JP2001074437A - Device and method for inspecting circuit pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable efficient setting of inspection conditions by performing defect detecting inspection by high-speed image acquisition, and a review which is performed by imaging a detected specific narrow part and observing it with the naked eye, through the use of detection circuits provided with routes optimized independently, respectively. SOLUTION: First of all, rough alignment is performed with an optical microscope, after a wafer is loaded. The alignment is performed by a wide-visual-field low-magnification optical microscope with a precision of about several tens μm. Next condition setting for an electronic optical system is performed. Irradiating energy of an electron beam, pixel size (the smallest element of a picture image), beam current, etc., are set by the kind of the pattern of the wafer to be inspected. Next, a pixel size corresponding to the size of a defect which is wanted to note especially is set, and then a beam current is set. Next a picture image by an electron beam of the wafer to be inspected is displayed, and a focal point and astigmatism are corrected. Next, precise alignment of the picture image by an electron beam is performed. Consequently, a stage coordinate system and a wafer coordinate system are matched accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for inspecting a circuit pattern, and more particularly to an apparatus and method for inspecting a circuit pattern of a wafer or the like in a process of manufacturing a semiconductor device.

[0002]

2. Description of the Related Art In a semiconductor device manufacturing process, two or more LSIs on one wafer are used as an inspection method for comparing and detecting defects of a circuit pattern formed on the wafer.
An apparatus has been put to practical use for acquiring images of the same kind of patterns and comparing them for inspection.

[0003] In particular, an apparatus for comparing and inspecting patterns using an electron beam is disclosed in Japanese Patent Application Laid-Open No. 59-192943, J. Vac. Sci. Tech.
ol. 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 Engine
ering) Vol.2439, and JP-A-5-258703. There, it is necessary to acquire an image at a very high speed in order to obtain a practical throughput. In order to secure the S / N ratio of the image acquired at high speed, the electron beam current of 100 times or more (10 nA or more) of the ordinary scanning electron microscope is used, and the S / N ratio of the image is secured while maintaining a practical inspection speed. are 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 the energy width of the electrons is widened, so that the chromatic aberration is increased, the brightness of the electron gun is limited, and the Coulomb effect is limited.

An image formed by such an electron optical system is
The image is sent to the image processing system, and the image of the same adjacent pattern portion is compared and inspected. If there is a portion having different brightness when comparing the images, it is regarded as a defect and the coordinates of the portion are stored.

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

Japanese Patent Application Laid-Open No. 7-078855 discloses an apparatus for inspecting semiconductor defects by applying a voltage to a sample and an electrode near the sample to reduce energy of an electron beam.
JP-A-09-181139, JP-A-10-019
538, JP-A-10-027834, JP-A-10-027835, JP-A-11-02590
No. 1 publication. However, there is no description of the review function described below or a statement that it also has an energy analysis function.

[0007]

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

The above parameters have different optimum values 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 value while confirming whether a defect to be detected is detected.

[0009] Further, it is necessary to obtain an image of the defect coordinate portion after the inspection and to confirm what kind of defect has been detected by the operator.

That is, in order to detect the presence of a defect, an image is acquired at a high speed, and not only the defect is detected by image processing, but also a specific narrow visual field is imaged in the same manner as in a normal scanning electron microscope. The function of observing with the naked eye is also essential. In the present specification, this is hereinafter referred to as a review. In the case where it is necessary to particularly distinguish the review and the inspection by the high-speed image acquisition for detecting the presence of a defect over a relatively large area, the latter is used. Will be referred to as a defect detection inspection.

At the time of review, it is not necessary to form an image at a higher speed than at the time of defect detection inspection. On the other hand, since it is necessary to recognize not only the presence or 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 designed so as to be optimal for obtaining an image by high-speed scanning with a large current, and it is not possible to obtain a sufficient resolution as a review image. Therefore, the accuracy for determining whether the detected defect is a true defect or an erroneous detection caused by improper parameter setting is low. For this reason, the inspection is often performed without setting the setting parameter to an optimum value.

An object of the present invention is to provide an inspection apparatus for inspecting a sample, for example, inspecting an electron beam for defects, foreign matter, residues, etc. of the same design pattern of a semiconductor device on a wafer in the process of manufacturing the semiconductor device. An object of the present invention is to provide an inspection apparatus capable of setting conditions efficiently.

[0014]

The inspection apparatus of the present invention achieves the above object by the following constitution.

That is, a first invention according to claim 1 of the present invention provides an electron optical system which converges an electron beam emitted from an electron source by an electron lens and irradiates the electron beam onto a sample for scanning. A stage on which the sample is mounted, a movable stage so that a desired position on the sample is irradiated with an electron beam, and a detector for detecting backscattered electrons or secondary electrons obtained from an irradiated portion of the sample. The output from the detector is a first
A first circuit that amplifies at an amplification factor of, a second circuit including an amplifier that amplifies an output from the detector at an amplification factor greater than the first amplification factor, and a high-frequency component cut filter; An image forming apparatus that forms an image of the sample based on a detection signal from a detector, and an image signal obtained by the image forming apparatus, and an image signal similarly obtained from another place on the sample. Means for comparing and detecting the difference between the two image signals; and means for detecting the difference between the two image signals from the detector in a first case in which the electron beam is scanned over the sample at a relatively large area, a relatively large current, and a relatively high speed. An output is input to the first circuit, and 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 lower than the relatively high speed. In the second case, the output from the detector is switched to the second circuit. An inspection device provided with a switching means for example input.

According to a second aspect of the present invention, in the inspection apparatus of the first aspect, the second case is a minimum unit of an image formed in the first case. An inspection apparatus that forms an image with a pixel size smaller than a certain 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, a spot size of the electron beam on the sample is reduced. An inspection apparatus characterized by being smaller than the first 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 A second lens disposed on the electron source side, wherein in the second case, the second lens is adjusted so that the magnification of the electron optical system is set to be small. It is.

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 stop having an aperture having a plurality of diameters. An inspection apparatus characterized in that, in the second case, the diameter of the stop 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,
An inspection apparatus characterized in that a position of a crossover formed by the electron beam is moved.

According to a seventh aspect of the present invention, in the inspection apparatus according to any one of the first to sixth aspects, in the second case, the scanning deflection area of the electron beam is provided. An inspection apparatus characterized in that the deflection area is reduced to half or less of that in the first case.

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 is more than the first circuit. And the response speed is low.

According to a ninth aspect of the present invention, in the inspection apparatus according to any one of the first to eighth aspects, a difference between the two image signals in the first case is detected. The magnification of the electron optical system, the current value of the electron beam, the scanning speed of the electron beam, and the number of times of addition of the image in the image forming apparatus in the second case in accordance with the output result of the means for performing the operation. An inspection apparatus characterized by comprising means.

Also, the tenth aspect of the present invention is the tenth aspect.
The invention of a first electron source that emits a first electron beam,
A first objective lens having a first focal length and focusing the first electron beam on a sample located at a first sample position, and placing the first electron beam at the first sample position. A first electron optical system including a first scanning deflector that scans a sample located thereon; first detection for detecting secondary charged particles generated from the sample located at the first sample location With vessel; second
A second electron source that emits an electron beam, and 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. Second
A second electron optical system, comprising: an objective lens described above; and a second scanning deflector for scanning the second electron beam on a sample located at the second sample position; and the second sample position. A second detector for detecting secondary charged particles generated from the sample located at the first and second sample positions based on outputs from the first detector and the second detector. And a stage for moving the sample from the first sample position to the second sample position, wherein the first electron optical system and the second The first optical detector, the first detector, the second detector, and the stage are housed in the same vacuum vessel, and the output from the first detector with respect to the sample located at the first sample position A specific position on the sample selected based on the image data formed based on Is moved to the second sample position, and the specific position is moved to the second sample position.
Is an inspection device that performs magnified observation using the electron optical system.

Further, the eleventh aspect of the present invention provides the eleventh aspect.
In the inspection apparatus according to claim 10, the acceleration voltage for the second electron beam in the second electron optical system is higher than the acceleration voltage for the first electron beam in the first electron optical system. An inspection device characterized by being low.

Further, the twelfth aspect of the present invention is the twelfth aspect.
In the inspection apparatus according to claim 10 or 11, the negative electrode applied to the stage and the sample in order to decelerate the electron beam to a desired energy immediately before the stage and the sample on the stage. The inspection apparatus is characterized in that the voltage is a negative voltage at the second sample position smaller than the negative voltage applied at the first sample position.

Also, the thirteenth aspect of the present invention provides a thirteenth aspect.
The inspection apparatus according to any one of claims 10 to 12, further comprising an X-ray detector that detects an X-ray generated from the sample located at the second sample position. Device.

Further, the fourteenth aspect of the present invention is the fourteenth aspect.
The inspection apparatus according to any one of claims 10 to 12, further comprising an energy filter configured to filter energy of secondary electrons emitted from the sample located at the second sample position, An inspection apparatus characterized by detecting a potential at a position irradiated with an electron beam.

Further, the fifteenth aspect of the present invention provides the fifteenth aspect.
According to the invention, an electron optical system that converges an electron beam emitted from an electron source by a lens and irradiates and scans the sample on a sample, mounts the sample, and irradiates a desired position on the sample with the electron beam A movable stage, a first detector for detecting, at a first sensitivity, backscattered electrons or secondary electrons obtained from an irradiated portion of the sample; and The second to detect the obtained backscattered electrons or secondary electrons at a second sensitivity higher than the first sensitivity
Detector, an image forming apparatus that forms an image of the sample based on a detection signal from the detector, an image signal obtained by the image forming apparatus, similarly from other places on the sample Means for comparing the obtained image signal and detecting a difference between the two image signals, and applying the electron beam to the sample over a first area;
When scanning at 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 directed on the sample over an area smaller than the first area, A current value smaller than the first current value, when scanning at a speed lower than the first speed, a deflection circuit for guiding the backscattered electrons or secondary electrons to the second detector. is there.

Further, the sixteenth aspect of the present invention is the sixteenth aspect.
An electron optical system for irradiating and scanning a sample on which a circuit pattern is formed with a converged electron beam, a detector for detecting backscattered electrons or secondary electrons obtained from an irradiated portion of the sample, An image forming apparatus that forms an image of the sample based on a detection signal from the detector, and comparing an image signal obtained by the image forming apparatus with a reference image signal to detect a difference between the two image signals. Preparing a difference detecting means to perform the first step; and scanning the relatively large area of the sample with the electron beam at a relatively large current and a relatively high speed to obtain an output from the detector as a first step. The signal amplified by the amplifier having the amplification factor is supplied to the image forming apparatus to form an image signal, and the image signal is obtained by the difference detecting means and the image signal is obtained in advance from another region on the sample. Compared to the image signal of both images By detecting the difference between the issue,
Determining the coordinates of the location where the difference occurs; and, by using the electron beam, a small current area smaller than the relatively large current, The output from the detector obtained by scanning at a low speed lower than the relatively high speed is output to the first
Supplying an image signal to the image forming apparatus through a circuit including an amplifier that amplifies at an amplification factor greater than the amplification factor and a high-frequency component cut filter to form an image signal and observing a location where the difference occurs. This is a circuit pattern inspection method including the following.

[0031]

(Embodiment 1) A first embodiment of the present invention will be described with reference to FIGS. 1 and 2 are configuration 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,
It comprises a scanning deflector 8, a stop 5, and an objective lens 7. FIG. 1 shows a case where the secondary electron detector 9 is located below the objective lens 7, but the position of the detector 9 may be provided on the objective lens 7. In that case, the secondary electrons reach the detector 9 after passing through the objective lens 7. When the detector 9 is located below the objective lens 7, the deflection range of the objective lens 7 can be widened, but the resolution at the time of review is limited due to the large aberration of the objective lens 7. On the other hand, if the detector 9 is provided on the objective lens 7, the resolution of the review can be further increased because the aberration of the objective lens 7 can be reduced, but there is a disadvantage that the deflection range is reduced. Both have advantages and disadvantages, and either configuration may be selected as necessary. A high positive voltage is applied to the detector 9. Further, the ground levels of the preamplifier 12 and the detection circuit 30 connected to the detector 9 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 an optical transmitter 34, and the light is received by an optical receiver 35 at the ground potential level and converted into an electric signal.
Sent to 5.

In FIG. 1, the condenser lens 4 is constituted by an electromagnetic lens, but may be constituted by an electrostatic lens as shown in FIG. 2. The electrostatic lens is constituted by, for example, three electrodes, and the electrodes on both sides are arranged. A so-called Einzel lens, which applies a positive or negative voltage to the central electrode as a ground potential, is optimal, but the same is not particularly true for an Einzel lens. By using an electrostatic lens, the size of the electron optical system can be reduced.

Returning to FIG. 1, the sample chamber 102 includes the stage 24,
It comprises an optical sample height measuring device 29, a laser position 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 and output from the control unit 104. Conditions such as an acceleration voltage at the time of generation of an electron beam, an electron beam deflection width, a deflection speed, a moving speed of a sample stage, and a signal fetch timing of a detector are input to the control unit 104 in advance. Also, the signal of the optical sample height measuring device 29 and the stage position measuring device 31
A correction signal is generated from the signal of the objective lens power source 7 and the scanning signal generator 1 so that the electron beam 6 is always irradiated to a correct position.
Send the correction signal to 3.

FIG. 3 is a diagram showing a flow of a semiconductor pattern appearance inspection using an electron beam. A flow for carrying out a pattern appearance inspection of a 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 an electron beam scanning image, and there is a possibility that the alignment mark does not fall within the scanning range of the electron beam only by mechanical positioning during loading. Therefore, alignment is performed with an accuracy of approximately several tens of μm using a low-magnification optical microscope having a wide field of view.

Next, conditions for the electron optical system are set. The irradiation energy of the electron beam, the pixel size (minimum element of the image), the beam current, and the like are set according to the type of the pattern of the wafer to be inspected. The optimum electron beam irradiation energy differs depending on the pattern material. Normally, conductive materials use higher energy of several keV or more to obtain high resolution, and 1.5 keV to prevent electrification in patterns containing insulators.
It is good to set below.

Next, a pixel size corresponding to the defect size of particular interest is set. Insignificantly reducing the pixel size increases the time required for inspection. Next, the beam current is set. The default value is unique to the apparatus, but it is preferable to set a smaller current especially for a wafer which is easily charged. If it is known in advance that the contrast of the defect to be detected is large, the current can be made smaller and the electron beam can be made smaller so that high-sensitivity inspection can be performed.

Next, an image of the wafer to be inspected by the electron beam is displayed, and the focus and astigmatism are corrected. This can be carried out automatically on a computer or by using an image processing device dedicated thereto, by taking in an image.

After the above setting is completed, fine alignment of the image by the electron beam is performed next. As a result, the coordinate system of the stage and the coordinate system of the wafer accurately match, and a desired position on the wafer can be inspected by measuring the coordinates of the stage with a laser length measuring device or the like.

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

Next, a test inspection is performed. The trial inspection is performed to determine whether the various parameters set above are appropriate. First, a part of the pattern to be inspected is specified. This is the trial inspection area designation. Then, a test inspection is performed. In the test inspection, an image is detected by an electron beam in the same operation as the actual defect detection inspection, but all the acquired images are loaded into the memory without passing through the image processing circuit.

Next, image processing conditions are set. This condition is a threshold value used by the image processing apparatus to determine whether or not there is a defect when comparing two adjacent images of the same pattern. When this threshold value is set low, the defect detection sensitivity is improved, but the possibility that non-defect portions are regarded as defects is increased. On the other hand, when the threshold value is increased, the detection sensitivity decreases.

In FIG. 3, the brightness threshold is a threshold of the difference between the luminance signals of two images. The image obtained by the electron beam is rougher than the optical microscope image (that is, the SN ratio of the image is poor). Therefore, even if the inspection objects to be compared are the same and the average brightness is the same, there is a slight variation in brightness when viewed from pixel to pixel. Therefore, a threshold value of the light-dark difference is provided, and by comparing the images and detecting only a portion where the light-dark difference is larger than the threshold value as a defect, the roughness of the image is not recognized as a defect.

The position shift threshold value is provided so that the incomplete registration of two images to be compared is not erroneously recognized as a defect. It is considered that the image position deviation exists about the threshold value set here, and only a case where a further difference occurs is regarded as a defect.

The filter type is a filter to be applied to the acquired image, and exists to reduce the roughness of the detected image and enhance the edge. In this method, an optimum one is selected by trial and error according to a type of a pattern and a 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. This inspection detects a defect, stores its coordinates, and displays the location of the defect on a control screen. If no defect is detected at this point, the sensitivity is increased by lowering the threshold value of the image processing parameter, and the comparison inspection is performed again using the two-dimensional information on the memory.

Next, an image of the coordinates detected in 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 a display of a control workstation or a display dedicated to image display, and the type of defect detected is visually observed. Here, the shape and type of a very large defect can be easily determined visually. However, fine defects close to the performance limit of the device and defects having low contrast often cannot be determined sufficiently and visually. Therefore, the condition of the electron optical system is switched to the review condition to display a high-resolution image. Thus, it is possible to easily determine whether the defect detected in the test inspection is a true defect or a defect that the user wants to detect. From the result, it is possible to find out a condition for reliably detecting a defect to be detected by repeatedly setting the parameters of the image processing and repeating the review.

In a conventional apparatus having no high-resolution review conditions, an image is formed by a high-current electron beam, and when observed for a long time, the sample is irradiated with a large amount of the electron beam and the sample is destroyed. And the image cannot be observed due to charging. Further, the purpose is to confirm the presence or absence of a defect, and the resolution is insufficient for judging the details of the defect by visual observation. For this reason, a great deal of time has been required for trial and error in this review and image processing parameter setting. 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 has been significantly reduced. As a result, the time required for manned work has been significantly reduced, and the overall operation efficiency of the apparatus 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 the defect detection inspection is completed, the review is performed again. After confirming whether the defect detected by this review is a true defect, the wafer is unloaded. If necessary, move to another analysis and inspection apparatus to 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 performed 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 settings, and the review is performed after the completion of the defect detection inspection. In this review, the detected defects are classified according to the type of the defect by ascertaining the type of the defect such as a foreign matter, an electrical defect, or a shape defect.

Next, the review conditions and the specifications, differences and features of the defect detection inspection conditions, which are the points of the present invention, will be described.

FIG. 5 shows a comparison of the performance between the defect detection inspection condition and the review condition.

The defect detection / inspection conditions enable extremely high-speed image acquisition because the entire wafer is inspected in a practical time. That is, a pixel size of 0.1 μm and 100 μm
The time for forming the corner image is 20 msec or less. The stage is continuously moved for high-speed image acquisition, and the electron beam is scanned in a direction substantially orthogonal to the stage. The beam current was designed to be 20 nA or more in order to realize an image formation with an SN ratio that can withstand inspection at high speed. Specifically, the current density obtained from the electron source was set to 0.2 mA / sr or more. In addition, the aperture of the lens is larger than that of the high-resolution SEM, and the angle of capture of the electron beam from the electron source α (that is, the electron beam emitted from the electron source at a wide angle Beam opening angle) was set to 6 mrad or more. The pixel size, which is the minimum unit of the image, was set equal to the minimum defect size to be detected. At present, the smallest defects that matter are almost
Since it is 0.05 μm, the pixel size is set to 0.05 μm or more. The meaning of 0.05 μm or more is described to indicate that the pixel size can be set to be larger than 0.05 μm because a defect size larger than 0.05 μm may be seen depending on a wafer. Also, depending on the process of the wafer to be inspected, the amount of secondary electrons generated is so small that sufficient brightness may not be obtained by only one electron beam scanning.
In that case, it is also possible to add images obtained by scanning the electron beam a plurality of times. However, there is a problem that the inspection time is delayed, so the smaller the number of additions, the better. Also, the larger the image forming range is, the better.
μm was used as a standard.

On the other hand, under the review condition, the current value does not need to be large because the image formation does not require high speed, and 5 nA or less is sufficient. The pixel size needs to be 1/5 or less of the defect size in order to observe the shape of the defect in detail. Therefore, the thickness is set to 0.02 μm or less. Addition of images
The number is 2 to the nth power, and there is no particular upper limit. In the review,
The stage is stationary and the electron beam is scanned two-dimensionally to observe a specific location. The image formation area must be small in order to further enlarge the defect.
μm or less.

In summary, there is a big difference in the concept of the pixel size between the case of the inspection and the case of the review mode. In the case of the inspection, even if the probe size is larger than the defect size, there is a difference. What is necessary is just to judge whether there is a defect. That is, it is sufficient that the probe size and the pixel size are equal or larger. If the pixel size is small, there is a problem that the amount of electrons irradiated to a unit area is small, so that the irradiation is performed for a long time, and the clock is slow, so that high-speed inspection cannot be performed. On the other hand, at the time of review, it takes a long time to obtain an image of the defect, and a probe of at least 1/5 of the defect size is required. An object of the present invention is to change a probe size at the time of an inspection and a review and to change a pixel size at the same time.

Next, how to switch between the defect detection inspection condition and the review condition will be specifically described.

First, the components of the electron optical system and the details of the operation will be described with reference to FIG. The electron source 1
A field emission electron source, particularly a diffusion-supply type thermal field emission electron source, is preferable. 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. This electron source can emit electrons stably for a long time.
In addition, by changing the extraction voltage, the emission angular current density can be reduced to 0.001m.
It can be set freely within the range of A / sr to 1mA / sr. However, when the current density is increased, the energy width of the emitted electrons also increases, so that the chromatic aberration increases. 20nA electron beam current during inspection
I needed to get more. Therefore, the emission angular 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 negative potential to the electron source 1. The acceleration voltage can be set to 10kV or more. This is because the use of a large current electron beam suppresses the chromatic aberration caused by the increase in the energy width of the electron beam described above, and also suppresses the phenomenon that the large current electron beam spreads due to the interaction of electrons and cannot be stopped (Coulomb effect). That's why. The electron beam 6 advances toward the stage 24 with energy corresponding to about 10 kV and is converged by the condenser lens 4.
Further, the light is radiated onto the substrate to be inspected 10 (eg, wafer or chip) which is narrowed down by the objective lens 7 and mounted on the stage 24. The distance between the objective lens 7 and the substrate 10 to be inspected (operating distance) was set to 25 mm in order to obtain a deflection region of 50 μm square or more and obtain an image without distortion even in the peripheral portion. As a result, the focal length of the objective lens 7 is as long as about 30 mm.

The substrate to be inspected 10 has negative voltage applying means for applying a negative voltage from the high voltage power supply 25. By adjusting the high-voltage power supply 25, it becomes easy to adjust the irradiation energy of the electron beam to the inspection target substrate 10 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 employed in which the electron beam 6 scans only one dimension and the stage 24 is continuously moved in a direction orthogonal to the scanning direction.

Signal detection for image formation is performed as follows. That is, the electron beam applied to the sample 10
6 generates secondary electrons. These secondary electrons are
It is very difficult to directly pull in the detector 9 because it is rapidly accelerated by the potential applied to the detector 9. Therefore, a deflector combining an electric field and a magnetic field, for example, 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 an electric field and a magnetic field are orthogonal to each other. The primary electron beam 6 incident on the ExB deflector 14 from above is deflected by a magnetic field and an electric field. The deflector is configured to cancel in the reverse direction, so that the deflector by the magnetic field and the deflector by the electric field are added to the secondary electrons incident on the ExB deflector 14 from below. It is.

After the secondary electrons are deflected by the ExB deflector 14, they are irradiated on 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 was used to realize high-current and 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 stores the data corresponding to the two-dimensional image of the sample obtained from the secondary electron signal. It is sent to 19. The substrate to be inspected 10 is moved by the movement of the stage 24, the electron beam 6 from the field emission cathode, which is the electron source 1, is irradiated on the substrate to be inspected 10, and the comparison inspection is executed using the secondary electron signal emitted.

According to the above method, several μm
The arithmetic unit 20 and the defect determination unit 21 compare and determine the images of the repeated portions of the same pattern that are adjacent to each other at a high speed to detect a defect. Defects can also be detected by comparing images of different chips of the same pattern on different chips.

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

The factors that limit the resolution in the defect detection inspection conditions are mainly: 1) chromatic aberration caused by focusing electrons with varied energy by a lens;
2) Coulomb effect caused by repulsion of electrons due to high current density, and 3) Finite light source diameter caused by the fact that the tip of the electron source is not a point light source. The basic idea of switching to the review condition is to reduce the electron beam current lower than that at the time of defect detection inspection to suppress factors that hinder the narrowing of the electron beam such as optical system aberration and Coulomb effect, And thereby to obtain a high resolution image. Specific methods are listed below.

The first is a method of reducing the density of the current drawn from the electron source. FIG. 6 shows a configuration diagram of the electron gun. Electron source
1 is a so-called Zr / O / W type Schottky electron source in which a coating layer made of zirconium and oxygen is provided on a tungsten tip. The filament of the electron source 1 is heated by passing a current from the heating power supply 405. An electron source 1 is inserted through a central hole of the suppressor electrode 403 for suppressing unnecessary thermoelectrons.
Has a protruding tip. A negative potential with respect to the electron source 1 is applied to the suppressor electrode 403 by the Vs power supply 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 the extraction power supply 406. Each power supply 405, 406, 407
Are floated negatively by a desired acceleration voltage by the acceleration power supply 408. As a result, the electron beam extracted from the electron source 1 is applied to the anode electrode 40 at the ground potential.
Accelerated by 4 In order to reduce the electron current density extracted in the electron gun having the above configuration, the extraction electric field at the tip of the electron source may be reduced. It has suppressor electrodes
This can be realized by a method of increasing the voltage value of the power supply 407 connected to 403 and a method of 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 current density per emission angle of electrons emitted from the electron source and the energy of the beam.
Half value width of the variation of (the energy width)
It is shown. The energy width causes chromatic aberration of the lens of the electron optical system, and the relationship is that the energy width and the chromatic aberration are proportional as shown in Equation 1. Therefore, if the energy width is reduced to １ ／, the chromatic aberration is also reduced to １ ／. Under the defect detection inspection conditions, the emission angular current density was 0.1 mA / sr to 1 mA / sr.
At the time of review, use at 0.001 to 0.01 mA / sr. As a result, the beam current is about 100 nA at the time of defect detection inspection and about 5 nA or less at the time of review, and the energy width is reduced to 1/3 from FIG.
And the chromatic aberration is also reduced to 1/3. As a result, the beam diameter becomes about 1/3 and the resolution is improved.

[0071]

(Equation 1)

A second method of improving the resolution by reducing the current is a method of reducing aberration by replacing the diameter of the stop (for example, the stop 5 in FIG. 1) with a smaller one. As shown in Equation 1, the chromatic aberration of the optical system is proportional to the beam opening angle α. Therefore, the diameter of the stop which determines the beam opening angle is 1 /
If it is set to 2, the chromatic aberration also becomes １ ／. If the opening angle is too small, the diffraction aberration that is inversely proportional to the opening angle increases, but 1 mr
If the opening angle is about ad or more, the diameter of the beam becomes almost の since the diffraction aberration does not matter. 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 changing the focal length of the lens and changing the magnification of the optical system to reduce the beam opening angle without moving the stop 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 is again focused on the sample by the objective lens. On the other hand, at the time of review, the taking-in angle from the electron source α
And the irradiation angle β of the objective lens also becomes narrow.
As a result, the chromatic aberration of the objective lens is reduced along with the reduction of the current value, and the resolution is improved. In addition, 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). As a result, the resolution can be further improved. The condenser lens uses an electromagnetic lens and includes a coil and a magnetic path. Since the strength of the lens action can be controlled by the value of the current flowing through the coil, the current may be set to zero when the lens action is made zero. Also, the case where the action of the condenser lens is set to zero has been described. However, similar effects can be expected by setting the lens condition weak enough that a crossover is not formed even if the action is not completely set to zero.

The resolution can also be improved by increasing the strength of the condenser lens as compared with the time of 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). As can be seen by comparing FIGS.
Since b is small and c is large, the magnification is small. Further, the irradiation angle β can be reduced.

The method of forming a high-resolution image at the time of review by reducing the beam current has been described above. On the other hand, when 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 the 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 add the image. However, a good image cannot be obtained.

Therefore, another circuit was prepared from the preamplifier to the input to the AD converter. That is, FIG.
In the above, two signal paths are provided in the detection circuit 30. The configuration is shown in FIG. At the time of the defect detection inspection, the signal from the detector 9 is sent to the A / D
Input directly to converter 304. On the other hand, at the time of review, the signal from the detector 9 decreases because the beam current value decreases. The signal path is switched to the high gain amplifier 302 having a higher gain. Further, the signal is input to the AD converter 304 via the high-frequency cut filter 303. FIG. 5 is a schematic diagram of a signal waveform at the time of a defect detection inspection and a review.
The operation of this circuit will be described with reference to FIG.

The case where the beam current at the time of the defect detection inspection is 100 nA and the beam current at the time of the review is 500 pA will be described as an example. The gain ratio between the low gain amplifier 301 and the high gain amplifier 302 was set to 200 which is equal to the ratio of the beam current. As a result, the average value of the outputs of both amplifiers becomes equal (arbitrary unit 10
0). 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. The noise amplitude is small because a large current beam is used. 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 swings from -100 to 300. When the analog signal fluctuates to the minus side, the digitized value becomes zero. Also, if it is too large, it will exceed the full scale of the A / D converter.
Accordingly, there is a problem that an accurate waveform cannot be obtained even when digital signals are averaged. To solve this, a high-frequency cut filter 303 is placed after the high-gain amplifier. The noise of the input signal to the A / D converter 304 is reduced as shown in the waveform of “with filtering” in FIG. 16B.
Further, after this waveform is digitized, an image signal having a sufficient SN ratio can be obtained by scanning the electron beam a plurality of times and adding the signals.

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 the present embodiment, in order to improve the resolution, the third method of mainly changing the excitation condition of the condenser lens is used, and the first method of varying the current value drawn from the electron source is used in an auxiliary manner. Specific numerical examples are shown below.

At the time of the defect detection inspection, the emission angular current density from the electron source was 0.5 mA / sr, the magnification of the optical system was 1, and the beam current was 100 nA. The resolution of the image at this time is 0.08
It was about μm. Line and space at this time
FIG. 10 shows the line profile of the pattern image.

In the review, the condenser lens current value was increased and the magnification was set to 0.2. In addition, the high-voltage power supply of the electron gun is controlled to reduce the emission angular current density from the electron source to 0.1 mA.
lowered to / sr. As a result, the beam current was reduced to 500 pA, so the gain of the preamplifier of the detection system was switched to 200 times,
The filter is passed through a filter whose frequency characteristic is reduced to about 1/10. The scanning speed of the electron beam is about 1 at the time of defect detection inspection.
/ 10. Further, in order to compensate for the deterioration of the SN ratio, the image addition is performed 64 times. The resolution of the image at this time was about 0.02 μm. The line profile of the image at this time is shown in FIG. It can be seen that the rising of the line profile at the time of review is sharp and the amplitude is also large. From this, it can be confirmed that the resolution is clearly improved and even a fine object can be observed.

(Embodiment 2) In Embodiment 1, the same detector is used at the time of review and at the time of defect detection inspection. But,
At the time of review, the gain of the preamplifier 12 needs to be increased by a factor of 200 to 1000 by the rate at which the current decreases because the detection signal sharply decreases. Further, if only the gain is multiplied while the frequency characteristic is high as in the defect detection inspection, 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 frequency, and the circuit becomes complicated. As a result, there is a possibility that noise is mixed in the detection signal at the time of the defect detection inspection or the frequency characteristic is deteriorated. In order to solve this, in this embodiment, a detector dedicated at the time of review is provided. FIG. 11 shows the configuration diagram. 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. Response characteristics are DC to 20MHZ
z. The secondary electrons emitted from the sample 10 are detected by the ExB deflector 14 during the defect detection inspection.
It is deflected in the direction of 9 and in the direction of the review detector during the review. The secondary electrons are applied to the conversion electrodes facing the respective detectors, and the secondary electrons emitted thereby are detected. A high positive voltage is applied to the front surface of the scintillator 52 by the power supply 53 to accelerate and collide secondary electrons to convert them into light. The light is multiplied by a photomultiplier tube 51 and detected. Switching of secondary electron deflection direction is Ex
This is achieved by reversing the polarity of the control power supply 31 of the B deflector 14 (reversing the polarity of the applied voltage and the deflection coil current). In conjunction with this, a signal from one of the detectors is displayed on the monitor 22 via the memory 18. The switching is performed by the control unit 104.

(Embodiment 3) Depending on the type of defect, the detected defect contrast may disappear if the review conditions are not made appropriate. For example, among the conduction defect of the conduction hole, there is a case where the contrast of the defect disappears during irradiation of the beam a plurality of times. Therefore, when reviewing such defects, it is necessary to limit the number of additions of images. Since the number of additions is limited, it is necessary to increase the beam current in order to obtain an image with a good SN ratio. Also, depending on the type of defect, the contrast of the defective portion is larger when the electric field (electric field for decelerating the electron beam applied to the inspection wafer) is larger in the case of a large current beam during defect detection inspection, but the retarding is smaller when the electric current is small. In some cases, the contrast is enhanced by weakening the electric field. Hereinafter, a condition setting method for reviewing a conduction defect 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 the drilling or embedding, it may be completely electrically open or have a very high resistance value. When such a process is inspected for defects, the conductive holes are bright and the non-conductive holes are dark. Further, in the case of a subtle high resistance value, the brightness becomes intermediate, so that it is detected as a defect by comparing with a hole having perfect conduction. If such defects are reduced in current during review and image addition is performed several tens of times, the brightness becomes the same as that of a hole that is completely conductive, and no information is often obtained even after review. Therefore, when conducting a defect detection inspection of a conduction hole, the brightness level is stored in combination with defect coordinates for each detected defect, and when a gray defect is reviewed, the beam current is automatically reduced to 5 nA or less. The optical conditions were set so as not to cause the number of images, and the number of times of image addition was suppressed to 10 or less. On the other hand, when reviewing very dark levels of defects, reduce the beam current as much as
The review was performed under the condition of 0 pA or less.

The above is merely an example. The point is that the types of defects are automatically classified by using information obtained from an image at the time of defect detection inspection, that is, brightness, defect size, shape, and the like. Optical conditions for the review, ie scanning range,
The beam current, the scanning speed, and the number of times of image addition are automatically associated. At this time, in the present invention, the change of the optical condition is minimized by the mechanical movement, that is, the movement of the stop, and the condition can be instantaneously switched for each defect.

(Embodiment 4) As a fourth embodiment of the present invention, the electron optical system for review is made independent of the electron optical system for defect detection and inspection. This will be described with reference to FIG. Figure 1
2 is a configuration diagram of the present embodiment.

The inspection apparatus is roughly composed of 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 review electron optical system 200, it 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, and an aperture 20.
5. It is composed of an objective lens 207. The secondary electron detector 209 is located 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.

A retarding voltage is applied to the sample stage 24. When the stage moves from below the optical system 101 for defect detection and inspection to below the electronic optical system for review, the retarding voltage depends on the structure of the stage. In some cases, it is preferable to move after interrupting once, so that the selection may be made according to the applied retarding voltage or the type of the substrate to be inspected.

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

The electron optical system 101 for defect detection / inspection can acquire images at a very high speed because the inspection of the entire surface of the wafer is performed in a practical time. That is, pixel size 0.1μ
m and the time for forming an image of 100 μm square is 20 msec or less. The stage is continuously moved for high-speed image acquisition, and the electron beam is scanned in the orthogonal direction. The beam current was designed to be at least 20 nA in order to realize an image formation with an SN ratio that can withstand inspection at high speed. Specifically, first, 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, the lens aperture is set to be larger than that of the high-resolution SEM, so that the sample 10 of the electron beam emitted from the electron source 1 at a wide angle (ie, the electron beam emitted from the electron source 1 at a wide angle) is irradiated. Opening angle of the electron beam to be used) was about 20 times.

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. Therefore, it is necessary to provide a margin in the electron beam scanning area. For this reason, the objective lens has a focal length and operating distance that are considerably longer than those of a normal high-resolution SEM.

Further, when the sample opening angle β of the electron beam is increased, the depth of focus becomes shallower. Since β is obtained by dividing α by the magnification M of the entire optical system, the magnification M cannot be made very small. Therefore, high-resolution SEM
The magnification is considerably larger than that of.

With the above design, a high current required for high-speed operation can be obtained while ensuring the resolution required for the defect detection inspection. This electron optical system has high resolution even if the electron beam current is simply reduced as described above.
The lack of resolution similar to SEM is due to the magnification of the optical system,
It is clear from the focal length and operating distance of the objective lens.

On the other hand, in an electronic optical system for review, high speed is not so important. Also, since the coordinates of the place to be observed are accurately known, a field of view of 20 μm is sufficient. Therefore, the electron beam current may be small. In addition, the focal length and operating distance of the objective lens can be short, and the magnification of the optical system can be reduced, so that ordinary high-resolution SEM
A high-resolution image similar to the above can be obtained.

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-supply type thermal field emission electron source similar to the electron optical system for defect detection inspection, was used. When the current density is increased, the energy width of the emitted electrons also increases, and chromatic aberration increases. In the review electron optical system, the beam current may be 100 pA or less, so the emission angular current density is set to 0.05 mA / Sr or less. Thereby, the energy width of the electron beam 206 is reduced to about 1/3 to 1/4 as compared with the case of the electron optical system for defect detection 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 negative potential to the electron source 201. In the review optical system 200, the accelerating voltage is 5
Variable from 00V to 10kV. Since the review optical system 200 requires a small current, the chromatic aberration is small and the Coulomb effect can be neglected as described above. Therefore, a sufficiently small beam diameter can be obtained with a low accelerating voltage, and the accelerating voltage is set to 2 kV as a standard. The electron beam 206 travels in the direction of the sample stage 24 with an energy equivalent to 2 kV, is converged by the condenser lens 204, further narrowed down by the objective lens 207, and mounted on the stage 24 (wafer or chip, etc.). Is irradiated. The objective lens 207 is very close to the substrate 10 to be inspected, and the operating distance is 5 m.
m. The focal length of the objective lens 207 is 8 mm. As a result, an objective lens with small aberration was realized. Resolution is mostly determined by chromatic aberration. Therefore, the aberration coefficient is about 1/4 as compared with the defect detection and inspection objective lens, and the energy width of the electron beam is about 1 / of that of the defect detection and inspection optical system.
Since it is 3, the resolution is about 1/12. The substrate to be inspected 10 is common for the defect detection inspection and for the review, so that a negative voltage can be applied by the high voltage power supply 25. By adjusting the high voltage power supply 25, the substrate 23 to be inspected is adjusted.
The electron beam irradiation energy can be adjusted to an optimum value. Since images having different contrasts can be obtained by changing the irradiation energy, information such as whether the defect is caused by a difference in shape, by a material, or by 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 similar to the optical system 101 for defect detection and inspection.
Is accelerated by the potential applied to The detector 209 is provided above the objective lens 207 because the objective lens 207 is very close to the inspection target substrate 10 at a distance of about 30 mm or less, and secondary electrons pass through the center of the objective lens 207. Since the potential applied to the substrate 10 to be inspected is lower than that of the optical system 101 for defect detection inspection, the energy of secondary electrons is weak,
It is still difficult to draw directly into Then, the conversion electrode 211 is irradiated, and secondary electrons emitted therefrom are detected by the detector 2.
Detected by 09. As the detector 209, a detector 209 using a phosphor and a photomultiplier used in a normal SEM was used. The secondary electron signal detected here is supplied to the preamplifier 21.
The data is amplified by the A / D converter 230 and A / D converted by the A / D converter 230, and is displayed on the monitor 22 for image observation, and can be stored as an image file in the external storage device 219 such as a disk or printed out as needed.

The fourth embodiment has been described above.
The numerical value of each function is an example. In short, an electron optics system for review that can achieve a beam diameter of about 1/10 compared to the electron optics system for defect detection and inspection should be arranged side by side on the same sample chamber as the electron optics system for defect detection and inspection. The essence of this embodiment is that the operation of the defect detection inspection and the review can be quickly switched only by the parallel movement of the sample table. (Embodiment 5) In the fifth embodiment, an X-ray detector is provided on the lower magnetic path of the objective lens 207 of the review electron optical system 200 of the fourth embodiment.
Characteristic X generated by electron beam irradiation with built-in 240
Enabled to detect lines. With this, EDX (Energy-
Dispersive X-ray) analysis has become possible, and the material of the defect can be specified at the time of review. FIG. 13 is a diagram showing the vicinity of an objective lens when an annular X-ray detector having a hole at the center is incorporated.

The X-ray analyzer may be inserted between the objective lens and the sample by making the operating distance of the objective lens slightly longer than in the first embodiment.

(Embodiment 6) In the inspection using an electron beam,
It is possible to inspect not only shape defects but also electrical continuity and non-conduction. This is because the conductive portion is not charged, and the energy and orbit of secondary electrons generated by charging only the non-conductive portion changes, resulting in a different brightness of the image. This occurs as a particularly large contrast due to the irradiation of the high-current electron beam. However, in a review electron optical system, the difference in electrification is small because the current is small, and it is unlikely to appear as a contrast difference. Therefore, a secondary electron energy filter capable of filtering even a small difference in the energy of secondary electrons with high sensitivity is 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. A potential in the range of about ± 20 V from the potential of the substrate 10 to be inspected is applied to the mesh 220 by the power supply 221. This makes it possible to visualize the state of charging of the substrate to be inspected. The secondary electrons are about 2
It has an energy distribution with a peak at eV. Therefore, the energy peak of the secondary electrons viewed from the ground potential is (−φ + 2) eV. For example, when a retarding potential of 500 V is applied to the substrate 10 to be inspected, the peak of the secondary electron energy becomes 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, the part is negatively charged. Then, the energy of the secondary electrons emitted therefrom is higher by the charged voltage. If the charging voltage is 5 V, it is 507 eV. 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 portion looks bright. In this way, a slight charge can be obtained as a contrast difference. Here, only the case of negative charging has been described. However, in an actual semiconductor, the mechanism of charging by electron beam irradiation is complicated and may be positively charged. In that case, the potential applied to the mesh 220 may be equal to or slightly higher than the retarding potential. In that case, the portion charged positively becomes dark and the other portions become bright.

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

[0100]

Since the present invention has been described above, it has the following effects. A defect detection inspection based on high-speed image acquisition for detecting the presence of a defect over a relatively large area, and a review for imaging a specific narrow part detected by the defect detection inspection and observing it with the naked eye, respectively. An image signal having a sufficient S / N ratio can be obtained by performing the detection through a detection circuit having independently optimized paths, and the inspection conditions can be set efficiently. As a result, the speed of the inspection process is increased and the reliability of the inspection result is improved.

A first electron optical system for a defect detection inspection for detecting the presence of a defect and a second dedicated to a review for observing a specific narrow portion detected by the defect detection inspection are provided.
The inspection apparatus of the present invention, in which the electron optical system of the present invention is arranged side by side in the same vacuum vessel and can be switched between the defect detection inspection and the review only by moving the stage on which the sample is mounted, has a quick and highly reliable Enables inspection.

Further, a first detector for defect detection inspection for detecting the presence of a defect, a second detector exclusively for review for observing a specific narrow part detected by this defect detection inspection, The backscattered electrons or secondary electrons generated from the sample by beam irradiation are guided to the first detector at the time of defect detection inspection, and the inspection apparatus of the present invention provided with a deflection circuit that is guided to the second detector at the time of review, A signal with little noise and little deterioration in high-frequency characteristics is obtained, enabling highly reliable inspection.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a device configuration according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a modification of the device configuration according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a test flow according to the present invention.

FIG. 4 is a diagram illustrating another example of the inspection flow of the present invention.

FIG. 5 is a diagram for explaining inspection and review conditions.

FIG. 6 is a diagram illustrating a part of the first embodiment of the present invention.

FIG. 7 is a diagram illustrating the operation principle of the first embodiment of the present invention.

FIG. 8 is a diagram illustrating the operation principle of the first embodiment of the present invention.

FIG. 9 is a diagram illustrating an example of an operation principle of the first embodiment of the present invention.

FIG. 10 is a diagram illustrating the effect of the first embodiment of the present invention.

FIG. 11 is a diagram illustrating a configuration of a second exemplary embodiment of the present invention.

FIG. 12 is a diagram illustrating a configuration of a third exemplary embodiment of the present invention.

FIG. 13 is a diagram illustrating a configuration of a fourth embodiment of the present invention.

FIG. 14 is a diagram illustrating a configuration of a fifth exemplary embodiment of the present invention.

FIG. 15 is a diagram illustrating a configuration of a detection circuit according to the first embodiment of the present invention.

FIG. 16 is a diagram illustrating signal waveforms at the time of defect detection inspection and at the time of review in the first embodiment 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: coated 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: Operation 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 instrument, 30: AD converter, 3
1: Stage position measuring instrument, 32: Preamplifier, 33: AD converter, 34: Transmitter, 35: Receiver, 101: Inspection electron optical system,
102: sample chamber, 104: control unit, 105: image processing unit, 200: electron optical system for review, 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
Line detector, 403: suppressor electrode, 404: anode, 405: heating power, 406: extraction power, 407: suppressor power, 408: acceleration power.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01J 37/28 H01J 37/28 B H01L 21/66 H01L 21/66 JL (72) Inventor: Takataka Ninomiya ▼ Nori 882 Ma, Hitachinaka-shi, Ibaraki Pref.Hitachi, Ltd.Measurement instrument group (72) Inventor Yuko Sasaki 882 Hitachika, Hitachinaka-shi, Ibaraki pref., Hitachi, Ltd.Measurement instrument group (72) Inventor Mari Nozoe 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Hisaya Murakoshi 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Ninomiya Inventor Taku 882 Ma, Hitachinaka-shi, Ibaraki Pref.Hitachi, Ltd.In the measuring instrument group (72) Inventor Yuji Kasai 882 Ma, Hitachinaka City, Castle Prefecture F-term (reference) 2F067 AA54 BB01 BB04 CC17 EE03 EE04 HH06 JJ03 JJ05 KK02 KK04 KK08 LL16 PP12 QQ02 QQ03 RR35 SS02 SS13 TT01 AU03A BA07 BA15 CA01 CA03 DA01 DA02 DA06 EA03 EA05 FA02 FA06 FA09 FA29 GA03 GA04 GA06 GA08 GA09 GA11 GA19 HA09 HA13 JA02 JA03 JA11 JA20 KA03 LA11 MA05 PA01 PA03 PA07 PA11 4M106 AA01 BA02 CA39 CA41 DB05 DH24 DH25 DH03 DJ04 NP04 NN03 UU01 UU02 UU03 UU04 UU05

Claims (16)

[Claims] 1. An electron optical system which converges an electron beam emitted from an electron source by an electron lens and irradiates and scans a sample, and mounts the sample on the sample and places the electron beam at a desired position on the sample. A stage movable to be irradiated, a detector for detecting backscattered electrons or secondary electrons obtained from the irradiated portion of the sample, and amplifying an output from the detector at a first amplification factor A second circuit comprising: an amplifier for amplifying an output from the detector at an amplification factor larger than the first amplification factor; and a high-frequency component cut filter; and An image forming apparatus for forming an image of the sample based on the signal; comparing an image signal obtained by the image forming apparatus with an image signal similarly obtained from another place on the sample; Means for detecting a difference between signals; An output from the detector in a first case, in which the system is scanned over the sample at a relatively large area, a relatively large current, and a relatively high speed, is input to the first circuit, and the electron beam is transmitted to the sample. The output from the detector in the second case of scanning 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 is output to the second case. A circuit pattern inspection apparatus comprising: a switching unit that switches and inputs a circuit. 2. The circuit according to claim 1, wherein in the second case, the image is formed with a pixel size smaller than the minimum pixel size of the image formed in the first case. Pattern inspection device. 3. The circuit pattern inspection apparatus according to claim 1, wherein in the second case, the spot size of the electron beam on the sample is smaller than in the first case. 4. The electron lens includes an objective lens closest to the sample and a second lens disposed on the electron source side, and in the second case, the second lens is adjusted. 4. The circuit pattern inspection apparatus according to claim 1, wherein the magnification of the electron optical system is set to be small. 5. The electron optical system according to claim 1, further comprising a stop having an aperture having a plurality of diameters, wherein the diameter of the stop is switched to a smaller diameter in the second case. 3. The circuit pattern inspection device according to 1. 6. The circuit pattern inspection according to claim 4, wherein the second lens is a condenser lens, and in the second case, a position of a crossover formed by the electron beam is moved. apparatus. 7. In the second case, the deflection area of the scanning deflection area of the electron beam is reduced to half or less the side length as compared with the first case. 7. The circuit pattern inspection device according to any one of 1 to 6. 8. The circuit pattern inspection device according to claim 1, wherein the second circuit has a lower response speed than the first circuit. 9. A magnification of the electron optical system in the second case, a current value of the electron beam, a current value of the electron beam, in accordance with an output result of a means for detecting a difference between the two image signals in the first case. 9. The circuit pattern inspection apparatus according to claim 1, further comprising: means for interlockingly switching an electron beam scanning speed and the number of times of addition of images in the image forming apparatus. 10. A first electron source which emits a first electron beam, has a first focal length, and transmits the first electron beam to a first electron beam.
A first objective lens that focuses on a sample located at the sample position, and a first scanning deflector that scans the sample located at the first sample position with the first electron beam. A first electron optical system; a first detector for detecting secondary charged particles generated from the sample located at the first sample position; a second electron source for emitting a second electron beam When,
A second objective lens having a second focal length that is shorter than the first focal length and focusing the second electron beam on a sample located at a second sample position; A second electron optical system having a second scanning deflector for scanning the sample located at the second sample position; and a secondary generated from the sample located at the second sample position. A second detector for detecting electrically charged particles; and imaging respective samples located at the first and second sample positions based on outputs from the first detector and the second detector. An image forming apparatus; a stage for moving the sample from the first sample position to the second sample position, wherein the first electron optical system, the second electron optical system, and the first
And the second detector and the stage are housed 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 from the detector, moved to the second sample position by moving the stage, the specific position Circuit pattern inspection apparatus for magnifying and observing by the second electron optical system. 11. The second electron optical system according to claim 2, wherein
11. The circuit pattern inspection apparatus according to claim 10, wherein an acceleration voltage for the electron beam is lower than an acceleration voltage for the first electron beam in the first electron optical system. 12. A negative voltage applied to said stage and said sample for decelerating said electron beam to a desired energy immediately before said stage and said sample on said stage,
12. The circuit pattern inspection apparatus according to claim 10, wherein the second sample position has a negative voltage smaller than the negative voltage applied at the first sample position. 13. The circuit pattern inspection apparatus according to claim 10, further comprising an X-ray detector for detecting an X-ray generated from a sample located at the second sample position. Characteristic circuit pattern inspection equipment. 14. An energy filter for filtering energy of secondary electrons emitted from a sample located at the second sample position, and detecting an electric potential at a position irradiated with the second electron beam. 13. The circuit pattern inspection device according to claim 10, wherein 15. An electron optical system that converges an electron beam emitted from an electron source by a lens and irradiates and scans a sample, and mounts the sample, and the electron beam is placed at a desired position on the sample. A stage movable so as to be irradiated, a first detector for detecting backscattered electrons or secondary electrons obtained from an irradiated portion of the sample with a first sensitivity, and an irradiated portion of the sample A second detector that detects backscattered electrons or secondary electrons obtained at a second sensitivity higher than the first sensitivity; and an image that forms an image of the sample based on a detection signal from the detector. A forming device, means for comparing an image signal obtained by the image forming device with an image signal similarly obtained from another place on the sample, and detecting a difference between the two image signals; and A beam is applied on the sample to a first area, a first current value, If scanning at the first rate leads to the back-scattered electrons or secondary electrons to the first detector, the area of the electron beam smaller than the first area of the upper sample, the first
And a deflection circuit for guiding the backscattered electrons or secondary electrons to the second detector when scanning at a current value smaller than the current value of the first speed or lower than the first speed. 16. An electron optical system for irradiating and scanning a sample on which a circuit pattern is formed with a converged electron beam, and a detector for detecting backscattered electrons or secondary electrons obtained from an irradiated portion of the sample. An image forming apparatus for forming an image of the sample based on a detection signal from the detector, and comparing an image signal obtained by the image forming apparatus with a reference image signal to determine a difference between the two image signals. Preparing a difference detecting means for detecting; and outputting an output from the detector obtained by scanning a relatively large area of the sample with the electron beam at a relatively large current and a relatively high speed. A signal amplified by an amplifier having an amplification factor of 1 is supplied to the image forming apparatus to form an image signal, and the image signal is obtained in advance from another region on the sample by the difference detecting means. Compared to similar image signals Detecting the difference between the image signals to determine the coordinates of the location where the difference occurs; and determining the area of the small area, including the coordinate position of the sample, smaller than the relatively large area by the electron beam. An amplifier that amplifies an output from the detector obtained by scanning at a low current smaller than the relatively large current and at a low speed lower than the relatively high speed at an amplification factor larger than the first amplification factor. And supplying the image signal to the image forming apparatus through a circuit including a filter and a high-frequency component cut filter to form an image signal and observe a location where the difference occurs.