JP2003197141A - Inspection device and inspection method using charged particle beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection device using a charged particle beam, capable of accurately detecting a defect hard to detect by an optical image by using an electron beam and of reducing erroneous detection of the defect without degrading inspection resolution by reducing noise of the inspection image causing trouble at that time. <P>SOLUTION: This inspection device is provided with: a vacuum column for isolating a charged particle beam irradiated on a sample from the atmosphere; a scan signal generator for generating a deflection signal for making the charged particle beam scan; a scan signal calculation part for dividing the deflection signal into n-poles; n-amplifiers fixed to the vacuum column for amplifying the divided deflection signals; an n-polar electrostatic scan deflector for deflecting the charged particle beam based on the amplified deflection signals. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device such as a memory having a fine circuit pattern, a semiconductor device such as LSI, a circuit pattern such as a liquid crystal and a photomask, and an inspection method, and particularly to an inspection device using a charged particle beam. And the inspection method.

[0002]

2. Description of the Related Art A semiconductor device such as a memory used for a computer or a microcomputer is manufactured by repeating a process of transferring a circuit pattern formed on a photomask onto a semiconductor wafer by a lithography process and an etching process. . The yield of semiconductor devices is greatly affected by the quality of the lithography process, etching process, and other processes in the manufacturing process of semiconductor devices, and the generation of foreign particles in the manufacturing process. Therefore, in order to detect the occurrence of processing abnormalities and defects early or in advance, it is necessary to inspect the pattern formed on each step of the semiconductor wafer in the manufacturing process.

As an example of a method for inspecting a defect existing in a pattern on a semiconductor wafer, an optical appearance inspection apparatus for comparing patterns using an optical image obtained by irradiating a semiconductor wafer with light has been put into practical use. There is. As an example of an inspection method using an optical image, as described in Japanese Patent Laid-Open No. 3-167456, an optically illuminated region on a substrate is imaged by a time delay integration sensor, and the image is input in advance. A method of detecting a defect by comparing the design characteristic with the existing one, or, as described in Japanese Patent Publication No. 6-58220, monitoring image deterioration at the time of image acquisition and correcting it at the time of image detection. Therefore, there is a method of performing a comparative inspection with a stable optical image.

When a semiconductor wafer is inspected in the manufacturing process by such an optical inspection method, it is impossible to detect a residue or a defect of a pattern having a silicon oxide film or a photosensitive photoresist material on the surface through which light is transmitted. It was In addition, it was not possible to detect an etching residue or a non-opening defect of a minute conductive hole, which is lower than the resolution of the optical system. Furthermore, the defect generated at the bottom of the step of the wiring pattern could not be detected.

As described above, with the miniaturization of circuit patterns, the complicated circuit pattern shapes, and the diversification of materials, it has become difficult to detect defects by an optical image. Therefore, a charged particle beam having a higher resolution than an optical image, For example, a method and apparatus for comparing and inspecting a circuit pattern using an image acquired by scanning an electron beam have been put into practical use.

[0006] For example, Japanese Patent Publication No. 59-19294.
3, Japanese Patent Publication No. 5-258703, Japanese Patent Publication No. 10-294345, Reference Sandland,
et al., “An electron-beam inspection system for x-
ray mask production ”, J. Vac. Sci. Tech. B, Vol.9,
No. 6, pp. 3005-3009 (1991), Reference Meisburger, et al.,
“Requirements and performance of an electron-bea
m columndesigned for x-ray mask inspection ”, J. V
ac. Sci. Tech. B, Vol.9, No.6, pp.3010-3014 (199
1), Literature Meisburger, et al., “Low-voltage electron
-optical system for the high-speed inspection of i
integrated circuits ”, J. Vac. Sci. Tech. B, Vol.1
0, No.6, pp.2804-2808 (1992), Reference Hendricks, et a
l., “Characterization of a New Automated Electron
-Beam WaferInspection System ”, SPIE Vol. 2439, p
The technology described in p.174-183 (20-22 February, 1995) is known.

In order to carry out high-throughput and high-precision inspection following the increase in the diameter of the wafer and the miniaturization of the circuit pattern, it is necessary to acquire an image with a high SN at a very high speed. Therefore, a normal scanning electron microscope (SEM, Scan
Ning Electron Microscope) 1000 times or more (100
The number of electrons irradiated with a large current beam of nA or more) is secured, and a high SN ratio is maintained. Furthermore, high-speed and highly efficient detection of secondary electrons and backscattered electrons generated from the substrate is essential.

Further, a semiconductor substrate having an insulating film such as a resist is irradiated with a low acceleration electron beam of 2 keV or less so as not to be affected by charging. Regarding this technology, "Electronic and Ion Beam Handbook (2nd edition)" edited by Japan Society for the Promotion of Science, 132nd Committee (Nikkan Kogyo Shimbun, 1986) 6
It is described on pages 22 to 623. But with a large current,
In addition, low-acceleration electron beams cause aberrations due to the space charge effect, making it difficult to perform high-resolution observation.

As a method of solving this problem, there is known a method of decelerating a highly accelerated electron beam immediately before the sample and irradiating the sample with a substantially accelerated electron beam. For example, Japanese Patent Publication No. 2-142045 and Japanese Patent Publication No. 6-
There is a technique described in Japanese Patent No. 139985.

Since the SEM type visual inspection apparatus irradiates a thin electron beam on a semiconductor wafer having a wide area, high-speed inspection is essential. Therefore, unlike an ordinary SEM, an electron beam having an electron beam current on the order of pA is not scanned at a low speed, or a large number of scans and superposition of images are not performed. Further, in order to suppress the charging of the insulating material, it is desirable that the electron beam is scanned at high speed once or several times and not many times.

Therefore, compared with the conventional SEM, about 100
It is necessary to form an electron beam image by scanning an electron beam having a large current of 0 times or more, for example, 100 nA, only once. Further, for high speed scanning, an electrostatic deflector having a better response than the magnetic field deflector is desirable.

In the SEM type appearance inspection apparatus for inspecting a semiconductor wafer by using the SEM as described above, the charged particle beam image is easily affected by noise and non-defective ones are detected for the following reasons. In some cases, the accuracy of inspection may be deteriorated, such that the desired defect is not detected. (1) When a charged particle beam image and an electron beam image are acquired by one scan instead of scanning the same place with the charged particle beam a plurality of times, noise reduction due to calculation of image data cannot be expected. (2) The electrostatic deflector used in the SEM appearance inspection device and the like is easily affected by noise because of its good responsiveness.

Such a problem is caused by SE using electron beam.
Not only M but also an inspection apparatus using charged particles other than electrons, for example, an ion beam having a positive charge, presents a similar problem.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and detects a defect which is difficult to detect in an optical image with a charged particle beam with high accuracy, and a problematic inspection at that time. An object of the present invention is to provide an inspection apparatus using a charged particle beam, which can reduce noise in an image and reduce false detection of defects without reducing inspection resolution.

[0015]

In order to solve the above-mentioned object, an embodiment of the present invention scans a sample with a charged particle beam and detects secondary charged particles generated from the sample to obtain an image signal, In an inspection apparatus using a charged particle beam for detecting a defect of a sample based on the image signal, a vacuum column for blocking the charged particle beam irradiated on the sample from the atmosphere and a deflection signal for scanning the charged particle beam are generated. Scanning signal generator, a scanning signal operation unit that divides the deflection signal into n poles, n amplification units that amplify the divided deflection signals, and a charged particle beam based on the amplified deflection signals. And an n-pole electrostatic scanning deflector for deflecting the beam, and the amplification section is fixed to the vacuum column.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

As an embodiment of the present invention, an electron beam is used as a charged particle beam to inspect the pattern of a semiconductor wafer, a mask, a reticle and the like and the presence or absence of foreign matter in a SEM type appearance inspection apparatus in a schematic vertical sectional view. As shown in FIG. The SEM appearance inspection apparatus 1 is an application of a scanning electron microscope as an inspection apparatus, and its configuration is roughly divided into an inspection chamber 2 including an electron optical system device, an optical microscope unit 4, and a sample chamber 8, and an image. The processing unit 5, the control unit 6, and the secondary electron detection unit 7 are included.

The electron optical system device includes an electron gun 10, an electron beam extraction electrode 11, a condenser lens 12, a blanking deflector 13, a diaphragm 14, and a scan, which are provided in a vacuum column 3 for keeping the inside vacuum. The deflector 15, the objective lens 16, the reflection plate 17, and the combination of electrostatic and magnetic field E
An electron beam 19 generated by the electron gun 10 and extracted by the extraction electrode 11 passes through the condenser lens 12, the diaphragm 14, and the objective lens 16 and is applied to the sample 9 through the condenser lens 12, the diaphragm 14, and the objective lens 16. It The electron beam 19 is a beam that is narrowed down, scans the sample 9 by the scanning deflector 15, and the sample 9 generates reflected electrons and secondary electrons 51. The secondary electrons have their trajectories bent by the ExB deflector 18 and irradiate the reflector 17 to generate second secondary electrons 52, which are detected by the secondary electron detector 20. On the other hand, by directing the electron beam 19 to the outside of the aperture of the diaphragm 14 by the blanking deflector 13, irradiation of the sample 9 with the electron beam 19 can be prevented.

The sample chamber 8 includes a sample table 30 and an X stage 3
1, a Y stage 32, a rotary stage 33, a position monitor length measuring device 34, and a sample height measuring device 35. The optical microscope section 4 includes the vacuum column 3 in the examination room 2.
Are installed in positions close to each other and to the extent that they do not affect each other, and the distance between the vacuum column 3 and the optical microscope unit 4 of the electron optical system device is known. Then, the X stage 31 or the Y stage 32 reciprocates a known distance between the vacuum column 3 and the optical microscope unit 4.

The optical microscope unit 4 is composed of a white light source 40, an optical lens 41, and a CCD (imaging device) camera 42, and although not shown, the acquired image is image-processed as in the case of an electron beam image described later. Sent to department 5.

As the position monitor length measuring device 34, a length measuring device by laser interference is used in this embodiment. X stage 31,
The positions of the Y stage 32 and the rotary stage 33 can be monitored in real time, and the position information can be sent to the control unit 6. Although not shown, the X stage 31, Y
Similarly, data such as the number of rotations of the motors of the stage 32 and the rotary stage 33 is configured to be sent from each driver to the control unit 6. Based on these data, the control unit 6 can accurately grasp the area and the position where the electron beam 19 is irradiated, and correct the positional deviation of the irradiation position of the electron beam 19 in real time if necessary. It can be corrected by using the control circuit 43. Even if the sample 9 is replaced, the area irradiated with the electron beam can be stored for each sample.

As the sample height measuring instrument 35, an optical measuring instrument which is a measuring method other than the electron beam, for example, a laser interferometer or a reflected light measuring instrument for measuring a change in the position of reflected light is used. The height of the sample 9 mounted on the X stage 31 and the Y stage 32 can be measured in real time. In this embodiment, a long white light that has passed through a slit is irradiated onto a sample 9 through a transparent window, the position of reflected light is detected by a position detection monitor, and the amount of change in height is calculated from the position change. Was used. Based on the measurement data of the sample height measuring instrument 35, the focal length of the objective lens 16 for narrowing down the electron beam 19 is dynamically corrected, so that the inspected area can always be irradiated with the focused electron beam 19. It has become. It is also possible to measure the warpage and height distortion of the sample 9 before the electron beam irradiation, and to set the correction condition for each inspection region of the objective lens 16 based on the data. .

In order to obtain an image of the sample 9, the sample 9 is irradiated with a narrowed electron beam 19 to generate secondary electrons 51, which are scanned by the electron beam 19 and the X stage 3 is used.
1, it is detected in synchronization with the movement of the Y stage 32.

The electron beam 19 is extracted from the electron gun 10 by applying a voltage between the electron gun 10 and the extraction electrode 11. The electron beam 19 is accelerated by applying a high voltage negative potential to the electron gun 10. As a result, the electron beam 19 advances toward the sample stage 30 with energy corresponding to the potential, is converged by the condenser lens 12, is further narrowed down by the objective lens 16, and is narrowed down by the X stage 31 and the Y stage 32 on the sample stage 30. The sample 9 mounted on the rotary stage 33 is irradiated.

The blanking deflector 13 has a scanning signal generator 44 for generating a scanning deflection signal and a blanking signal.
The objective lens power supply 45 is connected to the objective lens 16. Sample 9 has a retarding power supply 36
This allows a negative voltage to be applied. By adjusting the voltage of the retarding power source 36, the primary electron beam can be decelerated, and the electron beam irradiation energy to the sample 9 can be adjusted to an optimum value without changing the potential of the electron gun 10. When it is necessary to blank the electron beam 19, the blanking deflector 13 deflects the electron beam 19 so that the electron beam 19 can be controlled so as not to pass through the diaphragm 14.

The secondary electrons 51 generated by irradiating the sample 9 with the electron beam 19 are accelerated by the negative voltage applied to the sample 9. The E × B deflector 18 is arranged above the sample 9, and the secondary electrons 51 accelerated by this are deflected in a predetermined direction. The deflection amount can be adjusted by the voltage applied to the E × B deflector 18 and the strength of the magnetic field. Further, this electromagnetic field can be varied in association with the negative voltage applied to the sample. The secondary electrons 51 deflected by the E × B deflector 18 are reflected by the reflector 1 under predetermined conditions.
Clash with 7. This reflector 17 has a conical shape,
The electron beam 19 passes through the opening provided in the center.
When the accelerated secondary electrons 51 collide with the reflection plate 17, second secondary electrons 52 having an energy of several V to 50 eV are generated from the reflection plate 17.

The secondary electron detector 20 is arranged above the objective lens 16 in the examination room 2, detects the second secondary electron 52, and the output signal of the secondary electron detector 20 is the output signal of the examination room 2. The AD converter 22 is amplified by the preamplifier 21 installed outside.
Is converted into digital data by the light converting means 23 and the light transmitting means 24, and the electric converting means 2 of the image processing unit 5 is converted.
Sent to 5. If the reflector 17 is not provided,
The secondary electron 51 may be detected by the secondary electron detector 20 instead of the second secondary electron 52.

The high-voltage power supply 26 is a preamplifier drive power supply 27 for driving the preamplifier 21, and A for driving the AD converter 22.
A D converter drive power supply, and a power supply to a reverse bias power supply 29 that supplies a voltage applied to the secondary electron detector 20 to attract the second secondary electrons. The second secondary electrons 52 generated by colliding with the reflection plate 17 are guided to the secondary electron detector 20 by the attraction electric field generated in the secondary electron detector 20 by the supply of the reverse bias power source 29.

The secondary electron detector 20 is a second secondary electron generated when the secondary electrons 51 generated while the electron beam 19 is irradiated on the sample 9 are accelerated and then collide with the reflecting plate 17. 52 is detected in conjunction with the scanning timing of the electron beam 19.

The output signal of the secondary electron detector 20 is amplified by the preamplifier 21 installed outside the inspection room 2 and becomes digital data by the AD converter 22. AD converter 22
Is configured to convert the analog signal detected by the secondary electron detector 20 into a digital signal immediately after being amplified by the preamplifier 21 and transmit the digital signal to the image processing unit 5. In this way, since the detected analog signal is digitized and transmitted immediately after detection, it is possible to obtain a high-speed signal with a high SN ratio.

The sample 9 is mounted on the X stage 31 and the Y stage 32, and the X stage 3 is used during inspection.
1, a method of scanning the electron beam 19 two-dimensionally with the Y stage 32 stationary, and a method of continuously moving the X stage 31 and the Y stage 32 in the Y direction at a constant speed during inspection. Can be selected linearly in the X direction. The former method is effective for inspecting a specific relatively small area, and the latter method is effective for inspecting a relatively large area.

The image processing section 5 is composed of a first storage section 46, a second storage section 47, a calculation section 48, a defect determination section 49, and a monitor 50. The captured electron beam image or optical image is displayed on the monitor 50. The operation command and operation condition of each part of the device are input and output from the control part 6. In the control unit 6, conditions such as an acceleration voltage at the time of electron beam generation, an electron beam deflection width, a deflection speed, a signal acquisition timing of the secondary electron detector 20 and a moving speed of the sample table 30 are arbitrarily set according to the purpose. It is input to or to select and set. The control unit 6 uses the correction control circuit 43 to monitor the position and height deviations from the signals of the position monitor length measuring device 34 and the sample height measuring device 35, and generates a correction signal from the result, and generates an electron beam. The correction signal of the objective lens 16 is sent to the objective lens power supply 45 and the correction signal of the blanking deflector 13 is sent to the scanning signal generator 44 so that 19 is always irradiated to the correct position.

The image processing section 5 is composed of a first storage section 46, a second storage section 47, a calculation section 48, a defect determination section 49, and a monitor 50. The image signal of the sample 9 transmitted by the optical fiber 24 is converted into an electric signal again by the electric conversion means 25 and then stored in the first storage unit 46 or the second storage unit 47.

The arithmetic section 48 performs various image processings for aligning the stored image signal with the image signal of the other storage section, standardizing the signal level, and performing various image processings for removing noise signals, and outputs both images. Comparing the signals.

The defect determining section 49 compares the absolute value of the difference image signal calculated by the calculating section 48 with a predetermined threshold value, and if the difference image signal level is higher than the predetermined threshold value, the pixel is a defect candidate. Then, the position, the number of defects, etc. are displayed on the monitor 50. This predetermined threshold is called an inspection threshold.

Although the secondary electron detector 20 is applied with the reverse bias voltage by the reverse bias power supply 29 in the above embodiment, it may be configured so that the reverse bias voltage is not applied. In addition, in this embodiment, the secondary electron detector 20 has a PI
Although the N-type semiconductor detector is used, another type of semiconductor detector, such as a Schottky type semiconductor detector or an avalanche type semiconductor detector, may be used. Further, if conditions such as responsiveness and sensitivity are satisfied, MCP (micro channel plate) can be used as a detector.

Next, a case where a semiconductor wafer patterned in the manufacturing process is inspected by the SEM type appearance inspection apparatus 1 shown in FIG. 1 will be described with reference to FIG.

The sample 9 is loaded into a sample exchange chamber (not shown). The sample 9 is mounted on a sample holder (not shown) and held and fixed, and then the sample exchange chamber is evacuated. When the sample exchange chamber reaches a certain degree of vacuum, it is transferred to the inspection chamber 2.
In the inspection room 2, the sample holder is placed on the sample table 30 via the X stage 31, the Y stage 32, and the rotary stage 33, and is held and fixed.

The sample 9 is placed at a predetermined first coordinate below the optical microscope section 4 by moving the X stage 31 and the Y stage 32 in the X and Y directions based on a predetermined inspection condition registered in advance. The monitor 50 observes an optical microscope image of the circuit pattern formed on the sample 9. Then, the position correction value of the first coordinate is calculated by comparing with the equivalent circuit pattern image stored in advance for the position rotation correction. Next, move a certain distance from the first coordinate and move to the second coordinate where the circuit pattern equivalent to the first coordinate exists. Similarly, the optical microscope image is observed and stored for position rotation correction. Compared with the circuit pattern image,
The position correction value of the second coordinate and the amount of rotation deviation with respect to the first coordinate are calculated. The rotary stage 33 rotates and corrects by the calculated rotation deviation amount.

In this embodiment, the amount of rotation deviation is corrected by rotating the rotary stage 33, but the rotary stage 3
The rotation deviation amount can also be corrected by a method in which the scanning deflection position of the electron beam is corrected on the basis of the calculated rotation deviation amount without providing No. 3.

Next, for future position correction, the first coordinate, the position shift amount of the first circuit pattern by the optical microscope image observation, the second coordinate, the second circuit pattern by the optical microscope image observation, The positional deviation amount is stored and sent to the control unit 6.

Next, the circuit pattern formed on the sample 9 is observed by an optical microscope, and the positions of the chips having the circuit pattern, the distance between the chips, the repeating pitch of the repeating pattern such as a memory cell, and the like are previously determined. The measurement is performed and the measured value is input to the control unit 6. Further, a chip to be inspected and a region to be inspected in the chip are designated and input to the control unit 6. The image of the optical microscope can be observed at a comparatively low magnification, and when the surface of the sample 9 is covered with, for example, a silicon oxide film, the image can be observed through the base layer. The arrangement of chips and the layout of circuit patterns in the chips can be easily observed, and the area to be inspected can be easily set.

When the preparatory work such as the predetermined correction work and the inspection area setting by the optical microscope section 4 is completed as described above, the sample 9 is moved to the vacuum column of the electron optical system apparatus by the movement of the X stage 31 and the Y stage 32. Moved under 3. When the sample 9 is placed under the vacuum column 3 of the electron optical system device, the same work as the correction work and the inspection area setting performed by the optical microscope unit 4 is performed by the electron beam image. Acquisition of an electron beam image at this time is performed by the following method.

Based on the coordinate values stored and corrected by the alignment by the optical microscope image, the electron beam 19 is moved in the X and Y directions by the scanning deflector 15 in the same circuit pattern as that observed in the optical microscope unit 4. It is scanned two-dimensionally. By the two-dimensional scanning of the electron beam, the secondary electrons 51 are generated from the observed region, and the second secondary electrons 5 generated on the reflecting plate 17 are generated.
2 is detected by the secondary electron detector 20, and an electron beam image is acquired. Since simple inspection position confirmation, position adjustment, and position adjustment have already been performed using the optical microscope image, and rotation correction has already been performed in advance, large adjustment is not necessary. The electron beam image has a higher resolution than an optical image, and can perform alignment, position correction, and rotation correction with high magnification and high accuracy.

For the secondary electron detector 20, the conventional S
In the EM, a configuration including a scintillator (aluminum deposited phosphor), a light guide, and a photomultiplier tube is used. Since this type of detection device detects the light emission from the phosphor, it has poor frequency response and is not suitable for high-speed electron beam image formation. In order to solve this problem, as a detection device for detecting a high-frequency secondary electron signal,
Detection means using a semiconductor detector is disclosed in Japanese Patent Laid-Open No. 15545/1990.
Japanese Patent Laid-Open No. 5-258703 and Japanese Patent Laid-Open No. 5-258703, and a semiconductor detector is also used for high speed detection in the embodiment of the present invention.

In addition, the secondary electron detector 20 is used to detect secondary electrons, the detected image signal is digitized immediately after detection, and then optically transmitted. Can be reduced, and image signal data with a high SN ratio can be obtained. In the process of forming an electron beam image from the detected signal, the image processing unit 5 sets the desired pixel at the electron beam irradiation position designated by the control unit 6 to a desired pixel.
The detection signal corresponding to each corresponding time is used as the brightness gradation value according to the signal level and is stored in the first storage unit 46 or the second storage unit 4.
Sequentially store in 7. An electron beam image of the circuit pattern of the sample 9 is two-dimensionally formed by associating the electron beam irradiation position with the amount of secondary electrons associated with the detection time. It should be noted that in the present embodiment, the inspection method and apparatus for detecting the secondary electrons generated from the sample have been described, but backscattered electrons and reflected electrons are generated from the sample at the same time as the secondary electrons. These secondary charged particles as well as the secondary electrons can be similarly detected as an electron beam image signal.

When the image signal is transferred to the image processing section 5,
The electron beam image of the first area is stored in the first storage unit 46. The arithmetic unit 48 performs various image processing for aligning the stored image signal with the image signal of the other storage unit, standardizing the signal level, and removing noise signals.
Subsequently, the electron beam image of the second region is stored in the second storage unit 47, and the same circuit pattern of the electron beam image of the second region and that of the first electron beam image are stored while being subjected to the same arithmetic processing. And the image signals of the location are compared and calculated. Defect determination unit 49
Compares the absolute value of the difference image signal that has been compared and calculated by the calculation unit 48 with a predetermined threshold (inspection threshold), and if the difference image signal level is higher than the predetermined threshold (inspection threshold), the pixel is defective. The candidate is determined and the position, the number of defects, etc. are displayed on the monitor 50. Next, thirdly, the electron beam image of the region is stored in the first storage unit 46, and while being subjected to the same calculation, it is compared and calculated with the electron beam image of the second region previously stored in the second storage unit 47. The defect is judged. Thereafter, by repeating this operation, the image processing is executed for all the inspection areas.

With the above-described inspection method, a high-precision and high-quality electron beam image is acquired and comparatively inspected to detect a minute defect generated on a fine circuit pattern within an inspection time in accordance with practicality. You can Further, by acquiring an image using an electron beam, patterns formed by a silicon oxide film or a resist film and foreign matter / defects of these materials, which cannot be inspected because light is transmitted by the optical pattern inspection method, are detected. Be able to inspect. Further, even when the material forming the circuit pattern is an insulator, the inspection can be stably performed.

When the sample 9 is irradiated with the electron beam 19,
The place becomes charged. In order to avoid the influence of the electrification at the time of inspection, the circuit pattern which irradiates the electron beam 19 in the pre-inspection preparatory work such as the above-mentioned position rotation correction or inspection region setting is selected in advance from the region to be inspected. Alternatively, it is preferable that the control unit 6 can automatically select an equivalent circuit pattern in a chip other than the chip to be inspected. As a result, the inspection image is not affected by the irradiation of the electron beam 19. The scanning with the high-current electron beam may be performed only once or may be repeated several times.

The conditions for irradiating the sample with the electron beam are as follows.
The irradiation amount of the electron beam per unit area, the current value of the electron beam, the scanning speed of the electron beam, and the irradiation energy of the electron beam for irradiating the sample are mentioned. It is necessary to obtain optimum values of these parameters for each shape and material of the circuit pattern. For that purpose, it is necessary to freely adjust and control the irradiation energy of the electron beam with which the sample is irradiated. In this embodiment, a negative voltage for decelerating the primary electrons of the electron beam 19 is applied to the sample 9 by the retarding power supply 36, and the irradiation energy of the electron beam 19 can be adjusted appropriately by adjusting this voltage. I am configuring. Then, when the acceleration voltage applied to the electron gun 10 is changed, the axis of the electron beam 19 is changed and various adjustments are required. In the present embodiment, the electron gun 1 is used.
The irradiation energy of the electron beam 19 can be adjusted without changing the acceleration voltage applied to zero.

Next, the relationship between inspection performance and noise will be described. When n scanning deflectors 15 are provided (referred to as n-pole deflection), n transmission lines are formed up to the scanning deflector 15. At least nCn−2 GND loops are formed. G
A change in the magnetic flux that links the ND loop causes a dielectric electromotive force. A current flows in the GND loop due to the generated electromotive force. Alternatively, leakage current from the power source flows in the GND loop. Due to this current and the impedance of the GND line, a potential difference is generated between the transmission lines, resulting in noise. When noise is superimposed on GND, GND, which is the reference potential of the deflection signal, fluctuates in a short time. Therefore, the scanning deflection signal on which noise is superimposed is applied to the scanning deflector. This causes noise (referred to as image noise in order to distinguish it from noise superimposed on the scanning deflection signal) to be superimposed on the electron beam image to be subjected to the comparative inspection, which is one of the factors for erroneous detection of defects. The greater the image noise, the more false detections of defects. The amount of image noise that causes erroneous detection changes depending on the setting of the inspection threshold value described above. The inspection threshold is one of the parameters that determines the inspection resolution. Raising the inspection threshold reduces false detection of defects, but reduces the inspection resolution. It is assumed that the image noise that causes the false detection of the defect determined by the inspection threshold corresponds to α pixels. The allowable noise voltage for the scanning deflection signal Vpp at this time is α / Nx × Vpp, where Nx is the number of pixels in the horizontal scanning direction forming the electron beam image. For example, the inspection resolution is 0.
When it is 1 μm, α = 0.5, and when the number of pixels in the horizontal scanning direction Nx = 1024 and the deflection scanning voltage Vpp = 70V, it is necessary to suppress the noise voltage to about 34 mV or less.

Next, as an example of the above-mentioned n scanning deflectors, an embodiment in which n = 8, that is, an 8-pole deflector is adopted will be described. FIG. 2 shows a cross-sectional view of the vacuum column 3 of the electron optical system device shown in FIG. Since the driving method of the eight-pole electrostatic deflector is known from Japanese Patent Application Laid-Open No. 62-249344, details thereof will be omitted here. A scanning signal calculator 61 for dividing the scanning deflection signal (having a horizontal signal and a vertical signal) generated by the scanning signal generator 44 into eight poles.
To enter. However, the scanning signal calculation unit 61 is not described in FIG. The scanning deflection signals divided into eight poles by the scanning signal calculation unit 61 are input to the amplification unit 62. Amplifier 62
May have a function of a filter for reducing unnecessary noise. The scanning deflection signal output from the amplification unit 62 is input to the scanning deflector 15 arranged in a vacuum in the vacuum column 3 of the electron optical system device. The scanning deflector 15 is a capacitive load, and the C component of the scanning deflector 15 and the L component of the transmission line 63 may cause ringing (electrical vibration), so that the impedance of the transmission line 63 is minimized. The amplification section 62 is directly attached to the vacuum column 3 of the electron optical system device. With this structure, the scanning deflector 15 and the amplification unit 6
The impedance between the two can be minimized, image noise can be reduced, and false detection of defects can be reduced without reducing inspection resolution.

FIG. 3 is a view showing the arrangement of the vacuum column 3 and the scanning signal calculation section 61 of the electron optical system device of the SEM type visual inspection device 1. The upper figure is a cross section of the vacuum column 3, and the lower figure is a side view. As for the noise level allowed in the transmission line 63 between the scanning signal calculation unit 61 and the amplification unit 62, the allowable noise voltage in the scanning deflector 15 is α / Nx ×, as described above.
Since it is Vpp, if the gain of the amplifier 62 is G,
It is α / Nx / G × Vpp. Inspection resolution 0.1 μm
, Α = 0.5, and the number of pixels in the horizontal scanning direction is N
In the case of x = 1024, deflection scanning voltage Vpp = 70V, and gain G = 35, the allowable noise voltage is about 1 mV or less. In the transmission line 63, it is necessary to lower the impedance of the transmission line 63 so that noise of 1 mV does not occur due to an induced current due to an external magnetic field or a leakage current of a power source. Factors that determine the impedance of the transmission path 63 include (1) wiring length, (2) wiring material structure / material, (3) wiring connector contact resistance, and the like.

As shown in FIG. 3, the transmission line 63 is arranged in the scanning deflector 1 attached to the vacuum column 3 of the electron optical system device.
The amplification section 62 of No. 5 and the scanning signal calculation section 61 were radially connected so as to be the shortest. FIG. 4 shows the result of the tendency obtained by carrying out under the conditions of FIG. Has a long wiring length, but has a low noise level because the impedance of the wiring material and the entire connector is low. By properly selecting the wiring length, the wiring material, the wiring connector, and the like as in this embodiment, it is possible to reduce the impedance of the transmission lines of the calculation unit and the amplification unit, and reduce the image noise. Therefore, false detection of defects can be reduced without reducing the inspection resolution. Further, the scanning signal calculator 61, the scanning signal generator 44, the correction control circuit 43, which are not shown in FIG.
Even in a configuration in which the device is arranged close to the vacuum column 3 of the electro-optical system device, it is possible to realize a low impedance of the transmission path, it is possible to reduce image noise, and it is possible to reduce the error of defects without reducing the inspection resolution. Detection can be reduced.

Similar to FIG. 3, FIG. 6 shows a vacuum column 3 and a scanning signal calculator 6 of the electron optical system device of the SEM type visual inspection apparatus 1.
It is a figure showing the arrangement composition of No. 1. The upper figure is a cross section of the vacuum column 3, and the lower figure is a side view. As described above, a change in the magnetic flux interlinking the GND loop formed by the wiring path causes a dielectric electromotive force to flow a current, and the impedance of the transmission path causes induced noise in the wiring path. By reducing the area of this GND loop, the interlinkage magnetic flux is reduced and the induced noise can be reduced. In this embodiment, the wiring materials of the transmission path 63 from the scanning signal calculation unit 61 to the amplification unit 62 are bundled, and the vacuum column 3 of the electron optical system device having the GND potential is used.
The GND loop 64 shown in FIG. 3 is made small by arranging it in the vicinity of the sample chamber 8 and the apparatus frame which is a structure supporting these. Therefore, the interlinking magnetic flux is reduced, the induced current is reduced, image noise is reduced, and erroneous detection of defects can be reduced without reducing inspection resolution. Further, the scanning signal calculator 61, the scanning signal generator 44, the correction control circuit 43, which are not shown in FIG.
Since the GND loop can be made small even in the configuration in which is arranged close to the vacuum column 3 of the electron optical system device, image noise is similarly reduced, and erroneous detection of defects can be reduced without reducing inspection resolution.

As is apparent from the above embodiments, the inspection device using the charged particle beam further has the following configuration.

(1) A charged particle source for generating a charged particle beam, lens means for focusing the charged particle beam, a scanning signal generator for generating a scanning deflection signal of the charged particle beam, and the scanning deflection signal. It is arranged in a vacuum for scanning and deflecting the charged particle beam by a scanning signal operation unit for dividing into n poles, n amplification units for amplifying the divided scanning deflection signal, and the amplified scanning deflection signal. an n-pole electrostatic scanning deflector,
A detector for detecting secondary charged particles secondarily generated from the sample, and an image signal forming means for forming a charged particle beam image signal of a first region on the sample based on a signal from the detector. A storage unit for storing the charged particle beam image signal, and a charged particle beam image signal stored in the storage unit for a charged particle beam image signal in a second region in which the same pattern is formed on the sample. An inspection apparatus using a charged particle beam, comprising: comparison means for comparing with the above; and defect determination means for determining a defect in the pattern based on a comparison result of the comparison means.

(2) In the description of (1), the electrostatic scanning deflector is arranged in a vacuum in a vacuum column, and the amplifiers respectively connected to the electrostatic scanning deflector via a transmission line are An inspection apparatus using a charged particle beam, wherein the inspection section is arranged in the atmosphere and the amplification section is fixed to the column section.

(3) An inspection apparatus using a charged particle beam as described in (2), wherein the scanning signal calculation unit is fixed to the vacuum column.

(4) In the description of (1), a coaxial cable is provided in a part or all of the transmission lines between the scanning signal generator, the scanning signal calculating section, the amplifying section and the electrostatic scanning deflector. An inspection apparatus using a charged particle beam characterized by being used.

(5) In the description of (1), a part or all of the transmission lines between the scanning signal generator, the scanning signal calculating section, the amplifying section and the electrostatic scanning deflector are grounded. An inspection apparatus using a charged particle beam, characterized in that the inspection apparatus is arranged in the vicinity of the member.

(6) In the description of (1), the scanning signal generator is configured to perform high-speed scanning in the first direction on the sample,
An inspection apparatus using a charged particle beam, wherein a scanning deflection signal for alternately repeating low-speed scanning in a second direction different from the first direction is generated.

[0063]

As described above, according to the present invention, it is possible to detect a defect that is difficult to detect in an optical image with high accuracy by using a charged particle beam image, reduce image noise, and improve inspection resolution. False detection of defects can be reduced without reducing

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the outline of the apparatus configuration of an SEM type appearance inspection apparatus.

FIG. 2 is a cross-sectional view of a vacuum column of an electron optical system device in the case of an 8-pole deflection system.

FIG. 3 is an explanatory diagram of a transmission line configuration in the case of an 8-pole deflection system.

4 is an explanatory diagram of an image noise amount in the configuration of FIG. 3 under the condition of FIG.

5 is an explanatory view of the conditions of FIG.

FIG. 6 is a layout diagram of transmission lines in the case of the 8-pole changing method.

[Explanation of Codes] 1 ... SEM type visual inspection device, 2 ... inspection chamber, 3 ... vacuum column, 15 ... scanning deflector, 19 ... electron beam, 61 ... scanning signal arithmetic unit, 62 ... amplification unit, 63 ... transmission line , 64 ... GND loop, 65 ... GND potential.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhiro Gunji             882 Ichige, Ichima, Hitachinaka City, Ibaraki Prefecture             Ceremony company Hitachi High Technologies Design and manufacturing             Headquarters Naka Operations (72) Inventor Ryuichi Funatsu             882 Ichige, Ichima, Hitachinaka City, Ibaraki Prefecture             Ceremony company Hitachi High Technologies Design and manufacturing             Headquarters Naka Operations (72) Inventor Taku Ninomiya             882 Ichige, Ichima, Hitachinaka City, Ibaraki Prefecture             Ceremony company Hitachi High Technologies Design and manufacturing             Headquarters Naka Operations (72) Inventor Masatsugu Kamiya             502 Kintatemachi, Tsuchiura City, Ibaraki Japan             Tate Seisakusho Mechanical Research Center (72) Inventor Kenjiro Yamamoto             502 Kintatemachi, Tsuchiura City, Ibaraki Japan             Tate Seisakusho Mechanical Research Center F term (reference) 2G132 AA08 AD15 AE22 AE23 AF12                       AF13 AL11                 4M106 AA01 BA02 BA03 CA39 DB05                       DB11 DB30                 5C033 FF01 FF03 UU01 UU08

Claims (7)

[Claims] 1. An inspection apparatus using a charged particle beam for scanning a sample with a charged particle beam, detecting secondary charged particles generated from the sample to obtain an image signal, and inspecting the sample based on the image signal. At a vacuum column for blocking the charged particle beam with which the sample is irradiated from the atmosphere, a scanning signal generator for generating a deflection signal for scanning the charged particle beam, and the deflection signal for n.
A scanning signal calculation unit that divides the divided deflection signal, n amplification units that amplify the divided deflection signal, and an n-pole electrostatic scanning deflection that deflects the charged particle beam based on the amplified deflection signal. And a amplifying unit fixed to the vacuum column. 2. An inspection apparatus using a charged particle beam for scanning a sample with a charged particle beam, detecting secondary charged particles generated from the sample to obtain an image signal, and inspecting the sample based on the image signal. In the above, a vacuum column that shields the charged particle beam with which the sample is irradiated from the atmosphere, a scanning signal calculation unit that splits a deflection signal for scanning the charged particle beam, and the split fixed to the vacuum column. An amplification unit that amplifies the deflection signal and an electrostatic scanning deflector that deflects the charged particle beam based on the amplified deflection signal are provided, and the number of divisions of the deflection signal, the number of the amplification units, and the static An inspection apparatus using a charged particle beam, characterized in that the number of poles of the electric scanning deflector is the same. 3. The electrostatic scanning deflector according to claim 1, wherein the electrostatic scanning deflector is arranged in a vacuum in the vacuum column, and the amplifiers respectively connected to the electrostatic scanning deflector via a transmission line are provided. An inspection apparatus using a charged particle beam, which is arranged in the atmosphere. 4. The inspection apparatus using a charged particle beam according to claim 1, wherein the scanning signal calculation unit is fixed to the vacuum column. 5. The scanning signal generator according to claim 1, wherein the scanning signal generator performs high-speed scanning in a first direction on the sample and low-speed scanning in a second direction different from the first direction. An inspection apparatus using a charged particle beam, characterized in that a scanning deflection signal for alternately repeating is generated. 6. A charged particle beam for scanning a sample with a charged particle beam, detecting secondary charged particles generated from the sample to obtain an image signal, and detecting a defect in the sample based on the image signal. In the inspection method, a deflection signal for scanning the charged particle beam is divided into n poles, and the divided signal is divided by n amplifying units fixed to a vacuum column that shields the charged particle beam irradiated on the sample from the atmosphere. An inspection method using a charged particle beam, characterized in that a deflection signal is amplified and the charged particle beam is deflected by an electrostatic scanning deflector having an n-pole based on the amplified deflection signal. 7. The deflection signal according to claim 6, wherein high-speed scanning in a first direction on the sample and low-speed scanning in a second direction different from the first direction are alternately repeated. An inspection method using a charged particle beam, wherein the inspection signal is a signal to be generated.