JP2006302523A - Transmission electron microscope having scan image observation function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission electron microscope having a scan image observation function for always passing a main beam through the center of an annular dark-field scan image detector even when scanning is carried out by a tilted electron beam on a sample. <P>SOLUTION: An electron beam is incident on the sample 7 diagonally by means of a first deflection means 25, and secondary scanning is carried out while diagonally irradiating condition is maintained. Therefore, the main beam transmitted through the sample 7 passes a position displaced from the center of an annular detection face by the dark-field scan image detector 10 through a locus as shown by a dotted line. In one embodiment, a scan signal for returning the electron beam in compliance with a tilt angle of the electron beam radiated to the sample is generated between the sample 7 and the dark-field scan image detector 10 by means of a control part 12, and by two-step deflection by a second deflection means 28, the locus of the main beam is returned to surely pass through the center of the annular detection face for the dark-field scan image detector 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, an electron beam is focused on a sample by an irradiation lens system, and the irradiation position of the electron beam on the sample is two-dimensionally scanned to detect secondary electrons, reflected electrons, or transmitted electrons generated from the sample. The present invention relates to a transmission electron microscope and a scanning electron microscope having a scanning image observation function in which a detection signal is supplied to a monitor such as a cathode ray tube or a liquid crystal panel synchronized with scanning on a sample and a scanning image of the sample is displayed on a screen.

  Recent transmission electron microscopes have a scanning image observation function. At the time of observation of a transmission electron microscope image, an electron beam generated from an electron gun and accelerated is converted into a parallel beam by a plurality of condenser lenses, and irradiated to an observation region of the sample. The electrons that have passed through the sample project an enlarged image of the sample on the fluorescent screen by an imaging lens system composed of a plurality of imaging lenses arranged at the bottom of the sample, and recently, a sample image on the detection surface of a CCD camera. Is projected.

  Pixel signals from the CCD camera are supplied to a frame memory and subjected to image integration processing for noise reduction. Each pixel signal stored in the frame memory is read and supplied to a cathode ray tube or a liquid crystal display to display a transmission electron microscope image.

  In such a transmission electron microscope, a type in which a scanning image is observed is often used. When observing this scanned image, the sample is usually placed in a magnetic field formed by the objective lens. A thin electron beam is focused on the sample surface by an electron beam irradiation lens system including the front magnetic field of the condenser lens or objective lens sample. The electron beam irradiated on the sample is scanned two-dimensionally, and secondary electrons, reflected electrons, or transmitted electrons generated from the sample are detected at each point where the electron beam is irradiated. It is supplied to a display device synchronized with scanning.

  In the observation of the scanned image as described above, if the electron beam irradiated on the sample is accurately focused on the sample surface, and if the electron beam itself has aberration such as astigmatism, the resolution of the scanned image is adversely affected. Will be given. Therefore, as a procedure before the actual image observation, the focus state of the electron beam irradiated on the sample surface, the direction and magnitude of the electron beam aberration are detected in advance, and the detection results are determined accordingly. Thus, the actual optical observation is started by adjusting each optical system in front of the sample.

  Here, an example of a transmission electron microscope having the above-described scanning image observation function will be described with reference to FIG. In FIG. 1, electrons are generated from an emitter 1 which is a part of an electron gun, and the amount of current is controlled by a control electrode and an acceleration electrode (not shown) and applied to the acceleration electrode. It is accelerated according to an acceleration voltage (applied between the emitter 1 and the acceleration electrode) and enters the acceleration tube 2. The electron beam further accelerated by the accelerating tube 2 is focused toward the sample 7 by the irradiation system lens group 3. The sample 7 is arranged in a magnetic field formed by the objective lens. As a result, an objective front magnetic field 6 is formed in front of the sample 7, and an objective rear magnetic field 8 is formed behind the sample 7. Therefore, the electron beam is finely focused on the surface of the sample 7 by the irradiation system lens group (condenser lens group) 3 and the objective front magnetic field 6.

  The electron beam that has passed through the irradiation system lens group 3 is deflected in accordance with a scanning signal that flows through the first deflection coil 4 and the second deflection coil 5. The deflection direction of the first deflection coil 4 and the deflection direction of the second deflection coil 5 are opposite to each other. As a result, although the electron beam with respect to the sample 7 changes as the irradiation position is scanned, the electron beam always satisfies the normal incidence condition with respect to the sample 1 and has an arbitrary size range of 2 on the sample. Dimension scan.

  The electrons transmitted through the sample 7 are collected by the objective rear magnetic field 8 and the imaging lens group 9 formed behind the sample, and are detected by the donut-shaped dark field scanning image detector 10. Note that a secondary electron detector 13 is disposed on the side portion immediately above the sample 7, and secondary electrons generated by irradiation of the sample 7 with the electron beam are pulled in the direction of the detector 13 and detected. . Detection signals from the dark field scanning image detector 10 and the secondary electron detector 13 are supplied to the control unit 12. The control unit 12 has a wide range of functions. For example, the control unit 12 includes a scan generator and a deflection coil drive amplifier. A scan signal is supplied from the control unit 12 to the first deflection coil 4 and the second deflection coil 5. The

  Further, the control unit 12 supplies a detection signal to the built-in frame memory, and the detection signals of the dark field scanning image detector 10 and the secondary electron detector 13 have addresses corresponding to the scanning positions of the separate frame memories, respectively. Stored. In this frame memory, the signals detected by the dark-field scanning image detector 10 and the secondary electron detector 13 are integrated for each pixel to improve the signal-to-noise ratio of the signal.

  In the configuration of FIG. 1, secondary electrons from the sample 7 are detected by an example in which electrons transmitted through the sample are detected and a scanning transmission image is observed, and a secondary electron detector 10 disposed on the side of the sample. Although an example of detecting and acquiring a scanning secondary electron image has been described, observation of a scanning image with a transmission electron microscope is generated from a sample by arranging a secondary electron detector or a backscattered electron detector above the objective lens. The secondary electrons may be constrained by the objective front magnetic field 6 and taken out to the upper part of the objective lens and may be detected by the detector on the objective lens.

  Here, an operation for observing a transmission electron microscope image and an operation for obtaining a scanning image in a transmission electron microscope having a scanning image observation function as shown in FIG. 1 will be described. First, when a transmission electron microscope image is observed, the electron beam accelerated by the accelerating tube 2 is irradiated as a parallel beam to a range covering the observation region on the sample 7 by the irradiation system lens group 3. The electrons transmitted through the sample are imaged on a fluorescent plate (not shown) by the imaging system lens group 9. In general, the image projected on the fluorescent screen is observed, and when the image of the target field of view is confirmed, the fluorescent screen is removed from the optical axis, and a photograph of a desired transmission electron microscope image is obtained by a camera device below the fluorescent screen. Take a picture. Recently, a CCD camera is arranged at the position of the fluorescent screen, the image projected on the surface of this camera is captured for each pixel, each pixel signal is digitally processed, stored in the frame memory, and stored in the frame memory. A stored image signal is taken out and supplied to a display, and a transmission electron microscope image is observed on the display.

  Next, a case where a scanning electron microscope image is acquired will be described. In this case, the electron beam is finely focused on the sample by the irradiation system lens group 3 and the objective front magnetic field 3 in front of the sample. Further, the electron beam is deflected by the first deflection coil 4 and the second deflection coil 5. The first deflection coil 4 and the second deflection coil 5 are supplied with a two-dimensional scanning signal corresponding to the magnification from the control unit 12, and as a result, a desired two-dimensional region on the sample is scanned with an electron beam. Output signals from both detectors 10 and 13 of the transmitted electrons due to the electron beam irradiation on the sample and the secondary electrons generated from the sample 7 are respectively supplied to the control unit 12 and scanned in synchronization with the scanning of the electron beam. The image is supplied to the image monitor 11, and a secondary scanning electron image or a dark field scanning image is displayed on the monitor.

  As described above, transmission electron microscope images and scanning electron microscope images can be observed. However, in order to observe images with high resolution, the electron beam applied to the sample is in focus and aberrations are corrected. It is important that For this reason, in Patent Document 1, the field of view distant from the optical axis is irradiated in parallel by a two-stage deflection system arranged before and after the sample, and focusing, astigmatism correction, etc. are performed, and the field of view is taken. Is returned to the optical axis. The purpose of this method is to prevent contamination and damage of the sample surface caused by irradiating an electron beam continuously on the imaging field in the imaging region.

Patent Document 2 discloses a method of irradiating a sample with a finer electron probe by correcting the aberration of a focused electron beam by using a spherical aberration correction device in an irradiation system of a transmission electron microscope. One method for correcting aberrations using a spherical aberration corrector is to irradiate the sample with an electron probe tilted with respect to the optical axis of the electron beam and to obtain a cross-section of the electron probe obtained using the obtained dark-field scanning image There is a method of performing correction based on data such as a shape.
Japanese Patent Publication No.59-19408 JP 2003-92078 A

  The scanning image observation function in the conventional transmission electron microscope shown in FIG. 1 does not scan the electron beam with a large tilt angle, so that the main beam is the dark field image detector at the dark field image detector position. It was not detected in a state far from the center of. However, as described above, in order to correct the aberration of the electron beam by providing the aberration corrector 14 below the irradiation system lens group in the configuration of FIG. 1, it is necessary to obtain the current aberration value. For this reason, when scanning is performed with a probe having a large inclination, transmitted electrons are detected in a state of being largely deviated from the center of the dark field image detector 10 as described above. In this state, since correct signal detection is not performed, correct information for performing aberration correction cannot be obtained.

  FIG. 2 is a ray diagram of an electron beam when scanning is performed with a greatly inclined probe, and FIG. 3 is a plan view of the dark-field scanning image detector 10 as viewed from the light source direction. The position of the main beam is shown. In the figure, reference numeral 21 denotes a detection surface of the dark field scanning image detector 10. As indicated by 22, if the main beam perpendicular to the sample passes through the center of the detection surface 21, the probe shape can be obtained accurately by calculation. However, in the state indicated by 23 in which the main beam is inclined and does not pass through the center of the annular detection surface, each detection surface detects a biased scattering intensity, and the probe obtained by calculation based on this signal. Since the shape is measured, the aberration correction information is inaccurate.

  The present invention has been made in view of the above problems, and even when the electron beam is tilted and scanned on the sample, the main beam can always pass through the center of the annular dark field scanning image detector. A transmission electron microscope having a scanning image observation function is realized.

  A transmission electron microscope having a scanning image observation function based on the invention of claim 1 irradiates an electron beam from an electron gun as a parallel beam to a predetermined region of a sample by an irradiation lens system, and forms an image of electrons transmitted through the sample A transmission electron microscope mode that forms an image by a lens system to form a transmission electron microscope image, and an irradiation lens system finely focuses an electron beam on a sample, scans the electron beam in a two-dimensional region on the sample, A scanning electron microscope mode for detecting a signal generated from the sample by irradiation, a first deflecting means for scanning the electron beam irradiation side at a predetermined angle on the sample on the electron beam irradiation side; A dark-field scanning image detector having an annular detection surface for detecting electrons transmitted through the sample, and the sample and the dark-field scanning image detector. Electronic Is characterized in that a second deflection means for returning swing the optical axis in accordance with the inclination angle of the over arm.

  A transmission electron microscope having a scanning image observation function based on the invention of claim 2 is the transmission electron microscope according to claim 1, wherein the dark field scanning image detector having an annular detection surface is arranged on the diffraction image surface on the imaging side. It is characterized by being arranged so that the center of the annular detection surface coincides with the optical axis.

  A transmission electron microscope having a scanning image observation function based on the invention of claim 3 is the invention according to claims 1 to 2, wherein each of the first deflection means and the second deflection means is a two-stage deflection. Each of the two-stage deflections has two sets of deflection coils in the X and Y directions, respectively, one of the two sets of deflection coils each has a reduced number of turns for high magnification, and the other is It is characterized in that the number of turns of the coil is increased for low magnification.

  In the transmission electron microscope having the scanning image observation function based on the invention of claim 1, the irradiation lens system irradiates the electron beam from the electron gun as a parallel beam to a predetermined region of the sample, and forms an image of the electron transmitted through the sample A transmission electron microscope mode that forms an image by a lens system to form a transmission electron microscope image, and an irradiation lens system finely focuses an electron beam on a sample, scans the electron beam in a two-dimensional region on the sample, A scanning electron microscope mode for detecting a signal generated from the sample by irradiation, a first deflecting means for scanning the electron beam irradiation side at a predetermined angle on the sample on the electron beam irradiation side; A dark-field scanning image detector having an annular detection surface for detecting electrons transmitted through the sample, and the sample and the dark-field scanning image detector. Electric It is characterized in that a second deflection means for returning swing the optical axis in accordance with the inclination angle of the beam. As a result, the main beam can pass through the center of the annular dark field scanning image detector, and a signal due to the aberration of the accurate electron beam is obtained from the dark field scanning image detection signal. The aberration of the beam can be corrected with high accuracy.

  The transmission electron microscope having a scanning image observation function based on the invention of claim 2 is the same as that of the invention of claim 1, and the dark field scanning image detector having an annular detection surface is the connection of the invention of claim 1. It is characterized in that the center of the annular detection surface coincides with the optical axis on the diffraction image surface on the image side. As in the first aspect of the invention, accurate information corresponding to the aberration of the electron beam can be obtained, and the aberration correction of the electron beam can be performed accurately.

  A transmission electron microscope having a scanning image observation function based on the invention of claim 3 is the invention according to claims 1 to 2, wherein each of the first deflection means and the second deflection means is a two-stage deflection. Each of the two-stage deflections has two sets of deflection coils in the X and Y directions, respectively, one of the two sets of deflection coils each has a reduced number of turns for high magnification, and the other is It is characterized in that the number of turns of the coil is increased for low magnification. As a result, since a coil having a large number of turns is used for a scanning signal having a large amplitude when the magnification is low, the response to the signal having a large amplitude is good and the deflection electric field based on the scanning signal is not distorted. On the other hand, during high-magnification observation, a coil with a small number of turns is used for a scanning signal with a small amplitude, so that the deflection coil follows the high-speed repeated scanning signal, and the deflection electric field is delayed with respect to the scanning signal change. Nothing happens.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 4 shows a transmission electron microscope having a scanning image observation function based on the present invention. The same or similar components as those in the conventional apparatus of FIG. In FIG. 4, a first deflecting means 25 is provided on the side of the sample irradiated with the electron beam. The first deflection means 25 is composed of first and second deflection coils 26 and 27. The first and second deflection coils 26 and 27 have deflection coils in the X direction and the Y direction, respectively, and have a two-stage deflection configuration.

  The first and second deflection coils 26 and 27 have deflection coils in the X direction and the Y direction, respectively. Further, each may have two sets of deflection coils in the X direction and two sets of deflection coils in the Y direction. In that case, one of the two sets of coils in the X direction of the first deflection coil 26 is a coil with a large number of turns, and the other coil in the X direction is a coil with a small number of turns. One of the two sets of coils in the Y direction of the first deflection coil 26 is a coil with a large number of turns, and the other coil in the Y direction is a coil with a small number of turns. In both the X and Y directions, a coil with a large number of turns is used for low magnification observation, and a coil with a small number of turns is used for high magnification observation.

  Similarly, one of the two sets of coils in the X direction of the second deflection coil 27 is a coil with a large number of turns, and the other coil in the X direction is a coil with a small number of turns. One of the two sets of coils in the Y direction of the second deflection coil 27 is a coil with a large number of turns, and the other coil in the Y direction is a coil with a small number of turns. In both the X and Y directions, a coil with a large number of turns is used for low magnification observation, and a coil with a small number of turns is used for high magnification observation.

  As a result, since a coil having a large number of turns is used for a scanning signal having a large amplitude when the magnification is low, the response to the signal having a large amplitude is good and the deflection electric field based on the scanning signal is not distorted. On the other hand, during high-magnification observation, a coil with a small number of turns is used for a scanning signal with a small amplitude, so that the deflection coil follows the high-speed repeated scanning signal, and the deflection electric field is delayed with respect to the scanning signal change. Nothing happens.

  As shown in FIG. 4, the first deflecting means 25 causes the electron beam to enter the sample obliquely, and two-dimensional scanning is performed while maintaining the oblique irradiation state. As shown in this figure, normally, when an electron beam is incident obliquely on the sample 7, the main beam transmitted through the sample passes through a position off the center of the annular detection surface of the dark field scanning image detector 10. To do.

  In the present embodiment, the second deflecting means 28 is provided between the imaging system lens group 9 and the downstream dark field scanning image detector. The second deflection means 28 is composed of first and second deflection coils 29 and 30. The first and second deflection coils 29 and 30 have deflection coils in the X direction and the Y direction, respectively, and have a two-stage deflection configuration.

  The first and second deflection coils 29 and 30 have deflection coils in the X direction and the Y direction, respectively. Further, each of them may have two sets of deflection coils in the X direction and two sets of deflection coils in the Y direction. In that case, one of the two sets of coils in the X direction of the first deflection coil 29 is a coil with a large number of turns, and the other coil in the X direction is a coil with a small number of turns. One of the two sets of coils in the Y direction of the first deflection coil 29 is a coil with a large number of turns, and the other coil in the Y direction is a coil with a small number of turns. In both the X and Y directions, a coil with a large number of turns is used for low magnification observation, and a coil with a small number of turns is used for high magnification observation.

  Similarly, one of the two sets of coils in the X direction of the second deflection coil 30 is a coil with a large number of turns, and the other coil in the X direction is a coil with a small number of turns. One of the two sets of coils in the Y direction of the second deflection coil 30 is a coil with a large number of turns, and the other coil in the Y direction is a coil with a small number of turns. In both the X and Y directions, a coil with a large number of turns is used for low magnification observation, and a coil with a small number of turns is used for high magnification observation.

  As a result, since a coil having a large number of turns is used for a scanning signal having a large amplitude when the magnification is low, the response to the signal having a large amplitude is good and the deflection electric field based on the scanning signal is not distorted. On the other hand, during high-magnification observation, a coil with a small number of turns is used for a scanning signal with a small amplitude, so that the deflection coil follows the high-speed repeated scanning signal, and the deflection electric field is delayed with respect to the scanning signal change. Nothing happens.

  As described above, in the embodiment shown in FIG. 4, the first deflecting unit 25 causes the electron beam to enter the sample 7 obliquely, and two-dimensional scanning is performed while maintaining the oblique irradiation state. I made it. Therefore, the main beam transmitted through the sample 7 passes through a position off the center of the annular detection surface of the dark field scanning image detector 10 as indicated by the dotted line. In the present embodiment, the control unit 12 creates a scanning signal for returning the electron beam according to the tilt angle of the electron beam irradiated on the sample between the sample 7 and the dark field scanning image detector 10. However, due to the two-stage deflection by the second deflection means 28, the trajectory of the main beam is turned back and always passes through the center of the annular detection surface of the dark field scanning image detector 10.

  In this way, since the main beam always passes through the center of the annular detection surface, the current aberration value can be obtained based on the detection signal of the dark field scanning image detector 10, and this calculation is performed. If the aberration corrector 14 shown in FIG. 1 is controlled based on the obtained value, the electron beam aberration can be accurately corrected.

It is a figure which shows an example of the transmission electron microscope with the conventional scanning image observation function, and is a figure which shows the locus | trajectory of the main beam of an electron beam at the time of making an electron beam perpendicularly incident on a sample. It is a figure which shows the locus | trajectory of the main beam of an electron beam when inclining and scanning the electron beam irradiated to a sample. It is a figure which shows the relationship between the cyclic | annular detection surface of a dark field scanning image detector, and the passage position of a main beam. It is a figure which shows the transmission electron microscope which has the scanning image observation function which is one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Emitter 2 Accelerating tube 3 Irradiation system lens group 4, 5, 26, 27, 29, 30 Deflection coil 6 Objective front magnetic field 7 Sample 8 Objective back magnetic field 9 Imaging system lens group 10 Dark field scanning image detector 11 Monitor 12 Control Part 13 Secondary electron detector 25 First deflecting means 28 Second deflecting means

Claims (3)

  A transmission electron microscope mode that forms a transmission electron microscope image by irradiating an electron beam from an electron gun as a parallel beam to a predetermined area of the sample with the irradiation lens system and forming an image with the imaging lens system. And a scanning electron microscope mode in which the electron beam is finely focused on the sample by the irradiation lens system, the electron beam is scanned in a two-dimensional region on the sample, and a signal generated from the sample by the irradiation of the electron beam is detected. A dark field having a first deflecting means for scanning the electron beam on the beam irradiation side at a predetermined angle, and an annular detection surface for detecting electrons transmitted through the sample on the imaging side A second deflector disposed between the scanning image detector and the sample and the dark field scanning image detector for returning the main beam to the optical axis on the imaging side according to the tilt angle of the electron beam on the irradiation side. Means and equipment Transmission electron microscope having a scanning image observation function was.   2. The scanning image observation according to claim 1, wherein the dark-field scanning image detector having an annular detection surface is arranged on the diffraction image surface on the imaging side so that the center of the annular detection surface coincides with the optical axis. A transmission electron microscope with functions. Each of the first deflection means and the second deflection means is a two-stage deflection, and each of the two-stage deflections has two sets of deflection coils in the X and Y directions, respectively. 3. A transmission electron having a scanning image observation function according to claim 1, wherein one of the deflection coils has a reduced number of coil turns for high magnification and the other has a larger number of coil turns for low magnification. microscope.