Charged carrier beam device and sample observation method

Abstract

Charged carrier beam device comprising: an optical charge carrier system comprising a charged carrier beam source (1), a focusing lens (3) configured to focus a primary charged carrier beam (2) emitted from the charged carrier source (1), an objective lens (6) configured to focus the primary charged carrier beam (2) onto a sample (11), a deflection coil (7) configured to scan the sample (11) with the primary charged carrier beam (2), and a detection device (9) configured to detect secondary charge carriers generated by irradiating the sample (11) with the primary charge carriers; a control panel (34) configured to receive controls from an operator; an image display device (32) including a plurality of display areas; a control device (31) connected to the control panel (34) and the image display device (32) and including a device control unit (35) and a display control unit (36); and a storage device (33) configured to store image data acquired by the optical charge carrier system, wherein the device control unit (35) receives a control from the control panel (34), controls the optical charge carrier system and receives image data, the display control unit (36) displays a live image (100) obtained from the optical charge carrier system in a first display area (52) of the image display device (32) and displays a comparison image (101) stored in the storage device (33) in a second display area (56) of the image display device (32), characterized in that the display control unit (36) receives control from the control panel (34) and generates a superimposed image (104) obtained by making only certain areas of the comparison image (104) transparent and superimposing only the transparent areas of the comparison image (104) on the live image (100) at a corresponding position of the first display area (52) of the image display device (32).

Description

Technical FieldThe present invention relates to a charged particle beam apparatus and a sample observation method using the same.Background ArtA charged particle beam apparatus represented by a scanning electron microscope scans a desired region (field of view) on a sample with a charged particle beam, and records charged particle signals output from the scanned region in association with scanning positions, thereby imaging an observation point. PTL 1 discloses a technique of correcting an electron beam irradiation point using pattern matching to keep an electron beam irradiation range constant when images are continuously obtained or analysis result data is accumulated for a long time.On the other hand, PTL 2, although it is not a technique related to a charged particle beam apparatus, discloses an image processing technique for synthesizing still image data with moving image data displayed in real time and displaying a result of the synthesis. In order to more accurately acquire symmetric face images, when a left side face image is acquired, a right side face image acquired in advance is horizontally reversed and synthesized with a left side face image displayed in real time, and a result of the synthesis is displayed. Face images are acquired by adjusting the angle of the face such that the left-side face image displayed in real time coincides as much as possible with the right-side face image horizontally reversed, thereby more accurately acquiring a symmetric face image.PTL 3 shows an image processing apparatus including: first storage means for storing an original image for pattern matching; second storage means for storing an image of an observation object; display means for displaying the original image and the image of the observation object; area specification means for specifying an area in the image of the object to be used for the calculation of difference information related to the template image; and calculation means for calculating the difference information between the area of the image of the subject specified by the area specification means and the template image, and for displaying the result of the calculation on the display means.PTL 4 shows a sample observation method including: a step of defining an outline of an observation object with respect to a sample or a plurality of points arranged along the outline with respect to an electron microscope image; and a step of arranging a plurality of fields of view for an electron microscope along the outline, wherein electron microscope images of the plurality of fields of view defined by each of the above-mentioned steps and arranged along the shape of the observation object are acquired.Keep ListPatent LiteraturePTL 1: JP 2016 / 091 893 APTL 2: JP 2009 / 061 178 APTL 3: US 2007 / 0 045 538 A1PTL 4: EP 2 343 727 A1SUMMARY OF THE INVENTIONTechnical ProblemWhen a sample for observation is not changed with the passage of time or when a change of the sample is caused by an operation of an observer as in PTL 1, sufficient time can be used to adjust the field of view, and therefore, the precision of adjustment of the field of view can be emphasized and positional deviations of obtained image data can be digitized and controlled using various image processing techniques. On the other hand, there is a growing need for a charged particle beam apparatus to make in situ observations of microscopic changes caused by adding heat or applying a mechanical force to a sample. In such a case, an observer who is not an expert with respect to the charged particle beam apparatus must maintain the field of view of observation which changes from moment to moment while watching a monitor, and therefore, adjusting the field of view must be controllable in real time with good operability.The adjustment of the field of view is performed by comparing a reference comparison image with a live image of an observation. However, as the movement of the field of view becomes more important in observations at high magnifications, overlapping and displaying two images is considered effective to eliminate the need for an observer to move the line of sight. For this purpose, it is desirable to apply that disclosed in PTL 2. However, PTL 2 refers to an application field in which image acquisition conditions can be adjusted over a sufficient time and an object to be acquired is also a relatively large object, that is, a face. In contrast, in the case of observing a sample in situ, an observer attempts to observe changes occurring in the field of view. A live image and a comparison image displayed on a screen in sizes corresponding to an object for observation are not necessarily displayed on a screen having the same display size. Even in such a case, the present invention provides a scanning electron microscope and a sample observation method that allow an observer to focus on in situ observation while adjusting the field of view with a simple·operation by developing an interface to overlap two images without giving a burden to the observer.Solution of the ProblemThere is provided a charged particle beam apparatus including: a charged particle optical system including a charged particle beam source, a focusing lens configured to focus a primary charged particle beam emitted from the charged particle source, an objective lens configured to focus the primary charged particle beam on a sample, a deflection coil configured to scan the sample with the primary charged particle beam, and a detector configured to detect secondary charged particles generated by irradiation of the sample with the primary charged particles; an operation panel configured to receive controls of an operator; an image display apparatus including a plurality of display regions; a controller connected to the operation panel and the image display apparatus and including a device control unit and a display control unit; A storage device configured to store image data acquired by the charge carrier optical system, wherein the device control unit receives a controller from the operation panel, controls the charge carrier optical system, and obtains image data, the display control unit displays a live image obtained by the charge carrier optical system in a first display area of the image display device, and displays a comparison image stored in the storage device in a second display area of the image display device, and the display control unit receives a controller from the operation panel, and displays a superimposed image obtained by making the comparison image matching the size of the first display area transparent and superimposing the comparison transparent image on the live image at the position of the first display area of the image display device.Advantageous Effects of the InventionThe field of view may be adjusted without moving the line of sight of a live image on a display device.Brief Description of the Drawings[FIG. 1 ] FIG. 1 is a schematic diagram of a scanning electron microscope according to an embodiment of the present invention.[FIG. 2 ] FIG. 2 is a diagram showing an example of an operation screen.[FIG. 3] FIG. 3 is a diagram showing an example of an operation screen.[FIG. 4] FIG. 4 is a diagram showing an example of an operation screen.[FIG. 5 ] FIG. 5 is a diagram showing data processing according to the embodiment of the present invention.[FIG. 6 ] FIG. 6 is a flowchart of a process for superimposing a live image and a comparison image according to the embodiment of the present invention.[FIG. 7 ] FIG. 7 is a diagram showing an example of a transparency setting screen.[FIG. 8] FIG. 8 is a diagram showing an example of changing the transparency of a part of a comparative image.DESCRIPTION OF THE EMBODIMENTSHereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiments described below, a scanning electron microscope (SEM) is described as an example of a charged particle beam apparatus, but the present invention is not limited thereto. For example, the present invention can also be applied to a focused ion beam apparatus (FIB) that uses a liquid metal ion source or a gas ion source as a charged particle beam source and that irradiates a sample with an ion beam (charged particle beam) emitted therefrom, a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), a scanning ion microscope, a scanning probe microscope, an optical microscope, a laser microscope, and the like.FIG. 1 is a schematic diagram of a scanning electron microscope according to an embodiment of the present invention. A primary electron beam 2 emitted from an electron gun (charged particle beam source) 1 is once focused by a first focusing lens 3 and then broadens. The outer peripheral portion of the primary widened electron beam is shielded by an objective aperture 4, and therefore a central portion of the beam having a predetermined diameter is transmitted. By changing the focal position of the first focusing lens 3 and the aperture of the objective aperture 4, a beam current amount with which a sample 11 is to be irradiated can be adjusted. A primary electron beam having passed through the objective aperture 4 is focused by a second focusing lens 5 and an objective lens 6 on the sample 11 placed on a sample stage 8. The sample 11 is scanned with the primary electron beam by the action of a deflection coil 7. Signal electrons (secondary electrons) generated from the sample 11 by the irradiation with the primary electron beam are detected by the detector 9.This electron optical system is disposed in a lens barrel 20 which is vacuum-relieved, and the sample stage 8 is disposed in a sample chamber 21 which is vacuum-relieved. In addition, the hardware of the SEM is controlled by a controller 31. The controller 31 may be configured as hardware dedicated to the processing or may be configured as software to be executed using a general-purpose processor (e.g., a CPU, a GPU, a DSP, etc.). Further, an image display device 32, a storage device 33, and an operation panel 34 are connected to the controller 31. On the image display device 32, an image viewed with an SEM or an operation screen required for an observer to control the SEM is displayed as described later. In the storage device, an SEM control program and images (including a still image and a moving image) captured with the SEM are stored. The operation panel 34 is an interface for inputting an instruction of an observer, and is implemented in hardware such as a keyboard, a mouse, or a pointer. For example, while viewing an image displayed on the image display device 32, the observer moves the sample stage 8 in the XYZ direction (X and Y denote two axes in a plane vertical to the optical axis direction of a primary electron beam, and Z denotes an axis in the optical axis direction of the primary electron beam) to search a desired observation point.Here, in the example shown in FIG. 1, the sample 11 is placed on the sample table 8 by means of a sub-table 10. The sub-stage 10 is a stage that applies a predetermined measure to a sample, for example, heating the sample or applying a force to the sample. Then, when microscopic changes occurring by applying some measures to the sample 11 in the sample 11 are observed (which is referred to as in situ observation), a sub table that can apply a predetermined measure to the sample 11 is prepared. In order to load an under table into the sample chamber 21, a relatively large inlet is required in the sample chamber 21. In addition, some holes are provided in the sample chamber 21. The holes are normally closed. However, when the sub-table 10 is used, wires necessary for controlling the sub-table 10 will be pulled out of the holes. The pulled-out wires are connected to a power supply and a control unit to operate the sub-table 10. The control of the sub table 10 is normally performed by a separate controller (a PC or the like) different from the controller for the SEM, but the same controller may be used.The sample chamber 21 is connected to the lens barrel 20 by means of an opening 22 through which a primary electron beam passes. Therefore, when the degree of vacuum of the sample chamber 21 decreases, the degree of vacuum of the lens barrel 20 also decreases. In particular, since elements requiring a high degree of vacuum, such as the electron gun 1 and the lens aperture 4, are provided in the lens barrel 20, observation cannot be started unless the degree of vacuum reaches a predetermined level again. In order to reduce the time from sample introduction to start observations, it is desirable to reduce the influence of the decrease in the degree of vacuum of the sample chamber 21 on the lens barrel 20.Therefore, a mechanism for suppressing the decrease in the degree of vacuum of the sample chamber 21 from being transmitted to the lens barrel 20 side is provided. For example, by disposing a differential outlet throttle valve (not shown) for suppressing the decrease in the degree of vacuum in a region of the lens barrel 20 where the elements 1 and 4 require a particularly high degree of vacuum or using a Schottky electron gun as the electron gun 1, the time from opening the sample chamber 21 to initiate observation after further vacuum emptying can be reduced.For example, an example of observing a change of the sample 11 during heating of the sample 11 will be described. The sample chamber 21 is opened, and the sample heating sub-table 10 with the sample 11 placed thereon is placed on the sample table 8. The sample chamber is then evacuated. After vacuum emptying is completed, the sample 11 is irradiated with an electron beam, and an image of the current observation is displayed on the image display device 32. FIG. 2 shows an example of an operation screen 51 displayed on the image display device 32.The operation screen 51 includes a live image display area 52, a captured image display area 53, and an operation panel 55. various parameters for controlling the SEM for observation are displayed in the operation panel 55, and an observer performs parameter adjustment using the operation panel 34. Since parameters for acquiring appropriate images under predetermined conditions are stored in the storage device 33 in advance, appropriate parameters can be read from the storage device 33, and the observer may not need to change the predetermined parameters in most cases. In the live image display area 52, an image of the current observation is displayed with the SEM.In addition, when the observer captures an image during observation, corresponding image data is stored in the storage device 33. In addition, a reduced image 54- i(where i is an integer) of the captured image is displayed in the captured image display area 53. All of a series of images captured during a single observation are displayed in the captured image display area 53. Here, images may be not only still images but also moving images. In the case of a moving image, for example, an initial image is displayed as an image representative thereof.It is assumed that the observer observed changes in the sample 11 while gradually raising the temperature of the sample 11 from room temperature to a target temperature A and to a target temperature B. First, the sample stage 8 is moved at room temperature, and a field of view for observation is set. The field of view for observation includes marks that do not change their positions and shapes even when the temperature increases, such that the observer maintains the same field of view. For example, a foreign object included in the field of view may be used as a mark. When the field of view is set, an image thereof is captured. A reduced captured image 54 is displayed in the captured image display area 53.For example, when a double click is performed on a reduced image 54- 1, the reduced image 54- 1 is displayed in a comparative image display area 56. The comparative image display area 56 is a window different from the areas 52, 53, and 55, and displays the captured image 54- 1 as an image of the same size and magnification as in the live image display area 52. Since images in different windows are opened, the comparative image display area 56 can be displayed at any arbitrary position on the operation screen 51. The live image display area 52 and the comparison image display area 56 may be displayed with different display sizes. This is because it is desirable that a target of interest for an observer is displayed on an operation screen having an appropriate size.When the target temperature A has been set and the heating of the sample 11 is started, the temperature of the sample 11 starts to rise to the target temperature A. As the temperature of the sample 11 rises, the vicinity of the sample 11 is also heated and thermally expands as a whole, and therefore the field of view gradually moves from the observation position set at room temperature. Therefore, it is necessary to operate the sample stage 8 so as not to lose the field of view. When the live image display region 52 and the comparison image display region 56 are arranged adjacently to each other as shown in FIG. 3, comparison of two images can be facilitated. However, for example, it is difficult to determine whether a foreign object image 102 and a foreign object image 103 that are marks of the field of view are located at the same positions in a live image 100 and a comparison image 101. Since there is a case where a live image is immediately changed due to a temperature change, if an observer moves the line of sight to a comparative image at such a time, the target visual field may be lost.Therefore, in the present embodiment, a button 57 is provided in the upper portion of a window that displays the comparison image 101. When clicking the button 57, a superimposed image 104 obtained by making the comparison image 101 transparent and superimposed on the live image 100 is displayed as illustrated in FIG. 4. Because the images overlap each other, it is easy to determine whether a mark is a mark of the live image 100 or a mark of the comparison image 101, because it is not necessary to move the line of sight from the live image 100 to adjust the field of view and the comparison image 101 is transparent.When the temperature of the sample 11 has reached the target temperature A and stabilized, the movement of the field of view is stopped. The field of view is finely adjusted by operating the sample stage and an image is captured. A reduced image of the captured image is displayed in the captured image display area 53. When the button 57 is clicked again in the state where the images overlap with each other, the operation screen 51 returns to the state shown in FIG. 3. In other words, the comparison image 101 returns to its original transparency and is displayed in a different window at a position different from that in the live image. Alternatively, the comparison image 101 may be removed from the operation screen 51.Next, when the target temperature B has been set, the temperature of the sample 11 starts to rise to the target temperature B. The observer may use an image acquired at room temperature or an image acquired at the target temperature A as a comparative image. Since any captured image is displayed in the captured image display area 53, it is easy to make a selection. Thereafter, observation may be continued in the same manner.In addition, when a tension force is applied to the sample 11 and its changes are observed, an under table for drawing the sample 11 is prepared. When the sample 11 is pulled and deformed in two opposite directions, the field of view except the central part moves. In such a case, the field of view can be adjusted using the operation screen according to the present embodiment without moving the line of sight from the live image 100.A processing flow for overlapping images will be described with reference to FIGS. 5 and 6. Signal electrons detected by a detector 9 are converted into image data DL (P, X, Y) (1≤X≤L, 1≤Y≤M) in the controller 31. Image data is expressed as a set of pixel values P at the position (X, Y) in an image. In order to display the image data DL on the image display device 32, the image data DL is converted into display image data EL (p, x, y) (1≤x≤j, 1≤y≤k) that matches the size of the live image display region 52, and is displayed as the live image 100 in the live image display region 52 of the operation screen 51. On the other hand, when the observer captures an image, image data obtained from the recognizing means 9 is stored in the storing means 33 as DSi (P, X, Y) (1 ≤ i ≤ N, 1 ≤ X ≤ L, 1 ≤ Y ≤ M). N denotes the number of images taken by the observer.A captured image is converted into reduced display image data ETSi (p, x', y') (1≤x'≤j', 1≤y'≤k') that conform to the size of the captured image display area 53, and is displayed as the reduced image 54 in the captured image display area 53 of the operation screen 51 as described above. When a double click is performed on the reduced image 54 (assuming that a double click is performed on a reduced image of i=n), the display image data ESn (p, x, y) (1≤x≤j, 1≤y≤k) is adjusted to the size of the comparative image display area 56 and displayed in the comparative image display area 56 of the operation screen 51 as the comparative image 101.By detecting a click of the button 57 in this state (see FIG. 3 ), a display control unit 36 starts the processing (S 70). Here, a processing start instruction may be input by, for example, a predetermined key manipulation of the operation panel 34. First, it is checked whether a live image and a comparison image have the same size (S 72). In the example shown in FIG. 5, the size of the live image and that of the comparison image are the same. However, when the size of a live image is different from that of a comparison image, pixel data of the comparison image is obtained in the size of the live image (S 74). Next, the representative coordinates of the live image are obtained on the operation screen 51 (S 76).For example, as shown in FIG. 2, with a pixel 60 at the upper left corner of the operation screen 51 as the origin, the coordinates of an arbitrary pixel Q on the operation screen 51 are expressed as Q(a, b), and the upper left corner of the display area is used as the representative coordinate, and the coordinate QL(a1, b1) of a pixel 61 is obtained as the representative coordinate of the display area for live images. Here, the method of associating the coordinates of the operation screen 51 and the method of associating the representative image of the display area are not limited thereto, and any method may be used as long as the coordinate is identifiable. In addition, this step may be omitted when the live image display area 52 is fixed on the operation screen 51.Next, a superimposed image obtained by superimposing a comparison image of the same size and predetermined transparency with a live image is generated (S 78). For example, an alpha mixing technique is used to superimpose two images. In the alpha mixing technique, each pixel contains, as a pixel value, an alpha value α indicating transparency. As a result, by mixing colors of pixels of the live image and colors of pixels of the comparison image in ratios corresponding to the alpha values α, a superimposed image in which the comparison transparent image is superimposed on the live image can be generated. The generated superimposed image is displayed in the comparative image display area 56, and the comparative image display area 56 is displayed at the position of the representative coordinate of the live image (S 80). This can be realized by setting the value of the coordinate QC(ac, bc) of a pixel 62, which is the representative coordinate of the comparison image display area, to the coordinate (a1, a1).Here, the superimposed image may also be displayed in the live image display area 52. In this case, the comparative image display area 56 is not moved. Since the superimposed image is displayed in the live image display area 52, the same effect can be obtained.Further, as shown in FIG. 7, in order to adjust transparency, a transparency adjustment tool 58 is displayed when the mouse is moved over the button 57. The transparency can be adjusted by a slider 59 or by directly inputting a numerical value. At the present time, the transparency may be input as a ratio or a value of the alpha value α (0 to 255) may be input directly. The transparency set here is stored in the storage device 33.In the present embodiment, two images are overlapped with each other to adjust the field of view of a live image, but various methods of image processing may be considered. For example, contour lines may be extracted from a comparison image to be overlapped with a live image. However, the method of the present embodiment in which a comparison image is transparent and superimposed on a live image is considered to be advantageous in the following points: First, since only values of pixels to be displayed on the image display device 32 need to be calculated, the processing load is small, and therefore it is possible to easily follow the operation of the observer. In addition, when a foreign object is used as a mark, it may be difficult to align images without extracting contour lines at a certain precision.Although the present embodiment has been described above in detail, various changes may be made. For example, a plurality of comparative image display regions 56 may be displayed on the operation screen 51, and the button 57 is provided in each of the comparative image display regions 56. When clicking on the button 57 of any one of the comparative image display areas 56, a comparative image displayed in the corresponding comparative image display area 56 is made transparent, and a superimposed image obtained by superimposing a live image on the transparent comparative image is displayed. Further, in this state, when the button 57 of another comparative image display area 56 has been clicked, a comparative image displayed in the comparative image display area 56 in which the button 57 has been clicked is made transparent, and the superimposed image obtained by superimposing a live image with the comparative transparent image is replaced.If a plurality of comparison images are displayed, it is preferable to use a common transparency value for the target transparency value. In other words, the transparency set to a comparative image is also reflected in other comparative images. Since many images taken by one measurement are similar to each other, it is convenient for an observer to reflect a target value to all the comparison images instead of storing different target values for corresponding comparison images. Therefore, for example, recent transparency is used for a plurality of captured images displayed in the captured image display area 53. Further, when the brightness differs from one image to the next in a measurement, a transparency value may be set for a comparative image, and after the transparency value is reflected in all the comparative images, the observer may set a different transparency.In order to display display images of many different signals as live images on the operation screen 51 simultaneously, images may be displayed on multiple screens such as two screens or four screens in the live image display area 52. Since a screen for manually adjusting the brightness and contrast of an image needs to be limited to one screen even in the case of multiscreen display, only one screen is selected. When the live image display area 52 displays images in multiple screens and the button 57 of the comparative image display area 56 is pressed, a comparative image is superimposed on a live image whose brightness and contrast can be adjusted, i.e., a selected live image.Further, as shown in FIG. 8, regions to be made transparent are set as the regions 105 and 106 in the comparative image 101, and only the set regions of the comparative image 101 can be made transparent and superimposed, whereas the other regions of the comparative image are not superimposed (the transparency is set to 100%). As a result, there is an advantage that parts of a live image irrelevant to adjustment of the field of view can be clearly seen.List of reference characters1 Electron gun 2 Primary electron beam 3 First focusing lens 4 Lens aperture 5 Second focusing lens 6 Objective lens 7 Deflection coil 8 Sample stage 9 Detection device 10 Sub stage 11 Sample 20 Lens barrel 21 Sample chamber 31 Control device 32 Image display device 33 Storage device 34 Operation panel

Claims

A charged particle beam apparatus comprising: a charged particle optical system including a charged particle beam source (1), a focusing lens (3) configured to focus a primary charged particle beam (2) emitted from the charged particle source (1), an objective lens (6) configured to focus the primary charged particle beam (2) on a sample (11), a deflection coil (7) configured to scan the sample (11) with the primary charged particle beam (2), and a detector (9) configured to detect secondary charged particles generated by irradiation of the sample (11) with the primary charged particles; an operation panel (34) configured to receive controls of an operator; an image display device (32) including a plurality of display regions; a controller (31) connected to the operation panel (34) and the image display device (32) and including a device control unit (35) and a display control unit (36); and a storage device (33) configured to store image data acquired by the charge carrier optical system, wherein the device control unit (35) receives control from the operation panel (34), controls the charge carrier optical system, and obtains image data, the display control unit (36) displays a live image (100) obtained by the charge carrier optical system in a first display area (52) of the image display device (32), and displays a comparison image (101) stored in the storage device (33) in a second display area (56) of the image display device (32), characterized in that the display control unit (36) receives control from the operation panel (34) and generates a superimposed image (104), that is obtained by making only certain areas of the comparison image (104) transparent and only the transparent areas of the comparison image (104) are superimposed on the live image (100) at a corresponding position of the first display area (52) of the image display device (32).The charged particle beam apparatus according to claim 1, wherein the display control unit (36) generates image data of the superimposed image (104) by synthesizing image data of the live image (100) set to a first transparency with image data of the comparative image (101) set to a second transparency different from the first transparency.The charged particle beam apparatus according to claim 2, wherein the display control unit (36) displays a button in the second display area (56), and displays the superimposed image (104) at the position of the first display area (52) of the image display device (32) when the displayed button receives a first control from the operation panel (34).The charged particle beam apparatus according to claim 3, wherein the second display area (56) in which the superimposed image (104) is displayed is displayed at the position of the first display area (52) of the image display device (32).The charged particle beam apparatus according to claim 3, wherein the display control unit (36) displays the superimposed image (104) in the first display area (52).The charged particle beam apparatus according to claim 3, wherein the display control unit (36) displays a transparency adjustment tool for adjusting transparency when the button receives a second control from the operation panel (34).The charged particle beam apparatus according to claim 2, wherein the display control unit (36) displays a plurality of captured images stored in the storage device (33) as reduced images in a third display area of the image display device (32), the display control unit (36) displays one of the plurality of captured images selected by the operation panel (34) in the second display area (56) as the comparison image (101), and the transparency is set to a common value for the plurality of captured images.A sample observation method using a charged particle beam apparatus comprising an operation panel (34) configured to receive controls of an operator, an image display apparatus (32) including a plurality of display areas, a sample stage, a charged particle optical system, and a storage device (33) configured to store image data acquired by the charged particle optical system, the method comprising: disposing a sample by means of a sub stage on the sample stage; displaying a live image (100) obtained from the charged particle optical system in a first display area (52) of the image display apparatus (32), displaying a comparative image (101) stored in the storage device (33) in a second display area (56) of the image display apparatus (32); A control of the sub-table to apply a predetermined measure to the sample; characterized by displaying a superimposed image (104) generated by making certain areas of the comparison image (101) transparent, and superimposing the live image (100) at a corresponding position of the first display area (52) of the image display device (32) with the transparent certain areas of the comparison image (101), when control is obtained from the operation panel (34).The sample observation method according to claim 8, wherein image data of the superimposed image (104) is generated by synthesizing image data of the live image (100) set to a first transparency with image data of the comparative image (101) set to a second transparency different from the first transparency.The sample observation method according to claim 9, wherein a button is displayed in the second display area (56), and the superimposed image (104) is displayed at the position of the first display area (52) of the image display device (32) when the displayed button receives a first control from the operation panel (34).The sample observation method according to claim 10, wherein a transparency adjustment tool for adjusting transparency displays when the button receives a second control from the operation panel (34).The sample observation method according to claim 9, wherein a plurality of captured images stored in the storage device (33) are displayed in a third display area of the image display device (32) as reduced images, one of the plurality of captured images selected by the operation panel (34) is displayed in the second display area (56) as the comparative image (101), and the transparency is set to a common value for the plurality of captured images.

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