JPH03251787A - Apparatus for measuring cross-section of beam - Google Patents

Abstract

PURPOSE:To accurately measure and analyze the properties of charged corpuscular beam by providing a mesh electrode and a microchannel plate behind a small aperture plate in an integrally movable manner. CONSTITUTION:A small aperture plate H is vertically fixed to a base 1 and a microchannel plate (MCP) M and the mesh (m) provided in front thereof are provided behind the plate H in an integrally movable manner. The corpuscular beam passed through the small aperture of the small aperture plate H is incident to the MCP to show the pattern corresponding to the arrangement of the small aperture of the small aperture plate and the image of the pattern is taken by an imaging element 1 to be displayed on a CRT. At this time, arbitrary voltage suitable for the detection of an image can be applied across the MCP and the mesh (m) and, even when an electron track is bent between the mesh (m) and the MCP by said voltage, since the small aperture plate H is used, the effect of a curve is corrected to make it possible to accurately measure corpuscular beam.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for measuring the illuminance (particle density) distribution in a beam cross section of an electron beam, ion beam, or the like.

(Prior art) When designing and manufacturing ion optical devices, electron optical devices, etc., or designing and manufacturing radiation sources such as ion beams, it is necessary to directly measure the aberration properties of the formed beam, the brightness distribution of the radiation source, etc. It is necessary. Computer simulations are often used to design optical systems, but even in this case, it is difficult to improve the simulation method itself unless the quality of the calculation results is ultimately determined through actual measurements.

The properties of the beam aberrations and the sieve distribution of the radiation source mentioned above can be investigated by measuring the irradiation distribution of the cross section of the beam at several points before and after the beam. A method of taking a cross-sectional image and examining its humidity distribution was used, but this method was extremely inefficient for conducting experimental analysis of the beam being formed.

(Issues to be Solved by the Invention) The present invention aims to streamline the experimental analysis described above by providing an electronic device that can instantly measure and display the illuminance distribution of a beam cross section.

(Means for solving the problem) Mesh-like electrodes are placed in front of a two-dimensional microchannel plate (MCP) at a certain distance apart, and the mesh electrodes are set to 0 potential and placed in front of the MCP. The mesh electrode and MCP were integrally movable back and forth with respect to the small hole plate.

(Operation) The small hole plate and MCP are placed in an ion or electron beam. In Figure 1, H is the small hole plate, hl, h2. h3 is a small hole, M
7ri4MCP. bl, b2. b3 is three particle beams passing through small holes h1 to h3 in the beam. When the MCP is at the solid line position, the particle beams bl, b2. b3 is detected at positions Zl, Z2, and 23 on the MCP. When the MCP is retreated to the position indicated by the chain line in the figure, the particle beams b 1 , b2 . b311
It is detected at positions Zlo, Z2', and Z3' on McP. So, for example, in the example shown in the figure, the beam has spherical aberration in a narrow sense, but if there is no aberration, 21;Z2;23=Z1°
;Z2';Z3', the aberration of the beam can be known from the position of the receiving line point on the MCP corresponding to the small holes h1 to h3.

The mesh electrode is placed in front of the MCP so that there is no electric field in front of the mesh, and a potential difference is created between the mesh and the front surface of the MCP to accelerate particles between them and generate low-velocity (several tens of eV) positive ions at the MCP entrance surface. In order to increase the quantum efficiency of the MCP and improve the sensitivity of the MCP, the electric field between the mesh and the front surface of the MCP in the direction perpendicular to the front surface of the MCP bends the particle beam that is incident on the MCP at an angle from the perpendicular direction. When the particle beam travels straight, the point of incidence on the MCP cannot be determined accurately. However, in the case of the present invention, by using a small hole plate, the above-mentioned curvature can be corrected and the point of incidence on the MCP when the particle beam travels straight can be accurately determined. In other words, the small hole plate not only serves to separate the beam into several particle beams that make up the beam, but also contributes to accurately determining the inclination of each particle beam. This point will be explained with reference to FIG. In Figure 2, m is mesh, and small hole plate H
The particle beam passes through one small hole and has an inclination of θ with respect to the optical axis of the optical system. Since the distance e between the mesh and the front of the MCP is constant, it remains constant no matter how the MCP is moved forward or backward, and this is θ
is a function of the MC of the particle mb when changing the MCP.
The straight line connecting the positions az and z' of the point of incidence on P is parallel to the particle beam and is shifted by Δ.

Therefore, θ can be found as z and z' at the two positions before and after the MCP, and once θ is found, △ can be found, so it is possible to find the correct Zl, Z2, 23, etc. in Figure 1 and analyze the beam properties. It becomes.

(Example) FIG. 3 shows an example of the present invention. 1 is a device base with a small hole plate H vertically erected and fixed, and the top surface serves as a guide in the left and right direction as shown in the figure, with a microchannel plate M, a mesh m on the front side, and a fluorescent screen F on the back side for imaging. i sliding body 2 in which the element I is mounted on the sliding body 2 so that the sliding body 2 can move left and right on the upper surface of the base 1;
is driven left and right by the feed screw, and 3 in the figure is the joint at the end of the feed screw. This device is installed parallel to the optical axis of the ion optical system in a vacuum chamber in which an ion optical system is installed, and the joint end of the feed screw drive handle shaft and the feed screw 3, which pass through the wall of the vacuum chamber airtight. The sliding body can be moved by turning a feed screw from outside the vacuum container, and the amount of movement of the MCP can be determined by the amount of rotation of the feed screw. The particle beam that passes through the small holes in the small hole plate H enters the MCP, and a pattern corresponding to the arrangement of the small holes in the small hole plate H appears on the fluorescent screen F. This is the image sensor! The image is taken and enlarged and displayed on a CRT (not shown).

Image sensor! A solid-state image sensing device such as a CCD is used as the sensor, and the above-mentioned Z value is given by position data of a unit element of the CCD. In this explanation, we are considering only particle beams in the meridian plane that includes the optical axis of the optical system, but particle beams that are not in the meridian plane can also be considered in the same way. It is the angle between the particle beam and the perpendicular line erected on the front surface of the MCP at the fulcrum of the linear extension of the particle beam and the front surface of the MCP, and the direction of the deviation of △ is the angle between the particle beam and this This is the direction along the plane including the perpendicular line.Small hole plate H
The incident spot on the front surface of the MCP through the small hole itself has a size that is equal to the size of the incident spot, but it further expands when it enters the light receiving surface of the image sensor from the fluorescent plate F, so that the incident spot on the front surface of the MCP It is necessary to find the brightness distribution of the spot image formed by the following, and determine the value of Z as the center position. The method of such data processing is arbitrary.

The amount of parallel movement △ due to the electric field between the mesh m of the particle beam and the MCP and the inclination θ of the particle beam with respect to the optical axis described in the action section
Since the charged particles between the mesh and the MCP are accelerated by a constant parallel electric field, and move in the same manner as a projectile object dropped diagonally downward, the relationship is given by: Here, m is the mass of the charged particle, e is the electric charge, vo is the velocity of the particle in the particle beam direction, e is the distance between the mesh and the front surface of the MCP on the order of several mm, and E is the electric field strength. be. In addition, in the case of low-energy ion beam measurement, the potential difference between the front surface of the mesh MCP is -1 to -
The potential difference between the front and rear surfaces of 2kVMCP is +500~
1000V, the potential difference between the rear surface of the MCP and the fluorescent screen F is +
It is about 4kv.

(Effects of the Invention) According to the present invention, it is possible to apply an arbitrary voltage convenient for image detection between the MCP and the mesh on the front surface, and even if the particle beam trajectory is curved between the mesh MCP and ,
Since the influence of the curve can be detected and corrected by using a small hole plate, the properties of the charged particle beam can be accurately measured and analyzed.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of the present invention, FIG. 2 is an explanatory diagram of the main part, and FIG. 3 is a side view of an embodiment of the present invention. H...small hole plate, h1-h3...small hole, m...mesh, M...microchannel plate (MCP)
, F... Fluorescent screen, 1... Image sensor, l... Base, 2... Sliding body. Body 1 figure

Claims (1)

[Claims] A small hole plate, a microchannel provided behind the small hole plate so as to be movable back and forth with respect to the small hole plate, and a microchannel integrally arranged at a certain distance in front of the microchannel,
A beam cross-section measuring device characterized by comprising a mesh-like electrode that forms an electric field between it and the front surface of a microchannel.