One or more inserts configured into the filling space between the magnets.

22. The electron beam additive manufacturing apparatus according to claim 12, further comprising: A magnetic flux ring including a geometry for correctly positioning the magnets for the tilt angle.

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