JP5315195B2 - Scanning transmission electron microscope and scanning transmission image observation method - Google Patents

Description

  The present invention relates to a scanning transmission electron microscope.

In a semiconductor device assembled on a silicon single substrate, the orientation of the single crystal substrate is used as a reference for observing the orientation in order to accurately measure the thickness of the insulating film. This is because when the observation direction is not determined, the insulating film is observed obliquely, and accurate film thickness measurement becomes impossible. In the case of a polycrystalline sample, orientation is adjusted in order to accurately grasp the structure of the crystal interface. This is because if the orientation is not performed, the crystal interfaces may be observed to overlap each other, which may lead to erroneous results. For this reason, when a scanning transmission image of a crystalline sample is observed with a scanning transmission electron microscope (STEM Scanning Transmission Electron Microscope), it is necessary to align the crystal orientation with the optical axis of the STEM.

  A crystalline sample is a sample in which part or all of the sample has a regular arrangement. For example, a single crystal, a polycrystal that is a composite of a plurality of microcrystals, and a quasicrystal. A crystalline sample also includes a simple element or a compound composed of a plurality of elements.

  When aligning the crystal orientation using the STEM image, it is necessary to use a high-magnification image capable of observing the lattice fringes. In some cases, it is difficult to determine the final crystal orientation. On the other hand, an electron beam diffraction image does not depend on the magnification of a scanning transmission image, and the crystal orientation can be easily obtained from the brightness balance of diffraction spots, the position of the Kikuchi line, and the like. For this reason, in the observation of the crystalline sample by STEM, the crystal orientation is aligned using an electron beam diffraction image. This method includes a method in which the sample is tilted in a plurality of directions and a method in which the electron beam is tilted with respect to the optical axis. The latter introduces aberration due to the electron beam tilt from the reference electron optical axis. Since there is a limit to the angle at which tilting is possible, it is not generally used.

  Specifically, in the observation of the crystalline sample by the STEM, the observation region of the crystalline sample is searched while viewing the scanning transmission image on the display device, and the diffraction image formed below the crystalline sample is recorded. . A photographic film or a TV camera is used for recording. Then, while observing the electron diffraction pattern in the observation region, the holder on which the crystalline sample is mounted is physically tilted so that the crystal orientation is aligned with the optical axis of the STEM.

"Electron microdiffraction" Springer by J.C.H. Spence and J.M. Zuo.

  As a result of intensive studies on the scanning transmission image observation of the crystalline sample by the present inventor, the following knowledge has been obtained.

  Since observation and recording of the scanning transmission image and the electron diffraction image are performed by completely different means, the crystal alignment direction of the actual sample observed in the scanning transmission image does not necessarily match the direction of the electron diffraction image. The direction in which the sample should be tilted in order to match the crystal orientation cannot be determined directly from the electron diffraction pattern. Therefore, the direction in which the crystal orientation changes in the electron diffraction image when the sample is tilted around the X or Y axis in the scanning transmission image is displayed using a marker around the electron diffraction image. ing. Note that the position of the marker, that is, the changing direction of the electron beam diffraction image when the sample is tilted, is determined by observing the electron beam diffraction image while tilting the sample around the X axis or the Y axis in advance.

  However, in the crystal orientation adjustment, the observation visual field often moves when the sample is tilted. For this reason, it is necessary to repeat the operation of confirming whether or not the electron beam diffraction image is in the desired region of the sample with the scanning transmission image, and performing crystal orientation alignment with the electron beam diffraction image many times. Since it is necessary to determine the direction in which the sample should be tilted while always conscious of the position of the marker as well as the shape of the electron diffraction pattern, it takes time to align the crystal orientation and is often erroneous. It was.

  The object of the present invention relates to the orientation of crystalline samples accurately and quickly.

  The present invention relates to aligning a crystal arrangement direction of a sample in a scanning transmission image and a direction of an electron diffraction image in crystal orientation alignment using a scanning transmission image and an electron beam diffraction image. For example, the light receiving surface of a TV camera that captures an electron diffraction image is directly or indirectly rotated in conjunction with the crystal arrangement direction of the sample of the scanned transmission image. Further, for example, the current applied to the plurality of projection lenses is changed, and the direction of the electron beam diffraction image is changed by the action of the electromagnetic lens.

  According to the present invention, when aligning the crystal orientation of the sample with respect to the optical axis of the STEM, the direction in which the sample should be tilted can be directly determined from the shape of the electron diffraction image, so accurate and rapid crystal orientation alignment. Is possible.

1 is a schematic functional block diagram of a scanning transmission electron microscope in Embodiment 1. FIG. FIG. 3 is a schematic functional block diagram of a scanning transmission electron microscope in Example 2. The principle figure of the scanning mechanism of a scanning transmission electron microscope. The flowchart of crystal orientation alignment. The figure which shows the scanning transmission image of a silicon device. The figure which shows the electron beam diffraction image from which the direction shift | offset | difference differs with the crystal arrangement direction of a sample, and a big misalignment. The figure which shows the electron beam diffraction image from which the direction shift | offset | difference differs with the crystal arrangement direction of a sample small. The figure which shows the electron beam diffraction image in which the direction differs from the crystal arrangement direction of a sample. The figure which shows the electron-diffraction image with a big shift | offset | difference of an azimuth | direction where the direction and the crystal arrangement direction of the sample corresponded. The figure which shows the electron-diffraction image with a small orientation shift | offset | difference with which the direction and the crystal arrangement direction of the sample corresponded. The figure which shows the electron beam diffraction image in which the direction corresponded with the crystal arrangement direction of the sample, and the direction was in agreement. FIG. 4 is a diagram illustrating a rotation data table in the first embodiment. FIG. 10 is a diagram illustrating a rotation data table in the second embodiment.

  In the embodiment, an electron source that generates an electron beam, a sample stage that holds the sample, a scanner that scans the electron beam on the sample, a detector that detects the electron beam that has passed through the sample, and a diffraction that is diffracted from the sample. A TV camera that detects an electron beam and a display unit that displays a scanning transmission image and an electron beam diffraction image, controls the direction of the electron beam incident on the TV camera, and scans the direction of the electron beam diffraction image. Disclosed is a scanning transmission electron microscope that matches the crystal alignment direction of a sample in a transmission image.

  In addition, the embodiment discloses a scanning transmission electron microscope including a TV camera rotation mechanism that directly or indirectly rotates a light receiving surface of a TV camera.

  In addition, the embodiment discloses a scanning transmission electron microscope including one or more projection lenses that focus an electron beam transmitted through a sample onto a TV camera, a rotation data table in which observation conditions and rotation angle information of the TV camera are recorded. .

  In the embodiment, a plurality of projection lenses for focusing the electron beam transmitted through the sample to the TV camera are provided, and a scanning transmission for controlling the direction of the electron beam incident on the TV camera by changing the current applied to the projection lens. An electron microscope is disclosed.

  In the embodiment, a scanning transmission electron microscope having a rotation data table in which current information of the projection lens is recorded for each observation condition is disclosed.

  In the embodiment, an electron beam is scanned on the sample held on the sample stage, the electron beam transmitted through the sample is detected by the detector, the electron beam diffracted from the sample is detected by the TV camera, Controlling the direction of the incident electron beam, aligning the direction of the electron diffraction pattern with the crystal arrangement direction of the sample in the scanning transmission image, and displaying the scanning transmission image and electron beam diffraction image on the display unit A method is disclosed.

  Also, the embodiment discloses a scanning transmission image observation method in which the light receiving surface of the TV camera is directly or indirectly rotated by the TV camera rotating mechanism.

  Further, in the embodiment, the electron beam transmitted through the sample by one or more projection lenses is focused on the TV camera, and the TV camera rotation mechanism is controlled based on a rotation data table in which observation conditions and rotation angle information of the TV camera are recorded. A scanning transmission image observation method is disclosed.

  In the embodiment, an electron beam transmitted through a sample by a plurality of projection lenses is focused on a TV camera, a current supplied to the projection lens is changed, and a scanning transmission image for controlling the direction of the electron beam incident on the TV camera. An observation method is disclosed.

  Further, in the embodiment, a scanning transmission image observation method is disclosed in which the current supplied to the projection lens is changed based on a rotation data table in which current information of the projection lens is recorded for each observation condition.

  Hereinafter, the above and other novel features and effects will be described with reference to the drawings. It should be noted that the embodiments can be appropriately combined, and the specification discloses the combined form.

  FIG. 1 is a schematic functional block diagram of a scanning transmission electron microscope in the present embodiment. An electron beam (charged particle beam) 3 emitted from an electron beam source (charged particle beam source) 1 and accelerated by an accelerating electrode 2 includes a first focusing electromagnetic lens 4, a second focusing electromagnetic lens 5, and an objective electromagnetic lens 9. The sample 11 held on the sample stage 10 is irradiated via the previous magnetic field. When the sample 11 is irradiated with the electron beam 3, secondary electrons 8, forward scattered electrons 12, and transmitted electrons 13 having sample information are generated by the interaction between the sample 11 and the electron beam 3. The electron beam 3 irradiated to the sample is scanned on the sample by a scanning coil 6 arranged symmetrically with respect to the electron beam optical axis. An enlarged sample image is formed on the display device 62 by synchronizing the scanning of the electron beam and the scanning on the screen. The secondary electrons 8 generated from the sample cause the phosphor 18 to emit light. This light emission is detected by the photomultiplier tube 19, amplified by the minute current amplifier 32, and taken into the data bus by the ADC 46. Although a phosphor and a photomultiplier tube are used as the secondary electron detector, a semiconductor detector such as a multi-channel plate may be used. The forward scattered electrons 12 are detected by the forward scattered electron detector 14 via the projection lens 68. The transmitted electrons 13 are detected by the transmitted electron detector 15 via the projection lens 68. Note that the forward scattered electron detector 14 and the transmission electron detector 15 may be configured by a combination of a phosphor and a photomultiplier tube or a semiconductor detector. The electron diffraction image is taken by the TV camera 17 via the TV camera head 16 and displayed on the display device 62. At this time, the transmission electron detector 15 is moved to a position sufficiently away from the center of the electron beam (charged particle beam) 3 optical axis. For the TV camera, a detector having characteristics of high sensitivity, high S / N, and high linearity, such as a CCD or a harpicon camera, can be used to quantitatively record the electron beam diffraction image intensity. desirable.

  The electron beam source 1 and the acceleration electrode 2 transmit commands such as an acceleration voltage, an electron beam extraction voltage, and a filament current from the microprocessor 50 to the DACs 36 and 37 via the data bus, and convert them into analog signals. Then, the charged particle beam source power supply 20 and the acceleration high-voltage power supply 21 are set to drive. In the first focusing electromagnetic lens 4, the second focusing electromagnetic lens 5, and the objective electromagnetic lens 9, the microprocessor 50 sets the lens current condition, and the DACs 38, 39, and 43 that receive it set the excitation power supply for each lens. By doing so, a current is applied to the electromagnetic lens. The position of the sample 11 is set by the operator operating the sample stage 10 using the rotary encoder 59 or by driving the sample stage 10 according to the sample position driving pattern recorded in advance in the data storage device 51.

  The scanning amount of the electron beam on the sample can be arbitrarily changed by controlling the magnitude of the electric field or magnetic field applied to the electron beam by the scanning mechanism. For example, in the specimen magnified image (secondary electron image) by secondary electrons, the magnification is changed by changing the magnitude of the current applied to the scanning coil 6 and changing the scanning range of the electron beam 3 on the specimen. Is possible. If the scanning region of the electron beam on the sample is narrowed, the magnification of the secondary electron image is increased, and if the scanning region of the electron beam is widened, the magnification is reduced.

  FIG. 3 is a principle diagram showing an electron beam scanning mechanism. The electron beam 3 moves along the electron beam optical axis 63. An upper scanning coil 64 and a lower scanning coil 65 are arranged symmetrically in the X and Y directions on the electron beam optical axis. In order to apply an electron beam perpendicular to the sample, the scanning coils are arranged in two upper and lower stages. When a sawtooth waveform is applied to the upper scanning coil 64 and the lower scanning coil 65 and the electron beam reaches the front focal position on the optical axis of the objective electromagnetic lens 9, the electron beam enters the sample vertically. When the electron beam interacts with the sample, secondary electrons 8, forward scattered electrons 12, and transmitted electrons 13 are obtained. By synchronizing these secondary electrons 8, forward scattered electrons 12, and transmitted electrons 13 with the scanning waveform, a magnified sample image is formed. The magnification of the magnified sample image depends on the voltage of the scanning waveform applied to the X and Y scanning coils.

  A method for aligning the orientation of a crystalline sample accurately and quickly using a scanning transmission image and an electron beam diffraction image will be described with reference to the flowchart of FIG.

  In step S102, an arbitrary crystalline sample is mounted on the sample stage and inserted into the electron beam apparatus. In this embodiment, a silicon device is used as a sample. FIG. 5 shows a scanning transmission image obtained by photographing the silicon device. α and β indicate the crystal arrangement direction of the sample.

In step S103, the magnification of the scanning transmission electron microscope, electron beam diffraction image is set to the magnification M ₀ observable to determine the voltage applied to scan coils.

  In step S104, to obtain an enlarged image and an electron beam diffraction image of the sample inserted in step S102, such as the acceleration voltage of the electron beam, the electron beam irradiation amount, the irradiation range, the irradiation position, and the irradiation angle. Set the necessary measurement conditions.

  In step S105, observation of the scanning transmission image and electron beam diffraction image of the sample inserted in step S102 is started, and the actual crystal alignment direction of the sample is matched with the direction of the electron beam diffraction image. That is, the relationship between α and β in FIGS. 5 and 6 is made to be the relationship between α and β in FIGS.

  In crystal orientation alignment, first, the upper scanning coil 64 and the lower scanning coil 65 scan the sample with the electron beam (charged particle beam) 3 and align the approximate crystal orientation while observing the scanning transmission image. Thereafter, an electron beam (charged particle beam) 3 is irradiated onto a minute spot region on the sample, and an accurate crystal orientation is aligned while observing an electron beam diffraction image.

  In step S106, the observation area of the sample 11 is determined by driving the sample stage 10 using the rotary encoder 59 while viewing the scanning transmission image.

  In step S107, the crystal orientation is adjusted from the electron diffraction image. The method for adjusting the crystal orientation will be described with reference to FIGS. When there is no crystal orientation, the state is as shown in FIGS. From this state, the sample is tilted so that the diffraction pattern is isotropic, and the crystal orientation is adjusted. 9 and 10, the crystal orientation can be adjusted by inclining the sample in the α direction. FIG. 11 shows a state in which the crystal orientation is matched.

  In step S108, it is confirmed whether the electron diffraction pattern is in a desired region of the sample. When the sample is tilted, the observation field of view often moves. Therefore, after adjusting the crystal orientation, the scanning transmission image is confirmed again to confirm whether the electron diffraction pattern is in the desired region of the sample. If the electron diffraction pattern is not in the desired region of the sample, the process returns to step S106, and the observation region is adjusted again with the scanning transmission image. When the electron diffraction pattern is in the desired region of the sample, the crystal orientation is completed.

  In this embodiment, in the scanning transmission electron microscope composed of a single projection lens 68, the crystal arrangement of the actual sample is obtained by directly or indirectly rotating the light-receiving surface of a TV camera that takes an electron diffraction image. The direction and the direction of the electron diffraction image are matched. More specifically, the TV camera head 16 is rotated by motor driving. The rotation angle of the TV camera head 16 is determined by observing the direction in which the crystal orientation changes in the electron diffraction image while tilting the sample about the X axis or the Y axis. Here, every time the orientation of the sample is performed, the direction of the electron beam diffraction image is observed to determine the rotation angle of the TV camera head 16, but the direction of the electron beam diffraction image is observed in advance, and the TV camera head 16 is rotated. There is also a method in which the rotation angle of the camera head 16 is determined in advance. In that case, the rotation angle information of the TV camera head 16 is stored in the rotation data table 54, and the TV camera head 16 is rotated based on the information in the rotation data table 54 when aligning the sample. Just do it.

  Since the direction of the electron diffraction image also changes due to the action of the projection lens 68, the rotation angle information of the camera head stored in the rotation data table 54 is preferably set for each observation condition. FIG. 12 shows an example of the rotation data table 54 in the present embodiment.

  According to the present example, since the crystal arrangement direction of the actual sample and the direction of the electron beam diffraction image coincide with each other, the direction in which the sample should be inclined to match the crystal orientation is determined by the electron beam. The crystal orientation can be determined directly from the shape of the diffraction image, and the crystal orientation can be adjusted accurately and quickly. In addition, since the combination of the electron optical conditions is not limited, the camera length, that is, the magnification of the electron diffraction image can be freely selected.

  In this embodiment, in a scanning transmission electron microscope provided with a plurality of projection lenses, the actual crystal alignment direction of the sample and the direction of the electron beam diffraction image are matched by changing the current applied to each projection lens. . Hereinafter, the difference from the first embodiment will be mainly described.

  FIG. 2 is a schematic functional block diagram of the scanning transmission electron microscope in the present embodiment. In this embodiment, in the scanning transmission electron microscope composed of a plurality of projection lenses, here, the first projection lens 69 and the second projection lens 70, the conditions of the first projection lens 69 and the second projection lens 70, that is, each projection. The current applied to the lens is changed, and the direction of the electron diffraction image is changed by the action of the electromagnetic lens. The conditions of the first projection lens 69 and the second projection lens 70 are to observe the direction in which the crystal orientation changes in the electron diffraction image while tilting the sample about the X axis or the Y axis as in the first embodiment. It is decided by. When the orientation of the sample is performed, the conditions of the first projection lens 69 and the second projection lens 70 may be changed based on the information in the rotation data table 54 in which each projection lens condition is recorded for each observation condition. FIG. 13 shows the rotation data table 54 in this embodiment.

  As rotation correction when using two-stage lenses, the polarities of the first projection lens 69 and the second projection lens 70 are reversed, the rotation of the electron diffraction image by the first projection lens 69, and the second The rotation of the electron beam diffraction image by the projection lens 70 is combined so as to be reversed at exactly the same angle. Further, even when the first projection lens 69 and the second projection lens 70 have the same polarity, rotation correction is possible if one is increased in excitation and the other is decreased in excitation.

  According to this embodiment, since the camera rotation mechanism and its control are not required, the apparatus configuration can be simplified.

DESCRIPTION OF SYMBOLS 1 Charged particle beam source 2 Acceleration electrode 3 Charged particle beam 4 1st focusing electromagnetic lens 5 2nd focusing electromagnetic lens 6 Scan coil 7 Deflection coil 8 Secondary electron 9 Objective electromagnetic lens 10 Sample stage 11 Sample 12 Forward scattered electron 13 Transmission electron 14 Forward scattered electron detector 15 Transmitted electron detector 16 TV camera head 17 TV camera 18 Phosphor 19 Photomultiplier tube 20 Charged particle beam source power source 21 High-voltage power source 22 for acceleration 22 Sample drive device 23 TV camera head drive devices 24 and 25 Voltage stabilizers 26-28, 71-73 Electromagnetic lens power supply 29-31 Coil power supply 32-35 Micro current amplifiers 36-45, 74-76 Digital-analog converter (DAC)
46-49 Analog-to-digital converter (ADC)
50 Microprocessor 51 Data Storage Device 53 Deflection System Control Unit 54 Rotation Data Table 55 Magnification Comparator 56, 57 Interface 58, 59 Rotary Encoder 60 Keyboard 61 Display Device Driver 62 Display Device 63 Electron Beam Optical Axis 64 Upper Scanning Coil 65 Downward Scanning Coil 66 X scanning coil 67 Y scanning coil 68 Projection lens 69 First projection lens 70 Second projection lens

Claims (4)

An electron source that generates an electron beam;
A sample stage for holding the sample;
A scanner that scans the sample with the electron beam;
A detector for detecting an electron beam transmitted through the sample;
A TV camera that detects an electron beam diffracted from the sample;
In a scanning transmission electron microscope provided with a display unit that displays a scanning transmission image and an electron beam diffraction image,
One or more projection lenses for focusing the electron beam transmitted through the sample onto the TV camera;
A TV camera rotation mechanism for rotating the light receiving surface of the TV camera;
A data table that records the relationship between the conditions of the projection lens and the rotation angle information of the TV camera;
The TV camera is rotated by the rotation angle of the TV camera corresponding to the condition of the projection lens based on the data table, the crystal arrangement direction of the sample in the electron beam diffraction image, and the crystal of the sample in the scanning transmission image A scanning transmission electron microscope characterized by matching with the arrangement direction. The scanning transmission electron microscope according to claim 1, wherein
Multiple projection lenses that focus the electron beam that has passed through the sample onto the TV camera
Scanning transmission electron microscope according to claim Rukoto. Scan the electron beam on the sample held on the sample table,
The detector detects the electron beam that has passed through the sample,
The electron beam diffracted from the sample is detected by a TV camera,
In a scanning transmission image observation method of displaying a scanning transmission image and an electron beam diffraction image on a display unit,
Based on the data table that records the relationship between the conditions of the projection lens and the rotation angle information of the TV camera, the TV camera is rotated by the rotation angle of the TV camera corresponding to the conditions of the projection lens based on the data table. And aligning the crystal arrangement direction of the sample in the electron diffraction image with the crystal arrangement direction of the sample in the scanning transmission image.
A scanning transmission image observation method characterized by the above. In the scanning transmission image observation method according to claim 3,
A scanning transmission image observation method, wherein an electron beam transmitted through a sample by a plurality of projection lenses is focused on the TV camera.

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