JP2007003539A - Circuit pattern inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve efficiency of condition setting, to shorten inspection time, and to improve reliability of an inspection, in a circuit pattern inspection device for inspecting, with an electron beam, a defect, foreign substance, residue, or the like of the same design pattern of a semiconductor device on a wafer in a manufacturing process of the semiconductor device. <P>SOLUTION: The circuit pattern inspection device independently has a detection signal processing circuit for forming a large current high-speed image for detecting the presence of the defect, and a detection signal processing circuit for forming an image in a specific narrow part detected by this defect detecting inspection. Alternatively, a first electron optical system for the defect detecting inspection and a second electron optical system only for review for observing a specific narrow part detected by the defect detecting inspection are stored in parallel in the same vacuum vessel. Alternatively, a first detector for the defect detecting inspection and a second detector only for review for observing a specific narrow part detected by the defect detecting inspection are disposed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a circuit pattern inspection apparatus and inspection method, and more particularly to a circuit pattern inspection apparatus and inspection method for a wafer or the like in the process of manufacturing a semiconductor device.

  In the manufacturing process of a semiconductor device, as an inspection method for comparing and detecting defects in a circuit pattern formed on a wafer, images of two or more LSIs of the same pattern on one wafer are acquired and compared. An inspection apparatus has been put into practical use.

  In particular, Patent Documents 1 and 2 and Non-Patent Documents 1 to 3 describe pattern comparison inspection apparatuses using electron beams. In this case, it is necessary to acquire an image at a very high speed in order to obtain a practical throughput. In order to secure the SN ratio of the image acquired at high speed, the electron beam current of 100 times or more (10 nA or more) of a normal scanning electron microscope is used, and the SN ratio of the image is secured while maintaining a practical inspection speed. is doing. The beam diameter is considerably wider than that of a normal scanning electron microscope, and is about 0.05 μm to 0.2 μm. This is because the beam current is large and is limited by an increase in chromatic aberration due to the widening of the energy width of electrons, the limitation on the brightness of the electron gun, and the Coulomb effect.

  An image formed by such an electron optical system is sent to an image processing system, and a comparison inspection of images of adjacent identical pattern portions is performed. If there are places with different brightness when comparing the images, they are regarded as defects and the coordinates are stored.

  With the configuration as described above, it is possible to detect a defect having a size of about 0.1 μm.

  Further, Patent Documents 3 to 8 disclose apparatuses for inspecting a semiconductor defect by applying a voltage to a sample and an electrode near the sample to reduce energy of an electron beam. However, there is no description of the review function described below or an energy analysis function.

JP 59-192943 JP-A-5-258703 Japanese Unexamined Patent Publication No. 7-078855 Japanese Unexamined Patent Publication No. 09-181139 JP 10-019538 A, Japanese Patent Laid-Open No. 10-027834 Japanese Patent Laid-Open No. 10-027835 Japanese Patent Laid-Open No. 11-029501 J. Vac. Sci. Tech. B, Vol. 9, No. 6, pp. 3005-3009 (1991) J. Vac. Sci. Tech. B, Vol. 10, No. 6, pp. 2511-2515 (1992) SPIE (The International Society for Optical Engineering) Vol. 2439

  When an inspection is started using the above-described apparatus, there are many various parameters that need to be set in advance. First, the setting parameters of the electron optical system include electron beam irradiation energy, secondary electron (or charged particles such as backscattered electrons) signal detection system gain, pixel size (minimum element of the image), beam current and so on. On the other hand, when the image processing apparatus compares two adjacent images having the same pattern, there is a threshold value for determining whether or not the image is a defect. If this threshold value is set low, the defect detection sensitivity is improved, but the possibility that a non-defect portion is regarded as a defect increases. On the other hand, when the threshold value is increased, the detection sensitivity decreases.

  The optimum values of the parameters vary depending on the process to be inspected, the pattern size, and the type of defect to be detected. Therefore, it is necessary to perform a trial inspection before the inspection, display an image of the detected defect coordinates, and set the above parameters to an optimum one while confirming whether or not the defect to be detected is detected.

  There is also a need for an operator to obtain an image of the defect coordinate portion after the inspection and confirm what kind of defect has been detected.

  In other words, in addition to acquiring images at high speed to detect the presence of defects and detecting defects by image processing, a specific narrow field of view is imaged and observed with the naked eye, similar to a normal scanning electron microscope. The ability to do is also essential. In the present specification, this is hereinafter referred to as a review, and the latter is used when it is necessary to particularly distinguish between the review and the inspection by high-speed image acquisition for detecting the presence of defects over a relatively large area. Is called defect detection inspection.

  At the time of review, it is not necessary to form an image as fast as at the time of defect detection inspection. On the other hand, since it is necessary to recognize not only the presence / absence of a defect but also the shape and type of the defect to some extent, a high resolution image is required.

  However, in the conventional apparatus, the electron optical system is optimally designed for image acquisition by high-current high-speed scanning, and sufficient resolution as a review image cannot be obtained. Therefore, the accuracy for determining whether the detected defect is a true defect or a false detection caused by inappropriate parameter setting is low. For this reason, inspections are often performed without necessarily setting the setting parameters to optimum values.

  An object of the present invention is to make inspection conditions efficient in an apparatus for inspecting a sample, for example, inspecting a semiconductor device on a wafer in the process of manufacturing the same design pattern for defects, foreign matter, residues, etc. of the semiconductor device with an electron beam. It is to provide an inspection apparatus that can be set well.

The inspection apparatus of the present invention achieves the above object with the following configuration.
That is, according to a first aspect of the present invention, an electron optical system that converges an electron beam emitted from an electron source by an electron lens and irradiates and scans the sample, and the sample. A stage that can be moved so that an electron beam is irradiated to a desired position on the sample, a detector that detects backscattered electrons or secondary electrons obtained from the irradiated portion of the sample, and the detection A first circuit for amplifying the output from the detector with a first amplification factor, an amplifier for amplifying the output from the detector with an amplification factor greater than the first amplification factor, and a high frequency component cut filter A second circuit, an image forming apparatus that forms an image of the sample based on a detection signal from the detector, and an image signal obtained by the image forming apparatus from the other place on the sample And compare the difference between the two image signals. And an output from the detector in the first case in which the electron beam is scanned on the sample at a relatively large area, a relatively large current, and a relatively high speed, and is input to the first circuit. From the detector in the second case, the electron beam is scanned over the sample at a small area smaller than the relatively large area, a small current smaller than the relatively large current, and a low speed slower than the relatively high speed. Switching means for switching and inputting the output to the second circuit.
According to a second aspect of the present invention, in the inspection apparatus according to the first aspect, in the second case, a pixel size which is a minimum unit of an image formed in the first case An inspection apparatus that forms an image with a smaller pixel size.
According to a third aspect of the present invention, in the inspection apparatus according to the first or second aspect, in the second case, the spot size of the electron beam on the sample is the first size. It is an inspection apparatus characterized by being smaller than the case.
According to a fourth aspect of the present invention, in the inspection apparatus according to any one of the first to third aspects, the electron lens includes an objective lens closest to the sample, and the electron source. And a second lens arranged on the side, and in the second case, the second lens is adjusted, and the magnification of the electron optical system is set to be small.
According to a fifth aspect of the present invention, in the inspection apparatus according to any one of the first to fourth aspects, the electron optical system includes a diaphragm having openings having a plurality of diameters. In the second case, the inspection device is characterized in that the diameter of the diaphragm is switched to a smaller one.
According to a sixth aspect of the present invention, in the inspection apparatus according to the fourth aspect, the second lens is a condenser lens, and in the second case, the electron beam is formed. The inspection apparatus is characterized by moving the position of the crossover.
According to a seventh aspect of the present invention, in the inspection apparatus according to any one of the first to sixth aspects, the scanning deflection region of the electron beam is the first case in the second case. The inspection apparatus is characterized in that the deflection area is reduced to ½ or less compared to the case of the above.
In addition, according to an eighth aspect of the present invention, in the inspection apparatus according to any one of the first to seventh aspects, the second circuit has a response speed higher than that of the first circuit. Is an inspection apparatus characterized by being slow.
According to a ninth aspect of the present invention, in the inspection apparatus according to any one of the first to eighth aspects, a means for detecting a difference between the two image signals in the first case. According to an output result, there is provided means for switching the magnification of the electron optical system in the second case, the current value of the electron beam, the scanning speed of the electron beam, and the number of times of image addition in the image forming apparatus in conjunction with each other. This is an inspection apparatus characterized by that.
According to a tenth aspect of the present invention, there is provided a first electron source that emits a first electron beam, a first focal length, and the first electron beam is a first electron beam. A first objective lens that focuses on the sample located at the sample position, and a first scanning deflector that causes the first electron beam to scan over the sample located at the first sample position. A first detector for detecting secondary charged particles generated from a sample located at the first sample position; a second electron source for emitting a second electron beam; A second objective lens that has a second focal length shorter than the first focal length and focuses the second electron beam onto a sample located at a second sample position; and the second electron beam. A second electron optical system comprising: a second scanning deflector that scans a sample positioned at the second sample position; and A second detector for detecting secondary charged particles generated from a sample located at a sample position; and the first and second detectors based on outputs from the first detector and the second detector. An image forming apparatus that images each of the samples positioned at the sample position; and a stage for moving the sample from the first sample position to the second sample position, the first electron optical system, The second electron optical system, the first detector, the second detector, and the stage are accommodated in the same vacuum vessel, and the first detector for the sample located at the first sample position The specific position on the sample selected based on the image data formed based on the output of is moved to the second sample position by moving the stage, and the specific position is moved to the second position. This is an inspection apparatus for magnifying observation with an electron optical system.
According to an eleventh aspect of the present invention, in the inspection apparatus according to the tenth aspect, an acceleration voltage for the second electron beam in the second electron optical system is the first electron. An inspection apparatus having a lower acceleration voltage than the first electron beam in an optical system.
According to a twelfth aspect of the present invention, in the inspection apparatus according to the tenth or eleventh aspect, the electron beam is decelerated to a desired energy immediately before the stage and the sample on the stage. Therefore, the negative voltage applied to the stage and the sample is a negative voltage smaller than the negative voltage applied at the first sample position at the second sample position. Inspection equipment.
According to a thirteenth aspect of the present invention, in the inspection apparatus according to any one of the tenth to twelfth aspects, X-rays generated from a sample located at the second sample position are detected. An inspection apparatus including an X-ray detector.
According to a fourteenth aspect of the present invention, in the inspection apparatus according to any one of the tenth to twelfth aspects, the secondary electrons emitted from the sample located at the second sample position. An inspection apparatus comprising an energy filter for filtering energy and detecting a potential at a position irradiated with the second electron beam.
According to a fifteenth aspect of the present invention, the electron beam emitted from the electron source is converged by a lens and irradiated onto the sample for scanning, and the sample is mounted. , A stage movable to irradiate an electron beam to a desired position on the sample, and a first detector for detecting backscattered electrons or secondary electrons obtained from the irradiated portion of the sample with a first sensitivity. Detector, a second detector for detecting backscattered electrons or secondary electrons obtained from the irradiated portion of the sample with a second sensitivity higher than the first sensitivity, and detection from the detector An image forming apparatus that forms an image of the sample based on the signal, and an image signal obtained by the image forming apparatus is compared with an image signal obtained in the same manner from another location on the sample, and both images Means for detecting the difference between the signals and the electron beam When scanning on the sample with a first area, a first current value, and a first speed, the backscattered electrons or secondary electrons are guided to the first detector, and the electron beam is moved over the sample. Deflection for guiding the backscattered electrons or secondary electrons to the second detector when scanning at an area smaller than the first area, a current value smaller than the first current value, and a speed slower than the first speed An inspection apparatus including a circuit.
According to a sixteenth aspect of the present invention, there is provided an electron optical system for irradiating and scanning a sample on which a circuit pattern is formed with a focused electron beam, and a rear side obtained from the irradiated portion of the sample. A detector for detecting scattered electrons or secondary electrons, an image forming apparatus for forming an image of the sample based on a detection signal from the detector, and an image signal obtained by the image forming apparatus as a reference image Providing a difference detecting means for detecting a difference between the two image signals in comparison with the signal; scanning a relatively large area of the sample with the electron beam at a relatively large current and at a relatively high speed; The output from the detector obtained by amplification with an amplifier having a first amplification factor is supplied to the image forming apparatus to form an image signal. Obtained from other areas on the sample Detecting a difference between both image signals by detecting a difference between the two image signals in comparison with a similar image signal, and obtaining the relatively large area including the coordinate position of the sample; The output from the detector obtained by scanning a smaller area with a small current smaller than the relatively large current at a low speed slower than the relatively high speed by the electron beam is the first output. A step of supplying an image signal to the image forming apparatus via a circuit having an amplifier that amplifies at a gain larger than the gain and a high-frequency component cut filter, and observing the occurrence of the difference. A circuit pattern inspection method is included.

Since the present invention is as described above, the following effects can be obtained. Defect detection inspection by high-speed image acquisition for detecting the presence of defects over a relatively large area, and a review to visualize a specific narrow part detected by this defect detection inspection with the naked eye, respectively. By using a detection circuit having an independently optimized path, an image signal signal having a sufficient S / N ratio can be obtained, and inspection conditions can be set efficiently. This speeded up the inspection process and improved the reliability of the inspection results.
In addition, the first electron optical system for defect detection inspection for detecting the presence of defects and the second electron optical system dedicated for review for observing a specific narrow part detected by this defect detection inspection are the same. The inspection apparatus of the present invention configured to be accommodated side by side in a vacuum vessel and to be switched between defect detection inspection and review only by moving a stage on which a sample is placed enables rapid and highly reliable inspection.
In addition, a first detector for defect detection inspection for detecting the presence of a defect, a second detector dedicated to review for observing a specific narrow part detected by this defect detection inspection, and electron beam irradiation The inspection apparatus of the present invention provided with a deflection circuit that guides backscattered electrons or secondary electrons generated from the sample to the first detector at the time of defect detection inspection and to the second detector at the time of review is low in noise. A signal with little deterioration of high-frequency characteristics is obtained, and highly reliable inspection is possible.

Example 1
A first embodiment of the present invention will be described with reference to FIGS. 1 and 2 are block diagrams of the present invention.
The inspection apparatus is roughly composed of an electron optical system 101, a sample chamber 102, a control unit 104, and an image processing unit 105.
The electron optical system 101 includes an electron source 1, an electron beam extraction electrode 2, a condenser lens 4, a blanking deflector 17, a scanning deflector 8, an aperture 5, and an objective lens 7.

Although FIG. 1 shows the case where the secondary electron detector 9 is below the objective lens 7, the position of the detector 9 may be provided on the objective lens 7. In that case, secondary electrons reach the detector 9 after passing through the objective lens 7. When the detector 9 is located below the objective lens 7, a large deflection range of the objective lens 7 can be obtained, but there is a limit to the resolution at the time of review because the aberration of the objective lens 7 is large. On the other hand, when the detector 9 is provided on the objective lens 7, since the aberration of the objective lens 7 can be reduced, it is possible to increase the resolution at the time of review, but there is a disadvantage that the deflection range becomes small. Both are merits and demerits, and either configuration may be selected as necessary. A positive high voltage is applied to the detector 9. Further, the preamplifier 12 connected to the detector 9 and the ground level of the detection circuit 30 are also on the positive high potential applied to the detector 9. The output signal of the secondary electron detector 9 is amplified by the preamplifier 12 and converted into digital data by the detection circuit 30. This signal is converted into light by the optical transmitter 34, received by the optical receiver 35 at the ground potential level, converted into an electrical signal, and then sent to the image processing unit 105.
In FIG. 1, the condenser lens 4 is composed of an electromagnetic lens, but it may be composed of an electrostatic lens as shown in FIG. 2. The electrostatic lens is composed of, for example, three electrodes, and the electrodes on both sides have a ground potential. A so-called Einzel lens that applies a positive or negative voltage to the center electrode is optimal, but the same is true even if it is not an Einzel lens. The use of an electrostatic lens can reduce the size of the electron optical system.
Returning to FIG. 1, the sample chamber 102 includes a stage 24, an optical sample height measuring device 29, a laser length measuring device, or a stage position measuring device 31 using a linear scale.
The image processing unit 105 includes image storage units 18 and 19, a calculation unit 20, and a defect determination unit 21. The captured electron beam image is displayed on the monitor 22. Operation commands and operation conditions of each part of the inspection apparatus are input / output from the control unit 104. Conditions such as an acceleration voltage at the time of generating an electron beam, an electron beam deflection width, a deflection speed, a sample stage moving speed, and a signal capturing timing of a detector are input to the control unit 104 in advance. Further, a correction signal is generated from the signal of the optical sample height measuring device 29 and the signal of the stage position measuring device 31, and is supplied to the objective lens power source 7 and the scanning signal generator 13 so that the electron beam 6 is always irradiated to the correct position. Send a correction signal.

FIG. 3 is a diagram showing a flow of semiconductor pattern appearance inspection using an electron beam. The flow for carrying out the pattern appearance inspection of the semiconductor wafer according to the present invention will be described with reference to FIG.
First, after loading a wafer, rough alignment is performed by an optical microscope. This is because the scanning range is narrow in the electron beam scanning image, and the alignment mark may not fall within the scanning range of the electron beam only by mechanical positioning during loading. Therefore, alignment is performed with an accuracy of several tens of μm using a low magnification optical microscope with a wide field of view.
Next, the conditions of the electron optical system are set. The electron beam irradiation energy, pixel size (minimum element of the image), beam current, etc. are set according to the type of wafer pattern to be inspected. The optimum electron beam irradiation energy differs depending on the pattern material. Usually, it is preferable to set the energy to a high energy of several keV or more so that high resolution can be obtained in a conductive material, and to set it to 1.5 keV or less in a pattern including an insulator to prevent charging.
Next, the pixel size corresponding to the defect size to be particularly focused is set. If the pixel size is reduced meaninglessly, the time required for inspection increases. Next, the beam current is set. Although a default value exists in the apparatus, it is preferable to set a smaller current particularly for a wafer that is easily charged. If it is known in advance that the contrast of the defect to be detected is large, the electron beam can be made smaller and highly sensitive inspection can be performed by reducing the current.
Next, an electron beam image of the wafer to be inspected is displayed, and the focus and astigmatism are corrected. This can be automatically performed by taking an image and using a computer or a dedicated image processing apparatus.
When the above setting is completed, fine alignment of the image with an electron beam is performed. As a result, the coordinate system of the stage and the coordinate system of the wafer are exactly matched, and the desired position on the wafer can be inspected by measuring the coordinates of the stage with a laser length measuring machine or the like.

  Next, an area to be inspected is input from a control screen such as a display on the control workstation.

Next, a trial inspection is performed. The trial inspection is performed to determine whether the various parameters set above are appropriate. First, specify a part of the pattern you want to inspect. This is the trial inspection area designation. Then, a trial inspection is performed. In the trial inspection, an image is detected by an operation similar to that of the actual defect detection inspection using an electron beam, but all the acquired images are taken into the memory without passing through an image processing circuit.
Next, image processing conditions are set. This condition is a threshold value for determining whether or not there is a defect when the image processing apparatus compares two adjacent images of the same pattern. If this threshold value is set low, the defect detection sensitivity is improved, but the possibility that a non-defect portion is regarded as a defect increases. On the other hand, when the threshold value is increased, the detection sensitivity decreases.
In FIG. 3, the brightness threshold is a threshold of a difference between luminance signals of two images. The image by the electron beam has a larger roughness than the optical microscope image (that is, the image has a poor SN ratio). Therefore, even if the inspection objects being compared are the same and the average brightness is the same, there is a slight variation in brightness when viewed from pixel to pixel. Accordingly, a threshold value for contrast between light and dark is provided, and images are compared to detect only a place where a difference in light and darkness is larger than the threshold as a defect so that the roughness of the image is not recognized as a defect.
The misregistration threshold value is provided so that imperfect alignment of two images to be compared is not mistakenly recognized as a defect. It is assumed that there is a threshold value that is set here for the positional deviation of the image, and a defect is determined only when there is a further difference.
The filter type is a filter applied to the acquired image, and exists to reduce the roughness of the detected image or to enhance the edge. In this case, an optimum one is selected by trial and error according to the type of pattern and the defect to be detected.

After setting the above parameters, image processing is performed. In the image processing in the trial inspection, a comparative inspection is performed using a series of images already acquired. A defect is detected by this inspection, its coordinates are stored, and the location of the defect is displayed on the control screen. If no defect is detected at this time, the threshold value of the image processing parameter is lowered to increase the sensitivity, and the comparison inspection is performed again using the two-dimensional information on the memory.
Next, an image of coordinates detected by the trial inspection is observed. This is a review. Since the image of that portion has already been stored in the memory, the image is first displayed on the display of the control workstation, the display dedicated to image display, etc., and the defects detected are visually observed. Here, for a considerably large defect, the shape and type of the defect can be easily found by visual inspection. However, a fine defect close to the performance limit of the apparatus or a defect with low contrast cannot often be determined sufficiently clearly by visual observation. Therefore, the high-resolution image is displayed by switching the condition of the electron optical system to the review condition. As a result, it is possible to easily determine whether the defect detected by the trial inspection is a true defect or a defect that is desired to be detected. From the result, it is possible to find a condition for reliably detecting the defect to be detected by resetting the parameters of the image processing and repeating the review again.
Conventional devices that do not have high-resolution review conditions are designed to form images with a high-current electron beam. When observed for a long time, the sample is irradiated with a large amount of electron beam, causing the sample to be destroyed or charged. This makes it impossible to observe the image. Also, the purpose is to confirm the presence or absence of defects, and the resolution is insufficient to determine the details of the defects by visual observation. Therefore, trial and error must be repeated in this review and image processing parameter setting, and a great deal of time is required. However, according to the present invention, since the quality of the review screen is good, the quality of the selection of the image processing parameter can be accurately determined, and the number of trial and error is remarkably reduced. As a result, the time required for manned work has been greatly reduced, and the overall operating efficiency of the equipment has been improved.

  When the review for setting the conditions is completed, the defect detection inspection is started. This defect detection inspection is automatically performed unattended. When this defect detection inspection is completed, the review is performed again. After confirming whether or not the defect detected by this review is a true defect, the wafer is unloaded. If necessary, move to other analysis and inspection equipment and perform various inspection and analysis.

When automatically inspecting a wafer for which defect detection / inspection conditions have already been established, defect detection / inspection and review are carried out according to the flow shown in FIG. That is, as soon as the wafer is loaded, the defect detection inspection is performed under the existing condition setting, and the review is performed after the defect detection inspection is completed. In this review, the types of defects such as foreign matter, electrical defects, and shape defects are identified and classified for each defect.
Next, the review conditions and the specifications, differences, and features of the review conditions and defect detection inspection conditions, which are the points of the present invention, will be described.
FIG. 5 shows a comparison of the performance of the defect detection inspection condition and the review condition.
The defect detection / inspection condition allows very high-speed image acquisition in order to execute the entire wafer inspection in a practical time. That is, the time for forming a 100 μm square with a pixel size of 0.1 μm is 20 msec or less. The stage moves continuously for high-speed image acquisition, and the electron beam is scanned in the substantially orthogonal direction. Furthermore, in order to realize an image formation with an SN ratio that can withstand inspection at high speed, the beam current was designed to be obtained at 20 nA or more. Specifically, first, the current density obtained from the electron source was set to 0.2 mA / sr or more. Furthermore, the lens aperture is larger than that of the high-resolution SEM, and the electron beam capture angle α from the electron source (that is, the electron irradiated to the sample out of the electron beam emitted from the electron source with a wide angle) The beam opening angle was set to 6 mrad or more. The pixel size, which is the minimum unit of the image, is set equal to the minimum defect size to be detected. At present, the smallest defect that is a problem is about 0.05 μm, so the pixel size is set to 0.05 μm or more. Here, the meaning of 0.05 μm or more is described to indicate that the pixel size can be set larger than 0.05 μm because a defect size larger than 0.05 μm may be seen depending on the wafer. Further, depending on the process of the wafer to be inspected, the amount of secondary electrons generated is small, and sufficient brightness may not be obtained by only one electron beam scanning. In that case, images obtained by scanning the electron beam a plurality of times can be added. However, since there is a problem that the inspection time is delayed, the smaller the number of additions, the better. Since the image forming range should be as large as possible, it should be 50 μm or more, and 100 μm was standard.

  On the other hand, under the review conditions, since high speed is not required for image formation, the current value does not need to be large, and 5 nA or less is sufficient. The pixel size needs to be 1/5 or less of the size of the defect in order to observe the shape of the defect in detail. Therefore, it was 0.02 μm or less. Also, the addition of images is 2 n times, and there is no upper limit on the number of times. In the review, the stage is stationary and the electron beam is scanned two-dimensionally in order to observe a specific place carefully. Further, in order to enlarge the defect, the image forming range needs to be small and is 50 μm or less.

To summarize the above, there is a big difference in the way of thinking about the pixel size in the case of inspection and review mode, and in the case of inspection, there is a defect even if the probe size is larger than the defect size. What is necessary is just to judge whether or not. That is, the probe size and the pixel size should be equal or larger. If the pixel size is small, the amount of electrons radiated to the unit area is small, so that a long time is radiated and the clock is slowed down. On the other hand, in order to collect an image of the defect at the time of review, a probe having at least 1/5 of the defect size is required over time. The present invention is to change the probe size and change the pixel size at the time of inspection and review.
Next, how to switch between the defect detection inspection condition and the review condition will be specifically described.
First, components of the electron optical system and details of the operation will be described with reference to FIG. The electron source 1 is preferably a field emission electron source, particularly a diffusion replenishment type thermal field emission electron source, and a so-called Zr / O / W type electron source having a tungsten chip provided with a coating layer made of zirconium and oxygen is used. It was. This electron source can emit electrons stably for a long time. Moreover, the radiation angle current density can be freely set in the range of 0.001 mA / sr to 1 mA / sr by changing the extraction voltage. However, if the current density is increased, the energy width of the emitted electrons also increases, so that chromatic aberration increases. At the time of inspection, it was necessary to obtain an electron beam current of 20 nA or more. Therefore, the radiation angle current density of the electron beam emitted from the electron source 1 is used in the range of 0.2 to 1 mA / Sr. The electron beam 6 is extracted from the electron source 1 by applying a voltage to the extraction electrode 2. The electron beam 6 is accelerated by applying a high voltage negative potential to the electron source 1. The acceleration voltage can be set to 10kV or higher. This is because the high current electron beam is used to suppress the chromatic aberration due to the increase in the energy width of the electron beam, and to suppress the phenomenon (Coulomb effect) that the high current electron beam spreads due to the interaction of electrons and cannot be narrowed down. Because. The electron beam 6 travels in the direction of the stage 24 with energy equivalent to about 10 kV, is converged by the condenser lens 4, and is further narrowed down by the objective lens 7 and mounted on the stage 24 (wafer or chip, etc.). ). The distance (operating distance) between the objective lens 7 and the substrate to be inspected 10 was set to 25 mm in order to obtain a deflection area of 50 μm square or more and an image having no distortion even in the peripheral part. As a result, the focal length of the objective lens 7 is as long as about 30 mm.
The inspected substrate 10 has a negative voltage applying means for applying a negative voltage from the high voltage power source 25. By adjusting the high-voltage power supply 25, it becomes easy to adjust the electron beam irradiation energy to the substrate to be inspected to an optimum value. For example, if this voltage is -9.5 kV and the acceleration voltage of the electron beam is 10 kV, the irradiation energy to the sample is 500 eV.
For image formation, a method was adopted in which the electron beam 6 was scanned only one dimension and the stage 24 was continuously moved in a direction perpendicular to the scanning direction.
Signal detection for image formation is performed as follows. That is, secondary electrons are generated by the electron beam 6 irradiated on the sample 10. Since these secondary electrons are rapidly accelerated by the potential applied to the sample 10, it is very difficult to directly draw them into the detector 9. Therefore, a deflector combining an electric field and a magnetic field such as an ExB deflector 14 and a conversion electrode 11 for converting accelerated secondary electrons into low-speed secondary electrons are provided between the substrate 10 to be inspected and the detector 9.
The ExB deflector 14 is a deflector in which the electric field and the magnetic field are orthogonal to each other. For the primary electron beam 6 incident on the ExB deflector 14 from above, the deflecting action by the magnetic field and the deflecting action by the electric field are in opposite directions. This is a deflector that is designed to cancel, and that a secondary electron incident on the ExB deflector 14 from below is added with a deflection action by a magnetic field and a deflection action by an electric field.
Secondary electrons are deflected by the ExB deflector 14 and then irradiated to the conversion electrode 11. Then, secondary electrons generated from the conversion electrode 11 are detected by the detector 9. As the detector 9, a PIN type semiconductor detector is used in order to realize high-current high-speed detection of 10 nA or more. The secondary electron signal detected here is amplified by the preamplifier 12, is AD converted by the detection circuit 30, and is stored in the image storage unit 18 for storing data corresponding to the two-dimensional image of the sample obtained from the secondary electron signal. 19 is sent. The substrate 10 to be inspected is moved by the movement of the stage 24, and the inspection substrate 10 is irradiated with the electron beam 6 from the field emission cathode which is the electron source 1, and a comparative inspection is executed using the emitted secondary electron signal.

  According to the above method, defects are detected by comparing and determining images of repeated portions of the same pattern adjacent to each other by several μm away from the semiconductor pattern at high speed by the calculation unit 20 and the defect determination unit 21. Further, the defect can be detected by performing image comparison between the chips of the same pattern portion of different chips.

  Next, a method for switching to the review condition will be described.

  Factors that limit resolution in defect detection and inspection conditions are mainly 1) chromatic aberration caused by focusing electrons with different energy with a lens, and 2) Coulomb caused by repulsion of electrons due to high current density. Effect, 3) The finite light source diameter generated by the fact that the tip of the electron source is not a point light source. The basic idea of switching to review conditions is to reduce the electron beam current to be lower than that during defect detection inspection, thereby suppressing the factors that hinder the reduction of the electron beam, such as aberration of the optical system and the Coulomb effect. To form and thereby obtain a high resolution image. Specific methods are listed below.

The first is a method of reducing the current density drawn from the electron source. A block diagram of the electron gun is shown in FIG. The electron source 1 is a so-called Zr / O / W Schottky electron source in which a tungsten chip is provided with a coating layer made of zirconium and oxygen. The filament of the electron source 1 is heated by passing a current from the heating power source 405. The tip of the electron source 1 protrudes from the central hole of the suppressor electrode 403 for suppressing unnecessary thermoelectrons. The suppressor electrode 403 is given a negative potential with respect to the electron source 1 by the Vs power source 407. The tip of the electron source 1 faces the extraction electrode 2, and a positive potential with respect to the electron source 1 is applied to the extraction electrode 2 by an extraction power source 406. Each power source 405, 406, 407 is floated negatively by a desired acceleration voltage by the acceleration power source 408. As a result, the electron beam extracted from the electron source 1 is accelerated to the anode electrode 404 at the ground potential. In order to reduce the electron current density drawn in the electron gun having the above configuration, the extraction electric field at the tip of the electron source may be reduced. This can be realized by increasing the voltage value of the power source 407 connected to the suppressor electrode 403 and decreasing the potential of the extraction electrode 2.
Next, the reason why the aberration can be reduced by reducing the current density will be described. FIG. 7 shows the half-value width (referred to as energy width) of the current density per emission angle of electrons emitted from the electron source and the variation in energy of the beam. The energy width causes the chromatic aberration of the lens of the electron optical system, and the relationship is proportional to the energy width and the chromatic aberration as shown in Equation 1. Therefore, if the energy width is halved, the chromatic aberration is also halved. In the defect detection inspection conditions, the radiation angle current density is 0.1 mA / sr to 1 mA / sr, and 0.001 to 0.01 mA / sr at the time of review. As a result, the beam current is about 100 nA at the time of defect detection and inspection, about 5 nA or less at the time of review, the energy width becomes 1/3 from FIG. 7, and the chromatic aberration also becomes 1/3. As a result, the beam diameter is reduced to about 1/3 and the resolution is improved.

電流を低減して分解能を向上させる第２の方法は、絞り（例えば図１の絞り5）の直径を小さいものに交換して収差を低減する方法である。数１のように光学系の色収差はビームの開き角αに比例している。したがって、ビームの開き角を決定する絞りの直径を１／２にすれば色収差も１／２となる。開き角を小さくしすぎると開き角に反比例する回折収差が増大するが、1 mrad程度以上の開き角であれば回折収差は問題とならないのでビームの直径もほぼ１／２になる。ただしこの方法は機械的な絞りの移動機構が必要となり信頼性や簡便さといった点から問題が多い。

A second method for improving resolution by reducing the current is a method of reducing aberration by exchanging the diameter of the diaphragm (for example, diaphragm 5 in FIG. 1) with a smaller diameter. As in Equation 1, the chromatic aberration of the optical system is proportional to the beam opening angle α. Accordingly, if the diameter of the aperture that determines the beam opening angle is halved, the chromatic aberration is also halved. If the opening angle is made too small, diffraction aberration inversely proportional to the opening angle increases. However, if the opening angle is about 1 mrad or more, diffraction aberration does not cause a problem, so the beam diameter is also almost halved. However, this method requires a mechanical diaphragm moving mechanism and has many problems in terms of reliability and simplicity.

  As a third method, a method of reducing the beam opening angle without changing the aperture by changing the focal length of the lens to change the magnification of the optical system will be described. As a result, the size of the light source of the electron source can be reduced, which is superior to the second method. This will be described with reference to FIG. The electron beam emitted from the electron source is once focused (referred to as crossover) by the condenser lens under the defect detection inspection condition, and again focused on the sample by the objective lens. On the other hand, at the time of review, by reducing the lens action of the condenser lens to zero, the angle of capture α from the electron source is narrowed, and the irradiation angle β of the objective lens is also narrowed. As a result, the chromatic aberration of the objective lens is reduced and the resolution is improved as the current value decreases. Moreover, the magnification of the entire optical system at the time of defect detection inspection was (b / a) * (d / c), but at the time of review it was reduced to d / (a + b + c). The resolution can be further improved. The condenser lens uses an electromagnetic lens and is composed of a coil and a magnetic path. Since the strength of the lens action can be controlled by the current value flowing through the coil, the current can be made zero when the lens action is zero. Further, the case where the action of the condenser lens is made zero has been described, but the same effect can be expected by setting the lens conditions so weak that a crossover is not formed even if the action is not made completely zero.

It is also possible to improve the resolution by making the strength of the condenser lens stronger than in the defect detection inspection and moving the crossover position above the stop. This is shown in FIG. The effect obtained is the same as when the lens action of the condenser lens is made zero. That is, the magnification of the optical system is represented by (b / a) * (d / c), and as can be seen from a comparison between FIG. 8 and FIG. 9, the magnification is small because b is smaller and c is larger than in the defect detection inspection. Becomes smaller. Further, the irradiation angle β can be reduced.
In the above, the method of forming a high-resolution image at the time of review by reducing the beam current has been described. On the other hand, if the beam current is reduced, the signal that can be detected by the detector is greatly reduced. Therefore, if the amplification factor of the detection system is the same as that at the time of defect detection inspection, the input signal becomes less than the minimum bit of the detection circuit 30, and the electron beam is scanned over the sample a plurality of times to perform image addition. However, a good image cannot be obtained.
Therefore, another circuit was prepared from the preamplifier to the AD converter. That is, two signal paths are provided in the detection circuit 30 in FIG. The configuration is shown in FIG. At the time of defect detection inspection, the signal from the detector 9 is directly input to the A / D converter 304 via the low gain amplifier 301. On the other hand, since the beam current value decreases during the review, the signal from the detector 9 decreases. The signal path is switched to the high gain amplifier 302 having a higher gain accordingly. Further, the signal is input to the AD converter 304 via the high-frequency cut filter 303. The operation of this circuit will be described with reference to FIG. 16 which is a schematic diagram of signal waveforms at the time of defect detection inspection and review.

The case where the beam current at the time of defect detection inspection is 100 nA and the beam current at the time of review is 500 pA is taken as an example. The gain ratio between the low gain amplifier 301 and the high gain amplifier 302 is set to 200, which is equal to the ratio of the beam current. As a result, the average values of the outputs of both amplifiers are equal (arbitrary unit 100). FIG. 16A shows a signal waveform at the time of defect detection inspection when an image is formed on a non-patterned portion of a semiconductor. Since a large current beam is used, the noise amplitude is small. On the other hand, FIG. 16B shows a signal waveform at the time of review of the same part. The average of the signal is almost 100, but since a small signal is amplified with a high gain, the noise is large and the signal swings from −100 to 300. If the analog signal fluctuates on the minus side, the digitized value becomes zero. If it is too large, it will exceed the full scale of the A / D converter. Therefore, there arises a problem that an accurate waveform cannot be obtained even if the digital signals are averaged. In order to solve this problem, a high-frequency cut filter 303 is placed after the high gain amplifier. Noise in the input signal to the A / D converter 304 is reduced as shown in the “filter processing” waveform in FIG. Further, after digitizing this waveform, scanning the electron beam a plurality of times and adding the signals together makes it possible to obtain an image signal having a sufficient SN ratio.
The three methods for improving the resolution and the method for solving the problem caused by reducing the beam current have been described above. In this embodiment, in order to improve the resolution, the third method that mainly changes the excitation condition of the condenser lens is used, and the first method that changes the current value drawn from the electron source is used supplementarily. Specific numerical examples are shown below.
At the time of defect detection inspection, the radiation angle current density from the electron source was set to 0.5 mA / sr, the optical system magnification was set to 1 and the beam current was set to 100 nA. The resolution of the image at this time was about 0.08 μm. The line profile of the line and space pattern image at this time is shown in FIG.
In the review, the condenser lens current value was increased and the magnification was set to 0.2. Further, the high voltage power source of the electron gun was controlled, and the radiation angle current density from the electron source was lowered to 0.1 mA / sr. As a result, since the beam current decreased to 500 pA, the gain of the preamplifier of the detection system was switched to 200 times so as to pass through a filter that makes the frequency characteristic about 1/10. The scanning speed of the electron beam was about 1/10 at the time of defect detection inspection. Further, the image addition is performed 64 times to compensate for the deterioration of the SN ratio. The resolution of the image at this time was about 0.02 μm. The line profile of the image at this time is shown superimposed on FIG. It can be seen that the rise of the line profile at the time of review is sharp and the amplitude is also large. This clearly confirms that the resolution is improved and that even fine objects can be observed.
(Example 2)
In Example 1, the same detector was used at the time of review and at the time of defect detection inspection. However, since the detection signal drastically decreases at the time of review, it is necessary to increase the gain of the preamplifier 12 by 200 to 1000 times by the rate at which the current decreases. Furthermore, when only the gain is increased while the frequency characteristic is high as in the defect detection inspection, there is a problem that the circuit oscillates or the noise amplitude of the circuit becomes larger than the average signal amount. Therefore, it is necessary to add a circuit for cutting high frequencies, and the circuit becomes complicated. As a result, there is a possibility that noise is mixed in the detection signal at the time of defect detection inspection or the frequency characteristic is deteriorated. In order to solve this, in this embodiment, a dedicated detector for review is provided. The configuration diagram is shown in FIG. A review detector is provided at a position substantially symmetrical with respect to the optical axis of the electron beam of the defect detection / inspection detector 9. This detector is used in an ordinary scanning electron microscope, and includes a scintillator 52 and a photomultiplier tube 51. The response characteristic is DC to 20 MHz. The secondary electrons emitted from the sample 10 are deflected by the ExB deflector 14 in the direction of the defect detection inspection detector 9 during the defect detection inspection and in the direction of the review detector during the review. The secondary electrons are applied to the conversion electrodes facing the respective detectors, thereby detecting the secondary electrons emitted. A positive high voltage is applied to the front surface of the scintillator 52 by the power supply 53, and the secondary electrons are accelerated and collided to be converted into light. The light is multiplied by a photomultiplier tube 51 and detected. Switching of the deflection direction of the secondary electrons is achieved by reversing the polarity of the control power supply 31 of the ExB deflector 14 (reversing the polarity of the applied voltage and the deflection coil current). In conjunction with this, the signal from one of the detectors is displayed on the monitor 22 via the memory 18. These switching operations are performed by the control unit 104.

(Example 3)
Depending on the type of defect, the detected defect contrast may disappear if the review conditions are not appropriate. For example, among the defective conduction defects in the conduction holes, the defect contrast may disappear while the beam is irradiated a plurality of times. Therefore, when reviewing such defects, it is necessary to limit the number of image additions. Since the number of additions is limited, it is necessary to increase the beam current in order to obtain an image with a good S / N ratio. Also, depending on the type of defect, the contrast of the defect is greater when the retarding electric field (electric beam deceleration electric field applied to the inspection wafer) is stronger in the large current beam at the time of defect detection and inspection, but the retarding occurs when the current is small. In some cases, the contrast is enhanced when the electric field is weakened. In the following, a condition setting method for reviewing defective continuity defects will be described as an example.

  In the semiconductor process, there is a step of making a hole and embedding a conductive material in the hole in order to establish vertical conduction between the upper layer and the lower layer. If there is a defect in this drilling or embedding, it becomes completely electrically open or has a very high resistance value. When such a process is detected and inspected for defects, conductive holes are bright and non-conductive holes are dark. Furthermore, in the case of a delicate high resistance value that is slightly defective, it becomes an intermediate brightness, so that it is detected as a defect by comparing with a hole with perfect conduction. When such an image is subjected to image addition several tens of times with a reduced current during review, the brightness becomes the same as that of a completely conducting hole, and no information can be obtained even when reviewed. Therefore, when detecting and inspecting a through hole for defects, the brightness level is stored in combination with the defect coordinates for each detected defect, and when reviewing a gray defect, the beam current is automatically set to 5 nA or less. The optical conditions were set so as not to occur, and the number of image additions was suppressed to 10 or less. On the other hand, when reviewing defects at very dark levels, the beam current was lowered as much as possible, and the review was conducted under conditions of 500 pA or less.

  The above is an example. In short, the type of defect is automatically classified using information obtained from the image at the time of defect detection inspection, that is, brightness, defect size, shape, etc., for review according to each. The optical conditions, that is, the scanning range, beam current, scanning speed, and number of image additions are automatically associated with each other. At this time, in the present invention, since the change of the optical conditions is not accompanied by the mechanical movement, that is, the movement of the diaphragm as much as possible, the conditions can be switched instantaneously for each defect.

(Example 4)
In the fourth embodiment of the present invention, the electron optical system for review is independent from the electron optical system for defect detection inspection. This will be described with reference to FIG. FIG. 12 is a block diagram of the present embodiment.

  The inspection apparatus is roughly divided into a defect detection inspection electron optical system 101, a review electron optical system 200, a sample chamber 102, a control unit 104, and an image processing unit 105. Except for the reviewing electron optical system 200, the second embodiment is substantially the same as the first embodiment.

  The review electron optical system includes an electron source 201, an electron beam extraction electrode 202, a condenser lens 204, a scanning deflector 208, a diaphragm 205, and an objective lens 207. The secondary electron detector 209 is above the objective lens 207, and the output signal of the secondary electron detector 209 is amplified by the preamplifier 212 and sent to the low-speed image display circuit 218.

  Although a retarding voltage is applied to the sample stage 24, when the stage moves from under the defect detection inspection optical system 101 to under the review electron optical system, the retarding voltage is cut off once due to the stage structure. In some cases, it may be preferable to move the substrate, and the selection may be made according to the retarding voltage to be applied and the type of the substrate to be inspected.

  Next, specifications, differences, and features of the review electron optical system and the defect detection inspection optical system, which are points of the present embodiment, will be described.

  Since the electron optical system 101 for defect detection inspection executes inspection of the entire wafer surface in a practical time, it can acquire an image at a very high speed. That is, the time for forming a 100 μm square with a pixel size of 0.1 μm or less is 20 msec or less. The stage moves continuously for high-speed image acquisition, and the electron beam is scanned in the orthogonal direction. Furthermore, in order to realize image formation with an S / N ratio that can withstand inspection at high speed, the beam current was designed to be 20 nA or more. Specifically, first, the current density obtained from the electron source 1 was set to about 1 mA / sr, which is a limit value that can be obtained stably. This is about 20 times the high resolution SEM. Further, a lens aperture larger than that of the high-resolution SEM is used, and the sample 10 is irradiated with an electron beam capture angle α from the electron source 1 (that is, an electron beam emitted from the electron source 1 with a wide angle). The opening angle of the electron beam is about 20 times.

  In addition, if the peripheral portion of the image is distorted or the resolution is lower than that of the central portion, the inspection sensitivity becomes non-uniform, so it is necessary to provide a margin for the scanning region of the electron beam. Therefore, the focal length and operating distance of the objective lens are considerably longer than those of ordinary high-resolution SEM.

  Moreover, when the sample irradiation opening angle β of the electron beam increases, the depth of focus becomes shallow. Since β is obtained by dividing α by the magnification M of the entire optical system, the magnification M cannot be made too small. Therefore, the magnification is considerably larger than that of the high resolution SEM.

  With the above design, it is possible to obtain a large current necessary for high speed while ensuring a resolution necessary for defect detection inspection. As described above, this electron optical system cannot obtain the same resolution as a high-resolution SEM even if the electron beam current is simply reduced from the magnification of the optical system, the focal length of the objective lens, and the operating distance. it is obvious.

On the other hand, high speed is not so important in the review electron optical system. In addition, since the coordinates of the place to be observed are known accurately, a visual field of 20 μm is sufficient. Therefore, the electron beam current may be small. In addition, since the focal length and operating distance of the objective lens can be short, and the magnification of the optical system can be reduced, a high-resolution image similar to a normal high-resolution SEM can be acquired.
Next, the review electron optical system 200 will be described. As the electron source 201, a Zr / O / W type electron source, which is a diffusion replenishment type thermal field emission electron source similar to the electron optical system for defect detection and inspection, was used. Increasing the current density also increases the energy width of the emitted electrons and increases chromatic aberration. In the review electron optical system, the beam current may be 100 pA or less, so the radiation angle current density is 0.05 mA / Sr or less. As a result, the energy width of the electron beam 206 is reduced to about 1/3 to 1/4 as compared with the electron optical system for defect detection and inspection, and the chromatic aberration is also reduced accordingly. The electron beam 206 is extracted from the electron source 201 by applying a voltage to the extraction electrode 202. The electron beam 206 is accelerated by applying a high voltage negative potential to the electron source 201. In the review optical system 200, the acceleration voltage can be varied from 500V to 10kV. Since the review optical system 200 requires a small current, the chromatic aberration is small as described above, and the Coulomb effect can be ignored. Therefore, since a sufficiently small beam diameter can be obtained with a low acceleration voltage, the acceleration voltage is set to 2 kV as a standard. The electron beam 206 travels in the direction of the sample stage 24 with energy equivalent to 2 kV, is converged by the condenser lens 204, is further narrowed down by the objective lens 207, and is mounted on the stage 24 (wafer or chip). Is irradiated. The objective lens 207 is very close to the substrate 10 to be inspected, and the operating distance is 5 mm. The focal length of the objective lens 207 is 8 mm. As a result, an objective lens with small aberration was realized. The resolution is almost determined by chromatic aberration. Therefore, since the aberration coefficient is about 1/4 and the energy width of the electron beam is about 1/3 of the defect detection / inspection optical system, the resolution is about 1/12. The substrate 10 to be inspected is common for the defect detection inspection and the review, and therefore a negative voltage can be applied by the high voltage power supply 25. By adjusting the high-voltage power supply 25, the electron beam irradiation energy to the substrate to be inspected 23 can be adjusted to an optimum value. Since images with different contrasts can be obtained by changing the irradiation energy, information such as whether the defect is due to a difference in shape, due to the material, or due to electrical conduction can be obtained from various angles.
For image formation, the electron beam 206 is scanned two-dimensionally. That is, the stage 24 is fixed. Secondary electrons generated by the electron beam 206 applied to the substrate 10 to be inspected are accelerated by the potential applied to the substrate 10 to be inspected in the same manner as the defect detection inspection optical system 101. Since the objective lens 207 is very close to the inspected substrate 10 at about 30 mm or less, the detector 209 is provided above the objective lens 207, and the secondary electrons pass through the center of the objective lens 207. Compared with the defect detection / inspection optical system 101, the potential applied to the substrate 10 to be inspected is low, so the energy of secondary electrons is weak, but it is still difficult to directly draw it into the detector 209. Therefore, the conversion electrode 211 is irradiated and secondary electrons emitted therefrom are detected by the detector 209. As the detector 209, a detector 209 using a phosphor and a photomultiplier tube, which is used in a normal SEM, was used. The secondary electron signal detected here is amplified by the preamplifier 212 and AD-converted by the AD converter 230, displayed on the monitor 22 for image observation, and stored in an external storage device 219 such as a disk as needed. It can be printed or printed out.

Although the fourth embodiment has been described above, the numerical value of each function is an example. The point is that the review electron optical system that can achieve a beam diameter of about 1/10 of the electron optical system for defect detection inspection is arranged side by side on the same sample chamber as the electron optical system for defect detection inspection, The essence of the present embodiment is that the defect detection inspection and the review operation can be quickly switched only by the parallel movement of the sample stage.
(Example 5)
In the fifth embodiment, an X-ray detector 240 is incorporated in the lower magnetic path of the objective lens 207 of the review electron optical system 200 of the fourth embodiment so that characteristic X-rays generated by electron beam irradiation can be detected. did. This makes it possible to perform EDX (Energy-Dispersive X-ray) analysis, and to identify the material of the defect at the time of review. FIG. 13 shows the vicinity of the objective lens when an annular X-ray detector having a hole in the center is incorporated.

Also, the X-ray analyzer may be inserted between the objective lens and the sample with the operating distance of the objective lens being slightly larger than that of the first embodiment.
(Example 6)
In the inspection by the electron beam, not only the shape defect but also the electrical conduction / non-conduction can be inspected. This is because the conducting portion is not charged, and the energy and orbit of secondary electrons generated by charging only the non-conducting portion changes, resulting in different image brightness. This occurs as a particularly large contrast by irradiation with a high-current electron beam. However, in the review electron optical system, since the current is small, the difference in charging is small and it is difficult to appear as a contrast difference. In view of this, a secondary electron energy filter capable of high sensitivity filtering even with a slight difference in energy of secondary electrons was provided. The energy filter was provided on the objective lens. A diagram of this analyzer is shown in FIG. A hemispherical mesh 220 is provided above the objective lens 207 so as to block the secondary electron trajectory. In the center of the mesh 220, a hole through which the primary electron beam 206 passes is formed. The mesh 220 is supplied with a potential in a range of about ± 20 V from the potential of the substrate 10 to be inspected by the power source 221. Thereby, the state of charging of the substrate to be inspected can be imaged. The secondary electrons have an energy distribution having a peak at about 2 eV with respect to the potential φ at the place of emission. Therefore, the energy peak of the secondary electron viewed from the ground potential is (−φ + 2) eV. For example, assuming that a retarding potential of 500 V is applied to the substrate to be inspected 10, the peak of secondary electron energy is 502 eV. If the primary beam irradiation position is originally a place to be electrically connected to the substrate 10 but only that part is non-conductive due to a pattern defect, that part is negatively charged. Then, the energy of the secondary electrons emitted from there is higher by the charged voltage. If the charging voltage is 5V, it is 507eV. Therefore, if −505 V is applied to the mesh 220, most of the secondary electrons from the uncharged portion cannot pass through the mesh 220. Therefore, only the charged part appears bright. In this way, a slight charge can be obtained as a contrast difference. Here, only the case of negative charging has been described, but in an actual semiconductor, the mechanism of charging by electron beam irradiation is complicated, and there are cases where it is positively charged. In that case, the potential applied to the mesh 220 may be set to the same potential as the retarding potential or slightly positive. In that case, the positively charged part is dark and the other parts are bright.

  The resolution of the energy analyzer of this embodiment can obtain about 0.1V. Therefore, since the electron beam current is small at the time of review, the contrast due to the potential is emphasized even if the charge amount of the defect portion is small, so that the defect can be easily identified.

It is a figure explaining an example of the apparatus structure of Example 1 of this invention. It is a figure explaining the modification of the apparatus structure of Example 1 of this invention. It is a figure explaining an example of the flow of an inspection of the present invention. It is a figure explaining another example of the flow of inspection of the present invention. It is a figure explaining the conditions of a test | inspection and a review. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining a part of Example 1 of the present invention. FIG. 3 is a diagram for explaining an operation principle of the first embodiment of the present invention. FIG. 3 is a diagram for explaining an operation principle of the first embodiment of the present invention. FIG. 5 is a diagram for explaining an example of the operation principle of Embodiment 1 of the present invention. FIG. 6 is a diagram for explaining the effect of Example 1 of the present invention. It is a figure explaining the structure of Example 2 of this invention. It is a figure explaining the structure of Example 3 of this invention. It is a figure explaining the structure of Example 4 of this invention. It is a figure explaining the structure of Example 5 of this invention. FIG. 3 is a diagram illustrating a configuration of a detection circuit in Embodiment 1 of the present invention. It is a figure explaining the signal waveform at the time of defect detection inspection and review in Example 1 of the present invention.

Explanation of symbols

1: Electron source, 2: Extraction electrode, 3: Insulator, 4: Condenser lens, 5: Aperture, 6: Electron beam, 7: Objective lens, 8: Scanning deflector, 9: Secondary electron detector, 10: Subject Inspection board, 11: Conversion electrode, 12: Preamplifier, 13: Scan signal generator, 14: ExB deflector, 17: Blanking deflector, 18: Image storage unit, 19: Image storage unit, 20: Calculation unit, 21 : Defect determination unit, 22: Monitor, 24: Stage, 25: High-voltage power supply, 26: Objective lens power supply, 27: Correction control circuit, 29: Optical sample height measuring device, 30: AD converter, 31: Stage position Measuring instrument, 32: Preamplifier, 33: AD converter, 34: Transmitter, 35: Receiver, 101: Electron optical system for inspection, 102: Sample chamber, 104: Control unit, 105: Image processing unit, 200: For review Electron optical system, 201: electron source, 202: extraction electrode, 204: condenser lens, 205: aperture, 206: electron beam, 207: objective lens, 208: scanning deflector, 209: detector, 211: conversion electrode, 212 : Preamplifier, 218: Image storage unit, 219: external storage device, 220: mesh, 221: power supply, 230: AD converter, 240: X-ray detector, 403: suppressor electrode, 404: anode, 405: heating power supply, 406: extraction power supply, 407: Suppressor power supply, 408: Acceleration power supply.

Claims (1)

An electron optical system that converges the electron beam emitted from the electron source with a lens and irradiates and scans the sample;
A stage on which the sample is mounted and movable so that an electron beam is irradiated to a desired position on the sample;
A first detector for detecting, with a first sensitivity, backscattered electrons or secondary electrons obtained from the irradiated part of the sample;
A second detector for detecting backscattered electrons or secondary electrons obtained from the irradiated portion of the sample with a second sensitivity higher than the first sensitivity;
An image forming apparatus for forming an image of the sample based on a detection signal from the detector;
Means for comparing an image signal obtained by the image forming apparatus with an image signal obtained in a similar manner from another place on the sample, and detecting a difference between the two image signals;
When the electron beam is scanned over the sample at a first area, a first current value, and a first speed, the backscattered electrons or secondary electrons are guided to the first detector, and the electron beam is When the sample is scanned at an area smaller than the first area, a current value smaller than the first current value, and a speed slower than the first speed, the backscattered electrons or secondary electrons are scanned as the second electrons. A circuit pattern inspection apparatus comprising a deflection circuit leading to a detector.

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