JP2002031519A - Electron beam inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron beam inspection device capable of efficiently collecting the electrons reflected from a specimen and increasing the throughput of an inspection. SOLUTION: This electron beam inspection device comprises an electron beam radiation system having an objective lens for radiating the electron beam 14 from an electron source 13 to an expanded specified area zone on the surface of the specimen 1, a power supply 3 for applying a negative voltage to the specimen, an image forming means for forming an expanded image by focusing the reflected electrons obtained from the area radiated by the electron beam, and an image signal acquisition means for converting the expanded image formed by the image forming means to an image signal. The image obtained by the image signal acquisition means is compared with the image signal prepared by a design pattern to inspect for a defect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electron beam inspection apparatus suitable for use in inspecting semiconductor devices.

[0002]

2. Description of the Related Art In a conventional semiconductor device manufacturing process, a formed pattern is inspected for defects, and the inspection result is fed back to a manufacturing process to improve the semiconductor device manufacturing yield. The defect is, for example, a defect that a pattern to be connected is separated, a defect such as a short-circuited pattern to be formed apart, or the presence of a foreign substance.

As an apparatus for this defect inspection, a scanning electron microscope is usually used. For example, a primary electron beam is scanned in a predetermined region of a semiconductor device, and a secondary electron image is obtained based on a signal obtained by the scanning.
This image is used to inspect a pattern or the like and the presence of a foreign substance.

In a scanning electron microscope, an electron beam is narrowly focused on a sample, and a predetermined range on the sample is scanned with the electron beam. Secondary electrons are generated by irradiating the sample with an electron beam. The secondary electrons are detected, and the detection signal is supplied to a cathode ray tube synchronized with the scanning of the primary electron beam to display a scan image of the sample. Like that.

[0005]

In the above-described defect inspection using a scanning electron microscope, it is necessary to two-dimensionally scan an electron beam narrowly narrowed for each predetermined area, so that the inspection time is long. Therefore, there is a strong demand for an improvement in inspection throughput. Therefore, it has been proposed to use a reflection electron microscope for inspection instead of a normal scanning electron microscope.

As an example of such a reflection electron microscope,
The configuration described in JP-A-11-108864 can be exemplified. In the method described in this publication, an electron beam (area beam) having a certain area is irradiated on the surface of a semiconductor sample kept at a negative potential, and reflected electrons from the sample surface are imaged by an imaging lens. I have to. Then, images of a plurality of regions on the surface of the semiconductor sample are acquired and stored, and the stored images are compared with each other by using a method such as pattern matching. Inspection is performed.

In the above-mentioned conventional method, a plurality of actual images must be acquired and stored. However, this step needs to be performed for an extremely large number of patterns included in the wafer, which hinders an improvement in inspection throughput. It has become. Further, it is necessary to sufficiently capture the reflected electrons, but the shape of the conventional objective lens is insufficient. because,
This is because the angle distribution emitted by the reflected electrons is emitted in a wide range.

The present invention has been made in view of the above points, and an object of the present invention is to provide an electron beam inspection apparatus capable of efficiently capturing reflected electrons from a sample and improving the inspection throughput. To be.

[0009]

According to a first aspect of the present invention, there is provided a scanning electron microscope, comprising: an electron beam irradiating system including an objective lens for irradiating an electron beam from an electron source onto a predetermined area on a surface of a sample. Voltage applying means for applying a negative voltage to the sample, image forming means for forming a magnified image by imaging reflected electrons obtained from the area irradiated with the electron beam,
An image signal acquiring unit that converts an enlarged image formed by the image forming unit into an image signal; and a unit that compares an image obtained by the image signal acquiring unit with an image signal created from the design pattern. Features.

According to the first aspect of the invention, the defect of the sample is inspected by comparing the reflected electron image with the image created from the design pattern, thereby improving the inspection throughput. Claim 2
The scanning electron microscope according to the invention of the present invention is provided with an electron beam irradiation system including an objective lens for irradiating an electron beam from an electron source onto a predetermined area of a sample surface and irradiating the electron beam, and a positive voltage A collecting electrode to which is applied, a voltage applying means for applying a negative voltage to the sample, and an image forming means for forming a magnified image by forming reflected electrons obtained from an area irradiated with the electron beam. Image signal obtaining means for converting an enlarged image formed by the image forming means into an image signal,
It is characterized by comprising means for comparing the image obtained by the image signal obtaining means with the image signal created from the design pattern.

According to the second aspect of the present invention, the reflected electron image is compared with the image formed from the design pattern to inspect the defect of the sample, thereby improving the inspection throughput and the reflected electron near the tip of the objective lens. Is provided, the reflected electrons from the sample can be efficiently captured to form an image.

According to a third aspect of the present invention, in the electron beam inspection apparatus according to the second aspect, the objective lens is a semi-in-lens type objective lens, and the collection electrode is disposed inside the inner electrode.

According to a fourth aspect of the present invention, in the electron beam inspection apparatus according to the first to third aspects, the electron beam from the electron gun is bent by the beam separator and irradiated onto the sample. According to the fifth aspect of the present invention, in the electron beam inspection apparatus according to the first to third aspects, the electron beam from the electron gun travels straight through the beam separator and irradiates the sample.

According to a sixth aspect of the present invention, in the electron beam inspection apparatus of the first to fifth aspects, an energy filter is provided in the image forming means for forming a magnified image by imaging the reflected electrons, and the reflection in a specific energy range is provided. Electrons were selectively extracted to form a magnified image.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an example of an electron beam inspection system according to the present invention. In the figure, a sample 1 is placed on a stage 2, and a negative voltage is applied to the sample 1 from a sample bias power supply 3. The stage 2 is movable in the horizontal direction by a motor 5 driven by a motor driver 4. The position of the stage 2 is detected by a stage position sensor 6, and the detection signal is supplied to a stage position measuring device 7.

Above the sample 1, an objective lens 8 for irradiating the sample 1 with an electron beam is arranged. The objective lens 8 has, for example, a semi-in-lens type lens configuration in which the lens magnetic field protrudes to the sample 1. A collecting electrode 11 for efficiently collecting reflected electrons generated from the sample is provided inside the objective lens 8. A positive voltage is applied to the collecting electrode 11 from a collecting electrode power supply 12.

The sample 1 is irradiated with an electron beam 14 generated and accelerated from an electron gun 13. The electron beam 14 from the electron gun 13 is converged by a converging lens 15,
The light enters the beam separator 16. Beam separator 1
Numeral 6 acts so that electrons of a specific energy go straight and electrons of other energies are bent by a combination of an electric field and a magnetic field. The electron beam incident on the separator 16 is bent at a right angle by the separator 16 and is incident on the objective lens 8.

The electron beam is converged by the objective lens 8 and irradiates a predetermined area of the sample 1. The electron beam directed to the sample 1 is reflected near the surface of the sample 1 by the negative voltage applied to the sample 1. The reflected electrons are efficiently collected on the optical axis by the magnetic field of the objective lens 8 and the electric field of the collection electrode 11. The reflected electrons are extracted upward and enter the beam separator 16. The electric field and magnetic field of the beam separator 16 are adjusted to an intensity that allows the reflected electrons to go straight, and the reflected electrons go straight through the beam separator 16 toward the intermediate lens 17.

The reflected electrons converged by the intermediate lens 17 enter the energy filter 18, and only the reflected electrons of a specific energy pass through the filter 18 and enter the projection lens 19. The image based on the reflected electrons is projected on the fluorescent screen 20 by the projection lens 19. Fluorescent screen 2
The image projected to 0 is converted into a video signal by the CCD camera 21. The signal of the sample image obtained by the CCD camera 21 is supplied to and stored in the first image storage memory 22.

The above-mentioned sample bias power source 3, objective lens 8, collecting electrode power source 11, converging lens 15, intermediate lens 1
7, the energy filter 18, and the projection lens 19 are controlled by an electron optical system control circuit 22. Further, the electronic optical system control circuit 23, the motor driver 4, and the stage position measuring device 7 are controlled by the control computer 24.

The first image storage memory 22 is provided in an image processing unit 25.
There is also provided a design image memory 26 for storing design image information obtained in advance by, for example, and a second image storage memory 27 for storing a part or all of the image information stored in the design image memory 26. . Furthermore,
The image processing unit 25 includes a first image storage memory 2
Image information stored in the second image storage memory 2
Arithmetic unit 28 for performing a comparison operation with the image information stored in memory 7
And a defect determining unit 2 for determining a defect calculated by the calculating unit
9, a monitor 30 for monitoring the image stored in the first image storage memory 22 is included.

The result judged by the defect judging unit 29 is sent to the data collecting unit 31 and stored in the memory 32 connected to the data collecting unit 31. In the configuration described above, the deflector 33 is provided above the objective lens 8 so as to adjust the irradiation position of the electron beam 14 on the sample. In addition, many slits are provided at various parts of the electron optical system to cut unnecessary electron beams and electrons. The operation of such a configuration will now be described.

First, a semiconductor wafer sample 1 to be inspected for defects
Is mounted on the stage 2, and the stage 2 is moved by the motor 5 so that the defect inspection area of the sample is positioned on the optical axis of the electron beam. When the stage 2 is moved, the stage position is monitored by the stage position sensor 6 and the stage position measuring device 7, and as a result, the defect inspection area of the sample is located on the electron beam optical axis. In this state, the sample 1 is supplied to the sample 1 from the sample bias power supply 3.
A negative voltage of about kV is applied. The voltage value from the sample bias power supply 3 is controlled by the electron optical system control circuit 23 so that an optimum voltage is applied to the sample.

In this state, the accelerated electron beam 14 generated from the electron gun 13 in the electron beam column C is converged by the converging lens 15 and enters the beam separator 16. The electron beam 14 is bent at a substantially right angle by the beam separator 16 and enters the objective lens 8.
The electron beam is converged by the objective lens 8, and an electron beam having a predetermined diameter is directed to the sample.

The electron beam directed to the sample 1 is reflected in the vicinity of the sample surface by a negative voltage applied to the sample. The reflected electrons are collected by the magnetic field of the objective lens 8 and the electric field by the collecting electrode 11, accelerated, and taken out upward. At this time, a positive voltage of several kV is applied to the collecting electrode 11 arranged inside the inner magnetic pole of the objective lens 8. As a result, reflected electrons from the sample are efficiently collected by the electric field generated by the collecting electrode.

The backscattered electrons taken out above the objective lens 8 travel straight in the beam separator 16 and enter the intermediate lens 1.
The reflected electron image of a predetermined area of the sample is enlarged and projected on the fluorescent screen 20 by the projection lens 7 and the projection lens 14. At this time, the reflected electrons pass through the energy filter 18 so that unnecessary energy electrons are removed, and the reflected electrons having the same energy are imaged on the fluorescent screen 20.

The reflected electron image of the sample formed on the fluorescent screen 20 is converted into a video signal by a CCD camera 21, and the signal is supplied to a first image memory 22 in an image processing unit 25 and stored. The backscattered electron image of the sample stored in the image memory 22 can be appropriately observed by the monitor 30. The image processing unit 25 includes a design image memory 26. Of the image information in the memory 26, image data of a defect inspection portion is stored in the second image memory 2.
7 and stored.

In this state, the operation unit 2 in the image processing unit 25
8, the image signal in the first image memory 22 and the second
The comparison operation with the image signal in the image memory 27 is performed.
As an example of this comparison operation, a correlation coefficient between images is calculated, and the coefficient is sent to the defect determination unit 29. Defect judgment unit 2
9 determines whether the inspection area of the sample is normal or has a defect based on the magnitude of the correlation coefficient.

In this case, the defect judging section 29 has a threshold, and makes a defect judgment based on the magnitude of the threshold. Further, the defect determination unit 29 classifies the type of the defect when there is a defect based on the calculation result by the calculation unit 28. Examples of this classification include whether the pattern formed on the sample is short-circuited, whether the patterns to be connected are not connected, and are open. The information on the presence or absence of a defect obtained by the defect determination unit 29 or the information on the type of the defect is sent to the memory 32 via the data collection unit 31 and stored. Such a defect inspection is performed while changing the irradiation position of the electron beam by the deflector 33, or changing the sample portion on the optical axis of the electron beam by moving the stage 2.

When the stage is moved, any of a step-and-repeat system and a continuous running system can be used. In the case of the continuous running method, since it is necessary to irradiate a predetermined area of the sample with the electron beam for a certain period of time, the control computer 24 sends the stage position information from the stage position measuring device 7 to the electron optical system control circuit 23, 33, it is necessary to deflect the electron beam in a direction opposite to the moving direction of the stage.

As the CCD camera 21, a camera having a large number of pixels is preferably used. For example, if the number of pixels is 2048
In the case of using a × 2048 camera, when storing an image signal in the image memory 22, the CCD area is divided (for example, 512 × 5
High-speed image reading becomes possible by making it possible to read in multiple channels in parallel by dividing the image by 12 dots).

FIG. 2 is a diagram showing another embodiment of the present invention. In FIG. 2, the column 4 of the primary electron beam
0 is arranged in the vertical direction, and the imaging system of the reflected electrons is arranged horizontally. With such a configuration, the same operation and effect as in FIG. 1 can be achieved.

FIG. 3 also shows another embodiment of the present invention. In this embodiment, the image in the design image memory 26 is
When the image data is sent to the image memory 27, the image data is transmitted through the pre-processing unit 41. This causes a difference in scale, a difference in inclination, and the like when the actual pattern is directly compared with the design pattern. For this reason, the image data from the design image memory 26 is sent to the pre-processing unit 41 to correct a difference in scale or a difference in inclination, and is sent to the second image memory 27.

In the arithmetic section 28, the actual image stored in the first image memory 22 or the second image memory 27
The pattern matching process is performed after performing scale matching or pattern tilt matching on any of the reference images stored in the above, but when such processing is performed in the first calculation, such Before proceeding to proper pattern matching, necessary preprocessing is performed and stored in the image memory 27. With this configuration, the load on the calculation unit is reduced, and the processing time can be reduced. Such scanning may be performed periodically when several rows of chips are inspected or when a wafer is replaced.

[0035]

As described above, according to the first aspect of the present invention, the defect inspection of the sample is performed by comparing the reflected electron image with the image created from the design pattern. Can be improved.

According to the second aspect of the present invention, the defect of the sample is inspected by comparing the backscattered electron image with the image created from the design pattern, thereby improving the inspection throughput, and improving the inspection throughput near the tip of the objective lens. Since the backscattered electron collecting electrode is provided, the backscattered electrons from the sample can be efficiently captured to form an image.

According to the third aspect of the present invention, in the electron beam inspection apparatus according to the second aspect, the objective lens is a semi-in-lens type objective lens, and the collection electrode is disposed inside the inner electrode. It can capture well and form an image.

According to the fourth and fifth aspects of the present invention, in the electron beam inspection apparatus according to the first to third aspects, since the electron beam from the electron gun is incident on the beam separator and then irradiated onto the sample, the electron gun is inspected. Etc., the degree of freedom of layout can be increased.

According to a sixth aspect of the present invention, in the electron beam inspection apparatus according to the first to fifth aspects, an energy filter is provided in an image forming means for forming a magnified image by forming reflected electrons, and the reflection in a specific energy range is provided. Since an enlarged image is formed by selectively extracting electrons, a reflected electron image with high resolution can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an electron beam inspection device according to the present invention.

FIG. 2 is a diagram showing another electron beam inspection apparatus according to the present invention.

FIG. 3 is a diagram showing another electron beam inspection apparatus that performs pattern matching.

[Explanation of symbols]

 Reference Signs List 1 sample 2 stage 3, 12 power supply 4 motor driver 5 motor 6 sensor 7 stage position measuring instrument 8 objective lens 11 collecting electrode 13 electron gun 14 electron beam 15 convergent lens 16 beam separator 17 intermediate lens 18 energy filter 19 projection lens 20 fluorescent plate Reference Signs List 21 CCD camera 22 First image memory 23 Electro-optical system control circuit 24 Control computer 25 Image processing unit 26 Design image memory 27 Second image memory 28 Operation unit 29 Defect judgment unit 30 Monitor 31 Data collection unit 32 Memory

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01J 37/141 H01J 37/22 502A 5C033 37/22 502 37/244 37/244 37/29 37/29 H01L 21/66 J H01L 21/66 G01R 31/28 LF term (reference) 2F067 AA54 AA62 BB01 BB04 CC17 HH06 HH13 JJ05 KK04 KK08 LL00 LL16 PP12 QQ02 RR24 RR30 UU02 2G001 AA03 BA15 CA03 EA05 GA01 FA01 FA06 HA12 HA13 JA02 JA04 JA05 JA13 KA03 LA11 MA05 SA01 SA04 2G011 AA00 AE03 2G032 AD08 AF08 4M106 AA01 BA02 CA39 DB04 DB05 DJ04 DJ11 DJ18 DJ21 5C033 AA05 DD02 DD09 DE06 NN02 NP01 NP05 SS01 SS03 SS08

Claims (6)

[Claims] An electron beam irradiating system including an objective lens for irradiating an electron beam from an electron source onto a predetermined area of a surface of a sample and irradiating the electron beam; voltage applying means for applying a negative voltage to the sample; Image forming means for forming a magnified image by imaging reflected electrons obtained from a region irradiated with the beam; image signal obtaining means for converting the magnified image formed by the image forming means into an image signal; An electron beam inspection apparatus comprising: means for comparing an image obtained by the means with an image signal created from a design pattern. 2. An electron beam irradiation system including an objective lens for expanding and irradiating an electron beam from an electron source to a predetermined area on the surface of a sample, and a positive voltage is disposed near the tip of the objective lens. A collecting electrode, a voltage applying means for applying a negative voltage to the sample, an image forming means for forming a magnified image by forming reflected electrons obtained from a region irradiated with the electron beam, and an image forming means 1. An electron beam inspection apparatus comprising: an image signal acquisition unit that converts an enlarged image formed by the above into an image signal; and a unit that compares an image obtained by the image signal acquisition unit with an image signal created from a design pattern. 3. The electron beam inspection apparatus according to claim 2, wherein the objective lens is a semi-in-lens type objective lens, and a collection electrode is arranged inside the inner electrode. 4. The electron beam inspection apparatus according to claim 1, wherein an electron beam from the electron gun is bent by a beam separator and irradiated onto a sample. 5. The electron beam inspection apparatus according to claim 1, wherein the electron beam from the electron gun travels straight through the beam separator and irradiates the sample. 6. An image forming means for forming a magnified image by imaging reflected electrons, wherein an energy filter is provided, and a magnified image is formed by selectively taking out reflected electrons in a specific energy range. An electron beam inspection apparatus according to any one of claims 1 to 5.