Dose cup assembly for an ion implanter

Abstract

A dose cup assembly is disclosed that provides particle reduction within a process chamber. The dose cup assembly includes a faceplate having an opening attached to a rear wall of the process chamber, an aperture plate defining a plurality of slots, and a tunnel having a wall and a sidewall and having a proximal end and a distal end, the tunnel being disposed between the faceplate and the aperture plate such that the proximal end is adjacent to the faceplate and the distal end is adjacent to the aperture plate. At least one of the faceplate, wall, sidewall, or aperture plate has one or more exposed outer surfaces comprising silicon. The exposed outer surfaces may be silicon. In some embodiments, the faceplate, wall, sidewall, or aperture plate may be graphite, aluminum, or stainless steel coated with silicon or silicon carbide.

Description

[Technical Field]

[0001] This application claims priority to U.S. patent application Ser. No. 18 / 101,260, filed Jan. 25, 2023, the entire disclosure of which is incorporated by reference.

[0002] This disclosure describes embodiments of a dose cup assembly used in an ion implanter to measure ion beam current. [Background technology]

[0003] Semiconductor devices are manufactured using several processes, some of which involve implanting ions into a workpiece. Some implanters have the capability to monitor an ion beam as it is directed toward the workpiece. The incident ion beam is typically very narrow in height but has a width greater than the diameter of the workpiece. This width can be achieved using a ribbon ion beam or by scanning a spot ion beam.

[0004] To monitor this incident ion beam, one or more current sensors (which may be Faraday cups or different sensors) may be placed within the process chamber. Such current sensors may be positioned so that the ion beam strikes the current sensor when the workpiece is not in its operating position. The current sensors may then be used to measure the incident beam current as a function of widthwise position. In some embodiments, there are multiple widthwise positioned current sensors. In other embodiments, a single width-translatable current sensor is used.

[0005] A structure called a dose cup assembly is used to align and direct the ion beam toward the current sensor. Due to the location of the current sensor, the dose cup assembly, which protects the current sensor, is exposed to the ion beam. This exposure can cause a film to form on the dose cup assembly, which can interfere with the operation of the current sensor. This film is brittle and can easily crack. As a result, cracking of this film can result in the formation of particles within the process chamber. Such particles can increase the frequency of preventive maintenance (PM) routines, reducing the overall throughput of the ion implanter.

[0006] Therefore, it would be beneficial to have a dose cup assembly that is more resistant to this film buildup, or if exposure of the dose cup assembly to the ion beam results in the formation of a different type of film that is less susceptible to cracking. Summary of the Invention

[0007] An ion implanter is disclosed that includes an ion source for generating an ion beam, a platen disposed within a process chamber for supporting a workpiece to be treated with the ion beam, and a dose cup assembly for reducing particles within the process chamber. The dose cup assembly includes a faceplate attached to a rear wall of the process chamber and defining an opening, an aperture plate defining a plurality of slots, and a tunnel having a wall and a sidewall and having a proximal end and a distal end, the tunnel being disposed between the faceplate and the aperture plate such that the proximal end is adjacent to the faceplate and the distal end is adjacent to the aperture plate. One or more current sensors are disposed behind the plurality of slots in the aperture plate such that the ion beam passes through the plurality of slots to the one or more current sensors. At least one of the faceplate, the wall, the sidewall, or the aperture plate has one or more exposed outer surfaces comprising silicon. The exposed outer surfaces may be silicon. In some embodiments, the faceplate, walls, sidewalls, or aperture plate may be graphite, aluminum, or stainless steel coated with silicon or silicon carbide. In some embodiments, the faceplate, walls, sidewalls, and aperture plate all have one or more exposed outer surfaces comprising silicon. In some embodiments, the one or more exposed outer surfaces comprise silicon. In some embodiments, the one or more exposed outer surfaces comprise a coating of silicon or silicon carbide. In certain embodiments, the substrate underlying the coating comprises graphite, aluminum, or stainless steel. In some embodiments, the walls of the tunnel are parallel to one another and are made of silicon or coated with silicon or silicon carbide. In some embodiments, the spacing between the tunnel walls is wider at the proximal end than at the distal end, such that the spacing tapers inward toward the aperture plate.In some embodiments, the spacing between the tunnel sidewalls is narrower at the proximal end than at the distal end such that the spacing tapers outward toward the aperture plate. In some embodiments, the aperture plate comprises an anterior support member and a slotted posterior member, the anterior support member being made of silicon or coated with silicon or silicon carbide. In certain embodiments, the anterior support member and the slotted posterior member are permanently bonded. In certain embodiments, the anterior support member and the slotted posterior member are mechanically joined.

[0008] In another embodiment, a dose cup assembly configured to be disposed within a process chamber of an ion implanter is disclosed. The dose cup assembly includes: a faceplate configured to be attached to a rear wall of the process chamber of the ion implanter, the faceplate defining an aperture; an aperture plate defining a plurality of slots; and a tunnel having a wall and a sidewall and having a proximal end and a distal end, the tunnel being disposed between the faceplate and the aperture plate such that the proximal end is adjacent to the faceplate and the distal end is adjacent to the aperture plate. At least one of the faceplate, the wall, the sidewall, or the aperture plate has one or more exposed outer surfaces comprising silicon. In some embodiments, all of the faceplate, the wall, the sidewall, and the aperture plate have one or more exposed outer surfaces comprising silicon. In some embodiments, the one or more exposed outer surfaces comprise silicon. In some embodiments, the one or more exposed outer surfaces comprise a coating of silicon or silicon carbide. In certain embodiments, a substrate underlying the coating comprises graphite, aluminum, or stainless steel. In some embodiments, the spacing between the tunnel walls is wider at the proximal end than at the distal end, tapering inward as one progresses toward the aperture plate. In some embodiments, the spacing between the tunnel sidewalls is narrower at the proximal end than at the distal end, tapering outward as one progresses toward the aperture plate. In some embodiments, the aperture plate comprises a front support member and a slotted rear member, the front support member being made of silicon or coated with silicon or silicon carbide. In certain embodiments, the front support member and the slotted rear member are permanently bonded. In certain embodiments, the front support member and the slotted rear member are mechanically joined.

[0009] According to another embodiment, a system for measuring beam current of an ion beam is disclosed, comprising the dose cup assembly described above and one or more current sensors positioned behind a plurality of slots in the aperture plate, the ion beam adapted to pass through the plurality of slots to the one or more current sensors.

[0010] For a better understanding of the present disclosure, reference is made to the accompanying drawings, in which like elements are designated with like reference numerals and in which: [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram of an ion implanter using a dose cup assembly according to one embodiment. [Figure 2] FIG. 1 is a block diagram of a process chamber with a dose cup assembly and a current sensor. [Figure 3A] 1 shows the dose cup assembly. [Figure 3B] 1 shows the components that make up the dose cup assembly. [Figure 4] 1 illustrates an aperture plate used as part of a dose cup assembly, according to one embodiment. [Figure 5A] 1 illustrates one embodiment of a tunnel used as part of a dose cup assembly. [Figure 5B] 1 illustrates one embodiment of a tunnel used as part of a dose cup assembly. DETAILED DESCRIPTION OF THE INVENTION

[0012] FIG. 1 illustrates an ion implanter including a process chamber 100 and a dose cup assembly 10. An ion source 200 is used to generate an ion beam 250. The ion source 200 may be an indirectly heated cathode (IHC) ion source. Alternatively, the ion source 200 may be a capacitively coupled plasma source, an inductively coupled plasma source, a Bernas source, or another source. Thus, the type of ion source is not limited by this disclosure. Extraction optics 205, which may include one or more electrodes, are positioned near the exterior of the extraction aperture of the ion source 200.

[0013] Downstream of the extraction optics 205 is a mass analyzer 210. The mass analyzer 210 uses a magnetic field to guide the path of the extracted ion beam. The magnetic field affects the flight path of ions depending on their mass and charge. At the output (i.e., distal end) of the mass analyzer 210 is a mass resolving device 220 having a resolving aperture 221. By appropriately selecting the magnetic field, only ions of the ion beam 250 having a selected mass and charge will be directed through the resolving aperture 221. Other ions will collide with the walls of the mass resolving device 220 or mass analyzer 210 and will not progress further in the system.

[0014] A collimator 230 may be positioned downstream of the mass resolving device 220. The collimator 230 receives ions from the ion beam 250 that has passed through the resolving aperture 221 and generates an ion beam. The ion beam is formed of multiple parallel or nearly parallel beamlets. The output (i.e., distal end) of the mass analyzer 210 and the input (i.e., proximal end) of the collimator 230 may be positioned at a fixed distance. The mass resolving device 220 is positioned in the space between these two components.

[0015] An acceleration / deceleration stage 240 may be positioned downstream of the collimator 230. The acceleration / deceleration stage 240 is a beamline lens component configured to individually control the deflection, deceleration, and focusing of the ion beam. For example, the acceleration / deceleration stage 240 may be an electrostatic filter (EF). The ion beam 250 exits the acceleration / deceleration stage 240 and enters the process chamber 100.

[0016] The process chamber 100 includes a platen 110 on which a workpiece 112 may be disposed. When in an operating position, an ion beam 250 impinges on the workpiece 112. Additionally, a dose cup assembly 10 is disposed on a rear wall 101 of the process chamber 100. One or more current sensors 120 may be disposed behind the dose cup assembly 10.

[0017] Controller 280 may be in communication with one or more of the power supplies so that the voltage or current provided by such power supplies may be monitored and / or modified. Controller 280 may include a processing unit (such as a microcontroller, a personal computer, a dedicated controller, or another suitable processing unit). Controller 280 may also include non-transitory storage elements (such as semiconductor memory, magnetic memory, or another suitable memory). This non-transitory storage element may contain instructions and other data that enable controller 280 to perform the functions described herein.

[0018] In certain embodiments, the ion source 200 may generate a ribbon beam that travels through the above-described components. Of course, other ion implanters may be utilized. For example, an ion implanter may generate a scanned ion beam rather than a ribbon ion beam. Such an ion implanter includes an ion source that generates a spot beam. This type of ion implanter also includes the mass analyzer and mass resolving device described above. In addition, a scanner (which may be an electrostatic scanner or another type of scanner) is used to generate the scanned ion beam. The scanned ion beam may pass through an angle corrector. The angle corrector is designed to deflect ions in the scanned ion beam to generate an ion beam with parallel ion trajectories, thereby focusing the scanned ion beam. Specifically, the angle corrector is used to change diverging ion trajectory paths into a substantially parallel path for the ion beam 250. In some embodiments, the angle corrector may include magnetic pole pieces spaced apart to define a gap and magnet coils coupled to a power supply. The scanned ion beam passes through a gap between the pole pieces and is deflected according to the magnetic field within the gap. In another embodiment, the angle corrector can be an electrostatic lens (sometimes referred to as a collimating lens).

[0019] FIG. 2 shows the process chamber 100 of FIG. 1 in more detail. The process chamber 100 includes one or more current sensors 120. A dose cup assembly 10 is positioned between the incident ion beam 250 and the current sensor 120. A platen 110 is also positioned within the process chamber 100. The platen 110 may be an electrostatic platen used to clamp and hold a workpiece 112 while the ion beam 250 is directed into the process chamber 100. In some embodiments, the platen 110 may be raised and lowered in a Y direction 118 via movement of a shaft 115. Additionally, the platen 110 may rotate about an X axis 111. In certain embodiments, the platen 110 may be rotated 90° so that the clamping surface of the platen 110 is horizontal, allowing the workpiece 112 to be placed on the platen 110. The platen 110 then rotates to the operating position (i.e., implantation position) shown in FIG. 2.

[0020] To monitor the ion beam 250, the platen 110 is lowered by actuating the shaft 115 in the Y direction 118. This movement moves the platen 110 out of the path of the ion beam 250. Therefore, the ion beam 250 is unobstructed as it travels toward the current sensor 120. As described in more detail below, the dose cup assembly 10 is used to guide and align the ion beam 250 with the current sensor 120.

[0021] FIG. 3A shows a diagram of the dose cup assembly 10 used in the process chamber 100 of FIG. 2. FIG. 3B shows an exploded view of the dose cup assembly 10, illustrating the individual components. The dose cup assembly 10 includes a faceplate 20. As visible in FIG. 2, the faceplate 20 is attached to the rear wall 101 of the process chamber 100 and covers the gap between the rear wall 101 and the tunnel 30. The faceplate 20 defines an opening 21 that allows ions to pass through to the current sensor 120.

[0022] The tunnels 30 extend rearward from the faceplate 20. The term "rearward" refers to a direction along the direction of the ion beam 250, further away from the source of the ion beam 250. In some embodiments, the proximal ends 31 of the tunnels 30 abut the back surface 22 of the faceplate 20. In other embodiments, there may be a gap between the proximal ends 31 of the tunnels 30 and the back surface 22 of the faceplate 20.

[0023] An aperture plate 40 is coupled to the tunnel 30. The aperture plate 40 defines a plurality of slots 41 through which ions may pass. In some embodiments, the slots 41 may be between 2 and 6 inches high and between 1 / 16 and 1 / 4 inch wide. A bracket 35 may be used to secure the tunnel 30 to the aperture plate 40. In some embodiments, the aperture plate 40 abuts the distal end 32 of the tunnel 30. In other embodiments, a gap may exist between the aperture plate 40 and the distal end 32. In one embodiment, seven current sensors 120 are positioned behind seven corresponding slots 41. Of course, other numbers of slots and current sensors may be utilized. In another embodiment, one current sensor 120 that translates across the width of the ion beam 250 is used to collect current from each slot 41.

[0024] Thus, tunnel 30 is disposed between faceplate 20 and aperture plate 40, with proximal end 31 of tunnel 30 adjacent rear surface 22 of faceplate 20 and distal end 32 of tunnel adjacent aperture plate 40. In some embodiments, proximal end 31 may contact or be attached to rear surface 22 of faceplate 20. In some embodiments, distal end 32 may be in partial contact with aperture plate 40. In some embodiments, tunnel 30 is attached to aperture plate 40 using bracket 35.

[0025] Each component is described in more detail below. The aperture plate 40 may be between 0.25 and 0.75 inches thick and, in some embodiments, may be made from a single piece of silicon. This single piece of silicon may be crystalline silicon or polysilicon. In other embodiments, the aperture plate 40 may be constructed from graphite, aluminum, or stainless steel, which is then coated with silicon or silicon carbide. This coating may be between 50 and 100 μm thick.

[0026] In another embodiment, shown in FIG. 4, the aperture plate 40 is made of multiple pieces. The front support member 42 includes an opening 43 that is wider and longer than the slot 41 so as not to obstruct the slot 41. This front support member 42 is used to provide structural integrity. The slotted rear member 44 includes the slot 41. The combined thickness of the front support member 42 and the slotted rear member 44 can be between 0.25 and 0.75 inches. In one embodiment, the rear surface of the front support member 42 is permanently bonded to the front surface of the slotted rear member 44. This can be achieved using indium bonding. In another embodiment, the two components are mechanically joined using fasteners. In some embodiments, the front support member 42 and the slotted rear member 44 can be made of silicon (which can be crystalline silicon or polysilicon). Alternatively, these components can be made of silicon- or silicon carbide-coated graphite, aluminum, or stainless steel, as described above. In another embodiment, the front support member 42 is made of silicon or coated with silicon or silicon carbide, while the slotted rear member 44 is graphite.

[0027] In one embodiment, the tunnel 30 shown in FIG. 3B includes a set of parallel walls 33a, 33b. The tunnel 30 also includes a set of parallel sidewalls 34a, 34b. The walls 33a, 33b and sidewalls 34a, 34b extend from the proximal end 31 to the distal end 32 over a distance of between 4 and 8 inches. The walls 33a, 33b may have a width dimension of between 12 and 17 inches. The sidewalls 34a, 34b may have a height dimension of between 2 and 6 inches. The thickness of the walls and sidewalls may be approximately 1 inch. In certain embodiments, the walls 33a, 33b and sidewalls 34a, 34b are fabricated from silicon, which may be crystalline silicon or polysilicon. In other embodiments, the walls 33a, 33b and side walls 34a, 34b may be made of silicon or silicon carbide coated graphite, aluminum, or stainless steel, as described above.

[0028] Other embodiments are possible. Figure 5A shows a second embodiment of tunnel 30 in which walls 33a and 33b are closer to each other at distal end 32 than at proximal end 31. In other words, the walls 33a, 33b taper inward as they advance toward the aperture plate 40. In certain embodiments, the side walls 34a, 34b also taper inward as they advance toward the aperture plate 40. In some embodiments, the spacing between the walls 33a, 33b at the proximal end 31 is at least 1 inch wider than the spacing between the walls 33a, 33b at the distal end 32. In some embodiments, the spacing between the walls 33a, 33b at the proximal end 31 can be more than 2 inches wider than the spacing at the distal end 32. Similarly, in some embodiments, the spacing between the side walls 34a, 34b at the proximal end 31 is at least 1 inch wider than the spacing between the side walls 34a, 34b at the distal end 32. In some embodiments, the spacing between the side walls 34a, 34b at the proximal end 31 can be more than 3 inches wider than the spacing at the distal end 32.

[0029] 5B shows a third embodiment of tunnel 30 in which side walls 34a, 34b are spaced farther apart at distal end 32 than at proximal end 31. In other words, side walls 34a, 34b taper outward as they progress toward aperture plate 40. In some embodiments, the spacing between side walls 34a, 34b at proximal end 31 is at least 1 inch narrower than the spacing between side walls 34a, 34b at distal end 32. In some embodiments, the spacing between side walls 34a, 34b at proximal end 31 can be at least 3 inches narrower than the spacing at distal end 32.

[0030] 3B and 5A-5B, the walls 33a, 33b and sidewalls 34a, 34b may be made of silicon (which may be crystalline silicon or polysilicon). Alternatively, the walls 33a, 33b and sidewalls 34a, 34b may be made of silicon or silicon carbide coated graphite, aluminum, or stainless steel, as described above.

[0031] In summary, the dose cup assembly includes a faceplate 20. As described above, the faceplate 20 defines an opening 21. This opening is sized at the proximal end 31 to be approximately the same dimension as the periphery formed by the walls 33a, 33b and sidewalls 34a, 34b. This aligns the opening 21 with the proximal end of the tunnel 30. Therefore, the size of the opening 21 may vary depending on which embodiment of the tunnel 30 is used. The thickness of the faceplate 20 may be between 0.25 and 1 inch. The faceplate 20 may be constructed of silicon (which may be crystalline silicon or polysilicon). In other embodiments, the faceplate 20 may be coated with silicon or silicon carbide. In these embodiments, the faceplate may be graphite or a metal (such as aluminum or stainless steel).

[0032] Thus, in some embodiments, at least one of the components comprising the dose cup assembly has one or more exposed exterior surfaces comprising silicon. Such exposed exterior surfaces may be pure silicon or silicon-containing compounds (such as silicon carbide). In some embodiments, the exposed exterior surface is a silicon or silicon carbide coating, with an underlying substrate being graphite, aluminum, or stainless steel. In some embodiments, all of the above components comprising the dose cup assembly have one or more exposed exterior surfaces comprising silicon.

[0033] The systems and methods herein have numerous advantages. In certain current configurations, ion beam species can interact with materials used to form the components that make up the dose cup assembly. For example, boron ions can interact with graphite components to form a boron carbide film. This film can crack and form particles. The formation of this boron carbide film can be reduced or minimized by redesigning one or more of the components of the dose cup assembly to have an outer surface that includes silicon.

[0034] Additionally, varying the geometry of the tunnel 30 can have additional benefits. When the walls are parallel to one another, low-energy ion beams (such as boron or phosphorus) can strike these walls at a glancing angle, creating a buildup that can flake off. Varying the geometry of the tunnel 30 can address this issue. For example, if the tunnel 30 tapers outward as it advances toward the aperture plate 40, fewer ions can strike the walls 33 a, 33 b and sidewalls 34 a, 34 b. Fewer ions strike the walls and sidewalls of the tunnel 30, reducing the likelihood of unwanted film buildup. Alternatively, if the tunnel 30 tapers inward as it advances toward the aperture plate 40, the angle at which ions strike the walls and sidewalls increases. This increased angle of incidence allows ions to more easily sputter material from the walls, reducing the likelihood of unwanted film buildup.

[0035] The present disclosure is not limited in scope by the specific embodiments described herein. Indeed, various other embodiments and modifications thereto, in addition to the embodiments of the present disclosure described herein, will be apparent to those skilled in the art from the foregoing description and accompanying drawings. Accordingly, such other embodiments and modifications are intended to be included within the scope of the present disclosure. Moreover, while the present disclosure is described herein in the context of particular implementations in particular environments for particular purposes, those skilled in the art will recognize that the utility of the present disclosure is not limited to such contexts, and that the present disclosure may be beneficially implemented in several environments for several purposes. Accordingly, the claims set forth below should be construed in light of the full scope and nature of the present disclosure as described herein.

Claims

1. 1. An ion implantation apparatus comprising: an ion source for generating an ion beam; a platen positioned within a process chamber of the ion implanter for supporting a workpiece to be treated with the ion beam; 1. A dose cup assembly comprising: a faceplate attached to a rear wall of the process chamber of the ion implanter, the faceplate defining an opening; an aperture plate defining a plurality of slots; a dose cup assembly comprising: a tunnel having a wall and a sidewall and having a proximal end and a distal end, the tunnel being positioned between the faceplate and the aperture plate such that the proximal end is adjacent the faceplate and the distal end is adjacent the aperture plate; one or more current sensors positioned behind the plurality of slots in the aperture plate, the ion beam passing through the plurality of slots to the one or more current sensors; Equipped with at least one of the faceplate, the wall, the sidewall, or the aperture plate has one or more exposed outer surfaces comprising silicon; Ion implantation equipment.

2. 10. The ion implanter of claim 1, wherein the faceplate, the wall, the sidewall, and the aperture plate all have one or more exposed outer surfaces comprising silicon.

3. The ion implanter of claim 1 , wherein the one or more exposed exterior surfaces comprise silicon.

4. 10. The ion implanter of claim 1, wherein the one or more exposed exterior surfaces comprises a coating of silicon or silicon carbide.

5. 5. The ion implanter of claim 4, wherein the substrate underlying the coating comprises graphite, aluminum, or stainless steel.

6. 2. The ion implanter of claim 1, wherein the walls of the tunnel are parallel to one another and are made of silicon or coated with silicon or silicon carbide.

7. 2. The ion implanter of claim 1, wherein the spacing between the walls of the tunnel is wider at the proximal end than at the distal end so as to taper inwardly toward the aperture plate.

8. 2. The ion implanter of claim 1, wherein the spacing between the sidewalls of the tunnels is narrower at the proximal end than at the distal end such that the spacing tapers outwardly toward the aperture plate.

9. 10. The ion implanter of claim 1, wherein the aperture plate comprises a front support member and a slotted rear member, the front support member being made of silicon or coated with silicon or silicon carbide.

10. 10. The ion implanter of claim 9, wherein said front support member and said slotted rear member are permanently bonded together.

11. 10. The ion implanter of claim 9, wherein said front support member and said slotted rear member are mechanically joined.

12. 1. A dose cup assembly configured to be disposed within a process chamber of an ion implanter, comprising: a faceplate configured to be attached to a rear wall of the process chamber of the ion implanter, the faceplate defining an opening; an aperture plate defining a plurality of slots; a tunnel having a wall and a sidewall and having a proximal end and a distal end, the tunnel being positioned between the faceplate and the aperture plate such that the proximal end is adjacent to the faceplate and the distal end is adjacent to the aperture plate; Equipped with at least one of the faceplate, the wall, the sidewall, or the aperture plate has one or more exposed outer surfaces comprising silicon; Dose cup assembly.

13. 13. The dose cup assembly of claim 12, wherein the faceplate, the wall, the sidewall, and the aperture plate all have one or more exposed outer surfaces comprising silicon.

14. The dose cup assembly of claim 12 , wherein the one or more exposed outer surfaces comprise silicon.

15. 13. The dose cup assembly of claim 12, wherein the one or more exposed exterior surfaces comprises a coating of silicon or silicon carbide.

16. 16. The dose cup assembly of claim 15, wherein a substrate underlying the coating comprises graphite, aluminum, or stainless steel.

17. 13. The dose cup assembly of claim 12, wherein the spacing between the walls of the tunnel is wider at the proximal end than at the distal end such that the spacing tapers inwardly toward the aperture plate.

18. 13. The dose cup assembly of claim 12, wherein the spacing between the side walls of the tunnel is narrower at the proximal end than at the distal end such that the spacing tapers outwardly toward the aperture plate.

19. 13. The dose cup assembly of claim 12, wherein the aperture plate comprises a front support member and a slotted rear member, the front support member being made of silicon or coated with silicon or silicon carbide.

20. 1. A system for measuring beam current of an ion beam, comprising: A dose cup assembly according to claim 12; one or more current sensors positioned behind the plurality of slots in the aperture plate; Equipped with the ion beam is adapted to pass through the plurality of slots to the one or more current sensors; system.

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