JP2020129545A - Charged particle beam device - Google Patents

Abstract

To provide a light guide, a detector, and a charged particle beam device that can guide light generated by a scintillator to a light receiving element with high efficiency.SOLUTION: A light guide (3) that guides light generated by a scintillator to a light receiving element includes a scintillator housing portion including a first surface (3a) facing a surface (5c) opposite to a charged particle entrance surface of the scintillator (5) and a second surface (3e1) facing a surface (5d) different from the opposite surface of the charged particle entrance surface of the scintillator, and an inclined surface (3e2) that reflects light incident from the second surface toward the inside of the light guide.SELECTED DRAWING: Figure 3

Description

The present invention relates to a light guide, a detector including a light guide, and a charged particle beam device, and more particularly to a charged particle beam device including a light guide that guides light to a light receiving element with high efficiency.

A charged particle beam device for detecting charged particles obtained by irradiating a sample with a charged particle beam such as an electron beam is equipped with a detector for detecting charged particles. For example, when the electron emitted from the sample is detected by scanning the sample with an electron beam, the electron is guided to the scintillator of the charged particle detector by applying a positive voltage of about 10 kV to the electron detector. The light generated by the scintillator due to the collision of electrons is guided to the light guide and converted into an electric signal by a light receiving element such as a photoelectric tube, and becomes an image signal or a waveform signal.

Patent Document 1 describes a light guide attached to a scintillator. Further, Patent Document 1 describes a configuration in which a light guide is provided with an inclined surface in order to guide light emitted from a scintillator to a PMT (Photomultiplier Tube). Patent Document 2 describes a light guide using a material having high transparency such as acrylic resin. Further, Patent Document 2 discloses an apparatus in which light generated by a scintillator is guided by a light guide and is made incident on a photoelectric conversion element including a photomultiplier tube or a semiconductor light receiving element. Further, a scintillator structure in which a surface opposite to an electron incident surface is an inclined surface in order to guide light to the light guide with high efficiency is described.

USP 8,895,935 JP-A-2014-67526 (corresponding US Patent Publication US201 5/0214002)

On the other hand, the light generated by the scintillator is guided to the light receiving element by the light guide, and some light collides with the wall surface of the light guide in the process of reaching the light receiving element. The light that collides goes to the light receiving element by reflection, but there is also light that penetrates outside the light guide. If the light can be guided to the light receiving element while suppressing the transmission of light to the outside of the light guide, the SN of the charged particle beam device can be improved. According to the light guide disclosed in Patent Document 1, the light generated in the scintillator can be guided to the PMT by reflecting the light generated in the scintillator by the inclined surface of the light guide opposite to the scintillator mounting surface. However, as described above, some of the light that collides with the light guide wall surface passes through without being reflected, and there is a limit to high efficiency detection. Also, in order to reflect as much of the light incident on the inclined surface as possible, it is possible to increase the relative angle between the inclined surface on the side opposite to the scintillator mounting surface and the mounting surface. It is conceivable that the dimension of the electron microscope or the like in the optical axis direction becomes large, which makes it unsuitable as a member arranged in a limited space in the vacuum chamber.

According to the detector structure disclosed in Patent Document 2, the light emitted from the side of the scintillator can be guided to the light receiving element, but the light is transmitted from the surface of the scintillator on the side opposite to the charged particle collision surface. However, there is a limit to high-efficiency detection.

Below, a charged particle beam device provided with a light guide for guiding the light generated by the scintillator to the light receiving element with high efficiency is proposed.

In order to achieve the above object, a scintillator, an incident surface on which light from the scintillator is incident, an emission surface for emitting light incident from the incident surface, and a light incident on the incident surface is guided to the emission surface side. A charged particle beam device including a light guide having a surface to be charged, wherein the charged particle beam device further includes an electron optical system capable of bending toward the scintillator, and the scintillator includes a sample. Secondary particles or tertiary particles emitted from the light guide are directly incident, the light guide has a bent portion, and the bent portion emits light in a region other than the region between the incident surface and the emission surface. We propose a charged particle beam device that has a surface that guides the surface.

According to the above configuration, the light generated by the scintillator can be guided to the light receiving element with high efficiency.

The figure which shows the structure of an electron microscope. The figure which shows an example of the locus|trajectory of the passage of the light in a scintillator. The figure which shows an example of the light guide provided with the accommodation space of a scintillator, and a side surface prism. The figure explaining the modification of a side surface prism. The figure which shows the structure of an electron microscope. The figure which shows an example of the light guide provided with the bending part. FIG. 4 is a diagram illustrating an example of a light guide including an inclined portion that connects a bent portion and a linear portion. The figure which shows the example which fitted the cross-sectional shape of a bending part using the equation of a circle. The figure explaining the concrete shape of a light guide. The figure explaining the concrete shape of a light guide. The figure which looked at the light-incidence surface of a light guide from various directions. The figure explaining the concrete shape of a light guide. The figure explaining the concrete shape of a light guide.

In a charged particle detector using a scintillator as a detection element, highly efficient detection of charged particles can be realized by guiding the light emitted inside the scintillator to the light receiving element with high efficiency. On the other hand, a three-dimensional scintillator has multiple surfaces and emits from the surface of all scintillators that do not have a reflecting material that reflects light, but guides the light emitted from the scintillator surface that does not face the light guide. It is not possible. That is, only the light emitted from a part of the surface can enter the light guide. If the light guide is not straight and has a bent portion, light leaks at the bent portion and does not reach the light receiving element. Therefore, the light emitted from the scintillator cannot be sufficiently propagated to the light receiving element. That is, an optical system using a light guide often has a low ratio of light reaching the light receiving element (light use efficiency) to light emitted from the scintillator.

Hereinafter, a charged particle beam device provided with a light guide for improving light utilization efficiency will be described. In the present embodiment, a charged particle beam device including a detector having a scintillator as a detection element and a light guide between the scintillator and the light receiving element will be described. In the examples described below, an electron microscope, particularly an example of a scanning electron microscope will be described, but the invention is not limited to this, and examples described below include other examples such as a scanning ion microscope using an ion beam. Can also be applied to a charged particle beam device. Further, it is also applicable to a semiconductor pattern measuring device, an inspection device, an observing device and the like using a scanning electron microscope.

The scintillator in this specification refers to an element that emits light by entering a charged particle beam. The scintillator in this specification is not limited to the ones shown in the embodiments, and can have various shapes and structures.

<<First Embodiment>>
FIG. 1 is a diagram showing a basic configuration of the electron microscope 1. 1 is a side view of the electron microscope, and FIGS. 2 and 3 are detailed views of the scintillator 5 and the light guide 3. The sample 50 is irradiated with the primary electron beam 100 emitted from the electron source 2, and secondary particles 101 such as secondary electrons and reflected electrons are emitted. The secondary particles 101 collide with the signal particle limiting plate 6 and then enter the scintillator 5. Note that the particles after colliding with the signal particle limiting plate 6 may be referred to as tertiary particles, but in order to simplify the description, the secondary particles emitted from the sample 50 and the secondary particles emitted from the sample are Secondary electrons and the like generated by collision with the signal particle limiting plate 6 will be referred to as secondary particles. In this embodiment, a scintillator 5 having a circular secondary particle incident surface will be described. In the present embodiment, a cylindrical scintillator whose size in the height direction is relatively small with respect to the size of the incident surface of the secondary particles will be described as an example. When the secondary particles 101 are incident on the scintillator 5, the scintillator 5 emits light. The light emitted from the scintillator 5 is guided by the light guide 3 and converted into an electric signal by the light receiving element 4. Hereinafter, the scintillator 5, the light guide 3, and the light receiving element 4 may be collectively referred to as a detection system.

In the case of a scanning electron microscope, the signal obtained by the light receiving element 4 is stored in a storage medium such as a frame memory in synchronization with the scanning of the primary electron beam (electron beam). By displaying the brightness corresponding to the obtained signal amount at the image position (pixel) corresponding to the electron beam irradiation position, a contrast image of the scanning region can be obtained. In FIG. 1, an electron optical system for focusing and irradiating the primary electron beam 100 on the sample, that is, a deflector, a lens, a diaphragm, an objective lens and the like are omitted.

A vacuum state is maintained inside the electron optical lens barrel 60 forming the electron optical system, and the beam is configured to pass through the vacuum space. The sample 50 is placed on a sample stage that moves the sample in at least the XY directions (when the ideal optical axis of the primary electron beam is the Z direction), and the sample 50 and the sample stage are arranged in the sample chamber 61. To be done. The sample chamber 61 is generally kept in a vacuum state during electron beam irradiation. Although not shown, the electron microscope is provided with a control unit for controlling the operation of the whole and each component, a display unit for displaying an image, an input unit for a user to input an operation instruction of the electron microscope, and the like. Further, a negative voltage application power source (not shown) is connected to the sample stage, and a deceleration electric field for the electron beam can be formed. The decelerating electric field for the electron beam is an accelerating electric field for the secondary particles (secondary electrons and backscattered electrons) emitted from the sample, so that the secondary particles are accelerated toward the electron source 2 and the signal particles It collides with the limiting plate 6 and the like.

This electron microscope is one example of the configuration, and other configurations can be applied as long as the electron microscope includes the scintillator 5, the light guide 3, and the light receiving element 4. In the example of FIG. 1, has been described an example of detecting a new secondary particles (tertiary particles) generated on the basis of the collision of the secondary particles to the signal grains restriction plate 6, the position of the signal grains restriction plate 6 Alternatively, a scintillator may be arranged and the light generated by the scintillator may be guided to the light receiving element by the light guide.

The secondary particles 101 also include transmitted electrons, scanning transmitted electrons, and the like. Further, for simplicity, only one detector is shown, but a plurality of detectors may be provided. The detector for backscattered electron detection and the detector for secondary electron detection may be separately provided, or a plurality of detectors may be provided for discriminating and detecting the azimuth angle or the elevation angle.

Next, the scintillator 5 of this embodiment will be described in detail with reference to FIG. In FIG. 2, the front direction DF is parallel to the normal line of the bottom surface of the cylindrical scintillator 5 (to be referred to as the upper bottom surface 5c to distinguish the upper and lower bottom surfaces of the cylinder), and the secondary particles 101 propagate. It is the direction to come. The side direction DS is a direction perpendicular to the front direction DF. The figure is a view of the cylindrical scintillator 5 as viewed from the side surface direction DS. The scintillator 5 is composed of a light emitting unit 5a that converts the energy of the incident secondary particles 101 into light and emits light, and a conductive layer 5b that applies a voltage to the scintillator 5. The conductive layer 5b is a layer formed by stacking on the light emitting portion 5a, and is an Al layer in the present embodiment. However, the scintillator 5 is not limited to this configuration as long as it has the light emitting unit 5a.

As a material of the light emitting portion 5a, a powder phosphor Y2SiO5: which is used as a film formed on a substrate such as a semiconductor (GaN, Si, SiC), a ceramic phosphor YAG (Y3Al5O12:Ce), YAP (YAlO4:Ce), or glass. Such as Ce. As an example of the semiconductor scintillator, there is a semiconductor in which a structure in which InGaN and GaN are laminated to form a quantum well is used as a light conversion unit. The InGanN layer and the GaN layer are stacked in the incident direction of charged particles.

The secondary particles 101 incident on the scintillator 5 pass through the conductive layer 5b and are converted into light by the light emitting section 5a, and the converted light propagates through the light emitting section 5a and is emitted to the outside of the scintillator 5. Since the conductive layer 5b functions as a reflection member for light, light is emitted from all the surfaces without the conductive layer 5b.

Examples of light rays are shown as RayF1, RayF2, RayS1, and RayS2 in the figure. RayF1 and F2 are examples in which light is emitted from the upper and lower surface 5c in the front direction DF, and RayF2 is an example in which light is reflected by the conductive layer 5b and emitted. RayS1 and RayS2 are examples in which they propagate in the side surface direction DS and are emitted from the side surface 5d. RayS2 shows an example in which it is totally reflected on the upper bottom surface 5c, reflected by the conductive layer 5b, and emitted from the side surface 5d, and is an example in which light is guided in the light emitting section 5a and emitted from the side surface 5d. Since the light emitting portion 5a has a higher refractive index than air, part of the light is totally reflected on the surface of the scintillator 5 and guided.

The ratio of the sum total of light emitted from the side surface 5d (side surface emission light amount Is) and the total light emitted from the upper bottom surface 5c (planar emission light amount Ip) depends on the internal structure of the scintillator 5. When using a scintillator made of a semiconductor or ceramic phosphor material, or when using a substrate on which a powder phosphor is formed as a scintillator and extracting and utilizing light from the substrate as well, the refractive index of the material is generally larger than 1.5. When the refractive index is 1.5, the total reflection angle on the surface of the scintillator 5 is about 40 degrees. Therefore, about 75% or more of the light incident on the surface is totally reflected. If the inside of the light emitting unit 5a has a structure in which scattering is likely to occur, it may diffusely reflect and reach the surface again to be emitted from the surface. However, in the case of the above scintillator, since light scattering is difficult to occur, the side surface 5d The light is guided up to and a lot of light is emitted from the side surface 5d. According to the simulation, in the case of the scintillator 5 made of GaN, the height of the cylinder is 0.5 mm, the diameter of the circle is 9 mm, and Ip:Is=1:1. Further, by introducing a pattern structure such as a pyramid or a cone or a pattern structure having a wavelength equal to or less than the wavelength of light into the light emitting portion 5a, the light guide is suppressed by scattering and the plane emission light amount Ip from the upper bottom surface 5c is improved. Even if technology is introduced, Ip:Is=7:3. Therefore, it is important to capture the side emission light amount Is with the light guide and improve the light yield.

Next, the light guide 3 will be described with reference to FIG. FIG. 3 is a sectional view of the light guide 3, and the light guide 3 has a rotationally symmetrical shape with respect to the center line CL. As a material for the light guide 3, PMMA resin, cycloolefin polymer (COP) resin, silica, quartz, or the like may be used. However, the present invention is not limited to the material.

A separation flange 3c is provided on the side surface 3d of the cylinder of the light guide to separate the vacuum inside the electron optical lens barrel 60 from the outside atmosphere. The separation flange 3c may or may not depend on the structure of the electron microscope 1. In the case of the present embodiment, since the light receiving element 4 is arranged outside the electron optical lens barrel 60 and the scintillator 5 is arranged inside the electron optical lens barrel 60, the light guide 3 is provided with the separation flange 3c. ..

The emission surface 3b of the light guide 3 is circular and is a surface that is arranged so as to face the light receiving element 4. The surface facing the upper bottom surface 5c of the scintillator 5 is the incident surface 3a (first surface) of the light guide 3. A part of the light incident from the incident surface 3a is absorbed by the light guide 3, but most of the light reaches the emission surface 3b. RayF3 is an example of light rays that enter the light guide through the incident surface 3a and exit through the outgoing surface 3b.

The portion of the scintillator 5 that faces the side surface 5d is a side surface prism 3e. The side surface prism 3e faces the side surface 5d of the scintillator 5 and receives the light from the side surface 5d. 2 sides). The side prism entrance surface 3e1 is a side wall surface having a surface direction different from the entrance surface 3a of the light guide 3.

Further, the entrance surface 3a of the light guide 3 and the side surface prism entrance surface 3e1 form a housing space surrounding the scintillator 5. In order to take in all the light from the scintillator 5, it is preferable that the accommodation space is formed so as to face all the surfaces of the scintillator 5 from which the light is emitted. However, even if the accommodating space has a structure in which only a part of the surface of the scintillator 5 that emits light is formed, a side wall surface has the effect of improving the light utilization efficiency. ..

The side surface prism 3e has a reflection surface 3e2 (an inclined surface) that reflects the light incident from the side surface prism entrance surface 3e1 so that the light is directed to the exit surface 3b. The reflecting surface 3e2 is formed so as to surround the side surface prism entrance surface 3e1. RayS3 is an example of a light ray that enters the side surface prism 3e from the entrance surface 3e1, is totally reflected by the reflecting surface 3e2, and exits from the exit surface 3b. In the present embodiment, the reflecting surface 3e2 has a predetermined angle θe2 with the normal direction 3eN of the side surface prism entrance surface 3e1 so that light incident in the normal direction 3eN of the side surface prism entrance surface 3e1 can be totally reflected. Is.

Note that total reflection occurs only when the incident angle of light on the reflecting surface 3e2 is larger than the critical angle θc. The incident light also has light of an angle other than the normal direction 3eN, and in order to reflect more light, it is better to provide a reflecting member on the surface of the reflecting surface 3e2. Examples of the reflecting member include aluminum, silver, and a multilayer reflective film.

The angle θe2 is preferably larger than 20 degrees and smaller than 70 degrees from the viewpoint of reflecting in the direction of the emission surface 3b. However, the upper limit of the angle depends on the shape of the light guide 3, and is another value in the case of the bent light guide 3, for example. By appropriately setting the angle θe2, it becomes possible to propagate the reflected light toward the emission surface 3b, and thus an effect of improving the light utilization efficiency is achieved.

The angle θe2 reflected in the normal direction 3aN of the incident surface 3a does not depend on the shape of the light guide 3 and may be in the range of 45°±15°. Most of the light traveling in the normal direction 3aN of the incident surface 3a can be guided to the light guide 3 without leaking from other than the emission surface of the light guide 3, and thus the effect of improving the light utilization efficiency can be obtained. Play.

The side surface prism 3e allows the light emitted from the side surface 5d of the scintillator 5 to also enter the light guide 3, is reflected by the reflection surface 3e2 toward the emission surface 3b, and propagates more light toward the light receiving element 4. Therefore, there is an effect that the light utilization efficiency is improved. Further, in the scintillator, usually, the dimension in the thickness direction of the surface (side surface) in the direction orthogonal to the incident surface is sufficiently smaller than the dimension in the surface direction of the incident surface of charged particles. Therefore, the light emitted from the upper bottom surface 5c is configured to be guided in the direction of the center line CL of the light guide (the optical path direction of the light guide) without being reflected by a prism or the like, and emitted from the side surface of the scintillator. The formed light is guided in the light guide optical path direction along with the reflection using the side surface prism. That is, when the accommodation space of the scintillator 5 is formed in the light guide 3, the dimension of the side prism entrance surface 3e1 in the height direction is set smaller than that of the entrance surface 3a, and the side surface 5d of the scintillator 5 and the side surface of the light guide 3 are formed. The prism entrance surface 3e1 and the upper bottom surface 5c of the scintillator are arranged to face the entrance surface 3a of the light guide 3, respectively.

According to the above configuration, it is possible to efficiently guide the light emitted from each surface of the scintillator to the detection element while reducing the amount of light that changes the propagation direction by reflection in the light guide.

Next, a modified example of the reflecting surface 3e2 will be described with reference to FIG. FIG. 4 is an enlarged sectional view of the vicinity of the side surface prism 3e.

FIG. 4A shows an example in which the reflecting member 3e2R is attached to the surface of the reflecting surface 3e2. By providing the reflection member 3e2R, it is possible to reflect light that cannot be totally reflected by the reflection surface 3e2 and penetrates, and the light utilization efficiency is improved. The light ray RayS4 is light that passes through the reflection surface 3e2 and becomes a loss when there is no reflection member 3e2R, but is reflected and guided toward the emission surface 3b when there is the reflection member 3e2R. The reflection member may be attached by various methods such as vapor deposition other than the attachment, and the present embodiment is not limited to the attachment method. Here, in the present embodiment, the entire light guide is not covered with the reflecting member, and is attached only to a part (reflection surface) of the light guide. Since a general reflector absorbs a part of light at the time of reflection, it is not attached to the side surface 3d of the light guide where light is reflected a plurality of times. The absorption rate when metal is used as the reflecting material is about 5 to 15%. It is important that the side surface 3d is guided by total reflection that does not cause light absorption.

FIG. 4B shows a case where the shape of the reflecting surface 3e2 is not a straight line but a polygonal line. The propagation direction of light is changed by multiple reflections. As an example, the ray example RayS5 is illustrated.

FIG.4(c) has shown the case where the shape of the reflective surface 3e2 is not a straight line but a curved line. The propagation direction of light is changed by multiple reflections. As an example, the ray example RayS6 is illustrated. Various shapes such as a circle, an ellipse, a parabola, and a hyperbola can be considered as the shape of the curve. Further, not only the curved line but also a combination of a curved line and a polygonal line or a curved line and a straight line may be used. If the reflection surface 3e2 has a shape in which light is reflected so as to propagate toward the emission surface 3b, the light utilization efficiency is improved.

<<Second Embodiment>>
5 and 6 are diagrams for explaining the second embodiment. Description of the same parts as those of the first embodiment or parts having the same functions will be omitted. In addition, the portions having the same reference numerals in the drawings have the same function. 5A is a view of the electron microscope viewed from the side, and FIG. 5B is a view of the electron microscope 1 viewed from the direction of arrow A in FIG. 5A. When the plane including the dotted line B and the center of the emission surface is plane S1, FIG. 6A is a cross-sectional view of the light guide 3 on the plane S1. The plane S1 is a plane including the center of the incident surface 3a.

The electron microscope as illustrated in FIG. 5 does not have the signal particle limiting plate as illustrated in FIG. 1, and the secondary particles 101 directly enter the scintillator 5. Further, compared with the example of FIG. 1, the light guide shape is different. In the light guide 3 of the present embodiment, the incident surface 3a and the emission surface 3b do not face each other (there is no emission surface of the scintillator in the normal direction of the incidence surface of the scintillator), and therefore the light guide 3 has the bent portion 3f. It is provided.

For simplicity, only one detection system is shown, but a plurality of detection systems may be provided, or another detection system having a signal particle limiting plate may be provided. Although not shown in the present embodiment, another detection system having a signal particle limiting plate is provided closer to the sample 50 than the detection system shown.

In the electron optical system of this embodiment, the primary electron beam 100 emitted from the electron source 2 goes straight toward the sample 50, but the secondary particle 101 has an optical system capable of bending toward the scintillator 5. Since the secondary particles 101 directly enter the scintillator 5, it is possible to detect the secondary particles 101 traveling straight from the sample 50 with high sensitivity.

As shown in FIG. 5B, the light guide 3 has a bent portion 3f, and light is also guided toward the emission surface 3b while reflecting the bent portion 3f and reaches the light receiving element 4. The cross-sectional shape will be described in detail with reference to FIG. The cross-sectional shape is large and consists of three parts. There are three parts, that is, bent parts 3f1 and 3f2, inclined parts 3g1 and 3g2 whose shape changes gently from the bent part, and straight parts 3h1 and 3h2.

The shape of the straight line portion 3h is a cylinder having the emission surface 3b as a bottom surface (a circle having a radius ra, see FIG. 6B). A separation flange 3c is provided on the straight line portion 3h. By providing the separation flange 3c on the straight line portion 3h, the separation flange 3c can be pressed vertically against the side wall of the electron optical lens barrel 60, etc., and the atmosphere is prevented from flowing into the vacuum.

The shape of the inclined portion 3g is a shape that connects the bent portion 3f and the straight portion 3h. The cross-sectional shapes 3g1 and 3g2 are curves that change gently. The sectional shape is not limited to a curved line, and may be a straight line, a broken line, a curved line and a straight line, a combination of a curved line and a broken line, or the like.

In the present embodiment, the cross-sectional shapes 3f1 and 3f2 of the bent portion are arcs having a central angle of 60 degrees to 89 degrees. The cross-sectional shape may be a curve deviating from an arc, a part may be an arc or a curve, and the other may be a straight line or a polygonal line. The bent portion has a complicated shape in order to reduce the amount of light leaking from the surface of the bent portion to the outside of the light guide. The incident surface 3a has the shape shown in FIG. 6C, and the cross-sectional shapes 3f1 and 3f2 are connected to the points D and E, respectively. The left half is a circle 3a1 and the right half is an ellipse 3a2 with the dotted line F as a boundary. The radius of the circle is ra, and the lengths of 1/2 of the short axis and the long axis of the ellipse are ra and rb, respectively (ra<rb). The center of the scintillator 5 is arranged at a position substantially opposite to the intersection of the dotted line F and the line segment connecting the points D and E.

When the plane perpendicular to the plane S1 and including the dotted line C is the plane S2, the cross-sectional shape of the light guide 3 on the plane S2 is the same circle as the emission surface 3b. The shape of the bent portion 3f is a shape obtained by connecting the circle and the shape of the incident surface 3a with the cross-sectional shapes 3f1 and 3f2 as contours. For example, by using a general 3D CAD (three-dimensional computer aided design system), the shape of the bent portion can be created by lofting the shape of the circle and the incident surface 3a with the sectional shapes 3f1 and 3f2 as contours. FIG. 6D is a perspective view of the light guide 3 of this embodiment. Reference numeral 3i indicates a portion for fixing the light guide 3 and the scintillator 5.

The shape of the bent portion will be described in more detail with reference to FIG. 7. FIG. 7A is a cross-sectional view on the plane S1 for explaining the factor of light leakage at the bent portion 3f. In this example, the inclined portion 3g does not exist unlike the light guide shown in FIG. The shapes of the entrance surface 3a and the exit surface 3b are circles shown in FIG. 6(b), and the cross-sectional shapes 3f1 and 3f2 of the bent portions are arcs having a central angle of 90 degrees and starting from the entrance surface 3a. The bent portion 3f and the emitting surface 3b are connected by a straight portion 3h. It is the simplest light guide shape that connects the entrance surface 3a and the exit surface 3b.

A light ray path through which representative light leaks will be described using three light ray examples. The ray RayF5 reaches the cross section 3f1 of the bent portion, and the angle with the normal line 3N1 of the surface at the reaching point is smaller than the critical angle of total reflection, and is an example of being transmitted through the surface. All the light rays whose angles from the normal line of the incident surface 3a and the light rays emitted from the incident surface 3a are larger than the angle shown in the figure are transmitted through the bent portion 3f and become a loss.

The ray RayF6 (shown by a dotted line to distinguish it from other rays) is totally reflected in the normal direction of the incident surface 3a at the cross section 3f2 of the bent portion, reaches the cross section 3f1 of the bent portion, and reaches the surface of the reaching point. The angle with the normal 3N2 of 3 is smaller than the critical angle of total reflection, so that the surface is transmitted. Light emitted from a position close to the cross section 3f2 of the bent portion is reflected by the cross section 3f2 of the bent portion and leaks from the light guide 3 in the same light path.

The ray RayF7 is inclined from the normal line of the incident surface 3a toward the emission surface 3b, and the light ray emitted from the incident surface 3a reaches the cross section 3h1 of the straight line portion and forms an angle with the normal line 3N3 of the plane at the arrival point. Is smaller than the critical angle of total reflection, and is an example of transmitting light through the surface. Light reaching a surface having a normal line substantially parallel to the normal line of the incident surface 3a has a high probability of passing through the surface. The transmittance follows that of Fresnel.

The light guide 3 shown in FIG. 6A has a shape that suppresses these light leaks. The light guide shown in FIG. 7B is the light guide 3 shown in FIG. 6A, and the light leakage suppressing effect will be described with reference to the drawing. The main features of the light guide 3 in FIG. 7B are that the radius of curvature of the cross section 3f1 of the bent portion is larger than that in FIG. 7A and the shape of the incident surface 3a is shown in FIG. 6C. The point is that the major axis has a shape including an ellipse in the direction of the emission surface. Since the curvature radius of the cross section 3f1 of the bent portion is large, the surface of the light guide 3 that guides the light to the emission surface 3b exists in addition to the region between the incident surface 3a and the emission surface 3b. The area between the entrance surface 3a and the exit surface 3b is the area indicated by the arrow DA in FIG. 7(b). The dotted line indicated by the arrow is an auxiliary line for indicating the region, the lower dotted line in the figure corresponds to the end of the incident surface 3a, and the upper dotted line corresponds to the end of the emitting surface 3b. In the light guide having no inclined portion shown in FIG. 7A, the surface of the light guide 3 that guides light to the emission surface 3b does not exist except for the area. The fixed portion such as the separation flange 3c is not a surface that guides light to the emission surface 3b.

When the radius of curvature of the cross section 3f1 of the bent portion is large, total reflection easily occurs at the bent portion. The ray RayF8 is a ray emitted from the incident surface 3a at the same angle as the ray RayF5, but the angle of incidence on the cross section 3f1 of the bent portion is larger than that of the ray RayF5 and is totally reflected. Since the radius of curvature is large, the normal 3N4 at the position where the light is incident on the circular arc is incident at a position largely inclined from the normal of the incident surface 3a. Therefore, the amount of light totally reflected at the bent portion is increased, and the light utilization efficiency of the light guide is improved.

The ray RayF10 is a ray emitted from the incident surface 3a at the same angle as the ray RayF7. Since the radius of curvature is large, the ray RayF10 is incident on the cross section 3f1 of the bent portion near the end point, and is totally reflected and guided. Since the normal 3N6 of the cross section 3f1 of the bent portion near the end point is inclined from the incident surface 3a in the direction opposite to the exit surface 3b, the angle between the normal 3N6 and the incident light ray becomes large, and total reflection becomes easy. Since the Fresnel reflectance is improved even when total reflection is not performed, the amount of reflected light is increased and the light utilization efficiency of the light guide is improved.

When the scintillator 5 is a cylinder with a diameter of 9 mm, the incidence surface 3a is a circle with a diameter of 10 mm, and the radii of curvature of the cross sections 3f1 and 3f2 of the bent portion are changed from 15 mm, 5 mm to 18 mm, and 8 mm, respectively, to improve the light utilization efficiency. It was confirmed by ray-tracing calculation that the value was improved by 37%.

The ray RayF9 is a ray emitted from the incident surface 3a at the same angle as the ray RayF6. By making a part of the entrance surface 3a an ellipse whose major axis is in the direction of the exit surface and moving the cross section 3f2 of the bent portion to the exit surface 3b side, the ray RayF9 does not reflect at the cross section 3f2 and the cross section of the inclined portion is reflected. It is possible to reach 3g1. The ray RayF9 does not always undergo total reflection in the cross section 3g1, but the angle between the ray RayF9 and the normal 3N5 at the incident point of the cross section 3g1 becomes larger than that in the case of the ray RayF6, so that the Fresnel reflectance increases, The amount of light guided increases, and the light utilization efficiency improves.

Here, the shape of the elliptical portion of the incident surface 3a will be described. For example, in the case where the scintillator 5 has a radius of 4.5 mm, in FIG. 6C, if ra and rb are 4.5 mm and 5.5 mm, respectively, a comparison is made when the incident surface 3a is a circle having a diameter of 9 mm. Then, it was confirmed by ray tracing calculation that the light utilization efficiency was improved by several percent. In the present embodiment, a part of the entrance surface 3a is elliptical and the shape is elongated toward the exit surface to move the cross section 3f2 to the exit surface side to improve the light utilization efficiency. Is not limited to an ellipse, and the shape may be elongated toward the emission surface side. In other words, the distance from the center of the scintillator 5 to the end of the incident surface 3a differs between the emission surface direction and the opposite direction, and the distance in the emission surface direction may be long.

Next, the shape when a part or the whole of the bent portion 3f is an arc will be described with reference to FIGS. 7(c) and 7(d). The cross-sectional shape 3f1 of the bent portion is the arc shape of the present embodiment. The cross-sectional shape 3f1C (shown by a dotted line) has a center CP1 of an arc in a plane SP (shown by a dotted line) including the incident surface 3a, and the tangent line rising from the incident surface 3a of the cross-sectional shape 3f1C is the normal 3aN of the incident surface. It is a cross-sectional shape in the case of being parallel. The cross-sectional shape 3f1C is the shape of the bent portion in the case of forming the light guide without the inclined portion shown in FIG. 7A, and can be said to be the simplest shape as the bent portion.

The cross-sectional shape 3f1 is configured such that the center CP2 of the arc does not exist in the plane SP, and is located below the incident surface 3a (in the direction away from the light guide 3). Further, the tangent line 3f1T rising from the incident surface 3a of the sectional shape 3f1 and the normal line 3aN of the incident surface have a predetermined angle θt. The angle θt is preferably in the range of 2 degrees to 10 degrees from the viewpoint of improving the light utilization efficiency. The angle θt of the light guide 3 shown in FIG. 7B is 2.5 degrees. The distance between the center CP2 and the plane SP is 1 mm. The distance is preferably in the range of 0.3 mm to 5 mm.

When the surface of the light guide 3 is divided by a certain line into an outer curved surface and an inner curved surface, the cross-sectional shape 3f1 is included in the outer curved surface starting from the end of the incident surface 3a, and the cross-sectional shape 3f2 is the inner curved surface. included. The above-described configuration is a configuration in which the outer curved surface has a tangent line inclined to the incident surface side with respect to the normal line 3aN of the incident surface at the contact point between the outer curved surface and the incident surface 3a.

The ray RayF11 is a ray emitted from a substantially center of the incident surface 3a to a bent portion in a direction parallel to the normal 3aN of the incident surface. The intensity of light emitted from the scintillator 5 is generally highest in the direction and position. Reference numerals 3f1N and 3f1CN indicate normal lines at the intersections of the cross sections 3f1 and 3f1C and the ray RayF11, respectively. The angles θ1 and θ2 are angles formed by the normal 3f1N and the ray RayF11 and the ray 3f1CN and the ray RayF11, respectively. FIG. 7D is a diagram for comparing the angles θ1 and θ2, and is a diagram in which the intersection point of the ray RayF11 and each cross section is matched. As can be seen from this figure, the angle θ1 is larger than the angle θ2. Therefore, since the angle of incidence of the ray RayF11 on the cross section 3f1 is larger than that of the cross section 3f1, the ratio of the total reflected light flux to the light flux incident on the light guide 3 is increased, and the Fresnel reflectance is also increased. Leakage is reduced and light utilization efficiency is improved.

That is, when a part of the cross-sectional shape 3f1 (desirably, the part where RayF11 enters) is an arc and the center CP2 of the arc does not exist in the plane SP including the entrance surface 3a, the light utilization efficiency is improves. Further, when the tangent 3f1T rising from the incident surface 3a of the cross-sectional shape 3f1 and the normal 3aN of the incident surface have a predetermined angle θt, the light utilization efficiency is improved.

It is desirable that the cross-sectional shape 3g1 and the cross-sectional shape 3g2 of the inclined portion be substantially parallel as in the present embodiment. This is because, as shown in FIG. 7B, when the height of the light guide decreases toward the emission surface 3b, the incident angle on the cross-sectional shape 3g1 decreases each time light enters the cross-sectional shape 3g1. However, the angle of incidence on the cross-sectional shape 3g2 increases each time light is incident on the cross-sectional shape 3g2 (the phenomenon is reversed when the height of the light guide increases), so that the angle of incidence is compensated. Therefore, the incident angle when first incident on the inclined portion 3g does not largely change in the middle of light guiding, and the incident angle becomes smaller than the total reflection angle, and an effect of suppressing light leakage is exerted.

In the present embodiment, the cross-sectional shapes 3f1 and 3f2 of the bent portion are arcs, but the present invention is not limited to this, and curved lines or polygonal lines deviated from the equation of circles may be used. However, it is desirable that the cross-sectional shape 3f1 on the outer side of the bent portion is a shape that is partially fitted using the equation of circle, ellipse, and parabola.

An example of fitting the cross-sectional shape 3f1 of the bent portion using the equation of circle will be described with reference to the graph of FIG. For reference, the position of the incident surface 3a is entered in the graph. In this graph, the cross-sectional shape 3f1 is shown in the direction opposite to the cross-sectional shape of the light guide shown in FIGS. 6 and 7. The horizontal axis represents position coordinates [mm] parallel to the incident surface, and the vertical axis represents position coordinates [mm] in a direction parallel to the normal to the incident surface. The dotted line is an example of the cross-sectional shape 3f1 of the bent portion, and is not a perfect arc. The solid line 3f1F is the result of fitting the dotted line with the circle equation. The dotted line and the solid line are in good agreement except in the vicinity of the end of the entrance surface 3a. The center P1 of the arc may be obtained using this fitting result.

In the present embodiment, the shapes of the incident surface 3a and the exit surface 3b are circles, partial circles and ellipses, but the present invention is not limited to this. For example, if the scintillator 5 is a quadrangular prism, the incident surface may be a quadrangle, and if the light receiving element has a quadrangular shape, the exit surface may be a quadrangular shape, and various shapes are possible. Further, for example, the cross-sectional shape of the plane parallel to the emission surface is not limited to a circle or the like, and various shapes such as a square and a hexagon can be considered.

<<Third Embodiment>>
FIG. 9 is a diagram for explaining the third embodiment. Description of the same parts as those of the first embodiment or parts having the same functions will be omitted. In addition, the portions having the same reference numerals in the drawings have the same function. The difference from the first embodiment is that the light guide 3 having the bent portion 3f is provided with the side surface prism 3e. FIG. 9 is a sectional view focusing on the bent portion 3f and the side surface prism 3e. The shape of the light guide 3 of this embodiment is the same as that of the light guide described in the second embodiment with reference to FIG. 6B, except for the portion where the side surface prism 3e is provided.

FIG. 9A is an example in which the side surface prism 3e is installed in a portion of the entrance surface 3a where the scintillator 5 does not face. The relevant part is the tip of the ellipse in the long axis direction of the incident surface 3a, which is a position where light hardly enters from the beginning, and does not affect the shape of the light guide after the incident surface 3a. Absent. Therefore, when the side surface prism 3e is installed at the position, the light guide shape after the entrance surface 3a and the side surface prism 3e can be independently optimized.

By installing the side surface prism 3e, it is possible to improve the light utilization efficiency. The side prism 3e can be modified in various ways as described with reference to FIG. 4 in the first embodiment. In particular, by providing a reflective member on the surface of the reflective surface 3e2, it is possible to effectively improve the light utilization efficiency. Reference numeral RayS7 is an example of light rays.

FIG. 9B shows an example in which the side surface prism 3eo is also installed in the outer bent portion 3f1, and the outer side surface prism 3eo needs to rotate the propagation direction of light by approximately 180 degrees and reflect it to the emission surface side. The configuration has two or more reflecting surfaces. That is, the side surface prism 3eo has a reflection surface shape that reflects light twice or more. FIG. 9B has a side surface prism entrance surface 3eo1 that faces the side surface 5d of the scintillator 5 and that receives light from the side surface 5d, and the light is reflected by the reflecting surface 3eo2 substantially in the normal direction of the entrance surface 3a. In this example, the reflecting surface 3eo3 reflects light in the direction of the substantially outgoing surface 3b. With such a structure, the effect of improving the light utilization efficiency is achieved. However, in the case of the outer side surface prism 3eo, the cross-sectional shape 3f1 is changed, which affects the light guide. Therefore, it is preferable to reduce the shape so that a large light leakage occurs due to the influence of the side surface prism 3eo and the light utilization efficiency as a whole does not decrease. In addition, for example, it is preferable that the reflection surface 3eo3 is formed as a part of the cross-sectional shape 3f1 and has a continuous shape up to substantially the same position as the incident surface 3a, as in a cross-sectional shape 3f1' shown by a dotted line. Reference numeral RayS8 is an example of light rays.

A modified example of FIG. 9B will be described with reference to FIG. FIG. 10A is a sectional view focusing on the bent portion 3f and the side surface prism 3e. The difference between this modification and the shape of FIG. 9B is that a gap is provided between the outer side surface prism 3eo and the bent portion 3f. As described above, since a change in the cross-sectional shape 3f1 affects the light guide, a void is provided so as not to affect it. The light incident from the incident surface 3a is reflected and guided by the cross-sectional shapes 3f1 and 3f2, and the light incident from the side prism incident surfaces 3e1 and 3eo1 is reflected and guided by the side prisms 3e and 3eo. ..

FIG. 10B is a sectional view illustrating the side surface prism 3eo in more detail. The light enters from the surface 3eo1 facing the scintillator, is reflected by the reflecting surfaces 3eo2 and 3, is emitted from the side surface prism exit surface 3eo4 facing the bent portion 3f, and enters the bent portion 3f. The reflective surfaces 3eo2 and 3eo3 can be variously modified as described with reference to FIG. 4 in the first embodiment. For example, the reflecting surface 3eo2 and the reflecting surface 3eo3 may be continuous curved surfaces. In this case, the curved surface may have a function of reflecting light in the direction of the normal to the incident surface 3a and then reflecting light in the direction of the substantially emitting surface 3b. Further, when a reflecting member such as aluminum is provided on the reflecting surfaces 3eo2 and 3eo3, the light utilization efficiency can be effectively improved.

Although the space between the side surface prism output surface 3eo4 and the bent portion 3f is shown as a space, a part of the space may be connected. For example, the position of the side surface prism output surface 3eo4 close to the entrance surface 3a may be coupled to the bent portion 3f. This is because if the coupling portion is small, the influence of the light incident from the incident surface 3a on the light guide is small.

Although the outer side prism 3eo and the light guide 3 may be integrated, the side prism 3eo may be attached to the light guide 3 as a separate body because a space is provided.

FIG. 10C is a perspective view from the direction in which the incident surface 3a can be seen. FIG. 11A is a view of the light guide 3 viewed from the direction of the arrow a in the figure (the direction normal to the incident surface 3a). 11B is a diagram viewed from the direction of arrow b in the figure, and FIG. 11C is a diagram viewed from the direction of arrow c in the diagram. From FIG. 11A, it can be seen that the side surface prisms 3e and 3eo are arranged along the scintillator 5 (illustrated by a dotted line). There is an air gap AIR between the incident surface 3a and the outer side surface prism 3eo.

With the configuration of this modification, the effect of improving the light utilization efficiency can be achieved while eliminating the influence of the provision of the side surface prism 3eo on the guiding of the incident light from the incident surface 3a.

Next, another modification will be described with reference to FIG. 12 showing a cross section on the plane S1. In this modification, the curved shape of the bent portion 3f is one curve. A part of the light incident from the incident surface 3a is reflected by the cross-sectional shape 3f1 as in the ray example RayF12, is incident on the linear portion 3h, and is guided. A part of the light incident from the side surface prism entrance surface 3eo1 is reflected by the reflective surface 3eo2 and reflected by the reflective surface 3eo3 that is continuously connected to the curved surface of the bent portion 3f as in the ray example RayS9, and is emitted. Light is guided toward the surface 3b. The light incident from the side wall surface 3e1' is guided toward the exit surface 3b as in the ray example RayS10. In this modification, by providing the curved surface facing the entrance surface 3a, the entrance surface 3a, the accommodation space surrounded by the side surface prism entrance surface 3eo1 and the side wall surface 3e1′, and the side surface prism 3eo1, all the light emitted from the scintillator 5 is provided. It is possible to take the light of the azimuth into the light guide 3 and guide the light, and thus it is possible to improve the light utilization efficiency. The accommodation space of the present modification has a surface on which light is incident and faces all the surfaces of the scintillator 5 that emit light, but faces a part of the surface of the scintillator 5 that emits light. Then, the effect of improving the light utilization efficiency is also obtained by having the surface on which the light is incident.

Next, another modification will be described with reference to FIG. 13 showing a cross section on the plane S1. In this modification, the light receiving elements 4 are arranged on both left and right sides in a certain cross section, and in order to propagate light to both sides, the light guide 3 is bifurcated at a position facing the scintillator 5. In this modification, the cross section 3f1 has a bilaterally symmetrical shape with respect to a center line CL1 passing through the center of the scintillator 5. With the left-right symmetry, the angle of rotation of the propagation direction of the light incident from the incident surface 3a can be made small (within approximately 90 degrees). In general, as the angle of rotation of the light propagation direction increases, it becomes more difficult to reflect the light so that it reaches the light receiving element 4, and more light leaks from the light guide 3. Therefore, by making the cross section 3f1 of the bent portion symmetrical with respect to the center line CL1, there is an effect that the light utilization efficiency is improved. The side prism entrance surface 3e1 is arranged so as to face the side surfaces 5d on both sides of the scintillator 5. Examples of light rays incident on the left and right light receiving elements 4 are described as RayS11 and RayS12. In each case, the light enters from the side prism entrance surface 3e1, is reflected by the reflecting surface 3e2, is sequentially reflected by the cross-sectional shapes 3f2, 3f1, is reflected by the straight line portion 3h2, and is incident on the light receiving element 4 from the exit surface 3b. Here is an example. Even if the light receiving elements 4 are arranged on both the left and right sides, the light utilization efficiency can be improved by the structure having the side surface prism. In this configuration, there is no or almost no light beam that can be rotated in the propagation direction by 180 degrees by the side surface prism 3e. Therefore, since the angle of rotation of the light propagation direction is small, there is an effect that the light utilization efficiency is improved. Further, since there is no side surface prism 3eo installed in the outer bent portion 3f1 shown in FIG. 9B, the outer bent portion 3f1 and the side surface prism 3e can be separately optimized, and the light utilization efficiency is improved. Play. Although there is no slanted portion between the straight section 3h1 and the bent section 3f1 in FIG. 13, the radius of curvature of the bent section 3f1 is increased to improve the light utilization efficiency and the slanted section may be provided. good.

As described above, the configuration in which the light receiving elements 4 are provided on both sides when viewed in a certain cross section as in the present configuration has an effect of improving the light utilization efficiency. Further, the reflecting surface 3e2 can have various shapes described in the first to third embodiments. Note that the scintillator 5 as donut-like shape, along the center line CL1, such primary electron beam 100, in the case through which the particles, the light guide 3 may also be provided with through holes along the center line CL1. The through hole may have various shapes such as a circle and a square. As described above, the first to third embodiments have been described, but the matters described in each may be appropriately combined, and a larger effect may be obtained by combining them.

According to the above configuration, it is possible to improve the light utilization efficiency.

DESCRIPTION OF SYMBOLS 1 Electron microscope 2 Electron source 3 Light guide 3a Incident surface, 1st surface 3b Exit surface 3e Side surface prism 3e1 Side surface prism entrance surface, Side wall surface, 2nd surface 3e2 Reflective surface (inclined surface)
3f Bent portion 3f1 Outer curved surface, bent portion, cross-sectional shape of bent portion 3f2 Bent portion, cross-sectional shape of bent portion 3g Sloped portion 3g1 Sloped portion 3g2 Sloped portion 3h Straight portion 3h1 Straight portion 3h2 Straight portion 4 Light receiving element 5 Scintillator 6 Signal particle Limiting plate 50 Sample 60 Electron optical lens barrel 61 Sample chamber 100 Primary electron beam 101 Secondary particles

Claims (12)

A scintillator,
An incident surface on which the light from the scintillator is incident, an emission surface that emits the light incident from the incident surface, and a light guide having a surface that guides the light incident from the incident surface to the emission surface side, A charged particle beam device provided with,
The charged particle beam device further includes an electron optical system capable of bending toward the scintillator, and secondary particles or tertiary particles emitted from a sample directly enter the scintillator,
The light guide is
Has a bend,
The charged particle beam device, wherein the bent portion has a surface that guides light to the emission surface, other than a region between the incident surface and the emission surface. In claim 1,
In the light guide, a scintillator accommodating space composed of the incident surface and a side wall surface having a surface direction in a direction different from the incident surface, and a reflecting surface for reflecting light incident from the side wall surface are formed. Characterized charged particle beam device. In claim 2,
The charged particle beam device having a light guide, wherein the reflecting surface has a shape that reflects light twice or more. In claim 1,
The charged particle beam device according to claim 1, wherein the light guide includes an inclined portion on the exit surface side with respect to the bent portion. In claim 4,
The charged particle beam device according to claim 1, wherein the inclined portion has a cross-sectional shape formed by straight lines that are substantially parallel to each other when the light guide is cut along a plane including the incident surface and the emission surface. The charged particle beam device according to claim 1, wherein
The light guide is
The scintillator is formed of a first surface facing a surface opposite to the charged particle incident surface of the scintillator and a second surface facing a surface different from the surface opposite to the charged particle incident surface of the scintillator. A scintillator accommodating portion that constitutes a scintillator accommodating space for accommodating, and an inclined surface that reflects light incident from the second surface toward the inside of the light guide,
The charged particle beam device, wherein the first surface is the incident surface. In claim 6,
The charged particle beam device, wherein the first surface is larger than the second surface. In claim 6,
A charged particle beam device, wherein a reflecting member is provided on the inclined surface. In claim 6,
The charged particle beam device according to claim 1, wherein the inclined surface is formed of a plurality of surfaces facing different directions or a curved surface. In claim 6,
The charged particle beam device according to claim 1, wherein the light guide includes a bent portion that guides light incident from the first surface and the second surface in different directions. In claim 10,
The charged particle beam device, wherein the light guide includes a linear portion that guides the light to the emission surface, and an inclined portion that is formed between the linear portion and the bent portion. The surface of the bent portion has an outer curved surface that is a curved surface on the outer side in the bending direction of the light guide, starting from an incident surface end that is an end portion of the incident surface.
A cross section of the outer curved surface when the light guide is cut by a plane including the entrance surface and the exit surface has a portion that can be approximated by a circle equation, and the center of the circle is a surface parallel to the entrance surface. A charged particle beam device, wherein the charged particle beam device is located farther from the light guide than any of the points therein.

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