JP4376754B2 - Charged particle beam apparatus and sample image observation method - Google Patents

Description

  The present invention relates to a charged particle beam apparatus such as an electron microscope apparatus and a sample image observation method, and more particularly to a stereoscopic image acquisition method and a stereoscopic image display method.

A microscope using a charged particle beam, such as an electron microscope, has a deep depth of focus and is less suitable for observing an object with irregularities on the surface because the image blur before and after the focus is small. However, the image display is a planar two-dimensional display. As long as the state of the surface is observed, a two-dimensional display is sufficient. For example, in the field of semiconductor devices, nanomaterials, micromachines, etc. Since it is necessary to observe stereoscopically in a state, an apparatus capable of easily displaying stereoscopic images is desired. As a method of stereoscopically observing an image, a method of stereoscopically observing a sample by inclining the sample left and right by a parallax angle and detecting a signal from the sample at each angle to form a stereo pair image has been conventionally known. Yes. Instead of tilting the sample, there is also a method in which a stereo pair image is constructed from each image acquired using two electron guns that are tilted by a parallax angle and stereoscopically observed (see Patent Document 1). In addition, instead of inclining the sample by the parallax angle, there is a method in which two reflected electron detectors having directivity for electron detection are installed for the right eye and for the left eye, and a stereo pair image is obtained from each image ( Patent Document 2).
JP-A-5-41195 Japanese Patent Application Laid-Open No. 11-144661

  As described above, various methods for obtaining a stereo pair image have been devised, and a stereo pair image is usually created by using the parallax between two images due to sample inclination. For this purpose, the sample must be adjusted so that the tilt direction of the sample is left and right when viewed on the screen, and the operation is usually performed by rotating the electromagnetic field of view. Changing the viewing conditions causes image rotation, which is very time consuming. In addition, it takes a lot of skill to synthesize the images acquired for the right eye and the left eye, and the image capture must be repeated several times until the optimal image is obtained. There was also a point.

  The present invention relates to acquisition of a stereo pair image using a charged particle beam apparatus, and an object thereof is to improve operability.

  In the charged particle beam apparatus according to the present invention, an operation button for switching to a stereo image acquisition mode is provided on a monitor for operation and image display, and when this button is pressed, the left-right direction of the image matches the tilt direction of the sample. As described above, the rotation angle of the image is automatically set by the electromagnetic visual field rotation means. However, since charged particle beam devices usually cause image rotation due to the influence of a magnetic field, even if alignment is performed in the scanning direction at the scanning coil position of the charged particle beam and the tilt direction of the sample, Inclination directions do not match. Since the rotation amount of the image rotation is determined by lens conditions such as the distance between the objective lens and the sample, by calculating the image rotation amount due to the magnetic field from the lens conditions, the left / right direction of the image and the sample tilt direction are matched. Automatically corrects the angle deviation by rotating the visual field. In that state, one side of the image is captured and displayed on the monitor, and the live image with the sample tilted by the parallax angle and the previously captured image are overlaid and displayed in different colors. However, it is possible to efficiently set the optimum state for stereoscopic observation by finely adjusting the tilt angle of the sample and the shift amount of the image.

  According to the present invention, it is easy to adjust the tilt angle of a sample at the time of stereo pair image acquisition, that is, parallax angle adjustment, adjustment of image overlay deviation amount, and the like, and the operability of stereo pair image acquisition is improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, a scanning electron microscope will be described as an example. However, the present invention is similarly applied to other charged particle beam apparatuses that acquire a sample image by scanning a charged particle beam on a sample, such as a FIB (focused ion beam) apparatus. Applicable.

  FIG. 1 is a schematic diagram showing a configuration example of a scanning electron microscope according to the present invention. The primary electron beam 1 emitted from the electron beam source 12 passes through a lens system 10 such as a condenser lens, and is scanned on the sample 5 held on the sample stage 6 by the scanning coil 8. Secondary electrons 2 emitted from the sample 5 by electron beam irradiation are detected by a secondary electron detector 3. The detection signal of the secondary electron detector 3 is sent to the signal processing unit 4, and the signal processing unit 4 sends a signal synchronized with scanning to the monitor 100, and the signal intensity is displayed on the monitor 100 as an image 102. The electron beam source 12 is controlled by the electron beam controller 13, the scanning coil 8 is controlled by the scanning coil controller 9, and the lens system 10 is controlled by the lens controller 11. The sample stage 6 is controlled by the sample stage control unit 7. Each control unit is under the control of the overall control unit 14. The scanning coil controller 9 can rotate the image 102 without rotating the sample 5 by changing the scanning direction of the primary electron beam on the sample.

  FIG. 2 is a diagram showing the relationship in the scanning direction of the primary electron beam by the sample stage and the scanning coil. FIG. 3 is a diagram for explaining the inclination of the sample stage. The sample stage 6 can rotate the held sample 5 in the plane, and has an inclined rotation shaft 15, and can tilt the sample around the inclined rotation shaft 15. The sample stage control unit 7 controls the tilt angle φ and the rotation angle ψ of the sample stage 6 that can tilt in one direction. The incident angle of the primary electron beam 1 on the sample 5 can be changed by changing the tilt angle φ. It can be changed (see FIG. 3). Further, the scanning direction 16 of the primary electron beam can be changed by the scanning coil controller 9 as shown in FIGS. 2 (a) and 2 (b). By changing the scanning direction of the primary electron beam, the scanning area 17 on the sample also changes as shown in FIGS. 2A and 2B, and the image 102 displayed on the monitor 100 rotates.

  FIG. 4 is a diagram showing a screen configuration of the monitor. On the screen of the monitor 100, a stereo image acquisition mode switching button 101, an image display window 103, and various operation buttons (not shown) are displayed.

  FIG. 8 is a flowchart showing a processing procedure of stereo pair image acquisition according to the present invention. According to the image acquisition method of the present invention, first, when the stereo image acquisition mode switching button 101 is pressed in step 1, the mode is switched to the stereo image acquisition mode, and the process proceeds to step 2 and step 3 where the left-right direction of the image and the inclination of the sample The rotation angle of the image is automatically set by the control of the scanning coil control section 9 by the electromagnetic field rotation means so that the directions coincide.

  The control of the rotation angle of the image returns the angle θ1 that the image is intentionally rotated by the electromagnetic visual field rotation function, and further corrects the angle θ2 of the image rotation caused by the influence of the magnetic field. Is. Image rotation due to the influence of the magnetic field is defined as follows: θ2 is the rotation angle, m is the mass of the charged particle, e is the charge amount of the charged particle, Φ is the axial potential, B is the magnetic flux density, and z is the position on the magnetic lens axis. It is expressed by the following formula (Katsumi Ura, “Electron / Ion Beam Optics”, Kyoritsu Shuppan, August 25, 1994, p. 39).

走査コイル制御部９は走査コイル８を制御して、上記のようにして求めた角度θ１及びθ２だけ走査方向を回転させ、画像の左右方向と試料の傾斜方向が一致した状態、すなわち図２（ｂ）に示すように試料５上における一次電子線の走査方向１６が試料ステージ６の傾斜回転軸１５と直交している状態とする。

The scanning coil control unit 9 controls the scanning coil 8 to rotate the scanning direction by the angles θ1 and θ2 obtained as described above, so that the horizontal direction of the image and the inclination direction of the sample coincide, that is, FIG. As shown in b), the scanning direction 16 of the primary electron beam on the sample 5 is assumed to be orthogonal to the inclined rotation axis 15 of the sample stage 6.

  Next, proceeding to step 4, the sample stage control unit 7 rotates the sample stage by (θ1 + θ2) by the rotation mechanism of the sample stage 6 and changes the scanning direction of the primary electron beam. Restore the perspective. At this time, in the sample image displayed on the monitor screen, if the direction in which the stereoscopic view is desired is not the left-right direction, the sample stage 6 is appropriately rotated so that the direction in which the stereoscopic view is desired becomes the left-right direction of the monitor screen (sample Adjustment) so that the direction is perpendicular to the stage rotation tilt axis 15.

  Next, in step 5, the sample stage controller 7 rotates the sample stage 6 around the tilt rotation axis 15 by the parallax angle as shown in FIG. 3A to tilt the sample. A still image of the sample, which is an image on one side of the image, is captured and displayed on the monitor in FIG. When the still image capture on one side is completed, the process proceeds to step 7, and as shown in FIG. 3 (b), the sample is tilted in the opposite direction by about 8 ° corresponding to the parallax angle so that the image on the other side can be captured. In step 8, as shown in FIG. 4, the live image 111 is displayed so as to overlap with the previous captured image 110 in different colors.

  In this state, in Step 9, stereoscopic observation is performed with colored glasses, and the tilt angle of the sample, that is, the parallax angle, and the shift amount of the left and right images are set to an optimum state for stereoscopic observation. When the optimum state is set in step 10, the process proceeds to step 11 to capture the other image, and in step 12, the right-eye capture image and the left-eye capture images 110 and 112 are combined and displayed as shown in FIG. Thus, a still image of a stereo pair image is obtained.

  Regarding the stereoscopic display method, different color display may be used, or only parallax may be used. When displaying different colors, the left and right parallax images are displayed in a single image display area, but when using only parallax, the left and right parallax images are displayed side by side in the image display area adjacent to the left and right. Such a method is also common.

  When acquiring an image with parallax, the sample is tilted left and right by the parallax angle to acquire two images. When the stereo image acquisition mode switching button 101 is pressed, one of the images is automatically acquired. By tilting the sample to the parallax angle and then automatically tilting the sample to the opposite parallax angle after executing image capture, the labor of manually tilting the sample for each parallax angle is saved, and stereo pair images are acquired. It is also possible to facilitate the operability.

  With the above method, a still image of a stereo pair image can be acquired more efficiently than before.

  5 and 6 are diagrams showing modifications of the present invention, and show an example in which a window for displaying only a live image is provided in addition to a combined image display window for a captured image and a live image. In the case of the example shown in FIG. 5, a window 106 for displaying only the live image is provided side by side on the combined image display window 104 of the captured image and the live image. In the case of the example shown in FIG. 6, only the live image is displayed in a small window 106 as compared with the combined image display window 104 of the captured image and the live image. By providing the display window 105 or 106 only for the live image, it becomes easy to focus the live image, and a stereo pair image can be acquired more efficiently.

  In the stereo pair image acquisition method, the captured image and the live image may be automatically overlapped. As an example of the automation method, first, two points having a step on the sample are extracted, and a lens condition in focus at each point is found. Based on the above lens conditions, the height difference between the two points extracted previously is calculated, and the parallax between the two points on the screen is determined based on the database of the height difference and the optimum image shift amount, which is determined in advance for samples with known height differences. I ask if I just need it. Based on the result, the image overlay position is shifted by image shift or sample movement. By the method as described above, the adjustment of the image overlay can be automated.

  Also, regarding the overlay of the captured image and the live image, it is determined in advance how many pixels the image shift amount due to the parallax will be on the screen, and the shift amount of the overlay by the image processing becomes a predetermined number of pixels. Images may be arranged, and final fine adjustment may be performed manually while stereoscopically observing.

Schematic which shows the structural example of the scanning electron microscope by this invention. The figure which shows the relationship of the scanning direction of the primary electron beam by a sample stage and a scanning coil. The figure explaining the inclination of a sample stage. The figure which shows the screen structure of a monitor. The figure which shows the example of an image display on a monitor. The figure which shows the example of an image display on a monitor. The figure which shows the example of an image display on a monitor. The flowchart which shows the process sequence of the stereo pair image acquisition by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Primary electron beam 2 Secondary electron 3 Secondary electron detector 4 Signal processing part 5 Sample 6 Sample stage 7 Sample stage control part 8 Scanning coil 9 Inspection coil control part 10 Lens system 11 Lens control part 12 Electron source 13 Electron Radiation source control unit 14 Overall control unit 15 Tilt rotation axis 16 Primary electron beam scanning direction 17 Scanning area 100 Monitor 101 Stereo mode switching button 102 Image 103 Image display window 104 Composite image display window 105 Live image display sub-window 106 Live Image display sub-window 110 Captured image 111 Live image 112 Captured image

Claims (8)

A charged particle beam source;
A lens system that converges and irradiates a primary charged particle beam emitted from the charged particle beam source onto a sample;
Scanning means for scanning the sample with the primary charged particle beam;
A sample stage having a tilt rotation axis for holding the sample rotatably and tilting the sample with respect to the primary charged particle beam;
A detector for detecting a secondary signal emitted from the sample by irradiation of the primary charged particle beam;
A display unit for displaying a sample image based on the signal of the detector;
A control unit for controlling the sample stage and the display unit,
The control unit includes a sample captured image obtained by rotating the sample stage by a predetermined angle around the tilt rotation axis, and a sample in a state in which the sample stage is rotated in the reverse direction around the tilt rotation axis. An image superimposed with a live image is displayed on the display unit,
A charged particle beam apparatus , wherein a tilt angle of a sample and an image shift amount when acquiring the live image are adjusted based on the superimposed images . The charged particle device according to claim 1, a charged particle beam apparatus characterized by displaying the live image and the overlay image on the display unit. 3. The charged particle beam apparatus according to claim 1 , wherein an image shift amount due to parallax is calculated, and the images are automatically superimposed. The charged particle beam apparatus according to claim 1 , further comprising an operation button that causes the control unit to execute the series of processes. A secondary signal emitted from the sample by irradiating the sample, which is rotatably held on a sample stage having an inclined rotation axis for inclining the sample with respect to the primary charged particle beam, by scanning the primary charged particle beam with a scanning means. In a sample image observation method for displaying a sample image on an image display device based on
Displaying the captured image obtained by rotating the sample stage around the tilt rotation axis by a predetermined angle on the image display device;
Rotating the sample stage around the tilt rotation axis in the reverse direction of the predetermined angle;
Displaying an image obtained by superimposing the live image in the state on the capture image in the image display device;
Adjusting the tilt angle of the sample and the amount of image shift when acquiring the live image based on the superimposed image;
A sample image observation method characterized by comprising: In the sample image observation method according to claim 5 ,
Obtaining a difference in elevation between two points on the sample;
Obtaining an image shift amount corresponding to the height difference;
Sample image observation method characterized by comprising the step of shifting the overlapping position of the live image and the captured image by the image shift amount. A charged particle beam source;
A lens system that converges and irradiates a primary charged particle beam emitted from the charged particle beam source onto a sample;
Scanning means for scanning the sample with the primary charged particle beam;
A sample stage having a tilt rotation axis for holding the sample rotatably and tilting the sample with respect to the primary charged particle beam;
A detector for detecting a secondary signal emitted from the sample by irradiation of the primary charged particle beam;
A display unit for displaying a sample image based on the signal of the detector;
A control unit for controlling the sample stage and the display unit;
And data defining the relationship between the height difference on the sample and the amount of image shift,
The control unit is a captured image of a sample obtained by rotating the sample stage by a predetermined angle around the tilt rotation axis, and
A sample live image obtained by rotating the sample stage by the predetermined angle around the tilt rotation axis in a reverse direction, and
Furthermore, the difference in height between two points on the sample is obtained,
An image shift amount is obtained based on the data from the height difference between the two points,
The overlapping position of the captured image and the live image is shifted by the image shift amount.
A charged particle beam apparatus characterized by that. A secondary signal emitted from the sample by irradiating the sample, which is rotatably held on a sample stage having an inclined rotation axis for inclining the sample with respect to the primary charged particle beam, by scanning the primary charged particle beam with a scanning means. In a sample image observation method for displaying a sample image on an image display device based on
Rotating the sample stage by a predetermined angle around the tilt rotation axis to obtain a captured image of the sample;
Obtaining a live image of the sample obtained by rotating the sample stage around the tilt rotation axis in the reverse direction by the predetermined angle;
Furthermore, obtaining a difference in height between two points with a step on the sample;
Obtaining an image shift amount based on data defining a relationship between the height difference on the sample and the image shift amount from the height difference of the two points;
Shifting the overlapping position of the captured image and the live image by the image shift amount;
A sample image observation method characterized by comprising:

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