JP2011249273A - Scanning electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning electron microscope capable of efficiently detecting reflection electrons emitted by a sample at a small angle without degradation of resolution at the time of capturing a sample image.SOLUTION: A scanning electron microscope includes: an electron beam source for emitting an electron beam; an objective lens for focusing the electron beam emitted by the electron beam source on a sample; a scanning deflector for scanning the focused electron beam on the sample; an inner tube through which the electron beam from the electron beam source goes; a first scintillator provided on an inner wall of the inner tube, which emits light when first electrons as subjects of detection arising from the sample with scanning the electron beam impinge thereon; and a photodetector for detecting first light which results from the light emission and travels toward the electron beam source in the inner tube. The scanning electron microscope forms a scan image based on a detection result by the photodetector.

Description

  The present invention relates to a scanning electron microscope for acquiring a scanned image of a sample by scanning a focused electron beam on the sample surface.

  In the scanning electron microscope, the primary electron beam is focused on the sample surface so that the probe diameter becomes small by excitation with the objective lens. In this state, the electron beam is scanned two-dimensionally on the sample surface by the scanning deflector, whereby detected electrons such as reflected electrons generated from the sample are detected as luminance signals by the electron detector.

  Usually, an electron detector for detecting such detected electrons is installed below (sample side) or above (electron beam source side) the objective lens, and the detected luminance signal is an amplifier. Is amplified.

  The amplified luminance signal is sent to the image processing board. The image processing board forms scanned image data based on the luminance signal and the scanning signal. The scan image data thus formed is sent to a display unit such as an LCD (Liquid Crystal Display), and an image based on the scan image data is displayed on the display unit as a scan image.

  Examples of electron detectors arranged above the objective lens include detectors that are arranged near the optical axis with an opening formed at a position corresponding to the optical axis of the primary electron beam, and are off the optical axis. There is a detector placed in position.

  Further, among those that are arranged outside the optical axis and detect the luminance signal, there are those that detect the secondary electrons generated from the reflecting plate by colliding the reflected electrons from the sample with the reflecting plate.

  Here, when the electron detector is arranged above the objective lens, the spatial limit is large, so the electron detector is often arranged below the objective lens.

  In addition, in order to detect only the reflected electrons among the detected electrons generated from the sample, the secondary electrons collide with the inner wall of the inner tube through which the primary electron beam passes to absorb it, and the reflection that has risen inside the inner tube Some devices selectively detect electrons inside the inner tube (see Patent Document 1).

  Of the reflected electrons generated from the sample in response to the scanning of the primary electron beam, electrons emitted at a particularly low angle (for example, 30 degrees or less) are information on the surface of the sample and information on the crystal structure. It contains a lot of very useful information. Therefore, efficient detection of reflected electrons emitted at such a low angle is desired.

Japanese Patent Laid-Open No. 10-134754

  In a normal scanning electron microscope, a secondary electron detector is disposed at a position away from the lower surface of the objective lens for the purpose of detecting secondary electrons from a sample. Since the distance between the secondary electron detector and the sample surface is large, it is difficult for the above-described reflected electrons emitted at a low angle to reach the secondary electron detector. Therefore, such reflected electrons cannot be detected using this secondary electron detector.

  Therefore, in order to detect the reflected electrons, a disk-shaped electron detector is inserted below the objective lens and between the lower surface of the objective lens and the sample, and the reflected electrons are detected using the electron detector. (Including low-angle emission backscattered electrons and high angle emission backscattered electrons).

  However, in such a configuration, the presence of the electron detector limits the approach of the sample surface to the lower surface of the objective lens, which inevitably increases the working distance (WD) from the lower surface of the objective lens to the sample surface. As a result, the resolution at the time of obtaining the sample image (scanned image) is reduced.

  In addition, a configuration in which the diameter of a hole through which an electron beam provided at the lower part of the objective lens passes is increased and an electron detector is disposed inside the objective lens to detect reflected electrons or the like has been studied. A large spatial restriction occurs inside the objective lens.

  The present invention has been made in view of the above points, and scanning that can efficiently detect low-angle emission backscattered electrons from a sample without degrading resolution at the time of acquiring a sample image. The purpose is to provide an electron microscope.

  A scanning electron microscope according to the present invention scans an electron beam source that emits an electron beam, an objective lens that focuses the electron beam emitted from the electron beam source on the sample, and the focused electron beam on the sample. In a scanning electron microscope comprising a scanning deflector for scanning and an inner tube through which an electron beam from an electron beam source passes, a first scintillator is provided on the inner wall of the inner tube and generated from a sample in response to scanning of the electron beam A first detector to be detected collides with the first scintillator to emit light, and a light detector is installed to detect the first light traveling toward the electron beam source inside the inner tube due to the light emission. The scanning image is formed on the basis of the detection result by the photodetector.

  In the present invention, the detected electrons from the sample collide with the scintillator provided on the inner wall of the inner tube through which the electron beam from the electron beam source passes, so that the scintillator emits light, thereby causing the inner scintillator to emit light. Detection of light toward the electron beam source side is performed inside the tube.

  As a result, it is possible to efficiently detect electrons to be detected such as reflected electrons from the sample without placing an electron detector between the objective lens and the sample, with the sample surface close to the lower surface of the objective lens. it can. As a result, the working distance at the time of sample observation can be shortened, and a reduction in resolution when acquiring a sample image can be prevented.

  In particular, in the case of the present invention, low-angle emission reflected electrons can be made to collide with the scintillator as electrons to be detected from the sample, so that detection of the low-angle emission reflected electrons can be performed efficiently without causing a reduction in resolution. It can be carried out.

It is a schematic block diagram which shows the scanning electron microscope in this invention. It is a figure which shows the principal part of the scanning electron microscope in this invention. It is a figure which shows the principal part of the modification in this invention.

  A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a scanning electron microscope in the present invention.

  In the figure, an electron beam 7 emitted from an electron gun (electron beam source) 1 is accelerated by a predetermined acceleration voltage and is focused toward an objective aperture 10 by a magnetic field generated by a focusing lens 2. A hole 10 a is formed in the objective aperture 10, and the focused electron beam 7 passes through the hole 10 a of the objective aperture 10. Furthermore, the electron beam 7 that has passed through the hole 10 a passes through the light guide (light guide member) 25 and the opening 23 provided in the scintillator 24 that constitute the electron / light detection means 6.

  Here, the electron beam 7 emitted from the electron gun 1 passes through the front part (not shown) of the inner tube (vacuum pipe) 8 from the electron gun 1 to the opening 23 of the detection means 6. To do. Then, the electron beam 7 that has passed through the opening 23 of the detection means 6 passes through the inner portion 8 a of the inner tube 8 and reaches the sample 5.

  The detection means 6 is located between the front part and the rear part (hereinafter, the rear part is referred to as “rear inner tube”) 8 a of the inner tube 8. And the scintillator (1st scintillator) 9 is provided in the inner wall in the lower end part of the back | latter stage inner tube 8a. The scintillator 9 is provided by a method such as applying a powdered scintillator material. The lower end portion of the rear inner tube 8 a is located in the electron beam passage hole of the objective lens 4 and is disposed so as to face the sample 5.

  The electron beam 7 that has passed through the rear inner tube 8 a is focused on the sample 5 as an electron probe by the magnetic field generated by the objective lens 4. At this time, the focused electron beam 7 scans the upper surface of the sample 5 based on the operation of the scanning deflector 3. The scanning deflector 3 is disposed outside the rear inner tube 8a. The sample 5 is placed on a sample stage (not shown).

  Based on the scanning of the electron beam 7 on the sample 5, electrons to be detected (detection target electrons) such as reflected electrons are generated from the scanning region on the sample 5. The detection of the detected electrons will be described later.

  The electron gun 1, the focusing lens 2, the scanning deflector 3, and the objective lens 4 are driven by corresponding driving power sources 1a to 4a, respectively. Each drive power source 1 a to 4 a is connected to the bus line 12. A CPU 13 is connected to the bus line 12. As a result, the drive power supplies 1 a to 4 a are driven and controlled by the CPU 13 via the bus line 12.

  The detection means 6 includes a light guide (light guide member) 25, and a scintillator (second scintillator) 24 provided on a lower surface of the tip portion of the light guide 25 and located in the inner tube 8. , A photomultiplier tube (PMT) 26 connected to the base end of the light guide 25. The scintillator 24 is positioned so as to face the sample 5 through the rear inner tube 8a. The scintillator emits light in response to incidence of detected electrons. In the present invention (first embodiment), the photomultiplier tube 26 serves as a photodetector.

  An output signal (detection signal) from the photomultiplier tube 26 constituting the detection means 6 is sent to the image processing unit 11. At the same time, a scanning signal for scanning the electron beam 7 by the scanning deflector is sent to the image processing unit 11 from the CPU 13 via the bus line 12. The image processing unit 11 creates scanned image data based on the detection signal and the scanning signal. The scanned image data is sent to the memory 14 via the bus line 12 and stored in the memory 14 as appropriate.

  Scanned image data stored in the memory 14 is read out under the control of the CPU 13 and sent to the display unit 15 via the bus line 12. The display unit 15 displays a scanned image (sample image) based on the scanned image data.

  Note that the scan image data 11 from the image processing unit 11 may be sent to the display unit 15 via the bus line 12 under the control of the CPU 13. In this case, a scanning image as a live image is displayed on the display unit 15.

  In the above configuration, the drive power supplies 1a to 4a, the image processing unit 11, the memory 14, and the display unit 15 are controlled by the CPU 13, respectively. In addition, the input unit 16 in the figure includes a pointing device such as a mouse and a key device such as a keyboard.

  The above is the configuration of the scanning electron microscope in the present invention. Next, the operation of the present scanning electron microscope will be described with reference to FIG.

  The electron beam 7 emitted from the electron gun 1 reaches the upper surface of the sample 5 after passing through the focusing lens 2, the hole 10 a of the objective aperture 10, the opening 23 of the detection means 6, and the inner tube 8 as described above. . At this time, as described above, the electron beam 7 is focused on the sample 5 by the magnetic field of the objective lens 4, and a predetermined region on the sample 5 is scanned based on the operation of the scanning deflector 3. The scanning on the sample 5 by the electron beam 7 is performed based on a scanning signal supplied from the CPU 13 to the driving power supply 3a.

  Electrons to be detected such as reflected electrons are generated from the sample 5 by scanning the electron beam 7. The reflected electrons 21 having various emission angles in the detected electrons generated in this manner are captured by the magnetic field generated by the objective lens 4 or the electric field attached thereto, and rise inside the objective lens 4 as shown in FIG. To do.

  Among the reflected electrons 21, the low-angle emission reflected electrons 21a emitted at 30 degrees or less with respect to the surface (upper surface) of the sample 5 are the scintillators 9 (first first) provided on the inner wall at the lower end of the rear inner tube 8a. Of the scintillator).

  As a result, the scintillator 9 emits light based on the amount of the reflected electrons 21a that collide. The light 22 (first light) due to this light emission travels upward from the lower end of the rear inner tube 8a inside the rear inner tube 8a.

  The light 22 traveling to the upper end portion of the rear inner tube 8 passes through the scintillator 24 of the detection means 6 and reaches the light guide 25. Here, the scintillator 24 (second scintillator) of the detection means 6 is made of a material through which light 22 generated from the scintillator 9 provided on the inner wall of the lower end portion of the rear inner tube 8a is transmitted.

  Further, in the inner tube 8, at least the inner wall portion of the entire rear inner tube 8a is preliminarily mirror-finished. Accordingly, of the inner wall portion of the rear inner tube 8a, the inner wall portion that is not covered by the scintillator 9 has a mirror surface exposed, and the light 22 generated from the scintillator 9 is efficiently guided upward in the rear inner tube 8a. be able to.

  The light 22 that has reached the light guide 25 of the detection means 6 is guided from the distal end portion of the light guide 25 to the proximal end side within the light guide 25. The light 22 thus guided is detected by a photomultiplier tube 26 which is a photodetector.

  Of the reflected electrons generated by the scanning of the electron beam 7 described above, most of the high-angle emission reflected electrons 21b emitted at an angle exceeding 30 degrees with respect to the surface of the sample 5 are inside the objective lens 4. After rising, the inside of the rear inner tube 8a is lifted as it is without colliding with the inner wall of the rear inner tube 8a.

  In this way, the reflected electrons 21b that have moved up in the rear inner tube 8a collide with the scintillator 24 of the detection means 6. Due to this collision, the scintillator 24 emits light, and the light (second light) enters the light guide 25. Similarly to the first light, the second light is guided through the light guide 25 to the base end side. The second light guided in this way is also detected by the photomultiplier tube 26.

  As a result, the photomultiplier tube 26 constituting the detection means 6 outputs a detection signal including both the low angle emission reflected electrons 21 a and the high angle emission reflected electrons 21 b generated from the sample to the image processing unit 11.

  As described above, the image processing unit 11 creates scan image data based on the detection signal from the photomultiplier tube 26 and the scan signal from the CPU 13. The scanned image data is stored in the memory 14, and then read out from the memory 14 and sent to the display unit 15 under the control of the CPU 13. The display unit 15 displays a scanned image based on the scanned image data.

  The scanned image data created by the image processing unit 11 can be sent to the display unit 15 via the bus line 12 under the control of the CPU 13. Also in this case, the display unit 15 displays a scanned image based on the scanned image data.

  Each scanned image displayed in this way is a sample image based on information on both the low-angle emission reflected electrons 21a and the high-angle emission reflected electrons 21b generated from the sample.

  Next, a second embodiment of the present invention will be described below. In the second embodiment, the wavelength of the first light emitted from the first scintillator 9 and the wavelength of the second light emitted from the second scintillator 24 differ according to the collision of the reflected electrons. . For example, the wavelength of the first light generated from the first scintillator 9 is about 600 nm, and the wavelength of the second light generated from the second scintillator 24 is about 400 nm. This can be set by selecting the material of each scintillator 9, 24.

  Further, a spectroscope (not shown) is provided between the light guide 25 and the photomultiplier tube 26 constituting the detection means 6. The spectroscope has a function of selecting either the first light or the second light and guiding it to the photomultiplier tube 26 based on the difference in wavelength.

  Thereby, in the detection means 6, when the first light is selected by the spectroscope and guided to the photomultiplier tube 26, the acquired scanning image data is an image based on the low-angle emission reflected electrons 21a. It becomes data. In addition, when the second light is selected by the spectroscope and guided to the photomultiplier tube 26, the acquired scanned image data is image data based on the high-angle emission reflected electrons 21b. Here, by canceling the spectroscopic function of the spectroscope, it is also possible to acquire scanned image data based on both reflected electrons 21a and 21b.

  Furthermore, as a modification of the first and second embodiments, the first scintillator 9 can be provided as shown in FIG. FIG. 3 shows only the right-side cross-section portion of the rear stage inner tube 8a in FIGS.

  In FIG. 3, a large number of step portions 8b are formed on the inner wall surface of the lower end portion of the rear inner tube 8a. A first scintillator 9 is provided on each of the surfaces (upper side surfaces) facing upward in each of the step portions 8b. Furthermore, the upper surface of each step 8b is a mirror surface.

  With such a configuration, the first light 22 generated by the collision of the reflected electrons 21a with the first scintillator 9 provided on the upper surface of each step 8b is more efficiently moved upward in the rear inner tube 8a. It can be guided.

  As another modification, the first scintillator 9 provided on the inner wall surface of the lower end of the rear inner tube 8a can be a scintillator made of a single crystal.

  Further, a semiconductor element (semiconductor detector) can be used as an element for detecting the high-angle emission reflected electrons 21b in the detection means 6 without using a scintillator. In this case, the first light 22 can be detected simultaneously by the semiconductor detector without providing the light guide 25 and the photomultiplier tube 26. In this case, the semiconductor detector constitutes a photodetector.

  As described above, the scanning electron microscope according to the present invention includes the electron beam source 1 that emits the electron beam 7, the objective lens 4 that focuses the electron beam 7 emitted from the electron beam source 1 on the sample 5, and the focusing. In the scanning electron microscope comprising the scanning deflector 3 for scanning the electron beam 4 on the sample 5 and the inner tube 8 (8a) through which the electron beam 7 from the electron beam source 1 passes, the inner tube 8 (8a The first scintillator 9 is provided on the inner wall of the first scintillator 9, and the first detected electrons 21 a generated from the sample 5 according to the scanning of the electron beam 7 collide with the first scintillator 9 to emit light. A photodetector 26 for detecting the first light 22 traveling toward the electron beam source 1 side is installed inside the inner tube 8 (8a), and a scanning image is obtained based on the detection result by the photodetector 26. Form.

  The first scintillator 9 is formed on a large number of step portions 8b formed on the inner wall of the inner tube 8 (8a), and each light emitting surface can be configured to face the electron beam source 1 side. . At this time, the surface on which the scintillator 9 is provided in each step 8b may be a mirror surface.

  Further, on the inner wall of the inner tube 8 (8a), a mirror surface portion can be provided on the exposed surface other than the portion where the first scintillator 9 is provided. Thereby, the first light 22 can be efficiently guided.

  Further, a light guide member 25 that receives the first light 22 is disposed, and the light guided by the light guide member 25 is detected by the photodetector 26. At this time, the second scintillator 24 is disposed on the light receiving surface of the light guide member 25, and the second detected electrons 21 b generated from the sample 5 collide with the second scintillator 24 according to the scanning of the electron beam 7. The second light generated as a result is also detected by the photodetector 26. The second scintillator 24 is made of a material that can transmit the first light 22 generated from the first scintillator 9.

  The wavelength of the first light 22 generated from the first scintillator 9 is different from the wavelength of the second light generated from the second scintillator 24, and either the first or second light is used. It is also possible to provide the light guide member with spectroscopic means capable of guiding one to the photodetector.

  As a modification, the photodetector for detecting the first light 22 is a semiconductor detector composed of a semiconductor element, and the second detected electrons generated from the sample in response to scanning of the electron beam are also the semiconductor. It can also be detected by a detector.

  In the present invention, by providing the scintillator 9 on the inner wall of the inner tube 8a, it becomes possible to obtain a scanned image based on the reflected electrons 21a of low angle emission, which has been difficult to detect so far.

  In this case, since the signal resulting from the detection of the reflected electrons 21a is scintillation light passing through the inner tube 8a, the signal is detected using the detection means 6 in which the detection surface is located near the optical axis of the electron beam 7. Therefore, it is not necessary to provide a separate detector and the apparatus is not complicated.

  Since the signal is light, the signal can be efficiently detected even if the detection unit is separated from the lower surface of the objective lens 4 to some extent.

  Further, a spectroscope is provided that changes the wavelength of the scintillation light 22 based on the detection of the first detected electron 21a and the wavelength of the scintillation light based on the detection of the second detected electron 21b, and further selects these lights. Thus, it is possible to obtain different images by performing spectroscopy.

  DESCRIPTION OF SYMBOLS 1 ... Electron gun (electron beam source), 2 ... Condensing lens, 3 ... Scanning deflector, 4 ... Objective lens, 5 ... Sample, 6 ... Detection means, 7 ... Electron beam, 8 ... Inner tube, 8a ... Later stage inner tube , 9 ... 1st scintillator, 10 ... Objective stop, 11 ... Image processing unit, 12 ... Bus line, 13 ... CPU, 14 ... Memory, 15 ... Display unit, 16 ... Input unit, 2 ... Reflected electron, 21a ... Low Angle emission reflected electrons, 21b ... High angle emission reflected electrons, 22 ... First light, 24 ... Second scintillator, 25 ... Light guide (light guide member), 26 ... Photomultiplier tube (photo detector)

Claims (9)

An electron beam source that emits an electron beam, an objective lens that focuses the electron beam emitted from the electron beam source on the sample, a scanning deflector that scans the focused electron beam on the sample, and an electron beam In a scanning electron microscope including an inner tube through which an electron beam from a source passes, a first scintillator is provided on the inner wall of the inner tube, and first detected electrons generated from a sample in response to scanning of the electron beam are first A photodetector for detecting the first light traveling toward the electron beam source side inside the inner tube by the light emission caused by colliding with the scintillator of the first scintillator, and the detection result by the photodetector A scanning electron microscope characterized in that a scanning image is formed based on the above. 2. The scanning electron microscope according to claim 1, wherein the first scintillator is formed at a number of steps formed on the inner wall of the inner tube, and each light emitting surface faces the electron beam source side. 3. The scanning electron microscope according to claim 1, wherein the inner wall of the inner tube has a mirror surface portion on an exposed surface other than a portion where the first scintillator is provided. The scanning electron microscope according to claim 1, wherein a light guide member that receives the first light is disposed, and the light guided by the light guide member is detected by a photodetector. A second scintillator is disposed on the light receiving surface of the light guide member, and the second light generated by the second detected electrons generated from the sample colliding with the second scintillator in response to the scanning of the electron beam is detected by the photodetector. The scanning electron microscope according to claim 1, wherein the scanning electron microscope is detected. 5. The scanning electron microscope according to claim 4, wherein the second scintillator is made of a material that allows transmission of the first light generated from the first scintillator. The wavelength of the first light generated from the first scintillator is different from the wavelength of the second light generated from the second scintillator, and either the first or second light is detected by a photodetector. 7. The scanning electron microscope according to claim 5 or 6, wherein the light guide member is provided with a spectroscopic means capable of guiding the light to the light source. 4. The scanning electron microscope according to claim 1, wherein the photodetector is a semiconductor detector composed of a semiconductor element. 9. The scanning electron microscope according to claim 8, wherein the semiconductor detector detects second detected electrons generated from the sample in response to scanning with an electron beam.

Images