JP3608451B2 - Inspection apparatus and inspection method using a scanning electron microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inspection apparatus and an inspection method using a scanning electron microscope for inspecting a semiconductor device having a fine pattern, a substrate, a photomask (exposure mask), a liquid crystal, and the like.
[0002]
[Prior art]
A semiconductor device such as a memory or a microcomputer used for a computer or the like is manufactured by repeating a process of transferring a pattern such as a circuit formed on a photomask by an exposure process, a lithography process, an etching process, or the like. In the manufacturing process of a semiconductor device, the quality of the results of lithography processing, etching processing, and other processing, and the presence of defects such as generation of foreign matter greatly affect the manufacturing yield of the semiconductor device. Therefore, in order to detect the occurrence of abnormality or defect early or in advance, a pattern on the semiconductor wafer is inspected at the end of each manufacturing process.
[0003]
As an example of a method for inspecting a defect present in a pattern on a semiconductor wafer, an optical appearance inspection apparatus that compares patterns using an optical image obtained by irradiating a semiconductor wafer with light has been put into practical use. As an example of an inspection method using an optical image, as described in Japanese Patent Laid-Open No. 3-167456, an optically illuminated region on a substrate is imaged by a time delay integration sensor, and the image and the image are input in advance. As described in Japanese Patent Publication No. 6-58220, a method for detecting a defect by comparing with a design characteristic that has been used and Japanese Patent Publication No. 6-58220 monitor image deterioration at the time of image detection. Thus, there is a method of performing a comparative inspection with a stable optical image.
[0004]
As described above, the defect inspection method using an optical image has already been put into practical use as an optical appearance inspection apparatus, but has the following problems. That is, in the case of inspection of a semiconductor wafer in the manufacturing process, foreign matters and defects in the case of inspection of a pattern having a silicon oxide film or a photosensitive photoresist material on the surface through which light can be transmitted cannot be detected. Further, it is impossible to detect an etching residue that is below the detection limit or a non-opening defect of a minute conduction hole due to the resolution of the optical system. Further, it is impossible to detect a defect generated at the bottom of the step of the wiring pattern.
[0005]
As described above, with the miniaturization of circuit patterns, the complexity of circuit pattern shapes, and the diversification of materials, it is difficult to detect such defects in optical images, so electron beam images with higher resolution than optical images. Have been put to practical use as a method for inspecting defects such as patterns and an apparatus for the inspection.
[0006]
For example, JP 59-192943 A, JP 5-258703 A, Sandland, et al. , * An electro-beam inspection system for x-ray mask production *, J. et al. Vac. Sci. Tech. B, Vol. 9, no. 6, pp. 3005-3009 (1991), literature Meisburger, et al. * Requirements and performance of an electron-beam column designed for x-ray mask inspection *, J. Vac. Sci. Tech. B, Vol. 9, no. 6, pp. 3010-3014 (1991), literature Meisburger, et al. , * Low-voltage electron-optical system for the high-speed inspection of integrated circuits *, J. et al. Vac. Sci. Tech. B, Vol. 10, no. 6, pp. 2804-2808 (1992), Hendricks, et al. * Characterization of a New Automated Electron-Beam Wafer Inspection System *, SPIE Vol. 2439, pp. 174-183 (20-22 February, 1995)) and the like are known.
[0007]
To perform high-throughput and high-accuracy inspection following wafer diameter increase and circuit pattern miniaturization, images with a high S / N ratio (the ratio of noise to the signal is small) are acquired at a very high speed. There is a need to. Therefore, the number of electrons irradiated using a high-current electron beam of 100 times or more, for example, 10 nA or more of a normal scanning electron microscope (hereinafter referred to as SEM) is secured, and a high SN ratio is maintained. Furthermore, high-speed and highly efficient detection of secondary electrons and reflected electrons generated from the substrate is essential.
[0008]
Further, a low acceleration electron beam of 2 KeV or less is irradiated so that a semiconductor substrate with an insulating film such as a resist is not affected by charging. This technology is described in pages 622 to 623 of the “Electron / Ion Beam Handbook (2nd edition)” edited by the 132nd Committee of the Japan Society for the Promotion of Science (Nikkan Kogyo Shimbun, 1986). However, aberrations due to the space charge effect occur in a high-current and low-acceleration electron beam, and high-resolution observation is difficult.
[0009]
As a method for solving this problem, there is known a method in which a high acceleration electron beam is decelerated immediately before a sample and irradiated on the sample as a substantially low acceleration electron beam. For example, there are techniques described in JP-A-2-142045 and JP-A-6-139985.
[0010]
The inspection apparatus using the above SEM has the following two problems.
[0011]
For one, the conventional method of forming an electron beam image by SEM requires a very long time, and therefore it takes a very long time to inspect a circuit pattern over almost the entire surface of a semiconductor wafer. Therefore, in order to obtain a practical throughput in a semiconductor device manufacturing process or the like, it is necessary to acquire an electron beam image at a very high speed. In order to achieve this high speed, a method of acquiring an image by scanning the sample with an electron beam while continuously moving the sample stage as described in Japanese Patent Laid-Open No. 5-258703 can be considered. Moreover, it is necessary to ensure the SN ratio of the electron beam image acquired at high speed and to maintain a predetermined accuracy.
[0012]
Another problem is that unlike the optical type, the pixel information constituting the image is detected one by one in order, so that the image displayed on the display is inverted depending on the direction of acquisition. . This problem does not occur in a general SEM because the specimen is fixed and the electron beam is always scanned in a fixed direction, and the correspondence between the direction and the scanning direction of the display screen is kept. However, in the case of an inspection apparatus, in order to pursue the high speed of the first problem, it is necessary to acquire an image while continuously moving the sample stage. However, the image may be reversed depending on the moving direction. For this reason, the user may have erroneously recognized the position, shape, direction, etc. of the defect.
[0013]
[Problems to be solved by the invention]
The present invention has been made in view of such points, and at the same time, a defect difficult to detect in an optical image is detected with high accuracy using an electron beam image. Another object of the present invention is to provide an inspection apparatus and an inspection method using a scanning electron microscope excellent in accuracy.
[0014]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present invention scans a sample with an electron beam, compares a first image generated based on a detection signal of a secondary charged particle generated, and a second image, In an inspection apparatus using a scanning electron microscope that detects defects in the pattern of The control unit that detects the scanning direction of the primary electron beam and the direction of the line pitch, and the detection unit that detects the image formed based on the signal from the detector to be an erect image. Based on the scanning direction of the primary electron beam and the direction of the line pitch A display means for displaying is provided.
[0015]
The present invention also provides: Regardless of the scanning direction of the primary electron beam, display means for always displaying an image formed based on a signal from the detector based on a predetermined coordinate system, and a stage for spatially moving the sample stage And acquiring the image data of the first region and the second region based on the movement of the sample stage by the stage mechanism, and the same set of electron optical devices, When acquiring image data of the first area and the second area, the moving direction of the stage is reversed. It is characterized by that.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0018]
(Example 1)
1 to 2 show a first embodiment of the present invention.
[0019]
FIG. 1 is a longitudinal sectional view showing a configuration of an SEM visual inspection apparatus 1 which is an example of an inspection apparatus using a scanning electron microscope to which the present invention is applied. The SEM visual inspection apparatus 1 includes an inspection chamber 2 in which the chamber is evacuated, and a preliminary chamber (not shown in the present embodiment) for transporting the sample substrate 9 into the inspection chamber 2. The spare chamber is configured to be evacuated independently of the examination chamber 2. The SEM visual inspection apparatus 1 includes an image processing unit 5, a control unit 6, and a secondary electron detection unit 7 in addition to the inspection room 2 and the spare room.
[0020]
The inspection chamber 2 is roughly divided into an electron optical system mechanism 3, a sample chamber 8, and an optical microscope section 4. The electron optical system mechanism 3 includes an electron gun 10 and an electron beam extraction electrode.
11, a condenser lens 12, a blanking deflector 13, a diaphragm 14, a scanning deflector 15, an objective lens 16, a reflecting plate 17, and an E-cross B deflector 18. Of the secondary electron detector 7, the secondary electron detector 20 is disposed above the objective lens 16 in the examination room 2.
[0021]
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, and the X stage 31, Y on the sample stage 30. The sample substrate 9 mounted on the stage 32 and the rotary stage 33 is irradiated. The sample substrate 9 is a substrate having a fine circuit pattern such as a semiconductor wafer, a chip, or a liquid crystal or a mask. A scanning signal generator 44 for generating a scanning signal and a blanking signal is connected to the blanking deflector 13, and an objective lens power supply 45 is connected to the objective lens 16.
[0022]
The output signal of the secondary electron detector 20 is amplified by a preamplifier 21 installed outside the examination room 2, and an analog signal is converted into a digital signal by an AD converter 22 to create digital data.
[0023]
The sample chamber 8 includes a sample stage 30, an X stage 31, a Y stage 32, and a rotary stage.
33, a position monitor length measuring device 34, and a sample substrate height measuring device 35. The optical microscope unit 4 is provided in the vicinity of the electron optical system mechanism 3 in the examination room 2 and at a position separated from each other so as not to affect each other, and between the electron optical system mechanism 3 and the optical microscope unit 4. The distance of is known. Then, the X stage 31 or the Y stage 32 reciprocates a known distance between the electron optical system mechanism 3 and the optical microscope unit 4. The optical microscope unit 4 includes a light source 40, an optical lens 41, and a CCD camera 42.
[0024]
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. The captured electron beam image or optical image is displayed on the monitor 50.
[0025]
Operation commands and operation conditions of each part of the apparatus are input / output from the control unit 6. In the control unit 6, 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, a moving speed of the sample stage 30, and the like are arbitrarily set according to the purpose. It is entered so that it can be selected or set. The control unit 6 uses the correction control circuit 43 to monitor the position and height deviation from the signals of the position monitor length measuring device 34 and the sample substrate height measuring device 35, and generates a correction signal based on the result. A correction signal is sent to the objective lens power supply 45 and the scanning signal generator 44 so that the electron beam is always applied to the correct position.
[0026]
In order to acquire an image of the sample substrate 9, a finely focused electron beam 19 is irradiated onto the sample substrate 9 to generate secondary electrons 51, which are scanned by the electron beam 19 and the X stage 31 and Y stage 32. By detecting in synchronization with the movement, an image of the sample substrate 9 is obtained.
[0027]
In the SEM visual inspection apparatus 1, it is essential that the inspection speed is high. Therefore, unlike an ordinary SEM of the conventional method, scanning with an electron beam having a current of pA order is not performed at a low speed, and multiple scanning and superimposition of each image are not performed. In order to suppress charging of the insulating material, it is necessary to scan the electron beam once or several times at a high speed so as not to perform many scans. Therefore, in this embodiment, an image is formed by scanning an electron beam with a large current of about 100 times or more, for example, 100 nA, as compared with a conventional SEM, only once.
[0028]
The electron gun 10 uses a diffusion replenishment type thermal field emission electron source. By using this electron gun 10, a stable electron beam current can be ensured as compared with a conventional tungsten filament electron source or a cold field emission electron source. Therefore, an image with little brightness fluctuation can be obtained. In addition, since the electron beam current can be set large by the electron gun 10, a high-speed inspection as described later can be realized.
[0029]
A negative voltage can be applied to the sample substrate 9 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 substrate 9 can be adjusted to an optimum value without changing the potential of the electron gun 10.
[0030]
Secondary electrons 51 generated by irradiating the sample substrate 9 with the electron beam 19 are accelerated by a negative voltage applied to the sample substrate 9. Above the sample substrate 9, an E-cross B 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 arranged. The secondary electrons 51 are deflected in a predetermined direction. The amount of deflection can be adjusted by the strength of the electric field and magnetic field applied to the E-cross B deflector 18. The electric field and magnetic field can be varied in conjunction with the negative voltage applied to the sample substrate 9.
[0031]
The secondary electrons 51 deflected by the E-cross B deflector 18 collide with the reflecting plate 17 under a predetermined condition. The reflection plate 17 has a conical shape, and also has a function of a shield pipe that shields an electron beam 19 that passes through the inside of the reflection plate 17 and is irradiated on the sample substrate 9. 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.
[0032]
The secondary electron detector 7 is provided with a secondary electron detector 20 in the evacuated examination chamber 2, and a preamplifier 21, an AD converter 22, a light conversion means 23, a light transmission means outside the examination room 2. 24, electrical conversion means 25, high voltage power supply 26, preamplifier drive power supply 27,
An AD converter drive power supply 28 and a reverse bias power supply 29 are provided.
[0033]
Of the secondary electron detector 7, the secondary electron detector 20 is disposed above the objective lens 16 in the examination room 2. Secondary electron detector 20, preamplifier 21, AD converter
22, the optical conversion means 23, 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. The second secondary electrons 52 generated by colliding with the reflecting plate 17 are guided to the secondary electron detector 20 by the suction electric field generated by this positive potential.
[0034]
The secondary electron detector 20 is configured to detect the second secondary electrons 52 generated when the secondary electrons 51 collide with the reflecting plate 17 in conjunction with the scanning timing of the electron beam 19. . 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 22.
[0035]
The AD converter 22 is configured to amplify the analog signal detected by the secondary electron detector 20 by the preamplifier 21 and immediately convert it to a digital signal and transmit it to the image processing unit 5. Since the detected analog signal is digitized and transmitted immediately after detection, it is possible to obtain a signal having a higher speed and a higher S / N ratio than before.
[0036]
The sample substrate 9 is mounted on the X stage 31 and the Y stage 32, and the X stage 31 and the Y stage 32 are stationary when the inspection is performed, and the electron beam 19 is scanned two-dimensionally. Either the 31 or the Y stage 32 can be continuously moved at a constant speed in one direction and the electron beam 19 can be linearly scanned in a direction perpendicular to the direction. In the case of inspecting a specific relatively small area, the former method of inspecting with the sample substrate 9 stationary. When inspecting a relatively wide area, the sample substrate 9 is continuously moved at a constant speed. An inspection method is effective. When the electron beam 19 needs to be blanked, the blanking deflector 13 deflects the electron beam 19 so that the electron beam does not pass through the aperture 14.
[0037]
As the position monitor length measuring device 34 for monitoring the positions of the X stage 31 and the Y stage 32, a length meter based on laser interference is used in this embodiment. The positions of the X stage 31 and the Y stage 32 can be monitored in real time, and the results are transferred to the control unit 6. Similarly, data such as the number of rotations of the motors of the X stage 31, the Y stage 32, and the rotary stage 33 is also transferred from each driver to the control unit 6, and the control unit 6 receives these data. Based on the above, the region and position where the electron beam 19 is irradiated can be accurately grasped. Therefore, the position of the irradiation position of the electron beam 19 can be corrected by the correction control circuit 43 in real time as necessary. In addition, the region irradiated with the electron beam 19 can be stored for each sample substrate 9.
[0038]
The sample substrate 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 sample substrate 9 can be measured in real time. In this embodiment, the sample substrate 9 is irradiated with 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. The method is used. Based on the measurement data of the sample substrate 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 possible to measure the warpage and height distortion of the sample substrate 9 in advance before the electron beam irradiation, and to set correction conditions for each inspection region of the objective lens 16 based on the data. It is.
[0039]
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, and a monitor 50. The image signal of the sample substrate 9 detected by the secondary electron detector 20 is amplified by the preamplifier 21, digitized by the AD converter 22, converted into an optical signal by the light conversion means 23, and then converted by the light transmission means 24. After being transmitted and converted into an electrical signal again by the electrical conversion means 25, it is stored in the first image storage unit 46 or the second image storage unit 47. The calculation 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.
[0040]
The overall configuration of the SEM visual inspection apparatus 1 has been described above, but the first embodiment of the present invention will be described below.
[0041]
FIG. 2 shows a first embodiment of the image data transfer system of the present invention, and is a top view of the sample substrate 9 and an image displayed on the monitor 50. FIG. 2 shows an example of a method of scanning the inspection cell 200 on the sample substrate 9. In the drawing, the number “5” is used instead of the actual circuit pattern for the sake of simplicity of explanation.
[0042]
In FIG. 2, similarly to the conventional SEM, the electron beam 19 is scanned two-dimensionally while the sample substrate 9 is stationary, and an image of the inspection cell 200 is formed. Then, the acquired image of the adjacent inspection cell 200 is stored in the first image storage unit 46 or the second image storage unit 47 shown in FIG. 1, the images are compared by the calculation unit 48, and the defect is determined by the defect determination unit 49. doing.
[0043]
As can be seen from the enlarged view of the inspection cell 200, the line pitch direction is different between the image on the upper side and the image on the lower side with respect to the paper surface in FIG. That is, the upper image is first scanned for one line (pixel pitch is positive) as shown in the scanning direction (X direction) of the electron beam 19 from the upper left to the right with respect to the paper surface of the region of the inspection cell 200. ), The next line is advanced downward by the line pitch (the line pitch is negative), and this is repeated in the same manner. Since this scanning method is the same as the scanning direction 201 of the monitor display (this is called a raster scanning method), if the pixel data acquired in the scanning direction of the electron beam 19 is sequentially sent to the monitor 50, the scanning method shown in FIG. As shown in the image 501 of the upper monitor, an “5” erect image can be obtained.
[0044]
Here, the broken line indicates the period during which the electron beam 19 is turned back. Actually, the electron beam 19 is not irradiated as shown by the broken line, but is blanked so that the electron beam 19 is not irradiated on the sample substrate 9 during this period. ing. As a result, the electron beam can be uniformly and spatially irradiated onto the sample substrate 9. In the blanking, the electron beam 19 is deflected by the blanking deflector 13 so as not to pass through the diaphragm 14.
[0045]
On the other hand, in the lower image in FIG. 2, the above-described line pitch direction is positive, and the electron beam 19 is scanned from the lower side to the upper side with respect to the paper surface. For this reason, when the pixel data is sequentially sent to the monitor 50, a vertically inverted image of “5” is displayed as shown in the monitor image 502. At this time, since the control unit 6 in FIG. 1 can detect that the line pitch has changed from negative to positive, by reversing the transfer order of the line data, as shown in the monitor image 503, a positive value of “5” is obtained. A statue can be obtained.
[0046]
That is, assuming that the number of lines is 10, pointers corresponding to the order of (10) (9) (8) (7)... In the first image storage unit 46 or the second image storage unit 47 shown in FIG. The scanning data may be transferred to the monitor 50 in the order of (10) (9) (8) (7). As a result, the user can correctly and easily grasp the position, shape, direction, etc. of the defect, and the efficiency of the inspection work can be remarkably improved.
[0047]
(Example 2)
A second embodiment of the present invention is shown in FIG. FIG. 3 is a view similar to FIG. 2, and shows a second embodiment of the image data transfer system of the present invention, and is a top view of the sample substrate 9 and an image displayed on the monitor 50. The electron beam 19 is two-dimensionally scanned with the sample substrate 9 stationary to form an image of the inspection cell 200.
[0048]
The upper monitor image 504 in FIG. 3 shows a state in which an erect image is obtained, similarly to the monitor image 501 shown in FIG. It has been reversed. Also in this case, since the control unit 6 shown in FIG. 1 can detect that the pixel pitch has changed from positive to negative, the transfer order of the pixel data constituting one line is reversed, so that the monitor in FIG. In the image 506, an erect image of “5” can be obtained.
[0049]
That is, for example, assuming the case of 10 pixels, the last pixel data of each line of the first image storage unit 46 or the second image storage unit 47 shown in FIG. 1 is reversed (10) (9) (8) ( The scanning data may be transmitted to the monitor 50 in the order of 7). Since the top, bottom, left, and right of the monitor image 506 are displayed in the same manner as the image 504, the user can correctly and easily grasp the position, shape, direction, etc. of the defect, and the efficiency of the inspection work is remarkably increased. Can be improved.
[0050]
Example 3
4 to 5 show a third embodiment of the present invention. FIG. 4 shows a third embodiment of the image data transfer system of the present invention, and is a top view of the sample substrate 9 and a diagram of an image displayed on the monitor 50. FIG. 5 is a top view showing a direction in which the inspection cell is scanned with an electron beam.
[0051]
In the two-dimensional scanning of the electron beam 19 in a state where the sample substrate 9 is stationary as shown in the first embodiment and the second embodiment described above, when inspecting all over a wide area, each image acquisition area It takes a long time to scan the electron beam in a stationary state and a moving time in which acceleration, deceleration and position setting of the sample substrate 9 are added, and the entire inspection time takes a long time. Therefore, in order to perform inspection at a higher speed, the electron beam 19 is scanned in one direction at a high speed in a direction perpendicular to or intersecting with the moving direction of the sample substrate 9 while moving the sample substrate 9 continuously in one direction at a constant speed. Thus, an inspection method for acquiring an image of the region to be inspected may be used. Thereby, the acquisition time of the electron beam 19 for one scanning width of the predetermined distance can be set only to the time for which the stage moves by the predetermined distance.
[0052]
FIG. 5 shows the direction in which the inspection cell 200 is scanned with the electron beam 19, and while the Y stage 32 shown in FIG. 1 is continuously moving at a constant speed in the Y direction in FIG. 19 is scanned in the X direction. The electron beam 19 is scanned only in one direction indicated by the solid line, and blanking is performed so that the electron beam 19 is not irradiated onto the sample substrate 9 during the swinging back of the electron beam 19 indicated by the broken line. As a result, the electron beam 19 can be uniformly and spatially irradiated onto the sample substrate 9. In the blanking, the electron beam 19 is deflected by the blanking deflector 13 so as not to pass through the diaphragm 14.
[0053]
In consideration of the continuous constant speed movement of the Y stage 32 in the Y direction, the electron beam 19 is scanned slightly obliquely in the Y direction, not in the X direction. As a result, the scanning direction on the sample substrate 9 can be set to the X direction.
[0054]
FIG. 5B shows a scanning method different from that shown in FIG. 5A, in which the electron beam 19 reciprocates at a constant speed. The sample substrate 9 continuously moves at a constant speed in the Y direction, and the electron beam
When 19 is scanned in the X direction from one end to the other at a constant speed, the sample substrate 9 is sent in the Y direction by one pitch of the scanning width of the electron beam, and then the electron beam 19 is moved in the direction opposite to the X direction. Scan to the original edge at a constant speed. In the case of this method, the returning time of the electron beam 19 can be omitted.
[0055]
Also in this case, the electron beam 19 is scanned slightly obliquely in consideration of the continuous movement speed in the Y direction, not in the X direction.
[0056]
The region or position where the electron beam 19 is irradiated is obtained by transmitting measurement data from the position monitor length measuring device 34 installed on the X stage 31 and the Y stage 32 to the control unit 6 every moment. Be grasped in detail. In this embodiment, a laser interferometer is employed. Similarly, the fluctuation of the height of the region or position irradiated with the electron beam 19 is grasped in detail by measuring data from the sample substrate height measuring device 35 being transferred to the control unit 6 every moment. . Based on these data, deviations in the irradiation position and focal position of the electron beam 19 are calculated, and these deviations are automatically corrected by the correction control circuit 43.
[0057]
FIG. 4 shows an example in which the sample substrate 9 shown in FIG. 5 is continuously moved in the Y direction at a constant speed, and the electron beam 19 is scanned in the X direction at a high speed in a direction perpendicular to or intersecting with the moving direction. is there. The movement direction 210 of the center of the electron beam 19 accompanying the movement of the sample substrate 9 is as shown in FIG. 4 and is opposite to the movement direction. In order to increase the inspection speed, the sample substrate 9 moves in a zigzag pattern so that unnecessary movement is eliminated as much as possible. Therefore, the monitor image 507 of the upper inspection cell 200 in FIG. 4 shows the case where the sample substrate 9 moves in the positive direction of the Y axis and the electron beam 19 scans in the opposite direction (line pitch is negative). The monitor image 508 and the image 509 on the lower side show a case where the sample substrate 9 and the electron beam 19 are moved and scanned in completely opposite directions. This result is exactly the same as that of the first embodiment shown in FIG. 2 when the line pitch is reversed, but in this embodiment, the inversion of the line pitch is also detected from the moving direction of the sample substrate 9. it can. That is, the control unit 6 shown in FIG. 1 also manages the moving direction of the sample substrate 9, and more accurate judgment can be made if the information is taken into consideration. As a result, the user can not only speed up the inspection but also correctly and easily grasp the position, shape, direction, etc. of the defect, and the efficiency of the inspection work can be remarkably improved.
[0058]
In the first embodiment, the second embodiment, and the third embodiment, the two inspection cells to be compared are in the same direction in both the pixel pitch and the line pitch. It is not limited to. For example, when the sample substrate 9 shown in the third embodiment moves in a zigzag shape, the inspection cell at the upper end is on the upper side, and the inspection cell at the lower end has no inspection cell adjacent to the lower side. It is impossible to determine the defect. Therefore, the inspection cell at the upper end can be discriminated by comparing in the horizontal direction between the upper ends adjacent to the left and right, and the inspection cell at the lower end between the lower ends adjacent to the left and right. Is different from the case of other inspection cells. Even in such a case, the present invention is applied so as not to change the top, bottom, left, and right of the image on the monitor, so that the inspection work can proceed efficiently.
[0059]
Further, in comparison between inspection cells having different moving directions of the sample substrate 9, there may be a difference in the quality of the obtained image. By utilizing this fact, the moving direction information of the sample substrate 9 can be sent to the image processing unit 5 shown in FIG. 1 to be used for defect comparison and discrimination.
[0060]
In the SEM appearance inspection apparatus 1 shown in FIG. 1, storing all image information of the inspection of almost the entire surface of the sample substrate 9 is not performed very much because a huge storage capacity is required. Normally, only an image of a location recognized as a defect during inspection is stored, and after the inspection is completed, the position of the stored defect is designated, and the sample substrate 9 is scanned again with the electron beam 19 to generate an image. Is often acquired and reconfirmed. In this case, since the location is specified and the inspection time is not long, the sample substrate 9 is moved to that location and the image is obtained by two-dimensional scanning with the electron beam 19 in a stationary state. In such a case, an image on the monitor is displayed by the method shown in the first and second embodiments of the present invention.
[0061]
Prior to the inspection of almost the entire surface of the sample substrate 9, a trial inspection for designating inspection conditions is performed. In this case, the monitor image is displayed by the method shown in the third embodiment of the present invention. In the trial inspection, an image for several stripes or one chip is once taken into the first image storage unit 46, various inspection parameters are repeatedly changed for the captured image, and an optimum inspection parameter is determined while monitoring the image. It is. Since this trial inspection is an off-line operation, high speed is not required so much, but since the same inspection method as the next main inspection must be performed, the inspection is performed by reciprocating the sample substrate 9 as in the third embodiment. To do. The importance of the trial inspection is, for example, that the mechanical characteristics of the moving mechanism of the X stage 31 and the Y stage 32 are slightly different depending on whether the sample substrate 9 is raised or lowered, resulting in a difference in speed. It is in eliminating the possibility of impact. The moving direction of the sample substrate 9 can be said to be an important evaluation factor.
[0062]
In addition to the movement of the sample substrate 9 described above, the inspection parameters include pixel lateral shift, image brightness, image filter strength, and the like. While appropriately adjusting these inspection parameters, the moving direction of the sample substrate 9 is changed, and the evaluation is quickly performed while visually checking the acquired image. In this case, when the display image is inverted depending on the moving direction of the sample substrate 9, the user may misrecognize the test result if the correction is not performed. As a result, it is conceivable that the main inspection will be performed for a long time with inappropriate inspection parameters, and the damage caused by this misrecognition will be enormous. According to the present invention, since an erect image can always be obtained even when the image acquisition direction changes, the above-described damage can be prevented in advance.
[0063]
Example 4
FIG. 6 shows a fourth embodiment of the present invention. FIG. 6 shows a fourth embodiment of the image data transfer system of the present invention, and is a top view of the sample substrate 9 and a diagram of an image displayed on the monitor 50. The electron beam 19 is scanned in the Y direction while moving the sample substrate 9 in the opposite direction to the X direction, and the sample substrate 9 is moved by one stripe in the Y direction at the end of the sample substrate 9 so that the next stripe is the same as the previous one. Scans the electron beam 19 in the Y direction while moving the sample substrate 9 in the opposite X direction. This method is performed when the scanning direction is rotated by 90 degrees from the above-described embodiment, and defects are easier to detect by applying an electron beam in the Y direction due to the internal structure and characteristics of the sample substrate 9.
[0064]
An image 510 of the upper monitor in FIG. 6 shows a case where the line pitch direction is the positive direction of X and the scanning line by the electron beam 19 is sent from the left side to the right side with respect to the paper surface. However, when the pixel data is sequentially sent to the monitor 50, as shown in an image 511, a clockwise rotated 90 degree image of “5” is displayed. In this case, since the control unit 6 shown in FIG. 1 knows the state of the pixel pitch and line pitch, the monitor image 510 is transmitted by transmitting data in ascending order of the line pitch every descending order of the pixel pitch. An upright image of “5” can be obtained.
[0065]
The lower image in FIG. 6 is a case where the line pitch is in the negative direction of X, and when pixel data is sent to the monitor 50 in order, an inverted image of the top, bottom, left, and right as shown in the monitor image 512 is obtained. In this case, by transferring data in the descending order of the line pitch every descending order of the pixel pitch, an “5” erect image can be obtained in the monitor image 513. As described above, according to the present invention, an erect image can be always displayed on the monitor 50 regardless of the moving direction of the sample substrate 9 and the scanning direction of the electron beam 19, so that the user can determine the position and shape of the defect, The directionality and the like can be grasped correctly and easily, and the efficiency of the inspection work can be significantly improved.
[0066]
The contents of this embodiment can also be applied to the two-dimensional scanning of the electron beam 19 in a state where the sample substrate 9 is stationary as in the first or second embodiment. That is, as described in the third embodiment, when reconfirming a place recognized as a defect by two-dimensional scanning, this embodiment is used when scanning at a low speed in the X direction while scanning at a high speed in the Y direction. If implemented, an easy-to-see erect image can be obtained. In this case, even when the sample substrate 9 is continuously moved in the X direction and inspected, at the time of defect confirmation, high-speed scanning in the X direction is performed as in the first or second embodiment instead of the present embodiment. , Low-speed two-dimensional scanning in the Y direction may be used.
[0067]
The effects obtained by the present invention are shown below.
[0068]
(1) Unlike an optical image, an electron beam image in which pixel information is sequentially detected one by one may be reversed and displayed on a monitor depending on the acquisition direction. There was a risk of misrecognizing the shape and direction. According to the present invention, an erect image can always be displayed under any conditions, and an inspection apparatus and inspection method excellent in visibility and accuracy can be provided.
[0069]
(2) By applying the inspection apparatus according to the present invention to the semiconductor manufacturing process, the occurrence of abnormality can be detected quickly and accurately, so that a large number of defects can be prevented in advance. As a result, the occurrence of defects itself can be reduced, so that the reliability of semiconductor devices and the like can be improved, the development efficiency of new products and the like can be improved, and the manufacturing cost can be reduced.
[0070]
【The invention's effect】
As described above, according to the present invention, defects that are difficult to detect in an optical image can be detected with high accuracy using an electron beam image, and at the same time, the high speed of inspection and the visibility of the inspection screen, which are problematic in that case, An inspection apparatus and an inspection method using a scanning electron microscope with excellent accuracy can be provided.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a device configuration of an SEM type visual inspection apparatus.
FIG. 2 is a top view of a sample substrate and a diagram of an image displayed on a monitor, showing a first embodiment of the image data transfer system of the present invention.
FIG. 3 is a top view of a sample substrate and a diagram of an image displayed on a monitor, showing a second embodiment of the image data transfer system of the present invention.
FIG. 4 is a top view of a sample substrate and an image displayed on a monitor according to a third embodiment of the image data transfer system of the present invention.
FIG. 5 is a top view showing a direction in which an inspection cell is scanned with an electron beam.
FIG. 6 is a top view of a sample substrate and a diagram of an image displayed on a monitor, showing a fourth embodiment of the image data transfer system of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... SEM type visual inspection apparatus, 3 ... Electro-optical system mechanism, 5 ... Image processing part, 6 ... Control part, 7 ... Secondary electron detection part, 9 ... Sample substrate, 19 ... Electron beam, 20 ... Secondary electron detection , 43 ... correction control circuit, 46 ... first image storage unit, 47 ... second image storage unit,
49 ... Defect determination unit, 50 ... Monitor, 51 ... Secondary electron, 52 ... Second secondary electron,
200: Inspection cell.

Claims (4)

An electron source for generating a primary electron beam; lens means for focusing the primary electron beam; a sample stage on which a sample is placed; and primary electron beam scanning means for scanning the focused primary electron beam on the sample. A detector for detecting secondary charged particles generated from the sample, a storage means for storing an image signal of a first region on the sample based on a signal from the detector, and a storage means stored in the storage means. Image comparing means for comparing the image of the first area with the image of the second area on which the same pattern as the first area on the sample is formed; and from the comparison result of the comparing means, In an inspection apparatus using a scanning electron microscope provided with a defect determining means for determining a defect , based on a signal from the detector, a control unit for detecting the scanning direction of the primary electron beam and the direction of the line pitch, and Shape As image becomes an erect image, scanning, characterized in that comprising a display means for displaying an image based on the direction of the direction and the line pitch of the scanning of the primary electron beam detected by the control unit Inspection device using an electron microscope. The sample is irradiated with a primary electron beam for scanning, secondary charged particles generated from the sample are detected, an image signal of a first region on the sample is stored, and the first signal stored in the storage means is stored. The image of the region is compared with the image of the second region in which the same pattern as the first region on the sample is formed, and an inspection using a scanning electron microscope that discriminates the defect on the sample from the comparison result In the method, the scanning direction of the primary electron beam and the direction of the line pitch are detected, and the detected primary electron beam is detected so that an image formed based on a signal from the detector becomes an erect image. An inspection method using a scanning electron microscope, wherein an image is displayed based on a scanning direction and a line pitch direction. An electron source for generating a primary electron beam; lens means for focusing the primary electron beam; a sample stage on which a sample is placed; and primary electron beam scanning means for scanning the focused primary electron beam on the sample. A detector for detecting secondary charged particles generated from the sample, a storage means for storing an image signal of the first region on the sample based on a signal from the detector, and a storage means stored in the storage means. Image comparing means for comparing the image of the first area with the image of the second area on which the same pattern as the first area on the sample is formed; and from the comparison result of the comparing means, In an inspection apparatus using a scanning electron microscope provided with a defect discriminating unit for discriminating a defect, an image formed based on a signal from the detector is always a predetermined image regardless of the scanning direction of the primary electron beam. In the coordinate system Display means, and a stage mechanism that spatially moves the sample stage, and acquisition of image data of the first area and the second area is performed by the stage mechanism. Based on the movement, the detection means includes a detection means for detecting a repetitive direction of lines constituting the image and a display for displaying the image. This is based on a raster scanning method in which the order of the image data to be sent to the display device is changed based on the direction obtained in (1), and the display device performs a low-speed scan in the downward direction while performing a high-speed scan from the upper left to the right of the screen Detecting the inversion of the repetition direction of the lines based on the moving direction of the stage, and inverting the order of the lines constituting the image of the data to be sent to the display. Inspection apparatus using a scanning electron microscope. An electron source for generating a primary electron beam; lens means for focusing the primary electron beam; a sample stage on which a sample is placed; and primary electron beam scanning means for scanning the focused primary electron beam on the sample. A detector for detecting secondary charged particles generated from the sample, a storage means for storing an image signal of the first region on the sample based on a signal from the detector, and a storage means stored in the storage means. Image comparing means for comparing the image of the first area with the image of the second area on which the same pattern as the first area on the sample is formed; and from the comparison result of the comparing means, In an inspection apparatus using a scanning electron microscope provided with a defect discriminating means for discriminating a defect, it is formed based on a signal from the detector regardless of the scanning direction of the primary electron beam. Display means for always displaying the obtained image based on a predetermined coordinate system, and a stage mechanism for spatially moving the sample stage, and image data of the first area and the second area The acquisition is performed by the same set of electron optical devices based on the movement of the sample stage by the stage mechanism, and the stage is acquired when acquiring image data of the first area and the second area. Inspection apparatus using a scanning electron microscope characterized by reversing the moving direction.

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