JPH11233058A - Electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly precisely extract particle in a wide area of a specimen for a long duration by setting the binary threshold value corresponding to the alteration of electron beam at the time of extracting particle from an image. SOLUTION: Electron beam 1 passes a route kept in highly vacuum state, is deflected by a magnetic field of a deflecting coil 2, and scan a specimen while being converged upon the specimen 5 by an objective lens 3. When electron beam 1 is radiated to the specimen 5, specimen signals of reflected electrons and secondary electrons are generated while reflecting the shape of the specimen 5 and the specimen signals are detected by a detector 7, converted into digital signals, and stored in an image memory 8. After that, the signals are displayed as an image on a display apparatus 10 by a control and processing device 9. In this case, the brightness level of the reflected electron signals is increased more as the atomic number increases more, and utilizing such a characteristic property, particle extraction is carried out and reflected electron image is obtained. A black and white binary image is constituted by previously setting the threshold value and the particle extraction is carried out in the binary image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly accurate particle extraction method for extracting particles using an image of a scanning electron microscope.

[0002]

2. Description of the Related Art In particle extraction of a sample by using an image of a scanning electron microscope, reflected electrons generated by scanning a sample inserted into a sample chamber maintained in a high vacuum with a small area on the sample with an electron beam. Using the brightness level of the image,
A fixed threshold value is set, and a target particle is extracted by the binarization process.

[0003]

According to the above-mentioned extraction method, extraction is possible when the luminance level of reflected electrons is stable, such as in a short time within a small area on the sample. However, when performing a wide area for a long time, if the luminance level of the reflected electrons fluctuates due to fluctuations of the electron beam or the like, the relationship between the threshold and the luminance changes, so that accurate particle extraction cannot be performed. An object of the present invention is to perform highly accurate particle extraction for a long time.

[0004]

According to the present invention, the threshold value for the binarization processing is set in conjunction with the fluctuation of the luminance level of the backscattered electron image, thereby setting the luminance level and the threshold value. The purpose is achieved by keeping the relationship constant.

That is, the present invention provides a deflecting means for scanning an electron beam on a specimen, a specimen moving means for moving the specimen, an image memory for storing an image detected by the above, and an image memory for the image memory. Means for processing the stored image, image display means, and in a scanning electron microscope comprising means for controlling each, when performing particle extraction from the image,
By setting the threshold value to a constant multiple of the base luminance level from the 0 level of the backscattered electron luminance, the threshold value for binarization is always calculated and set in accordance with the fluctuation of the base level, so that it can be used for a long time. It is characterized in that a wide area of a sample is extracted with high precision.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a scanning electron microscope according to the present invention. In the drawing, reference numeral 1 denotes an electron beam, and 2 denotes a deflection coil for scanning the surface of the electron beam or irradiating a point or a line on the sample, and includes deflection coils for X and Y directions. Reference numeral 3 denotes an objective lens for focusing the electron beam 1 on the sample, 4 denotes a sample chamber maintained in a high vacuum state, 5
Denotes a sample, 6 denotes a sample moving means, and 6a denotes a sample stage for loading the sample. The sample moving means 6 comprises a well-known XY stage (sample moving stage) in which a motor and a rotary encoder are mounted on a rotating shaft for moving the sample.
The coordinate position of the sample can be managed. 7 is a detector for detecting signals such as backscattered electrons generated from the sample;
Is an image memory for digitizing the detection signal from the detector 7 and storing it as image data. Reference numeral 9 denotes a control and processing device using a microcomputer or the like, and 10 denotes an image display device. The control device 9 is connected to input means 11 such as a mouse and a keyboard. Reference numeral 12 denotes a detector for elemental analysis for detecting characteristic X-rays generated from a sample, and reference numeral 13 denotes a control unit for performing elemental analysis based on the energy of the detected X-rays. This device has a function of detecting the electron beam current of the reflected electrons obtained by the detector.

The electron beam 1 passes through a path maintained in a high vacuum state, is deflected by the magnetic field of the deflection coil 2, is focused on the sample 5 by the objective lens 3, and scans the sample 5. When the sample 5 is irradiated with an electron beam, sample signals such as reflected electrons and secondary electrons are generated reflecting the shape of the sample 5. The sample signal generated from the sample 5 is detected by the detector 7, digitally converted and stored in the image memory 8,
An image is displayed on the display device 10 via the control device 9.

In this case, in particular, since the luminance level of the reflected electron signal increases as the atomic number increases, particles are extracted by utilizing the characteristic. For example, a backscattered electron image as shown in FIG. 3 is obtained as an example in which metal particles having a large atomic number are scattered in a light element base such as carbon (C: atomic number 6). Although not shown in this figure, different types of particles are displayed with different shades. The corresponding histogram diagram (distribution frequency diagram of the luminance level) is as shown in FIG. 2, and a black-and-white binary image is formed by setting a threshold value (threshold) in advance. That is, the carbon base and other particles are displayed in black and white, and are truly displayed as shown in FIG.

[0010] Particles are extracted from the binarized image shown in FIG. 3 and the position, size, and the like are calculated by the processing unit 9.
Here, the position calculation is based on the position on the image and the sample moving stage 6.
The above coordinates are converted. As an application, the calculated coordinate position is irradiated with an electron beam, the characteristic X-ray generated from the extracted particle portion is detected by the detector 12, and the elemental analysis of the particle can be automatically performed by the control processing portion 13. The combination of the sample moving stage 6 enables automatic elemental analysis of a wide area.

However, when performing long-time particle extraction, the amount of current of the electron beam may be reduced due to a change in the electron source of the scanning electron microscope or the like, and the luminance level of the reflected electron image obtained is also reduced.

FIG. 4 shows a histogram when the luminance level is reduced. Here, in the conventional binarization method, since the threshold is a fixed value that is initially set, a binarized image as shown in FIG. 5 is obtained, and accurate particle extraction may not be performed as compared with FIG. This is because particles having brightness near the threshold may not be able to be extracted due to fluctuations in the electron beam current.

The processing of the embodiment of the present invention will be described below. First, as shown in FIG. 6, when the reflected electron signal in the state where the electron beam is OFF is set to 0, the luminance level of the element serving as a base (carbon in the example) is set to A, and the threshold value is set to a constant α times the base level A. And initial settings. Here, the constant α can be arbitrarily set according to the atomic number of the particle to be extracted.

At the time of analysis for a long time, a histogram of the base level is calculated at any time. Since the threshold value changed, reliable particle extraction became possible. In addition, in order to further subdivide the extraction of particles by atomic number, constants α and β can be set as shown in FIG. 8, and a ternary or higher threshold can be set in the same manner.

[0015]

According to the present invention, in a scanning electron microscope or the like, the accuracy of automatic elemental analysis or the like by particle extraction based on a wide area image on a sample is improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a scanning electron microscope according to the present invention.

FIG. 2 is a diagram showing a state in which a threshold is set on a histogram.

FIG. 3 is a view showing a sample image obtained by a scanning electron microscope according to the present invention.

FIG. 4 is a diagram illustrating a histogram when a luminance level is reduced.

FIG. 5 is a diagram showing a binarized image based on an initially set threshold.

FIG. 6 is a diagram showing a histogram when the threshold is changed.

FIG. 7 is a diagram showing a histogram when the threshold is changed.

FIG. 8 is a diagram showing a threshold and a histogram when ternarization is performed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron beam, 2 ... Deflection coil, 3 ... Objective lens, 4
... Sample chamber, 5 ... Sample, 6 ... Sample moving stage, 6a ... Sample stage, 7 ... Detector, 8 ... Image memory, 9 ... Control / processing device, 10 ... Display device, 11 ... Input means, 12 ... Elemental analysis Detector 13; control circuit for elemental analysis.

Claims (3)

[Claims] 1. A deflection means for scanning a focused electron beam on a sample, a means for detecting a signal such as a reflected electron generated from the sample, a means for moving the sample, and an image detected by the means. In the scanning electron microscope including an image memory that stores the image, a unit that processes the image stored in the image memory, an image display unit, and a unit that controls each unit, when performing particle extraction from the image, By setting the threshold value in conjunction with the fluctuation of the electron beam,
An electron microscope characterized by extracting particles from a wide area of a sample with high precision for a long time. 2. The electron microscope according to claim 1, wherein, at the time of the particle extraction, the image is classified into three or more values. 3. The electron microscope according to claim 1, wherein an elemental analysis using X-rays or the like is automatically executed by sequentially irradiating an electron beam to a particle position extracted by the particle extraction.