Patent Publication Number: US-10763078-B2

Title: Charged particle beam device and image processing method in charged particle beam device

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/776,404 filed on May 15, 2018, which claims the benefit of priority under 35 U.S.C. § 119 of International Application No. PCT/JP2015/083488, filed on Nov. 27, 2015, the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a charged particle beam device and an image processing method in the charged particle beam device. 
     BACKGROUND ART 
     A microscope or the like using a charged particle beam scans a sample with the charged particle beam which the sample is irradiated in two dimensions of the horizontal direction and the vertical direction and detects a secondary signal generated from an irradiation region. The microscope amplifies and integrates the detected signal by an electric circuit and correlates the detected signal with scanning coordinates of the charged particle beam, thereby generating a two-dimensional image. 
     Here, regarding a device that performs image formation, an image forming method for improving a signal-to-noise ratio (S/N ratio) by integrating a plurality of pieces of two-dimensional image data is known. In PTL 1, PTL 2, PTL 3, PTL 4, and PTL 5, in order to suppress the influence of noise as described above, a technique in which the same imaging region is scanned a plurality of times and adds and averages signals obtained by the scanning is described. By performing adding and averaging, it becomes possible to suppress irregularly occurring noise to some extent. 
     In PTL 1, a method of controlling a gain of a multiplier for integration computation as an input pixel luminance value largely fluctuates due to the influence of noise is described. In PTL 2, a method in which a plurality of frame memories necessary for frame integration are mounted, a frame image before two frames is also set as a target of integration computation, and a multiplication rate thereof is switched is described. In PTL 3, a frame integration method in which an averaging arithmetic expression of frame integration computation multiplied by an exponent and divided by the exponent is used as an arithmetic expression is described. In PTL 4, a method of appropriately adjusting signal intensity of an image to be integrated is described. In PTL 5, a method of detecting positional deviation and variably setting a frame integration number with respect to the degree of positional deviation is described. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP-A-2010-182573 
     PTL 2: JP-A-2000-182556 
     PTL 3: JP-A-2008-186727 
     PTL 4: JP-A-9-330679 
     PTL 5: JP-A-2012-049049 
     PTL 6: JP-A-7-130319 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the conventional frame integration method, a frame-integrated image is generated by dividing an input image by a frame integration number which is set in advance and addition is made thereto by the integration number. Accordingly, the conventional frame-integrated image is initially in a dark state in an integration process and then gradually becomes a bright state and thus, the user cannot confirm the image in the integration process. 
     Accordingly, the present invention provides a technique for displaying a frame-integrated image with no sense of discomfort (no dark display) in the integration process. 
     Solution to Problem 
     For example, in order to solve the problem described above, a configuration described in the claims is adopted. Although the present application includes plurality of means for solving the problem described above, as an example thereof, there is provided a charged particle beam device which includes a charged particle beam source, a charged particle beam optical system that irradiates a sample with a charged particle beam from the charged particle beam source, a detector that detects a secondary signal generated from the sample by irradiation with the charged particle beam, and an image processing unit that executes integration processing of image data obtained from the secondary signal and outputting an integrated image, and in which the image processing unit executes a normalization integration computation of outputting an integrated image in which a luminance value of the integrated image is always “1” in integration process. 
     Also, according to another example, there is provided a charged particle beam device which includes a charged particle beam source, a charged particle beam optical system for irradiating each of a plurality of divided regions in a sample with a charged particle beam from the charged particle beam source, a detector for detecting a secondary signal generated from each of the plurality of divided regions by irradiation with the charged particle beam, an image processing unit for executing integration processing of image data obtained from the secondary signal and outputting an integrated image, and a display unit for displaying the integrated image for each of the plurality of divided regions, and in which the image processing unit determines the end of the integration processing according to image quality of the integrated image for each of the plurality of divided regions. 
     According to still another example, there is provided an image processing method in a charged particle beam device, which includes a step of irradiating a sample with a charged particle beam from the charged particle beam source, by a charged particle beam optical system, a step of detecting a secondary signal generated from the sample by irradiation with the charged particle beam, by a detector, a step of executing integration processing of image data obtained from the secondary signal and outputting an integrated image, by an image processing unit, and in which the outputting step includes executing normalization integration computation of outputting an integrated image in which a luminance value of the integrated image is always “1” in integration process. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to display a frame-integrated image with no sense of discomfort (no dark display) in the integration process. Further features relating to the present invention will become apparent from description of the present specification and accompanying drawings. Also, the problems, configurations, and effects other than those described above will be clarified by description of the following embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration of a charged particle beam device relating to conventional frame-integrated image acquisition. 
         FIG. 2  is an internal configuration diagram of a conventional image processing unit. 
         FIG. 3  is a diagram for explaining conventional frame integration computation. 
         FIG. 4  is a flowchart for explaining a conventional frame-integrated image acquisition procedure. 
         FIG. 5  is a GUI when a conventional frame-integrated image is acquired. 
         FIG. 6  is a diagram illustrating a configuration of a charged particle beam device relating to frame-integrated image acquisition of the present invention. 
         FIG. 7  is an internal configuration diagram of an image processing unit of the present invention. 
         FIG. 8  is a diagram for explaining frame integration computation of the present invention. 
         FIG. 9  is a flowchart for explaining a frame-integrated image acquisition processing flow of the present invention. 
         FIG. 10  is a GUI when a frame-integrated image of the present invention is acquired. 
         FIG. 11  is a diagram illustrating a display example of the frame-integrated image. 
         FIG. 12  is a flowchart for explaining an operation procedure of frame-integrated image acquisition of the present invention. 
         FIG. 13  is a GUI for selecting an image evaluation method of the present invention. 
         FIG. 14  is a diagram for explaining an image evaluation index (SNR). 
         FIG. 15  is a diagram for explaining the image evaluation index (SNR). 
         FIG. 16  is a diagram for explaining the image evaluation index (SNR). 
         FIG. 17  is a diagram for explaining another image evaluation index (degree of SN improvement). 
         FIG. 18  is a diagram for explaining the image evaluation index (degree of SN improvement). 
         FIG. 19  is a diagram for explaining the image evaluation index (degree of SN improvement). 
         FIG. 20  is a diagram for explaining the image evaluation index (degree of SN improvement). 
         FIG. 21  is a diagram for explaining another image evaluation index (CNR). 
         FIG. 22  is a diagram for explaining the image evaluation index (CNR). 
         FIG. 23  is an internal configuration diagram of an image evaluation unit of the present invention. 
         FIG. 24  is a diagram for explaining a comparison between integrated image display in an integration process of the prior art and that of the present invention. 
         FIG. 25  is a flowchart for explaining a processing flow of extremely low magnification image acquisition in which a conventional frame-integrated image acquisition function is implemented. 
         FIG. 26  is a diagram for explaining an outline of scanning of extremely low magnification image acquisition in which the conventional frame-integrated image acquisition function is implemented. 
         FIG. 27  is a GUI when the conventional extremely low magnification image is acquired. 
         FIG. 28  is a flowchart for explaining an operation procedure of the conventional extremely low magnification image acquisition. 
         FIG. 29  is a flowchart illustrating a processing flow of extremely low magnification image acquisition in which frame-integrated image acquisition function of the present invention is implemented. 
         FIG. 30  is a diagram for explaining an outline of scanning of extremely low magnification image acquisition in which the frame-integrated image acquisition function of the present invention is implemented. 
         FIG. 31  is the GUI when the extremely low magnification image of the present invention is acquired. 
         FIG. 32  is a flowchart for explaining an operation procedure of extremely low magnification image acquisition of the present invention. 
         FIG. 33  is a flowchart for explaining a processing flow of extremely low magnification image acquisition (integrated image parallel-acquisition type) in which the frame-integrated image acquisition function of the present invention is implemented. 
         FIG. 34  is a diagram for explaining an outline of scanning of extremely low magnification image acquisition (integrated image parallel-acquisition type) of the present invention. 
         FIG. 35  is a diagram for explaining the outline of scanning of extremely low magnification image acquisition (integrated image parallel-acquisition type) of the present invention. 
         FIG. 36  is a diagram for explaining the outline of scanning of extremely low magnification image acquisition (integrated image parallel-acquisition type) of the present invention. 
         FIG. 37  is a diagram for explaining the outline of scanning of extremely low magnification image acquisition (integrated image parallel-acquisition type) of the present invention. 
         FIG. 38  is a diagram for explaining the outline of scanning of extremely low magnification image acquisition (integrated image parallel-acquisition type) of the present invention. 
         FIG. 39  is a diagram for explaining the outline of scanning of extremely low magnification image acquisition (integrated image parallel-acquisition type) of the present invention. 
         FIG. 40  is a GUI when the extremely low magnification image (integrated image parallel-acquisition type) of the present invention is acquired. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The accompanying drawings illustrate specific examples according to the principle of the present invention, but these are for understanding of the present invention and are not used to limitedly interpret the present invention in any way. 
     The embodiments described below relate to an image forming apparatus for forming an image by integrating image data obtained by a charged particle beam device for scanning a charged particle beam at a high speed, and more particularly to a function of forming an image by integrating image data in units of frames. 
     Comparative Example 
       FIG. 1  is a diagram for explaining an outline of a scanning electron microscope, which is an example of a snorkel lens type scanning electron microscope (SEM). 
     The scanning electron microscope includes an electron optical system constituted with optical elements such as an electron gun  102 , a focusing lens  104 , a deflection coil  105 , and an objective lens  106 . 
     A sample  107  is disposed on a sample stage  108  in a vacuum column  101 . A predetermined position of the sample  107  is irradiated with an electron beam  103  generated by the electron gun  102 . The electron beam  103  is focused by the focusing lens  104  and further narrowed by the objective lens  106 . The electron beam  103  is controlled to be deflected by the deflection coil  105 . Secondary electrons, reflected electrons, and other secondary signals are generated from a surface of the sample  107  irradiated with the electron beam  103 . These secondary signals are detected by a detector  110 . 
     An information processing unit  117  is a control unit that comprehensively controls the scanning electron microscope. The information processing unit  117  controls a lens control unit (not illustrated), a stage control unit  118 , a deflection control unit  119 , and an image processing unit  113  by a control signal  123 . 
     For example, the information processing unit  117  includes a processor (also, referred to as a computation unit) and a storing unit (for example, a memory or the like). The information processing unit  117  may be realized by executing a program of desired computation processing by a processor. 
     The information processing unit  117  is connected to an information input device  120 . That is, the information processing unit  117  has an interface with an external device. The information input device  120  is, for example, a keyboard, a mouse, or the like. The information processing unit  117  is connected to an information transmission apparatus  121 . The information processing unit  117  displays a state of each portion which is a management target and the detected image on a display device (for example, a monitor or the like) of the information transmission apparatus  121 . 
     The sample stage  108  is controlled by a stage control unit  118 . Deflection of the electron beam  103  is controlled by a deflection control unit  119 . The deflection control unit  119  controls a deflection current to be supplied to the deflection coil  105  to change magnetic field strength and causes the electron beam  103  to scan in the horizontal direction and the vertical direction. The deflection control unit  119  also supplies a signal (deflection signal  122 ) for controlling the degree of deflection to an image processing unit  113 . Lens intensities of the focusing lens  104  and the objective lens  106  are adjusted by a lens control unit (not illustrated). The image processing unit  113  detects the secondary signal generated in synchronization with scanning by the deflection signal through the detector  110 . 
     The signal detected by the detector  110  is amplified by an amplifier  111  and converted into a digital signal by an analog-to-digital converter (ADC)  112 . Image data converted to digital is input to a multiplier  115  in the image processing unit  113 . The multiplier  115  multiplies image data converted to digital described above by a coefficient K 1 . The coefficient K 1  is set by the image processing unit  113 . The multiplied image data is input to an adder  116 . The adder  116  adds the input image data and image data read from a frame memory  114 , and outputs the added image data  124  to the frame memory  114  and the information processing unit  117 . 
     The image processing unit  113  stores the image data  124  in the frame memory  114 . In this case, the image processing unit  113  receives the deflection signal from the deflection control unit  119  as described above, and generates an address (pixel unit) of the two-dimensional coordinate for storing image data in the frame memory based on the deflection signal. According to this address, the image processing unit  113  stores the image data  124  output from the adder  116  in the frame memory  114 . Similarly, the image processing unit  113  reads image data stored in the frame memory  114  according to the address of the two-dimensional coordinate and inputs the image data to the adder  116 . The information processing unit  117  outputs the image data  124  to the display unit of the information transmission apparatus  121 . 
     Next, a conventional integration processing will be described based on the configuration described above. Since the multiplier  115 , the adder  116 , and the frame memory  114  are configured as described above, the image data detected by the detector  110  according to deflection control and image data one scan before (one frame before) stored in the frame memory  114  are input to the adder  116 . The image data detected by the detector  110  is multiplied by the coefficient K 1  by the multiplier  115 . Here, the coefficient K 1  is a reciprocal of an integration number N. 
       FIG. 2  is an internal configuration diagram of the image processing unit  113  and  FIG. 3  is an expression expressing integration process. I i (x,y) represents pixel data corresponding to x, y coordinates. I i (x,y) is input to a multiplier  201 . The multiplier  201  multiplies I i (x,y) by the coefficient K 1  (1/N), and outputs multiplied data to an adder  202 . S i (x,y) represents pixel data corresponding to the x, y coordinates of the i-th frame input to a frame memory  203 . S i-1 (x,y) represents pixel data corresponding to the x, y coordinates of the (i−1)-th frame output from the frame memory  203 . A calculation expression of S i (x,y) is as expressed in Expression (1-a) of  FIG. 3 . The adder  202  executes integration processing of the multiplied data (I i (x,y)/N) and the pixel data S i-1  (x, y) one frame before, and the pixel of the i-th frame and outputs data S i (x,y). 
     The calculation expression of the integrated pixel data S N (x,y) is as expressed in Expression (1-b) of  FIG. 3 . S N (x,y) means that pixel data corresponding to the x, y coordinates of an input frame is added from a first frame to an integration number N-th frame and is divided by the integration number N. The image processing unit  113  multiplies input pixel data by a reciprocal of the integration number N and adds the multiplied pixel data by the number of integration N times, thereby averaging processing of the pixel data. 
     Due to the computation processing described above, a luminance value of averaged pixel data becomes a luminance value “1” to be obtained originally when addition of an N-th integration is completed. In the present specification, the luminance value “1” defines a luminance value of a pixel obtained when the luminance value of the input pixel is added N times and is divided by N as “1”. 
     As is generally known, detection signals such as reflected electrons and secondary electrons are invariable in time and thus, correlation between frames is extremely large. In contrast, noise generated in a process of signal detection often contributes randomly and there is almost no correlation between frames. Accordingly, it is possible to reduce noise components and improve the S/N ratio of the image can be improved by an averaging processing (frame integration processing) between frames. 
       FIG. 4  illustrates an operation flow for obtaining a frame-integrated image using a frame integration circuit having the configuration described above after an observation region for which a frame-integrated image is intended to be acquired is determined by searching a viewing field.  FIG. 5  illustrates a graphical user interface (GUI) for acquiring frame-integrated images. 
     A screen  401  is displayed on the display device of the information transmission apparatus  121 . The user starts acquiring the frame-integrated image (STEP  301 ). Next, the user inputs a frame integration number for the observation region to a setting unit  402 , and presses a setting button  403  (STEP  302 ). In this case, when the integration number is small, an image with poor S/N ratio may be obtained. When the integration number is large, by excessive electron beam irradiation, sample destruction can be caused, contamination can be generated, a sample can be charged up, or an image on which the influence of luminance value saturation and drift is superimposed can be obtained. The user needs to set an optimal integration number for obtaining an image having image quality expected by the user, but it is difficult to ascertain the optimal integration number in advance. 
     After setting the integration number, the user presses a frame-integrated image acquisition button  405  to execute integrated image acquisition (STEP  303 ). The scanning electron microscope executes a frame integration scan and an integration computation process. The frame-integrated image is displayed on an image display window  404  (STEP  304 ). The user confirms whether the image displayed on the image display window  404  is the image having image quality expected by the user (STEP  305 ). When it is an image having the image quality expected by the user, the frame-integrated image acquisition is ended (STEP  306 ). However, when it is not the image having the image quality expected by the user, it is necessary to reset the integration number again, execute screen acquisition, and confirm an acquired image (STEP  302  to STEP  305 ). The user needs to repeat operations of STEP  302  to STEP  305  until the image having the image quality expected by the user can be acquired. 
     The frame integration number to be set is greatly influenced by composition elements and structures of the sample and observation conditions (accelerating voltage, irradiation yield, degree of vacuum, working distance (WD), and the like). For that reason, it is difficult to ascertain the optimum integration number considering the structure of the sample and observation conditions when the frame-integrated image is acquired. Accordingly, conventionally, cases where the operations of STEP  302  to STEP  305  are repeated to obtain the optimum integration number to acquire the frame-integrated image often occur. 
     As a result, conventionally, there were the following problems. 
     (a) It takes time and effort to perform repetitive image acquisition. 
     (b) Since image acquisition is repeatedly performed, the image acquisition time increases. 
     (c) The electron beam irradiation time for the sample is increased (electron beam irradiation amount increases) by the b. There is a high possibility of causing secondary problems such as an increase in the amount of electron beams with which the sample is to be irradiated, causing sample destruction, causing occurrence of contamination, and charging the sample. 
     In the method described above, for the frame-integrated image, the input pixel data is divided by a frame integration number N which is set in advance and integration processing with pixel data one frame past is executed. This integration processing is repeated until the N-th frame. Here, when it is assumed that definition of the luminance value “1” is as described above, the luminance value of the frame-integrated image of a first frame becomes 1/N and a frame-integrated image up to a second frame is 2/N. Accordingly, the luminance value of the conventional frame-integrated image becomes the “number of input images/integration number N” in the integration process. Therefore, in order for the luminance value to be “1”, it is necessary to wait for integration processing up to the N-th frame. As such, since the conventional frame-integrated image is initially in a dark state in the integration process and thereafter gradually becomes a bright state, the user cannot confirm the image in the integration process. 
     First Embodiment 
     In the following, embodiments for solving the above problem will be described.  FIG. 6  illustrates an example of a charged particle beam device according to a first embodiment, which is an example of a snorkel lens type scanning electron microscope (SEM). 
     In the following description, a scanning electron microscope, which is an example of a charged particle beam device, will be described as an example, but is not limited thereto. The present invention can also be applied to other charged particle beam devices such as an ion beam apparatus for synthesizing secondary signals such as images to form a combined signal. 
     Means for realizing an image processing part in the following embodiment may be subjected to function realization by software or by hardware. In the following example, function realization by hardware will be described. 
     The scanning electron microscope includes an electron optical system (charged particle beam optical system) constituted with optical elements such as an electron gun (charged particle beam source)  502 , a focusing lens  504 , a deflection coil  505 , and an objective lens  506 . The electron beam optical system may include other constituent elements (lens, electrode, and the like) other than the components described above, and is not limited to the configuration described above. 
     A sample  507  is disposed on a sample stage  508  in a vacuum column  501 . A predetermined position of the sample  507  is irradiated with an electron beam  503  generated by the electron gun  502 . The electron beam  503  is focused by the focusing lens  504  and further narrowed by the objective lens  506 . The electron beam  503  is controlled to be deflected by the deflection coil  505 . Secondary electrons, reflected electrons, and other secondary signals are generated from a surface of the sample  507  irradiated with the electron beam  503 . These secondary signals are detected by a detector  510 . 
     An information processing unit  517  is a control unit that comprehensively controls the scanning electron microscope. The information processing unit  517  controls a lens control unit (not illustrated), a stage control unit  518 , a deflection control unit  519 , an image processing unit  513 , and an image evaluation unit  522  by a control signal  523 . 
     For example, the information processing unit  517  includes a processor (also, referred to as a computation unit) and a storing unit (for example, a memory or the like). The information processing unit  517  may be realized by executing a program of desired computation processing by a processor. 
     The information processing unit  517  is connected to an information input device  520 . That is, the information processing unit  517  has an interface with an external device. The information input device  520  is, for example, a keyboard, a mouse, or the like. The information processing unit  517  is connected to an information transmission apparatus  521 . The information processing unit  517  displays a state of each portion which is a management target and the detected image on a display device (for example, a monitor or the like) of the information transmission apparatus  521 . 
     The image processing unit  513  executes integration processing of the image data obtained from the secondary signal and outputs an integrated image. The image processing unit  513  includes a frame memory  514 , a multiplier  515 , a multiplier  525 , and an adder  516 . 
     The sample stage (stage)  508  is controlled by a stage control unit  518 . Deflection of the electron beam  503  is controlled by a deflection control unit  519 . The deflection control unit  519  controls a deflection current to be supplied to the deflection coil  505  to change magnetic field strength and causes the electron beam  503  to scan in the horizontal direction and the vertical direction. The deflection control unit  519  also supplies a signal (deflection signal  524 ) for controlling the degree of deflection to an image processing unit  513 . Lens intensities of the focusing lens  504  and the objective lens  506  are adjusted by a lens control unit (not illustrated). The image processing unit  513  detects the secondary signal generated in synchronization with scanning by the deflection signal through the detector  510 . 
     The signal detected by the detector  510  is amplified by an amplifier  511  and converted into a digital signal by an ADC  512 . Image data converted to digital is input to a multiplier  515  in the image processing unit  513 . The multiplier  515  multiplies image data converted to digital described above by a first coefficient K 2  and outputs first image data (K 2 ×image data). The first coefficient K 2  is set by the image processing unit  513 . The first image data (K 2 ×image data) is input to the adder  516 . The image data  527  one frame past is input from a frame memory  514  to a multiplier  525 . The multiplier  525  multiplies image data  527  one scan before (one frame before) by a second coefficient K 3  and outputs second image data (K 3 ×image data). The second coefficient K 3  is set by the image processing unit  513 . The second image data (K 3 ×image data) is input to the adder  516 . The adder  516  adds the first image data (K 2 ×image data) from the multiplier  515  and the second image data (K 3 ×image data) from the multiplier  525 , and adds added image data  528  to the frame memory  514 , the information processing unit  517 , and the image evaluation unit  522 . 
     The image processing unit  513  stores the image data  528  in the frame memory  514 . In this case, the image processing unit  513  receives the deflection signal from the deflection control unit  519  as described above, and generates an address (pixel unit) of the two-dimensional coordinate for storing image data in the frame memory  514  based on the deflection signal. According to this address, the image processing unit  513  stores the image data  528  output from the adder  516  in the frame memory  514 . The information processing unit  517  outputs the image data  528  to a display unit of the information transmission apparatus  521 . The image evaluation unit  522  evaluates the image data  528  and outputs an evaluated result  526  to the information processing unit  517 . The information processing unit  517  controls an integration scan and integration processing of the image processing unit  513  based on the evaluated result  526 . 
     Next, integration processing of the present embodiment will be described based on the configuration described above.  FIG. 7  is an internal configuration diagram of the image processing unit  513  and  FIG. 8  is an expression representing integration processing. The image processing unit  513  includes an integration counter  601 , a first coefficient calculation unit  602 , a second coefficient calculation unit  603 , a multiplier  604 , a multiplier  605 , an adder  606 , and a frame memory  607 . 
     I i (x,y) represents pixel data corresponding to the x, y coordinates of an i-th frame input from the detector  510  via the amplifier  511  and the ADC  512 . I i (x,y) is input to the multiplier  604 . The integration counter  601  counts and identifies what frame number of image data that is currently detected and inputted based on the deflection signal input from the deflection control unit  519 . The integration counter  601  outputs a frame count value i to the first coefficient calculation unit  602 . The first coefficient calculation unit  602  outputs the reciprocal of the input frame count value i as a first coefficient K 2  (Expression (6-d) in  FIG. 8 ). The first coefficient calculation unit  602  outputs the first coefficient K 2  to the multiplier  604  and the second coefficient calculation unit  603 . The second coefficient calculation unit  603  calculates a second coefficient K 3  based on the value of the first coefficient K 2 . The second coefficient K 3  is calculated as in Equation (6-e) in  FIG. 8 . Accordingly, the sum of the first coefficient K 2  and the second coefficient K 3  is 1 (K 2 +K 3 =1) (Expression (6-c) in  FIG. 8 ). 
     The multiplier  604  multiplies I i (x,y) by the first coefficient K 2  and outputs multiplied data to the adder  606 . S i (x,y) represents pixel data corresponding to the x, y coordinates of the i-th frame input to the frame memory  607 . Also, S i-1 (x,y) represents pixel data corresponding to the x, y coordinates of the (i−1)-th frame from the frame memory  607 . The multiplier  605  multiplies (x,y) by the second coefficient K 3  and outputs multiplied data to the adder  606 . The calculation expression of S i (x,y) is as illustrated in Equation (6-b) in  FIG. 8 . The adder  606  executes integration processing of the multiplied data (K 2 ×I i (x,y)) and the multiplied data (K 3 ×S i-1 (x, y)) and outputs i-th frame pixel data S i (x,y). 
     From the matters as described above, the first coefficient K 2  and the second coefficient K 3  vary according to the input frame count value i of the integration counter  601 . The sum of the first coefficient K 2  and the second coefficient K 3  is always “1”. This means that the luminance value of the integrated image is always “1” in the integration process. That is, in the present embodiment, a normalization process (hereinafter, referred to as a normalization integration computation) is realized in such a way that the luminance value of the integrated image is always “1” in the integration process. From the matters as described above, matters in which the integration computation result is represented in the case where the integration number is N is expressed in Equation (6-f) in  FIG. 8  based on the normalization integration computation. This computation result is exactly the same integration result as the conventional frame integration computation result illustrated in Equation (1-b) in  FIG. 3 , and averaging processing of pixel data similar to the conventional frame integration computation is realized. 
     From the matters as described above, the frame normalization integration computation of the present embodiment is a method that can always output the integrated image being integrated with its luminance value which is in a state of being “1”, in addition to averaging processing of image luminance values which the conventional frame integration computation is realizing. 
     Next, while illustrating an internal processing flow and an operation flow of the user, the means for realizing the image acquisition by the frame normalization integration computation of the present embodiment and the effect thereof will be described in detail.  FIG. 9  illustrates a processing flow for obtaining a frame-integrated image using a frame integration circuit having the configuration described above.  FIG. 10  illustrates a GUI for acquiring the frame-integrated image.  FIG. 12  illustrates the operation flow of the user. 
     A screen  801  is displayed on a display device of the information transmission apparatus  521 . When an observation region for which a frame-integrated image is intended to be acquired is determined, the user executes image acquisition (STEP  701 ). An execution instruction is input from the information input device  520  to the information processing unit  517 , and the integration scan by one frame is executed (STEP  702 ). 
     Detected image data is input to the image processing unit  513 , and the normalization integration computation described above is applied thereto. In this case, a count value of the integration counter  601  becomes “1”, and it is recognized as an integrated image of the first frame. A value corresponding to the first frame is set for the first coefficient K 2  and the second coefficient K 3 , and the integration computation is performed. After the normalization integration computation, the image processing unit  513  outputs frame-integrated image data to the frame memory  514 , the information processing unit  517 , and the image evaluation unit  522 . The frame-integrated image data output to the frame memory  514  is stored in the frame memory  514  as integrated image data of the first frame (integrated image data to which one-time integration is applied). The integrated image data output to the information processing unit  517  is transferred to the information transmission apparatus  521  and displayed as a frame-integrated image in an image display window  805 . 
     The image evaluation unit  522  evaluates the input frame-integrated image data (STEP  703 ). The image evaluation unit  522  determines whether the frame-integrated image data obtained by the normalization integration process satisfies a certain evaluation condition or not. When the image is better than an image having image quality expected by the user (for example, when the frame-integrated image data satisfies the evaluation condition described later), the image evaluation unit  522  transmits a scan stop instruction to the information processing unit  517  (STEP  704 ). When the stop instruction is received, the information processing unit  517  stops the integration scan and ends acquisition of the frame-integrated image (STEP  705 ). 
     On the other hand, in a case where the image is not better than an image expected by the user, the image evaluation unit  522  transmits an instruction to continue the integration scan to the information processing unit  517 , and the information processing unit  517  executes the integration scan for the next frame (Step  702 ). Image data of the second frame detected by the second the integration scan is input to the image processing unit  513 , and the normalization integration computation described above is applied thereto. In this case, the count value of the integration counter  601  becomes “2”, which is recognized as an integrated image of the second frame. For the first coefficient K 2  and the second coefficient K 3 , values corresponding to the second frame are set and is subjected to integration computation. After the normalization integration computation, the image processing unit  513  outputs frame-integrated image data to the frame memory  514 , the information processing unit  517 , and the image evaluation unit  522 . The integrated image data output to the frame memory  514  is stored in the frame memory  514  as integrated image data of the second frame (integrated image data to which integration is applied twice). The integrated image output to the information processing unit  517  is transferred to the information transmission apparatus  521  and displayed as a frame-integrated image in the image display window  805 . 
     The image evaluation unit  522  evaluates the input second frame-integrated image (STEP  703 ). In a case where the integrated image is better than an image having image quality expected by the user (for example, in a case where the frame-integrated image data satisfies an evaluation condition to be described later), the process proceeds to STEP  704 , and in a case where the image is not good, the process returns to STEP  702  again. The process of STEP  702  to STEP  703  is repeated until the frame-integrated image becomes better than the image having image quality expected by the user. That is, the image processing unit  513  repeatedly executes the normalization integration computation until the evaluation condition is satisfied. In this case, each time the process described above is repeated, the count value of the integration counter  601  of the normalization integration computation unit is incremented by 1, and the frame integration number i is incremented. 
     From the matters as described above, in the present embodiment, image evaluation is performed on the integrated image being integrated, and integration processing (the integration scan and integration computation) is ended at the time when an expected image is obtained. When automatic evaluation is performed, it is possible to realize frame-integrated image acquisition without being conscious of the number of integration (it is not necessary to set the integration number). This is because an image with the luminance value which is in a state of being “1” can be output during integration by the normalization integration computation. The point of the present embodiment is that the integrated image has the luminance value which is in a state of being “1” can be output during the integration and evaluation can be performed on the integrated image with its luminance value which is in a state of being “1” during the integration. 
     Next, an operation flow of  FIG. 12  will be described together with an operation of the screen of  FIG. 10 . A screen  801  includes a frame integration mode setting portion  802 , a frame integration number display portion  804 , an image display window  805 , an image acquisition execution button  806 , an evaluation method setting button  808 , and an integrated image evaluation value display portion  809 . 
     When an observation region for which a frame-integrated image is intended is determined, the user performs various settings on the screen  801  and executes image acquisition (STEP  901 ). In the frame integration mode setting portion  802 , it is possible to select either an automatic mode or an integration number designation mode. 
     The automatic mode is a mode for performing automatic evaluation by the image evaluation unit  522 . The user sets an image evaluation method in a case of selecting the automatic mode. The user clicks the evaluation method setting button  808 .  FIG. 13  illustrates an evaluation method setting window  1001 . When the evaluation method setting button  808  is clicked, the evaluation method setting window  1001  is displayed. The evaluation method setting window  1001  includes an evaluation method selection portion  1002  and an evaluation reference value setting portion  1003 . The user selects an evaluation method in the evaluation method selection portion  1002 . Details of various evaluation methods displayed here will be described later. With this, it is possible to select an appropriate evaluation method depending on what image the user intends to acquire in image acquisition (according to the definition of the image having image quality expected by the user). Thereafter, the user inputs an evaluation reference value to the evaluation reference value setting portion  1003 . The evaluation reference value input here is a threshold value for determining whether it is image quality expected by the user. The user inputs the evaluation reference value to the evaluation reference value setting portion  1003 , and then clicks the setting button  1004 . The user can also reset the evaluation reference value to a default value of an apparatus device by using the reset button  1005 . In this case, a default evaluation reference value stored in the information processing unit  517  may be set again in the image evaluation unit  522 . 
     The integration number designation mode is a mode in which a frame integration number is designated in advance. In the case of the integration number designation mode, the user inputs the integration number to the integration number setting portion  803 . In this case, integration processing may be executed up to a set integration number, and the integrated image may be evaluated by the user himself/herself. 
     After the setting described above is ended, the user clicks the image acquisition execution button  806  to obtain a frame-integrated image (STEP  902 ). In both the automatic mode and the integration number designation mode, the frame-integrated image is displayed in the image display window  805  for one frame. The integration number of the frame-integrated images is displayed on the frame integration number display portion  804 . In a case where the automatic mode is set, an evaluation value of the selected evaluation method is displayed on the integrated image evaluation value display portion  809 . With the configuration as described above, the user can confirm the frame-integrated image, the integration number, and the evaluation value for one frame. 
     As another example, at the time when integration processing is executed frame by frame and an integrated image displayed in the image display window  805  becomes image quality expected by the user, a function of stopping integration processing by the user&#39;s input may be provided. With this the user can stop integration processing (the integration scan and integration computation) while viewing the frame-integrated image in the integration process. 
     As described above, in the case of the automatic mode, the user can acquire the frame-integrated image only by the operation of “image acquisition execution” without being never conscious of the setting of the integration number. That is, it is not necessary to set the frame integration number. In conventional frame integration processing, in a case where an image having image quality expected by the user cannot be obtained, the integration number has to be set again and a plurality of image acquisition have to be executed. In contrast, in frame integration processing of the present embodiment, it is possible to acquire a frame-integrated image by one image acquisition operation. With this, it is possible to greatly improve time and effort for acquiring the frame-integrated image. It is possible to greatly reduce the time required for image acquisition. 
     The present embodiment has the following effects. 
     (a) In contrast to the conventional plural image acquisition operations, in the present embodiment, a frame-integrated image is obtained by one image acquisition operation. 
     (b) In the present embodiment, it is possible to perform the integration scan with the minimum required number of integration by one image acquisition operation. 
     (c) By both effects described above, it is possible to reduce the irradiation time of the electron beam with which the sample is irradiated as much as possible. 
     (d) By suppressing the amount of electron beam with which the sample is irradiated to be minimized, it is possible to obtain secondary effects that suppresses sample destruction, contamination generation, generation of luminance value saturation and drift due to the influence of charging to be minimized. 
     Next, the definition of the “image having image quality expected by the user” described above will be described. As an image having image quality expected by the user, for example, an image having a good SN ratio, an image in which the degree of SN improvement is saturated, an image without an influence of charge (an image without luminance value saturation due to charge, an image without drift due to charge), and the like are included. In the present embodiment, the definition of the “image having image quality expected by the user” is switched according to what image the user intends to acquire in the image acquisition. 
       FIG. 11  illustrates another example of the image display window  805 . Information other than the frame-integrated image may be displayed in the image display window  805 . For example, an image evaluation value (numerical value)  811  and an image evaluation graph  812  to be described below may be displayed in the image display window  805 . 
     Next, an image evaluation method will be described. An execution subject of an evaluation process described below is the image evaluation unit  522 . As the image evaluation method, for example, an evaluation method using the SN ratio as an evaluation index, an evaluation method using the degree of SN improvement as an evaluation index, an evaluation method using a contrast-to-noise ratio (CNR) as an image noise evaluation index, an evaluation method using a histogram as an evaluation index, and the like are included. Accordingly, the evaluation condition of the integrated image is one of the condition using the SN ratio as the evaluation index, the condition using the degree of SN improvement as the evaluation index, the condition using the contrast-to-noise ratio (CNR) as the image noise evaluation index, the condition using the histogram as the evaluation index or a combination thereof may be adopted. 
       FIG. 14  to  FIG. 16  are diagrams for explaining the image evaluation index (SNR). In the case where the SN ratio is used as an evaluation index, an image without noise (or an image having little noise and determined as good by the user) is acquired in advance as a reference image  1101  ( FIG. 14 ). A frame-integrated image  1102  to which the normalization integration computation described above is applied is obtained ( FIG. 15 ). The image evaluation unit  522  calculates the SN ratio between the reference image  1101  and the frame-integrated image  1102  ( FIG. 16 ). When the calculated SN ratio reaches a value equal to or greater than a SN ratio (evaluation reference value) by the user, the integration scan and integration computation is ended. 
       FIGS. 17 to 20  are diagrams for explaining the image evaluation index (degree of SN improvement). The degree of SN improvement means the degree of the difference in luminance value between the current integrated image and the integrated image one frame before. The difference value is used as an evaluation index. Matters that the difference value becomes smaller is assumed that the SN ratio of each integrated image becomes better. That is, it is a method of indirectly determining the state of the SN ratio of each integrated image by representing (quantifying) the degree of S/N ratio improvement between the integrated images by the difference value of the luminance value of the integrated image and using this difference value as an evaluation index (using the degree of SN ratio improvement as an evaluation index). 
     That is, the SN ratio is indirectly evaluated using the following relationship. 
     The SN ratio of each integrated image is improved. 
     The luminance value of each integrated image is focused on the signal component (there is no noise component). 
     The luminance value difference between the integrated images becomes zero. 
     In  FIG. 17 , the reference numeral  1201  denotes the difference value δ i  of the luminance value between frames in the process of performing the integration processing using the integration number N.  FIG. 18  illustrates an expression of the difference value δ i (x, y) of the luminance value. δ i (x, y) represents the difference between S i (x, y) and S i-1  (x, y) corresponding to the x and y coordinates. 
       FIG. 19  illustrates a graph  1202  illustrating the relationship of the difference value of the luminance value with respect to the number of times of integration. As illustrated in the graph  1202 , the image evaluation unit  522  may determine whether the difference value of the luminance value is less than a predetermined threshold value δth. The image evaluation unit  522  may use an inclination of a curve as an evaluation index, and determine whether the inclination is less than a predetermined threshold value. In a case where the conditions described above are satisfied, the integration scan and the integration computation are ended. 
       FIG. 20  illustrates an example  1203  in which a range is set for a threshold value. A range designation to some extent may be performed with respect to a threshold value of the difference value of the luminance value and a threshold value of the inclination. The characteristics of the relationship between the difference value of the luminance value and the number of times of integration varies depending on an observation sample and an observation condition (optical condition). Accordingly, as illustrated in  FIG. 20 , the evaluation reference value may not be fixed and an evaluation condition having a certain range may be set. 
       FIGS. 21 to 22  are diagrams for explaining the image evaluation index (CNR: Contrast-to-noise ratio). This evaluation method is a method of determining a noise amount of image using the CNR. Naturally, the detected signal is represented as a luminance value in the image. The amount of noise is evaluated by using a luminance value contrast of a noise-free signal component (grayscale difference in a luminance value between a pixel having the largest signal amount and a pixel having smallest signal amount) and luminance value variation which is the noise component. The image evaluation unit  522  may calculate the CNR in each integrated image and compare the CNR with the evaluation reference. The image evaluation unit  522  may determine that the integrated image expected by the user is acquired at the time when the CNR exceeds the evaluation reference value. 
     Next, a histogram evaluation method will be described. In a case where a histogram of luminance values is used as an evaluation index, a histogram representing a frequency distribution of luminance values of pixels constituting a frame image is used. The image evaluation unit  522  may evaluate at least one of the expected grayscale, the degree of noise removal, brightness, and contrast using statistical values such as an average value and standard deviation of the histogram. The image evaluation unit  522  may determine that the integrated image that is equal to or greater than the image quality expected by the user is acquired if the statistical value exceeds a fixed evaluation reference value. 
       FIG. 23  illustrates an internal configuration of the image evaluation unit  522 . The image evaluation unit  522  includes the functions described in the example described above, that is, a histogram evaluation module  1401 , an SN ratio evaluation module  1402 , an SN improvement degree evaluation module  1403 , and a CNR evaluation module  1404 . The information processing unit  517  transmits an evaluation method which is set by the evaluation method selection portion  1002  to the image evaluation unit  552 . The image evaluation unit  522  selects an evaluation module corresponding thereto and executes image evaluation of input integrated image data  1411 . The image evaluation unit  522  returns an evaluation result  1412  to the information processing unit  517 . 
     Although the evaluation reference value used by the image evaluation unit  522  at the time of image evaluation is prepared in the apparatus in advance, the reference value may be changed by the user. With this, it is possible to acquire a frame-integrated image that is close to an image expected by the user. 
     In the automatic mode, in order to avoid that the evaluation value does not reach the evaluation reference value even if integration processing is repeated and the frame-integrated image cannot be acquired forever, an upper limit value of the integration number may be set in the information processing unit  517 . In a case where the upper limit value of the integration number reaches the upper limit value (in a case where a count value of the integration counter  601  reaches the upper limit value), the information processing unit  517  may forcibly end acquisition of the integrated image. For ease of use, it is also possible to consider a case the user may want to acquire an integrated image with as little noise as possible by setting the integration number to large. In this case, the upper limit of the number of integration may be set to large. 
     In the present embodiment, a frame normalization integration function capable of computing (outputting) the luminance value of the integrated image always in a state of “1” in the frame integration process and an image evaluation function capable of performing image evaluation of the integrated image in the frame integration process, and it is possible to automatically end the frame-integrated image acquisition process at the time when the integrated image expected by the user is obtained. 
     In the present embodiment, the user can confirm information on the relationship between the frame-integrated image and the integration number. This has the following advantages. 
     (a) It is possible to obtain reference information at the time of acquiring an image using conventional frame-integrated image acquisition (integration number designation mode). 
     (b) It is possible to know the relationship between occurrence of sample destruction, occurrence of contamination, luminance value saturation, and drift caused by charging and the integration number, as reference information. 
     (c) It is possible to know the relationship between the integration number and image evaluation information, and the relationship between the integration number and the degree of improvement in the integration process. 
       FIG. 24  is a diagram for explaining the effect of display in the frame integration process of the present embodiment. In the frame normalization integration computation of the present embodiment, an integrated image of luminance value 1 even during integration can be output. Conventionally, when acquisition of a frame-integrated image having a large number of integration numbers is performed, in image display being integrated, as illustrated in the upper part of  FIG. 24 , dark display continues for a long time period of several tens of seconds from the start of integration, there was a problem of giving a sense of discomfort to the user. In contrast, in the frame normalization integration computation of the present embodiment, since the integrated image in the state can be instantaneously displayed from the first start of integration, as illustrated in the lower part of  FIG. 24 , image display without giving a sense of discomfort to the user is possible. 
     Conventionally, since the luminance value at the start of integration is not “1” as described above, it was image display by which it was difficult to confirm the S/N improvement process by integration computation. In contrast, in the present embodiment, the S/N improvement process can also be confirmed and usability is further improved. 
     Second Embodiment 
     In this embodiment, an example in which the frame-integrated image acquisition function of the first embodiment is applied to an extremely low magnification image creation function will be described. 
     In general, an electron microscope such as an SEM is effective for observation at high magnification, but display with low magnification is not good. The magnification of the electron microscope can be displayed at a maximum of several ten thousand times to several hundreds of thousands times or several million times, whereas the lowest magnification is on the order of several times to several tens of times. For example, the lowest magnification observable with the SEM is generally about 5 to 50 times. If the whole sample can be observed at lowest magnification, the viewing field search can be gradually shifted to high magnification from the state in which the viewing field is widened, that is, from the state in which it is displayed at low magnification, and gradually narrows the viewing field. However, if the entire sample cannot be observed even at the lowest magnification, it is necessary to move the stage and perform the viewing field search, and a work to finally find a place intended to be observed on the sample becomes difficult. 
     Accordingly, PTL 6 has been proposed as a solution method for the viewing field search in a condition that the entire region of the sample cannot be observed even at the lowest magnification. This is to divide the sample into a plurality of regions, acquire respective observation images, and join the observation images on a memory so as to create an extremely low magnification image of the entire sample, thereby overcoming the problem described above. Firstly, this overview will be described. 
     Since an example of a configuration of the charged particle beam apparatus described here is the same as that in  FIG. 1 , the description thereof will be omitted. Further, frame integration processing here is the same as that described in  FIGS. 2 and 3 . 
       FIG. 25  illustrates a processing flow of creating a conventional extremely low magnification image, and  FIG. 26  illustrates an outline of scanning of creating an extremely low magnification image.  FIG. 27  illustrates a GUI for acquiring an extremely low magnification image. 
     A screen  1801  is displayed on the display device of the information transmission apparatus  121 . The user decides the observation region for which the frame-integrated image is intended to be acquired, performs various setting, and then executes low magnification image acquisition (STEP  1601 ). When an execution instruction is received, the information processing unit  117  moves the sample stage (stage)  108  to the initial coordinates via the stage control unit  118  based on coordinate data set on the screen  1801  (STEP  1602 ). 
     Next, the information processing unit  117  sets the coefficient K 1  of the multiplier  115  based on the frame integration number set on the screen  1801 . The information processing unit  117  sets the scanning speed (integration number) and the number of scanning lines in the deflection control unit  119  (STEP  1603 ). Next, the information processing unit  117  sets a recording range of the frame memory  114  (STEP  1604 ). The information processing unit  117  sets a recording start point of the frame memory  114  in a region corresponding to the stage position (STEP  1605 ). 
     Next, the image processing unit  113  executes conventional frame integration processing ( FIGS. 2 and 3 ) and stores the frame-integrated image in the frame memory  114  (STEP  1606 ).  FIG. 26  illustrates an example in which the sample is divided into a plurality of regions. In this example, the sample is divided into 16 regions. An image acquisition target region at this time is region  1  ( 1701 ). The image processing unit  113  performs conventional frame integration processing ( FIG. 2  and  FIG. 3 ) for the region  1  ( 1701 ). 
     When the frame-integrated image acquisition is completed, the information processing unit  117  confirms whether the stage position is the final region  16  ( 1703 ) or not (STEP  1607 ). In a case where it is the final region  16  ( 1703 ), acquisition of the extremely low magnification image is ended (STEP  1609 ). 
     Since the frame-integrated image of the region  1  ( 1701 ) is now acquired, the information processing unit  117  moves the stage to the next region  2  ( 1702 ) via the stage control unit  118  (STEP  1608 ). 
     Thereafter, STEP  1605  to STEP  1608  are repeated until the frame-integrated image of region  16  ( 1703 ) is acquired. For example, as illustrated in  FIG. 26 , the image processing unit  113  acquires frame-integrated images along the order of dotted arrows. After the frame-integrated image of the entire region is acquired, the information processing unit  117  transfers image data of the entire region to the information transmission apparatus  121 . 
     Next, the operation flow of  FIG. 28  will be described together with the operation of the screen of  FIG. 27 . The screen  1801  includes an image display window  1802 , an extremely low magnification image setting portion  1803 , a division number setting portion  1804 , an integration mode setting portion  1805 , and an image acquisition execution button  1807 . 
     When the observation region for which an extremely low magnification image is intended to be determined is determined, the user sets the size and coordinates of the extremely low magnification image in the extremely low magnification image setting portion  1803  (STEP  1901 ). Next, the user sets the division number of the image in the division number setting portion  1804 . In the present example, the division number is set to 16 (STEP  1902 ). The user may set the size of the divided image in the division number setting portion  1804 . In this case, the region which is set in the extremely low magnification image setting portion  1803  is divided by the designated image size. 
     Next, a scanning method of the divided image is set. In general, as a method of integrating images, there are a method of integrating in continuous time in pixel units and a method of integrating in units of frames. In this example, since frame integration becomes a target, a case of setting the frame integration number is described. The user selects the frame integration mode in the integration mode setting portion  1805 , and sets the integration number in the integration number setting portion  1806  (STEP  1903 ). Accordingly, the same integration number is set for all the divided regions. The number of scanning lines and the size of the horizontal pixel when acquiring a divided image are the same as those described in PTL 6. The information processing unit  117  automatically calculates the number of scanning lines and the horizontal pixel size based on information of the division number setting portion  1804 . 
     When various setting described above is completed, the user clicks the image acquisition execution button  1807  to execute acquisition of the extremely low magnification image (STEP  1904 ). When the frame-integrated images of all the divided regions are acquired by the flow described in  FIG. 25 , the information processing unit  117  transfers these frame-integrated images to the display device of the information transmission apparatus  121 . The extremely low magnification image is displayed on the image display window  1802  (STEP  1905 ). As illustrated in  FIG. 27 , in the image display window  1802 , the frame-integrated images of all the divided regions are displayed in a form joined together. 
     Next, the user confirms the extremely low magnification image of the image display window  1802  (STEP  1906 ). Here, in a case where the obtained extremely low magnification image is an image having image quality expected by the user, acquisition of the low magnification image is ended (STEP  1907 ). On the other hand, in a case where the acquired extremely low magnification image is not an image having image quality expected by the user, the integration number needs to be set again to acquire the frame-integrated image of the region which becomes a target. In  FIG. 27 , an image having image quality that is not expected by the user is acquired in a divided region  1808 , and an image having an image quality expected by the user is acquired in another divided region  1809 . As such, when an image that is not expected by the user is included in the extremely low magnification image, the integration number needs to be set again to acquire the frame-integrated image of the region which becomes the target. That is, the user needs to repeat STEP  1903  to STEP  1906  until an extremely low magnification image to be expected is obtained. 
     In this example, the same integration number is uniformly set for all the divided regions, but a method of setting the integration number for each region is also conceivable. However, as described above, the frame integration number to be set is greatly influenced by the composition elements and structures of the sample, and observation conditions (accelerating voltage, irradiation yield, degree of vacuum, WD, and the like). For that reason, it is difficult to ascertain the optimum integration number considering the structure of the sample and observation condition in advance when the frame-integrated image is acquired. Accordingly, conventionally, cases where the operations of STEP  1903  to STEP  1906  are repeated to obtain the optimum integration number to acquire the frame-integrated image often occur. 
     As a result, conventionally, there were the following problems. 
     (a) It takes time and effort to perform repetitive image acquisition. 
     (b) Since image acquisition is repeatedly performed, the image acquisition time increases. 
     (c) The electron beam irradiation time for the sample is increased (electron beam irradiation amount increases) by the b. There is a high possibility of causing secondary problems such as an increase in the amount of electron beams with which the sample is to be irradiated, causing sample destruction, causing occurrence of contamination, and charging the sample. In particular, as the number of divided regions M increases, the above problem increases by M times. 
     In the following, embodiments for solving the above problem will be described. An example of the charged particle beam apparatus configuration according to the present embodiment is the same as that in  FIG. 6  and thus, description thereof is omitted. Frame integration processing here is the same as that described with reference to  FIGS. 7 and 8 . 
     In the following description, a scanning electron microscope, which is an example of a charged particle beam apparatus, will be described as an example, but is not limited thereto. The present invention can also be applied to other charged particle beam devices such as an ion beam device for combining secondary signals such as images to form a combined signal. 
     Means for realizing an image processing part in the following embodiment may be subjected to function realization by software or by hardware. In the following example, function realization by hardware will be described. 
     Each of the plurality of divided regions in the sample  507  is irradiated with the electron beam  503  in the electron beam optical system and the image processing unit  513  outputs the integrated image obtained by the normalization integration computation with respect to each of the plurality of divided regions. The image processing unit  513  updates the integrated image on the display unit of the information transmission apparatus  521  according to the number of times of execution of integration processing (normalization integration computation) for each of the plurality of divided regions. The image processing unit  513  determines the end of integration processing according to image quality of the integrated image for each of the plurality of divided regions. 
     In detail, the image processing unit  513  repeatedly executes the normalization integration computation until the evaluation condition for each of the plurality of divided regions is satisfied. That is, after an image having image quality expected by the user is obtained for one divided region, it moves to the next divided region. Since the image evaluation is performed in each of the plurality of divided regions and the end of the normalization integration computation is determined, there is a case where the number of times of execution (that is, the integration number of integrated images) of the normalization integration computation is different among the plurality of divided regions. 
       FIG. 29  illustrates the processing flow for creating an extremely low magnification image according to the present embodiment, and  FIG. 30  illustrates the outline of scanning for creating the extremely low magnification image.  FIG. 31  illustrates a GUI when the extremely low magnification image is acquired and  FIG. 32  illustrates an operation flow when an extremely low magnification image is obtained. 
     A screen  2201  is displayed on the display device of the information transmission apparatus  521 . The user decides the observation region for which the frame-integrated image is intended to be acquired, performs various setting, and then executes low magnification image acquisition (STEP  2001 ). When an execution instruction is received, the information processing unit  517  moves the sample stage (stage)  508  to the initial coordinates via the stage control unit  518  based on coordinate data set on the screen  2201  (STEP  2002 ). 
     Next, the information processing unit  517  sets the number of scanning lines in the deflection control unit  519  (STEP  2003 ). Next, the information processing unit  517  sets the recording range of the frame memory  514  (STEP  2004 ). The information processing unit  517  sets the recording start point of the frame memory  514  in the region corresponding to the stage position described above (STEP  2005 ). 
     Next, the image processing unit  513  executes the frame normalization integration computation ( FIGS. 7 and 8 ) described in the first embodiment, and stores the frame-integrated image in the frame memory  514  (STEP  2006 ).  FIG. 30  illustrates an example in which the sample is divided into a plurality of regions. In this example, the sample is divided into 16 regions. The image acquisition target region at this time is region  1  ( 2101 ). The image processing unit  513  executes the frame normalization integration computation ( FIGS. 7 and 8 ) described in the first embodiment for the region  1  ( 2101 ). 
     When the frame-integrated image acquisition is completed, the information processing unit  517  confirms whether the stage position is the final region  16  ( 2103 ) or not (STEP  2007 ). In a case where it is the final region  16  ( 2103 ), acquisition of the extremely low magnification image is ended (STEP  2009 ). 
     Since the frame-integrated image of the region  1  ( 2101 ) is now acquired, the information processing unit  517  moves the stage to the next region  2  ( 2102 ) via the stage control unit  118  (STEP  2008 ). 
     Thereafter, STEP  2005  to STEP  2008  are repeated until the frame-integrated image of region  16  ( 2103 ) is acquired. For example, as illustrated in  FIG. 30 , the image processing unit  513  acquires frame-integrated images along the order of dotted arrows. In this example, after the frame-integrated image of the entire region is acquired, the information processing unit  517  transfers image data of the entire region to the information transmission apparatus  521 . As another example, the information processing unit  517  may transfer the frame-integrated image to the information transmission apparatus  521  every time the frame normalization integration computation is completed. As another example, the information processing unit  517  may transfer the frame-integrated image to the information transmission apparatus  521  when the frame normalization integration computation is completed in one divided region (at the time when the image having image quality expected by the user is obtained). 
     Next, the operation flow of  FIG. 32  will be described together with the operation of the screen of  FIG. 31 . The screen  2201  includes an image display window  2202 , an extremely low magnification image setting portion  2203 , a division number setting portion  2204 , an integration mode setting portion  2205 , an image acquisition execution button  2207 , and an evaluation method setting button  2208 . 
     When the observation region for which an extremely low magnification image is intended to be determined is determined, the user sets the size and coordinates of the extremely low magnification image in the extremely low magnification image setting portion  2203  (STEP  2301 ). Next, the user sets the division number of the image in the division number setting portion  2204 . In the present example, the division number is set to 16 (STEP  2302 ). The user may set the size of the divided image in the division number setting portion  2204 . In this case, the region which is set in the extremely low magnification image setting portion  2203  is divided by the designated image size. 
     Next, a scanning method of the divided image is set. In general, as a method of integrating images, there are a method of integrating in continuous time in pixel units and a method of integrating in units of frames. In this example, since frame integration becomes a target, a case of setting the frame integration number is described. The user selects the frame integration mode and sets the integration number in the integration number in the integration mode setting portion  2205  (STEP  2303 ). The number of scanning lines and the size of the horizontal pixel when acquiring a divided image are the same as those described in PTL 6. The information processing unit  517  automatically calculates the number of scanning lines and the horizontal pixel size based on information of the division number setting portion  2204 . 
     In the integration mode setting portion  2205 , it is possible to select either the automatic mode or the integration number designation mode. The automatic mode is a mode for performing automatic evaluation by the image evaluation unit  522 . The user sets an image evaluation method in a case of selecting the automatic mode. The user clicks the evaluation method setting button  2208 . The window displayed when the evaluation method setting button  2208  is clicked is the evaluation method setting window  1001  illustrated in  FIG. 13 . The method of selecting the evaluation method is the same as that of the first example, and thus description thereof will be omitted. 
     The integration number designation mode is a mode in which a frame integration number is designated in advance. In the case of the integration number designation mode, the user inputs the integration number to the integration number setting portion  2206 . In this case, integration processing may be executed up to the set integration number, and the integrated image may be evaluated by the user himself/herself. As another example, at the time when integration processing is executed frame by frame and an integrated image displayed in the image display window  2202  becomes image quality expected by the user, a function of stopping integration processing by the user&#39;s input and moving to the next divided region may be provided. 
     When various setting described above is completed, the user clicks the image acquisition execution button  2207  to execute acquisition of an extremely low magnification image (STEP  2304 ). When the frame-integrated images of all the divided regions are acquired by the flow described in  FIG. 29 , the information processing unit  517  transfers these frame-integrated images to the display device of the information transmission apparatus  521 . In the image display window  2202 , the extremely low magnification image is displayed (STEP  2305 ). As illustrated in  FIG. 31 , in the image display window  2202 , frame-integrated images of all the divided regions are displayed in a form of being joined together. Here, the frame-integrated image of each divided region is evaluated by the selected evaluation method and is integrated until the evaluation reference value is satisfied. Accordingly, in all the divided regions of the image display window  2202 , images having image quality expected by the user are acquired. By the operation described above, acquisition of the extremely low magnification image is ended (STEP  2306 ). 
     On the screen  2201 , the number of times of executions (that is, the integration number) of frame normalization integration computation of each divided region, the evaluation value of each divided region, and the like may be displayed. The user can confirm the difference in the number of times of execution of the normalization integration computation among the plurality of divided regions, the difference in the evaluation value among the plurality of divided regions, and the like. 
     In the conventional extremely low magnification image acquisition, in a case where the displayed extremely low magnification image is confirmed and an image which does not have image quality expected by the user is included, it is necessary to set the integration number again and repeatedly acquire the repeated integrated image. In contrast, in the present embodiment, similarly as in the first embodiment, it is possible to acquire an extremely low magnification image having image quality expected by the user by one image acquisition operation. 
     As illustrated in the operation flow illustrated in  FIG. 32 , the user can acquire the extremely low magnification image only by the operation of “image acquisition execution” without being never conscious of the setting of the integration number. With this, it is possible to greatly improve time and effort for acquiring the extremely low magnification image. The time spent on image acquisition can also be greatly reduced. 
     The present embodiment has the following effects. 
     (a) In contrast to the conventional plural image acquisition operations, in the present embodiment, a frame-integrated image is obtained by one image acquisition operation. 
     (b) In the present embodiment, it is possible to perform the integration scan with the minimum required number of integration by one image acquisition operation. 
     (c) By both effects described above, it is possible to reduce the irradiation time of the electron beam with which the sample is irradiated as much as possible. 
     (d) By suppressing the amount of electron beam with which the sample is irradiated to be minimized, it is possible to obtain secondary effects that suppresses sample destruction, contamination generation, generation of luminance value saturation and drift due to the influence of charging to be minimized. 
     In a case where it is applied to the extremely low magnification image acquisition function, the effects described above increases by M times according to the number M of division regions. 
     In the automatic mode, in order to avoid that the evaluation value does not reach the evaluation reference value even if integration processing is repeated and the frame-integrated image cannot be acquired forever, an upper limit value of the integration number may be set in the information processing unit  517 . In a case where the upper limit value of the integration number reaches the upper limit value (in a case where a count value of the integration counter  601  reaches the upper limit value), the information processing unit  517  may forcibly end acquisition of the integrated image. For ease of use, it is also possible to consider a case the user may want to acquire an integrated image with as little noise as possible by setting the integration number to large. In this case, the upper limit of the number of integration may be set to large. 
     In the present embodiment, when the frame-integrated images of all the divided regions are acquired, the information processing unit  517  transfers image data of all the divided regions to the information transmission apparatus  521 . The transferred image data is displayed on the image display window  2202 . As another example, the information processing unit  517  may transfer image data to the information transmission apparatus  521  at the time when acquisition of the frame-integrated image of each division region is completed. The transferred image data of each divided region may be sequentially displayed in the image display window  2202 . By adopting this display system, the user can know the acquisition situation of extremely low magnification image acquisition and the difference in frame integration number for each division region, thereby improving usability for a user. 
     Third Embodiment 
     In the second embodiment, the extremely low magnification image creation function which sequentially completes the frame normalization integration computation for each divided region (that is, a method of completing the frame normalization integration computation for each region from region  1  to region  16 ) is described. In the present embodiment, an extremely low magnification image creation function that processes all the divided regions in parallel by sequentially processing the frame normalization integration computation in each divided region integration computation by integration computation will be described. 
     As described above, the frame integration number to be set is greatly influenced by composition elements and structures of the sample and observation conditions (accelerating voltage, irradiation yield, degree of vacuum, working distance (WD), and the like). Here, it is generally known that these observation conditions are influenced by disturbance in a peripheral environment of apparatus such as temperature, vibration, electric field, and magnetic field and a slight change occurs in the optical characteristics. That is, there is concern that the frame integration number may also be influenced by the disturbance of the peripheral environment of apparatus. 
     That is, in the extremely low magnification image creation function described in the second embodiment, in a short period of time within a period of time from the start of the integrated image acquisition of the region  1  to the completion of the integrated image acquisition of the final region  16 , in a case where “vibration”, for example, greatly fluctuates in the peripheral environment of apparatus, in the method of the second embodiment, the region just under the integration computation at the time of the fluctuation is greatly influenced by the “vibration”. As a result, there is concern that only in that region, image quality is bad, noise is added, and the integration number is extremely increased. Accordingly, as a method to smooth this influence as much as possible, an example of an extremely low magnification image creation function of the present embodiment is proposed. 
     Also, attention is paid to charge of the sample. In the frame-integrated image acquisition of the second embodiment, a plurality of frame images are acquired in each divided region in order to acquire a frame-integrated image in each divided region. Here, in order to acquire the first frame image, a frame scan is performed to acquire a frame image. Thereafter, in order to acquire the second frame image, second frame scan is performed to acquire a second frame-integrated image. As such, the process described above is repeated until an image index (evaluation reference value) defined by the user is satisfied. This means that the frame scan is continuously executed on the same sample region until a frame-integrated image satisfying the image index can be constructed. Here, in the case of a sample that is easy to charge, there is concern that the sample will be charged by continuous beam irradiation and luminance value saturation and drift due to the change will occur. The extremely low magnification image creation function of the third embodiment also exhibits an effective effect against this problem. 
       FIG. 33  illustrates a processing flow of creation of an extremely low magnification image according to the present embodiment, and  FIGS. 34 to 39  illustrate an outline of scanning for creating an extremely low magnification image.  FIG. 40  illustrates a GUI for acquiring an extremely low magnification image. 
     The image processing unit  513  updates the integrated image on the display unit of the information transmission apparatus  521  according to the number of times of execution of integration processing (normalization integration computation) for each of the plurality of divided regions. The image processing unit  513  determines the end of integration processing according to the image quality of the integrated image for each of the plurality of divided regions. 
     More specifically, the image processing unit  513  executes the normalization integration computation once for each of the plurality of divided regions. The image processing unit  513  executes the normalization integration computation only for the divided regions that do not satisfy the evaluation condition on the next time and thereafter. In the following, the first, second, (M−1)-th, and M-th normalization integration computation the will be described. 
     A screen  2601  is displayed on the display device of the information transmission apparatus  521 . The user decides the observation region for which the frame-integrated image is intended to be acquired, performs various settings, and then executes the low magnification image acquisition (STEP  2401 ). When the execution instruction is received, the information processing unit  517  moves the sample stage (stage)  508  to the initial coordinates via the stage control unit  518  based on coordinate data which is set on the screen  2601  (STEP  2402 ). 
     Next, the information processing unit  517  sets the number of scanning lines in the deflection control unit  519  (STEP  2403 ). Next, the information processing unit  517  sets the recording range of the frame memory  514  (STEP  2404 ). 
     &lt;Acquisition of First Integrated Image&gt; 
     A case of acquiring the first integrated image will be described with reference to  FIGS. 34 and 35 . The information processing unit  517  determines whether acquisition of the frame-integrated image is completed in a target divided region (STEP  2405 ). Since it is now immediately after the start of extremely low magnification image acquisition and the image of the first frame of region  1  ( 2501 ) is not acquired, the information processing unit  517  sets a recording start point of the frame memory  514  in a region corresponding to the region  1  ( 2501 ) coordinates (STEP  2406 ). 
     Next, the frame scan is executed once and the image processing unit  513  acquires image data. The image processing unit  513  executes the frame normalization integration computation ( FIGS. 7 and 8 ) described in the first embodiment. Here, because it is the image of the first frame, the image processing unit  513  outputs the acquired image as it is to the frame memory  514 , the information processing unit  517 , and the image evaluation unit  522 . Image data  2511  is stored in the frame memory  514  as integrated image data of the first frame (integrated image data to which integration is applied once). The image evaluation unit  522  evaluates the input image data  2511  (STEP  2409 ). Here, it is assumed that the image data  2511  of the region  1  ( 2501 ) is an image that does not having image quality expected by the user. The information processing unit  517  determines that acquisition of the frame-integrated image of the region  1  ( 2501 ) is incomplete. 
     The image data  2511  output to the information processing unit  517  is transferred to the information transmission apparatus  521 . In an image display window  2602 , the image data  2511  is displayed as an integrated image being integrated. Next, the information processing unit  517  determines whether the stage position is the final position, that is, the region  16  ( 2503 ) or not (STEP  2411 ). Since the image of the region  1  ( 2501 ) is now acquired, the information processing unit  517  moves the stage to the next region  2  ( 2502 ) via the stage control unit  518  (STEP  2412 ). Thereafter, STEP  2405  to STEP  2412  described above are repeated to acquire image data  2512  of the region  2  ( 2502 ) to image data  2513  of the region  16  ( 2503 ). 
     Here, as illustrated in  FIG. 35 , it is assumed that integrated image data acquired in the first the frame scan is not the image having image quality expected by the user in any region of 16 regions of an extremely low magnification image  2510 . After image data  2513  of the region  16  ( 2503 ) is acquired, the information processing unit  517  determines whether acquisition of the integrated image is completed in all regions (STEP  2413 ). In this case, since an image that does not having image quality expected by the user is obtained in any region, the information processing unit  517  moves the stage to the initial position  2501  via the stage control unit  518  (STEP  2414 ). 
     &lt;Acquisition of Second Integrated Image&gt; 
     Next, a case of acquiring a second integrated image will be described with reference to  FIG. 36 . STEP  2405  to STEP  2412  described above are repeated. The information processing unit  517  determines whether acquisition of the frame-integrated image is completed in a divided region which becomes a target (STEP  2405 ). Here, since the acquisition of the frame-integrated image of the region  1  ( 2501 ) is not completed, the information processing unit  517  sets the recording start point of the frame memory  514  in the region corresponding to the region  1  ( 2501 ) coordinates (STEP  2406 ). 
     Next, the frame scan is executed once and the image processing unit  513  acquires image data. The image processing unit  513  executes the frame normalization integration computation ( FIGS. 7 and 8 ) described in the first embodiment. The image processing unit  513  executes the frame normalization integration computation of image data detected by the current the frame scan and image data which is stored in the frame memory  514  and corresponds to the region  1  ( 2501 ). 
     The image processing unit  513  outputs image data (frame-integrated image)  2521  to the frame memory  514 , the information processing unit  517 , and the image evaluation unit  522 . The image data  2521  is stored in the frame memory  514  as integrated image data of the second frame (integrated image data to which integration is applied twice). The image evaluation unit  522  evaluates the input image data  2521  (STEP  2409 ). Here, it is assumed that the image data  2521  of the region  1  ( 2501 ) is an image that does not have image quality expected by the user. The information processing unit  517  determines that acquisition of the frame-integrated image of the region  1  ( 2501 ) is incomplete. 
     The image data  2521  output to the information processing unit  517  is transferred to the information transmission apparatus  521 . In the image display window  2602 , the image data  2521  is displayed as an integrated image being integrated. Next, the information processing unit  517  determines whether the stage position is the final position, that is, the region  16  or not ( 2503 ) (STEP  2411 ). Since the image of the region  1  ( 2501 ) is now acquired, the information processing unit  517  moves to the next region  2  ( 2502 ) via the stage control unit  518  (STEP  2412 ). Thereafter, STEP  2405  to STEP  2412  described above are repeated to acquire image data  2522  of the region  2  ( 2502 ) to image data  2523  of region  16  ( 2503 ). 
     Here, as illustrated in  FIG. 36 , it is assumed that the second frame-integrated image data is an image that does not have image quality expected by the user in any region of 16 regions of an extremely low magnification image  2520 . After image data  2523  of the region  16  ( 2503 ) is acquired, the information processing unit  517  determines whether acquisition of the integrated image is completed in all regions (STEP  2413 ). Here, since an image that does not have image quality expected by the user is obtained in any region, the information processing unit  517  moves the stage to the initial position  2501  via the stage control unit  518  (STEP  2414 ). 
     &lt;Acquisition of (M−1)-th Integrated Image&gt; 
     Thereafter, a case where STEP  2405  to STEP  2414  are repeated a plurality of times to acquire an (M−1)-th integrated image will be described with reference to  FIG. 37 . The information processing unit  517  determines whether acquisition of the frame-integrated image is completed in the divided region which becomes a target (STEP  2405 ). Here, since the acquisition of the frame-integrated image of the region  1  ( 2501 ) is not completed, the information processing unit  517  sets the recording start point of the frame memory  514  in the region corresponding to the region  1  ( 2501 ) coordinates (STEP  2406 ). 
     Next, the frame scan is executed once, and the image processing unit  513  acquires image data. The image processing unit  513  executes the frame normalization integration computation ( FIGS. 7 and 8 ) described in the first embodiment. The image processing unit  513  executes the frame normalization integration computation of image data detected by the current the frame scan and image data stored in the frame memory  514  corresponding to the region  1  ( 2501 ). 
     The image processing unit  513  outputs image data (frame-integrated image)  2531  to the frame memory  514 , the information processing unit  517 , and the image evaluation unit  522 . The image data  2531  is stored in the frame memory  514  as integrated image data of the (M−1)-th frame (integrated image data to which integration is applied (M−1) times). The image evaluation unit  522  evaluates the input image data  2531  (STEP  2409 ). Here, it is assumed that the image data  2531  of the region  1  ( 2501 ) is an image having image quality expected by the user. The information processing unit  517  determines that acquisition of the integrated image in the region  1  ( 2501 ) is completed. The information processing unit  517  stores in a storing unit of the information processing unit  517  that acquisition of the frame-integrated image of the region  1  ( 2501 ) is completed (STEP  2410 ). 
     The image data  2531  output to the information processing unit  517  is transferred to the information transmission apparatus  521 . In the image display window  2602 , the image data  2531  is displayed as an integrated image being integrated. Next, the information processing unit  517  determines whether the stage position is the final position, that is, the region  16  ( 2503 ) or not (STEP  2411 ). Since the image of the region  1  ( 2501 ) is now acquired, the information processing unit  517  moves the stage to the next region  2  ( 2502 ) via the stage control unit  518  (STEP  2412 ). Thereafter, STEP  2405  to STEP  2412  described above are repeated to acquire image data  2532  of the region  2  ( 2502 ) to image data  2533  of the region  16  ( 2503 ). 
     Here, as illustrated in  FIG. 37 , it is assumed that if the image data  2531  of the region  1 , image data  2534  of the region  7 , image data  2535  of the region  8 , and image data  2536  of the region  9  are images having image quality expected by the user. After the image data  2533  of the region  16  ( 2503 ) is acquired, the information processing unit  517  determines whether acquisition of the integrated image is completed in all regions of the extremely low magnification image  2530  (STEP  2413 ). Here, since the image having image quality expected by the user is still not obtained in all regions of the extremely low magnification image  2530 , the information processing unit  517  moves the stage to the initial position  2501  via the stage control unit  518  (STEP  2414 ). 
     &lt;Acquisition of M-th Integrated Image&gt; 
     Next, a case of acquiring an M-th integrated image will be described with reference to  FIG. 38 . STEP  2405  to STEP  2412  described above are repeated. The information processing unit  517  determines whether acquisition of the frame-integrated image is completed in the divided region which becomes the target (STEP  2405 ). Here, since acquisition of the frame-integrated image of the region  1  ( 2501 ) is completed, the information processing unit  517  moves the stage to the next region  2  ( 2502 ) via the stage control unit  518  (STEP  2407 ). As described above, the region where acquisition of the frame-integrated image is completed is skipped, and a frame-integrated image is acquired only for the region for which acquisition of the frame-integrated image is not completed. 
     Next, the information processing unit  517  determines whether acquisition of the frame-integrated image is completed in the region  2  or not ( 2502 ) (STEP  2405 ). Here, since acquisition of the frame-integrated image of the region  2  ( 2502 ) is not completed, the information processing unit  517  sets the recording start point of the frame memory  514  in the region corresponding to the region  2  ( 2502 ) coordinates (STEP  2406 ). 
     Next, the frame scan is executed once, and the image processing unit  513  acquires image data. The image processing unit  513  executes the frame normalization integration computation ( FIGS. 7 and 8 ) described in the first embodiment. The image processing unit  513  executes the frame normalization integration computation of image data detected by the current frame scan and image data stored in the frame memory  514  corresponding to the region  2  ( 2502 ). 
     The image processing unit  513  outputs image data (frame-integrated image)  2542  to the frame memory  514 , the information processing unit  517 , and the image evaluation unit  522 . The image data  2542  is stored in the frame memory  514  as integrated image data of the M-th frame (integrated image data to which integration is applied M times). The image evaluation unit  522  evaluates the input image data  2542  (STEP  2409 ). Here, it is assumed that the image data  2542  of the region  2  ( 2502 ) is an image that does not have image quality expected by the user. The information processing unit  517  determines that acquisition of the frame-integrated image of the region  2  ( 2502 ) is incomplete. 
     The image data  2542  output to the information processing unit  517  is transferred to the information transmission apparatus  521 . On the image display window  2602 , the image data  2542  is displayed as an integrated image being integrated. Next, the information processing unit  517  determines whether the stage position is the final position, that is, the region  16  ( 2503 ) or not (STEP  2411 ). Since the image of the region  2  ( 2502 ) is now acquired, the information processing unit  517  moves the stage to the next region  3  via the stage control unit  518  (STEP  2412 ). Thereafter, STEP  2405  to STEP  2412  described above are repeated until image data  2543  of the region  16  ( 2503 ) is acquired. However, as described above, acquisition of the image data  2534  of the region  7 , the image data  2535  of the region  8 , and the image data  2536  of the region  9  is been completed. Accordingly, the regions  7 ,  8  and  9  are skipped, and image data of the regions  3  to  6  and  10  to  16  which do not satisfy the evaluation condition are acquired (dotted arrow  2548 ). 
       FIG. 39  illustrates an extremely low magnification image  2550  for which acquisition of the frame-integrated image is completed in all the divided regions. In the present embodiment, it is possible to construct an extremely low magnification image  2550  which becomes to have image quality expected by the user in all the regions. 
     In the example described above, the movement between the divided regions is executed by the stage, but is not limited thereto. An irradiation position of the electron beam may be moved by the deflection coil  505  as long as it is within a range changeable by deflection by the deflection coil  505 . Also, the movement between the divided regions may be performed using both the stage and the deflector. 
     The operation flow when acquiring an extremely low magnification image is the same as that in  FIG. 32  and thus, description thereof will be omitted.  FIG. 40  illustrates a GUI when acquiring an extremely low magnification image. A screen  2601  includes an image display window  2602 , an extremely low magnification image setting portion  2603 , a division number setting portion  2604 , an integration mode setting portion  2605 , an image acquisition execution button  2607 , and an evaluation method setting button  2608 . The constituent elements  2602  to  2608  of the screen  2601  are the same as the constituent elements  2202  to  2208  of the screen  2201  of  FIG. 31  and thus, description thereof will be omitted. 
     On the screen  2601 , the number of times of execution (that is, the integration number) of the frame normalization integration computation of each divided region, the evaluation value of each divided region, and the like may be displayed. 
     As in the operation flow illustrated in  FIG. 32 , the user can acquire an extremely low magnification image only by operation of “image acquisition execution” without being never conscious of setting of the integration number. With this, it is possible to greatly improve time and effort for acquiring the extremely low magnification image. It is possible to greatly reduce the time required for image acquisition. 
     The present embodiment has the following effects. 
     (a) In contrast to the conventional plural image acquisition operations, in the present embodiment, a frame-integrated image is obtained by one image acquisition operation. 
     (b) In the present embodiment, it is possible to perform the integration scan with the minimum required number of integration by one image acquisition operation. 
     (c) By both effects described above, it is possible to reduce the irradiation time of the electron beam with which the sample is irradiated as much as possible. 
     (d) By suppressing the amount of electron beam with which the sample is irradiated to be minimized, it is possible to obtain secondary effects that suppresses sample destruction, contamination generation, generation of luminance value saturation and drift due to the influence of charging to be minimized. 
     In a case of being applied to the extremely low magnification image acquisition function, the above problem increases by M times according to the number M of division regions. 
     The present embodiment corresponds to the extremely low magnification image creation function of sequentially processing integration computations in each divided region one integration computation by one integration computation so as to process all regions in parallel. As described above, the frame integration number is influenced by the disturbance in the peripheral environment of apparatus. In a short period of time within a period of time from the start of the integrated image acquisition to the completion of the integrated image acquisition, in a case where “vibration”, for example, greatly fluctuates in the peripheral environment of apparatus, the region just under the integration computation at the time of the fluctuation is greatly influenced by the “vibration”, in the method of the second embodiment. As a result, there is concern that only in that region, image quality is bad, noise is added, and the integration number is extremely increased. 
     In the acquisition method of the present embodiment, a possibility that the influence can be dispersed as much as possible to a plurality of regions can be expected, and as a result, it is possible to smooth fluctuation of disturbance in the plurality of regions. Not only fluctuations in a short period of time but also, for example, even when the surrounding “temperature” of the apparatus fluctuates slowly over a long period of time, the influence of fluctuation can be smoothed in the plurality of regions by the same mechanism as described above. 
     As described above, the present embodiment has an advantage that it is possible to acquire a stable integrated image with little difference in the influence of fluctuation between the regions by smoothing the influence of fluctuation of the disturbance around the apparatus in comparison with the second embodiment. When attention is paid to charge of the sample, in the frame-integrated image acquisition of the second embodiment, the frame scan is continuously executed for the same region until the frame integration image satisfying the image index can be constructed in each of the divided regions. In the case of a sample which is easy to charge, there is a possibility of charging due to this continuous beam irradiation and generating saturation of luminance value and drift due to charging. In the present embodiment, since integration computation is performed one integration computation by one integration computation for each of the divided regions, it is intermittent beam irradiation from the viewpoint of each region. That is, charge generation can be suppressed, and an effect of charge reduction can also be obtained. 
     In the automatic mode, in order to avoid that the evaluation value does not reach the evaluation reference value even if integration processing is repeated and the frame-integrated image cannot be acquired forever, an upper limit value of the integration number may be set in the information processing unit  517 . In a case where the upper limit value of the integration number reaches the upper limit value (in a case where a count value of the integration counter  601  reaches the upper limit value), the information processing unit  517  may forcibly end acquisition of the integrated image. For ease of use, it is also possible to consider a case the user may want to acquire an integrated image with as little noise as possible by setting the integration number to large. In this case, the upper limit of the number of integration may be set to large. 
     In the present embodiment, an example in which each divided region is scanned by moving a scan table is described, but is not limited to this example, and coordinate control of the region may be performed by another method, for example, using a coil or a lens. 
     In the present embodiment, an example in which the integrated image is displayed on the image display window  2602  at any time during the integration is described. By displaying the integrated image being integrated at any time in the image display window, the user can confirm the process in which an image of the entire region is gradually constructed (process of being integrated) in real time. There is an advantage that it is possible to visually ascertain the process of the integration situation and the degree of integration. In the present embodiment, an example in which the integrated image is displayed on the image display window  2602  at any time during the integration is described, but is not limited thereto. The integrated images of all the regions may be displayed in the image display window  2602  all together after completion of construction. 
     The present invention is not limited to the embodiments described above, but includes various modification examples. The embodiments described above have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. A portion of the configuration of a certain example can be replaced by the configuration of another example. The configuration of another example can be added to the configuration of a certain example. It is possible to add, delete, and replace other configurations for a portion of the configuration of each example. 
     Each of the configurations, functions, processing units, processing means, and the like described above may be realized in hardware by designing a portion or all of them with, for example, an integrated circuit. Each of configurations, functions, and the like described above may be realized by software by allowing a processor to interpret and execute a program which realizes each function. Information such as programs, tables, files, and the like that realize each function can be stored in various types of non-transitory computer readable medium. As the non-transitory computer readable medium, for example, a flexible disk, a CD-ROM, a DVD-ROM, a hard disk, an optical disk, a magneto-optical disk, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, and the like are used. 
     In the embodiments described above control lines and information lines indicate what is considered to be necessary for explanation, and do not necessarily indicate all control lines and information lines for products. All the configurations may be connected to each other. 
     REFERENCE SIGNS LIST 
     
         
         
           
               501 : vacuum column 
               502 : electron gun (charged particle beam source) 
               503 : electron beam (charged particle beam) 
               504 : focusing lens 
               505 : deflection coil 
               506 : objective lens 
               507 : sample 
               508 : sample stage 
               510 : detector 
               511 : amplifier 
               512 : ADC 
               513 : image processing unit 
               514 : frame memory 
               515 : multiplier 
               516 : adder 
               517 : information processing unit 
               518 : stage control unit 
               519 : deflection control unit 
               520 : information input device 
               521 : information transmission apparatus 
               522 : image evaluation unit 
               523 : multiplier 
               524 : deflection signal 
               525 : control signal 
               526 : image evaluation result 
               527 : image data