JPH05325860A - Method for photographing image in scanning electron microscope - Google Patents

Abstract

PURPOSE:To provide a method for phoptographing images using a scanning electron microscope whereby precise sample images can be taken even if the samples are likely to be damaged by heating due to exposure to an electron beam. CONSTITUTION:The portion of a sample to be photographed is disposed on an electron beam optical axis and then a cursor signal is generated from a cursor signal generator 10 and is fed to a cathode-ray tube together with an image signal. As a result, e.g. four cursors are superimposed in a scanned image and displayed on the screen of the cathode-ray tube 9. An operator controls the generator 10 so that the portion of the sample to be photographed is surrounded by the four cursors. In the photographic mode, a scanning signal from a scanning signal generator circuit 6 indicates a relatively slow scanning speed suitable for photographing in the portion of the sample which corresponds to the area surrounded by the four cursors, while in the areas other than that surrounded by the four cursors the scanning speed is held at that for rapid scanning.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image capturing method in a scanning electron microscope which is optimal for capturing a scanned image of a sample which is easily damaged by an electron beam.

[0002]

2. Description of the Related Art In a scanning electron microscope, when a scan image of a sample is taken, first, a desired region of the sample is scanned with an electron beam at a relatively high scanning speed and, for example, a secondary scan generated based on this scanning The electrons are detected and a detection signal is supplied to the cathode ray tube. At this time, focusing of the electron beam and correction of astigmatism are performed. Of course, the field of view of the part where you want to take a picture is also searched in parallel. Then, after the focusing of the electron beam and the correction of astigmatism are completed and the field of view is also completed, the electron beam is changed to a relatively slow scanning speed, and the electron beam scanning of a predetermined sample region is performed. The secondary electron signal obtained at the slow scanning speed is supplied to the cathode ray tube synchronized with the electron beam scanning on the sample to display the scanning secondary electron image. A photographic camera is arranged in front of the cathode ray tube, and as a result, a scan image is taken. The reason why the scanning speed of the electron beam at the time of image capturing is slowed is that the staying time of the electron beam on the sample is lengthened and a large amount of secondary electron signals from the sample are generated correspondingly to improve the SN ratio of the detection signal. This is to make it happen.

[0003]

In the above-mentioned photographing method, since the electron beam is slowly scanned over the entire observation region of the sample at the time of image capturing, the temperature of the observation region of the sample becomes extremely high, and the resist pattern, etc. In the image capturing, the sample is severely damaged, and in some cases, the surface shape of the sample is deformed so as to be different from the original shape, and an accurate image cannot be captured. Alternatively, the pattern after the electron beam scanning for photography is destroyed, and the nondestructive inspection which is a characteristic of the scanning electron microscope cannot be achieved. For example, after taking a photo of a resist pattern, the imaged part was scanned with an electron beam at a high scanning speed for observation and the image was observed. It became clear that it has spread. In order to reduce the damage to the sample, a protective metal film (for example, Au) is formed on the sample surface.
Even if -Pd) is vapor-deposited thickly or the accelerating voltage or beam current of the electron beam is lowered, the shape change of the sample surface due to the slow electron beam scanning for photography is inevitable. The present invention has been made in view of the above circumstances, and an object thereof is to provide a scanning electron microscope capable of capturing a precise sample image even for a sample that is easily damaged by heating due to electron beam irradiation. To realize the image capturing method in.

[0004]

An image capturing method in a scanning electron microscope according to the present invention comprises scanning a sample with an electron beam and converting a signal from the sample obtained by the electron beam irradiation into an electron beam scan on the sample. In a scanning electron microscope that is adapted to display a sample image on a synchronized cathode ray tube, the electron beam is scanned on the sample at a relatively high scanning speed, and the cathode ray is scanned based on the signal obtained from the sample by this scanning. A sample image is displayed on the tube, a specific area is selected based on this sample image, and electron beam scanning is performed at a relatively slow scanning speed only on the sample part of the selected area. The sample image is displayed on the cathode ray tube based on the signal, and the sample image is photographed.

[0005]

In the image capturing method for the scanning electron microscope according to the present invention, a specific region in a sample image displayed in advance is selected, and electron beam scanning is performed at a relatively slow scanning speed only in the sample portion in the selected region. The sample image is displayed on the cathode ray tube based on the signal obtained from the sample by this scanning, and the sample image is photographed.

[0006]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an example of a scanning electron microscope for carrying out the present invention, and 1 is an electron gun. The electron beam generated from the electron gun 1 is finely focused on the sample 4 by the focusing lens 2 and the objective lens 3. The irradiation point of the electron beam on the sample 4 can be changed by deflecting the electron beam by the deflection coil 5. A scanning signal from the scanning signal generation circuit 6 is supplied to the deflection coil 5. Sample 4
The secondary electrons generated by the irradiation of the electron beam on the
It is detected by the secondary electron detector 7. The signal detected by the detector 7 is amplified by the amplifier 8 and then supplied to the cathode ray tube 9 to which the scanning signal from the scanning signal generation circuit 6 is supplied. Reference numeral 10 denotes a cursor signal generator. The cursor signal from the cursor signal generator 10 is added to the signal from the detector 8 in the adder 11 and supplied to the cathode ray tube 9. Reference numeral 12 is a control circuit, and the control circuit 1
2 controls the waveform of the scanning signal from the scanning signal generation circuit 6 arbitrarily and based on the cursor signal from the cursor signal generator 10. The operation of such a configuration will be described below.

First, the control circuit 12 controls the scanning signal generating circuit 6 in order to focus the electron beam with which the sample 4 is irradiated, correct astigmatism, and search the field of view.
A scanning signal having a relatively high scanning speed (rapid scanning) such as a commercial TV scanning speed is generated. Focusing of the electron beam and correction of astigmatism are performed in such a rapid scanning state, and further, the operation of selecting the observation visual field is executed by moving the sample 4. After the sample portion to be photographed is placed on the optical axis of the electron beam by the field-of-view searching operation, a cursor signal is generated from the cursor signal generator 10 and supplied to the cathode ray tube 9 together with the image signal. As a result, four cursors C _{1 to} C ₄ are displayed on the screen of the cathode ray tube 9 so as to be superimposed on the scanning image, as shown in FIG. The positions of the cursors C _{1 to} C ₄ can be changed by controlling the cursor signal generator 10, and the operator controls the generator 10 so that the image portion to be photographed is surrounded by four cursors. ..

After the area designation by the four cursors is completed, the control circuit 12 executes the photography mode.
In this photography mode, the scanning signal from the scanning signal generation circuit 6 causes the sample portion corresponding to the area A surrounded by the _four cursors C _{1 to} C ₄ to perform a relatively slow scanning suitable for photography. Areas other than the area A surrounded by the four cursors are maintained at the scanning speed of rapid scanning. As a result, in the area A, S
Secondary electrons can be detected with a good N ratio, and a clear image is captured. Then, the amount of the electron beam applied to the sample 4 during the scanning of the electron beam for one screen is significantly reduced as a whole because it is in the rapid scanning state except for the target portion selected by the cursor. .. Therefore, the sample is less heated by the electron beam irradiation, and the sample 4 can be prevented from being damaged, so that a photograph can be taken without breaking the shape of the sample surface.

Although the embodiment of the present invention has been described in detail above, the present invention is not limited to this embodiment. For example, the case of displaying a secondary electron image has been described in detail, but the present invention can also be applied to the case of capturing a backscattered electron image, a cathode luminescence image, an X-ray image, or the like. Also, a single cathode ray tube was used, but there are two types, one for visual observation (for visual field search) and one for photography.
You may use one cathode ray tube. Further, although the attention area to be photographed is selected by the cursor, the luminance of the attention area may be set higher than the others. Then, the electron beam may not be scanned except for the selected photographed portion. Furthermore, it is also possible to display two cursors in a specific direction so that a long and narrow area can be selected, and conversely, four or more cursors can be used to designate a plurality of photography areas at once. It may be configured.

[0010]

As described above, the image capturing method in the scanning electron microscope according to the present invention selects a specific area in a sample image displayed in advance, and relatively selects only the sample portion in the selected area. Electron beam scanning is performed at a slow scanning speed,
Since the sample image is displayed on the cathode ray tube based on the signal obtained from the sample by this scanning and the sample image is photographed, even if the sample is easily damaged by heating due to electron beam irradiation. , It is possible to take a precise sample image. Moreover, the sample surface is not destroyed by the electron beam scanning after the photography. Further, since only the portion to be photographed is scanned with the electron beam at a low speed and the other portion is scanned at a high speed or the electron beam is not scanned, the photographing time can be remarkably shortened.

[Brief description of drawings]

FIG. 1 shows an example of a scanning electron microscope for carrying out the method according to the invention.

FIG. 2 is a diagram showing a sample image and a cursor displayed on a cathode ray tube.

[Explanation of symbols]

 1 electron gun 2 focusing lens 3 objective lens 4 sample 5 deflection coil 6 scanning signal generating circuit 7 secondary electron detector 8 amplifier 9 cathode ray tube 10 cursor signal generator 11 adder 12 control circuit

Claims (1)

[Claims] 1. A sample image is displayed by scanning an electron beam on the sample and supplying a signal from the sample obtained by the electron beam irradiation to a cathode ray tube synchronized with the electron beam scanning on the sample. In a scanning electron microscope, electron beam scanning is performed on a sample at a relatively high scanning speed, a sample image is displayed on the cathode ray tube based on the signal obtained from the sample by this scanning, and a specific area is displayed based on this sample image. The electron beam scanning is performed at a relatively slow scanning speed only in the sample portion of the selected area, and the sample image is displayed on the cathode ray tube based on the signal obtained from the sample by this scanning. An image capturing method in a scanning electron microscope adapted to photograph an image.