JPH06251741A - Automatic magnifying power setting method in scanning electron microscope - Google Patents

Abstract

PURPOSE:To provide an automatic magnifying power setting method in a scanning electron microscope by which observation magnifying power optimum for the size of an attention area of a sample or a recessed and projecting condition on a sample surface can be set automatically. CONSTITUTION:A computer 12 controls a scanning circuit 6 through a DA converter 13, and changes a scanning width of an electron beam on a sample 4 from the minimum to the maximum. A secondary electron generated according to scanning of the electron beam is detected by a detector 7, and the detecting signals are supplied to the computer 12 through a filter circuit 10 and an AD converter 11. The computer 12 integrates and stores the detecting signals during the single time two dimensional scanning on the sample 4. The computer 12 detects a scanning width when the maximum signal strength is obtained, and sets the scanning width of the electron beam in the value, and when an image is obtained in this scanning width, an attention area of the sample can be observed in the.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention two-dimensionally scans an electron beam on a sample, detects secondary electrons and backscattered electrons obtained based on this scanning, and detects the sample based on this detection signal. The present invention relates to an automatic magnification setting method in a scanning electron microscope which obtains a scanning image.

[0002]

2. Description of the Related Art A scanning electron microscope is constructed so that an observation magnification can be arbitrarily set, and an operator of the scanning electron microscope manually sets a desired magnification before observing a sample, or a fixed magnification. Is used to observe the image.

[0003]

In the observation of the above-mentioned scanning image, it is necessary to set the magnification so that the region of interest can be optimally observed in the sample to be observed. However, if the size of the region of interest of the sample is already known, it is possible to set the optimum magnification for that size, but it is usually difficult to know the size of the region of interest of the sample, so it is optimal. Finding and setting the magnification is not only a tedious task, but also requires skill. Further, an appropriate magnification must be set depending on the state of the unevenness of the sample surface (whether it is rough unevenness or fine unevenness), but this magnification setting must also depend on the skill of the observer.

The present invention has been made in view of the above points, and an object thereof is to be able to automatically set an optimum observation magnification for the size of the region of interest of the sample and the unevenness of the sample surface. It is to realize an automatic magnification setting method in a scanning electron microscope.

[0005]

An automatic magnification setting method in a scanning electron microscope based on the present invention is obtained from a sample by finely focusing the electron beam on the sample and scanning the electron beam two-dimensionally on the sample. In a scanning electron microscope configured to obtain a scanning image of a sample based on the information obtained, the scanning width of the electron beam on the sample is gradually changed, and the intensity of the signal obtained from the sample is stored for each scanning width, It is characterized in that the scanning width at the maximum value of the stored signal intensity for each scanning width is detected and the electron beam is scanned by this scanning width to obtain a scanned image of the sample.

[0006]

The automatic magnification setting method in the scanning electron microscope according to the present invention gradually changes the scanning width of the electron beam on the sample, stores the intensity of the signal obtained from the sample for each scanning width, and stores it. The scanning width at the maximum value of the signal intensity for each scanning width is detected, and the image is observed by setting the magnification based on this scanning width.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an example of a scanning electron microscope for carrying out the automatic magnification setting method according to the present invention.
1 is an electron gun. The electron beam EB generated and accelerated by the electron gun 1 is focused on the sample 4 by the focusing lens 2 and the objective lens 3. Further, the electron beam EB is transmitted to the deflector 5
The sample 4 is deflected, and the sample 4 is two-dimensionally scanned.
A scanning signal is supplied to the deflector 5 from the scanning circuit 6.

Secondary electrons generated by the irradiation of the sample 4 with the electron beam are detected by the secondary electron detector 7. The detection signal of the detector 7 is amplified by the amplifier 8 and then supplied to the cathode ray tube 9 and the filter circuit 10. The output signal of the filter circuit 10 is
It is supplied to the computer 12 via the AD converter 11. The computer 12 controls the scanning circuit 6 via the DA converter 13 and controls the filter circuit 10 via the DA converter 14. The operation of such a configuration will be described below.

First, when observing a normal secondary electron image,
From the scanning circuit 6, the deflector 5 is supplied with a scanning signal for two-dimensionally scanning a desired region on the sample 4 with an electron beam. Secondary electrons generated based on the scanning of the electron beam on the sample 4 are detected by the detector 7. Detector 7
The detection signal of is supplied as a brightness modulation signal to the cathode ray tube 9 synchronized with the two-dimensional scanning of the electron beam, so that the secondary electron image of the sample is displayed on the cathode ray tube 9.

Next, a method of setting the optimum magnification in the region of interest on the sample 4 will be described with reference to the flowchart of FIG. First, when the computer 12 is instructed to start the automatic magnification setting function, the computer 12 controls the scanning circuit 6 via the DA converter 13 to generate a scanning signal that minimizes the scanning width of the electron beam on the sample 4. . As a result, the electron beam performs two-dimensional scanning of the smallest area on the sample 4. That is, the electron beam is scanned in the highest magnification state.

Secondary electrons generated by the scanning of the electron beam are detected by the detector 7, and the detection signal is supplied to the filter circuit 10. The filter circuit 10 is a band-pass filter and passes a signal in a frequency band corresponding to the scanning speed of the electron beam, which is determined by the scanning width of the electron beam. The pass frequency band of the filter circuit 10 is controlled by the computer 12 based on the scanning speed of the electron beam on the sample according to the scanning width at that time. The output signal of the filter circuit 10 is converted into a digital signal by the AD converter 11 and then supplied to the computer 12. The computer 12 integrates the signals supplied from the AD converter 11 during one two-dimensional scanning on the sample 4 and stores it.

Next, the scanning width of the electron beam on the sample 4 is expanded by a certain length (scanning width is increased), and the two-dimensional scanning of the electron beam on the sample and the integration and storage of the detection signals are performed.
The integration and storage of the signal intensity while changing the scanning width is repeatedly performed up to the maximum value of the scanning width of the electron beam. That is, from the highest magnification to the lowest magnification, 1
Calculate the integrated value of the detection signal for each frame. FIG. 3 shows the relationship between the scanning width of the electron beam and the signal intensity thus obtained. The horizontal axis of the figure is the scanning width (frequency), and the vertical axis is the integrated value of the signal intensity.

In the relationship of FIG. 3, the scanning width D when the maximum signal intensity is obtained is detected, and the scanning width (magnification) of the electron beam is set to that value, and if the image is obtained, the sample is noticed. The area can be observed in the optimum condition. In other words, when the region of interest partially exists in the smooth sample surface, the signal intensity becomes maximum when the region of interest is efficiently included in the scanning region of the electron beam, and the signal intensity becomes maximum. If the image is obtained by scanning the electron beam with the scanning width of
The attention area is displayed on the entire screen. In this case, it is desirable that the attention area is arranged on the optical axis in advance.

Further, when unevenness exists uniformly on the sample surface, the scanning width is changed to detect the maximum scanning width of the signal intensity, and the electron beam is two-dimensionally scanned with the scanning width of the maximum signal intensity. When the image is obtained, the unevenness is most clearly displayed.

Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment. For example, although secondary electrons are detected, similar results can be obtained by detecting reflected electrons. Further, when the scanning width is changed, the state of high magnification is changed to the state of low magnification, but conversely, the state of low magnification may be changed to the state of high magnification. Further, the automatic magnification adjusting operation based on the present invention can be used together with the automatic focusing function, the automatic image quality adjusting function such as contrast and brightness, or the automatic astigmatism correcting function.

[0016]

As described above, the automatic magnification setting method in the scanning electron microscope according to the present invention gradually changes the scanning width of the electron beam on the sample, and the signal obtained from the sample for each scanning width. Of the sample, the scanning width at the time of the maximum value of the signal strength for each scanning width stored was detected, and the image was observed by setting the magnification based on this scanning width. The optimum observation magnification can be automatically set according to the size of the region of interest or the unevenness of the sample surface.

[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 flowchart of an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between secondary electron detection signal strengths corresponding to electron beam scanning widths.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electron gun 2 Focusing lens 3 Objective lens 4 Sample 5 Deflector 6 Scanning circuit 7 Secondary electron detector 8 Amplifier 9 Cathode ray tube 10 Filter circuit 11 AD converter 12 Computer 13,14 DA converter

Claims (1)

[Claims] 1. A scanning electron microscope in which an electron beam is finely focused on a sample, the electron beam is two-dimensionally scanned on the sample, and a scan image of the sample is obtained based on information obtained from the sample. , The scanning width of the electron beam on the sample is gradually changed, the intensity of the signal obtained from the sample is stored for each scanning width, and the scanning width at the time of the maximum value of the signal intensity stored for each scanning width Is detected and the electron beam is scanned by this scanning width to obtain a scan image of the sample.