JP2010033723A - Scanning electron microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation of throughput in a scanning electron microscope having a function of imaging a defect on a semiconductor wafer and transferring a captured image to an external device. <P>SOLUTION: The scanning electron microscope includes at least two memories for temporarily storing image data; a control part for starting to transfer first image data stored in the first memory out of the two memories, to the external device and setting imaging conditions for the second image data; and a memory selecting part for temporarily storing the second image data imaged under the set imaging conditions, into the second memory. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a scanning electron microscope that images defects on a semiconductor wafer. In particular, the present invention relates to a scanning electron microscope having a function of transferring a captured image as image data to an external device in order to analyze the cause of the occurrence of a defect.

  In the process of manufacturing a semiconductor element by forming a circuit pattern on a semiconductor wafer, defects on the surface and inside of the semiconductor wafer are factors that greatly affect the product yield. Therefore, it is necessary to observe and analyze defects in a short time, find out the cause of the defects, and reflect the countermeasures on the production line at an early stage. 2. Description of the Related Art Conventionally, for inspection of circuit pattern defects, inspection apparatuses that detect light by irradiating light to detect reflected light are known. However, miniaturization and high integration of semiconductor elements have progressed so much that they cannot be detected at the wavelength of light, and a scanning electron microscope (hereinafter sometimes referred to as SEM) using an electron beam instead of light. It has come to be used for inspection. As the resolution increases, the number of pixels per image increases and the field of view for each defect decreases, resulting in an increase in the number of images taken per semiconductor wafer. Increasingly. Furthermore, in order to analyze defects, imaging is performed multiple times with different imaging conditions for one defect, which is performed on one semiconductor wafer, and then all defects are analyzed. Therefore, a very large amount of data is generated at one time. Therefore, a new external device is provided in addition to the scanning electron microscope, and each time an image is captured, the data is transferred to the external device so that a large amount of data can be stored and stored, and the defect can be analyzed. A system has been developed (see, for example, Patent Document 1).

JP-A-8-111202

  In the scanning electron microscope described above, image data obtained by imaging a defect is temporarily stored in a built-in memory. When the imaging operation is completed, the image data held in the memory is transferred to the external device. When the transfer is completed, the next imaging process is started. As described above, since the imaging process and the image transfer process are alternately performed sequentially, the next defect cannot be imaged until the transfer of the image data to the external device is completed. In particular, the miniaturization of a semiconductor element increases the capacity of one image data, and the waiting time until the transfer is completed is long. Therefore, the total throughput of the scanning electron microscope is reduced.

  An object of the present invention is to prevent a decrease in throughput in a scanning electron microscope having a function of imaging a defect on a semiconductor wafer and transferring the captured image to an external device.

  In order to solve the above object, an embodiment of the present invention provides at least two memories for temporarily storing image data and an external device for first image data stored in the first memory of the memories. The controller for setting the imaging condition of the next second image data at the start of the transfer of the image, and the memory selection unit for temporarily storing the second image data captured under the set imaging condition in the second memory The scanning electron microscope provided with these is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of a throughput can be prevented in the scanning electron microscope which images the defect of a semiconductor wafer and transfers a captured image to an external device.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a longitudinal sectional view showing a main configuration of a scanning electron microscope. In general, the SEM casing unit 100, the SEM control unit 101, the SEM image processing unit 102, the input device 103, and the result display device 104 are configured. The SEM image processing unit 102 is connected to an external device 105. Yes. In the present embodiment, the external device 105 is described as a device separate from the scanning electron microscope, but may be configured as a part of the scanning electron microscope.

  The operator of the scanning electron microscope first instructs the input device 103 to set imaging conditions and start imaging. In accordance with the instruction, the SEM control unit 101 causes the SEM casing unit 100 to perform an imaging operation. The SEM housing unit 100 mounts a sample 116 such as a semiconductor wafer on the sample stage 113 by a loader (not shown). Since it is necessary to keep the inside of the SEM casing 100 in a vacuum, a transfer chamber (not shown) is provided so as to maintain airtightness between the outside air and the inside of the SEM casing 100. When the coordinates of the sample 116 are determined, the sample stage 113 moves and aligns the sample 116 at a position where an image is to be acquired. An electron beam 111 is irradiated from the electron source 110 and converged on the sample 116 by the electron lens 112. Since the electron beam 111 is narrowed down, it is necessary to scan the sample 116 with the deflector 117 in order to acquire an image. An information signal 114 such as secondary electrons or reflected electrons is emitted from the portion irradiated with the electron beam 111, detected by the detector 115, converted into an electrical signal, and an image is generated by the SEM image processing unit 102. The information signal 114 detected by the detector 115 is an analog signal, but is converted into a digital signal by the SEM image processing unit 102 and stored as image data in a memory inside the SEM image processing unit 102. Further, the SEM image processing unit 102 transfers the image data stored in the memory to the external device 105 in accordance with an instruction from the SEM control unit 101. The image data stored in the memory of the SEM image processing unit 102 is sent to the result display device 104 and displayed on a display (not shown). The external device 105 stores image data and displays an image and supplementary information on a display (not shown), thereby being used as a defect analysis tool for the operator.

  FIG. 2 is a flowchart showing a procedure for capturing an image by the scanning electron microscope. First, the sample 116 is moved to a position to be imaged such as a defect position (step 201). Next, imaging conditions are set (step 202). Imaging conditions include the acceleration voltage and probe current of the electron beam 111, the size of the field of view of the image to be acquired, and the magnification. The sample 116 is imaged under the conditions set in the above process (step 203). The image data stored in the memory of the SEM image processing unit 102 is transferred to the external device 105 (step 204). In order to manage the image data, the imaging conditions of the imaging data are also transferred. The captured image is displayed on the result display device 104, and the operator confirms the image, and if it is determined that imaging is to be performed again while changing the imaging condition, the process returns to step 202 (step 205). When a desired image is obtained for the operator, it is determined whether or not another image such as a defect is to be captured, and if necessary, the process returns to step 201 (step 206). When imaging of a desired defect is completed, the procedure shown in FIG. 2 is ended, and when imaging a defect of a different sample 116, the procedure shown in FIG. 2 is repeated.

  FIG. 3 is a configuration diagram showing the contents of data processing of the SEM image processing unit 102. FIG. 4 is a flowchart illustrating a data processing procedure performed by the SEM control unit 101 and the SEM image processing unit 102. First, the SEM control unit 101 receives a determination as to whether it is necessary to set an imaging condition for the operator (step 401). It is determined whether or not the conditions for imaging from now on are the same as the currently set conditions. If they are the same, the new imaging condition is not set. If the settings are different, only the different settings are accepted, and the settings with the same contents are omitted. Thereby, the time required for setting the imaging conditions can be shortened. If the imaging condition needs to be set in step 401, the imaging condition is set (step 402). Imaging is performed under the set imaging conditions (step 403). The SEM image processing unit 102 receives the electrical signal 301 sent from the detector, and acquires image data (step 404). The electric signal 301 which is an analog signal is converted into digital image data 303 by the A / D converter 302 (step 405). Next, the image data 303 is temporarily stored in a memory having a capacity for one image data. Initially, since the image data 303 is not stored in either the memory 304 or the memory 305, a command sent from the SEM control unit 101 is used. The memory selection unit 306 stores the image data 303 in the memory 304 (step 406). When the image data is stored in the memory 304, the SEM control unit 101 sends an instruction to select the memory 304 to the output selection unit 307, and the image data stored in the memory 304 is stored in the external device 105 and the result display device 104. (Step 407). Before this transfer is completed, the SEM control unit 101 determines whether another imaging is necessary, and if there is, the process returns to step 401 to start imaging (step 408). Since there is image data being transferred to the memory 304, new image data 303 is stored in the memory 305 selected by the memory selection unit 306 (step 406). When the new image data 303 is stored in the memory 305, the output selection unit 307 selects the memory 305, and the image data stored in the memory 305 is transferred to the external device 105 and the result display device 104 (step 407). . If it is determined that there is another captured image again, the next image data 303 is stored not in the memory 305 in which the image data is being transferred but in the memory 304 in which the transfer has been completed (step 408). The image data stored in the memory 304 may be erased while being transferred, or may be overwritten with new image data. As described above, in this embodiment, the memory for temporarily storing the image data 303 is changed from the conventional one to two, and the image data that is captured and transmitted is stored in one memory. The image data is later transferred to an external device, and the next image data is stored in another memory during the transfer, and this is repeated alternately. As a result, the waiting time at the time of transferring the image data can be assigned to the time for capturing and storing the next image data, thereby preventing a reduction in the throughput of the entire apparatus.

  FIG. 5 is a timing chart of the data processing procedure shown in FIG. 4, and schematically shows the time required from imaging condition setting to transfer to an external device for two images. In the conventional processing flow shown in FIG. 5A, the required time for the first image data is the sum of the condition setting time 501, the imaging time 502, and the image transfer time 503. The required time for the second image data is The condition setting time 504, the imaging time 505, and the image transfer time 506 are the sum, but since there is only one image data memory for temporarily storing the image data shown in FIG. 3, transfer of the first image data is performed. The second image data cannot be temporarily stored in the memory until after the image processing is completed. Further, conventionally, since the control from the start of the imaging condition setting process to the start of the storage process of the captured image data in the memory cannot be controlled, it is not after the transfer of the first image data is completed. And the setting of the imaging conditions for the second image data could not be started.

  FIG. 5B is a timing chart showing an improved process flow (example 1) according to an embodiment of the present invention. The processing time for the first image data is the sum of the condition setting time 507, the imaging time 508, and the image transfer time 509, as in the past, but the image transfer is started and the imaging condition setting for the next image data is started. Is possible. Therefore, the processing time of the second image data is the sum of the condition setting time 510, the imaging time 511, and the image transfer time 512, but the processing time for two images is the overlapping first image transfer time. It is shortened by the length of 509. Further, the three pieces of image data can be stored in the memory in which the first piece of image data is stored. At the start of the image transfer time 512 of the second piece of image data, the imaging of the third piece of image data (not shown) is performed. Since the condition setting can be started, the time is shortened by the length of the image transfer time 512 of the overlapping second image data. Therefore, as a whole, the time can be significantly reduced as compared with the case of one memory. Note that if the number of memories is increased, imaging and image data transfer can proceed at the same time. However, since the image data cannot be transferred unless imaging is completed, at least two are required to achieve the purpose of time reduction. Memory is enough.

  FIG. 5C illustrates a case where the condition setting time 516 for capturing the second image data is significantly shortened compared to the case of FIG. The processing time for the first image data is the sum of the condition setting time 513, the imaging time 514, and the image transfer time 515, as in the past, but the image transfer is started and the imaging condition setting for the next image data is started. Is possible. Here, as described above, only different conditions are set, and only the set time becomes the condition set time 516. The processing time of the second image data is the sum of the condition setting time 516, the imaging time 517, and the image transfer time 518, and the condition setting time 516 is shorter than the condition setting time 510 shown in FIG. The entire processing time can be shortened by that time. Similarly to FIG. 5B, the third image data (not shown) can be stored in the memory in which the first image data is stored, and the image transfer time 518 of the second image data starts. Since the setting of conditions for capturing the third image data (not shown) can be started, the overall time can be significantly reduced as compared with the case of one memory.

  6 and 7 are screen diagrams showing examples of screens displayed on the display of the result display device 104 or the display of the external device 105 shown in FIG. 1 or FIG. As shown in FIG. 3, the image data is transferred to the result display device 104 and the external device 105, and an image is displayed on each display. In FIG. 6, the display is divided into an area where an image is displayed and an area where incidental information is displayed. A defect 602 is displayed in the image 601. As the incidental information, for example, the image ID 603, the coordinate X604 of the defect 602, the coordinate Y605, the magnification 606, the voltage 607 and current 608 of the electron beam, and the pixel number 609 of the image 601 are displayed. With the EXIT button 610, it is possible to return to the previous screen (not shown) of the screen shown in FIG. Since the image data is transferred to both the result display device 104 and the external device 105 and the image is displayed on the display, the operator is installed at a remote location even in front of the result display device 104 of the scanning electron microscope. Even in front of the external device 105, the defect can be confirmed by viewing the same image. In addition, the external device 105 has a storage device with a large capacity and stores all transferred image data, so that it becomes easy to analyze the defect after the defect detection is completed. If the coordinates of the defect have not been obtained, the coordinates of the center of the image 601 may be displayed instead of the coordinates X604 of the defect 602 and the coordinates Y605.

  In the embodiment shown in FIG. 3, the image data is transferred to both the result display device 104 and the external device 105, and the image is displayed on each display. However, the image transfer to the result display device 104 or The image display may be performed only by the external device 105 without performing the image display. Thereby, the capacity of the memory for storing the image data of the result display device 104 can be reduced.

  The display of FIG. 7 is divided into an area where an image is displayed and an area where incidental information is displayed, as in the case of FIG. A defect 702 is displayed in the image 701. As the accompanying information, for example, an image ID 703, a coordinate X704 of a defect 702, a coordinate Y705, an enlargement magnification 706, an electron beam voltage 707 and a current 708, and the number of pixels 709 of the image 701 are displayed. With the EXIT button 710, it is possible to return to the previous screen (not shown) of the screen shown in FIG. The enlargement magnification 706 is displayed in a different manner, for example, by changing the color. This indicates that there is a difference between the previous imaging conditions shown in FIG. 6 and the current conditions. In this way, by highlighting the conditions so that the difference from the previously displayed imaging conditions can be understood, the operator can immediately know the reason for the difference between the previous image and the current image.

  As described above, the addition of one memory of the image processing unit of the scanning electron microscope, the distribution of the image data alternately, and the transfer to the external device are adopted to complete the transfer of the image data. Since it is possible to capture the next image without waiting, it is possible to prevent a decrease in throughput from image capturing to image data transfer.

The longitudinal cross-sectional view which shows schematic structure of a scanning electron microscope. The flowchart which shows the procedure of the image pick-up of a scanning electron microscope. The block diagram which shows the content of the data processing of a SEM image process part. The flowchart which shows the procedure of the data processing performed with a SEM control part and a SEM image process part. 5 is a timing chart of the data processing procedure shown in FIG. 4. The screen figure which shows the example of the screen displayed on a display. The screen figure which shows the example of the screen displayed on a display.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 SEM housing | casing part 101 SEM control part 102 SEM image processing part 103 Input device 104 Result display apparatus 105 External apparatus 301 Electric signal 302 A / D converter 303 Image data 304,305 Memory 306 Memory selection part 307 Output selection part

Claims (6)

In a scanning electron microscope that generates image data of a sample based on a signal generated from a sample irradiated with an electron beam under preset imaging conditions,
At least two memories for temporarily storing the image data;
The controller for setting the imaging condition of the next second image data together with the start of transfer of the first image data stored in the first memory of the memory to the external device, and the set imaging A scanning electron microscope comprising: a memory selection unit that temporarily stores second image data captured under conditions in a second memory.   2. The scanning electron microscope according to claim 1, wherein the setting of the same condition is omitted between the imaging condition of the first image data and the imaging condition of the second image data.   2. The scanning electron microscope according to claim 1, wherein one of the memories has a capacity for one piece of the image data.   2. The control unit according to claim 1, wherein the control unit sets an imaging condition for the next third image data at the start of transfer of the second image data stored in the second memory to an external device. The scanning electron microscope is characterized in that the memory selection unit temporarily stores the third image data in the first memory.   2. The scanning electron microscope according to claim 1, wherein imaging conditions of the image data are transferred together with the image data transferred to the external device.   2. The scanning electron microscope according to claim 1, wherein the external device has a storage device for storing the transferred image data, and a defect included in the image data is analyzed.

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