JP2007242514A - Transmission electron microscope, and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission electron microscope which electrically performs a tilt adjustment impossible for a person or a sample tilt mechanism to control, and achieves a precise tilt adjustment. <P>SOLUTION: An electron beam E generated and accelerated by an electron gun 1 connected to a high voltage power source is focused by a focusing lens 3 formed of condenser lenses, tilted by two stages of deflection coils of a deflection part 4, and applied to a sample 5a on a sample setting table in a sample room 5. The electron beam having passed through the sample 5a put and held on the sample setting table enters an objective lens 6. An aberration corrector 7 corrects aberration caused in the objective lens 6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a transmission electron microscope that irradiates a sample with an electron beam and obtains an image of the sample by transmission electrons transmitted through the sample, and a control method thereof.

  A transmission microscope (hereinafter also referred to as a TEM) irradiates a sample with an electron beam, obtains a high-resolution transmission electron image of the sample by transmission electrons transmitted through the sample, and observes the sample. Elemental analysis is also performed by obtaining an electron diffraction image, a scanning transmission image, or an energy loss image capable of examining the arrangement of molecules and atoms. In recent years, the transmission electron microscope has been used to not only reflect the image of transmitted electrons, but also the reflected surface reflected from the sample, secondary electrons generated from the sample, Auger electrons, X-rays, etc. Various analyzes such as structural observation and elemental analysis of samples are also performed.

  In order to observe a crystalline material with high resolution by a transmission electron microscope, a specific orientation of the sample must be accurately aligned with the incident direction of the electron beam. For example, it is required to align the direction of incidence of the electron beam with an accuracy of 0.1 degrees or less. Conventionally, this is performed by tilting the sample.

  FIG. 5 is a diagram showing a method of aligning crystal orientation with a conventional electron beam. First, a rough orientation is adjusted using a diffraction pattern or Kikuchi line. After that, place a limited field stop at the target location, observe the diffraction pattern, and precisely align the crystal orientation. Specifically, a sample tilting mechanism (goniometer) that mechanically tilts the sample independently in each of the biaxial directions of x and y is used.

  Patent Document 1 below discloses a technique of an automatic tilting apparatus using a sample tilting mechanism. If the sample is not on the tilt axis, the sample is displaced when the sample is tilted around the tilt axis. For this reason, the target sample is deviated from the observation field of view, and much time is required for alignment. In particular, it is very difficult to align the orientation of microcrystalline particles of about several tens of nanometers. Therefore, it is necessary to correct the position of the sample as described above, but conventionally, a transmission microscope has not been provided with means for positively correcting the positional deviation.

  Therefore, in Patent Document 1 below, the sample tilt angle necessary for crystal orientation alignment and the sample positional deviation caused by the sample tilt are mathematically calculated, and the sample is automatically tilted based on the calculated sample tilt angle. In addition, a configuration has been disclosed in which the sample is automatically moved so as to eliminate the calculated sample displacement.

Specifically, the electron diffraction pattern of the sample is recognized by the image recognition means through the TV for imaging, and the necessary sample inclination from the electron diffraction pattern to the crystal orientation and the target orientation to be observed therefrom is analyzed by the analysis means. The azimuth and tilt angle are calculated. The sample tilting mechanism is controlled by the position correction means, the sample image is tilted so fine that it does not deviate from the screen of the image display means, and the resulting positional deviation of the sample is calculated by the analysis means. The position correction unit controls the sample moving mechanism and the deflection coil so as to eliminate the positional deviation, and performs position correction control. Such sample tilt and position correction control is repeated until the calculated tilt angle is reached.
Japanese Patent Laid-Open No. 11-288679

  By the way, in the conventional technique as described above, that is, the technique of tilting the direction of the sample with respect to the direction of the electron beam, the position correction may be performed to realize the target tilt depending on the accuracy of the sample tilting mechanism (goniometer). There is a risk that the calculation of control takes time.

  In addition, since the sample is usually curved locally, even if the orientation is aligned with the limited field diffraction pattern, the orientation of the target location may be shifted.

  FIG. 6 is a diagram showing that the observation direction is different while the orientation is due to the curvature. In particular, the distortion is large at a place where a defect is introduced.

  Whether or not the target inclination has been achieved is determined by the intensity of various pots in the diffraction pattern, but there is a limit in the accuracy of human eyes. From the image taken, it can be seen that the tilt was slightly off. It is difficult to determine which one should change the inclination from the observed image. It also takes time and introduces radiation damage. Furthermore, coma aberration is introduced by making an electron beam enter the sample obliquely.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a transmission electron microscope that electrically performs a tilting mechanism that cannot be controlled by a sample tilting mechanism or a human and realizes precise tilt alignment and a control method thereof. To do.

  In order to solve the above-described problems, a transmission electron microscope according to the present invention deflects an electron beam generated by an electron gun in the transmission electron microscope and tilts the electron beam on a sample.

  The transmission electron microscope according to the present invention includes an electron gun that generates an electron beam, an electron beam generated by the electron gun, and a deflected electron beam to solve the problem. A deflection unit, a sample holding unit holding a sample irradiated with the electron beam deflected by the deflection unit, and an objective lens for imaging an electron beam transmitted through the sample held by the sample holding unit; An aberration correction unit that corrects aberrations generated in the objective lens on an electron beam, a fluorescent plate on which a sample image composed of an electron beam corrected by the aberration correction unit is projected, and a sample image projected on the fluorescent plate An imaging unit that performs imaging and a control unit that controls a deflection angle in the deflection unit in accordance with an input from an operator.

  This transmission electron microscope preferably uses a crystalline material as a sample. In addition, the control unit calculates the amount of variation necessary for tilting based on the tilt amount input by the operator and the number of shots, controls the deflection unit to perform automatic tilting, and controls the shooting unit. It is preferable to perform shooting. The aberration correction unit preferably uses two multipole elements to correct coma and spherical aberration.

  The method for controlling an electron microscope according to the present invention includes a deflection unit that deflects an electron beam applied to a sample generated by an electron gun, and an image of the sample irradiated with the electron beam deflected by the deflection unit. An electron microscope control method including an imaging unit and a control unit for controlling the deflection unit and the imaging unit, wherein the control unit inputs an amount of tilting an electron beam incident on the sample, and the sample A step of inputting the number of images to be photographed, a step of calculating the amount of mutation required for the sample, a step of automatically tilting an electron beam by the deflecting unit, and a step of photographing an image of the sample by the photographing unit; Is used to control the electron microscope.

  The transmission electron microscope and the control method thereof according to the present invention electrically perform tilting that cannot be controlled by a sample tilting mechanism or a human to achieve precise tilt alignment.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a transmission electron microscope 1 according to an embodiment. The transmission electron microscope 1 is used for performing high-resolution observation of the crystalline material 5a using a crystalline material as a sample 5a. In FIG. 1, a transmission electron microscope 1 includes an electron gun 2 that emits an electron beam, a converging lens 3 that converges the electron beam emitted from the electron gun 2 and irradiates a sample 5a described later, and this convergence. The deflecting unit 4 for tilting the electron beam converged by the lens 3 on the sample 5a, the sample chamber 5 in which the sample mounting table for mounting and supporting the sample 5a is disposed, and the sample mounting table is supported by the sample mounting table. An objective lens 6 on which an electron beam transmitted through the sample 5a is incident, an aberration corrector 7 for correcting an aberration generated by the objective lens 6, and an electron beam whose aberration in the objective lens 6 is corrected by the aberration corrector 7 are incident. An intermediate lens 8, a projection lens 9 that projects an electron beam onto the fluorescent plate 10 as a sample image, a fluorescent plate 10 onto which the sample image is projected by the projection lens 9, and a CCD that captures an image of the sample 5a projected onto the fluorescent plate 10 Collect camera Consisting of the camera chamber 11 for. The objective lens 6, the intermediate lens 8, and the projection lens 9 constitute an imaging lens system for forming a sample image on the fluorescent plate 10.

  FIG. 2 is a diagram showing a specific example of each lens. The convergent lens 3 is composed of a condenser lens. The deflection unit 4 includes two stages of deflection coils 4a and 4b, and can slightly tilt the electron beam E. 1 and 2 show the converging lens 3 and the deflecting unit 4 separately, the deflecting unit 4 may be provided inside the converging lens 4 so that the electron beam E is inclined.

  The two-stage deflection coils 4a and 4b of the deflection unit 4 tilt the electron beam E while synchronizing, and irradiate the sample 5a radially. Although the deflection angle of the electron beam E is changed by the deflection unit 4, it is not always necessary to correct the aberration by the aberration corrector 7 every time the deflection angle is changed, and the aberration correction may be constant. Of course, the aberration corrector 7 may correct the aberration according to the deflected angle. The objective lens 6, the intermediate lens 8, and the projection lens 9 of the imaging lens system are magnetic lenses.

  This transmission electron microscope 1 is different from the conventional transmission electron microscope in that an aberration corrector 7 is disposed between the objective lens 6 and the intermediate lens 8 constituting the imaging lens system. It is characteristic.

  The electron gun 2, the converging lens 3, the deflection unit 4, the sample chamber 5, the objective lens 6, the aberration corrector 7, the intermediate lens 8, the projection lens 9, and the CCD camera 11a are an electron source control unit 12, a converging lens control unit 13, Controlled by the main controller 21 via the deflection controller 14, the placement controller 15, the objective lens controller 16, the aberration correction controller 17, the intermediate lens controller 18, the projection lens controller 19, and the imaging controller 20. The

  The main control device 21 is connected to an input unit 22, and the electron gun 2, the converging lens 3, the deflecting unit 4, the sample chamber 5, the objective lens 6, and aberration correction via each control unit based on the operation instructions of the operator. The driving of the device 7, the intermediate lens 8, the projection lens 9, and the CCD camera 11a is controlled. The main control device 21 is a workstation, a personal computer, or the like. Of course, the display unit 23 may be provided and a sample image taken by the camera 11a may be displayed.

  The electron beam E generated and accelerated from the electron gun 1 connected to the high voltage power source is converged by the converging lens 3 made of a condenser lens, and then tilted by the two-stage deflection coils 4a and 4b of the deflecting unit 4 to be sampled. The sample 5 a on the sample mounting table in the chamber 5 is irradiated.

  The position of the sample 5a on the sample mounting table can be moved by movement control in the xy and z directions of the sample mounting table through the mounting control unit 15 by the main controller 21.

  The electron beam E transmitted through the sample 5 a forms an image on the fluorescent plate 10 through the objective lens 6, the intermediate lens 8, and the projection lens 9 constituting the imaging lens group, and this sample image is stored in the camera chamber 11. Images are taken by a CCD camera 11a or the like.

  At this time, the aberration corrector 7, which is composed of the objective lens 6 and the intermediate lens 8 and is disposed between the imaging system, corrects aberrations such as coma and spherical aberration generated by the objective lens 6 that is a magnetic lens. Since this aberration corrector 7 can correct aberrations such as coma and spherical aberration, the electron beam E can be inclined in the deflecting unit 4.

  In this way, the transmission electron microscope 1 tilts the electron beam by the deflection coils 4 a and 4 b subsequent to the converging lens 3 in order to tilt the electron beam of the irradiation system, and mount control by the main controller 21. The position movement of the sample mounting table in the xy direction and the z direction through the unit 15 is controlled. Then, the electron beam of the irradiation system can be tilted on the sample by the two-stage deflection coils 4a and 4b and the main controller 21 attached to the electron microscope. Therefore, even if the irradiation electron beam is tilted, the influence of the resolution reduction is reduced.

  Conventionally, in a transmission electron microscope, tilting the optical axis of an electron beam has not been performed because it causes a reduction in resolution. The aberration corrector can correct aberrations such as coma and spherical aberration, so that the resolution does not drop even if the optical axis of the electron beam is tilted.

  FIG. 3 is a configuration diagram of a specific example of the aberration corrector 7. After passing through the objective lens 6, the electron beam E transmitted through the sample 5 a passes through the first axisymmetric lens 31 and the second axisymmetric lens 32, and then passes through the first multipole 33 such as a hexapole. Further, the electron beam E passes through the third axisymmetric lens 34 and the fourth axisymmetric lens 35 and then passes through a second multipole 36 such as a hexapole. After that, the electron beam E is converged by the adapter lens 37 and is incident on the intermediate lens 8 after the field of view is limited by the field limiting aperture SA.

  The first axially symmetric lens 31 is arranged with a focal length interval of the axially symmetric lens 31 from the coma aberration-free surface 39 of the objective lens 6. The second axisymmetric lens 32 has a distance obtained by combining the focal lengths of the two axial target lenses 31 and 32, and the second axial target lens 32 is formed from the coma aberration-free surface 40 of the first multipole element 33. The distance is equal to the focal length of the second axisymmetric lens.

  With such an optical system shown in FIG. 3, spherical aberration correction can be performed. If the spherical aberration is corrected, the coma aberration originating from the spherical aberration is also corrected. For this reason, there is little reduction in resolution due to the introduction of aberration accompanying the electron beam tilt.

  The aberration correction setting by the aberration corrector 7 is previously adjusted using, for example, an amorphous material so that aberration can be taken.

  Under the condition that the spherical aberration is corrected by the aberration corrector 7, the resolution of the image is hardly lowered when the electron beam is tilted at several tens of mRad. Utilizing this feature, the present invention adjusts the crystal orientation to the electron beam direction to some extent by a human hand, and then automatically changes the tilt according to the following procedure and shoots on a film or CCD camera.

  FIG. 4 is a flowchart showing a processing procedure in the transmission electron microscope 1. First, an amount of tilting the electron beam is input by the input unit 22 connected to the main controller 21 (step S1). Next, the number of images to be shot is input from the input unit 22. This is to input the number of images to be photographed on the circumference when the beam is tilted (tilted on a cone) from the current observation direction at a predetermined angle (step S2).

  Next, the amount of mutation necessary for the inclination is calculated (step S3). Here, the amount of mutation refers to a variation in current for tilting the electron beam as much as necessary. Then, automatic tilting is started using the deflection coils 4a and 4b following the condenser lens 3 (step S4). Then, a photograph is taken (step S5). Thereafter, the process proceeds to the next inclination, and in order to take a picture, steps S3, 4 and 5 are repeated, and the picture is taken as many times as set in step S2. Then, an optimum inclination angle is determined based on these photography.

  According to the transmission electron microscope 1 described above, photography can be performed while the electron beam is inclined stepwise. At that time, the aberration corrector 7 disposed behind the sample 5a removes image distortion caused by the electron beam inclination. This method is useful for high-resolution observation of crystalline materials, particularly for observation of defects such as crystal grain boundaries and surface defects, because the observation image is sensitive to electron beam irradiation. Regardless of the skill of the observer, a high resolution image capable of structural analysis can be taken in a short time.

  According to the present invention, since the electron beam can be tilted automatically, a tilt that cannot be controlled by a goniometer or a human can be electrically performed to perform precise tilt alignment. In addition, in a sample that is curved, since the inclination varies depending on the location, an inclination that cannot be performed by humans can be electrically performed.

It is a block diagram of a transmission electron microscope. It is a figure which shows the specific example of each lens. It is a block diagram of the specific example of an aberration corrector. It is a flowchart which shows the process sequence in a transmission electron microscope. It is a figure which shows how to match the crystal orientation with the conventional electron beam. It is a figure which shows that an observation direction differs while having an azimuth | direction by curvature

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transmission electron microscope 2 ... Electron gun 3 ... Converging lens 4 ... Deflection part 5 ... Sample chamber 6 ... Objective lens 7 ... Aberration corrector 8 ... Middle Lens 9 ... Projection lens 10 ... Fluorescent screen 11 ... Camera room 21 ... Main controller

Claims (6)

In a transmission electron microscope,
A transmission electron microscope characterized by deflecting an electron beam generated by an electron gun and tilting the electron beam on a sample. An electron gun that generates an electron beam;
A deflecting unit that converges the electron beam generated by the electron gun and deflects the converged electron beam;
A sample holding unit for holding a sample irradiated with the electron beam deflected by the deflection unit;
An objective lens for imaging an electron beam transmitted through the sample held by the sample holding unit;
An aberration correction unit that corrects the aberration generated in the objective lens on an electron beam;
A fluorescent screen on which a sample image made of an electron beam whose aberration is corrected by the aberration correction unit is projected;
A photographing unit for photographing the sample image projected on the fluorescent plate;
A transmission electron microscope comprising: a control unit that controls a deflection angle in the deflection unit according to an input of an operator.   The transmission electron microscope according to claim 1, wherein a crystal material is used as the sample.   The control unit calculates the amount of variation necessary for tilting based on the tilt amount input by the operator and the number of shots, controls the deflecting unit to perform automatic tilting, and controls the shooting unit for shooting. The transmission electron microscope according to claim 2, wherein:   The transmission electron microscope according to claim 2, wherein the aberration correction unit corrects coma aberration and spherical aberration by using two multipole elements. A deflection unit that deflects an electron beam applied to a sample generated by an electron gun; an imaging unit that captures an image of the sample irradiated with the electron beam deflected by the deflection unit; and the deflection unit and the imaging unit. And a control unit for controlling the electron microscope, wherein the control unit includes:
Inputting an amount of tilting the electron beam incident on the sample;
Inputting the number of images of the sample;
Calculating the amount of mutation required for the sample;
Automatically tilting the electron beam at the deflection unit;
And a step of taking an image of the sample by the photographing unit.

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