WO2013175972A1 - Electron microscope and electron detector - Google Patents

Electron microscope and electron detector Download PDF

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Publication number
WO2013175972A1
WO2013175972A1 PCT/JP2013/063084 JP2013063084W WO2013175972A1 WO 2013175972 A1 WO2013175972 A1 WO 2013175972A1 JP 2013063084 W JP2013063084 W JP 2013063084W WO 2013175972 A1 WO2013175972 A1 WO 2013175972A1
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Prior art keywords
electron
scintillator
detector
sample
electron beam
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PCT/JP2013/063084
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French (fr)
Japanese (ja)
Inventor
裕介 丹波
長沖　功
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株式会社日立ハイテクノロジーズ
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Publication of WO2013175972A1 publication Critical patent/WO2013175972A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/244—Detectors; Associated components or circuits therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/244—Detection characterized by the detecting means
    • H01J2237/2443—Scintillation detectors

Definitions

  • the present invention relates to an electron microscope and an electron detector used for the electron microscope.
  • the resolution and image quality (definition) of an image observed with an electron microscope are determined by the irradiation conditions (acceleration voltage, beam current) of the primary electron beam, the performance of the electron lens, and the like. For example, when the irradiation conditions of the primary electron beam are the same, an observation image with higher resolution can be obtained when the focal length of the objective lens is shorter.
  • FIG. 9 is a diagram schematically showing the structure of three types of objective lenses in a conventional electron microscope.
  • the lens magnetic field 150 is formed in the objective lens 15a, and the sample 60 is disposed outside the objective lens 15a.
  • the lens magnetic field 150 functions as a lens that focuses the primary electron beam 12
  • the sample 60 is disposed at a position away from the lens. That is, the focal length of the lens (objective lens 15a) must be long. Accordingly, the out-lens objective lens 15a cannot sufficiently achieve the goal of improving the resolution of the observation image.
  • the lens magnetic field 150 is formed in the objective lens 15a, and the sample 60 is also arranged in the objective lens 15b. That is, since the sample 60 is disposed almost at the same place as the lens magnetic field 150, the focal length of the objective lens 15b is naturally shortened. Accordingly, the in-lens objective lens 15b can improve the resolution of the observation image.
  • the in-lens type since the sample 60 is arranged in the objective lens 15b, there is a demerit that the large sample 60 cannot be observed.
  • the out-lens type since the sample 60 is disposed outside the objective lens 15a, there is an advantage that the large sample 60 can be observed. Therefore, the semi-in-lens type is put to practical use as a compromise between the out-lens type and the in-lens type.
  • the lens magnetic field 150 is formed outside the objective lens 15c, and the sample 60 is also in the vicinity of the lens magnetic field 150 outside the objective lens 15c. Placed in. Therefore, with the semi-in-lens type objective lens 15c, the large sample 60 can be observed, and the resolution of the observation image can be improved even if the in-lens type is not possible.
  • the arrangement position of the secondary electron detector 20 that detects the secondary electrons 122 emitted from the sample 60 is also the resolution of the observation image, Affects image quality (sharpness).
  • the secondary electron detector 20 is disposed on the outer upper side of the in-lens type objective lens 15b.
  • FIG. 1 of Patent Document 1 discloses an example in which a sample and a secondary electron detector are both arranged in an in-lens objective lens.
  • the secondary electron detector can capture more secondary electrons emitted from the sample, and therefore an observation image generated by the detection signal.
  • S / N Signal to Noise Ratio
  • both the sample and the scintillator are arranged in an in-lens objective lens, and the fluorescence emitted from the scintillator is converted to photoelectrons arranged outside the objective lens via a light guide.
  • a multiplier tube also referred to as a photomultiplier tube (PMT)
  • PMT photomultiplier tube
  • the scintillator is a glass substrate coated with a phosphor, and emits fluorescence from the phosphor when an electron beam enters the phosphor.
  • the photomultiplier tube is a photoelectric conversion element that generates electrons by receiving the fluorescence emitted from the scintillator, and multiplies the generated electrons to generate electricity corresponding to the brightness of the received fluorescence. Output a signal.
  • the electron detector in addition to the secondary electron detector, a reflected electron detector, a transmission electron detector ( Scattered electron detectors (also called dark field detectors) are used.
  • Scattered electron detectors also called dark field detectors
  • the secondary electron detector, the backscattered electron detector, the transmitted electron detector, and the scattered electron detector are collectively referred to simply as an electron detector.
  • Patent Documents 1 and 2 describe that the sample and the secondary electron detector are surely arranged in an in-lens type objective lens.
  • the gap between the upper magnetic pole and the lower magnetic pole of a general in-lens objective lens is only about 10 mm. Therefore, because of the physical size of the electron detector (secondary electron detector, backscattered electron detector, scattered electron detector, etc.), the sample and the electron detector can actually be accommodated in the gap. Is not limited.
  • the electron detector when the electron detector is composed of a scintillator and a photomultiplier tube, it has been conventionally difficult to accommodate the electron detector in the gap between the upper magnetic pole and the lower magnetic pole of the objective lens.
  • Patent Document 2 only the scintillator portion of the electron detector is disposed in the gap between the upper magnetic pole and the lower magnetic pole of the objective lens, and the photomultiplier tube portion is disposed outside the objective lens.
  • Cited Document 1 Although what is used as an electron detector is not particularly described, it is assumed that it is a semiconductor electron detector. Since a semiconductor electron detector is small in size, it can be accommodated in the gap between the upper magnetic pole and the lower magnetic pole of the objective lens.
  • the efficiency of capturing electrons by the electron detector is improved by arranging the electron detector in the immediate vicinity of the sample, in the next stage, the sharpness of the observation image (in other words, S / N ) Is determined by the electron detection sensitivity of the electron detector itself. That is, how to improve the electron detection sensitivity of the electron detector is a technical problem to be solved next.
  • an object of the present invention is to provide an electron microscope capable of improving the electron detection sensitivity and acquiring a clear observation image having a high S / N, and an electron detector used in the electron microscope.
  • An electron microscope includes, for example, an electron gun that emits a primary electron beam, an irradiation lens that focuses the primary electron beam emitted from the electron gun and irradiates a sample to be observed, and a focusing by the irradiation lens.
  • a scanning coil for deflecting the primary electron beam thus scanned and scanning the irradiation position of the primary electron beam on the sample, and a focal point of the primary electron beam focused by the irradiation lens and deflected by the scanning coil on the sample.
  • An objective lens for adjusting to the electron beam, an electron detector for detecting electrons reflected or scattered by the sample when the primary electron beam is irradiated onto the sample, and a detection signal detected by the electron detector.
  • a detection signal processing unit that is acquired in synchronization with a scanning control signal that controls the scanning coil, and a detection signal acquired by the detection signal processing unit is the scanning control signal.
  • a detection signal acquired by the detection signal processing unit is the scanning control signal.
  • the electron detector includes, for example, a thin plate scintillator made of a ceramic phosphor, and a photomultiplier tube disposed at an end of the thin plate scintillator, and the surface of the scintillator A light reflecting layer is formed except for the portion where the photomultiplier tube is disposed, and the thin plate scintillator allows the primary electron beam or the electron beam transmitted through the sample to pass therethrough. For this purpose, a through hole is formed.
  • an electron microscope capable of acquiring a clear observation image with a high S / N and an electron detector used for the electron microscope are provided.
  • FIG. 1 is a diagram showing an example of the configuration of a scanning transmission electron microscope according to a first embodiment of the present invention.
  • FIG. 1 is a diagram showing an example of the configuration of a scanning transmission electron microscope according to the first embodiment of the present invention.
  • the electron microscope 100 is mainly configured to include an electron optical system device 10 and a control system device 70.
  • the electron optical system apparatus 10 includes an electron gun 11, an irradiation lens 13, a scanning coil 14, an objective lens 15, a sample image moving coil 16, an intermediate lens 17, a projection lens 18, a secondary electron detector 20, and reflected electron detection.
  • the secondary electron detector 20 emits secondary electrons (several eV to several 10 eV) emitted from the sample 60 when the sample 60 is irradiated with the primary electron beam 12 emitted from the electron gun 11 and focused by the irradiation lens 13. ) With a degree of energy.
  • the backscattered electron detector 30 detects backscattered electrons reflected by the sample 60 when the sample 60 is irradiated with the primary electron beam 12.
  • the dark field detector 40 detects scattered electrons obtained by scattering the primary electron beam 12 by the sample 60.
  • the bright field detector 50 detects transmitted electrons that have passed through the sample 60 by the primary electron beam 12.
  • the objective lens 15 is an in-lens type, and the sample 60, the backscattered electron detector 30, and the dark field detector 40 are included in the objective lens 15, that is, the upper magnetic pole of the objective lens 15. And the lower magnetic pole.
  • the backscattered electron detector 30 and the dark field detector 40 have a unique structure, and details thereof will be described with reference to a separate drawing.
  • control system device 70 includes an electron optical system control unit 71, a detection signal processing unit 72, an image processing unit 73, a control computer 74, a display device 75, and the like.
  • the electron optical system control unit 71 controls the acceleration voltage and beam current of the primary electron beam 12 emitted from the electron gun 11 in accordance with instructions from the control computer 74, the irradiation lens 13, the scanning coil 14, the objective lens 15, An excitation current for operating the sample image moving coil 16, the intermediate lens 17, the projection lens 18 and the like is supplied to the electron optical system device 10.
  • the detection signal processing unit 72 includes a detection signal detected by the secondary electron detector 20, the backscattered electron detector 30, the dark field detector 40, the bright field detector 50, and the like.
  • the signal is acquired and amplified in synchronization with the scanning control signal when controlling the signal, and signal processing such as A / D (Analog-to-Digital) conversion is performed.
  • the image processing unit 73 processes the detection signal A / D converted by the detection signal processing unit 72 and the scanning control signal from the electro-optical system control unit 71 to generate pixel data of the observation image, An observation image based on the pixel data is displayed on the display device 75.
  • control computer 74 acquires various information (observation mode, magnification, brightness, focus adjustment, etc.) for acquiring an observation image input by the user, and controls the electron optical system control unit 71 based on the information. Through this, the acceleration voltage of the electron gun 11 in the electron optical system device 10 and the excitation current of each lens are controlled.
  • FIG. 2 is a diagram schematically showing the arrangement of electron detectors for detecting secondary electrons, scattered electrons, and transmitted electrons in the scanning transmission electron microscope 100.
  • FIG. 2 in order to simplify the explanation and make it easy to understand, description of some components of the electron optical system device 10 such as the objective lens 15 and the backscattered electron detector 30 is omitted.
  • the primary electron beam 12 emitted from the electron gun 11 is finely focused by the irradiation lens 13 and irradiated to the sample 60 disposed in the objective lens 15 (not shown in FIG. 2).
  • the At this time, secondary electrons 122 are emitted from the surface portion of the sample 60 irradiated with the primary electron beam 12. Since the emitted secondary electrons 122 have low energy (several eV to several tens eV), they are wound up by the magnetic field of the objective lens 15 and emitted outside the objective lens 15. Since the secondary electron detector 20 to which a positive voltage is applied is provided just outside the objective lens 15, the secondary electrons 122 are attracted by the positive voltage and detected by the secondary electron detector 20.
  • the scattered electrons 125 are detected by a disk-shaped dark field detector 40 having a hole in the center provided below the sample 60.
  • the bright field detector 50 is provided further below the dark field detector 40 and detects the transmitted electrons 124 that have passed through the sample 60 and have passed through the central hole of the dark field detector 40. .
  • the scanning coil 14 receives a scanning control signal from the electron optical system control unit 71 and sequentially deflects the primary electron beam 12 to thereby change the irradiation position of the primary electron beam 12 on the sample 60 so-called horizontal scanning and vertical. Let it scan.
  • the detection signal processing unit 72 acquires the detection signals from the secondary electron detector 20, the dark field detector 40, and the bright field detector 50 in synchronization with the scanning control signal of the scanning coil 14, and performs A / D conversion. Then, pixel data of the observation image is generated. Two-dimensional images are generated and displayed on the display device 75 as secondary electron observation images, scattered electron observation images, and transmission electron observation images, respectively.
  • reflected electrons are similarly detected by the reflected electron detector 30, a transmission electron observation image is generated by the image processing unit 73, and the generated transmission electron observation image is displayed on the display device. 75.
  • FIG. 3 is a diagram showing an example of a cross-sectional structure of the main part of the objective lens 15 when the backscattered electron detector 30 and the dark field detector 40 are arranged in the objective lens 15.
  • FIG. 4 is a diagram showing (a) an example of a top view of the backscattered electron detector 30 and (b) an example of a top view of the dark field detector 40.
  • the sample 60, the backscattered electron detector 30, and the dark field detector 40 are disposed in the gap between the upper magnetic pole 151 and the lower magnetic pole 152 of the objective lens 15.
  • the backscattered electron detector 30 and the dark field detector 40 are each constituted by thin scintillators 31 and 41 that are horizontally long, and further, at one end thereof.
  • Photomultiplier tubes 32 and 42 are disposed in the section. Further, through holes 33 and 43 for allowing the primary electron beam 12 or the transmitted electrons 124 to pass therethrough are provided near the other end of the scintillators 31 and 41.
  • the reflected electrons 123 are detected by the reflected electron detector 30 disposed immediately above the sample 60, and the scattered electrons 125 are detected by the dark field detector 40 disposed immediately below the sample 60. Detected by. As described above, since the gap between the upper magnetic pole 151 and the lower magnetic pole 152 of the objective lens 15 is about 10 mm, the distance from the sample 60 to the backscattered electron detector 30 or the dark field detector 40 is at most several. It is about mm. Therefore, since the distance is small, most of the reflected electrons 123 and scattered electrons 125 can be captured by the reflected electron detector 30 or the dark field detector 40.
  • the secondary electron detector 20 is provided on the outer upper side of the objective lens 15.
  • the secondary electrons 122 emitted from the sample 60 are rolled up by the magnetic field of the objective lens 15, pass through the through-hole 33 provided in the backscattered electron detector 3, and further outside the objective lens 15. And is detected by the secondary electron detector 20.
  • detection signals of the secondary electron detector 20, the backscattered electron detector 30, and the dark field detector 40 are input to the detection signal processing unit 72.
  • the detection signal processing unit 72 includes an amplification circuit 721 that amplifies each detection signal, an A / D conversion circuit 722 that converts the amplified detection signal into a digital signal, and the like. Note that the timing at which A / D conversion is performed by the A / D conversion circuit 722 is determined by a scanning control signal for controlling the scanning coil 14 supplied from the electron optical system control unit 71.
  • FIG. 5 is a diagram showing (a) an example of a longitudinal sectional structure of the backscattered electron detector 30 and (b) an example of a longitudinal sectional structure of the dark field detector 40.
  • the cross-sectional structures of the backscattered electron detector 30 and the dark field detector 40 are almost the same. That is, the scintillators 31 and 41 are configured by coating the thin plate-like ceramic phosphors 311 and 411 with the light reflecting layers 312 and 412.
  • the ceramic phosphors 311 and 411 are sintered bodies in which particulate phosphors are vitrified by heating to 1000 degrees Celsius, and the thickness of the cross section is preferably about 200 to 300 ⁇ m.
  • the ceramic phosphors 311 and 411 phosphors having an afterimage time of 200 nsec or less are preferably used.
  • P47 Y 2 SiO 2 ; Ce is available.
  • an observation image of 320 ⁇ 240 pixels As a moving image of 30 frames per second.
  • An observation image of 640 ⁇ 480 pixels can be acquired as a moving image of about 7 frames per second.
  • the light reflecting layers 312 and 412 are formed by vapor-depositing a metal such as aluminum on the ceramic phosphors 311 and 411.
  • a metal such as aluminum on the ceramic phosphors 311 and 411.
  • the metal to vapor-deposit is not limited to aluminum, Gold and platinum may be sufficient.
  • the thickness of the deposited layer is about 10 to 30 nm, preferably about 20 nm on the surface side where the reflected electrons 123 or scattered electrons 125 are incident. Further, the thickness of the vapor deposition layer on the side opposite to the surface on which the reflected electrons 123 or the scattered electrons 125 are incident may be about 10 to 30 nm, but it may be made thicker than that.
  • the aluminum vapor deposition layer is about 10 to 30 nm, an electron beam having energy of several hundred eV or more can pass through the vapor deposition layer.
  • the fluorescence emitted in the ceramic phosphors 311 and 411 is not transmitted through the aluminum vapor deposition layers (light reflecting layers 312 and 412) but reflected inward.
  • the scintillators 31 and 41 in the backscattered electron detector 30 and the dark field detector 40 are composed of the ceramic phosphors 311 and 411, and the ceramic phosphors 311 and 411 are light. It is characterized by being coated with reflective layers 312 and 412. As a matter of course, the light reflecting layers 312 and 412 are not coated on the surfaces of the ceramic phosphors 311 and 411 where the photomultiplier tubes 32 and 42 are connected.
  • FIG. 6 is a diagram showing (a) an example of an observation image of a cross section of a conventional scintillator, and (b) an example of an observation image of a cross section of a ceramic phosphor according to the present embodiment.
  • a conventional scintillator is obtained by forming a granular phosphor coating film having a thickness of about 30 ⁇ m on a glass substrate having a thickness of several hundreds ⁇ m.
  • the electron beam spreads in a triangular pyramid shape while being scattered by the phosphor atoms, and fluorescence is emitted from the phosphor atoms with which the electrons collide.
  • the conventional general backscattered electron detector and dark field detector it is necessary to provide a photomultiplier tube directly on the opposite surface of the glass substrate of the scintillator where the granular phosphor coating film is formed. .
  • the physical size of the backscattered electron detector and the dark field detector is increased, and the backscattered electron detector and the dark field detector are disposed in the gap between the upper magnetic pole 151 and the lower magnetic pole 152 of the objective lens 15. could not.
  • the ceramic phosphor according to the present embodiment has the same physical properties as amorphous glass, and is excellent in translucency.
  • the cross-sectional structure (fracture surface) has a structure very similar to the fracture surface of glass, as shown in FIG.6 (b).
  • the thickness of the ceramic phosphor is about 200 to 300 ⁇ m, which is much thicker than the thickness of the conventional granular phosphor coating film (about 20 ⁇ m). Therefore, the ceramic phosphor itself has sufficient mechanical strength as a substrate, and a conventional glass substrate for supporting the granular phosphor coating film becomes unnecessary.
  • the ceramic phosphor is excellent in translucency (almost transparent), so that the fluorescence emitted from the phosphor atoms passes through the thin plate-like ceramic phosphor in three dimensions. Spread in the direction. That is, the fluorescence spreads farther in the ceramic phosphor even in the direction (lateral direction) parallel to the thin plate surface of the ceramic phosphor.
  • the ceramic phosphors 311 and 411 are coated with light reflecting layers 312 and 412 that can enter an electron beam and reflect fluorescence. Therefore, when the electron beam enters, the fluorescence generated in the ceramic phosphors 311 and 411 is confined in the ceramic phosphors 311 and 411 and is reflected by the coated light reflecting layers 312 and 412 while being reflected by the scintillators 31 and 41. The light is guided to the photomultiplier tubes 32 and 42 provided at the ends.
  • the photomultiplier tubes 32 and 42 can be provided at the end portions of the scintillators 31 and 41, the reflected electrons composed of the scintillators 31 and 41 and the photomultiplier tubes 32 and 42 are provided.
  • the detector 30 and the dark field detector 40 can be disposed in the gap between the upper magnetic pole 151 and the lower magnetic pole 152 of the objective lens 15.
  • FIG. 7 is a diagram showing an example of a measurement result obtained by measuring the acceleration voltage dependence characteristic of the electron beam penetration depth into the ceramic phosphor.
  • the horizontal axis represents the acceleration voltage (kV) of the incident electron beam
  • the vertical axis represents the electron beam penetration depth ( ⁇ m).
  • the electron beam when an electron beam accelerated at 100 kV is incident on the ceramic phosphor, the electron beam enters to a depth of about 20 ⁇ m. Further, when an electron beam accelerated at 300 kV is incident, it enters to a depth of about 200 ⁇ m. Furthermore, according to FIG. 7, when the acceleration voltage is 50 kV or less, the electron beam enters only about several ⁇ m at most from the surface of the ceramic phosphor.
  • the thickness of the granular phosphor coating film of the conventional scintillator is about 30 ⁇ m, and the ceramic phosphors 311 and 411 of the scintillators 31 and 41 according to the present embodiment.
  • the scintillators 31 and 41 according to the present embodiment greatly improve the electron detection sensitivity.
  • the reason why the electron detection sensitivity is improved will be described. Since the penetration depth of the electron beam is almost the same in both the case of the granular phosphor coating film and the case of the ceramic phosphor, in the following description, the measurement result of FIG. 7 is used as the penetration depth of the electron beam. To do.
  • the acceleration voltage of the electron beam is high.
  • the acceleration voltage of the entering electron beam is 300 kV
  • the entering depth is about 200 ⁇ m. Therefore, the electron beam having an acceleration voltage of 300 kV has energy penetrating through the granular phosphor coating film having a thickness of about 30 ⁇ m in the conventional scintillator.
  • the thicknesses of the ceramic phosphors 311 and 411 of the scintillators 31 and 41 are about 200 to 300 ⁇ m, an electron beam with an acceleration voltage of 200 kV has the thickness. It does not lead to penetrating.
  • the electron beam travels about 200 ⁇ m in the phosphor, whereas in the conventional case, the electron beam travels only about 30 ⁇ m in the phosphor. Therefore, in the present embodiment, the number of times the electron beam collides with the atoms of the phosphor increases as much as the electron beam continues in the phosphor longer than in the conventional case, and the fluorescence emitted from the phosphor increases accordingly.
  • the ceramic phosphors 311 and 411 in this embodiment emit about seven times as much fluorescence as the conventional granular phosphor coating film.
  • the ceramic phosphors 311 and 411 in this embodiment have high translucency and the surfaces thereof are covered with the light reflecting layers 312 and 412, they also function as light guides (optical waveguides). That is, the fluorescence emitted in the ceramic phosphors 311 and 411 spreads in a three-dimensional direction (that is, in all directions) and is reflected by the light reflecting layers 312 and 412, and almost all of the fluorescence is transmitted to the photomultiplier tubes 32 and 42. Light is guided. Therefore, much more fluorescence is incident on the photomultiplier tubes 32 and 42 of this embodiment than in the conventional case.
  • the present embodiment It can be seen that the electron detection sensitivity of the backscattered electron detector 30 and the dark field detector 40 according to the present invention is improved as compared with the conventional electron detector comprising a scintillator and a photomultiplier tube.
  • the reflected electrons 123 and scattered electrons 125 may be regarded as having the same acceleration energy as that of the primary electron beam 12 although the accelerated primary electron beam 12 is slightly decelerated.
  • the acceleration voltage of the electron beam is low, for example, the acceleration voltage of the entering electron beam is 50 kV or less.
  • the electron beam has a depth of several ⁇ m from the surface of the granular phosphor coating film or the ceramic phosphors 311 and 411 in both the conventional case and the present embodiment. Only enters.
  • the fluorescence emitted when the electron beam enters is emitted in a region from the surface of the granular phosphor coating film or the ceramic phosphors 311 and 411 to a depth of several ⁇ m. Therefore, in the case of a conventional scintillator, the fluorescence generated in a relatively shallow region having a depth of several ⁇ m of the granular phosphor coating film passes through the granular phosphor coating film to about 20 ⁇ m to the glass substrate side. become.
  • the translucency of the granular phosphor coating film is low, the fluorescence is attenuated when passing through the granular phosphor coating film. That is, since the attenuated fluorescence is incident on the photomultiplier tube electrons, the electron detection sensitivity of the electron detector using the conventional scintillator and the photomultiplier tube is lowered.
  • the ceramic phosphors 311 and 411 have high translucency, and the surfaces thereof are covered with the light reflecting layers 312 and 412. Therefore, almost all of the fluorescence emitted from the surface of the ceramic phosphors 311 and 411 in the three-dimensional direction from the surface of the ceramic phosphors 311 and 411 is reflected by the light reflecting layers 312 and 412 when the electron beam enters. The light is guided to the photomultiplier tubes 32 and 42.
  • the backscattered electron detector 30 and the dark field detector 40 according to the present embodiment have the same electron detection sensitivity as that of the conventional scintillator and photomultiplier tube. It turns out that it improves compared with the vessel.
  • the backscattered electron detector 30 and the dark field according to the present embodiment are also mostly used for the same reason when the acceleration voltage of the electron beam is 50 kV or more and 130 kV or less.
  • the electron detection sensitivity of the detector 40 is higher than the electron detection sensitivity of an electron detector composed of a conventional scintillator and a photomultiplier tube.
  • the effect of improving the electron detection sensitivity of the reflected electron detector 30 and the dark field detector 40 is obtained. Therefore, the S / N of the observation image is improved, and a clearer observation image can be obtained.
  • FIG. 8 is a diagram showing an example of the structure of a dark field detector according to the second embodiment of the present invention, in which (a) is an example of a longitudinal sectional view and (b) is an example of a top view. Also in the second embodiment, the configuration of the scanning transmission electron microscope 100 shown in FIG. 1 is the same, and only the dark field detector 40 is different. Therefore, description of the configuration of the electron microscope 100 is omitted here.
  • the dark field detector 40a is configured to include a scintillator 41a and a photomultiplier tube 42, and the scintillator 41a has different hole diameters.
  • One through hole 43, 43a is provided.
  • the dark field detector 40a has a movement control mechanism (not shown) for moving the dark field detector 40a in the horizontal direction from the outside of the objective lens 15. Then, the control computer 74 (see FIG. 1) selects one of the through holes 43 and 43a by controlling the movement control mechanism via the electron optical system control unit 71, and selects the selected through hole 43 or 43a. It is assumed that the dark field detector 40 a can be moved so that the center of the dark field coincides with the optical axis of the primary electron beam 12.
  • the dark field detector 40 a detects the scattered electrons 125 in which the primary electron beam 12 is scattered by the sample 60.
  • the dark field detector 40a detects both the scattered electrons 125 having a small scattering angle and the scattered electrons 125 having a large scattering angle.
  • the dark field detector 40a detects the scattered electrons 125 having a large scattering angle and does not detect the scattered electrons 125 having a small scattering angle.
  • an appropriate dark field observation image corresponding to the constituent element of the sample 60 can be obtained by selecting the size of the diameter of the through holes 43 and 43a according to the sample 60.
  • the scintillator 41a is provided with two through holes having different diameters (in FIG. 8, through holes 43 and 43a). However, three or more through holes having different diameters may be provided. .
  • the plurality of through holes 43 and 43a having different diameters are provided in the scintillator 41a of the dark field detector 40a.
  • the plurality of through holes 33 are provided in the backscattered electron detector 30. You may do it.
  • the reflected electron observation image by the reflected electrons 123 having a large reflection angle includes information representing the shape of the surface of the sample 60, and the reflected electron observation image by the reflected electrons 123 having a small reflection angle is information representing the components of the sample 60. Is said to be included.
  • the scintillator portion may be made of a ceramic phosphor, and the ceramic phosphor may be covered with a fluorescent reflecting film such as aluminum.
  • the secondary electron detector 20 and the bright field detector 50 do not need to be provided with a through hole for allowing an electron beam to pass therethrough.
  • the electron microscope 100 is a scanning transmission electron microscope, but may be a scanning electron microscope.
  • the configuration of the scanning electron microscope is roughly the same as that of the electron microscope 100 of FIG. 1, but the dark field detector 40, the bright field detector 50, the sample image moving coil 16, the intermediate lens 17, and the projection lens.
  • the present invention is not limited to the embodiment described above, and includes various modifications.
  • the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described.
  • a part of the configuration of an embodiment can be replaced with a part of the configuration of another embodiment, and further, a part or all of the configuration of the other embodiment is added to the configuration of the certain embodiment. Is also possible.
  • Electron system apparatus 11
  • Electron gun 12
  • Primary electron beam 13
  • Irradiation lens 14
  • Scanning coil 15
  • Objective lens 16
  • Intermediate lens 18
  • Secondary electron detector 30
  • Photomultiplier tube 33, 43, 43a Through hole 40, 40a Dark field detector 50
  • Bright field detector 60
  • Sample 70
  • Control system device 71
  • Electron optical system control unit 72
  • Detection signal processing unit 73
  • Image processing unit 74
  • Control computer 75
  • Display device 100
  • Electron microscope 122
  • Secondary electron 123 Reflected electron 124
  • Transmitted electron 125
  • Lens magnetic field 151
  • Upper magnetic pole 152
  • Light reflecting layer 721
  • Amplifying circuit 722 A / D conversion circuit

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  • Analytical Chemistry (AREA)
  • Measurement Of Radiation (AREA)

Abstract

When a reflected electron (123) or a scattered electron (125) which is emitted from a specimen (60) passes through a light reflection layer (312, 412) and enters a ceramic fluorescent light body (311, 411) of a scintillator (31, 41), fluorescent light is generated therewithin. The ceramic fluorescent light body (311, 411) is highly translucent, and the generated fluorescent light is reflected internally with the light reflecting layer (312, 412), and thus efficiently light guided to a photomultiplier tube (32, 42). Accordingly, the electron detection sensitivity of a reflected electron detector (30) and a dark-field detector (40) comprising the scintillator (31, 41) is improved.

Description

電子顕微鏡および電子検出器Electron microscope and electron detector
　本発明は、電子顕微鏡およびその電子顕微鏡に用いられる電子検出器に関する。 The present invention relates to an electron microscope and an electron detector used for the electron microscope.
　一般に、電子顕微鏡による観察画像の分解能や像質（鮮明度）は、一次電子線の照射条件（加速電圧、ビーム電流）、電子レンズの性能などによって定まる。例えば、一次電子線の照射条件が同じ場合には、対物レンズの焦点距離が短いほうが高分解能の観察画像が得られる。 Generally, the resolution and image quality (definition) of an image observed with an electron microscope are determined by the irradiation conditions (acceleration voltage, beam current) of the primary electron beam, the performance of the electron lens, and the like. For example, when the irradiation conditions of the primary electron beam are the same, an observation image with higher resolution can be obtained when the focal length of the objective lens is shorter.
　従来、電子顕微鏡の対物レンズは、レンズ磁場と試料との配置関係などにより、アウトレンズ型、インレンズ型、セミインレンズ型の３つのタイプに分類されている。図９は、従来の電子顕微鏡における３つのタイプの対物レンズの構造を模式的に示した図である。 Conventionally, the objective lens of an electron microscope is classified into three types: an out-lens type, an in-lens type, and a semi-in-lens type, depending on the arrangement relationship between the lens magnetic field and the sample. FIG. 9 is a diagram schematically showing the structure of three types of objective lenses in a conventional electron microscope.
　図９（ａ）に示すように、アウトレンズ型の対物レンズ１５ａでは、そのレンズ磁場１５０は、対物レンズ１５ａの中に形成され、試料６０は、対物レンズ１５ａの外に配置される。このとき、レンズ磁場１５０は、一次電子線１２を集束させるレンズとして機能するので、試料６０は、レンズから離れた位置に配置されることになる。つまり、そのレンズ（対物レンズ１５ａ）の焦点距離は、長くならざるを得ない。従って、アウトレンズ型の対物レンズ１５ａでは、観察画像の分解能を向上させるという目標を十分には達成することができない。 As shown in FIG. 9A, in the out-lens type objective lens 15a, the lens magnetic field 150 is formed in the objective lens 15a, and the sample 60 is disposed outside the objective lens 15a. At this time, since the lens magnetic field 150 functions as a lens that focuses the primary electron beam 12, the sample 60 is disposed at a position away from the lens. That is, the focal length of the lens (objective lens 15a) must be long. Accordingly, the out-lens objective lens 15a cannot sufficiently achieve the goal of improving the resolution of the observation image.
　それに対し、図９（ｂ）に示すように、インレンズ型の対物レンズ１５ｂでは、レンズ磁場１５０は、対物レンズ１５ａの中に形成され、試料６０も、対物レンズ１５ｂの中に配置される。つまり、試料６０は、レンズ磁場１５０とほとんど同じ場所に配置されるので、対物レンズ１５ｂの焦点距離は、自ずと短くなる。従って、インレンズ型の対物レンズ１５ｂでは、観察画像の分解能の向上を図ることができる。 On the other hand, as shown in FIG. 9B, in the in-lens type objective lens 15b, the lens magnetic field 150 is formed in the objective lens 15a, and the sample 60 is also arranged in the objective lens 15b. That is, since the sample 60 is disposed almost at the same place as the lens magnetic field 150, the focal length of the objective lens 15b is naturally shortened. Accordingly, the in-lens objective lens 15b can improve the resolution of the observation image.
　ただし、別の観点から見れば、インレンズ型の場合、試料６０が対物レンズ１５ｂの中に配置されるので、大きな試料６０の観察ができないというデメリットがある。一方、アウトレンズ型の場合、試料６０が対物レンズ１５ａの外に配置されるので、大きな試料６０の観察もできるというメリットがある。そこで、アウトレンズ型とインレンズ型とを折衷したものとして、セミインレンズ型が実用に供されている。 However, from another viewpoint, in the case of the in-lens type, since the sample 60 is arranged in the objective lens 15b, there is a demerit that the large sample 60 cannot be observed. On the other hand, in the case of the out-lens type, since the sample 60 is disposed outside the objective lens 15a, there is an advantage that the large sample 60 can be observed. Therefore, the semi-in-lens type is put to practical use as a compromise between the out-lens type and the in-lens type.
　図９（ｃ）に示すように、セミインレンズ型の対物レンズ１５ｃでは、そのレンズ磁場１５０は、対物レンズ１５ｃの外に形成され、試料６０も、対物レンズ１５ｃの外のレンズ磁場１５０の近傍に配置される。従って、セミインレンズ型の対物レンズ１５ｃでは、大きな試料６０の観察ができ、インレンズ型の場合には及ばないにしても、観察画像の分解能の向上を図ることができる。 As shown in FIG. 9C, in the semi-in-lens type objective lens 15c, the lens magnetic field 150 is formed outside the objective lens 15c, and the sample 60 is also in the vicinity of the lens magnetic field 150 outside the objective lens 15c. Placed in. Therefore, with the semi-in-lens type objective lens 15c, the large sample 60 can be observed, and the resolution of the observation image can be improved even if the in-lens type is not possible.
　また、走査型電子顕微鏡では、一次電子線１２が試料６０に照射されたとき、試料６０から放出される二次電子１２２を検出する二次電子検出器２０の配置位置も、観察画像の分解能や像質（鮮明度）に影響を及ぼす。例えば、図９（ｂ）では、二次電子検出器２０は、インレンズ型の対物レンズ１５ｂの外側上方に配置されている。 In the scanning electron microscope, when the sample 60 is irradiated with the primary electron beam 12, the arrangement position of the secondary electron detector 20 that detects the secondary electrons 122 emitted from the sample 60 is also the resolution of the observation image, Affects image quality (sharpness). For example, in FIG. 9B, the secondary electron detector 20 is disposed on the outer upper side of the in-lens type objective lens 15b.
　それに対し、特許文献１の図１には、試料および二次電子検出器がともにインレンズ型の対物レンズの中に配置されている例が開示されている。このように二次電子検出器を試料のすぐ近傍に配置すると、二次電子検出器が試料から放出される二次電子をより多く捕捉することができるため、その検出信号により生成される観察画像のＳ／Ｎ（Signal to Noise Ratio）が向上する。 On the other hand, FIG. 1 of Patent Document 1 discloses an example in which a sample and a secondary electron detector are both arranged in an in-lens objective lens. When the secondary electron detector is arranged in the immediate vicinity of the sample in this way, the secondary electron detector can capture more secondary electrons emitted from the sample, and therefore an observation image generated by the detection signal. S / N (Signal to Noise Ratio) is improved.
　また、特許文献２の図４には、試料およびシンチレータをともにインレンズ型の対物レンズの中に配置し、シンチレータから発せられた蛍光を、ライトガイドを介して対物レンズの外に配置された光電子増倍管（ホトマル、ＰＭＴ（Photomultiplier Tube）とも呼ばれる）まで導光する例が開示されている。 In FIG. 4 of Patent Document 2, both the sample and the scintillator are arranged in an in-lens objective lens, and the fluorescence emitted from the scintillator is converted to photoelectrons arranged outside the objective lens via a light guide. An example in which light is guided to a multiplier tube (also referred to as a photomultiplier tube (PMT)) is disclosed.
　ところで、シンチレータは、ガラス基板に蛍光体を塗布したものであり、電子線がその蛍光体に入射すると、その蛍光体から蛍光を発する。また、光電子増倍管は、光電変換素子であり、シンチレータから発せられた蛍光を受光することにより電子を生成するとともに、その生成した電子を増倍させ、受光した蛍光の明るさに応じた電気信号を出力する。 Incidentally, the scintillator is a glass substrate coated with a phosphor, and emits fluorescence from the phosphor when an electron beam enters the phosphor. The photomultiplier tube is a photoelectric conversion element that generates electrons by receiving the fluorescence emitted from the scintillator, and multiplies the generated electrons to generate electricity corresponding to the brightness of the received fluorescence. Output a signal.
　すなわち、特許文献２の例では、二次電子を捕捉するシンチレータが試料のすぐ近傍に配置されているので、シンチレータと光電子増倍管とからなる二次電子検出器による二次電子の捕捉効率が向上し、その検出信号により生成される観察画像のＳ／Ｎが向上する。 That is, in the example of Patent Document 2, since the scintillator that captures secondary electrons is arranged in the immediate vicinity of the sample, the efficiency of capturing secondary electrons by the secondary electron detector including the scintillator and the photomultiplier tube is increased. The S / N of the observation image generated by the detection signal is improved.
特開平０５－４７３３１号公報JP 05-47331 A 特開２００４－２５９４６９号公報JP 2004-259469 A
　詳しい説明は、実施形態の説明の中でするが、とくに透過走査型の電子顕微鏡の場合、電子検出器としては、二次電子検出器のほかにも、反射電子検出器、透過電子検出器（明視野検出器ともいう）、散乱電子検出器（暗視野検出器ともいう）が用いられる。なお、本明細書では、二次電子検出器、反射電子検出器、透過電子検出器、散乱電子検出器を総称して、単に、電子検出器という。 The detailed description will be given in the description of the embodiment. Particularly in the case of a transmission scanning electron microscope, as the electron detector, in addition to the secondary electron detector, a reflected electron detector, a transmission electron detector ( Scattered electron detectors (also called dark field detectors) are used. In the present specification, the secondary electron detector, the backscattered electron detector, the transmitted electron detector, and the scattered electron detector are collectively referred to simply as an electron detector.
　特許文献１，２には、確かに試料および二次電子検出器をインレンズ型の対物レンズの中に配置することが記載されている。しかしながら、一般的なインレンズ型の対物レンズの上磁極と下磁極との間隙は、１０ｍｍ程度でしかない。従って、電子検出器（二次電子検出器、反射電子検出器、散乱電子検出器など）の物理的な大きさの問題から、実際に、試料と電子検出器とをともにその間隙に収容できるとは限らない。 Patent Documents 1 and 2 describe that the sample and the secondary electron detector are surely arranged in an in-lens type objective lens. However, the gap between the upper magnetic pole and the lower magnetic pole of a general in-lens objective lens is only about 10 mm. Therefore, because of the physical size of the electron detector (secondary electron detector, backscattered electron detector, scattered electron detector, etc.), the sample and the electron detector can actually be accommodated in the gap. Is not limited.
　とくに、電子検出器がシンチレータと光電子増倍管で構成されている場合、その電子検出器を対物レンズの上磁極と下磁極との間隙に収容することは、従来困難とされていた。ちなみに、特許文献２の例では、電子検出器のうちシンチレータ部分のみが対物レンズの上磁極と下磁極との間隙に配置され、光電子増倍管部分は、対物レンズの外に配置されている。 In particular, when the electron detector is composed of a scintillator and a photomultiplier tube, it has been conventionally difficult to accommodate the electron detector in the gap between the upper magnetic pole and the lower magnetic pole of the objective lens. Incidentally, in the example of Patent Document 2, only the scintillator portion of the electron detector is disposed in the gap between the upper magnetic pole and the lower magnetic pole of the objective lens, and the photomultiplier tube portion is disposed outside the objective lens.
　なお、引用文献１には、電子検出器としてどのようなものを用いるかについては、とくに記載はされていないが、半導体の電子検出器であろうと推測される。半導体の電子検出器ならサイズが小さいので、対物レンズの上磁極と下磁極との間隙に収容可能である。 In Cited Document 1, although what is used as an electron detector is not particularly described, it is assumed that it is a semiconductor electron detector. Since a semiconductor electron detector is small in size, it can be accommodated in the gap between the upper magnetic pole and the lower magnetic pole of the objective lens.
　いずれにせよ、電子検出器を試料のすぐ近傍に配置することによって、電子検出器による電子の捕捉効率が向上したとすれば、次の段階では、観察画像の鮮明度（言い換えれば、Ｓ／Ｎ）は、電子検出器自身の電子検出感度などに律せられることになる。つまり、電子検出器の電子の検出感度を如何にして向上させるかが次に解決すべき技術課題となる。 In any case, if the efficiency of capturing electrons by the electron detector is improved by arranging the electron detector in the immediate vicinity of the sample, in the next stage, the sharpness of the observation image (in other words, S / N ) Is determined by the electron detection sensitivity of the electron detector itself. That is, how to improve the electron detection sensitivity of the electron detector is a technical problem to be solved next.
　そこで、本発明は、電子検出感度の向上を図り、Ｓ／Ｎが高い鮮明な観測画像を取得することが可能な電子顕微鏡、および、その電子顕微鏡に用いられる電子検出器を提供することを目的とする。 Accordingly, an object of the present invention is to provide an electron microscope capable of improving the electron detection sensitivity and acquiring a clear observation image having a high S / N, and an electron detector used in the electron microscope. And
　本発明に係る電子顕微鏡は、例えば、一次電子線を出射する電子銃と、前記電子銃から出射された一次電子線を集束させて観察対象の試料に照射する照射レンズと、前記照射レンズにより集束された一次電子線を偏向させ、前記試料における前記一次電子線の照射位置を走査させる走査コイルと、前記照射レンズにより集束され、前記走査コイルにより偏向された一次電子線の焦点を、前記試料上に合わせる対物レンズと、前記一次電子線が前記試料に照射されたとき、前記試料によって反射された電子または散乱された電子を検出する電子検出器と、前記電子検出器によって検出された検出信号を、前記走査コイルを制御する走査制御信号に同期して取得する検出信号処理部と、前記検出信号処理部で取得した検出信号を前記走査制御信号に同期して処理して前記試料の観察画像を生成し、表示装置に表示する画像処理部と、を備える。 An electron microscope according to the present invention includes, for example, an electron gun that emits a primary electron beam, an irradiation lens that focuses the primary electron beam emitted from the electron gun and irradiates a sample to be observed, and a focusing by the irradiation lens. A scanning coil for deflecting the primary electron beam thus scanned and scanning the irradiation position of the primary electron beam on the sample, and a focal point of the primary electron beam focused by the irradiation lens and deflected by the scanning coil on the sample. An objective lens for adjusting to the electron beam, an electron detector for detecting electrons reflected or scattered by the sample when the primary electron beam is irradiated onto the sample, and a detection signal detected by the electron detector. A detection signal processing unit that is acquired in synchronization with a scanning control signal that controls the scanning coil, and a detection signal acquired by the detection signal processing unit is the scanning control signal. Was treated synchronously generate an observation image of the sample, and an image processing unit for displaying on the display device.
　そして、前記電子検出器は、例えば、セラミック蛍光体からなる薄板状のシンチレータと、前記薄板状のシンチレータの端部に配設された光電子増倍管と、を含んで構成され、前記シンチレータの表面には、前記光電子増倍管が配設される部分を除いて、光反射層が形成され、さらに、前記薄板状のシンチレータには、前記一次電子線または前記試料透過後の電子線を通過させるための貫通孔が形成されていることを特徴とする。 The electron detector includes, for example, a thin plate scintillator made of a ceramic phosphor, and a photomultiplier tube disposed at an end of the thin plate scintillator, and the surface of the scintillator A light reflecting layer is formed except for the portion where the photomultiplier tube is disposed, and the thin plate scintillator allows the primary electron beam or the electron beam transmitted through the sample to pass therethrough. For this purpose, a through hole is formed.
　本発明によれば、Ｓ／Ｎが高い鮮明な観測画像を取得することが可能な電子顕微鏡、および、その電子顕微鏡に用いられる電子検出器が提供される。 According to the present invention, an electron microscope capable of acquiring a clear observation image with a high S / N and an electron detector used for the electron microscope are provided.
本発明の第１の実施形態に係る走査透過型の電子顕微鏡の構成の例を示した図。1 is a diagram showing an example of the configuration of a scanning transmission electron microscope according to a first embodiment of the present invention. 本発明の第１の実施形態に係る走査透過型の電子顕微鏡における二次電子、散乱電子および透過電子の検出機構の配置を模式的に示した図。The figure which showed typically arrangement | positioning of the detection mechanism of the secondary electron, a scattered electron, and a transmission electron in the scanning transmission electron microscope which concerns on the 1st Embodiment of this invention. 対物レンズ内に反射電子検出器および暗視野検出器を配置した場合の対物レンズ要部の断面構造の例を示した図。The figure which showed the example of the cross-section of the principal part of an objective lens at the time of arrange | positioning a backscattered electron detector and a dark field detector in an objective lens. （ａ）反射電子検出器の上面図の例、（ｂ）暗視野検出器の上面図の例を示した図。(A) The example of the top view of a backscattered electron detector, The figure which showed the example of the top view of (b) dark field detector. （ａ）反射電子検出器の縦断面構造の例、（ｂ）暗視野検出器の縦断面構造の例を示した図。(A) The example of the longitudinal cross-section of a backscattered electron detector, (b) The figure which showed the example of the longitudinal cross-section of a dark field detector. （ａ）従来のシンチレータの断面の観察画像の例、（ｂ）本実施形態に係るセラミック蛍光体の断面の観察画像の例を示した図。(A) The example of the observation image of the cross section of the conventional scintillator, (b) The figure which showed the example of the observation image of the cross section of the ceramic fluorescent substance concerning this embodiment. セラミック蛍光体への電子線進入深さの加速電圧依存特性を測定した測定結果の例を示した図。The figure which showed the example of the measurement result which measured the acceleration voltage dependence characteristic of the electron beam penetration depth to a ceramic fluorescent substance. 本発明の第２の実施形態に係る暗視野検出器の構造の例を示した図であり、（ａ）は縦断面図の例、（ｂ）は上面図の例。It is the figure which showed the example of the structure of the dark field detector which concerns on the 2nd Embodiment of this invention, (a) is an example of a longitudinal cross-sectional view, (b) is an example of a top view. 従来の電子顕微鏡における３つのタイプの対物レンズの構造を模式的に示した図であり、（ａ）はアウトレンズ型、（ｂ）はインレンズ型、（ｃ）はセミインレンズ型。It is the figure which showed typically the structure of three types of objective lenses in the conventional electron microscope, (a) is an out lens type, (b) is an in lens type, (c) is a semi-in lens type.
　以下、本発明の実施形態について、図面を参照して詳細に説明する。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
（第１の実施形態）
　図１は、本発明の第１の実施形態に係る走査透過型の電子顕微鏡の構成の例を示した図である。図１に示すように、電子顕微鏡１００は、大きくは電子光学系装置１０と制御系装置７０とを含んで構成される。 (First embodiment)
FIG. 1 is a diagram showing an example of the configuration of a scanning transmission electron microscope according to the first embodiment of the present invention. As shown in FIG. 1, the electron microscope 100 is mainly configured to include an electron optical system device 10 and a control system device 70.
　ここで、電子光学系装置１０は、電子銃１１、照射レンズ１３、走査コイル１４、対物レンズ１５、試料イメージ移動コイル１６、中間レンズ１７、投射レンズ１８、二次電子検出器２０、反射電子検出器３０、暗視野検出器４０、明視野検出器５０などを含んで構成される。 Here, the electron optical system apparatus 10 includes an electron gun 11, an irradiation lens 13, a scanning coil 14, an objective lens 15, a sample image moving coil 16, an intermediate lens 17, a projection lens 18, a secondary electron detector 20, and reflected electron detection. Device 30, dark field detector 40, bright field detector 50, and the like.
　二次電子検出器２０は、電子銃１１から出射され、照射レンズ１３によって集束された一次電子線１２が試料６０に照射されたとき、試料６０から放出される二次電子（数ｅＶ～数１０ｅＶ程度のエネルギーを持つ）を検出する。また、反射電子検出器３０は、一次電子線１２が試料６０に照射されたとき、試料６０により反射された反射電子を検出する。また、暗視野検出器４０は、一次電子線１２が試料６０により散乱された散乱電子を検出する。また、明視野検出器５０は、一次電子線１２が試料６０を透過した透過電子を検出する。 The secondary electron detector 20 emits secondary electrons (several eV to several 10 eV) emitted from the sample 60 when the sample 60 is irradiated with the primary electron beam 12 emitted from the electron gun 11 and focused by the irradiation lens 13. ) With a degree of energy. The backscattered electron detector 30 detects backscattered electrons reflected by the sample 60 when the sample 60 is irradiated with the primary electron beam 12. Further, the dark field detector 40 detects scattered electrons obtained by scattering the primary electron beam 12 by the sample 60. The bright field detector 50 detects transmitted electrons that have passed through the sample 60 by the primary electron beam 12.
　ここで、本実施形態の場合、対物レンズ１５は、インレンズ型であり、試料６０、反射電子検出器３０および暗視野検出器４０は、対物レンズ１５の中、すなわち、対物レンズ１５の上磁極と下磁極との間隙に配置される。そして、その反射電子検出器３０および暗視野検出器４０については、独特の構造を有するものとなっているが、その詳細については、別途図面を参照して説明する。 Here, in the present embodiment, the objective lens 15 is an in-lens type, and the sample 60, the backscattered electron detector 30, and the dark field detector 40 are included in the objective lens 15, that is, the upper magnetic pole of the objective lens 15. And the lower magnetic pole. The backscattered electron detector 30 and the dark field detector 40 have a unique structure, and details thereof will be described with reference to a separate drawing.
　さらに、図１に示すように、制御系装置７０は、電子光学系制御部７１、検出信号処理部７２、画像処理部７３、制御コンピュータ７４、表示装置７５などを含んで構成される。 Further, as shown in FIG. 1, the control system device 70 includes an electron optical system control unit 71, a detection signal processing unit 72, an image processing unit 73, a control computer 74, a display device 75, and the like.
　電子光学系制御部７１は、制御コンピュータ７４の指示に従って、電子銃１１から出射される一次電子線１２の加速電圧やビーム電流を制御する信号や、照射レンズ１３、走査コイル１４、対物レンズ１５、試料イメージ移動コイル１６、中間レンズ１７、投射レンズ１８などを動作させるための励磁電流を電子光学系装置１０へ供給する。 The electron optical system control unit 71 controls the acceleration voltage and beam current of the primary electron beam 12 emitted from the electron gun 11 in accordance with instructions from the control computer 74, the irradiation lens 13, the scanning coil 14, the objective lens 15, An excitation current for operating the sample image moving coil 16, the intermediate lens 17, the projection lens 18 and the like is supplied to the electron optical system device 10.
　検出信号処理部７２は、二次電子検出器２０、反射電子検出器３０、暗視野検出器４０、明視野検出器５０などによって検出された検出信号を、電子光学系制御部７１が走査コイル１４を制御するときの走査制御信号に同期して取得、増幅し、さらにＡ／Ｄ（Analog to Digital）変換などの信号処理を行う。 The detection signal processing unit 72 includes a detection signal detected by the secondary electron detector 20, the backscattered electron detector 30, the dark field detector 40, the bright field detector 50, and the like. The signal is acquired and amplified in synchronization with the scanning control signal when controlling the signal, and signal processing such as A / D (Analog-to-Digital) conversion is performed.
　また、画像処理部７３は、検出信号処理部７２でＡ／Ｄ変換された検出信号および電子光学系制御部７１からの走査制御信号を処理して、観察画像の画素データを生成し、生成した画素データに基づく観察画像を表示装置７５に表示させる。 Further, the image processing unit 73 processes the detection signal A / D converted by the detection signal processing unit 72 and the scanning control signal from the electro-optical system control unit 71 to generate pixel data of the observation image, An observation image based on the pixel data is displayed on the display device 75.
　また、制御コンピュータ７４は、ユーザによって入力される観察画像取得のための様々な情報（観察モード、倍率、明るさ、焦点調整など）を取得し、その情報に基づき、電子光学系制御部７１を介して、電子光学系装置１０内の電子銃１１の加速電圧や各レンズの励磁電流などを制御する。 In addition, the control computer 74 acquires various information (observation mode, magnification, brightness, focus adjustment, etc.) for acquiring an observation image input by the user, and controls the electron optical system control unit 71 based on the information. Through this, the acceleration voltage of the electron gun 11 in the electron optical system device 10 and the excitation current of each lens are controlled.
　図２は、走査透過型の電子顕微鏡１００において二次電子、散乱電子および透過電子をそれぞれ検出する電子検出器の配置を模式的に示した図である。なお、図２では、説明を簡素化し、分かり易くするため、対物レンズ１５や反射電子検出器３０など電子光学系装置１０の一部の構成要素の記載を省略している。 FIG. 2 is a diagram schematically showing the arrangement of electron detectors for detecting secondary electrons, scattered electrons, and transmitted electrons in the scanning transmission electron microscope 100. In FIG. 2, in order to simplify the explanation and make it easy to understand, description of some components of the electron optical system device 10 such as the objective lens 15 and the backscattered electron detector 30 is omitted.
　図２に示すように、電子銃１１から出射された一次電子線１２は、照射レンズ１３によって細く集束させられて、対物レンズ１５（図２では図示省略）内に配置された試料６０に照射される。このとき、一次電子線１２が照射された試料６０の表面部分からは、二次電子１２２が放出される。この放出された二次電子１２２は、エネルギーが低い（数ｅＶ～数１０ｅＶ程度）ので、対物レンズ１５の磁場に巻き上げられて対物レンズ１５の外に放出される。対物レンズ１５のすぐ外側には、正電圧が印加された二次電子検出器２０が設けられているので、二次電子１２２は、その正電圧によって誘引され、二次電子検出器２０によって検出される。 As shown in FIG. 2, the primary electron beam 12 emitted from the electron gun 11 is finely focused by the irradiation lens 13 and irradiated to the sample 60 disposed in the objective lens 15 (not shown in FIG. 2). The At this time, secondary electrons 122 are emitted from the surface portion of the sample 60 irradiated with the primary electron beam 12. Since the emitted secondary electrons 122 have low energy (several eV to several tens eV), they are wound up by the magnetic field of the objective lens 15 and emitted outside the objective lens 15. Since the secondary electron detector 20 to which a positive voltage is applied is provided just outside the objective lens 15, the secondary electrons 122 are attracted by the positive voltage and detected by the secondary electron detector 20. The
　また、試料６０に進入した一次電子線１２のうち、試料６０を透過したものは、透過電子１２４と呼ばれ、試料６０を構成する原子によって散乱されたものは、散乱電子１２５と呼ばれる。ここで、散乱電子１２５は、図２に示すように、試料６０の下方に設けられた中央に孔部を有する円盤状の暗視野検出器４０によって検出される。また、明視野検出器５０は、暗視野検出器４０のさらに下方に設けられており、試料６０を透過し、さらに、暗視野検出器４０の中央の孔部を通過した透過電子１２４を検出する。 Further, among the primary electron beams 12 that have entered the sample 60, those that have passed through the sample 60 are referred to as transmitted electrons 124, and those that are scattered by the atoms constituting the sample 60 are referred to as scattered electrons 125. Here, as shown in FIG. 2, the scattered electrons 125 are detected by a disk-shaped dark field detector 40 having a hole in the center provided below the sample 60. The bright field detector 50 is provided further below the dark field detector 40 and detects the transmitted electrons 124 that have passed through the sample 60 and have passed through the central hole of the dark field detector 40. .
　また、走査コイル１４は、電子光学系制御部７１からの走査制御信号を受けて、一次電子線１２を順次偏向させることにより、一次電子線１２の試料６０における照射位置を、いわゆる水平走査および垂直走査させる。検出信号処理部７２は、二次電子検出器２０、暗視野検出器４０および明視野検出器５０からの検出信号をそれぞれ、走査コイル１４の走査制御信号と同期して取得し、Ａ／Ｄ変換し、観察画像の画素データを生成する。二次元画像を生成し、それぞれ二次電子観察画像、散乱電子観察画像および透過電子観察画像として表示装置７５に表示する。 Further, the scanning coil 14 receives a scanning control signal from the electron optical system control unit 71 and sequentially deflects the primary electron beam 12 to thereby change the irradiation position of the primary electron beam 12 on the sample 60 so-called horizontal scanning and vertical. Let it scan. The detection signal processing unit 72 acquires the detection signals from the secondary electron detector 20, the dark field detector 40, and the bright field detector 50 in synchronization with the scanning control signal of the scanning coil 14, and performs A / D conversion. Then, pixel data of the observation image is generated. Two-dimensional images are generated and displayed on the display device 75 as secondary electron observation images, scattered electron observation images, and transmission electron observation images, respectively.
　なお、図２では、図示を省略したが、反射電子についても反射電子検出器３０により同様に検出され、画像処理部７３により透過電子観察画像が生成され、生成された透過電子観察画像が表示装置７５に表示される。 Although not shown in FIG. 2, reflected electrons are similarly detected by the reflected electron detector 30, a transmission electron observation image is generated by the image processing unit 73, and the generated transmission electron observation image is displayed on the display device. 75.
　図３は、対物レンズ１５内に反射電子検出器３０および暗視野検出器４０を配置した場合の対物レンズ１５要部の断面構造の例を示した図である。また、図４は、（ａ）反射電子検出器３０の上面図の例、（ｂ）暗視野検出器４０の上面図の例を示した図である。 FIG. 3 is a diagram showing an example of a cross-sectional structure of the main part of the objective lens 15 when the backscattered electron detector 30 and the dark field detector 40 are arranged in the objective lens 15. FIG. 4 is a diagram showing (a) an example of a top view of the backscattered electron detector 30 and (b) an example of a top view of the dark field detector 40.
　図３に示すように、本実施形態では、試料６０、反射電子検出器３０および暗視野検出器４０は、対物レンズ１５の上磁極１５１と下磁極１５２との間隙に配置される。
　また、図４（ａ）、（ｂ）に示すように、反射電子検出器３０および暗視野検出器４０は、それぞれ横に長い薄板状のシンチレータ３１，４１によって構成され、さらに、その一方の端部には、光電子増倍管３２，４２が配設される。また、シンチレータ３１，４１の他方の端部寄りには、一次電子線１２または透過電子１２４を通過させるための貫通孔３３，４３が設けられている。 As shown in FIG. 3, in this embodiment, the sample 60, the backscattered electron detector 30, and the dark field detector 40 are disposed in the gap between the upper magnetic pole 151 and the lower magnetic pole 152 of the objective lens 15.
As shown in FIGS. 4A and 4B, the backscattered electron detector 30 and the dark field detector 40 are each constituted by thin scintillators 31 and 41 that are horizontally long, and further, at one end thereof. Photomultiplier tubes 32 and 42 are disposed in the section. Further, through holes 33 and 43 for allowing the primary electron beam 12 or the transmitted electrons 124 to pass therethrough are provided near the other end of the scintillators 31 and 41.
　図３に示したように、反射電子１２３は、試料６０の直上部に配置された反射電子検出器３０によって検出され、散乱電子１２５は、試料６０の直下部に配置された暗視野検出器４０によって検出される。また、前記したように、対物レンズ１５の上磁極１５１と下磁極１５２との間隙は、１０ｍｍ程度であるから、試料６０から反射電子検出器３０または暗視野検出器４０までの距離は、高々数ｍｍ程度である。従って、その距離が小さいがゆえに、反射電子１２３や散乱電子１２５のほとんどを反射電子検出器３０または暗視野検出器４０で捕捉することが可能になる。 As shown in FIG. 3, the reflected electrons 123 are detected by the reflected electron detector 30 disposed immediately above the sample 60, and the scattered electrons 125 are detected by the dark field detector 40 disposed immediately below the sample 60. Detected by. As described above, since the gap between the upper magnetic pole 151 and the lower magnetic pole 152 of the objective lens 15 is about 10 mm, the distance from the sample 60 to the backscattered electron detector 30 or the dark field detector 40 is at most several. It is about mm. Therefore, since the distance is small, most of the reflected electrons 123 and scattered electrons 125 can be captured by the reflected electron detector 30 or the dark field detector 40.
　さらに、図３に示すように、本実施形態では、二次電子検出器２０は、対物レンズ１５の外側上方に設けられるものとする。この場合、試料６０から放出される二次電子１２２は、対物レンズ１５の磁場によって上方に巻き上げられて、反射電子検出器３に設けられた貫通孔３３を通過し、さらに、対物レンズ１５の外側に放出され、二次電子検出器２０によって検出される。 Further, as shown in FIG. 3, in the present embodiment, the secondary electron detector 20 is provided on the outer upper side of the objective lens 15. In this case, the secondary electrons 122 emitted from the sample 60 are rolled up by the magnetic field of the objective lens 15, pass through the through-hole 33 provided in the backscattered electron detector 3, and further outside the objective lens 15. And is detected by the secondary electron detector 20.
　また、図２の説明とやや重複するが、二次電子検出器２０、反射電子検出器３０および暗視野検出器４０の検出信号は、検出信号処理部７２に入力される。検出信号処理部７２は、それぞれの検出信号を増幅する増幅回路７２１、増幅された検出信号をディジタル信号に変換するＡ／Ｄ変換回路７２２などを含んで構成される。なお、Ａ／Ｄ変換回路７２２でＡ／Ｄ変換を実行するタイミングは、電子光学系制御部７１から供給される走査コイル１４を制御する走査制御信号によって定められる。 Further, although slightly overlapping with the description of FIG. 2, detection signals of the secondary electron detector 20, the backscattered electron detector 30, and the dark field detector 40 are input to the detection signal processing unit 72. The detection signal processing unit 72 includes an amplification circuit 721 that amplifies each detection signal, an A / D conversion circuit 722 that converts the amplified detection signal into a digital signal, and the like. Note that the timing at which A / D conversion is performed by the A / D conversion circuit 722 is determined by a scanning control signal for controlling the scanning coil 14 supplied from the electron optical system control unit 71.
　図５は、（ａ）反射電子検出器３０の縦断面構造の例、（ｂ）暗視野検出器４０の縦断面構造の例を示した図である。図５に示すように、反射電子検出器３０も暗視野検出器４０もその断面構造は、ほとんど同じである。すなわち、シンチレータ３１，４１は、薄板状のセラミック蛍光体３１１，４１１に光反射層３１２，４１２がコーティングされて構成される。 FIG. 5 is a diagram showing (a) an example of a longitudinal sectional structure of the backscattered electron detector 30 and (b) an example of a longitudinal sectional structure of the dark field detector 40. As shown in FIG. 5, the cross-sectional structures of the backscattered electron detector 30 and the dark field detector 40 are almost the same. That is, the scintillators 31 and 41 are configured by coating the thin plate-like ceramic phosphors 311 and 411 with the light reflecting layers 312 and 412.
　ここで、セラミック蛍光体３１１，４１１は、粒子状の蛍光体を摂氏数１０００度に加熱してガラス化した焼結体であり、その断面の厚さは、２００～３００μｍ程度が好ましい。また、セラミック蛍光体３１１，４１１としては、残像時間が２００ｎｓｅｃ以下の蛍光体を用いるのがよく、そのような蛍光体としては、例えば、Ｐ４７（Ｙ２ＳｉＯ２；Ｃｅ）がある。 Here, the ceramic phosphors 311 and 411 are sintered bodies in which particulate phosphors are vitrified by heating to 1000 degrees Celsius, and the thickness of the cross section is preferably about 200 to 300 μm. As the ceramic phosphors 311 and 411, phosphors having an afterimage time of 200 nsec or less are preferably used. As such phosphors, for example, P47 (Y 2 SiO 2 ; Ce) is available.
　なお、セラミック蛍光体３１１，４１１の残像時間が２００ｎｓｅｃ以下である場合には、３２０×２４０画素の観察画像を１秒間に３０フレームの動画像として取得することが可能である。また、６４０×４８０画素の観察画像であれば、１秒間に７フレーム程度の動画像として取得することができる。 When the afterimage times of the ceramic phosphors 311 and 411 are 200 nsec or less, it is possible to acquire an observation image of 320 × 240 pixels as a moving image of 30 frames per second. An observation image of 640 × 480 pixels can be acquired as a moving image of about 7 frames per second.
　また、光反射層３１２，４１２は、セラミック蛍光体３１１，４１１にアルミニウムなどの金属を蒸着して形成したものである。なお、蒸着する金属は、アルミニウムに限定されず、金や白金であってもよい。 The light reflecting layers 312 and 412 are formed by vapor-depositing a metal such as aluminum on the ceramic phosphors 311 and 411. In addition, the metal to vapor-deposit is not limited to aluminum, Gold and platinum may be sufficient.
　ここで、蒸着する金属がアルミニウムの場合、その蒸着層の厚さは、反射電子１２３または散乱電子１２５が入射される面側で、１０～３０ｎｍ程度、好ましくは２０ｎｍ程度とするのがよい。また、反射電子１２３または散乱電子１２５が入射される面の反対面側の蒸着層の厚さは、１０～３０ｎｍ程度あればよいが、それよりももっと厚くしても構わない。 Here, when the metal to be deposited is aluminum, the thickness of the deposited layer is about 10 to 30 nm, preferably about 20 nm on the surface side where the reflected electrons 123 or scattered electrons 125 are incident. Further, the thickness of the vapor deposition layer on the side opposite to the surface on which the reflected electrons 123 or the scattered electrons 125 are incident may be about 10 to 30 nm, but it may be made thicker than that.
　なお、アルミニウムの蒸着層が１０～３０ｎｍ程度である場合、数１００ｅＶ以上のエネルギーを有する電子線は、その蒸着層を透過することができる。一方、セラミック蛍光体３１１，４１１内で発光する蛍光は、そのアルミニウムの蒸着層（光反射層３１２，４１２）を透過せず、内側に反射される。 When the aluminum vapor deposition layer is about 10 to 30 nm, an electron beam having energy of several hundred eV or more can pass through the vapor deposition layer. On the other hand, the fluorescence emitted in the ceramic phosphors 311 and 411 is not transmitted through the aluminum vapor deposition layers (light reflecting layers 312 and 412) but reflected inward.
　以上のように、本実施形態に係る反射電子検出器３０および暗視野検出器４０におけるシンチレータ３１，４１は、蛍光体がセラミック蛍光体３１１，４１１で構成され、そのセラミック蛍光体３１１，４１１が光反射層３１２，４１２でコーティングされていることに特徴がある。なお、当然であるが、セラミック蛍光体３１１，４１１の表面のうち、光電子増倍管３２，４２が接続される部分については、光反射層３１２，４１２はコーティングされていないものとする。 As described above, the scintillators 31 and 41 in the backscattered electron detector 30 and the dark field detector 40 according to the present embodiment are composed of the ceramic phosphors 311 and 411, and the ceramic phosphors 311 and 411 are light. It is characterized by being coated with reflective layers 312 and 412. As a matter of course, the light reflecting layers 312 and 412 are not coated on the surfaces of the ceramic phosphors 311 and 411 where the photomultiplier tubes 32 and 42 are connected.
　続いて、図６および図７を参照しながら、シンチレータ３１，４１をセラミック蛍光体３１１，４１１で構成し、その表面を光反射層３１２，４１２でコーティングした理由やその効果などについて説明する。図６は、（ａ）従来のシンチレータの断面の観察画像の例、（ｂ）本実施形態に係るセラミック蛍光体の断面の観察画像の例を示した図である。 Subsequently, the reason why the scintillators 31 and 41 are made of the ceramic phosphors 311 and 411 and the surfaces thereof are coated with the light reflecting layers 312 and 412 and the effects thereof will be described with reference to FIGS. FIG. 6 is a diagram showing (a) an example of an observation image of a cross section of a conventional scintillator, and (b) an example of an observation image of a cross section of a ceramic phosphor according to the present embodiment.
　図６（ａ）に示すように、従来のシンチレータは、厚さが数１００μｍのガラス基板に厚さが３０μｍ程度の粒状蛍光体塗布膜を形成したものである。この粒状蛍光体塗布膜に電子線が進入すると、電子線は、蛍光体原子に散乱されながら三角錐状に広がるとともに、電子が衝突した蛍光体原子からは蛍光が発せられる。ところが、この粒状蛍光体塗布膜は、透光性に劣るため、三角錐状の領域内の蛍光体原子から発せられた蛍光は、粒状蛍光体内で急速に減衰し、蛍光が粒状蛍光体塗布膜内を横方向に広がることはなかった。 As shown in FIG. 6A, a conventional scintillator is obtained by forming a granular phosphor coating film having a thickness of about 30 μm on a glass substrate having a thickness of several hundreds μm. When an electron beam enters the granular phosphor coating film, the electron beam spreads in a triangular pyramid shape while being scattered by the phosphor atoms, and fluorescence is emitted from the phosphor atoms with which the electrons collide. However, since this granular phosphor coating film is inferior in translucency, the fluorescence emitted from the phosphor atoms in the triangular pyramid region is rapidly attenuated in the granular phosphor, and the fluorescence is granular phosphor coating film. The inside did not spread laterally.
　そのため、従来の一般的な反射電子検出器や暗視野検出器では、シンチレータのガラス基板の粒状蛍光体塗布膜が形成された反対側の面に直接光電子増倍管を設けることが必要であった。その結果、反射電子検出器や暗視野検出器の物理的なサイズが大きくなり、反射電子検出器や暗視野検出器を対物レンズ１５の上磁極１５１と下磁極１５２との間隙に配置することはできなかった。 Therefore, in the conventional general backscattered electron detector and dark field detector, it is necessary to provide a photomultiplier tube directly on the opposite surface of the glass substrate of the scintillator where the granular phosphor coating film is formed. . As a result, the physical size of the backscattered electron detector and the dark field detector is increased, and the backscattered electron detector and the dark field detector are disposed in the gap between the upper magnetic pole 151 and the lower magnetic pole 152 of the objective lens 15. could not.
　一方、本実施形態に係るセラミック蛍光体は、非晶質のガラスと同様の物理的性質を有しており、透光性に優れている。そして、その断面構造（破断面）は、図６（ｂ）に示すように、ガラスの破断面によく似た構造を有している。また、セラミック蛍光体の厚さは、前記したように２００～３００μｍ程度であり、従来の粒状蛍光体塗布膜の厚さ（２０μｍ程度）に比べ、はるかに厚い。従って、セラミック蛍光体自体が基板として十分な機械的強度を有しており、従来のような粒状蛍光体塗布膜を支持するガラス基板は不要となる。 On the other hand, the ceramic phosphor according to the present embodiment has the same physical properties as amorphous glass, and is excellent in translucency. And the cross-sectional structure (fracture surface) has a structure very similar to the fracture surface of glass, as shown in FIG.6 (b). Further, as described above, the thickness of the ceramic phosphor is about 200 to 300 μm, which is much thicker than the thickness of the conventional granular phosphor coating film (about 20 μm). Therefore, the ceramic phosphor itself has sufficient mechanical strength as a substrate, and a conventional glass substrate for supporting the granular phosphor coating film becomes unnecessary.
　ところで、電子線がセラミック蛍光体に進入すると、従来の粒状蛍光体の場合と同じように、電子線は、蛍光体原子に散乱されながら三角錐状に広がり、電子が衝突した蛍光体原子から蛍光が発せられる。一方、従来の粒状蛍光体の場合とは異なり、セラミック蛍光体が透光性に優れている（ほとんど透明）ため、その蛍光体原子から発せられた蛍光は、薄板状のセラミック蛍光体内を３次元方向に広がる。すなわち、蛍光は、セラミック蛍光体内を、セラミック蛍光体の薄板面に平行な方向（横方向）であっても、遠くに広がる。 By the way, when the electron beam enters the ceramic phosphor, the electron beam spreads in a triangular pyramid shape while being scattered by the phosphor atoms as in the case of the conventional granular phosphor, and the fluorescence is emitted from the phosphor atoms with which the electrons collide. Is emitted. On the other hand, unlike the conventional granular phosphor, the ceramic phosphor is excellent in translucency (almost transparent), so that the fluorescence emitted from the phosphor atoms passes through the thin plate-like ceramic phosphor in three dimensions. Spread in the direction. That is, the fluorescence spreads farther in the ceramic phosphor even in the direction (lateral direction) parallel to the thin plate surface of the ceramic phosphor.
　さらに、本実施形態では、図５に示したように、セラミック蛍光体３１１，４１１には、電子線が入射可能で、蛍光を反射する光反射層３１２，４１２がコーティングされている。そのため、電子線が進入することにより、セラミック蛍光体３１１，４１１の中で発生した蛍光は、その中に閉じ込められるとともに、コーティングされた光反射層３１２，４１２に反射されながら、シンチレータ３１，４１の端部に設けられた光電子増倍管３２，４２へ導光される。 Further, in the present embodiment, as shown in FIG. 5, the ceramic phosphors 311 and 411 are coated with light reflecting layers 312 and 412 that can enter an electron beam and reflect fluorescence. Therefore, when the electron beam enters, the fluorescence generated in the ceramic phosphors 311 and 411 is confined in the ceramic phosphors 311 and 411 and is reflected by the coated light reflecting layers 312 and 412 while being reflected by the scintillators 31 and 41. The light is guided to the photomultiplier tubes 32 and 42 provided at the ends.
　従って、本実施形態では、光電子増倍管３２，４２をシンチレータ３１，４１の端部に設けることが可能になるので、シンチレータ３１，４１と光電子増倍管３２，４２とで構成される反射電子検出器３０および暗視野検出器４０を、対物レンズ１５の上磁極１５１と下磁極１５２との間隙に配置することが可能になる。 Therefore, in the present embodiment, since the photomultiplier tubes 32 and 42 can be provided at the end portions of the scintillators 31 and 41, the reflected electrons composed of the scintillators 31 and 41 and the photomultiplier tubes 32 and 42 are provided. The detector 30 and the dark field detector 40 can be disposed in the gap between the upper magnetic pole 151 and the lower magnetic pole 152 of the objective lens 15.
　また、従来のように、光電子増倍管をシンチレータの電子線入射面の反対側の面に設けなくて済むことから、薄板状のシンチレータ３１，４１に、一次電子線１２または透過電子１２４を通過させるための貫通孔３３，４３を設けることも可能になる。 Further, unlike the prior art, it is not necessary to provide a photomultiplier tube on the surface opposite to the electron beam incident surface of the scintillator, so that the primary electron beam 12 or the transmitted electron 124 passes through the thin scintillators 31 and 41. It is also possible to provide the through holes 33 and 43 for the purpose.
　図７は、セラミック蛍光体への電子線進入深さの加速電圧依存特性を測定した測定結果の例を示した図である。図７において、横軸は、入射電子線の加速電圧（ｋＶ）、縦軸は、電子線進入深さ（μｍ）を表す。 FIG. 7 is a diagram showing an example of a measurement result obtained by measuring the acceleration voltage dependence characteristic of the electron beam penetration depth into the ceramic phosphor. In FIG. 7, the horizontal axis represents the acceleration voltage (kV) of the incident electron beam, and the vertical axis represents the electron beam penetration depth (μm).
　図７によれば、例えば、１００ｋＶで加速された電子線がセラミック蛍光体へ入射された場合には、その電子線は、およそ２０μｍの深さまで進入する。また、３００ｋＶで加速された電子線が入射した場合には、およそ２００μｍの深さまで進入する。さらに、図７によれば、加速電圧が５０ｋＶ以下である場合には、電子線は、セラミック蛍光体の表面からせいぜい数μｍ程度しか進入しないことになる。 According to FIG. 7, for example, when an electron beam accelerated at 100 kV is incident on the ceramic phosphor, the electron beam enters to a depth of about 20 μm. Further, when an electron beam accelerated at 300 kV is incident, it enters to a depth of about 200 μm. Furthermore, according to FIG. 7, when the acceleration voltage is 50 kV or less, the electron beam enters only about several μm at most from the surface of the ceramic phosphor.
　以上、図７に示された測定結果に加えて、従来のシンチレータの粒状蛍光体塗布膜の厚さが３０μｍ程度であること、本実施形態に係るシンチレータ３１，４１のセラミック蛍光体３１１，４１１の厚さを２００～３００μｍ程度としたことを考慮すれば、本実施形態に係るシンチレータ３１，４１では、電子検出感度が大幅に向上する。以下、電子検出感度が向上する理由について説明する。
　なお、粒状蛍光体塗布膜の場合でも、セラミック蛍光体の場合でも、電子線の進入深さはおおむね同じであるので、以下の説明では、図７の測定結果を電子線の進入深さとして利用する。 As described above, in addition to the measurement results shown in FIG. 7, the thickness of the granular phosphor coating film of the conventional scintillator is about 30 μm, and the ceramic phosphors 311 and 411 of the scintillators 31 and 41 according to the present embodiment. Considering that the thickness is about 200 to 300 μm, the scintillators 31 and 41 according to the present embodiment greatly improve the electron detection sensitivity. Hereinafter, the reason why the electron detection sensitivity is improved will be described.
Since the penetration depth of the electron beam is almost the same in both the case of the granular phosphor coating film and the case of the ceramic phosphor, in the following description, the measurement result of FIG. 7 is used as the penetration depth of the electron beam. To do.
　まず、電子線の加速電圧が高い場合を考える。図７によれば、例えば、進入する電子線の加速電圧が３００ｋＶであるとすれば、その進入深さは、２００μｍ程度である。従って、加速電圧が３００ｋＶの電子線は、従来のシンチレータにおける厚さ３０μｍ程度の粒状蛍光体塗布膜を貫通するエネルギーを有している。一方、本実施形態では、シンチレータ３１，４１のセラミック蛍光体３１１，４１１の厚さを、２００～３００μｍ程度であるとしているため、加速電圧２００ｋＶの電子線がその厚さのセラミック蛍光体３１１，４１１を貫通するには至らない。 First, consider the case where the acceleration voltage of the electron beam is high. According to FIG. 7, for example, if the acceleration voltage of the entering electron beam is 300 kV, the entering depth is about 200 μm. Therefore, the electron beam having an acceleration voltage of 300 kV has energy penetrating through the granular phosphor coating film having a thickness of about 30 μm in the conventional scintillator. On the other hand, in the present embodiment, since the thicknesses of the ceramic phosphors 311 and 411 of the scintillators 31 and 41 are about 200 to 300 μm, an electron beam with an acceleration voltage of 200 kV has the thickness. It does not lead to penetrating.
　すなわち、本実施形態では、電子線は、蛍光体の中を２００μｍ程度進むのに対し、従来の場合、電子線は、蛍光体の中を３０μｍ程度しか進まない。従って、本実施形態では、電子線が蛍光体の中を従来の場合よりも長く進み続ける分だけ、蛍光体の原子に衝突する回数が増加し、その分蛍光体から発せられる蛍光が増加する。 That is, in this embodiment, the electron beam travels about 200 μm in the phosphor, whereas in the conventional case, the electron beam travels only about 30 μm in the phosphor. Therefore, in the present embodiment, the number of times the electron beam collides with the atoms of the phosphor increases as much as the electron beam continues in the phosphor longer than in the conventional case, and the fluorescence emitted from the phosphor increases accordingly.
　すなわち、電子線が蛍光体中を通過する距離が３０ミクロンと２００ミクロンとでは、７倍程度の相違があるから、単純な計算で判断すれば、両者の蛍光体から発せられる蛍光の量も７倍程度の相違が生じることになる。従って、本実施形態におけるセラミック蛍光体３１１，４１１は、従来の粒状蛍光体塗布膜に比べ、およそ７倍もの蛍光を発することになる。 That is, since the distance that the electron beam passes through the phosphor is 30 microns and 200 microns, there is a difference of about 7 times. Therefore, if judged by simple calculation, the amount of fluorescence emitted from both phosphors is also 7 A difference of about twice will occur. Therefore, the ceramic phosphors 311 and 411 in this embodiment emit about seven times as much fluorescence as the conventional granular phosphor coating film.
　さらに、本実施形態におけるセラミック蛍光体３１１，４１１は、透光性が高く、その表面が光反射層３１２，４１２で覆われているので、ライトガイド（光導波路）としても機能を有する。すなわち、セラミック蛍光体３１１，４１１内で発せられた蛍光は、３次元方向（すなわち、四方八方）に広がり、光反射層３１２，４１２で反射されつつ、ほとんどすべてが光電子増倍管３２，４２に導光される。従って、本実施形態の光電子増倍管３２，４２には、従来の場合よりもはるかに多くの蛍光が入射されることになる。 Furthermore, since the ceramic phosphors 311 and 411 in this embodiment have high translucency and the surfaces thereof are covered with the light reflecting layers 312 and 412, they also function as light guides (optical waveguides). That is, the fluorescence emitted in the ceramic phosphors 311 and 411 spreads in a three-dimensional direction (that is, in all directions) and is reflected by the light reflecting layers 312 and 412, and almost all of the fluorescence is transmitted to the photomultiplier tubes 32 and 42. Light is guided. Therefore, much more fluorescence is incident on the photomultiplier tubes 32 and 42 of this embodiment than in the conventional case.
　以上の説明からは、電子線の加速電圧が、その電子線による進入深さが３０ミクロンを超えるような加速電圧（図７から判断すれば、１３０ｋＶ程度以上）である場合には、本実施形態に係る反射電子検出器３０や暗視野検出器４０の電子検出感度は、従来のシンチレータと光電子増倍管からなる電子検出器に比べ向上することが分かる。 From the above description, in the case where the accelerating voltage of the electron beam is an accelerating voltage such that the penetration depth by the electron beam exceeds 30 microns (as judged from FIG. 7, about 130 kV or more), the present embodiment It can be seen that the electron detection sensitivity of the backscattered electron detector 30 and the dark field detector 40 according to the present invention is improved as compared with the conventional electron detector comprising a scintillator and a photomultiplier tube.
　なお、反射電子１２３や散乱電子１２５は、加速された一次電子線１２がやや減速はされているものの、その加速エネルギーは、一次電子線１２と同程度とみなしても差し支えない。 The reflected electrons 123 and scattered electrons 125 may be regarded as having the same acceleration energy as that of the primary electron beam 12 although the accelerated primary electron beam 12 is slightly decelerated.
　次に、電子線の加速電圧が低い場合、例えば、進入する電子線の加速電圧が５０ｋＶ以下である場合を考える。図７によれば、５０ｋＶ以下の低い加速電圧では、電子線は、従来の場合も、本実施形態の場合も、粒状蛍光体塗布膜あるいはセラミック蛍光体３１１，４１１の表面から数μｍの深さまでしか進入しない。 Next, consider a case where the acceleration voltage of the electron beam is low, for example, the acceleration voltage of the entering electron beam is 50 kV or less. According to FIG. 7, at a low accelerating voltage of 50 kV or less, the electron beam has a depth of several μm from the surface of the granular phosphor coating film or the ceramic phosphors 311 and 411 in both the conventional case and the present embodiment. Only enters.
　従って、電子線が進入することにより発せられる蛍光は、粒状蛍光体塗布膜あるいはセラミック蛍光体３１１，４１１の表面から深さ数μｍまでの領域で発せられることになる。そのため、従来のシンチレータの場合、粒状蛍光体塗布膜の深さ数μｍの比較的浅い領域で発生した蛍光は、ガラス基板側まで、２０数μｍ程度、粒状蛍光体塗布膜の中を通過することになる。前記したように粒状蛍光体塗布膜の透光性は低いので、蛍光は、粒状蛍光体塗布膜を通過するとき減衰する。つまり、その減衰した蛍光が光電子増倍管電子に入射されることになるので、従来のシンチレータと光電子増倍管による電子検出器の電子検出感度は低下する。 Therefore, the fluorescence emitted when the electron beam enters is emitted in a region from the surface of the granular phosphor coating film or the ceramic phosphors 311 and 411 to a depth of several μm. Therefore, in the case of a conventional scintillator, the fluorescence generated in a relatively shallow region having a depth of several μm of the granular phosphor coating film passes through the granular phosphor coating film to about 20 μm to the glass substrate side. become. As described above, since the translucency of the granular phosphor coating film is low, the fluorescence is attenuated when passing through the granular phosphor coating film. That is, since the attenuated fluorescence is incident on the photomultiplier tube electrons, the electron detection sensitivity of the electron detector using the conventional scintillator and the photomultiplier tube is lowered.
　一方、本実施形態の場合、前記したように、セラミック蛍光体３１１，４１１の透光性が高く、しかも、その表面が光反射層３１２，４１２で覆われている。そのため、電子線が進入することによって、セラミック蛍光体３１１，４１１の表面から深さ数μｍの領域から３次元方向へ発せられた蛍光は、光反射層３１２，４１２で反射されつつ、ほとんどすべてが光電子増倍管３２，４２に導光される。 On the other hand, in the case of the present embodiment, as described above, the ceramic phosphors 311 and 411 have high translucency, and the surfaces thereof are covered with the light reflecting layers 312 and 412. Therefore, almost all of the fluorescence emitted from the surface of the ceramic phosphors 311 and 411 in the three-dimensional direction from the surface of the ceramic phosphors 311 and 411 is reflected by the light reflecting layers 312 and 412 when the electron beam enters. The light is guided to the photomultiplier tubes 32 and 42.
　従って、電子線の加速電圧が５０ｋＶ以下である場合にも、本実施形態に係る反射電子検出器３０や暗視野検出器４０の電子検出感度は、従来のシンチレータと光電子増倍管からなる電子検出器に比べ向上することが分かる。 Therefore, even when the acceleration voltage of the electron beam is 50 kV or less, the backscattered electron detector 30 and the dark field detector 40 according to the present embodiment have the same electron detection sensitivity as that of the conventional scintillator and photomultiplier tube. It turns out that it improves compared with the vessel.
　また、以上の説明では、省略したが、電子線の加速電圧が５０ｋＶ以上、１３０ｋＶ程度以下である場合についても、おおむねこれと同様の理由により、本実施形態に係る反射電子検出器３０および暗視野検出器４０の電子検出感度は、従来のシンチレータと光電子増倍管からなる電子検出器の電子検出感度に比べ高くなる。 Although omitted in the above description, the backscattered electron detector 30 and the dark field according to the present embodiment are also mostly used for the same reason when the acceleration voltage of the electron beam is 50 kV or more and 130 kV or less. The electron detection sensitivity of the detector 40 is higher than the electron detection sensitivity of an electron detector composed of a conventional scintillator and a photomultiplier tube.
　以上の通り、本実施形態では、反射電子検出器３０および暗視野検出器４０の電子検出感度が向上するという効果が得られる。よって、観察画像のＳ／Ｎが向上し、より鮮明な観察画像が得られる。 As described above, in the present embodiment, the effect of improving the electron detection sensitivity of the reflected electron detector 30 and the dark field detector 40 is obtained. Therefore, the S / N of the observation image is improved, and a clearer observation image can be obtained.
（第２の実施形態）
　図８は、本発明の第２の実施形態に係る暗視野検出器の構造の例を示した図であり、（ａ）は縦断面図の例、（ｂ）は上面図の例である。なお、第２の実施形態においても、図１に示した走査透過型の電子顕微鏡１００の構成は、同じであり、暗視野検出器４０の部分だけが相違する。そこで、ここでは、電子顕微鏡１００の構成の説明を省略する。 (Second Embodiment)
FIG. 8 is a diagram showing an example of the structure of a dark field detector according to the second embodiment of the present invention, in which (a) is an example of a longitudinal sectional view and (b) is an example of a top view. Also in the second embodiment, the configuration of the scanning transmission electron microscope 100 shown in FIG. 1 is the same, and only the dark field detector 40 is different. Therefore, description of the configuration of the electron microscope 100 is omitted here.
　図８（ａ），（ｂ）に示すように、第２の実施形態に係る暗視野検出器４０ａは、シンチレータ４１ａと光電子増倍管４２とを含んで構成され、シンチレータ４１ａに孔径の異なる２つの貫通孔４３，４３ａが設けられていることを特徴とする。 As shown in FIGS. 8A and 8B, the dark field detector 40a according to the second embodiment is configured to include a scintillator 41a and a photomultiplier tube 42, and the scintillator 41a has different hole diameters. One through hole 43, 43a is provided.
　また、暗視野検出器４０ａは、対物レンズ１５の外側から暗視野検出器４０ａを水平方向に移動させる移動制御機構（図示省略）を有している。そして、制御コンピュータ７４（図１参照）は、電子光学系制御部７１を介して、その移動制御機構を制御することにより、貫通孔４３，４３ａの一方を選択し、選択した貫通孔４３または４３ａの中心が一次電子線１２の光軸に一致する位置になるように、暗視野検出器４０ａを移動させることができるものとする。 Further, the dark field detector 40a has a movement control mechanism (not shown) for moving the dark field detector 40a in the horizontal direction from the outside of the objective lens 15. Then, the control computer 74 (see FIG. 1) selects one of the through holes 43 and 43a by controlling the movement control mechanism via the electron optical system control unit 71, and selects the selected through hole 43 or 43a. It is assumed that the dark field detector 40 a can be moved so that the center of the dark field coincides with the optical axis of the primary electron beam 12.
　従って、ユーザは、暗視野観察画像を取得するとき、貫通孔４３，４３ａの径のうちいずれかを選択することができる。暗視野検出器４０ａは、一次電子線１２が試料６０によって散乱された散乱電子１２５を検出するものである。 Therefore, the user can select one of the diameters of the through holes 43 and 43a when acquiring the dark field observation image. The dark field detector 40 a detects the scattered electrons 125 in which the primary electron beam 12 is scattered by the sample 60.
　一般に、貫通孔の径が小さい（図８では、貫通孔４３ａ）場合には、暗視野検出器４０ａは、散乱角が小さい散乱電子１２５も散乱角が大きい散乱電子１２５も検出する。一方、貫通孔の径が大きい（図８では、貫通孔４３）場合には、暗視野検出器４０ａは、散乱角が大きい散乱電子１２５を検出し、散乱角が小さい散乱電子１２５を検出しない。 Generally, when the diameter of the through hole is small (the through hole 43a in FIG. 8), the dark field detector 40a detects both the scattered electrons 125 having a small scattering angle and the scattered electrons 125 having a large scattering angle. On the other hand, when the diameter of the through hole is large (the through hole 43 in FIG. 8), the dark field detector 40a detects the scattered electrons 125 having a large scattering angle and does not detect the scattered electrons 125 having a small scattering angle.
　また、一般に、試料６０に重い原子が含まれている場合には、散乱電子１２５の散乱角は大きくなり、軽い原子だけの場合には、散乱角は小さくなる。従って、本実施形態では、試料６０に応じて貫通孔４３，４３ａの径の大きさを選択することにより、試料６０の構成元素に応じた適切な暗視野観察画像を得ることができる。 In general, when the sample 60 contains heavy atoms, the scattering angle of the scattered electrons 125 increases, and when only the light atoms are included, the scattering angle decreases. Therefore, in this embodiment, an appropriate dark field observation image corresponding to the constituent element of the sample 60 can be obtained by selecting the size of the diameter of the through holes 43 and 43a according to the sample 60.
　さらに、貫通孔４３，４３ａの径を変えて取得した２つの暗視野観察画像の対応する画素同士を加算演算や差分演算をすれば、例えば、軽い原子や重い原子それぞれに特徴のある暗視野観察画像を生成することも可能になる。また、試料６０に含まれる原子によって定まる散乱角に応じて、貫通孔４３の径の大きさを適切に定めておけば、その観察画像から試料６０に含まれる原子を推定することも可能になる。 Furthermore, if addition calculation or difference calculation is performed between corresponding pixels of two dark field observation images acquired by changing the diameters of the through holes 43 and 43a, for example, dark field observation characteristic of light and heavy atoms, respectively. It is also possible to generate an image. Moreover, if the size of the diameter of the through-hole 43 is appropriately determined according to the scattering angle determined by the atoms included in the sample 60, the atoms included in the sample 60 can be estimated from the observation image. .
　なお、以上の説明では、シンチレータ４１ａに、互いに径の異なる貫通孔を２つ設ける（図８では、貫通孔４３，４３ａ）としているが、互いに径の異なる貫通孔を３つ以上設けてもよい。 In the above description, the scintillator 41a is provided with two through holes having different diameters (in FIG. 8, through holes 43 and 43a). However, three or more through holes having different diameters may be provided. .
（第２の実施形態の変形例）
　第２の実施形態では、暗視野検出器４０ａのシンチレータ４１ａに互いに径の異なる複数の貫通孔４３，４３ａを設けるとしたが、同様に、反射電子検出器３０に互いに複数の貫通孔３３を設けるようにしてもよい。一般に、反射角の大きい反射電子１２３による反射電子観察画像は、試料６０の表面の形状を表す情報が含まれ、反射角の小さい反射電子１２３による反射電子観察画像は、試料６０の成分を表す情報が含まれているといわれている。 (Modification of the second embodiment)
In the second embodiment, the plurality of through holes 43 and 43a having different diameters are provided in the scintillator 41a of the dark field detector 40a. Similarly, the plurality of through holes 33 are provided in the backscattered electron detector 30. You may do it. In general, the reflected electron observation image by the reflected electrons 123 having a large reflection angle includes information representing the shape of the surface of the sample 60, and the reflected electron observation image by the reflected electrons 123 having a small reflection angle is information representing the components of the sample 60. Is said to be included.
　従って、反射電子検出器３０のシンチレータ３１に径の異なる複数の貫通孔３３を設けておき、ユーザが制御コンピュータ７４を介して自在に選択できるようにしておけば、ユーザは、反射角の大きい反射電子１２３による反射電子観察画像も、反射角の小さい反射電子１２３による反射電子観察画像も、容易に取得することが可能になる。 Therefore, if a plurality of through-holes 33 having different diameters are provided in the scintillator 31 of the backscattered electron detector 30 so that the user can select freely through the control computer 74, the user can reflect with a large reflection angle. Both the reflected electron observation image by the electrons 123 and the reflected electron observation image by the reflected electrons 123 having a small reflection angle can be easily acquired.
（その他の変形例）
　以上の実施形態の説明では、二次電子検出器２０および明視野検出器５０の構造については、とくにその説明をしていないが、二次電子検出器２０および明視野検出器５０についても、そのシンチレータ部分がセラミック蛍光体で構成され、そのセラミック蛍光体がアルミニウムなどの蛍光反射膜で覆われているものであっても構わない。 (Other variations)
In the above description of the embodiment, the structures of the secondary electron detector 20 and the bright field detector 50 are not particularly described, but the secondary electron detector 20 and the bright field detector 50 are also described. The scintillator portion may be made of a ceramic phosphor, and the ceramic phosphor may be covered with a fluorescent reflecting film such as aluminum.
　なお、二次電子検出器２０や明視野検出器５０には、電子線を通過させるための貫通孔を設ける必要はない。 The secondary electron detector 20 and the bright field detector 50 do not need to be provided with a through hole for allowing an electron beam to pass therethrough.
　また、以上の実施形態の説明では、電子顕微鏡１００は、走査透過型の電子顕微鏡であるとしているが、走査型電子顕微鏡であってもよい。その場合には、その走査型電子顕微鏡の構成は、おおむね、図１の電子顕微鏡１００の構成から、暗視野検出器４０、明視野検出器５０、試料イメージ移動コイル１６、中間レンズ１７、投射レンズ１８などを除いた構成になる。 In the above description of the embodiment, the electron microscope 100 is a scanning transmission electron microscope, but may be a scanning electron microscope. In that case, the configuration of the scanning electron microscope is roughly the same as that of the electron microscope 100 of FIG. 1, but the dark field detector 40, the bright field detector 50, the sample image moving coil 16, the intermediate lens 17, and the projection lens. The configuration excluding 18 and the like.
　なお、本発明は、以上に説明した実施形態に限定されるものでなく、さらに様々な変形例が含まれる。例えば、前記の実施形態は、本発明を分かりやすく説明するために、詳細に説明したものであり、必ずしも説明したすべての構成を備えるものに限定されるものではない。また、ある実施形態の構成の一部を他の実施形態の構成の一部で置き換えることが可能であり、さらに、ある実施形態の構成に他の実施形態の構成の一部または全部を加えることも可能である。 Note that the present invention is not limited to the embodiment described above, and includes various modifications. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with a part of the configuration of another embodiment, and further, a part or all of the configuration of the other embodiment is added to the configuration of the certain embodiment. Is also possible.
　１０　　電子光学系装置
　１１　　電子銃
　１２　　一次電子線
　１３　　照射レンズ
　１４　　走査コイル
　１５　　対物レンズ
　１６　　試料イメージ移動コイル
　１７　　中間レンズ
　１８　　投射レンズ
　２０　　二次電子検出器
　３０　　反射電子検出器
　３１，４１，４１ａ　シンチレータ
　３２，４２　　光電子増倍管
　３３，４３，４３ａ　貫通孔
　４０，４０ａ　暗視野検出器
　５０　　明視野検出器
　６０　　試料
　７０　　制御系装置
　７１　　電子光学系制御部
　７２　　検出信号処理部
　７３　　画像処理部
　７４　　制御コンピュータ
　７５　　表示装置
　１００　電子顕微鏡
　１２２　二次電子
　１２３　反射電子
　１２４　透過電子
　１２５　散乱電子
　１５０　レンズ磁場
　１５１　上磁極
　１５２　下磁極
　３１１，４１１　セラミック蛍光体
　３１２，４１２　光反射層
　７２１　増幅回路
　７２２　Ａ／Ｄ変換回路 DESCRIPTION OF SYMBOLS 10 Electron system apparatus 11 Electron gun 12 Primary electron beam 13 Irradiation lens 14 Scanning coil 15 Objective lens 16 Sample image moving coil 17 Intermediate lens 18 Projection lens 20 Secondary electron detector 30 Reflected electron detector 31, 41, 41a Scintillator 32 , 42 Photomultiplier tube 33, 43, 43a Through hole 40, 40a Dark field detector 50 Bright field detector 60 Sample 70 Control system device 71 Electron optical system control unit 72 Detection signal processing unit 73 Image processing unit 74 Control computer 75 Display device 100 Electron microscope 122 Secondary electron 123 Reflected electron 124 Transmitted electron 125 Scattered electron 150 Lens magnetic field 151 Upper magnetic pole 152 Lower magnetic pole 311, 411 Ceramic phosphor 312, 412 Light reflecting layer 721 Amplifying circuit 722 A / D conversion circuit

Claims (11)

  1. 　一次電子線を出射する電子銃と、
    　前記電子銃から出射された一次電子線を集束させて観察対象の試料に照射する照射レンズと、
    　前記照射レンズにより集束された一次電子線を偏向させ、前記試料における前記一次電子線の照射位置を走査させる走査コイルと、
    　前記照射レンズにより集束され、前記走査コイルにより偏向された一次電子線の焦点を、前記試料上に合わせる対物レンズと、
    　前記一次電子線が前記試料に照射されたとき、前記試料によって反射された電子または散乱された電子を検出する電子検出器と、
    　前記電子検出器によって検出された検出信号を、前記走査コイルを制御する走査制御信号に同期して取得する検出信号処理部と、
    　前記検出信号処理部で取得した検出信号を前記走査制御信号に同期して処理して前記試料の観察画像を生成し、表示装置に表示する画像処理部と、
    　を備え、
    　前記電子検出器は、セラミック蛍光体からなる薄板状のシンチレータと、前記薄板状のシンチレータの端部に配設された光電子増倍管と、を含んで構成され、
    　前記シンチレータの表面には、前記光電子増倍管が配設される部分を除いて、光反射層が形成され、さらに、前記薄板状のシンチレータには、前記一次電子線または前記試料を透過後の電子線を通過させるための貫通孔が形成されていること
    　を特徴とする電子顕微鏡。     An electron gun that emits a primary electron beam;
    An irradiation lens for focusing the primary electron beam emitted from the electron gun and irradiating the sample to be observed;
    A scanning coil that deflects the primary electron beam focused by the irradiation lens and scans the irradiation position of the primary electron beam on the sample;
    An objective lens that focuses the primary electron beam focused by the irradiation lens and deflected by the scanning coil on the sample;
    An electron detector that detects electrons reflected or scattered by the sample when the sample is irradiated with the primary electron beam;
    A detection signal processing unit that acquires a detection signal detected by the electron detector in synchronization with a scanning control signal for controlling the scanning coil;
    An image processing unit that processes the detection signal acquired by the detection signal processing unit in synchronization with the scanning control signal to generate an observation image of the sample, and displays the image on a display device;
    With
    The electron detector includes a thin plate scintillator made of a ceramic phosphor, and a photomultiplier tube disposed at an end of the thin plate scintillator,
    On the surface of the scintillator, a light reflecting layer is formed except for a portion where the photomultiplier tube is disposed. Further, the thin scintillator is passed through the primary electron beam or the sample. An electron microscope characterized in that a through-hole for passing an electron beam is formed.
  2. 　前記電子検出器は、前記対物レンズの上磁極と下磁極の間隙に配置されていること
    　を特徴とする請求の範囲第１項に記載の電子顕微鏡。     The electron microscope according to claim 1, wherein the electron detector is disposed in a gap between an upper magnetic pole and a lower magnetic pole of the objective lens.
  3. 　前記シンチレータには、互いに径が異なる複数の前記貫通孔が形成されており、
    　前記複数の貫通孔から選択した１つの貫通孔の中心が前記一次電子線の光軸に一致するように、前記シンチレータを含んだ前記電子検出器を移動させる移動制御機構
    　を、さらに、備えること
    　を特徴とする請求の範囲第１項に記載の電子顕微鏡。     The scintillator is formed with a plurality of the through holes having different diameters from each other,
    A movement control mechanism for moving the electron detector including the scintillator so that the center of one through hole selected from the plurality of through holes coincides with the optical axis of the primary electron beam. The electron microscope according to claim 1, characterized in that it is characterized in that:
  4. 　前記薄板状のシンチレータを構成する前記セラミック蛍光体の厚さは、３００μｍ以上であること
    　を特徴とする請求の範囲第１項に記載の電子顕微鏡。     The electron microscope according to claim 1, wherein the ceramic phosphor constituting the thin plate scintillator has a thickness of 300 µm or more.
  5. 　前記セラミック蛍光体は、その残像時間が２００ｎｓ以下であること
    　を特徴とする請求の範囲第１項に記載の電子顕微鏡。     The electron microscope according to claim 1, wherein the ceramic phosphor has an afterimage time of 200 ns or less.
  6. 　前記シンチレータの表面に形成された前記光反射層は、アルミニウムの蒸着膜であること
    　を特徴とする請求の範囲第１項に記載の電子顕微鏡。     The electron microscope according to claim 1, wherein the light reflection layer formed on the surface of the scintillator is a vapor deposition film of aluminum.
  7. 　セラミック蛍光体からなる薄板状のシンチレータと、前記薄板状のシンチレータの端部に配設された光電子増倍管と、を含んで構成され、
    　前記シンチレータの表面には、前記光電子増倍管が配設される部分を除いて、光反射層が形成され、さらに、前記シンチレータには、電子線を通過させるための貫通孔が形成されていること
    　を特徴とする電子検出器。     A thin plate scintillator made of a ceramic phosphor, and a photomultiplier tube disposed at an end of the thin plate scintillator,
    A light reflecting layer is formed on the surface of the scintillator except for a portion where the photomultiplier tube is disposed, and a through-hole for allowing an electron beam to pass through is formed in the scintillator. An electronic detector characterized by the above.
  8. 　前記シンチレータには、互いに径が異なる複数の前記貫通孔が形成されていること
    　を特徴とする請求の範囲第７項に記載の電子検出器。     The electron detector according to claim 7, wherein the scintillator is formed with a plurality of the through holes having different diameters.
  9. 　前記薄板状のシンチレータを構成する前記セラミック蛍光体の厚さは、３００μｍ以上であること
    　を特徴とする請求の範囲第７項に記載の電子検出器。     The electron detector according to claim 7, wherein the ceramic phosphor constituting the thin plate scintillator has a thickness of 300 µm or more.
  10. 　前記セラミック蛍光体は、その残像時間が２００ｎｓ以下であること
    　を特徴とする請求項７に記載の電子検出器。     The electron detector according to claim 7, wherein the ceramic phosphor has an afterimage time of 200 ns or less.
  11. 　前記シンチレータの表面に形成された前記光反射層は、アルミニウムの蒸着膜であること
    　を特徴とする請求の範囲第７項に記載の電子検出器。     The electron detector according to claim 7, wherein the light reflecting layer formed on the surface of the scintillator is an aluminum vapor deposition film.
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