Beam profile monitor

Abstract

A one dimensional projection spectrum of the beam is acquired over the circumferential direction of the beam.SOLUTION: The beam profile monitor 1 comprises a wire probe 2 which emits secondary electrons when it is hit by a beam B, a beam intensity measuring sensor 7 which measures the intensity of the beam by detecting the secondary electrons, and a rotating means which rotates the wire probe 2 in an autorotation mode so that the wire probe 2 crosses the beam. A two axis gimbal mechanism 3 configured to further rotate the wire probe 2 in a revolution manner along a circumferential direction of the beam, and a one dimensional projection spectrum acquisition unit 8 configured to acquire a one dimensional projection spectrum for each rotation angle in the revolution manner when the wire probe 2 traverses the beam, the one dimensional projection spectrum being measured by the beam intensity measurement sensor when the wire probe 2 traverses the beam by rotation in the rotation manner, the one dimensional projection spectrum indicating an intensity of the beam with respect to a traverse position in the beam.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wire-type beam profile monitor that makes it possible to acquire a one-dimensional projection spectrum of a beam over the circumferential direction of the beam. [Background technology]

[0002] Beam profile monitor technology that uses a wire to obtain the beam profile is known, and examples of such technology include those described in Patent Documents 1 and 2 below. The beam profile monitor described in Patent Document 1 comprises a bar 16 and wires (17 and 18 in FIG. 2(a)) attached to both ends of the bar 16 or two wires (17 and 19 in FIG. 3(a)) attached to one end of the bar 16, and the bar 16 is controlled to rotate around an axis 15 inclined at 45 degrees with respect to a plane (XY) perpendicular to the beam direction (Z). According to Prior Art 1, at positions z1 and z2 in the beam direction (Z), a vertical beam profile and a horizontal beam profile can be obtained as shown in FIG. 2(b) or FIG. 3(B).

[0003] The beam profile monitor described in Patent Document 2 includes a conductive probe 10A extending along the y-axis direction and a conductive probe 10B extending along the x-axis direction, and the conductive probe 10A is scanned in the x-direction relative to a bunch B of a charged particle beam to obtain a beam profile in the x-direction, and the conductive probe 10B is scanned in the y-direction to obtain a beam profile in the y-direction.

[0004] However, both of the beam profile monitors described in Patent Documents 1 and 2 obtain one-dimensional projection spectra of a beam along a fixed scanning direction, and do not have a configuration capable of obtaining one-dimensional projection spectra of a beam over the entire 360-degree circumferential direction of the beam. Therefore, it has been difficult to construct a two-dimensional profile image of a beam from one-dimensional projection spectra limited to these fixed scanning directions.

[0005] There are other beam profile monitors that can obtain two-dimensional profile images using other methods (such as fluorescent screens, semiconductor detectors such as CCDs, and scintillators), but these are limited in the beam intensity and energy that can be used.On the other hand, wire-type monitors are the most versatile and have a wide range of applications. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 6,972,551 [Patent Document 2] Japanese Patent Publication No. 2022-27504 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above-mentioned facts, and its object is to provide a wire-type beam profile monitor that makes it possible to acquire a one-dimensional projection spectrum of a beam over the circumferential direction of the beam. [Means for solving the problem]

[0008] In order to solve the above problem, the beam profile monitor of the present invention for measuring the intensity distribution of a beam comprises a wire probe used to measure the intensity of the beam, a two-axis gimbal mechanism that rotates the wire probe in a rotational manner so that the wire probe traverses the beam and further rotates the wire probe in a revolutional manner along the circumferential direction of the beam, wherein the wire probe rotates multiple times in a rotational manner for each revolution of the orbital manner, and a one-dimensional projection spectrum acquisition means that acquires one-dimensional projection spectra showing the intensity of the beam with respect to the crossing position within the beam, measured as the wire probe traverses the beam by rotating in the rotational manner, for each rotation angle in the revolutional manner as the wire probe traverses the beam.

[0009] Preferably, the two-axis gimbal mechanism includes a beam passage through which the beam passes, a first rotating unit that rotates the wire probe in a rotational manner around a first rotation axis extending in a direction crossing the beam passage as a rotation center, and a second rotating unit that further rotates the first rotating unit in a revolutional manner along the circumferential direction of the beam around a second rotation axis extending in a direction passing through the beam passage as a rotation center. The wire probe may extend from a position offset from the first rotation axis of the first rotating unit.

[0010] As an example, the wire probe extends substantially parallel to the first rotation axis, the second rotation axis extends along the axial direction of the beam passage, and the first rotation axis and the second rotation axis are perpendicular to each other.

[0011] Preferably, the apparatus further comprises reconstruction means for reconstructing a two-dimensional image of the beam from a plurality of one-dimensional projection spectra of the beam acquired for each rotation angle in the revolution manner by the one-dimensional projection spectrum acquisition means.

[0012] The reconstruction means may reconstruct a two-dimensional image of the beam from a plurality of one-dimensional projection spectra acquired for each rotation angle while the wire probe rotates 360 degrees in an orbital manner.

[0013] For example, the wire probe crosses itself twice in total at a first crossing position and a second crossing position that are different positions along the axial direction of the beam, every time the wire probe makes one rotation in the rotational manner. The reconstruction means may reconstruct a two-dimensional image of the beam from a plurality of one-dimensional projection spectra acquired for each rotation angle while the wire probe rotates 180 degrees half around in an orbital manner.

[0014] The reconstruction means can reconstruct a two-dimensional image of the beam at each of the first and second intersection positions from a plurality of one-dimensional projection spectra acquired for each rotation angle in the revolution manner at each of the first and second intersection positions.

[0015] Preferably, the apparatus further comprises a beam measurement means for measuring at least one of the traveling direction and the angular spread of the beam by comparing two-dimensional images of the beam at each of the first and second intersection positions.

[0016] Preferably, the reconstruction means acquires a plurality of two-dimensional images arranged in chronological order by sequentially reconstructing two-dimensional images each time the wire probe makes one or half revolution in an orbital manner.

[0017] The reconstruction means may reconstruct a three-dimensional image of the beam based on the plurality of two-dimensional images arranged in time order. The beam profile monitor includes a housing, and the two-axis gimbal mechanism as a preferred example includes a first bevel gear fixed relative to the housing and having a beam passage through which the beam passes, a second bevel gear to which the wire probe is attached, and a third bevel gear configured to be rotatable relative to the housing and having a beam passage aligned with the beam passage of the first bevel gear, the first bevel gear and the third bevel gear having the same diameter and number of teeth and arranged opposite each other with their gear surfaces facing each other, the second bevel gear is arranged so that it is sandwiched between the first and third bevel gears with the gear of the second bevel gear meshing with the gear of the first bevel gear and the gear of the third bevel gear, and when the third bevel gear rotates, the second bevel gear rotates in an orbital manner on the first bevel gear while rotating in an about-axis manner.

[0018] More preferably, the third bevel gear has another gear surface on the opposite side to the gear surface that meshes with the second bevel gear, and the two-axis gimbal mechanism includes a fourth bevel gear that meshes with the other gear surface of the third bevel gear, a motor that transmits rotational force to the fourth bevel gear, and Further provided are:

[0019] More preferably, the beam passage is sealed relative to the motor. The apparatus may further include a beam intensity measuring means for measuring the intensity of the entire beam, and the reconstruction means may convert the two-dimensional intensity distribution into an absolute value by normalizing the two-dimensional intensity distribution of the two-dimensional image so that an integral value over a beam cross-sectional area of ​​the reconstructed two-dimensional image coincides with the intensity of the entire beam measured by the beam intensity measuring means. For example, the beam intensity measuring means is a Faraday cup.

[0020] For example, the reconstruction means can reconstruct a two-dimensional image from the first-order projection spectrum using any one of a Fourier transform method, a filtered backprojection method, and a maximum likelihood-expectation maximization (ML-EM) method.

[0021] The beam profile monitor of the present invention may further include a beam intensity measurement sensor that, when the beam hits the wire probe, emits secondary electrons from the wire probe or charges from the beam flow into the wire probe, and measures the current due to the secondary electrons emitted from the wire probe or the charges flowing into the wire probe. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram of a wire-type beam profile monitor according to one embodiment of the present invention. [Figure 2] Figure 2 is an explanatory diagram showing the relationship between the two-dimensional intensity distribution of a beam and the one-dimensional projection spectrum acquired by the wire-type beam profile monitor according to this embodiment, as well as the one-dimensional projection spectrum (sinogram) from 360-degree directions. [Figure 3] FIG. 3 is a diagram for explaining a method for detecting a change in beam deflection and position beam diameter in the wire-type beam profile monitor according to this embodiment. [Figure 4] FIG. 4 is a diagram showing time-series data of a two-dimensional profile image of a beam reconstructed from one-dimensional projection spectra (sinograms) from 360-degree directions acquired by a wire-type beam profile monitor according to this embodiment. [Figure 5] 5A and 5B are diagrams showing the external configuration of a wire-type beam profile monitor according to this embodiment and an example of its installation, in which FIG. 5A shows an example of a beamline setup configuration to which the wire-type beam profile monitor according to this embodiment is attached, and FIG. 5B is a schematic diagram of an electromagnetic deflector provided in the example of the beamline setup configuration shown in FIG. 5A. [Figure 6] FIG. 6 is a schematic diagram of an example of the gear configuration of a gimbal mechanism provided in the wire-type beam profile monitor according to this embodiment. [Figure 7] FIG. 7 is a perspective view of an example of the gear configuration of the gimbal mechanism shown in FIG. [Figure 8] FIG. 8 is a diagram for explaining the Fourier transform (FT) method, which is an example of a method for calculating a two-dimensional profile image of a beam from a one-dimensional projection spectrum (sinogram) from 360-degree directions. [Figure 9] FIG. 9 is a diagram for explaining the filtered back projection (FBP) method, which is another example of a method for calculating a two-dimensional profile image of a beam from one-dimensional projection spectra (sinograms) from 360-degree directions. DETAILED DESCRIPTION OF THE INVENTION

[0023] A wire-type beam profile monitor according to an embodiment of the present invention will be described below with reference to the drawings. 1 shows a schematic configuration of a wire-type beam profile monitor according to one embodiment of the present invention. As shown in the figure, the beam profile monitor 1 for measuring the intensity distribution of a beam includes a wire probe 2 that emits secondary electrons when struck by a beam, a two-axis gimbal mechanism 3 for performing two-axis compound rotation of the wire probe 2, a beam intensity measurement sensor 7 that measures the beam intensity by detecting the secondary electrons emitted from the wire probe 2, and a one-dimensional projection spectrum acquisition unit 8 that acquires one-dimensional projection spectra for each rotation angle along the circumferential direction of the beam B. The beam profile monitor 1 may also include a two-dimensional image reconstruction unit 10, as necessary, that reconstructs a two-dimensional image of the beam B from the acquired one-dimensional projection spectra for each rotation angle.

[0024] Here, examples of beam B include a charged particle beam (electron beam, proton beam, positive ion beam, negative ion beam, etc.), a neutral particle beam (hydrogen, etc.), a laser, and electromagnetic waves (gamma rays, X-rays). However, the present invention does not limit beam B to these examples. Furthermore, wire probe 2 is a metal formed into a wire shape; for example, molybdenum, which has a high melting point, or molybdenum with an alkali surface coating is preferably used. The present invention is not limited to this example of wire probe 2; the wire probe 2 can be made of any material and have any shape, as long as it is possible to measure the intensity of beam B by generating a charge in accordance with the amount of beam B that strikes it, such as by emitting secondary electrons from wire probe 2 when beam B strikes it, or by causing the charge of the charged particle beam (e.g., electrons in the case of an electron beam) to flow into wire probe 2 as a current.

[0025] When the wire probe 2 emits secondary electrons upon being hit by the beam B, the beam intensity measurement sensor 7 can be composed of a metal plate arranged on the inner wall (not shown) of the housing of the beam profile monitor 1 so that the secondary electrons emitted from the wire probe 2 flow into it, and a current sensor that measures the secondary electron current flowing through the metal plate. Also, when the wire probe 2 is hit by the beam B and an electric charge flows into the wire probe 2, the beam intensity measurement sensor 7 may detect the current flowing through the wire probe 2.

[0026] The two-axis gimbal mechanism 3 includes a beam passage 3b through which the beam B passes, a first rotating unit (5, 6) that rotates the wire probe 2 in an autorotational manner (rotational direction r) around a first rotational axis A that extends in a direction crossing the beam passage 3b, and a second rotating unit 4 that further rotates the first rotating unit (5, 6) in an orbital manner (rotational direction R) along the circumferential direction of the beam B around a second rotational axis Z that extends in a direction passing through the beam passage 3b. In the example of FIG. 1, the second rotating unit 4 is formed as a ring with the beam passage 3b formed in its center, the wire probe 2 extends substantially parallel to the first rotational axis A, the second rotational axis Z extends along the axial direction of the beam passage 3b, and the first rotational axis A and the second rotational axis Z are perpendicular to each other, but the present invention is not limited to these examples.

[0027] The first rotating unit has a shaft 5 extending from the ring 4 to the beam passage 3b. The shaft 5 is configured to rotate in a rotation direction r around a first rotation axis A as a rotation center. The first rotating unit further has a bar 6 extending from the shaft 5 perpendicular to the first rotation axis A. A straight wire probe 2 is attached to one end of the bar 6. The wire probe 2 attached in this manner extends from a position offset from the first rotation axis A. This allows the wire probe 2 to traverse the beam B passing through the beam passage 3b when the first rotating unit (5, 6) rotates the wire probe 2 in an autorotational manner (rotation direction r). Alternatively, a shaft 5b and a bar 6b ​​extending from the shaft 5b may be provided at positions diametrically opposite the shaft 5 and the bar 6 in the ring 4, and the wire probe 2 may be stretched between one end of the bar 6 and one end of the bar 6b.

[0028] While the wire probe 2 is being rotated in a rotational manner (rotational direction r) by the first rotating units (5, 6), the second rotating unit 4 further rotates the first rotating units (5, 6) in an orbital manner (rotational direction R) around the second rotation axis Z as the center of rotation along the circumferential direction of the beam B, so that the wire probe 2 rotates three-dimensionally on two axes. Here, the rotational speed ratio between the first rotating unit and the second rotating unit is determined so that the wire probe 2 rotates multiple times in a rotational manner (rotational direction r) for every one revolution in the revolutional manner (rotational direction R).

[0029] The beam scanning by the two-axis compound rotation of the wire according to the present invention does not involve linear or reciprocating motion, but is performed by the wire using only rotational motion, making it possible to perform continuous scanning at a constant speed and period.

[0030] Next, a method for acquiring a one-dimensional projection spectrum by the one-dimensional projection spectrum acquisition unit 8 will be described with reference to FIG. As shown in Figure 2, the two-dimensional intensity distribution of the cross section of beam B is expressed as f(x, y). By measuring the current generated in wire probe 2 when scanning it in an arbitrary X-axis direction, a one-dimensional projection spectrum onto the X-axis is obtained.

[0031]

number

[0032] The angle θ between the X-axis and the x-axis is called the projection angle, and is adjusted between θ = 0 and 2π. Therefore, if the projection angle θ is changed between θ = 0 and 2π and a projection spectrum is obtained for each value of θ, multiple projection spectra (sinograms) from 360-degree directions can be obtained.

[0033] Here, scanning the wire probe 2 in the X-axis direction corresponds to rotating the wire probe 2 in a first rotation direction r around the first rotation axis A as the rotation center, thereby causing it to traverse within the beam B, as shown in FIG. 1, and adjusting the projection angle θ between 0 and 2π corresponds to rotating the first rotating part (5, 6) in a rotation direction R around the second rotation axis Z as the rotation center by an angle between 0 and 2π.

[0034] In reality, the X-axis shown in Fig. 2 is a straight line, whereas the wire probe 2 shown in Fig. 1 crosses the beam B while drawing an arc due to rotation in the first rotation direction r, which is a difference between the two. However, the crossing trajectory of the wire probe 2 while drawing an arc can be approximated as a straight line if the radius of the arc (the distance from the rotation axis A to the connection point of the wire probe 2 on the bar 6) is sufficiently larger than the radius of the beam B. Alternatively, the one-dimensional projected spectrum may be expressed as a projected spectrum on a curve, or may be mathematically corrected.

[0035] 2 is constant while the wire probe 2 scans the beam, whereas the wire probe 2 shown in FIG. 1 changes the rotation angle θ corresponding to the projection angle due to revolution in a second rotation direction R while traversing the beam B by rotation about its axis in a first rotation direction r. However, in this embodiment, the rotational speed ratio between the first and second rotating units is set so that the wire probe 2 rotates multiple times in the rotational mode (rotation direction r) for every one revolution in the revolution mode (rotation direction R). Therefore, the change Δθ in the angle of revolutionary rotation while the wire probe 2 traverses the beam B is considered to be sufficiently small. For example, if the rotational speed ratio between the rotational speed of the first and second rotating units is set to 360:1, the second rotating unit revolves only Δθ = 1 degree when the first rotating unit rotates 360 degrees about its axis. Moreover, for the wire probe 2 to traverse beam B, the first rotating part does not need to rotate 360 ​​degrees; in the example of Figure 1, only a rotation angle of 1 / n of Δθ is required. For example, if the wire probe 2 traverses beam B with a 30-degree rotation of the first rotating part, the second rotating part will only revolve by Δθ × 30 / 360 = 1 / 12 degrees each time the wire probe 2 traverses beam B. Therefore, an approximation can be made that ignores the change in the angle of revolutionary rotation, Δθ / n, that occurs while the wire probe 2 traverses beam B. Note that a mathematical correction that takes into account the change in the angle of revolutionary rotation may also be made.

[0036] In this way, by detecting the secondary electrons emitted from the wire probe 2 that is rotated in two axes by the beam two-axis gimbal mechanism 3 shown in Fig. 1, it is possible to obtain multiple projection spectra (sinograms) from 360 degrees. Here, the secondary electrons emitted from the wire probe 2 when crossing the beam are detected with a maximum gain of 10 11 1nA / cm by using a V / A low noise current amplifier 2 It is estimated that it is possible to measure weak beams up to the following levels with high sensitivity.

[0037] In the above example, where the rotational speed ratio between the first rotating unit and the second rotating unit is set to 360:1, a total of 360 one-dimensional projection spectra g(X, θ) (θ=1 degree, 2 degrees, ... 360 degrees) are acquired every Δθ=1 degree (actually, there is a fluctuation range change Δθ / n as described above) and stored in memory 9.

[0038] The two-dimensional image reconstruction unit 10 reconstructs a two-dimensional intensity distribution f(x, y) of the cross section of beam B, i.e., a two-dimensional image of the cross section of beam B, from multiple one-dimensional projection spectra g(X, θ) (sinograms) from 360-degree directions stored in memory 9.

[0039] Regarding the one-dimensional projection spectrum g(X,θ),

[0040]

number

[0041] Therefore, it is actually possible to create a sinogram by measuring θ=0 to π and reconstruct an image. An example of the installation of the beam profile monitor 1 according to the present embodiment will be described with reference to FIG. + Ar emitted from an ion source (beam energy 10 keV) + The figure shows a vacuum beamline 12 for transporting the beam, and a beam profile monitor 11 with a vacuum housing, the interior of which is kept vacuum by covering the beam profile monitor 1 with a housing 26 as shown in Figure 1. The beam profile monitor 11 is connected to the vacuum beamline 12 via an electromagnetic deflector 13, and detects the transported Ar + 5A, the sensor 7 is shown connected directly to the housing 26 of the beam profile monitor 11 to reduce noise, but it may be connected to the housing 26 via a cable or the like.

[0042] As shown in FIG. 5(B), the electromagnetic deflector 13 can apply a magnetic field in a direction perpendicular to the drawing. When no magnetic field is applied, the charged particle beam (Ar + The beam (Ar) is guided straight into the beam tube 14, and when a magnetic field is applied, the charged particle beam is deflected by the Lorentz force and guided into the beam tube 15. A beam profile monitor 11 with a vacuum housing is connected to the beam tube 14, and when the electromagnetic deflector 13 does not apply a magnetic field, the beam profile monitor 11 measures Ar + The beam profile can be measured. On the other hand, a Faraday cup 16 is connected to the beam tube 15, and as will be described later, + It is possible to measure the total current of the beam.

[0043] The two-dimensional image reconstruction unit 10 can reconstruct a two-dimensional image f(x, y) from a one-dimensional projection spectrum g(X, θ) using, for example, the Fourier transform method, the filtered back projection method, or the maximum likelihood estimation-expectation maximization (ML-EM) method. The optimal algorithm can be selected depending on the application, taking into consideration factors such as processing time and artifact characteristics. Each method will be described below.

[0044] The Fourier transform method is shown in Figure 8. The two-dimensional Fourier transform F(u, v) of the two-dimensional image f(x, y) is calculated from the measured first-order projection spectrum g(X, θ) as follows:

[0045]

number

[0046] Next, by performing a two-dimensional inverse Fourier transform on the two-dimensional Fourier transform F(u, v) of Equation 3, a two-dimensional image f(x, y) is obtained as shown in the following equation.

[0047]

number

[0048] The filtered back projection method is shown in Fig. 9. As shown in Fig. 9, the measured primary projection spectrum g(X, θ) is subjected to a one-dimensional Fourier transform to obtain G(ρ, θ) = F(ρcos θ, ρsin θ), which is then filtered (a Ramp filter or a Shepp-Logan filter) and subjected to a one-dimensional inverse Fourier transform to obtain q(X, θ), which is then back-projected to obtain a two-dimensional image f(x, y).

[0049] The maximum likelihood-expectation maximization (ML-EM) method is a method that performs iterative calculations to approximate an image that produces a projection that matches the measured sinogram. To improve real-time performance, the one-dimensional projection spectrum acquisition unit 8 and the two-dimensional image reconstruction unit 10 can be realized by a high-speed on-board processing circuit and data transfer system using an ADC and FPGA. In particular, the two-dimensional image reconstruction unit 10 uses a general-purpose IP core for fast Fourier transform (FFT) and image processing in the FPGA, and by combining it with a hardware program to reconstruct the image, it is thought that two-dimensional or three-dimensional image data can be acquired almost in real time.

[0050] By using the two-dimensional image f(x, y) reconstructed by the two-dimensional image reconstruction unit 10, the following applications (1) to (3) become possible. (1) Detection of beam direction and angular spread As shown in Figure 3, the linear wire probe 2 crosses beam B at two locations (z1 and z2) along the axial direction of beam B, so that with one rotation in the rotation direction r, it is possible to simultaneously measure the projected spectrum g1(X, θ) at position z1 and the projected spectrum g2(X, θ) at position z2. Using this, it is possible to reconstruct the two-dimensional intensity distributions f1(x, y) and f2(x, y) at z1 and z2 from the sinograms obtained at the two locations. By comparing the obtained f1(x, y) and f2(x, y), it is possible to measure the beam direction and angular spread. (2) Time-varying beam profile (movie observation) and acquisition of 3D images The scanning motion using two-axis compound rotation according to the present invention scans the beam with a wire using only rotational motion, without any linear or reciprocating motion, allowing for continuous scanning at a constant speed and period. That is, as shown in Figure 4, while continuously measuring the projection spectrum, a sinogram is created from any 360-degree (or 180-degree) data set to reconstruct a two-dimensional image, and time-series data of the two-dimensional image is created, allowing the time change of the two-dimensional beam image to be observed as a movie. The time resolution and frame rate of the movie can be adjusted by changing the rotation speed of the probe.

[0051] Furthermore, it is also possible to reconstruct a three-dimensional image of beam B based on multiple two-dimensional images arranged in chronological order. For example, if beam B is a particle beam and each particle is moving at a uniform velocity v, after time t it will have moved a distance v·t in the direction of beam propagation, so it can be understood that the two-dimensional image at time t represents a two-dimensional image of the beam cross section at a position v·t in the direction of beam propagation. Therefore, it is also possible to reconstruct a three-dimensional beam intensity distribution by adding the dimension z in the propagation direction to the two-dimensional beam cross-sectional intensity f(x, y). (3) Two-dimensional beam intensity distribution (A / mm 2 ) to get the absolute value Absolute measurements are possible using two methods: (a) When the secondary electron emission coefficient ε of the wire probe is known By converting the number of secondary electrons emitted from the wire probe into the number of particles in the beam using the coefficient ε, it becomes possible to measure the absolute value of the beam intensity distribution. (a) When the secondary electron emission coefficient ε of the wire probe is unknown The beam intensity I beam Measure the xy integral of the reconstructed image.

[0052]

number

[0053] is the beam intensity I beam By normalizing the beam intensity distribution in the reconstructed image to match the absolute value, the beam intensity distribution in the reconstructed image can be converted to an absolute value. If one wishes to measure only the beam position and shape, i.e., the relative distribution of two-dimensional beam intensity, using this beam profile monitor, the secondary electron emission coefficient ε of the wire probe is not necessary. (Example of gear configuration for a two-axis gimbal mechanism) Next, an example of the gear configuration of the gimbal mechanism 3 will be described with reference to FIGS.

[0054] As shown in Figure 6, in a beam profile monitor 11 having a housing 26 connected to a beam tube 14, the two-axis gimbal mechanism 3 includes a first bevel gear 19 fixed relative to the housing 26 and having a beam passage 3a through which the beam B passes, a second bevel gear 18 to which the wire probe 2 is attached, and a third bevel gear 17 rotatably mounted to the housing 26 via a bearing 25 and having a beam passage 3b aligned with the beam passage 3a of the first bevel gear 19.

[0055] The first bevel gear 19 and the third bevel gear 17 have the same diameter and number of teeth and are arranged facing each other with their gear surfaces facing each other, and the second bevel gear 18 is arranged so that it is sandwiched between the first and third bevel gears with the gear of the second bevel gear 18 meshing with the gear of the first bevel gear 19 and the gear of the third bevel gear 17.

[0056] As shown in Fig. 7, when the third bevel gear 17 rotates, the second bevel gear 18, which is in a state of meshing with the fixed first bevel gear 19 (Fig. 6) and the third bevel gear 17 (the three-dimensional shape of the gear is partially omitted), rotates in an axis-rotating manner (rotation direction r) and also rotates in an orbital manner (rotation direction R) on the first bevel gear 19 (Fig. 6). This enables beam scanning of the wire probe by two-axis compound rotation as described above.

[0057] As shown in FIG. 6 , the third bevel gear 17 has a gear surface 23 on the opposite side to the gear surface that meshes with the second bevel gear 18, and the two-axis gimbal mechanism 3 further includes a fourth bevel gear 22 that meshes with the gear surface 23 of the third bevel gear 17, and a motor 20 that transmits the rotational force to the fourth bevel gear 22. A rotating shaft 21 of the motor 20 is connected to the fourth bevel gear 22 and rotatably held via a bearing 24 attached to a housing 26. When the gear ratio of the number of teeth of the first and third bevel gears (17, 18) to the number of teeth of the second bevel gear 18 is N, the second bevel gear 18 revolves 360 / N degrees for each rotation (for example, when the gear ratio is 360, the second bevel gear 18 revolves 1 degree for each rotation). This makes it possible to continuously measure one-dimensional projected spectra while changing the projection angle θ as described above.

[0058] Normally, two-axis rotation requires two-axis rotational power (e.g., two motors), but by coupling the two-axis rotation using the bevel gear mechanism shown in Figures 6 and 7, complex three-dimensional scanning motion can be achieved with a single motor. In other words, the gear mechanism shown in Figures 6 and 7 achieves the beam scanning by the above-mentioned two-axis compound rotation with a single-axis rotational power.

[0059] The above gear mechanism makes it possible to configure the vacuum beam passage in the beam tube 14 and the beam passages 3a and 3b to be sealed from the motor 20, for example, by providing a seal on the bearing 24. Therefore, two-axis compound rotation can be achieved using only a motor placed on the atmosphere side outside the vacuum beamline, which solves problems such as vacuum deterioration due to outgassing and motor damage due to heat generated when a motor is placed in a vacuum, as well as the need to construct a mechanism (slip ring, etc.) in a vacuum to supply power to the motor while rotating the motor itself, and provides an extremely significant advantage in terms of practicality.

[0060] The above is an embodiment of the present invention, but the present invention is not limited to the above example, and can be arbitrarily and suitably modified within the scope of the present invention. For example, the present invention is not limited to the specific gear mechanisms shown in Figures 6 and 7, but includes any gear mechanism capable of realizing two-axis compound rotation. For example, other gear mechanisms that simultaneously rotate and revolve are also contemplated, and it is also possible to use a separate power transmission mechanism as the gear mechanism that transmits the motor's power to the third bevel gear 17, rather than a gear on another surface of the third bevel gear 17. Furthermore, the power source for the two-axis compound rotation can be means other than a motor, and it can be performed manually, for example. Note that while the above-mentioned effects can be achieved with a single motor, the scope of the present invention also includes the use of power sources such as multiple motors.

[0061] Furthermore, in this embodiment, a straight wire probe 2 is used as an example, but the present invention can also scan the beam using a wire probe 2 of any other shape, such as a curved shape or a shape that combines straight and curved lines, as long as the shape is suitable for beam scanning.

[0062] Furthermore, in the above example, the Fourier transform method, the filtered backprojection method, and the maximum likelihood estimation-expectation maximization (ML-EM) method were used as the methods for reconstructing a two-dimensional image by the two-dimensional image reconstruction unit 10, but the present invention is not limited to these, and any suitable method can be used as long as it can reconstruct a two-dimensional image from multiple one-dimensional projection spectra. [Explanation of symbols]

[0063] 1 Beam profile monitor 2 wire probe 3. 2-axis gimbal mechanism 3a, 3b Beam passage 4 Second rotating part 5, 5b Shaft portion (first rotating portion) 6, 6b Bar (first rotating part) 7 Beam intensity measurement sensor 8. One-dimensional projection spectrum acquisition unit 9 One-dimensional projection spectrum (sinogram) memory 10 2D image reconstruction unit 11 Beam profile monitor with housing 12 Vacuum Beamline 13 Electromagnetic deflector 14 Beam tube (to beam profile monitor) 15 Beam tube (to Faraday cup) 16 Faraday Cup 17 Third bevel gear 18 Second bevel gear 19 First bevel gear 20 motors 21 Rotating shaft 22 Fourth bevel gear 23 Another gear surface of the third bevel gear opposite to the gear surface that meshes with the second bevel gear 18 24 bearings 25 bearings 26 Housing

Claims

1. 1. A beam profile monitor for measuring an intensity distribution of a beam, comprising: a wire probe used to measure the intensity of the beam; a biaxial gimbal mechanism that rotates the wire probe in a rotational manner so that the wire probe crosses the beam and further rotates the wire probe in a revolutional manner along the circumferential direction of the beam, wherein the wire probe rotates multiple times in a rotational manner for each revolution of the wire probe; a one-dimensional projection spectrum acquiring means for acquiring one-dimensional projection spectra, which indicate the intensity of the beam with respect to the traversal position within the beam, measured when the wire probe traverses the beam by rotating in a rotational manner, for each rotation angle in the revolutional manner when the wire probe traverses the beam; A beam profile monitor comprising:

2. The two-axis gimbal mechanism includes: a beam passage through which the beam passes; a first rotating unit that rotates the wire probe in an autorotational manner around a first rotation axis that extends in a direction crossing the beam path; a second rotating unit that further rotates the first rotating unit in an orbital manner along the circumferential direction of the beam around a second rotation axis that extends in a direction passing through the beam passage; 10. The beam profile monitor of claim 1, comprising:

3. The beam profile monitor of claim 2 , wherein the wire probe extends from a position offset from the first axis of rotation of the first rotating part.

4. The beam profile monitor of claim 3 , wherein the wire probe extends substantially parallel to the first axis of rotation.

5. The beam profile monitor of claim 3 , wherein the second axis of rotation extends along an axial direction of the beam passage.

6. 6. The beam profile monitor of claim 5, wherein the first axis of rotation and the second axis of rotation are orthogonal.

7. 2. The beam profile monitor according to claim 1, further comprising a reconstruction means for reconstructing a two-dimensional image of the beam from a plurality of one-dimensional projection spectra of the beam acquired for each rotation angle in the revolution manner by the one-dimensional projection spectrum acquisition means.

8. 8. The beam profile monitor according to claim 7, wherein the reconstruction means reconstructs a two-dimensional image of the beam from a plurality of one-dimensional projection spectra acquired for each rotation angle while the wire probe rotates 360 degrees in an orbital manner.

9. 8. The beam profile monitor according to claim 7, wherein the wire probe crosses itself twice in total at a first crossing position and a second crossing position that are different positions along the axial direction of the beam, for each rotation in the rotational manner.

10. 10. The beam profile monitor according to claim 9, wherein the reconstruction means reconstructs a two-dimensional image of the beam from a plurality of one-dimensional projection spectra acquired for each rotation angle while the wire probe rotates 180 degrees half around in an orbital manner.

11. 10. The beam profile monitor according to claim 9, wherein the reconstruction means reconstructs a two-dimensional image of the beam at each of the first and second intersection positions from a plurality of one-dimensional projection spectra acquired for each rotation angle in the revolution manner at each of the first and second intersection positions.

12. 12. The beam profile monitor of claim 11, further comprising a beam measurement means for measuring at least one of a direction of travel of the beam and an angular spread of the beam by comparing two-dimensional images of the beam at each of the first and second intersection positions.

13. 8. The beam profile monitor according to claim 7, wherein the reconstruction means acquires a plurality of two-dimensional images arranged in chronological order by sequentially reconstructing two-dimensional images each time the wire probe rotates one revolution or half revolution in an orbital manner.

14. 14. The beam profile monitor according to claim 13, wherein said reconstruction means reconstructs a three-dimensional image of said beam based on said plurality of two-dimensional images arranged in time order.

15. the beam profile monitor comprises a housing; The two-axis gimbal mechanism includes: a first bevel gear fixed relative to the housing and having a beam passage through which the beam passes; a second bevel gear to which the wire probe is attached; a third bevel gear rotatably configured with respect to the housing, the third bevel gear having a beam path aligned with the beam path of the first bevel gear; Equipped with the first bevel gear and the third bevel gear have the same diameter and number of teeth, and are arranged facing each other with their gear surfaces facing each other; the second bevel gear is arranged so that it is sandwiched between the first and third bevel gears with its gear meshing with the gear of the first bevel gear and the gear of the third bevel gear; 2. The beam profile monitor according to claim 1, wherein when the third bevel gear rotates, the second bevel gear rotates in a rotational manner on its axis while rotating in a revolutional manner on the first bevel gear.

16. the third bevel gear has another gear surface on the opposite side to the gear surface that meshes with the second bevel gear, The two-axis gimbal mechanism includes: a fourth bevel gear meshing with the other gear surface of the third bevel gear; a motor that transmits a rotational force to the fourth bevel gear; 16. The beam profile monitor of claim 15, further comprising:

17. 17. A beam profile monitor according to claim 15 or 16, wherein the beam passage is sealed relative to the motor.

18. further comprising a beam intensity measuring means for measuring the intensity of the entire beam; 8. The beam profile monitor according to claim 7, wherein the reconstruction means converts the two-dimensional intensity distribution into absolute values ​​by normalizing the two-dimensional intensity distribution of the two-dimensional image so that an integral value over a beam cross-sectional area of ​​the reconstructed two-dimensional image coincides with the intensity of the entire beam measured by the beam intensity measurement means.

19. 20. The beam profile monitor of claim 18, wherein the beam intensity measuring means is a Faraday cup.

20. 8. The beam profile monitor according to claim 7, wherein the reconstruction means reconstructs a two-dimensional image from the first-order projection spectrum using any one of a Fourier transform method, a filtered back projection method, and a maximum likelihood-expectation maximization (ML-EM) method.

21. When the beam strikes the wire probe, secondary electrons are emitted from the wire probe or charges from the beam flow into the wire probe; 2. The beam profile monitor according to claim 1, further comprising a beam intensity measurement sensor that measures the secondary electrons emitted from the wire probe or a current due to charges that have flowed into the wire probe.

Images