JP2012221678A - Electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate adjustment of an optical axis of electron beam and observation of high-contrast dark field images in an electron microscope.SOLUTION: In an electron microscope, electron beam 104 from an electron source 103 is applied to a sample 110 through an irradiation lens 105 and deflection coils 106 and 107, and the electron beam having passed through the sample 110 is detected by a dark field detector 111 and a bright field detector 114 through an imaging lens 108. An electron beam image is formed on a fluorescent screen 112, the electron beam image on the fluorescent screen 112 is photographed by a camera 113, and a center of gravity coordinate of the electron beam is obtained from image data of the camera 113. A position of the electron beam or the dark field detector is controlled by a deflection coil control device 118 or a dark field detector control device 119 so that the center of gravity coordinate of the electron beam coincides with the center of the dark field detector 111. Thus, optical axis adjustment is facilitated and observation of high-contrast dark field images is achieved.

Description

  The present invention relates to an electron microscope, and more particularly to an electron microscope having an optical axis adjustment function for obtaining a high-contrast dark field image.

  Recent transmission electron microscopes have a scanning image observation function. A transmission electron microscope irradiates a sample with an electron beam generated from an electron gun and accelerated by a plurality of condenser lenses called irradiation lenses. The electrons that have passed through the sample are observed by projecting the sample image onto the detection surface of the television camera by a plurality of condenser lenses called imaging system lenses.

  A scanning transmission electron microscope includes a transmission electron microscope equipped with an electron beam scanning function and a bright field image and dark field image detector. When observing a scanned image, the electron beam is finely converged by the irradiation system lens and scanned two-dimensionally on the sample, detecting secondary electrons, reflected electrons, or transmitted electrons generated from the sample, and detecting the detection signal. It is supplied to a display device synchronized with the electron beam scanning. Electrons transmitted through the sample are diffracted inside the sample and are classified into scattered electrons having a large divergence angle and transmitted electrons having a small divergence angle. An output of the scattered electron detection signal as an image is called a dark field image, and an output of the transmitted electron detection signal as an image is called a bright field image.

  The dark field detector is an annular detector, and electrons passing through the center of the dark field detector are detected by the bright field detector. A difference occurs in the contrast of the scanned image detected by the optical axis of the electron beam irradiated to the sample. For example, when the optical axis of the electron beam is greatly deviated from the center, the transmitted electrons originally detected by the bright field image detector are detected by the dark field image detector and can be obtained from the originally dark field image. Information is lost.

  Thus, since the relationship between the dark field detection and the optical axis is important, for example, in Patent Document 1, even when the electron beam is tilted and scanned on the sample, the electron beam transmitted through the sample is detected by the deflection coil. It has been proposed to obtain a high-contrast dark field image by correcting the trajectory and allowing the optical axis of the electron beam to pass through the center of the annular detection surface of the dark field detector.

  In Patent Document 2, a dark field detector is arranged inside an in-lens objective lens, and the scattering angle of electrons transmitted through the sample is controlled by moving the detector along the optical axis of the electron beam. A technique is disclosed.

JP 2006-302523 A JP 2004-214065 A

  As described above, the relationship between dark field detection and the optical axis is an important issue in obtaining a high-contrast dark field image, and various techniques have been proposed so far. We needed operation.

  Therefore, an object of the present invention is to provide an electron microscope that facilitates optical axis adjustment during dark field image observation and can easily obtain a high-contrast dark field image.

  In order to achieve the above object, the present invention is characterized by irradiating a sample with an electron beam from an electron source via an irradiation system lens and a deflection coil, and passing the electron beam transmitted through the sample through an imaging lens. In an electron microscope that detects with a dark-field detector and a bright-field detector, an electron beam image is formed on a fluorescent plate, and an imaging device that takes an electron beam image of the fluorescent plate, and image data of the imaging device And a control device that moves the electron beam or the dark field detector so as to obtain a barycentric coordinate and match the center of the dark field detector.

  Other features will be clarified in the embodiments described below.

  According to the present invention, since it is possible to easily adjust the optical axis of an electron beam that is difficult to adjust with a detector, an electron microscope capable of easily observing a high-contrast dark field image is realized. Can do.

It is a main block diagram of the scanning transmission electron microscope which concerns on one Example of this invention. It is a screen figure which shows the image of the fluorescent screen displayed on a display. It is a screen figure which shows the image of the fluorescent screen displayed on a display. It is a screen figure which shows the image of the fluorescent screen displayed on a display. It is a screen figure which shows the image of the fluorescent screen displayed on a display. It is a screen figure which shows the image of the fluorescent screen displayed on a display. It is a screen figure which shows the image of the fluorescent screen displayed on a display. It is an operation screen figure of optical axis adjustment concerning one example of the present invention. It is a message screen figure of a display display concerning one example of the present invention. It is a flowchart of the optical axis adjustment processing procedure which concerns on one Example of this invention. It is a flowchart of the optical axis adjustment process sequence which concerns on the other Example of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram showing a main configuration of a scanning transmission electron microscope according to an embodiment of the present invention. The electron beam 104 irradiated to the sample 110 from the electron source 103 passes through the sample 110, is photographed by a photographing device such as a television camera 115, is sent to the image processing device 122, and is displayed on a display or the like. The electron source 103 is installed in a housing called an electron gun 101, and after the electron gun 101 and the body 102 of the electron microscope main body are connected, the inside is held in a vacuum. There are various types of electron sources 103 such as a tungsten filament, a lanthanum hexabolite filament, a thermionic gun, a field emission electron gun, a Schottky electron source, and the present invention is applicable to any electron source.

  The mirror body 102 is scanned with the irradiation system lens 105 for focusing the electron beam 104 on the sample 110, the imaging system lens 108 for focusing on the television camera 115, the sample stage 109 for fixing the sample 110, and the electron beam 104 on the surface of the sample. A deflection coil 107, a bright field image detector 114, and a dark field image detector 111 are incorporated.

  An acceleration voltage, a filament voltage, and a bias voltage are applied to the electron source 103 from the electron source control device 116, and the electron beam 104 is generated. The irradiation system lens 105 and the imaging system lens 108 are supplied with a current from the electromagnetic lens control device 117, and the lens intensity is changed. When obtaining a scanned image, the electron beam 104 is scanned by the scanning deflection coil 107. The scanning deflection coil 107 is supplied with current from the deflection coil controller 118 and controls the electron beam 104.

  When the processor 124 executes the program stored in the memory 123, a command to the electron source control device 116 that supplies an acceleration voltage to the electron source 103, a deflection coil control device 118 that scans the electron beam 104, and an electromagnetic lens control device The command to 117 is given. An image signal photographed by the television camera 115 is sent to the image processing device 122 and stored in the memory 123.

  In the transmission electron microscope, the operator adjusts the optical axis by visually observing the electron beam image of the fluorescent screen 112. In this embodiment, an electron beam image of the fluorescent screen 112 is photographed by the television camera 113, and image data from the television camera 113 is processed by the image processing device 120, thereby drawing the electron beam image formed on the fluorescent screen 112. Create an image. As will be described later, an electron beam image and a dark field detector image are also drawn in this drawn image, which are stored in the memory 123 and displayed on the display 125. Further, the detection surface of the dark field detector 111 is also displayed on the display 125 at the same time.

  In addition, a deflection coil 106 is provided inside the mirror body 102 for the purpose of adjusting the optical axis of the electron beam 104. Further, a scanning deflection coil 107 is provided for the purpose of scanning the electron beam 104 and is controlled by the coil control device 118.

  In FIG. 2, scattered electrons are expressed as 201 and transmitted electrons are expressed as 202. Electrons transmitted through the sample 110 are divided into scattered electrons 201 having a large scattering angle and transmitted electrons 202 having a small scattering angle. The scattered electrons 201 are mainly detected by the dark field detector 111, and the transmitted electrons 202 are mainly detected by the bright field detector 114. The dark field detector 111 is moved on the optical axis by the dark field detector control device 119, the bright field detector 114 is moved on the optical axis by the bright field detector control device 121, and the detected signal is processed in the memory 123. And displayed on the display 125. On the fluorescent screen 112, the transmitted electrons 202 are centered and the scattered electrons 201 are arranged around the center, and are displayed as an image as shown in FIG.

  FIG. 3 is an example of a screen showing the shape of the fluorescent screen 112 displayed on the display 125. An electron beam 104 shaped as shown in FIG. 2 is irradiated onto the fluorescent screen 112 and displayed on the display 125 as an image. When the operator adjusts the optical axis to acquire a transmission image with the television camera 115, the sample plate 109 is removed from the optical axis, the fluorescent screen 112 is inserted on the optical axis, and the television camera 113 is inserted. The captured image is viewed on the display 125, the electron beam 104 is guided onto the fluorescent screen 112 while controlling the current value of the deflection coil 106, and the center of gravity of the electron beam 4 is moved to the center of the fluorescent screen 112.

  When the operator adjusts the optical axis in order to acquire a scanning transmission image with the dark field detector 111 and the bright field detector 114, the operator inserts the sample stage 109 and the fluorescent plate 112 on the optical axis and transfers them to the television camera 113. The center of the dark field detector 111 and the center of the fluorescent screen 112 are assumed to be the same and the center of gravity of the electron beam 104 is moved to the center of the fluorescent screen 112 while controlling the current value of the deflection coil 106 while viewing the displayed image on the display 125. .

  Even when the center of the dark field detector 111 and the center of the fluorescent screen 112 are not the same, the operator looks at the display 125 so that the center of the drawing detection surface 401 and the center of gravity of the electron beam 104 are the same. A contrast scanning transmission image can be displayed on the display 125. Alternatively, the fluorescent plate 112 and the bright field detector 114 are removed from the optical axis, the dark field detector 111 is inserted on the optical axis, and the electron beam 4 that has passed through the center is photographed by the television camera 115. Adjustment is possible.

  When the memory 123 sends a signal to the electromagnetic lens control device 117 to control the current values of the irradiation system lens 105 and the imaging system lens 108 and change the spot diameter of the electron beam 104, the optical axis of the electron beam 104 moves. Therefore, it is necessary to adjust the optical axis. The operator adjusts the optical axis every time the spot diameter of the electron beam 104 is changed. By recording the current value sent to the deflection coil controller 118 at each spot diameter in the memory 123, the spot of the electron beam 104 is recorded. Optical axis adjustment for each change can be omitted.

  In the present embodiment, in order to realize a transmission electron microscope in which the optical axis adjustment can be performed manually by the operator and automatically performed by the memory 123, an image photographed by the television camera 113 as shown in FIG. A screen on which a drawing detection surface 401 coinciding with the detection surface of the dark field detector 111 is drawn is used. In this case, the optical axis adjustment is performed in a state where the sample stage 109 and the fluorescent plate 112 are inserted on the optical axis and the dark field detector 111 is removed from the optical axis. The memory 123 sends a signal to the deflection coil controller 118 to control the electron beam 104 so that the transmitted electrons 202 are moved to the center of the drawing detection surface 401 or the scattered electrons 201 are arranged on the drawing detection surface 401. .

  FIG. 5 shows the electron beam control operation. The center of gravity of the electron beam 501 is adjusted to the vicinity of the center of the drawing detection surface 401. Further, the memory 123 sends a signal to the dark field detector control device 119, controls the position of the center of the detection surface of the dark field detector 111, and moves to the position of the transmitted electrons 202, thereby adjusting the optical axis. It becomes.

  FIG. 8 is an example of an operation screen when the above operation is executed. When Beam alignment 801 is selected, the deflection coil 106 is controlled to perform the optical axis adjustment process. When “Spot move alignment” 802 is selected, the optical axis adjustment is performed when the spot diameter of the electron beam 104 is changed. When Beam 803 is selected, the electron beam 104 is controlled, and the electron beam 104 is controlled near the center of the drawing detection surface 401. When the Detector 804 is selected, the dark field detector 111 is controlled, and the dark field detector 111 is controlled near the center of gravity of the electron beam 104.

  When Beam 803 and Detector 804 are selected, the dark field detector 111 is set as the control target, the dark field detector 111 is controlled near the center of gravity of the electron beam 104, and then the electron beam 104 is set as the control target. This process is to control the electron beam 104 near the center. When the dark field detector 111 is controlled and the position is changed, the drawing detection surface 401 is drawn at a position corresponding to the position of the dark field detector 111.

  When Auto 805 is selected, the memory 123 enters Auto mode in which the optical axis is automatically adjusted using image data captured by the television camera 113. When Manual 806 is selected, a Manual mode is entered in which the operator adjusts the optical axis while viewing an image captured by the television camera 113 on the display 125. By selecting Adjust start 807, the optical axis adjustment is activated.

  In the Manual mode, a message 901 as shown in FIG. 9 is displayed on the display 125 and an operation instruction is given, so that even an operator who is not used to adjusting the optical axis can easily adjust the optical axis.

Hereinafter, automatic optical axis adjustment processing at the time of scanning transmission image photographing will be described.
FIG. 10 is a flowchart of processing in which the memory 123 automatically adjusts the optical axis of the electron beam 104 during scanning transmission image capturing. In a state where the fluorescent plate 112 is irradiated with the electron beam 104, image data captured by the television camera 113 is taken into the memory 123 and displayed on the display 125 (step 1001).

  Next, a dark field detection surface is added by adding the drawing detection surface 401 to the image data (step 1002). The barycentric coordinates of the electron beam portion of the display image are acquired from the image data (step 1003). If the control target selected on the operation screen at the time of optical axis adjustment in FIG. 8 is the electron beam 104, the process proceeds to step 1005, and if the control target is the dark field detector 111, the process proceeds to step 1006 (step 1004).

  In step 1005, the memory 123 sends a signal to the deflection coil controller 118, the electron beam 104 is controlled by the deflection coil 106, moved to the center of the drawing detection surface 401, and the operation ends. In step 1006, the memory 123 sends a signal to the dark field detector controller 119 to control the dark field detector 111 so that the center of the dark field detector 111 is the same as the barycentric coordinate of the electron beam 104. End the operation.

  Next, an optical axis adjustment process accompanying a change in the spot diameter of the electron beam 104 will be described. The electron beam 601 in FIG. 6 moves to the position of the electron beam 602 when the spot diameter is changed. If the barycentric coordinates of the electron beam 602 are not at the center of the fluorescent screen, the deflection coil control device 118 controls the electron beam 602 and moves it to the center of the fluorescent screen. This is shown in FIG. The electron beam 702 that deviates from the center of the fluorescent plate due to the spot change is controlled by the deflection coil controller 118 and moves to the position of the electron beam 701, that is, the center of the fluorescent plate. The electron beams 601, 602, 701, and 702 and the electron beam 104 are agreed.

  FIG. 11 is a flowchart of processing in which the memory 123 automatically performs optical axis adjustment when changing the spot of the electron beam 104. In a state where the fluorescent plate 112 is irradiated with the electron beam 104, an image photographed by the television camera 113 is taken into the memory 123 and displayed on the display 125 (step 1101).

  If the electron beam 104 is not at the center of the fluorescent screen, the electron beam 104 is moved to the center of the fluorescent screen at step 1102. The memory 123 sends a signal to the electromagnetic lens control device 117, and changes the spot diameter of the electron beam 104 by the irradiation system lens 105 and the imaging system lens 108 (step 1103).

  Since the position of the electron beam 104 is shifted by changing the spot diameter (FIG. 6), the barycentric coordinates of the electron beam 104 at the shifted position are acquired from the image data (step 1104). In step 1105, the memory 123 sends a signal to the deflection coil controller 118, and the electron beam 104 is controlled by the deflection coil 106 and moved to the center of the fluorescent screen (FIG. 7). At this time, the current value sent to the deflection coil controller is recorded in the memory 123 (step 1106).

  Then, it is determined whether or not all spot diameters have been performed (step 1107). If it is determined in step 1107 that all spot diameters have been processed, the operation is terminated. When the spot diameter of the electron beam 104 is changed after this processing is performed, the correction data value corresponding to each step is sent from the memory to the deflection coil control device, and the deviation of the electron beam 104 due to the spot diameter change is automatically performed. It is possible to correct and eliminate the deviation.

  A drawing detection surface 401 is added to the image data photographed by the television camera 113 and displayed on the display 125. While the fluorescent screen 112 is irradiated with the electron beam 104, the operator changes the spot diameter while viewing the display image, thereby efficiently irradiating the detection surface of the dark field detector 111 with the scattered electrons 201, and increasing the height. A contrast dark field image can be observed.

  DESCRIPTION OF SYMBOLS 101 ... Electron gun, 102 ... Mirror body, 103 ... Electron source, 104 ... Electron beam, 105 ... Irradiation system lens, 106 ... Deflection coil, 107 ... Scanning deflection coil 108 ... imaging system lens 109 ... sample stage 110 ... sample 111 ... dark field detector 112 ... fluorescent screen 113 ... TV camera 114 ... bright field Detector, 115 ... TV camera, 116 ... Electron source control device, 117 ... Electromagnetic lens control device, 118 ... Deflection coil control device, 119 ... Dark field detector control device, 120 ..Image processing device 121 ... Bright field detector control device 122 ... Image processing device 123 ... Memory 124 ... Processor 125 ... Display

Claims (9)

  In an electron microscope that irradiates a sample with an electron beam from an electron source via an irradiation system lens and a deflection coil, and detects the electron beam transmitted through the sample with a dark field detector and a bright field detector through an imaging lens An electron beam image is formed on the fluorescent screen, and an image capturing device for capturing the electron beam image of the fluorescent screen, and the barycentric coordinates of the electron beam are obtained from the image data of the image capturing device, and are aligned with the center of the dark field detector A control device that moves the electron beam or the dark field detector.   2. The electron microscope according to claim 1, wherein the control device is a deflection coil control device that controls the deflection coil, and moves the center of gravity of the electron beam so as to be aligned with the center of the dark field detector. .   2. The dark field detector control device according to claim 1, wherein the control device controls the position of the dark field detector, and moves the position of the dark field detector so as to match the center of gravity of the electron beam. An electron microscope.   The image processing apparatus according to claim 1, further comprising: an image processing device that creates a drawing image of the electron beam and the dark field detector using image data of the photographing device, and the control device detects the barycentric coordinates and dark field detection of the electron beam. An electron microscope characterized by controlling the center of gravity of the electron beam to match the center of the drawing image after controlling to match the center of the vessel.   2. The control device according to claim 1, wherein when the spot diameter of the electron beam is changed, the control device obtains a barycentric coordinate of the electron beam from image data of the imaging device, and matches the center of the dark field detector with the electron beam. An electron microscope characterized by moving the center of gravity of a line.   5. The deflection coil according to claim 4, wherein when the electron beam spot diameter is changed and the position of the electron beam is shifted, the control device controls the deflection coil so that the center of gravity of the electron beam becomes the center of the drawing image. An electron microscope characterized by that.   2. The image processing apparatus according to claim 1, further comprising: an image processing device that creates a drawing image of the electron beam and the dark field detector using image data of the photographing device; and a display device that displays the drawing image from the image processing device. An electron microscope characterized by that.   8. The electron microscope according to claim 7, wherein the display device displays a message indicating an operation method when performing optical axis adjustment to an operator.   9. The electron microscope according to claim 8, wherein the message includes a message instructing selection of a type of optical axis adjustment, selection of a control target at the time of optical axis adjustment, and selection of whether to perform automatically.

Images