JP2011003480A - Scanning electron microscope type visual inspection device and its image signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an SEM type visual inspection device capable of setting flexibly the scanning method and its image signal processing method.SOLUTION: The SEM type visual inspection device utilizes a concept of a scanning set 101 in which a plurality of scanning are handled as one unit of scanning. In the scanning set 101, a plurality of scanning are defined, for example, by the number of scanning lines "4" and the distance between the scanning lines "2". When information of the scanning set 101 is defined, a scanning control part of the SEM type visual inspection device carries out a scanning control to perform scanning of the scanning lines for the number of scanning lines "4" for every distance between the scanning lines "2" from the scanning line of a reference position address, based on the information of that scanning set 101. Further, when the scanning as defined by the scanning set 101 is completed, the scanning control part continues the scanning control by the same scanning set 101 while incrementing one by one the reference position address.

Description

  The present invention relates to a scanning electron microscope (SEM) type appearance inspection apparatus suitable for inspection of surface defects of a substrate such as a semiconductor wafer on which a fine pattern is formed, and an image signal processing method thereof.

  With the progress of microfabrication technology, SEM type visual inspection equipment has been actively used for inspection of surface defects of substrates such as semiconductor wafers. In the SEM type appearance inspection apparatus, the substrate surface to be inspected is irradiated with an electron beam, the generated secondary electrons are detected, and a surface image of the substrate is generated based on the detected amount of secondary electrons. In that case, since the amount of secondary electrons detected is very small, in order to improve the S / N (Signal to Noise Ratio), the same location is usually scanned many times, and the average of the detected values is reduced. It is done.

  In addition, since the SEM appearance inspection apparatus is used in a production line for mass-produced products such as semiconductor wafers, high throughput is required for the inspection. In addition, since the SEM visual inspection apparatus irradiates a sample to be inspected (such as a semiconductor wafer) with an electron beam, charges may be accumulated on the insulator portion on the surface of the sample to be inspected. In that case, an image signal with better contrast may be obtained when the next scanning is performed after waiting for the time for the electric charge to be discharged.

  In view of this, in the SEM type visual inspection apparatus including the SEM, various techniques have been conventionally used for obtaining and processing the image signal. For example, Patent Document 1 discloses that an SEM image signal obtained by performing an averaging process on an acquired SEM image signal is subjected to a filtering process between neighboring pixels in a two-dimensional space, thereby clarifying the image. Techniques for improving the toughness are disclosed.

JP-A-6-318250

  However, since the technique disclosed in Patent Document 1 is not intended for the SEM visual inspection apparatus, no consideration is given to improving the inspection throughput. Also, since the image signal processing method is fixedly determined, when it is applied to an SEM visual inspection apparatus, the user can devise a setting of a high-throughput scanning method or a sample to be inspected. It is not possible to set a scanning method that can cope with charging of the image.

  Accordingly, the present invention provides an SEM type visual inspection apparatus capable of flexibly setting a scanning method, such as a high-throughput scanning method and a scanning method capable of handling charging of a sample to be inspected, and an image signal processing method thereof. The purpose is to provide.

  In order to achieve the above object, the present invention uses the concept of a scan set that handles a plurality of scans as one unit scan. The scan set is defined by the number of scan lines and the distance between the scan lines. Therefore, when the information on the scan set is determined, the scan control unit of the SEM visual inspection apparatus determines the distance between the scan lines determined from the scan line at the address of the predetermined initial position based on the information on the scan set. Then, scanning control is performed to scan the scanning lines of the predetermined number of scanning lines. Further, when the scanning determined by the scanning set is completed, scanning control by the same scanning set is performed while incrementing the address of the predetermined initial position one by one.

  As described above, in the present invention, the scan control unit of the SEM type visual inspection apparatus executes the scan control according to the scan set. A simple scanning method can be set.

  ADVANTAGE OF THE INVENTION According to this invention, the SEM type external appearance inspection apparatus which can set a scanning method flexibly, and its image signal processing method can be provided.

The figure which showed the example of the structure of the SEM type external appearance inspection apparatus which concerns on embodiment of this invention. The figure which showed the example of a structure of the image signal process part contained in a secondary electron detection part. The figure which showed the example of the scanning set typically. The figure which showed the example of a structure of the image memory address control part which is contained in an addition controller and produces | generates the memory address for image memory access. The figure which showed the example of the data stored in the scanning set memory according to the structure of each scanning set. The figure which showed the example of the basic scanning method by the SEM type external appearance inspection apparatus which concerns on this embodiment. The figure which showed the example of the flowchart showing operation | movement of the image signal process part in the basic scanning method. The figure which showed the example of the addition scanning method with a precharge by the SEM type external appearance inspection apparatus which concerns on this embodiment. The figure which showed the example of the flowchart showing operation | movement of the image signal process part in the addition scanning method with a precharge. The figure which showed the example of the multiple line addition scanning method by the SEM type external appearance inspection apparatus which concerns on this embodiment. The figure which showed the example of the flowchart showing operation | movement of the image signal process part in the multiline addition scanning method. The figure which showed the example of the GUI operation screen in the SEM type external appearance inspection apparatus which concerns on this embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<1. Overall configuration of SEM visual inspection apparatus>
FIG. 1 is a diagram showing an example of the configuration of an SEM visual inspection apparatus according to an embodiment of the present invention. As shown in FIG. 1, an SEM visual inspection apparatus 1 includes an inspection chamber 2 in which the chamber is evacuated by a vacuum pump (not shown), and a spare chamber for transporting a sample 9 to be inspected into the inspection chamber 2. (Not shown). This spare chamber is normally configured so that it can be evacuated independently from the examination chamber 2. The SEM appearance inspection apparatus 1 includes an image processing unit 5, a control unit 6, a secondary electron detection unit 7, a correction control unit 43 and the like in addition to the inspection room 2 and the spare room.

  The inside of the examination room 2 is roughly divided into an electron optical system 3, a sample room 8, and an optical microscope unit 4. The electron optical system 3 includes an electron gun 10, an electron beam extraction electrode 11, a condenser lens 12, a blanking deflector 13, a scanning deflector 15, an aperture 14, an objective lens 16, a reflecting plate 17, and an ExB deflector 18. It is configured. The secondary electron detector 20 of the secondary electron detector 7 is disposed above the objective lens 16 in the examination room 2. The output signal of the secondary electron detector 20 is amplified by a preamplifier 21 in the secondary electron detection unit 7 installed outside the examination room 2, and an AD (Analog to Digital) converter 200 in the image signal processing unit 22. (See FIG. 2), it is converted into digital data.

  The sample chamber 8 includes a sample stage 30, an X stage 31, a Y stage 32, a position monitor length measuring device 34, and an inspected sample height measuring device 35. The optical microscope unit 4 is provided in the vicinity of the electron optical system 3 in the room of the examination room 2 and at a position away from each other so as not to affect each other. At this time, the distance between the electron optical system 3 and the optical microscope unit 4 is known, and the X stage 31 or the Y stage 32 reciprocates the known distance between the electron optical system 3 and the optical microscope unit 4. It has been calibrated to be able to. The optical microscope unit 4 includes a light source 40, an optical lens 41, and a CCD camera 42.

  The image processing unit 5 includes a first image storage unit 46, a second image storage unit 47, a calculation unit 48, and a defect determination unit 49. An electron beam image acquired via the secondary electron detector 7 or an optical image acquired via the CCD camera 42 is displayed on the monitor 50.

  The control unit 6 controls the entire operation of the SEM visual inspection apparatus 1, acquires information indicating various operation states from each part of the apparatus, and outputs various operation condition information and operation commands to each part of the apparatus. . Here, in the storage device of the control unit 6, operating conditions such as an acceleration voltage at the time of generating an electron beam, an electron beam deflection width, a deflection speed, a signal capturing timing of the secondary electron detection unit 7 and a sample stage moving speed are set in advance. The control section 6 can appropriately select or arbitrarily change the operation condition according to the purpose. Further, the control unit 6 monitors the position and height deviations by signals from the position monitor length measuring device 34 and the inspected sample height measuring device 35 via the correction control unit 43, and a correction signal is obtained based on the result. And a correction signal is sent to the objective lens power supply 45 and the scanning signal generator 44 so that the electron beam 19 is always irradiated to the correct position.

  Although not shown, the control unit 6 includes a user interface including an input device and a display device for an operator to set operation condition information and input an operation command. In that case, the user interface may be configured to also serve as the monitor 50 provided in the image processing unit 5.

  In order to acquire an image of the specimen 9 to be inspected, the SEM type visual inspection apparatus 1 irradiates the specimen 9 with a finely focused electron beam 19 to generate secondary electrons 51, which are emitted from the electron beam 19. By detecting in synchronization with scanning and movement of the X stage 31 and the Y stage 32, a scanned image of the sample 9 to be inspected is obtained.

  In general, since the SEM visual inspection apparatus 1 is assumed to be used in the manufacturing process of mass-produced semiconductor devices, a high inspection speed is an essential performance condition. Therefore, in the SEM type visual inspection apparatus 1 according to the present embodiment, the electron beam 19 having a current of pA order is not scanned at a low speed unlike a normal SEM, and each scanning is performed many times. It doesn't superimpose images. In the present embodiment, the electron beam 19 is scanned once or several times at a high speed in order to suppress the charging of the sample 9 to be inspected to the insulating material. The current of the line 19 is set to a large current (for example, 100 nA) that is about 1000 times or more that of a conventional SEM.

  The electron gun 10 uses a diffusion supply type thermal field emission electron source. By using this electron gun 10, a stable electron beam current can be ensured as compared with, for example, a conventional tungsten filament electron source or a cold field emission electron source. Therefore, an electron beam image with little brightness fluctuation can be obtained. In addition, since the electron beam current can be set large by the electron gun 10, high-speed inspection as described later can be realized. The electron beam 19 is extracted from the electron gun 10 by applying a voltage between the electron gun 10 and the extraction electrode 11.

  The electron beam 19 is accelerated by applying a high negative potential to the electron gun 10. As a result, the electron beam 19 travels in the direction of the sample stage 30 with energy corresponding to the potential, is converged by the condenser lens 12, and is further narrowed down by the objective lens 16 to be X stage 31, Y on the sample stage 30. The sample 9 to be inspected mounted on the stage 32 is irradiated. The sample 9 to be inspected includes a semiconductor wafer, a chip (die), a liquid crystal substrate, a substrate having a fine circuit pattern such as a mask, and the like.

  A scanning signal generator 44 that generates a scanning signal and a blanking signal is connected to the blanking deflector 13, and when it is necessary to blank the electron beam 19, the blanking deflector 13 deflects the electron beam 19. And control so that the electron beam 19 does not pass through the aperture 14. An objective lens power supply 45 is connected to the objective lens 16. Further, the aperture amount of the electron beam 19 is adjusted by a signal from the objective lens power supply 45.

  A negative voltage can be applied to the sample 9 to be inspected by a high voltage power source 36. By adjusting the voltage of the high voltage power source 36, the electron beam 19 can be decelerated and the electron beam irradiation energy to the sample 9 to be inspected can be adjusted to an optimum value without changing the potential of the electron gun 10.

  The secondary electrons 51 generated by irradiating the inspection sample 9 with the electron beam 19 are accelerated by the negative voltage applied to the inspection sample 9. An ExB deflector 18 for bending the trajectory of the secondary electrons without affecting the trajectory of the electron beam 19 by both the electric field and the magnetic field is disposed above the specimen 9 to be inspected, and the secondary beam thus accelerated. The electrons 51 are deflected in a predetermined direction. This amount of deflection can be adjusted by the strength of the electric field and magnetic field applied to the ExB deflector 18. The electric field and magnetic field can be varied in conjunction with the negative voltage applied to the sample 9 to be inspected.

  The secondary electrons 51 deflected by the ExB deflector 18 collide with the reflection plate 17 under a predetermined condition. The reflector 17 has a conical shape, and also has a function of a shield pipe that shields the electron beam 19 that irradiates the specimen 9 to be inspected. When the accelerated secondary electrons 51 collide with the reflector 17, second secondary electrons 52 having an energy of several eV to 50 eV are generated from the reflector 17.

  The secondary electron detector 7 includes a secondary electron detector 20 provided in the evacuated examination room 2, a preamplifier 21 provided outside the examination room 2, an image signal processor 22, a high voltage power supply 26, a preamplifier. A drive power supply 27, an AD converter drive power supply 28, and a reverse bias power supply 29 are provided. Of the secondary electron detector 7, the preamplifier 21, the image signal processor 22, the preamplifier drive power supply 27, and the AD converter drive power supply 28 are floated to a positive potential by the high voltage power supply 26.

  Of the secondary electron detector 7, the secondary electron detector 20 is disposed above the objective lens 16 in the examination room 2. The second secondary electrons 52 generated by colliding with the reflecting plate 17 are guided to the secondary electron detector 20 by the attractive electric field generated by the positive potential of the reverse bias power source 29.

  The secondary electron detector 20 is configured to detect the second secondary electrons 52 generated when the secondary electrons 51 collide with the reflector 17 in conjunction with the scanning timing of the electron beam 19. . The link between the scanning timing and the detection of the second secondary electrons 52 is performed by a synchronization signal 53 from a correction control unit 43 that controls the scanning timing. The output signal of the secondary electron detector 20 is amplified by a preamplifier 21 installed outside the examination room 2 and converted into digital data by an AD converter 200 (see FIG. 2) included in the image signal processing unit 22. .

  The image signal processing unit 22 includes an AD converter 200 (see FIG. 2), amplifies the output signal from the secondary electron detector 20 by the preamplifier 21, performs digital conversion by the AD converter 200, and performs digital conversion. The processed signal (image signal) is subjected to processing such as addition averaging every scan, for example, and transmitted to the image processing unit 5 via the light conversion unit 23, the optical transmission path 24, and the electric conversion unit 25. . The configuration and function of the image signal processing unit 22 will be described in detail separately with reference to the drawings.

  In the SEM type visual inspection apparatus 1 of the present embodiment, the X stage 31 and the Y stage 32 are used at the time of inspection as a scanning method of the electron beam 19 for scanning the specimen 9 mounted on the X stage 31 and the Y stage 32. A method in which the electron beam 19 is scanned two-dimensionally (for example, in the x and y directions) with respect to the sample 9 to be inspected, and the Y stage 32 (together with the X stage 31) is continuously moved in the y direction at a constant speed during inspection. And a method of scanning the electron beam 19 linearly in the x direction by moving the position in the above manner.

  In the case of the former scanning method, when a command instructing the scanning line for the forward scanning and the backward scanning input by the control unit 6 is sent to the correction control unit 43, the scanning deflector is scanned from the scanning signal generator 44 based on the command. A scanning signal is sent to 15, and deflection voltages Vx and Vy in the x and y directions are controlled. As a result, the amount of deflection of the electron beam in the x and y directions is adjusted, and the scanning line (two-dimensional in the x and y directions) and the scanning speed of the electron beam that scans the specimen 9 can be controlled. When inspecting a specific relatively narrow area, this method of inspecting the specimen 9 to be inspected is advantageous.

  In the latter scanning method, when a scanning line instruction command input by the control unit 6 is sent to the correction control unit 43, a scanning signal is sent from the scanning signal generator 44 to the scanning deflector 15 based on the instruction command. Then, the deflection voltage Vx in the x direction is controlled, and a position control signal is sent from the correction controller 43 to a position controller (not shown), and the position of the Y stage 32 is controlled based on this signal. Thereby, it is possible to control the scanning line (two-dimensional in the x and y directions) and scanning speed of the electron beam that scans the specimen 9 to be inspected. When inspecting a relatively wide area, this method of inspecting by inspecting the specimen 9 to be inspected continuously at a constant speed is effective.

  As the position monitor length measuring device 34 for monitoring the positions of the X stage 31 and the Y stage 32, a laser interference length meter is used here. The laser interference length meter can monitor the positions of the X stage 31 and the Y stage 32 in real time, and can transfer the length measurement results to the control unit 6. In addition, data such as the number of rotations of a motor (not shown) for driving the X stage 31 and the Y stage 32 is acquired and transferred from each driving unit to the control unit 6.

  Therefore, the control unit 6 can accurately grasp the region and position where the electron beam 19 is irradiated based on these data, and if necessary, the position shift of the irradiation position of the electron beam 19 can be performed in real time. Correction can be performed by the correction control unit 43. In addition, the region irradiated with the electron beam 19 can be stored in the storage device for each sample 9 to be inspected.

  The sample height measuring device 35 is an optical measuring device such as a laser interference measuring device or a reflected light measuring device that measures changes at the position of reflected light, and is mounted on the X stage 31 and the Y stage 32. The height of the inspected sample 9 can be measured in real time. In this embodiment, the inspected sample 9 is irradiated with the elongated white light that has passed through the slit through the transparent window, the position of the reflected light is detected by the position detection monitor, and the amount of change in height is calculated from the change in position. Is used. Based on the measurement data of the optical height measuring device 35, the focal length of the objective lens 16 is dynamically corrected so that the electron beam 19 focused on the region to be inspected can always be irradiated. Further, it is also possible to measure in advance the warpage and height distortion of the specimen 9 to be inspected before electron beam irradiation, and to set correction conditions for each inspection area of the objective lens 16 based on the data. Is possible.

  The image processing unit 5 includes a first image storage unit 46, a second image storage unit 47, a calculation unit 48, a defect determination unit 49, a monitor 50, and the like. An image signal transmitted from the image signal processing unit 22 via the light conversion unit 23, the optical transmission path 24, and the electrical conversion unit 25 is stored in the first image storage unit 46 or the second image storage unit 47.

  The arithmetic unit 48 aligns the image signal stored in the first image storage unit 46 with the image signal stored in the second image storage unit 47, normalizes the signal level, and removes various noise signals. Processing is performed, and both image signals are compared and calculated. The defect determination unit 49 compares the absolute value of the difference image signal calculated by the calculation unit 48 with a predetermined threshold value. If the difference image signal level is larger than the predetermined threshold value, the defect determination unit 49 It is determined as a defect candidate, and the position and the number of defects are displayed on the monitor 50. The configuration and function of the image processing unit 5 may be the same as the configuration and function of the image processing unit included in a conventional general SEM appearance inspection apparatus.

<2. Configuration and Function of Image Signal Processing Unit>
Next, the detailed configuration and function of the image signal processing unit 22 for realizing multiple scanning in which the operation of scanning a plurality of inspection lines is unitized will be described with reference to FIG. The inspection line refers to an electron beam irradiation trajectory line (scanning line) drawn on the surface of the sample 9 to be inspected by one scanning of the electron beam 19.

  FIG. 2 is a diagram illustrating an example of the configuration of the image signal processing unit 22 included in the secondary electron detection unit 7. As shown in FIG. 2, the image signal processing unit 22 includes an AD converter 200, a synchronization circuit 201, a rate conversion unit 202, an addition averaging unit 209, a PS (Parallel to Serial) conversion unit 203, an image memory 206, and a control register 207. It is comprised including.

  The AD converter 200 detects a signal obtained by depending on the material and shape on the inspection line of the sample 9 scanned by the electron beam 19, that is, is detected by the secondary electron detector 20, and is amplified by the preamplifier 21. The obtained signal (analog signal) is converted into a digital signal (digital image signal 210). In the present embodiment, it is assumed that, for example, identification numbers (referred to as addresses) are assigned to the inspection lines in order from the top.

  The synchronization circuit 201 adjusts the timing of the digital image signal 210 output from the AD converter 200 and the synchronization signal 211 (corresponding to the synchronization signal 53 in FIG. 1) input from the correction control unit 43. Here, based on the delay amount signal 212 specified by the control register 207, both signals are synchronized in units of clocks using a shift register.

  The rate conversion unit 202 converts the sampling rate of the AD converter 200 into a clock rate in which the addition averaging unit 209 performs addition and division (average processing). Here, the number of times of addition averaging is specified by the rate selection signal 213 from the control register 207. For example, if the digital image signal 210 sampled at 800 MHz is designated to be added and averaged twice by the rate selection signal 213, the actual sampling rate of the digital image signal is 400 MHz. Therefore, after the averaging, the data amount of the effective digital image signal is halved.

  The addition averaging unit 209 performs a process of adding and averaging the digital image signals 210 acquired by scanning the inspection line of the same address of the sample 9 to be inspected a plurality of times, respectively. Here, the addition averaging unit 209 includes an addition unit 204, a shift register 205, and an addition controller 208.

  The adder 204 adds the digital image signals 210 at the same pixel position on the inspection line of the same address obtained by scanning the number of times designated in advance by the control register 207. Here, the operation of the adding unit 204 supports the averaging of the digital image signal 210 by multiple scanning.

  That is, when the addition unit 204 receives the digital image signal 210 output from the AD converter 200 and supplied via the synchronization circuit 201 and the rate conversion unit 202, the digital image signal 210 is transmitted to the inspection line. If it is obtained by the first scan, the data of the digital image signal 210 is associated with the address and pixel position of the inspection line. Is saved (stored) in the image memory 206 at the specified address.

  When the digital image signal 210 is obtained by the second and subsequent scans, the digital image signal data 215 at the same pixel position is read back from the image memory 206 on the inspection line of the address, Data of the digital image signal 210 acquired by the current scan is added to the read back data 215. If the number of additions has not reached the number designated in advance, the addition result 214 is saved in the image memory 206 at the address associated with the address of the inspection line and the pixel position. On the other hand, when the number of additions reaches the number designated in advance, the addition result 218 is transferred to the shift register 205. At that time, the image memory 206 at the address position where the read back digital image signal data 215 has been saved is cleared to zero to release the memory area.

  The shift register 205 functions as a divider for obtaining an average. However, division by the shift register 205 is possible only when the divisor is a power of 2, such as 2, 4, 8,. Therefore, in the present embodiment, the number of additions by which the addition unit 204 adds the digital image signal 210 is limited to a power of 2. In this case, the division by the shift register 205 can obtain a division result by a simple shift operation, so that high-speed processing is possible and there is an advantage that division can be performed with a simple circuit.

  The addition controller 208 receives the scanning condition data 220 from the control register 207, and outputs an addition control signal 217 including the number of additions to the adding unit 204 based on the scanning condition data 220. Further, the addition controller 208 generates a memory address for storing the addition result 214 to the image memory 206 and outputs an image memory access signal 216 including a read / write control signal. The addition controller 208 further outputs a bit shift amount 221 for division to the shift register 205 and also outputs a status signal 219 indicating its own operation state including an error status to the control register 207. .

  The PS conversion unit 203 converts the parallel data 222 of the addition average value of the digital image signals 210 obtained by the division by the shift register 205 into serial data 223 and outputs the serial data 223 to the optical conversion unit 23. In this serial conversion, an error check code such as CRC (Cyclic Redundancy Code) is added.

  The image memory 206 is used to save the addition value when calculating the addition average of the digital image signals 210. In the case of a simple scanning method in which the inspection line at the same address is simply scanned a plurality of times, it is sufficient that the image memory 206 has a memory for the number of pixels of one inspection line. In the embodiment, as will be described later, since multiple scanning is performed with scanning of a plurality of inspection lines as one unit, a memory having the number of pixels corresponding to the plurality of inspection lines is required according to the method of the multiple scanning. . Note that the greater the storage capacity of the image memory 206, the greater the degree of freedom of the multiple scanning method.

  The control register 207 receives and holds the control data 224 transmitted from the control unit 6 and controls the operation in the image signal processing unit 22. The control data 224 includes scan condition data that defines a specific method of scanning, and includes data such as the number of scans and a scan pitch distance defined by a scan set described later. Further, the control data 224 includes data for controlling other blocks that constitute the secondary electron detector 7 such as the preamplifier 21. The control register 207 has status data 225 for displaying the operation state in the image signal processing unit 22 on the control unit 6.

<3. Unitization of multiple inspection line scans>
Next, the concept of “scanning set” that unitizes a series of scanning of a plurality of inspection lines as one scanning unit when multiple scanning of the inspection lines is performed will be described with reference to FIGS.

  FIG. 3 is a diagram schematically illustrating an example of a scan set. FIG. 3 shows an example of a scan set in which the scan multiplicity is “4” and the scan distance is “2”. In FIG. 3, the horizontal arrow represents the inspection line, and the scanning of the four inspection lines surrounded by the solid rectangle represents the scanning set 101. Here, the number in the rectangle represents the address of the inspection line to be scanned.

  In FIG. 3, the scan set 101 at the left end represents that the inspection lines with addresses 1, 3, 5, and 7 are scanned in order from the top, and the scan set 101 on the right is 2, 4, 6, 8 This indicates that the inspection lines at the addresses are sequentially scanned from the top, and so on. At this time, one address of the inspection line is jumped because the scanning distance is designated as “2”. The scanning distance is not limited to “2”, and may be “1”, “3”, “4”, and the like.

  When multiple scanning is performed using such a concept of the scan set 101, the scan set 101 is treated as if it were one inspection line, so that the inspection lines are scanned in the order determined in the scan set 101. Takes precedence. Therefore, in the example of FIG. 3, first, scanning of the inspection lines with addresses 1, 3, 5, and 7 is performed in the scanning set 101 at the left end, and then the address is scanned in the scanning set 101 on the right side. 2, 4, 6, and 8 are scanned, and thereafter, scanning is performed in the same order.

  At this time, the address of the uppermost inspection line in each scan set 101 is referred to as a reference position address 102, and is incremented by one every time scanning of the inspection line in the scan set 101 is completed. Accordingly, at most, each inspection line is scanned the number of times of scanning multiplicity when the number of times of scanning given by the scanning multiplicity × scanning distance is performed. Incidentally, in the example of FIG. 3, the inspection line with the address 7 is scanned four times in the 25th scan.

  Note that the data of the scanning multiplicity and the scanning distance for determining the scanning set 101 are set by the user via an input device and a display device provided in the control unit 6. Information (scanning multiplicity, scanning distance, etc.) defining the set scan set 101 is stored in the storage device of the control unit 6, and the control unit 6 corrects the correction control unit 43 based on the information defining the scan set 101. The scanning control of the electron beam 19 is executed via the above. Information for determining the scan set 101 is also set in the control register 207 (see FIG. 2) of the image signal processing unit 22.

  Incidentally, when the same inspection line is subjected to multiple scanning, it is necessary to calculate the addition average of the digital image signals of the inspection lines obtained in each scan. The addition average is calculated by the addition averaging unit shown in FIG. 209. As described above, the addition averaging unit 209 saves the added value of the digital image signal of the inspection line in the image memory 206 until the predetermined number of additions is completed. Therefore, the addition controller 208 frequently accesses the image memory 206. Therefore, the addition controller 208 includes an image memory address control unit that calculates an address of the image memory 206 suitable for multiple scanning using the scanning set 101.

  FIG. 4 is a diagram showing an example of the configuration of an image memory address control unit included in the addition controller 208 and generating a memory address for accessing the image memory 206. As shown in FIG. 4, the image memory address control unit 208a includes a pointer control unit 226, a scan set memory 227, a reference position generation unit 228, an address generation unit 229, and the like.

  The address generation unit 229 generates a memory address 234 for accessing the image memory 206. Note that the memory address 234 generated here is an image memory access signal 216 by combining the read / write control signals of the image memory 206 separately generated in the addition controller 208.

  The reference position generation unit 228 generates a reference position address 102 (see FIG. 3) of the scan set 101 including the inspection line scanned at that time, and supplies the reference position address 102 to the address generation unit 229. Further, the scan set memory 227 generates a relative address from the reference position address 102 for each inspection line in the scan set 101 and supplies the relative address to the address generator 229. Accordingly, the address generation unit 229 obtains the address of the inspection line being scanned based on the reference position address 102 and the relative address from the reference position address 102, and based on the inspection line address and the pixel position, A memory address 234 for accessing the image memory 206 can be generated.

  Here, the reference position generation unit 228 is configured by, for example, a counter, and the counter is initialized when an inspection target region in the sample 9 to be inspected is determined and inspection is started, and the scan set 101 is updated. This is incremented each time a scan set identification signal 230 indicating this is input. The scan set identification signal 230 is changed as a signal for identifying the scan set 101 every time the scan set 101 changes.

  The scan set memory 227 stores relative address data according to the configuration of each scan set 101, and the relative address data is selected by the pointer control unit 226. At this time, the pointer provided in the pointer control unit 226 is initialized (cleared to zero) when the scan set identification signal 230 is input, and is incremented when the synchronization signal 211 is input.

  FIG. 5 is a diagram illustrating an example of data stored in the scan set memory 227 according to the configuration of each scan set 101. 5A shows an example in which the scanning multiplicity is “2” and the scanning distance is “2”, and FIG. 5B shows an example in which the scanning multiplicity is “4” and the scanning distance is “3”. For example, (c) is an example when the scanning multiplicity is “8” and the scanning distance is “4”, and (d) is an example when the scanning multiplicity is “16” and the scanning distance is “2”. is there.

  In the case of the example of the scan set 101 shown in FIG. 3, the scan multiplicity is “4” and the scan distance is “2”. Therefore, the data stored in the scan set memory 227 is shown in FIG. This corresponds to the data set to 0, 2, 4 and 6.

  As described above, in this embodiment, the image memory address control unit 208a is provided in the addition controller 208, and the scan set memory 227 is provided in the image memory address control unit 208a. Even if the configuration is different, it is possible to cope with the problem by simply rewriting the data stored in the scan set memory 227. Therefore, the SEM visual inspection apparatus 1 according to the present embodiment can flexibly cope with various scanning methods.

<4. Basic scanning method>
Hereinafter, a specific example of the scanning method performed by the SEM visual inspection apparatus 1 according to the present embodiment will be described. FIG. 6 is a diagram showing an example of a basic scanning method by the SEM type visual inspection apparatus 1 according to the present embodiment. This basic scanning method corresponds to a scanning method that has been generally performed.

  FIG. 6A shows a state in which the electron beam 19 scans the inspection line 300 on the surface of the sample 9 to be inspected (see FIG. 1) in a predetermined direction (forward direction) at a predetermined line pitch 301 in order from the top. Has been. FIG. 6B shows the time transition of the deflection voltages Vx and Vy of the scanning deflector 15 during scanning, and the time transition of the synchronization signal sent to the secondary electron detector 7 and the scanning signal generator 44. (Here, it is assumed that the scanning deflector 15 is an electrostatic deflection system).

  Here, each of the scans 302 to 305 in FIG. 6A corresponds to the operation of the scanning deflector 15 in the time sections 302 to 305 in FIG. 6B is a horizontal synchronization signal (H-valid signal) for the image signal output from the secondary electron detector 20, and corresponds to the synchronization signal 53 of FIG.

  In FIG. 6B, Vx and Vy indicate changes in deflection voltages in the x and y directions applied to the scanning deflector 15 when the sample stage (X stage 31 and Y stage 32) is not moved. However, the sample stage may be moved in the y direction with Vy kept constant (the same applies to Vy in other scanning methods described later).

  Further, in this example of the basic scanning method, scanning (moving) in the y direction is not performed (Vy is constant) while the electron beam 19 is scanned in the x direction (Vx is in the ramp waveform rising to the right). However, it is not limited to that. For example, the electron beam 19 may be scanned in the ± x directions while moving the sample stage in the y direction (the same applies to other scanning method examples described later).

  FIG. 7 is a diagram showing an example of a flowchart showing the operation of the image signal processing unit 22 in the basic scanning method. Hereinafter, the operation of the image signal processing unit 22 will be described with reference to FIGS. 7 and 2.

  First, using the shift register in the synchronization circuit 201, the synchronization signal 211 input from the correction control unit 43 and the digital image signal 210 input from the AD converter 200 based on control data preset in the control register 207. (Step S10).

  Next, the rate conversion unit 202 adds the sampling rate in the AD converter 200 based on the control data set in advance in the control register 207 according to the number of times the addition average unit 209 adds the sampling rate. Conversion to a clock rate for division is performed (step S11). However, in the example of the basic scanning method of FIG. 6, since the addition processing in the addition averaging unit 209 is not performed, the sampling rate is not particularly converted.

  Next, the PS conversion unit 203 converts the parallel data of the digital image signal 210 obtained by the shift register 205 and subjected to the averaging process (however, in this example, which is not subjected to the averaging process) into serial data (step S1). S12), the serial data is transmitted to the optical conversion unit 23. The optical conversion unit 23 converts the received electrical signal of serial data into an optical signal (step S13).

<4. Additive scanning with precharge>
FIG. 8 is a diagram showing an example of the addition scanning method with precharge by the SEM type appearance inspection apparatus 1 according to the present embodiment.

  FIG. 8A shows precharge or discharge on the inspection line 300 on the surface of the specimen 9 to be inspected (see FIG. 1) at a predetermined line pitch 301 in order from the top by scanning in the backward direction (the direction of the broken arrow). In addition, a scan set 101 is shown in which an inspection scan for acquiring an image signal by the secondary electron detector 20 is performed twice in the forward direction (the direction of the solid line arrow). FIG. 8B shows the time transition of the deflection voltages Vx and Vy of the scanning deflector 15 during scanning, and the time transition of the synchronization signal sent to the secondary electron detector 7 and the scanning signal generator 44. It is shown.

  Here, the backward scans 302 and 303 and the forward scans 310 and 311 in FIG. 8A correspond to the operation of the scanning deflector 15 in the time sections 302, 303, 310, and 311 in FIG. 8B, respectively. Yes. Further, since the synchronization signal is a horizontal synchronization signal (H-valid signal) for the image signal output from the secondary electron detector 20, the synchronization signal is not turned on in the time interval of the backward scans 302 and 303.

  In FIGS. 8A and 8B, the backward scans 302 and 303 may be inspection scans for acquiring an image signal by the secondary electron detector 20 instead of charge or discharge scans. In that case, the image signal of the same inspection line is acquired four times. Therefore, the synchronization signal in FIG. 8B is also in the ON state during the time intervals of the backward scans 302 and 303.

  FIG. 9 is a diagram showing an example of a flowchart showing the operation of the image signal processing unit 22 in the addition scanning method with precharge shown in FIG. Hereinafter, the operation of the image signal processing unit 22 will be described with reference to FIGS. 9 and 2.

  First, using the shift register in the synchronization circuit 201, the synchronization signal 211 input from the correction control unit 43 and the digital image signal 210 input from the AD converter 200 based on control data preset in the control register 207. (Step S20).

  Next, the rate conversion unit 202 adds the sampling rate in the AD converter 200 based on the control data set in advance in the control register 207 according to the number of times the addition average unit 209 adds the sampling rate. Conversion is made to the clock rate for division (step S21).

  Next, the addition controller 208 adds the data of the digital image signal 210 obtained from the secondary electron detector 20 by the forward scans 310 and 311 (step S22). In the example of FIG. 8, the scan set 101 has a scan multiplicity of “2” and a scan distance of “0”. That is, the data of the digital image signal 210 of the inspection line of the same address is acquired twice and added. Note that the number of additions is set in the control register 207 in advance.

  Next, the addition controller 208 determines whether or not the addition process has been performed a predetermined number of times (the number set in the control register 207) (step S23), and the addition is repeated until the predetermined number of additions is completed (step S23). No in step S23). When the addition is performed a predetermined number of times (Yes in step S23), the addition controller 208 performs a division process by the shift register 205 (step S24), and averages the data of the added digital image signal 210. Get the value.

  The average value of the digital image signal data thus obtained is converted from parallel data to serial data by the PS converter 203 (step S24), and further converted from an electrical signal to an optical signal by the light converter 23. (Step S25).

  When the backward scans 302 and 303 are also inspection scans in which the secondary electron detector 20 acquires an image signal, the scan multiplicity of the scan set 101 is “4”. In this case, the address generation unit 229 (see FIG. 4) calculates the memory address of each pixel position with respect to the image memory 206 in the reverse direction in the forward scans 310 and 311 and the backward scans 302 and 303, respectively. There is a need.

  As described above, in the addition scanning method with precharge, the digital image signal data of the same inspection line 300 is acquired and averaged a plurality of times, so that the S / N can be improved and the digital image signal with higher accuracy can be improved. Can be obtained. Further, when the backward scan is also an inspection scan in which the secondary electron detector 20 acquires an image signal, the dead time for returning the electron beam 19 can be eliminated, so that a high-throughput multiple addition scan is realized. be able to.

<5. Multiple line addition scanning method>
FIG. 10 is a diagram showing an example of the multiple line addition scanning method by the SEM type visual inspection apparatus 1 according to the present embodiment. The multi-line addition scanning method is a scanning method that makes the most effective use of the concept of the scanning set 101 (see FIG. 3).

  FIG. 10A shows a scanning set 315 in which the electron beam 19 has a configuration in which the scanning multiplicity is “4” and the scanning distance is “1” on the inspection line 300 on the surface of the specimen 9 (see FIG. 1). The scanning is shown based on the above. In this scan set 315, not only forward scanning (scanning in the direction of solid arrows) but also backward scanning (scanning in the directions of broken arrows) is an inspection scan in which the secondary electron detector 20 acquires an image signal. It is said.

  Further, in FIG. 10A, the scanning order is as shown by arrows (1), (2), (3),..., But FIG. Is collectively shown for each scan set 315, as in FIG. From this figure, this operation method is such that one scan set 315 is advanced in the line pitch direction (y direction in the figure) by repeating the scan in which the forward scan and the backward scan are alternately repeated, and the line pitch is advanced four times one by one. It can be seen that this is a scanning method that is shifted and repeated.

  In FIG. 10B, the method and the order of scanning the inspection line in the scan set 315 are shown below the vertical axis, and the scan set 315 is executed to the right of the horizontal axis. The time transition is shown. Accordingly, FIG. 10B shows that the fourth inspection line 314 from the top has undergone four inspection scans for acquiring image signals in the thirteenth forward scan. The digital image signals thus obtained by scanning the same inspection line 314 are added together and averaged.

  In FIG. 10C, the time transition of the deflection voltages Vx and Vy of the scanning deflector 15 at the time of scanning, and the secondary electron detector 7 (see FIG. 1) and the scanning signal generator 44 are sent. A time transition of the synchronization signal 53 is shown.

  In the multi-line addition scanning method as described above, the same inspection line is not continuously scanned. For example, in the example of FIG. 10, each inspection line is not scanned for 1.5 reciprocating scans. Is secured. That is, the same inspection line is scanned at regular intervals. When the same inspection line is scanned at regular intervals rather than continuously, the charge control efficiency on the surface of the sample 9 to be inspected is significantly improved depending on the type of wafer and the processing process (scanning environment) of the wafer. In this case, high-accuracy and high-contrast image acquisition is possible, and as a result, surface defect detection performance is improved.

  FIG. 11 is a diagram showing an example of a flowchart showing the operation of the image signal processing unit 22 in the multiple line addition scanning method shown in FIG. Note that the operation of the image signal processing unit 22 in the multiple line addition scanning method is substantially the same as the operation of the image signal processing unit 22 shown in FIG. 9, and therefore, here, the addition processing (step S22 in FIG. 9). ) To the division process (step S24) will be described in detail in conformity with the multiple line addition scanning method.

  The addition controller 208 can know the start timing of the scan set 315 based on the scan set identification signal 230 (see FIG. 4) sent through the same path as the synchronization signal 211. Therefore, the addition controller 208 determines whether or not the scan is the first scan in the scan set 315. If the scan is the first scan (Yes in step S30), the addition controller 208 acquires the scan. Image data (data obtained as a digital image signal 210 output from the AD converter 200) is saved (stored) in the image memory 206 in association with the address of the inspection line to be scanned and the pixel position in the inspection line. (Step S34). On the other hand, if the scan is not the first scan in the scan set 315 (No in step S30), the scan is saved in association with the address of the inspection line to be scanned and the pixel position in the inspection line. Image data is read back from the image memory 206 (step S31).

  Next, the addition controller 208 performs an addition process between the image data read back from the image memory 206 and the image data acquired by the scanning (step S32), and the number of additions is determined by the scanning set 315. If (scan multiplicity) has not been reached (No in step S33), the image data obtained by the addition processing in the previous step corresponds to the address of the inspection line to be scanned and the pixel position in the inspection line. In addition, it is saved (stored) in the image memory 206 (step S34). On the other hand, when the number of additions has reached the number of additions (scanning multiplicity) determined by the scan set 315 (Yes in step S33), the image data obtained by the addition process in the previous step is used as the shift register 205. Forward to. The shift register 205 performs division processing by bit shift (step S34), and obtains an average of image data obtained by scanning the inspection line a plurality of times.

<5. GUI (Graphical User Interface)>
FIG. 12 is a diagram showing an example of a GUI operation screen in the SEM type appearance inspection apparatus 1 according to the present embodiment. As shown in FIG. 12, the GUI operation screen 500 includes an inspection condition window 510, an inspection result display window 520, a scanning method setting window 530, an operation menu bar 540, and the like. The GUI display screen 500 is displayed on a display device attached to the control unit 6 (see FIG. 1) or the monitor 50 of the image display unit 5.

  The scanning method setting window 530 is provided with input fields 560, 570, and 580 for designating a scanning method, a backtracking, multiple scanning, and the like. In the input column 560 for the scanning method, a one-way scanning (one-way) method, a two-way scanning (two-way) method with a back-up, or the like is designated. Also, in the input field 570 for returning, the role of the returning scan is set by the scanning method for performing the returning. That is, whether to acquire image data, precharge or discharge, etc. is set in the back-up scanning. In the multiple scanning input field 580, the number of times of scanning the same inspection line and the distance between the inspection lines to be scanned are set. Based on the information thus set, data constituting the scan set is set.

  Note that these input fields 560, 570, and 580 may be used as pull-down menus to allow the user to select setting data prepared in advance.

  Based on the scanning method set by the scanning method setting window 530, what kind of scanning is performed is displayed in the inspection condition window 510 in the form of an inspection line configuration 505 or a scanning set configuration (not shown). Therefore, the user can visually confirm what kind of scanning is performed by the set scanning method.

  The inspection condition window 510 displays an inspection index 550 related to the set scanning method. The inspection index 550 is an index amount that represents the quality and inspection throughput of the inspection obtained by the designated scanning method, and includes, for example, the number of scanning lines, charging stability, dose, and inspection speed.

  When the conditions for the inspection as described above are set, for example, when the inspection start button of the operation menu bar 540 is clicked, the control unit 6 sets the electron beam 19 based on the set various conditions and scan set data. The set inspection is executed while controlling the scanning. When the inspection is completed, the inspection result is displayed in the inspection result display window 520. In the inspection result display window 520, for example, the number of defects, the number of defect dies, the defect density, the inspection time, the inspection date and time, and the like are displayed. In addition, when a tab with “wafer” or “die” is clicked in the inspection condition window 510, the inspection condition window 510 displays a wafer map or a die map displaying defect positions in the wafer or die. Is done.

  Note that the setting data input in the scanning method setting window 530 or the like may be set in advance using a recipe or the like, for example. When the recipe creation start button on the operation menu bar 540 is clicked, a recipe creation support screen (not shown) is displayed. The user creates a recipe using the screen. be able to. If a recipe is created in advance, it is possible to save the user from setting data such as the intersection method when starting the inspection, so that the efficiency of the inspection can be improved and the input error of the user can be eliminated. Further, since there is no user input, the inspection can be automated.

DESCRIPTION OF SYMBOLS 1 SEM type external appearance inspection apparatus 2 Inspection room 3 Electron optical system 4 Optical microscope part 5 Image processing part 6 Control part 7 Secondary electron detection part 8 Sample room 9 Sample to be inspected 10 Electron gun 11 Electrode 12 Condenser lens 13 Blanking deflector DESCRIPTION OF SYMBOLS 15 Scanning deflector 16 Objective lens 17 Reflector 18 ExB deflector 19 Electron beam 20 Secondary electron detector 21 Preamplifier 22 Image signal processing part 23 Optical conversion part 24 Optical transmission line 25 Electrical conversion part 26 High voltage power supply 27 Preamplifier drive power supply 28 AD converter drive power supply 29 Reverse bias power supply 30 Sample stage 31 X stage 32 Y stage 34 Length monitor for position monitor 35 Measuring instrument 36 High voltage power supply 40 Light source 41 Optical lens 42 CCD camera 43 Correction controller 44 Scanning signal generator 45 Objective Lens power supply 46 First image storage unit 47 Second image storage unit 48 Arithmetic unit 49 Defect determination unit 50 Monitor 51 Secondary electron 52 Second secondary electron 53 Synchronization signal 101 Scan set 102 Reference position address 200 AD converter 201 Synchronization circuit 202 Rate conversion unit 203 PS conversion unit 204 Addition unit 205 Shift register 206 Image memory 207 Control register 208 Addition controller 208a Image memory address control unit 209 Addition averaging unit 210 Digital image signal 211 Synchronization signal 226 Pointer control unit 227 Scan set memory 228 Reference position generation unit 229 Address generation unit 230 Scan set identification signal 234 memory address

Claims (9)

A scanning control unit that controls scanning of the electron beam; and an image signal processing unit that processes an image signal of the substrate surface obtained by scanning the substrate surface with the electron beam, and the image signal processing unit performs processing. A SEM type visual inspection apparatus for inspecting the appearance defect of the substrate surface based on the image signal,
The scanning control unit
Based on the information of the scan set consisting of a plurality of scans determined by the number of scan lines to be scanned and the distance between the scan lines, the scan line determined by the information of the scan set from the scan line at the address of the predetermined initial position A first scan set scanning control process for performing a control of scanning the number of scan lines determined by the information of the scan set for each distance;
A second scan set scan control process that repeats the first scan set scan control process while incrementing the address of the predetermined initial position one by one;
The SEM type visual inspection apparatus characterized by performing The image signal processor is
The SEM type visual inspection apparatus according to claim 1, wherein the image signals acquired by scanning the scanning lines with the same address are added and averaged. The image signal processor is
An image memory that temporarily stores the acquired image signal; and an address control unit that controls an address for accessing the image memory.
The address control unit
An address for accessing the image memory is generated based on an address of an initial position of a scan set including a scan line scanned at that time and a relative address in the scan set of the scan line. The SEM type appearance inspection apparatus according to claim 2. The address control unit
A scan set memory storing a relative address from the initial position of each scan line in the scan set obtained based on the number of scan lines determined in the scan set and a distance between the scan lines;
The SEM type visual inspection apparatus according to claim 3, wherein a relative address in the scan set of the scanned scan line is obtained by reading the scan set memory. The scanning control unit
5. The scanning is controlled such that scanning in at least one of a forward direction and a backward direction is scanning for acquiring an image signal with respect to scanning determined by the scanning set. The SEM type visual inspection apparatus according to any one of the above. The scanning is performed so that the scanning in one of the forward direction and the backward direction is a scanning for acquiring an image signal, and the scanning in the other direction is a scanning for precharge or discharge with respect to the scanning determined by the scanning set. The SEM type visual inspection apparatus according to claim 1, wherein the SEM type visual inspection apparatus is controlled.


A scanning control unit that controls scanning of the electron beam; and an image signal processing unit that processes an image signal of the substrate surface acquired by scanning the substrate surface with the electron beam, and the image signal processing unit performs processing. An image signal processing method in an SEM type visual inspection apparatus that inspects defects on the appearance of the substrate surface based on the image signal,
The scanning control unit is
Based on the information of the scan set consisting of a plurality of scans determined by the number of scan lines to be scanned and the distance between the scan lines, the scan line determined by the information of the scan set from the scan line at the address of the predetermined initial position A first scan set scanning control process for performing a control of scanning the number of scanning lines determined by the information of the scanning set for each distance;
A second scan set scan control process in which the first scan set scan control process is repeated while incrementing the address of the predetermined initial position one by one;
When running
The image signal processing unit is
An image signal processing method in an SEM type visual inspection apparatus characterized in that image signals obtained by scanning of scanning lines with the same address are added together and averaged. The image signal processor is
An image memory for temporarily storing the acquired image signal;
An address for accessing the image memory is generated based on an address of an initial position of a scan set including a scan line scanned at that time and a relative address in the scan set of the scan line. An image signal processing method in the SEM type visual inspection apparatus according to claim 7. The image signal processor is
A scan set memory storing a relative address from the initial position of each scan line in the scan set obtained based on the number of scan lines determined in the scan set and a distance between the scan lines;
The image signal processing method in the SEM type visual inspection apparatus according to claim 8, wherein the relative address in the scan set of the scanned scan line is obtained by reading the scan set memory.

Images