JP2002184336A - Charged particle beam microscope device, charged particle beam application device, charged particle beam microscopic method, charged particle beam inspection method and electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron microscope device using a short focus objective lens that enables acquiring a good image of high resolution without any distortion in a wide range from low magnification to high magnification at the observation in low acceleration voltage condition. SOLUTION: In the electron microscope device that is constructed of an electron source 1, a focus lens 2, an upper stage deflection coil 4, a lower stage deflection coil 5, an objective lens 7, and a correction magnetic field lens 9 for electron beam deflection or the like, the distortion aberration that is generated in the objective lens 7 is cancelled by the reverse direction distortion aberration caused by the correction magnetic field lens 9 for electron deflection, and a good scanning electron microscopic image having a high resolution without any distortion in a wide range from low magnification to high magnification is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle beam apparatus for scanning a sample with a charged particle beam such as an electron beam to obtain an image signal of the sample, and more particularly to a charged particle beam microscope apparatus and a charged particle beam application apparatus. The present invention relates to a charged particle beam microscopy method, a charged particle beam inspection method, and an electron microscope device.

[0002]

2. Description of the Related Art For example, Japanese Patent Application Laid-Open No. 2000-48755 discloses that it can be achieved by changing a current condition of a deflector in order to correct distortion of an objective lens.

[0003] Also, HC Pfeiffer and W. Stickel
“゛ Large Field Electron Optics-Limitions and En
hancements ", Proc. SPIE, vol. 2522, pp. 23-30 (1995. 7.10) Correction with beam stop to dynamically correct aberration between upper and lower deflectors in objective lens A vessel is disclosed but is not described in detail.

A method of acquiring a scanning electron microscope image using a conventional electron microscope apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. H11-25.
No. 0850. Conventionally, as an optical system used for such a low-magnification image observation method, an objective lens is not used, but a deflection coil is used only in one stage, and at a high magnification, a deflection coil and an objective lens are used.

While switching these two optical conditions in this manner, the observation field of view is searched with a low magnification image, and the shape observation and high resolution observation are performed with a high magnification image.

Japanese Unexamined Patent Publication (Kokai) No. 6-283128 discloses a combination of a converging lens, a deflecting coil, and an objective lens having a configuration other than the above-described method for obtaining a scanning electron microscope image. This is a configuration in which a convergent lens and an objective lens are sequentially arranged below the deflection coil. This method employs an electron optical system that irradiates an electron beam deflected by a deflection coil on a sample placed in an objective lens with a converging lens and an objective lens and reducing the electron beam. In brief, the electromagnetic lens is disposed below the deflection coil and the objective lens is disposed below the electromagnetic lens. However, it is disclosed that the role of the electromagnetic lens here is to change the focal position when the sample is placed below or above the objective lens.

[0007]

Conventionally, an electron optical system, that is, a converging lens for converging an electron beam from an electron source, a deflector for scanning the electron beam, one object point and one image point. When an electron optical system including an objective lens is used and a scanning electron microscope image is acquired with a low acceleration voltage (about 5 kV or less),
Spread of the electron beam spot occurs due to chromatic aberration. The spread of the spot is constant regardless of the magnification. The resolution is determined by the ratio between the diameter of the electron beam spot and the electron beam scanning range. Therefore, the resolution decreases as the scanning range of the electron beam becomes narrower, that is, as the magnification becomes higher. Conversely, the resolution increases as the scanning range of the electron beam increases, that is, as the magnification decreases. Therefore, the magnification range in which a high-resolution image can be obtained is about 1000 times or less.

The magnification here indicates the ratio of the display range of the display device to the scan range on the sample.

On the other hand, in an optical system for high magnification of 10,000 times or more,
The objective lens is operated at a short focus for the purpose of achieving the resolution. In this case, a high-resolution scanning electron microscope image can be obtained by observing a high-magnification image of 10,000 times or more with a small amount of deflection off-axis. Since distortion occurs due to the lens, the magnification range in which a good image without distortion is obtained is about 10,000 times or more. As for the visual field search on the sample, there was no problem even if low resolution was not required at low magnification, but resolution was required at intermediate magnifications of 1000 to 10,000 times. However, no attempt has been made to increase the resolution at this intermediate magnification. That is, in the conventional electron optical system, in both the low-magnification optical system and the high-magnification optical system, a good image with high resolution and no distortion is obtained in an intermediate magnification range of about 1000 to 10,000 times (image plane conversion: 10 to 100 μm). Not obtained.

Further, in the conventional electron optical system, the combination of the lenses and coils used in the high and low magnification optical systems and the excitation conditions are all different, so that the magnetic hysteresis and optical axis at the time of switching are shifted. When switching between the low-magnification image and the high-magnification image, the image position at the same position on the sample is displayed with a shift, which causes a problem in the visual field searching operation.

As described above, for example, when a scanning electron microscope image is acquired using a short-focus objective lens at a low accelerating voltage, high image quality in an intermediate magnification range of about 1000 to 10,000 times is obtained. Therefore, there is a need for an electron optical system that enables observation in a wide magnification range from an intermediate magnification image to a high magnification image by changing excitation conditions of a deflection coil and a lens.

Accordingly, an object of the present invention is to correct distortion in the range of scanning on a sample at an intermediate magnification (1000 to 10,000 times and image plane conversion of 10 to 100 μm at a magnification of 1000 to 10,000) generated by an objective lens. It is an object of the present invention to provide a charged particle beam apparatus capable of acquiring a high-resolution and distortion-free good scanning electron microscope image or image signal in a wide magnification range up to a high magnification.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an objective lens having a charged particle beam deflection correction lens installed in front of an objective lens having one object point and one image point. Excitation is performed under the condition to correct the distortion caused by the above, and the charged particle beam is two-dimensionally scanned on the sample surface by the deflector, and the scanning charged particle beam microscope image or image signal with little aberration from low magnification to high magnification is obtained. get.

Further, according to the structure of the present invention, a correction lens for charged particle beam deflection is provided between the converging lens and the objective lens,
The present invention is configured so that the distortion generated by the objective lens is in the opposite direction.

Further, the configuration of the present invention lies in that the charged particle beam having passed through the correction lens forms an image at the position of the main surface of the objective lens.

Further, the configuration of the present invention resides in that the deflector is installed at a stage before the correction lens. In the configuration of the present invention, the deflector comprises a two-stage upper stage deflector and a lower stage deflector, and the correction lens is located below the upper stage deflector and the lower stage deflector or between the upper stage deflector and the lower stage deflector. Is located.

Further, the configuration of the present invention is characterized in that a sample chamber for mounting a sample is provided below the magnetic path of the objective lens.

Further, the present invention provides one or more electrostatic lenses for accelerating a primary electron beam generated from an electron source to a predetermined voltage, and a one-stage electrostatic lens for converging and irradiating the primary electron beam to a sample. In an electron microscope apparatus having the above-described converging lens and objective lens, and one or more deflectors for deflecting the primary electron beam, an electron beam deflecting correction magnetic lens installed in front of the objective lens is replaced by an objective lens. Is excited under the condition to correct the distortion generated in the above, the primary electron beam is two-dimensionally scanned on the sample surface by the electron beam deflection by the deflector, the correction magnetic lens and the objective lens, and the secondary electron beam is generated from the sample. The intensity of the secondary electron beam or the electron beam transmitted through the sample is detected in synchronization with the scanning of the primary electron beam, and the signal is displayed as a brightness modulation signal of the image display device as a scanning electron microscope image by the image display device. The way there to the point that you configured.

In searching for the visual field of the target object in the sample, the point is that the visual field is searched by continuously zooming up or down from the first magnification to the second magnification.

Still another object of the present invention is to compare a previously captured image of a predetermined magnification or a design image with a physical shape defect and an electrical defect of the sample. Further, the first area and the second area of the repetitive circuit pattern are detected as image signals at the first magnification, and the image signals are compared. If they do not match, the difference is again detected at a second magnification different from the first magnification. In the inspection method, the image signals of the areas to be read are fetched, compared again, and if they do not match, it is determined to be a defect.

Still another object of the present invention is to provide an electron optical system having low magnification and low peripheral blur.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electron source as a charged particle source,
An electron beam will be described as an example of a charged particle beam and will be specifically described.
A method of correcting a distortion generated in an objective lens using an electron microscope apparatus and acquiring a scanning electron microscope image or an image signal from a low magnification to a high magnification through an intermediate magnification will be described.

FIG. 1 is a diagram showing the configuration of an optical system for observing a high-magnification image using a conventional electron microscope apparatus. The primary electron beam generated from the electron source 1 is reduced by the converging lens 2 and forms an image on the image plane position 3 of the converging lens 2. Next, the upper deflection coil 4 and the lower deflection coil 5 are operated,
The deflection fulcrum 6 defined as the point where the primary electron beam deflected by the lower deflection coil 5 intersects with the optical axis 1 ′ is made to coincide with the front magnetic field focal plane position of the objective lens 7. At this time, the primary electron beam is imaged at a position distant from the optical axis 1 'by the lens action of the objective lens 7. As shown in FIG. 4, this off-axis position is called a deflection position, and the off-axis distance is called a deflection swing width r. Here, the objective lens 7 has one object point and an image point 29.

When the deflection angle of the upper deflection coil 4 is changed, the ratio of the deflection angles of the upper deflection coil 4 and the lower deflection coil 5 (deflection vertical ratio) is such that the position of the deflection fulcrum 6 is always constant. Can be determined by the geometric dimensions. If such a deflection up / down ratio is set, the deflection swing width becomes equal to the upper deflection coil 4.
Is determined by the deflection angle.

Here, the purpose of making the deflection fulcrum 6 coincide with the position (object point) of the front magnetic field focal plane of the objective lens 7 is that when the primary electron beam is off-axis from the optical axis on the sample 8, This is to make the irradiation angle constant at all deflection positions.

The deflection angle of the upper deflecting coil 4 is changed in two directions perpendicular to each other at a fixed step, and the intensity of the transmitted electron beam, the secondary electron beam, the reflected electron beam, etc. is detected in synchronism with this, and the luminance is modulated and displayed. By doing so, a scanning electron microscope image can be obtained. The deflection amplitude of the scanning electron microscope image is determined by setting the maximum value of the deflection angle of the upper deflection coil 4.

Here, the relationship between the coil deflection angle and the magnification of a scanning electron microscope image will be described using parameters such as typical coils, lens excitation conditions, and the distance between lenses. The distance between the upper deflection coil 4 and the lower deflection coil 5 is 34 m
m, the distance between the lower deflection coil 5 and the objective lens 7 is 93.
Assume that the position of the front magnetic field focal plane of the objective lens 7 is 2.5 mm above the objective lens 7.

First, let the deflection angles of the upper and lower deflection coils be θ1 and θ2, respectively. Fix the deflection fulcrum position,
The vertical ratio of the deflection angle for deflecting the electron beam on the sample surface is θ2 = (1 + 34 / (93.5-2.5)) θ1 =
1.38 θ1.

The upper and lower deflection ratios are set by winding the upper and lower deflection coils in opposite phases and setting the number of turns to upper: down = 1: 1.38, and energizing the upper and lower deflection coils in series. The deflection swing width r is r = 2.5 × 34/91 × θ1 = 0.94 ×
θ1.

Therefore, for example, when the deflection angle of the upper deflection coil is set to 50 mrad, the deflection swing width becomes r = 47.
μm. If you set the image display to 100mm square,
The magnification of the scanning electron microscope image is 100 × 1000 / (4
7 × 2) = 1064 times.

Here, since the maximum value of the deflection angle θ1 of the upper deflection coil is usually about 50 mrad, the minimum magnification in this optical system is about 1000 times. However,
In this case, since the distortion increases as the deflection swing width increases, the practically usable magnification has a lower limit.

FIG. 2 is an example showing the shape of an actual raster imaged on a sample surface by an objective lens when a square raster is formed by a deflection coil. As conditions, only the effect of distortion was considered, and the coefficient (complex value) of distortion was 5 × 10 ^{−5 for} both the real part and the imaginary part.

As shown in FIG. 2A, a magnification of 1000
In the case of double, the square raster is pincushion-shaped. If an image is obtained under these conditions, the image becomes a distorted image in which the magnification of the image is gradually reduced in the upward and downward directions from the center. On the other hand, as shown in FIG. 2B, when the magnification is 10,000 times, the raster is imaged in a square shape, and a good image without distortion is obtained. As mentioned above,
The electron optical system for obtaining a high-magnification image has a minimum magnification limit due to the influence of distortion.

Next, an optical system generally used for observing a scanning electron microscope image of a low magnification of 1000 times or less will be described with reference to FIG. In order to observe a low-magnification image, it is necessary to increase the deflection swing width on the sample 8. Therefore, the method of deflecting the electron beam by aligning the deflection fulcrum with the position of the front magnetic field focal plane of the objective lens is not preferable. The scanning deflection area cannot be enlarged by the lens action of the objective lens. Therefore, the excitation of the objective lens has been stopped before use. That is, an optical system is used in which the electron beam is inclined by one-stage deflection by the upper deflection coil 4 to increase the deflection swing width. Since the deflection by the objective lens is not used (the so-called one-step deflection), the excitation of the objective lens is set to zero, and the electron beam from the electron source 1 is set to be focused on the sample 8 by the converging lens 2.

The same coil as the above high magnification image observation condition,
When a lens is used, the relationship between the deflection angle θ3 of the one-stage deflection coil and the deflection swing width r is r = 127 × θ3.

That is, the deflection angle of the upper deflection coil is set to 5
When set to mrad, the deflection swing width r is 0.64 mm, and the magnification of the scanning electron microscope image is 100 / (0.64 mm).
× 2) = 78 times.

As described above, in this electron optical system, a sufficiently low-magnification image can be obtained by giving a small deflection angle to the deflection coil, but there are the following problems.
This is an electron optical system that forms an image of an electron source on a sample surface by using the converging lens 2 in only one stage. Since the electron optical magnification of the electron source is about a fraction, the converging lens 2 has low excitation. Used in.

In this case, the chromatic aberration coefficient of the converging lens 2 is 1
It is about 000 mm. The spread of the spot due to this chromatic aberration is calculated. The acceleration voltage is 1 kV, the energy spread of the electron source is 0.5 V, and the irradiation angle of the spot is 0.5 mra.
Assuming d, the spread amount of the spot is 1000 (chromatic aberration coefficient) × (0.5 (energy spread of the electron source) / 100
0 (acceleration voltage)) x 0.0005 (irradiation angle) = 0.25 µm
Becomes

On the other hand, when the magnification of the image is 1000 times,
The amount of electron beam deflection is 100 μm on one side and 500 μm on one side.
If an image is formed by pixels, the size of one pixel is 0.2μ
m. Therefore, in this optical system, one pixel (0.2 μm)
The spot spread (0.25 μm) is larger than that, and a high-resolution image cannot be obtained. The magnification at which the spot spread is the same as one pixel is 800 times, which is the upper limit of the magnification of this optical system.

Also, because of the single-stage deflection by the upper deflection coil 4, the electron beam deflected on the sample 8 is incident on the sample with an inclination as the deflection swing width is increased. An image is distorted toward the periphery, that is, a so-called peripheral blur of the image occurs. Further, the optical axis at the time of observing the high-magnification image and the optical axis at the time of observing the low-magnification image do not coincide with each other, resulting in image displacement between the low-magnification image and the high-magnification image.

As described above, the conventional optical system for observing a low-magnification image can obtain a low-magnification image sufficient for searching for a visual field.
There are various problems because the optical system is greatly changed as compared with the optical system for high magnification. Furthermore, the electron optical system for high magnification has a limitation on the low magnification side, and the electron optical system for low magnification has a limitation on the high magnification side. There is a problem that no good image can be obtained. Conventionally this intermediate magnification range
(The scanning area is in the range of 100 μm to 10 μm in terms of image plane).

In order to solve the above-mentioned problems of the conventional electron optical system, it is necessary to improve the quality of an image in an intermediate magnification range. An electron optical system that enables observation in a wide magnification range from a magnification image to a high magnification image has been desired.

Therefore, as a first embodiment of the present invention, a method is described in which distortion caused by an objective lens is corrected by another lens, and a scanning electron microscope image from low magnification to high magnification is obtained. The basic configuration of the embodiment will be described with reference to FIG.

The conventional converging lens 2, high-magnification lens 7, objective lens 7, upper-stage deflection coil 4 and lower-stage deflection coil 5 are used to deflect a primary electron beam on a sample 8 to obtain an image by using a conventional high-magnification image observation lens. A correction magnetic field lens 9 for electron beam deflection is newly added. Upper deflection coil 4 and lower deflection coil 5
The primary electron beam deflected by the electron beam is imaged one-to-one on the main surface position of the objective lens 7 by the correction magnetic lens 9 for electron beam deflection, and the electron beam is imaged on the sample 8 by the objective lens 7. I do.

At this time, distortion occurs in the correction magnetic lens 9 for electron beam deflection in accordance with the amount of deflection off-axis formed by the upper stage deflection coil 4 and the lower stage deflection coil 5, and the distorted deflection figure becomes the objective lens 7. An image is formed at the main surface position. further,
The objective lens 7 generates distortion according to the amount of deflection off-axis of the distorted deflection pattern, and the deflection pattern on the sample 8 is
Distort again.

Here, the correction magnetic lens 9 for electron beam deflection
By setting the lens polarity and the optical magnification so that the distortion generated by the objective lens 7 and the distortion generated by the objective lens 7 become the aberrations in the opposite directions, the deflection figure finally formed on the sample 8 is in the upper stage. Deflection coil 4 and lower deflection coil 5
The shape can be returned to the shape of the deflection figure formed by the above.

FIG. 5 shows the result of correcting the distortion by the present method. The conditions are the same as those of FIG. 1 described above, except that the magnification of image acquisition is 1000 times (the deflection amplitude is 50 μm on one side), and the real part and imaginary part of the distortion aberration coefficient (complex value) are 5 ×, respectively. 10 ⁻⁵ and 1 × 10 ⁻⁵ .

That is, as shown in FIG. 5A, a square raster created by the upper deflection coil 4 and the lower deflection coil 5 is a correction magnetic lens 9 for electron beam deflection.
As a result, distortion for canceling is generated in the direction opposite to the distortion of the objective lens. This canceling distortion is imaged as a distorted figure at the position of the main surface of the objective lens 7. FIG. 5B shows this state. By using this and exciting the objective lens 7 under the condition of generating distortion in the opposite direction to the figure, the raster on the sample 8 becomes substantially square as shown in FIG. It can be seen that under this magnification condition, a good image without distortion can be obtained.

In this case, the coil polarity and the excitation condition for generating the reverse distortion with respect to the objective lens are set for the correction magnetic lens 9 side. Distortion can also be corrected by changing the excitation conditions.

This correction method is applied not only to a visual field search for searching for a target in a wide area but also to a case where an electron beam or an ion beam is used to expose a resist coated wafer disposed under an objective lens. . Naturally, the present invention is also applicable to batch exposure using a mask or variable shaping, as well as a type in which dot drawing is performed using an electron beam. Furthermore, the present invention can be applied to inspection and processing by arranging a sample under an objective lens using an electron beam.

Even if the above contents are extended to an ion beam which is a charged particle beam, the following holds. A sample placed on a sample stage is irradiated with a primary charged particle beam (ion beam) from a charged particle source. The size on the display device with respect to the scanning width to be irradiated indicates the magnification, and the scanning is performed while varying the magnification from less than 1000 times of the low magnification to 5 million times of the high magnification area.
This is achieved by adding a lens for correcting deflection distortion (distortion aberration) generated when the primary charged particle beam scanned by the deflector passes through the objective lens. Here, an electrostatic deflector may be used as the correction lens.

Next, a method of determining excitation conditions for using the correction magnetic lens for electron beam deflection under the condition that distortion is corrected will be described. First, the acceleration voltage is set to a predetermined value. Next, a sample for evaluating the amount of distortion is placed on a sample stage at a predetermined sample position. For this sample, the amount of vertical and horizontal distortion can be clearly evaluated.
A grid mesh having from 2000 to 2000 orthogonal lines or a grating having a line width of about 5 to 0.5 μm is used. Next, the magnification of the electron microscope is set to the minimum magnification, and the objective lens is focused on the sample surface. At this time, the image is greatly distorted due to distortion, so focus at the center of the image, or if it is difficult to determine whether the focus is also coincident at the center, slightly increase the magnification and adjust the center of the image. The magnification may be reset to the minimum after focusing by the section. Next, a current is passed through the correction magnetic lens 9 for electron beam deflection to excite it. Here, the correction magnetic lens 9 for electron beam deflection generates a magnetic field in a direction opposite to that of the objective lens 7, for example, the same winding direction of the coil and the same current direction, or the same winding direction of the coil and the same current. It is set to be in the opposite direction. When the correction magnetic lens 9 for electron beam deflection is excited, the scanning electron microscope image is defocused and the amount of image distortion changes. While the deviation of the focus is corrected by changing the current excitation of the converging lens 2, the excitation is changed by the current supplied to the correction magnetic field lens 9 for electron beam deflection so that the distortion of the image is reduced. An image is acquired in the vicinity of the current value at which the image distortion is reduced,
Measure the vertical and horizontal ratio of the grid mesh sample, the ratio becomes appropriate, and the magnification error between the center and the periphery of the image is 5%
The excitation of the correction magnetic lens 9 for electron beam deflection is adjusted so as to be within the range, and the focus is accurately adjusted by the converging lens 2. The excitation current values of the electron beam deflection correction magnetic field lens 9 and the convergent lens 2 determined in this way are recorded with respect to the acceleration voltage, and the magnification and the correction value are displayed on the display device as necessary.

Next, the case where the acceleration voltage is changed will be described. The acceleration voltage at the time of incidence on the sample is changed by changing the retarding voltage applied between the electrode applied to the sample and the electrode provided below the magnetic path of the objective lens so that the sample table and the lower part of the objective lens are changed. A deceleration electric field is formed between them. Depending on the degree of the deceleration electric field, the speed of the primary electron beam changes and the deflection distortion also changes. The electric field due to this retarding voltage moves like a kind of electrostatic lens. The deflection current generated in this way is combined with the distortion of the objective lens, and the excitation current values of the correction magnetic field lens 9 for electron beam deflection and the convergent lens 2 are processed in the same manner as described above so that the correction magnetic field lens absorbs the distortion. To determine. The excitation current values of the correction magnetic lens 9 for electron beam deflection and the convergence lens 2 determined by the combination of all the acceleration voltage and the retarding voltage are incorporated in the apparatus control program as a table, and the acceleration voltage and the retarding voltage are determined. In this case, the distortion is corrected and the condition for focusing on the sample is automatically set.

On the other hand, an ion source is used as a charged particle source,
Even if an ion beam is applied as a charged particle beam, the invention of the present application is established. However, a positive polarity voltage is applied to the electrode as the retarding voltage. That is, the difference is that a voltage is applied to the electrode so that an electric field is formed so as to decelerate the ion beam.

The distortion increases the scanning range of the deflector,
That is, when the intermediate magnification is set, the deflection off-axis of the electron beam becomes large, and a large distortion occurs. Accordingly, the distortion becomes maximum at the lowest magnification. At a high magnification, the scanning width becomes narrow and the deflection off-axis becomes small. At this time, since the light passes through the correction magnetic lens 9 and the center portion of the objective lens 7, distortion generated when the light passes through a position apart from the center of the correction magnetic lens 9 and the objective lens 7 is extremely small. Therefore, the correction of the objective lens 7 by the correction magnetic lens 9 for electron beam deflection may not be necessary. In changing the magnification from the intermediate magnification to the high magnification or from the high magnification to the intermediate magnification, it is sufficient to prescribe the conditions of the correction magnetic field lens 9 and the converging lens 2 to reduce the deflection distortion at the intermediate magnification. Because, at high magnification, the electron beam passes near the center of the lens, even if the lens adjustment conditions are at medium magnification, there is no obstacle to image formation by the secondary charged particle beam obtained from the sample. There is. in this case,
It is not necessary to change the table of the exciting current values of the correction magnetic lens 9 for electron beam deflection and the converging lens 2 depending on the magnification. As described above, by controlling the electro-optical conditions by the acceleration voltage and the retarding voltage, the intermediate magnification (the scanning area is in a range of 100 μm to 10 μm in terms of the image plane) to the high magnification (the scanning area is in the range of less than 10 μm to 1 μm in terms of the image plane). Further, it is possible to acquire a high-resolution scanning electron microscope image without distortion from low magnification (the scanning area is in a range of more than 100 μm in image plane conversion and several hundred μm) to high magnification. At this time, the acquired image is displayed on the display device, and the magnification at the time of acquisition is also displayed.

Conventionally, the magnification of an image is divided into an intermediate magnification area of 1000 to 10,000 times and a high magnification area of 10,000 to 5 million times, and the desired magnification is adjusted by adjusting the lens conditions in each area. Was getting the image. For this reason, the diameter of the electron beam is set large in the intermediate magnification range. When switching to the high magnification area in this state, the resolution of the image deteriorates due to the large diameter of the electron beam, and only a blurred image is obtained, which is very difficult to see. On the other hand, according to the method of the present invention, it is possible to achieve display without shifting the center position of the image over an area where the magnification of the image is 1000 to 5,000,000 times. By the way, if the magnification error between the central part and the peripheral part of the image is larger than 5%, the displacement amount of the central position of the image can be judged by human eyes by 1 mm on the display screen.
(Equivalent to 0.1 μm in image plane conversion at a magnification of 10,000 times). Therefore, in the present method, a value smaller than this value is obtained.

As described above, in this optical system, the excitation conditions of the electron beam deflecting correction magnetic field lens 9 and the objective lens 7 are set to the conditions for correcting the distortion as described above, and the upper deflecting coil 4 and the lower There is an advantage that the magnification can be changed by changing the deflection current value of the deflection coil 5. That is, image observation in a wide range from low magnification to high magnification can be performed without blurring the image, and operability is improved.

Although the deflector has been described using a deflection coil as an example, the present invention is not limited to this, and can be applied to an electrostatic deflection plate.

Further, even if the electron source is an ion source and the correction magnetic field lens is changed to an electrostatic lens, the mounting operation can be performed so that the off-axis deflection distortion of the objective lens is canceled by the electrostatic lens. However, for the ion beam from the ion source, the acceleration voltage and the retarding voltage have polarities opposite to those of the electron beam. Next, the mounting configuration of the lens and coil for correcting the distortion generated in the objective lens and obtaining a scanning electron microscope image without blurring at intermediate magnification and high magnification will be described below with reference to FIGS. This will be described with reference to FIG.

FIG. 6 shows a second embodiment of the present invention, which is an example in which a correction magnetic lens for deflecting an electron beam is provided below a deflection coil. As shown in FIG. 6, a correction magnetic field lens path 12 for electron beam deflection is provided between the convergent lens path 10 and the objective lens path 14, and
And a lower deflection coil 5 wound around a deflection coil bobbin 16 and installed in a correction magnetic lens 13 for electron beam deflection.

The sample 8 is mounted on a sample stage 19,
It is arranged in the gap of the objective lens magnetic path. A converging lens coil 1 for exciting each lens is provided inside each lens.
1. A correction magnetic field lens coil 13 for electron beam deflection and an objective lens coil 15 are arranged. Since the gap of the lens magnetic path 12 of the correction magnetic field lens for electron beam deflection, that is, the lens main surface is below the lower deflection coil 5, it can be used as an optical system for correcting distortion as described above.

FIG. 7 shows an example of a configuration for realizing the above-mentioned optical system as in FIG. 6, and shows a third embodiment of the present invention. In this case, the correction magnetic field lens path 12 for deflecting the electron beam is disposed on the objective lens path 14, and the convergent lens path 1
A spacer 17 is arranged between the first and the second. By arranging the deflecting coil bobbin 16 at this spacer position, the configuration of the optical system similar to that of FIG. 6 can be obtained.

FIG. 8 shows an example of a configuration for realizing the above-mentioned optical system, similarly to FIG. 6, and shows a fourth embodiment of the present invention. In this case, the deflection coil bobbin 16 is arranged above and below the correction magnetic field lens magnetic path 12 for electron beam deflection, and the distortion for canceling the distortion of the objective lens at the intermediate stage of the deflection by the deflection coil is corrected by the electron beam deflection. An optical system similar to that shown in FIG. 6 is obtained by generating the correction magnetic field lens in the gap of the magnetic path. The sample 8 is held on a sample stage 19 in a sample chamber 18 installed below the objective lens magnetic path 14. This is an out-lens type objective lens generally used in a general-purpose scanning electron microscope, and can observe a large-sized sample unlike the in-lens type.

That is, a charged particle source, a converging lens for converging a charged particle beam generated from the charged particle source,
It has a sample stage on which a sample is mounted, and an objective lens for forming an image of a charged particle beam on the sample, and a correction for correcting distortion caused by the objective lens on the charged particle source side of the objective lens. The present invention is characterized in that a lens is arranged, and a first deflector and a second deflector are provided with a correction lens interposed therebetween.

FIG. 9 shows a fifth embodiment of the present invention, which is an example of a configuration for realizing the above-mentioned optical system using an out-lens type objective lens generally used in a general-purpose scanning electron microscope. is there. Above and below the objective lens magnetic path 14, a secondary electron detector 20 for detecting the intensity of the secondary electron beam generated from the sample by the irradiation of the primary electron beam is provided. An electric field magnetic field orthogonal type deflector (EXB type deflector ) 21 is installed in the objective lens magnetic path, and the secondary electrons can be efficiently supplied to the secondary electron detector 20 arranged on the objective lens without bending the primary electron beam. It is driven under conditions for good detection. The backscattered electron detector 22 includes the sample 8 and the objective lens magnetic path 14.
And detects the intensity of the electron beam reflected by the sample 8. The sample 8 is held on the sample stage 19 via the insulating plate 27. Note that the sample stage may be insulated in a two-stage structure. Sample 8 has a retarding voltage of 28.
Is applied to reduce the energy of the primary electron beam incident on the sample 8. This is to reduce the influence of aberration by passing a primary electron beam with high acceleration energy when passing through a deflector and an objective lens. This is because the energy of the primary electron beam is reduced immediately before the light is incident on the sample 8 to reduce the electron beam irradiation damage to the sample. The electrode 23 is grounded, and a
Forming an electric field for loading. Electron gun electrode 24
The electron gun acceleration voltage 26 is applied to the
It works to extract the primary electron beam from and accelerate it to a predetermined acceleration voltage.

An electron beam deflecting correction magnetic field lens for eliminating distortion of the magnetic field generated in the gap of the objective lens magnetic path 14 and aberration generated in the retarding electric field is provided by the objective lens magnetic path 14 and the deflectors 4 and 5. And the point provided between them.

In other words, in other words, a charged particle source and a deflector for deflecting the charged particle beam, a sample stage on which the sample is mounted, an objective lens for forming an image on the sample, the sample stage, and the objective A first lens for generating a deceleration electric field provided between the lens and a first lens for correcting a deflection distortion generated by the objective lens and the second lens on the charged particle source side of the objective lens; Is provided.

The second lens here has an electrode provided on the lower surface of the magnetic path of the objective lens and an electrode capable of applying a deceleration voltage to the sample on the sample stage. Work.

According to such a method, an image magnification of 10
It is possible to continuously display the image with a magnification error of 5% or less between the central portion and the peripheral portion of the image in the area of 00 to 5 million times.

Next, as a sixth embodiment of the present invention, an example in which the electron microscope apparatus is applied to inspection of a circuit pattern of a semiconductor element or the like will be described. In a defect inspection of a semiconductor element, a high-throughput inspection is required. On the other hand, one method is to shorten the total inspection time by enlarging one inspection area.

In the electron microscope of the present invention, distortion can be corrected at an intermediate magnification of the objective lens, so that even if the deflection width is increased, there is no distortion in the image. That is, since one image acquisition area can be made larger than that of the conventional method, the throughput can be improved by repeatedly using it for the inspection of the circuit pattern. In the conventional inspection method, inspection of one line is performed a predetermined number of times in synchronization with movement of the stage, and then inspection of the next line is sequentially performed by moving the stage. The throughput in the inspection of one line is determined by the time for comparing and inspecting one acquired image, and the total execution time is calculated by how many lines are repeated.

Here, a case where a 200 mm square area is inspected will be described. Conventionally, it is assumed that one inspection is performed on a 0.1 mm square, and in the present invention, the inspection is performed on a 1 mm square. First, the number of inspections for one image in the total inspection is reduced from 2000 × 2000 to 200 × 200. However, under the condition that the inspection is performed at the same resolution, the inspection pixels are also reduced when the inspection area is enlarged. Since it becomes large, there is no effect on improving the throughput in consideration of the calculation time. After the inspection of one line, the number of times the stage moves to the next line is reduced from 2,000 to 200.
If the time required for one stage movement is 1 second,
This results in a 30 minute throughput improvement. At present, the degree of throughput improvement is low because the total inspection time is as long as about 7 hours. However, if the total inspection time is reduced by improving the calculation time in the future, this method is one of effective means for improving the throughput. Become.

In other words, the sample having the repetitive circuit pattern is placed on the sample table, and the primary charged particle beam from the charged particle source is accelerated to image the primary charged particle beam on the sample. Irradiation is performed by passing through the objective lens, and the primary charged particle beam that has passed through the objective lens is decelerated by the decelerating electric field on the sample stage, and the deflection distortion generated when passing through the objective lens and the deflection distortion generated when passing through the decelerating electric field Is supplied to the correction lens that corrects the deflection. The first area of the repetitive pattern of the sample is scanned at a first intermediate magnification with a scanning area of 10 to 10 on the sample.
A range of 0 μm is scanned and detected and stored as a first image, and a second region is scanned and detected at a first magnification or a second intermediate magnification and stored as a second image. The circuit pattern is inspected for defects by comparing and inspecting the first and second images. At this time, a correction value determined in advance for the correction lens is set according to the magnification. The image obtained by the correction is stored as information on the magnification or the scanning range at the time of measurement, and the image and the information on the magnification or the scanning range are displayed on the screen upon request.

Thus, in the inspection apparatus, the scanning area is called for a correction value stored in advance by obtaining the deflection distortion due to the retarding voltage different depending on the sample in the range of 100 μm to 10 μm in terms of the image plane conversion, and the scanning area is converted to the image plane conversion 100
The detection in the range of [mu] m to 10 [mu] m has the effect of increasing the efficiency of the inspection.

Next, as a seventh embodiment, an inspection and review apparatus using the zoom function will be described.

The wafer has a chip on which a chip having a repeating pattern is formed. The wafer is placed on the sample stage, and the chip is divided into a plurality of regions. This area is 100
μm. After aiming at this area, the scanning width is set to 1
Scanning is performed while zooming up with a width of 00 μm to 10 μm. When the circuit pattern in the previous area is different, the scanning is stopped and the area having the defect is registered. When this process is performed on the entire chip, when a defect is large, it is detected at a low magnification, and a result can be obtained without scanning the entire 100 μm to 10 μm. This has the effect of shortening the defect inspection time of the circuit pattern. . By using this method, defects can be found in units of area, and parts without defects can be removed in units of area.
The area and the zooming range here are not limited to the embodiment, and may be any of low magnification, intermediate magnification, and high magnification.

A step of dividing a repetitive circuit pattern in a chip into a plurality of areas, a step of zooming up from a first scanning range to a second scanning range for each area, and a step of performing a defect pattern while zooming up. And a step of detecting the defect.

As an eighth embodiment, a combination of the present charged particle beam optical system and a eucentric sample stage will be described.

It is sometimes required that a sample is placed on a sample stage and a predetermined position, particularly the structure of the sample, is observed from various angles. At that time, the sample stage is tilted, and the charged particle beam is scanned using a deflector to scan an area including the target on the sample to search for the target. At this time, if the irradiation position changes in the height direction because the sample stage is inclined, the focal position shifts. In order to correct this and adjust the focus, the image plane position of the objective lens, that is, the focus is readjusted by changing the current of the objective lens. If the eucentric sample stage is used without going through such a process, the height of the irradiation position can always be the same in the inclined state, so that it is possible to obtain an in-focus image without having to re-focus. The reason is that if a correction lens operated to cancel the distortion when passing through the objective lens is arranged between the deflector and the objective lens, the field of view is searched even when the sample stage is inclined. It becomes possible. In this state, the scanning range of the charged particle beam is scanned at 100 μm or less, and the visual field search is performed with the ratio of displaying the image signal on the display screen at 1000 × to 10,000 × of the intermediate magnification. The microscopic observation enables a visual field search in a state where the sample stage is inclined. Here, the eucentric structure of the sample stage refers to a sample stage that can be adjusted so that the center of the field of view always coincides with the center of rotation of the sample stage when the charged particle beam is irradiated.

Next, a ninth embodiment will be described below.

An example in which the correction magnetic lens 9 operates as an auxiliary lens for assisting the deflector without using it for the distortion canceller will be described.

The magnification of the scanning electron microscope image can be changed by changing the deflection swing width. Here, it is assumed that the auxiliary magnetic field lens 9 is placed 66 mm above the objective lens in addition to the lens, the distance between the coils, and the excitation conditions used for the calculation of the deflection swing width in the optical system for high magnification image observation. The convergent lens image plane 3 is 78 mm above the auxiliary magnetic field lens 9.
Assume that The condition for matching the deflection fulcrum with the magnetic field focal plane before the objective lens is that the focal length of the auxiliary magnetic field lens 9 is 1 / (1/78 + 1/66) = 35.8 m.
m.

At this time, the deflection angle of the upper deflection coil is set to 50 m.
When set to rad, the deflection angle of the lower deflecting coil is 18 mrad from the condition of returning the electron beam to the center of the lens action of the auxiliary magnetic field lens 9, and the deflection swing width is 0.1 mm.
Becomes The image magnification under the same scanning electron microscope image display condition as above is 100 / 0.2 = 500 times. This is about twice as large as the deflection swing width r = 47 μm in the case of FIG. Therefore, without changing all the conditions of the converging lens 2, the objective lens 7, the upper deflecting coil 4 and the lower deflecting coil 5, only the lens action of the auxiliary magnetic field lens 9 reduces the intermediate magnification (1000 times) to one half. The image at the magnification can be observed.

An advantage of this optical system is that the optical axis of the auxiliary magnetic field lens 9 is made to coincide with the optical axis of the objective lens 7 mechanically or by a deflector, so that the displacement of the image at the time of switching between the intermediate magnification and the low magnification is reduced. It disappears and astigmatism is also common. Although not shown here, the astigmatism corrector is disposed between the objective lens and the charged particle source. This eliminates the need for adjustment at the time of switching. In some cases, the objective lens 7 can be used with the same excitation at the intermediate magnification and the high magnification. At that time, the image is not blurred due to hysteresis at the time of switching.

Further, since the swingback deflection system uses the upper stage deflection coil 4 and the lower stage deflection coil 5, there is no peripheral blurring of the image which occurs in the case of single stage deflection. The above embodiment is a case where the present invention is applied to a short-focus (2 mm lower) objective lens generally used in an in-lens type electron microscope, but a long focus (5 mm upper) used in an out-lens type electron microscope. When the above-mentioned optical system is applied to the objective lens, the effect is further enhanced. For example, if the focal length of the objective lens is assumed to be 10 mm in the above lens configuration, and the deflection angle of the upper deflection coil is set to 50 mrad, the deflection swing width is 0.4 mm and the image magnification is 100 mm.
A low magnification of /0.8=125 times is obtained.

That is, there is an effect that an image with less peripheral blur is obtained even at a low magnification.

[0087]

According to the present invention, in a charged particle beam apparatus, it is possible to obtain a high-resolution and distortion-free good image in a wide magnification range from low magnification to high magnification. It has become possible to continuously obtain images with little image shift between the low magnification image and the high magnification image.

[Brief description of the drawings]

FIG. 1 is a view showing a conventional high-magnification scanning electron microscope image observation optical system.

FIG. 2 is a diagram illustrating a result of distortion generated by an objective lens.

FIG. 3 is a view showing a conventional low magnification scanning electron microscope image observation optical system.

FIG. 4 is a diagram illustrating a basic configuration of the first embodiment of the present invention.

FIG. 5 is a diagram showing a result of correcting distortion generated in an objective lens according to the present invention.

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

FIG. 7 is a view for explaining a third embodiment of the present invention.

FIG. 8 is a view for explaining a fourth embodiment of the present invention.

FIG. 9 is a diagram illustrating a fifth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron source, 1 '... Optical axis, 2 ... Convergent lens, 3 ... Convergent lens image surface, 4 ... Upper deflection coil, 5 ... Lower deflection coil,
Reference numeral 6: deflection fulcrum, 7: objective lens, 8: sample, 9: correction magnetic lens (correction lens or correction magnetic lens) for electron beam deflection, 10: convergent lens magnetic path, 11: convergent lens coil, 12: electron beam Correction magnetic field lens magnetic path for deflection, 13 ...
Correction magnetic field lens coil (correction lens or correction magnetic field lens) for electron beam deflection, 14 ... objective lens magnetic path, 15 ... objective lens coil, 16 ... deflection coil bobbin, 17 ... spacer, 18 ... sample chamber, 19 ... sample stage, Reference numeral 20: secondary electron detector, 21: electric field magnetic field orthogonal type deflector, 22: reflected electron detector, 23: electrode, 24: electron gun electrode, 25: electron source chip, 26: electron gun acceleration voltage, 27: insulation Board, 28
... Retarding voltage. Objective lens image point

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsugu Sato 882 Ma, Hitachinaka-shi, Ibaraki Pref. Within the Measuring Instruments Group, Hitachi, Ltd. (72) Inventor Hiroyuki Shinada 1-280 Higashi-Koigabo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. In-house F-term (reference) 2H097 CA16 LA10 5C033 FF08 JJ05 UU01 UU02 5F056 AA01 EA05 EA06 EA08

Claims (14)

[Claims] 1. A converging lens for converging a charged particle beam, a sample stage on which a sample is mounted, an objective lens for forming an image of the charged particle beam on the sample, and distortion generated by the objective lens A correction lens that is excited so as to correct the aberration so as to cancel out the aberration, and a deflector for scanning the sample placed on the sample table with the correction lens therebetween with a charged particle beam. Charged particle beam microscope equipment. 2. A charged particle source, a converging lens for converging a charged particle beam generated from the charged particle source, and a deflector for deflecting the charged particle beam passing through the converging lens.
A sample stage on which a sample is placed, an objective lens for imaging the charged particle beam deflected by the deflector on the sample on the sample stage, and the objective lens between the objective lens and the deflector And a correction lens for correcting distortion generated in the charged particle beam application apparatus. 3. The charged particle beam application apparatus according to claim 2, wherein said deflector comprises an upper deflector and a lower swing back deflector. 4. The charged particle beam application apparatus according to claim 2, wherein the correction lens has a distortion in a direction to cancel the distortion of the objective lens. 5. A deflector for deflecting a charged particle beam, a sample stage on which a sample is mounted, and an objective for imaging the charged particle beam deflected by the deflector on the sample on the sample stage. A lens, a second lens provided between the sample stage and the objective lens, and a deflection distortion generated by the objective lens and the second lens between the objective lens and the deflector. Charged particle beam application apparatus, comprising a first lens for use in the apparatus. 6. An electrostatic lens formed by applying a voltage between an electrode provided on a lower surface of a magnetic path of the objective lens and an electrode capable of applying a deceleration voltage to a sample on the sample stage. The charged particle beam application device according to claim 5, wherein: 7. An objective lens for converging and irradiating a primary charged particle beam on a sample on a sample stage, a deflector for deflecting the primary charged particle beam, and provided below a magnetic path of the objective lens. A first electrode, a second electrode provided on the sample stage,
A correction lens is provided between the deflector and the objective lens for correcting an aberration received when a primary charged particle beam passes through a deceleration electric field generated between the first and second electrodes. Charged particle beam application equipment. 8. A step of placing a sample on a sample stage, and passing the charged particle beam through a charged particle beam optical system for focusing the charged particle beam so that the scanning width of the charged particle beam on the sample is in a range of 10 μm to 100 μm. Irradiation step of irradiating, a step of correcting the deflection distortion generated when the charged particle beam passes through the charged particle beam optical system in the irradiation step, and a visual field search step of detecting a target within the scanning range, A charged particle beam microscopy method characterized by having: 9. An image storing step of imaging and storing a signal from the detector as the visual field searching step, and displaying the stored image with a magnification error of 5% or less between a central portion and a peripheral portion of the image. The charged particle beam microscopy method according to claim 8, wherein: 10. A step of placing a sample on a sample stage, and a first scanning width which passes through a charged particle beam optical system for converging the charged particle beam and has a scanning width larger than 100 μm on the sample. A first scanning step of scanning the sample so that the display ratio on the display device when scanning is performed at a low magnification of less than 1000 times, and the charged particle beam passes through the charged particle beam optical system at the low magnification Correcting the first distortion generated when the first scanning is performed, a first detecting step of detecting a secondary charged particle based on a first scanning width from the sample with a detector, and a first detecting step from the detector. A first image storing step of imaging and storing the signal, a first image displaying step of displaying the stored first image, and a second scanning width of the charged particle beam on the sample having a scanning width of 100 μm to 10 μm. The display ratio on the display device when scanning at a size of 1000 times A second scanning step of scanning over the sample so as to display at an intermediate magnification of 10,000 times, and correcting a second distortion generated when the charged particle beam passes through the charged particle beam optical system at the intermediate magnification. A second detection step of detecting secondary charged particles based on a second scanning width from the sample from the detector, and a second image for imaging and storing a second signal from the detector. A charged particle beam microscopy method, comprising: a storage step; and a second image display step of displaying a stored second image. 11. A step of dividing a repetitive circuit pattern in a chip into a plurality of regions, and irradiating a first region of the plurality of regions with a charged particle beam to form a first region between a first scanning region and a second scanning region. A first scanning step of scanning so as to zoom in 1; a first image forming step of detecting a secondary charged particle from the wafer with a detector during the first zooming up to obtain a first image signal; A first storage step of storing the first image signal; and a second zooming-up operation between the first scanning range and the second scanning range by irradiating the second region of the plurality of regions with a charged particle beam. A second scanning step in which the secondary charged particles are scanned from the wafer by the second zooming up during the second scanning step, and the secondary charged particles from the wafer are detected by the detector.
A charged particle beam inspection method, comprising the steps of: forming an image; and detecting a defect pattern from the first and second image signals. 12. A step of mounting a sample having a repetitive circuit pattern on a sample stage, a step of accelerating a primary charged particle beam from a charged particle source, and an objective lens for imaging the primary charged particle beam on the sample. Irradiating through the objective lens, decelerating the primary charged particle beam passing through the objective lens by the deceleration electric field on the sample stage, passing through the deflection distortion and deceleration electric field generated by passing through the objective lens Supplying a deflection distortion correction amount to a correction lens that corrects the deflection distortion generated at the time of scanning; and scanning and detecting the first region of the repetitive pattern of the sample at the first magnification and storing the same as a first image. A first storage step, a second storage step of scanning and detecting a second area at a first magnification and storing the same as a second image, and comparing and inspecting the first and second images. Characterized charged particle beam detection Method. 13. An electrostatic lens having one or more stages for accelerating an electron beam generated from an electron source to a predetermined voltage, a converging lens having one or more stages for converging and irradiating the sample with the electron beam, and An objective lens and a 1 for deflecting the electron beam.
A deflector having more than one step, and a correction magnetic lens for correcting distortion generated in the objective lens, and an electron beam is deflected on the sample surface by electron beam deflection by the deflector, the correction magnetic lens, and the objective lens. An image display device that scans two-dimensionally at a time, detects the intensity of an electron beam secondary generated from the sample in synchronization with the scanning of the electron beam, modulates brightness, and displays a scanning electron microscope image. An electron microscope apparatus characterized in that: 14. An electron beam source, a converging lens for converging an electron beam generated from the electron beam source, a deflector for deflecting the electron beam passing through the converging lens, and a deflector for deflected by the deflector. Using an objective lens for forming an image of the electron beam on the sample, the electron beam is scanned over the sample, and an electron beam generated secondarily from the sample is detected to obtain a two-dimensional scanning electron microscope image. In an electron microscope apparatus configured to acquire
An electron microscope apparatus, comprising: an exciting magnetic field lens provided in a direction opposite to an exciting direction of the objective lens on an electron beam source side of the objective lens.