JP3876668B2 - Visual inspection equipment using electron beam - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an appearance inspection apparatus using an electron beam 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 JP-A-3-167456, an optically illuminated region on a substrate is imaged by a time delay integration sensor, and the image is input in advance. A method of detecting defects by comparing the design characteristics with each other, and monitoring image deterioration at the time of image acquisition and correcting it at the time of image detection as described in Japanese Patent Publication No. 6-58220. There is a method of performing comparative inspection with a more stable optical image.
[0004]
As described above, a defect inspection method or apparatus using an optical image has already been put into practical use, 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. A method and an apparatus for inspecting a pattern using the above have been put into practical use.
[0006]
For example, Japanese Patent Publication No. 59-192943, Japanese Patent Publication No. 5-258703, literature Sandland, et al., “An electron-beam inspection system for x-ray mask production”, J. 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), Meisburger, et al., “Low-voltage electron-optical system for the high-speed inspection of integrated circuits”, J. 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]
In order to perform high-throughput and high-precision inspection following the increase in wafer diameter and circuit pattern miniaturization, it is necessary to acquire a high SN image at a very high speed. Therefore, a normal scanning electron microscope (Scanning Electron Microscopy)
The number of electrons irradiated using a large current beam 100 times or more (specifically, 10 nA or more) of SEM is ensured, 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]
In addition, a low acceleration electron beam of 2 keV or less is irradiated so that the 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 Japanese Patent Publication No. 2-142045 and Japanese Patent Publication No. 6-139985.
[0010]
The inspection apparatus using the SEM as described above has the following problems not found in the optical system.
[0011]
One is that in the case of the SEM type, the wafer is irradiated with an electron beam for a long time, and dirt (contamination) accumulates on the wafer surface. This may hinder surface treatment such as film formation and etching in the next step. Furthermore, if the same location is irradiated with a charged particle beam over a plurality of processes, an excessive amount of the charged particle beam is irradiated on the portion as the sum of the irradiation amount, which gradually leads to destruction of the device function. It has become clear.
[0012]
As a method for solving this problem, for example, as disclosed in Japanese Patent Publication No. 10-144743, the inside of each chip on the wafer is divided into blocks of arbitrary size, and the integrated irradiation dose for each block. There is a method for managing (dose amount).
[0013]
However, the SEM type inspection apparatus requires more detailed control and management for the following reasons.
(1) The above-described SEM type inspection apparatus using a large current beam has a potential exceeding the limit amount of the inspection apparatus alone.
(2) There is a need to adjust the beam current amount of the electron gun depending on the type of defect to be inspected.
(3) Due to the miniaturization of the defect size associated with the miniaturization of the wafer pattern, there are many cases where inspection is performed at a lower speed with a smaller pixel size in the future, and the dose amount is likely to increase.
(4) Contrary to (3), there is also a demand for high throughput, the inspection conditions are diverse and the operation is complicated, and a large current may be applied to the same place even with a simple operation error .
[0014]
[Problems to be solved by the invention]
The present invention has been made in view of the above points, and at the same time, a defect that is difficult to detect in an optical image is detected with high accuracy using an electron beam image. It is an object of the present invention to provide an appearance inspection apparatus using an electron beam that can realize management with high accuracy by a simple operation.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, an embodiment of the present invention detects secondary charged particles generated by irradiating a sample with a primary electron beam, and uses an image generated based on the detected signal on the sample. In an appearance inspection apparatus using an electron beam for extracting a defect and inspecting a sample, the inspection speed and the primary electron are provided with means for determining an inspection speed and means for determining a primary electron dose irradiated on the sample. When one of the doses is determined, the other is automatically adjusted according to the result.
[0016]
Further, it has means for determining a primary electron dose per area irradiated on the sample, that is, a dose amount, and is adjusted so that the primary electron dose becomes a dose amount determined by the dose amount determination means. .
[0017]
Further, the apparatus has at least one of a means for inputting a dose amount, a means for inputting a type of defect to be inspected, and a means for inputting a process name of a sample to be inspected, and the dose amount is a dose amount input means, an inspection defect type. It is determined based on at least one input content of the input means or the process name input means.
[0018]
And a means for determining a pixel pitch which is a pitch in the electron beam scanning direction of pixels constituting the inspection image, or a means for determining a line pitch which is a pitch in the electron beam feeding direction of the pixels, and the inspection speed is These are determined based on the pixel pitch or line pitch determined by the pixel pitch determining means or the line pitch determining means.
[0019]
Further, it has means for determining a pixel period that is a period in the electron beam scanning direction of pixels constituting the inspection image, or means for determining a line period that is a period in the electron beam feeding direction of the pixels, and the inspection speed is It is determined based on the pixel period or line period determined by the pixel period determining means or the line period determining means.
[0020]
In addition, it has precharge means for adding charge before scanning to a region including a line to be scanned and inspected by means of scanning the primary electron beam, and the line period is added by the precharge means. It is determined on the basis of the amount of electric charge. Note that precharging may be performed by scanning the primary electron beam.
[0021]
Moreover, it has a means to change the detection period of the detector which detects a secondary charged particle, and changes a detection period according to the inspection speed determined by the inspection speed determination means. Note that the detection period may be changed to a period obtained by dividing the pixel period by an integer.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0023]
Example 1
1 to 2 show a first embodiment of the present invention. FIG. 1 is a longitudinal sectional view showing a configuration of an SEM type appearance inspection apparatus 1 which is an example of an appearance 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 substrate 9 to be inspected into the inspection chamber 2. This spare room is configured to be evacuated independently of the examination room 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.
[0024]
The inspection chamber 2 is roughly divided into an electron optical system 3, a sample chamber 8, and an optical microscope section 4. The electron optical system 3 includes an electron gun 10, an extraction electrode 11 for an electron beam 19, a condenser lens 12, a blanking deflector 13, a scanning deflector 15, a diaphragm 14, an objective lens 16, a reflector 17, and an ExB deflector 18. Has been. Of the secondary electron detector 7, the secondary electron detector 20 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 installed outside the examination room 2 and converted into digital data by an AD converter 22.
[0025]
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 a substrate height measuring device 35 to be inspected. The optical microscope unit 4 is installed in the vicinity of the electron optical system 3 in the examination room 2 and at a position that does not affect each other, and the distance between the electron optical system 3 and the optical microscope unit 4 Is known. Then, the X stage 31 or the Y stage 32 reciprocates a known distance between the electron optical system 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.
[0026]
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.
[0027]
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 electron beam generation, an electron beam deflection width, a deflection speed, a signal acquisition timing of a secondary electron detector, a sample stage moving speed, etc. are arbitrarily or arbitrarily selected according to the purpose. It is input so that it can be 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 inspected substrate height measuring device 35, and generates a correction signal based on the result. Then, 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 irradiated to the correct position.
[0028]
In order to acquire an image of the substrate 9 to be inspected, the substrate 9 to be inspected is irradiated with a finely focused electron beam 19 to generate secondary electrons 51, which are scanned by the electron beam 19 and the X stage 31, Y By detecting in synchronization with the movement of the stage 32, an image of the substrate 9 to be inspected is obtained.
[0029]
In the SEM type visual inspection apparatus, a high inspection speed is essential. Therefore, unlike an ordinary SEM of the conventional method, scanning with an electron beam having an electron beam current of the pA order is performed at a low speed, and multiple scanning and superposition of each image are not performed. Further, in order to suppress charging of the insulating material, it is necessary to perform the electron beam scanning once or several times at a high speed so as not to perform many times of scanning. Therefore, in this embodiment, an image is formed by scanning an electron beam with a large current of about 1000 times or more, for example, 100 nA, as compared with a conventional SEM, only once.
[0030]
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 electron beam image with little brightness fluctuation can be obtained. Further, 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.
[0031]
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 and Y stage on the sample stage 30. The substrate 9 to be inspected mounted on 32 is irradiated. The inspected substrate 9 is a substrate having a fine circuit pattern such as a semiconductor wafer, a chip, a liquid crystal, a mask or the like. 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.
[0032]
A negative voltage can be applied to the substrate 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 substrate 9 to be inspected can be adjusted to an optimum value without changing the potential of the electron gun 10.
[0033]
Secondary electrons 51 generated by irradiating the inspection substrate 9 with the electron beam 19 are accelerated by a negative voltage applied to the inspection substrate 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 substrate 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 substrate 9 to be inspected.
[0034]
The secondary electrons 51 deflected by the ExB deflector 18 collide with the reflection 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 the electron beam 19 applied to the substrate 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.
[0035]
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, and are constituted by these.
[0036]
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.
[0037]
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 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.
[0038]
The AD converter 22 is configured to immediately convert the analog signal detected by the secondary electron detector 20 into a digital signal after being amplified by the preamplifier 21 and transmit the digital signal 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.
[0039]
A substrate 9 to be inspected 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 of the method of moving the stage 31 and the Y stage 32 continuously in the Y direction at a constant speed and linearly scanning the electron beam 19 in the X direction can be selected. When inspecting a specific relatively small area, the former method of inspecting the inspected substrate 9 is stationary. When inspecting a relatively wide area, the inspected substrate 9 is continuously moved at a constant speed. The 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.
[0040]
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 rotational speeds of the motors of the X stage 31 and the Y stage 32 are also transferred from the respective drivers to the control unit 6, and the control unit 6 performs electronic control based on these data. The region and position where the line 19 is irradiated can be accurately grasped. Therefore, the position shift 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 substrate 9 to be inspected.
[0041]
As the substrate height measuring device 35 to be inspected, 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 is used, and is mounted on the X stage 31 and the Y stage 32. The height of the substrate 9 to be inspected can be measured in real time. In the present embodiment, elongated white light that has passed through the slit is irradiated onto the inspected substrate 9 through a transparent window, the position of the reflected light is detected by a 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, the warpage and height distortion of the substrate 9 to be inspected are measured in advance before the electron beam irradiation, and the correction condition for each inspection region of the objective lens 16 is set based on the data. Is possible.
[0042]
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 inspected substrate 9 detected by the secondary electron detector 20 is amplified by the preamplifier 21, digitized by the AD converter 22, converted to an optical signal by the light conversion means 23, and the light transmission means 24. And converted into an electrical signal again by the electrical conversion means 25 and then 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.
[0043]
FIG. 2 is a functional block diagram of the present invention. In the inspection apparatus 1 of the present invention, the control unit 6 includes means 210 for determining the inspection speed 220 and means 230 for determining the primary electron dose 240 from the electron gun 10. FIGS. 2A and 2B are block diagrams showing that when one of the two is determined, the other is automatically adjusted according to the result. (A) is the case where the inspection speed is determined first, and (b) is the case where the primary electron dose is determined first. In either case, the relationship between the two can be easily realized by formulating and programming the control unit 6 in advance and calculating the other value based on one result. FIG. 2 shows an example of a relational expression between the two so that the dose, which is the amount of electron beam irradiation per area, is kept constant. That is, in the case of (a), the dose amount 260 determined by the dose amount determining means 250 is input to the primary electron dose determining means 230, and the inspection speed 220 is increased, for example, by a factor of 2 so as to keep the dose amount. In this case, since the dose amount actually irradiated is halved, the primary electron dose 240 output from the primary electron dose determining means 230 is also automatically adjusted to double. In the case of (b) as well, an automatic adjustment function can be configured as described above. Here, the primary electron dose 240 is an irradiation amount from the electron gun 10, but may be a probe current amount that is an electron dose actually irradiated to the substrate 9 to be inspected.
[0044]
By adopting the configuration as shown in FIG. 2, the amount of beam current applied to the substrate 9 to be inspected is automatically adjusted to a desired value at any inspection speed, and sample protection can be realized more reliably. In addition, usability can be improved by reducing input parameters.
[0045]
(Example 2)
Next, a second embodiment of the present invention will be shown. FIG. 3 is a functional block diagram showing details of the dose amount determining means 250 in FIG. As a condition for determining the dose amount, first, when the user inputs the dose amount itself, the desired dose amount 315 is input to the dose amount determination unit 250 by the dose amount input unit 310 and is directly output as the dose amount 260. The
[0046]
When the type of defect to be inspected next can be predicted in advance, the type is input to the inspection defect type input means 320 and the dose amount is determined based on the defect type 325. In this case, for example, in the case of a potential contrast defect, the dose is increased, and when it is desired to inspect a minute foreign matter, the dose is decreased by reducing the primary electron dose.
[0047]
In addition, a process name input means 330 for inputting a wafer manufacturing process name is provided, and the dose amount is determined depending on the process name 335 by this. For example, in the CMP process for scraping a thin film, there are many defects of minute foreign matters, and it is possible to automatically adjust the optimum inspection conditions by adjusting the dose amount as described above.
[0048]
FIG. 4 shows a screen display example of the monitor 50, in which the three types of input means 310, 320, and 330 are shown on the display screen 300. Here, it is not necessary to equip all three types of input means, and the present invention is not limited to this.
[0049]
As an effect peculiar to the present embodiment, it is possible to automatically optimize inspection conditions by inputting a defect type, a process name, etc., and there is an effect of improving usability.
[0050]
(Example 3)
Next, a third embodiment of the present invention will be shown. FIG. 5 is a functional block diagram, and FIGS. 5A and 5B show details of the primary electron dose determining means 230 and the inspection speed determining means 210 in FIG. 2, respectively.
[0051]
FIG. 5A shows a case where the primary electron dose 240 itself is input. As described above, the probe current may be input instead.
[0052]
FIG. 5B shows a case where the inspection speed input means 402 for inputting the inspection speed 220 itself is provided in the same manner as described above, and the inspection speed desired by the user can be directly input.
[0053]
Further, as conditions for defining the inspection speed, a pixel pitch that is a pitch in a direction in which an electron beam is scanned at a high speed, a line pitch that is a pitch in a feed direction of a line formed by high-speed scanning, and a pixel period that represents a period in the same direction. , 4 types of line cycle are conceivable. By adopting a configuration equipped with each of the determining means 410, 430, 450, 470 and input means 405, 425, 445, 465 for inputting them, the user's desired speed can be set freely. However, it is not necessary to equip them all, and some fixed values may be used to reduce the user input.
[0054]
An example of the input screen in the present embodiment is shown in FIG. Here, on the screen 600, the primary electron dose input means 400 and the inspection speed input means 402 can be input in parallel. However, if one is determined as in the present invention, the other is automatically adjusted. It may be protected by software so that when the input is completed, the other cannot be input. Moreover, you may display the value adjusted automatically.
[0055]
Example 4
Next, a fourth embodiment of the present invention will be shown. FIG. 7 is a functional block diagram showing details of the line period determining means 470 in FIG. A period, which is a time interval between lines formed by scanning an electron beam at a high speed, depends on a precharge amount 520 required by the illustrated precharge unit 510. Depending on the type of defect to be inspected, there are cases where the detection rate is increased if charges are added (precharged) in advance before irradiation with the inspection beam. In this case, the present embodiment can be applied.
[0056]
FIG. 8 is a top view and a partially enlarged view of the substrate 9 to be inspected, and shows a method for precharging a semiconductor wafer as an example of the substrate 9 to be inspected. An area of the inspection stripe 500 in the direction indicated by the arrow is inspected while scanning the surface of the inspected substrate 9 shown in FIG. Details of the inspection stripe 500 will be described with reference to FIG. First, as shown by an arrow 550 in (1), a large electron beam is scanned across the inspection stripe 500 and precharged. As indicated by the arrow 560 in (2), the same line as the arrow 550 is scanned for the width of the inspection stripe 500 to be inspected this time. Thereafter, in (3), after the substrate 9 to be inspected moves in the direction indicated by the arrow in FIG. 8A by the above-mentioned line pitch, the next line is scanned larger as indicated by the arrow 570 and pre-scanned. In (4), only the width of the inspection stripe 500 is scanned as indicated by an arrow 580 in (4).
[0057]
In this example, the precharge is performed only once before the inspection scan. However, depending on the inspection object, it may be necessary to precharge a plurality of times. As a result, the time interval, that is, the period of the inspection scan is greatly affected, and therefore it is necessary to determine the line period by the line period determining means 470 shown in FIG. However, in this case, the increase / decrease in the line cycle does not directly lead to the increase / decrease in the inspection scan, and it is necessary to determine the actual inspection speed by the inspection speed determination means 210 shown in FIG. is there.
[0058]
(Example 5)
Next, a fifth embodiment of the present invention will be shown. FIG. 9 is a functional block diagram showing an embodiment of the detection cycle variable means 610 that changes the detection cycle 620 in conjunction with the inspection speed 220 determined by the inspection speed determination means 210.
[0059]
FIG. 10 is a time chart showing signal detection timing for each pixel, and shows a case where the time required for one line of the inspection scan 560 is doubled from 10.24 μs on the upper side to 5.12 μs on the lower side. This is realized by changing the pixel pitch of the digital scan from 0.1 μm to 0.2 μm. At this time, for example, if the detection cycle is set to 10 ns (detection clock 100 MHz), which is the same as the above, the resolution becomes coarse, and the defect detection rate may be lowered. Therefore, in this case, by setting only the detection clock to 200 MHz and setting the detection cycle to 5 ns, the same resolution as shown above can be maintained.
[0060]
In this way, the configuration that automatically changes the detection cycle in conjunction with changes in the inspection speed makes it possible to maintain excellent inspection performance at all times and eliminates the need for adjustment of the detection cycle as in the past. Therefore, improvement in usability can be expected.
[0061]
In this way, the current amount of the electron beam is automatically adjusted so that the low-speed inspection due to the miniaturization of the defect size accompanying the miniaturization of the pattern of the semiconductor wafer or the like and the high-speed inspection corresponding to the high throughput become equivalent inspection conditions. Thus, it is possible to provide an inspection apparatus and an inspection method using a scanning electron microscope, which are excellent in terms of stabilization of inspection performance, protection of a substrate to be inspected, and improvement in usability.
[0062]
【The invention's effect】
As described above, according to the present invention, defects that are difficult to detect in an optical image are detected with high accuracy using an electron beam image, and at the same time, dose amount and inspection speed management as a single inspection apparatus that becomes a problem at that time can be managed. It is possible to provide an appearance inspection apparatus using an electron beam that can be realized with high accuracy by a simple operation.
[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 functional block diagram.
FIG. 3 is a functional block diagram.
FIG. 4 is a screen diagram showing a display example of a screen.
FIG. 5 is a functional block diagram.
FIG. 6 is a screen diagram showing an example of an input screen.
FIG. 7 is a functional block diagram.
FIG. 8 is a top view and a partially enlarged view of a substrate to be inspected.
FIG. 9 is a functional block diagram.
FIG. 10 is a time chart showing signal detection timing for each pixel.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... SEM type external appearance inspection apparatus, 3 ... Electron optical system, 5 ... Image processing part, 6 ... Control part, 7 ... Secondary electron detection part, 9 ... Substrate to be inspected, 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, 210 ... Inspection speed determination means, 220 ... Inspection speed, 230 ... Primary electron dose determination means, 240 ... Primary electron dose, 250 ... Dose amount determination means, 260 ... Dose amount, 310 ... Dose amount input means, 320 ... Inspection defect type input Means 330 ... Process name input means 400 ... Primary electron dose input means 410 ... Pixel pitch determination means 430 ... Line pitch determination means 450 ... Pixel cycle determination means 470 ... Line cycle determination means 510 ... Precharge means , 6 0 ... detection period variable means.

Claims (5)

An electron source for generating a primary electron beam, lens means for focusing the primary electron beam generated by the electron source, a sample stage for placing a sample, and transporting the sample to a sample chamber including the sample stage Means, a primary electron beam scanning means for scanning the focused primary electron beam on the sample, a detector for detecting secondary charged particles generated secondarily from the sample, and a signal from the detector Storage means for storing the image signal of the first area on the sample based on the comparison means, comparison means for comparing the image of the area stored in the storage means with the image of the second area on the sample, and the comparison In the appearance inspection apparatus using an electron beam for inspecting the sample, including defect extraction means for extracting defects on the sample from the comparison result in the means,
A pixel pitch determination means to determine a pixel pitch of the digital scan is the pitch of the electron beam scanning direction of the pixels constituting the image into 0. 2 [mu] m from 0. 1 [mu] m, more determined to the pixel pitch determined hand stage and inspection speed determining means for speed detection period in which the inspected based on the pixel pitch is determined to 5ns from 10ns was a primary electron beam dose determining means for determining the primary electron beam dose of the primary electron beam to be irradiated onto the sample And detecting one of the inspection speed and the primary electron dose, the other is automatically adjusted according to the result, and the detection period of the secondary charged particles by the detector is changed. When the inspection speed determined by the inspection speed determination means is increased, the detection of the detector is interlocked with the pixel pitch of the digital scan. An appearance inspection apparatus using an electron beam, wherein the detection cycle of the detector is changed by the detection cycle variable means so that the cycle is increased. An electron source for generating a primary electron beam, lens means for focusing the primary electron beam generated by the electron source, a sample stage for placing a sample, and transporting the sample to a sample chamber including the sample stage Means, a primary electron beam scanning means for scanning the focused primary electron beam on the sample, a detector for detecting secondary charged particles generated secondarily from the sample, and a signal from the detector Storage means for storing the image signal of the first area on the sample based on the comparison means, comparison means for comparing the image of the area stored in the storage means with the image of the second area on the sample, and the comparison In the appearance inspection apparatus using an electron beam for inspecting the sample, including defect extraction means for extracting defects on the sample from the comparison result in the means,
With a line period determining means for determining a line period is the period of the electron beam feed direction of the pixels constituting the image,
The line period determined by the line period determining unit is determined by a precharge unit that charges the sample by adding a charge to the region including a line to be scanned and inspected by the primary electron beam scanning unit before scanning. is to be determined based on the added amount of charges, and inspection speed determining means for determining the rate at which the inspected based on the line period determined by the line period determining means,
Primary electron dose determining means for determining a primary electron dose of the primary electron beam irradiated on the sample, and when determining either the inspection speed or the primary electron dose, the other is in accordance with the result. A detection period variable means that is automatically adjusted and changes the detection period of the secondary charged particles by the detector. When the inspection speed determined by the inspection speed determination means is increased, the detection of the detector An appearance inspection apparatus using an electron beam, wherein the detection cycle of the detector is changed by the detection cycle variable means so that the cycle is increased. An electron source for generating a primary electron beam, lens means for focusing the primary electron beam generated by the electron source, a sample stage for placing a sample, and transporting the sample to a sample chamber including the sample stage Means, a primary electron beam scanning means for scanning the focused primary electron beam on the sample, a detector for detecting secondary charged particles generated secondarily from the sample, and a signal from the detector Storage means for storing the image signal of the first area on the sample based on the comparison means, comparison means for comparing the image of the area stored in the storage means with the image of the second area on the sample, and the comparison In the appearance inspection apparatus using an electron beam for inspecting the sample, including defect extraction means for extracting defects on the sample from the comparison result in the means,
The image forming apparatus includes a line period determining unit that determines a line period that is a period in the electron beam feeding direction of pixels constituting the image, and the line period determined by the line period determining unit is scanned by the primary electron beam scanning unit. It is determined on the basis of the amount of charge added by the precharge means for adding the charge to the sample before scanning for the region including the line to be inspected, and determined by the line period determining means. An inspection speed determining means for determining the inspection speed based on the line cycle, and a primary electron dose determining means for determining a primary electron dose of the primary electron beam irradiated on the sample, the inspection speed And the primary electron dose is determined, and the other is automatically adjusted according to the result. Location.   4. An appearance inspection apparatus using an electron beam according to claim 3, wherein the charge is added by the precharge means by scanning the primary electron beam by the primary electron beam scanning means. Appearance using an electron beam that detects secondary charged particles generated by irradiating a sample with a primary electron beam, extracts defects on the sample using an image generated based on the detected signal, and inspects the sample In inspection equipment,
Line period determining means for determining a line period, which is a period in the electron beam feeding direction of pixels constituting the image,
The line period determined by the line period determining unit is determined by a precharge unit that charges the sample by adding a charge to the region including a line to be scanned and inspected by the primary electron beam scanning unit before scanning. An inspection speed determining means for determining an inspection speed based on the line period determined by the line period determining means; and a primary electron dose irradiated on the sample. Determining means, and when one of the inspection speed and the primary electron dose is determined, the other is automatically adjusted according to the result, and the detection period of the secondary charged particles by the detector is changed. And a detection period variable means for causing the detection period of the detector to be increased when the inspection speed determined by the inspection speed determination means is increased. The detection period changing means by said detector detection period appearance inspection apparatus using an electron beam, characterized in that to change the.

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