JPH11185690A - Scanning electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning electron microscope suitable for automatic brightness and contrast regulation with a simple constitution even in a cathode luminescence optical system. SOLUTION: A secondary electron signal detected by a secondary electron detector 4 is led to a signal amplifying system and an A/D converter 13 to be converted to a digital signal, and the converted digital signal is stored in an image memory inside a signal processing means 32. A cathode luminescence signal detected by a cathode luminescence detector 23 is also led to an amplifier of a secondary electron processing system and the A/D converter 13 to be converted to a digital signal, and the converted signal is stored in the image memory inside the signal processing means 32. A resulting secondary electron image and a resulting cathode lumunescence image are selectively displayed on a display 16, and the superimposed image of them is displayed on an image synthesizing and displaying means 35 of a personal computor 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope, and more particularly to a scanning electron microscope which irradiates a sample with an electron beam, detects electrons and cathodoluminescence emitted from the sample, and displays respective images. About.

[0002]

2. Description of the Related Art When a sample is irradiated with an electron beam, fluorescence emitted from the sample in the ultraviolet to infrared region is collectively referred to as cathodoluminescence. The obtained cathodoluminescence light is guided to a spectroscope by an optical fiber, and its intensity is measured. In addition,
Dolescence gives important information along with characteristic X-rays, reflected electrons, secondary electrons, and the like generated by the interaction between an electron beam and a substance. Therefore, observation of a cathodoluminescence image is also performed. Since it is easy to narrow the electron beam for irradiating the sample, systems for obtaining a cathodoluminescence spectrum measurement and a cathodoluminescence image observation have been gradually spread to obtain electrical and optical characteristics in a minute area. I have.

In such a system, an electron beam irradiation unit of a scanning electron microscope (including a transmission electron microscope having a function of a scanning electron microscope and a scanning transmission electron microscope) can be used as it is. However, the light emission characteristics of cathodoluminescence differ greatly depending on the band gap of the sample, and are dependent on the electron beam irradiation conditions such as acceleration voltage and sample current, and scanning methods such as surface scanning, line scanning, and spot scanning. The inability to capture light well,
In addition, it is usual to set various electron beam irradiation conditions and observation conditions as needed for each measurement, such as difficulty in determining the brightness and contrast of an image for observation.

A Cassodo-Luminescence image is divided into two types: a single wavelength dispersion image in which wavelength dispersion is performed with a certain wavelength width, and a non-dispersion image in which light emission in the entire measurable range without wavelength dispersion is imaged. In order to accurately analyze the position information of the light emission, it is general to superimpose a secondary electron image on one of them and use it for evaluation. However, as compared with minerals, cathodoluminescence light of polymer materials, biological samples, and the like is often weak in intensity, and the sample is damaged by an electron beam. In many cases, it depends on the skill of the operator. In particular, since the intensity of the wavelength dispersion image is relatively weaker than that of the non-dispersion image, the analysis becomes more difficult.

[0005] In addition to the evaluation of only the presence or absence of Casso-Dolluminescence emission, Caso-Dolescence analysis often involves the evaluation of wavelength characteristics, such as the emission characteristics analysis of unknown samples, the emission due to defects, and the grasp of wavelength characteristics. Important
A great deal of information is obtained from chromatic dispersion images. However, switching between chromatic dispersion and non-dispersion by an actual spectroscope is performed by providing a switching mirror in the preceding stage of chromatic dispersion, and an interference filter for extracting a single specific wavelength light to the spectroscope also at the time of chromatic dispersion. In addition, a dichroic mirror that transmits only a certain wavelength range and reflects the other wavelength range is used. The spectroscope is constructed by performing such operations. Therefore, in particular, when observing a cathodoluminescence image or measuring a cathodoluminescence spectrum at the same site as the secondary electron image, it is necessary to set electron beam irradiation conditions and observation conditions as necessary each time. Further, many operations such as wavelength switching have to be performed manually, which is not only very troublesome, but also takes time, so that the information of the cathodoluminescence which changes with time due to electron beam irradiation can be obtained. It is difficult to properly evaluate

[0006]

In the above prior art, no consideration is given to automatic brightness, contrast adjustment, automatic focus adjustment and the like of a cathode-luminescence optical system which emits light by electron beam irradiation. In practice, the adjustment is manually performed by an operator from the electron microscope panel, which takes time. For this reason, there is a problem that not only a very troublesome operation is required, but also a change in the intensity of the cathodoluminescence light caused by damage to the sample by the electron beam.

SUMMARY OF THE INVENTION An object of the present invention is to provide a scanning electron microscope suitable for performing automatic brightness and contrast adjustment even for a cathode luminescence optical system with a simple configuration.

[0008] Another object of the present invention is to provide a scanning electron microscope suitable for reducing damage to a sample.

Still another object of the present invention is to provide a scanning electron microscope suitable for reducing costs.

[0010]

According to one aspect of the present invention, a sample is irradiated with an electron beam, whereby electrons obtained from the sample are detected by a detector to generate an electronic signal. In a scanning electron microscope that processes the generated electronic signal in a signal processing system and displays an electronic image of the sample based on the processed electronic signal, a cathode obtained from the sample by irradiating the sample with the electron beam. −
Detecting the luminescence light by the detector to generate a cathodoluminescence signal, processing the generated cathodoluminescence signal in the signal processing system, and performing the processing based on the processed cathodoluminescence signal. It is characterized in that a cathodoluminescence image of the sample is displayed.

According to another aspect of the present invention, an electron obtained from the sample comprises secondary electrons, and a detector for detecting the secondary electron signal and a detector for detecting the cathode luminescence signal. Each includes a photomultiplier tube, means for generating a high voltage to be applied to the two photomultiplier tubes, application of a high voltage from the high-voltage generating means to the two photomultiplier tubes, the electron image, and the Means for switching the display of the luminescence image in conjunction with each other.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. 1. An electron beam 1 emitted from an electron gun 1 is sampled by an electron lens 2 controlled by a lens control circuit 11. It is focused on the sample 5 on the die 6. The deflection control circuit 12 supplies a scanning signal to the deflector 3, whereby the sample 5 is scanned with the focused electron beam. Sample 5 is electron beam 1
, Secondary electrons, reflected electrons, cathodoluminescence light, and the like are generated from the sample 5. In the illustrated example, the generated secondary electrons 8 are detected by the secondary electron detector 4. The secondary electron detector 4 includes means for converting the detected secondary electrons into light, and a photomultiplier for converting the light into photoelectrons to generate an electric signal, that is, a secondary electron signal.

Referring to FIG. 2, signal switching means 29
The high-pressure switching means 30 is switched in conjunction with each other. This switching can be performed by operating the mouse 18 or the keyboard 19 of the personal computer 17. When the signal switching means 29 is switched to the (a) side, the high voltage switching means 30 is also switched to the (a) side, and when the signal switching means 29 is switched to the (b) side, the high voltage switching means 30 is also switched to the (b) side. Can be switched to

When the signal switching means 29 and the high voltage switching means 30 are switched to the side (a), a predetermined high voltage is supplied from the high voltage power supply 50 through the high voltage switching means 30 to the photomultiplier of the secondary electron detector 4. Is applied. At the same time, the secondary electron signal is transmitted through the signal switching means 29 to the amplifier and to the beam adjustment, brightness adjustment and contrast adjustment means 3.
1 and further into the A / D converter 13 where it is converted into a digital signal, and this converted digital signal is stored in an image memory in the signal processing means 32. The address signal of the image memory is generated by the address control circuit 14 in synchronization with the scanning signal of the electron beam.

The secondary electron image data of the image memory in the signal processing means 32 can be displayed on the display 16. The secondary electron image data in the image memory in the signal processing means 32 can be transferred to the image synthesizing and displaying means 35 at any time. The image synthesizing and displaying means 35 is a personal computer 17
The image data is read out and combined with the image data in the display memory, and is displayed on the image combining and displaying means 35 in real time. The image control means 15 displays the image signal stored in the image memory in the signal processing means 32 on the display 16 and displays the image signal stored in the personal computer 17 having the mouse 18 and the keyboard 19 on the display. 16 has the function of displaying.

An amplifier and beam adjustment, brightness adjustment and contrast adjustment means 31 amplify the secondary electron signal, and maintain the level and the change range of the amplified secondary electron signal at a predetermined magnitude and range, respectively. Thus, the gain of the amplifier and the high voltage applied to the photomultiplier of the secondary electron detector 4 are adjusted. Further, the lens control circuit 11 is controlled based on the amplified signal to change the lens current applied to the electronic lens 2 so that the lens current is focused on the sample 5.
Therefore, the brightness and contrast adjustment and the focus adjustment are automatically performed.

The cathodoluminescence light obtained from the sample 5 is efficiently propagated to the optical fiber 34 by the focusing mirror 10 and guided to the spectroscope 20. In the spectroscope 20,
The cathodoluminescence light is a fiber condensing mirror-21.
Is guided to the diffraction grating 24 via the reflection mirror 22. The wavelength-dispersed light / non-dispersed light by the diffraction grating 24 is detected by a cathodoluminescence detector 23 composed of a photomultiplier tube to generate a cathodoluminescence signal.

When the signal switching means 29 and the high voltage switching means 30 are switched to the side (b), the photoelectron image tube as the cathode-luminescence detector 23 is supplied from the high voltage power supply 50 via the high voltage switching means 30 to a predetermined position. High voltage is applied. At the same time, the cathode luminescence signal is transmitted through the signal switching means 29 to the amplifier and the beam adjuster.
Introduced into the brightness adjustment and contrast adjustment means 31;
Further, the digital signal is introduced into the A / D converter 13 and converted into a digital signal. The converted digital signal is stored in an image memory in the signal processing means 32. The address signal of the image memory is generated by the address control circuit 14 in synchronization with the scanning signal of the electron beam.

The image memory in the signal processing means 32
The luminescence image data can be displayed on the display 16. Also, the cathodoluminescence image data of the image memory in the signal processing means 32 can be transferred to the image synthesizing and displaying means 35 at any time. The image synthesizing and displaying means 35 reads out and synthesizes the image data with the image data in the display memory of the personal computer 17, and displays the image data on the image synthesizing and displaying means 35 in real time.

An amplifier and a beam adjustment, brightness adjustment and contrast adjustment means 31 amplify the cathode luminescence signal, and the level and change range of the amplified cathode luminescence signal are set to predetermined magnitudes and ranges. The gain of the amplifier and the high voltage applied to the photomultiplier tube as the cathodoluminescence detector 23 are adjusted so as to be maintained respectively. Further, the lens control circuit 11 is controlled based on the amplified signal to change the lens current applied to the electronic lens 2 so that the lens current is focused on the sample 5.
Therefore, also in the case of generating an image using the cathodoluminescence light, the brightness, contrast adjustment and focus adjustment are automatically performed.

The gains of the amplifier and the amplifier of the beam adjustment, brightness adjustment and contrast adjustment means 31 are generally different between the case of detecting secondary electrons and the case of detecting cathode luminescence. Also, the applied high voltage of the photomultiplier tube of the secondary electron detector 4 and the applied high voltage of the photoelectron image tube as the cathodoluminescence detector 23 are generally different. Therefore, in the embodiment of the present invention, these switchings are automatically switched in conjunction with the switching of the signal switching unit 29 and the high voltage switching unit 30.

As described above, in the case of secondary electron detection for obtaining an image and in the case of cathode luminescence light detection, brightness, contrast adjustment and focus adjustment are automatically performed using the same signal processing system. Will be That is, these adjustments are automatically performed, and the automatic adjustments are realized using the same signal processing system, so that the configuration is simplified and the cost is reduced. Further, signal switching and high voltage switching are performed by the signal switching unit 29 and the high voltage switching unit 3.
0 instantaneously, the secondary electron image and the cathodoluminescence image having appropriate brightness and contrast and being in focus are instantaneously switched and displayed, so that sample damage can be reduced. Can be

When the secondary electron signal is guided to the amplifier and the beam adjustment, brightness adjustment and contrast adjustment means 31, the cathode luminescence signal is converted into another independent signal processing system (not shown). ), And a cathodoluminescence spectrum measurement is performed. That is, when the secondary electron signal is guided to the amplifier and the beam adjustment, brightness adjustment and contrast adjustment means 31, the camera at the observation site corresponds to each scan of the surface, line, and spot of the secondary electron image. -A luminescence spectrum measurement is performed.

Referring to FIG. 3, the spectroscope 20 includes the fiber focusing mirror-21, the reflection mirror-22, and the diffraction grating 2.
4. Includes a CL light receiver 23, a slit 39, and a diffraction grating control means 40. The obtained cathodoluminescence light propagates through the optical fiber 34 and is transmitted through the diffraction grating 24 (for example, 900).
(The number of lines / mm), a non-dispersed light 37 and a wavelength-dispersed light 38 are obtained. The non-dispersed light 37 is light containing all wavelength range components, and from the non-dispersed light 37, the presence or absence of cathodoluminescence light can be detected.

On the other hand, the wavelength characteristic of the cathodoluminescence light can be analyzed by the wavelength dispersion light of the dispersion light 38 of the diffraction grating 24. The switching between the non-dispersive light 37 and the chromatic dispersion light 38, that is, the selective detection thereof, is performed by driving the diffraction grating 24 by the diffraction grating control means 40, forming an image on one of the slits 39, and detecting the Casodo-luminescence. The diffraction grating control means 40 is controlled by the spectroscope control means 36. The half width (for example, 5 nm and 20 nm) of the wavelength dispersion light 38 is defined by the slit width. Since the diffraction grating 24 is used, chromatic dispersion light / non-dispersion light can be obtained quickly. Also, since no wavelength dispersion means such as a filter is included in the optical path so that wavelength dispersion light / non-dispersion light can be obtained by one optical system, optical adjustment and maintenance of the spectroscope are easy, and A signal having a low S / N ratio and a low absorption of luminescence light is obtained.

FIG. 4 shows the result of the measurement of the cathode luminescence spectrum displayed on the screen synthesizing and displaying means 35 of the personal computer 17. FIGS. 5A and 5B show images displayed on the display 16, wherein FIG. 5A shows a secondary electron image,
(B) is a cathodoluminescence image. FIG. 5 (c)
Is a superimposed image of (a) and (b), which is displayed on the screen of the personal computer 17 and on the display means 35.

First, the secondary electron image shown in FIG. 5A is obtained and observed by a normal observation means of an electron microscope. Next, in order to confirm the presence or absence of the cathodoluminescence light at the observation site, a cathodoluminescence image obtained by non-dispersion light at the same site as the secondary electron image is obtained and observed (FIG. 5B). . After the confirmation, the secondary electron image is displayed again on the display for the emission wavelength characteristic analysis of the Caso-Dolluminescence image, and the electron beam is moved and fixed to a portion where the Casodo-Dolescence light is observed. Measure the cathodoluminescence spectrum in this state. Measurement conditions such as a measurement wavelength range of the spectroscope, a voltage applied to the cathodoluminescence detector 23, and a slit width are set in advance. FIG. 4 shows the measurement results of the thus obtained Casodo-luminescence spectrum. Finally, the cathodoluminescence spectrum is observed, the wavelength is set, and the cathodoluminescence image at that wavelength can be obtained and observed (FIG. 5).
(B)).

In FIGS. 5A and 5B, ABCC
There is a soft switch for automatic brightness and contrast adjustment (control), and AFC is a soft switch for automatic focus adjustment (control). Clicking these soft switches will automatically change the brightness and contrast. Adjustment and automatic focus adjustment are performed. In FIG. 4, CL indicated by 41 represents a soft switch which can be clicked to switch the display of the cathodoluminescence image, and λ indicated by 42 is displayed. This represents a soft switch used to set the wavelength of the power-cassette luminescence image.

In the embodiment, secondary electrons are exemplified as electrons to be detected. However, reflected electrons or transmitted electrons may be used instead.

[0030]

According to the present invention, there is provided a scanning electron microscope suitable for performing automatic brightness and contrast adjustment even for a cathode luminescence optical system with a simple configuration.

According to the present invention, there is also provided a scanning electron microscope suitable for reducing damage to a sample.

According to the present invention, there is further provided a scanning electron microscope suitable for reducing costs.

[Brief description of the drawings]

FIG. 1 is a conceptual view of a scanning electron microscope according to one embodiment of the present invention.

FIG. 2 is a specific processing circuit diagram as an example of a secondary electron signal and a cathode luminescence signal of FIG. 1;

FIG. 3 is a configuration diagram of a specific example of the spectroscope of FIG. 1;

FIG. 4 is an example of a cathodoluminescence spectrum displayed on the image synthesizing and displaying means of FIG. 1;

FIG. 5 is a diagram showing a secondary electron image, a cathode luminescence image, and a superimposed image thereof as an example displayed on the personal computer of FIG.

[Explanation of symbols]

1: electron gun, 4: secondary electron detector, 5: sample, 10: cathodoluminescence detector, 11: lens control means,
12: deflection control means, 13: amplifier and A / D converter,
14: address control circuit, 15: image control means, 16:
Display, 17: PC, 20: Spectroscope, 29:
Signal switching means, 30: high voltage switching means, 31: amplifier and beam adjustment, brightness adjustment and contrast adjustment means, 35: image synthesis and display means, 50: high voltage power supply.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yuzo Kurome 1040 Ichimo Ichimo, Hitachinaka City, Ibaraki Prefecture Inside Hitachi Science Systems Co., Ltd. Inside Science Systems (72) Inventor Junichiro Tomizawa 1040 Ichimo Ichimo, Hitachinaka City, Ibaraki Prefecture Inside Hitachi Science Systems Co., Ltd.

Claims (4)

[Claims] 1. A sample is irradiated with an electron beam, whereby electrons obtained from the sample are detected by a detector to generate an electronic signal, and the generated electronic signal is processed by a signal processing system. A scanning electron microscope for displaying an electron image of the sample based on the obtained electronic signal, and detecting, by a detector, cathodoluminescence light obtained from the sample by irradiating the sample with the electron beam, and performing a cathodic scan.
A luminescence signal is generated, and the generated
A scanning electron microscope wherein a dolescence signal is processed by the signal processing system, and a cathodoluminescence image of the sample is displayed based on the processed cathodoluminescence signal. 2. An electron obtained from the sample comprises secondary electrons, and the detector for detecting the secondary electron signal and the detector for detecting the cathodoluminescence signal each include a photomultiplier tube. The scanning electron microscope according to claim 1, wherein: 3. A means for generating a high voltage applied to the two photomultiplier tubes, applying a high voltage from the high voltage generating means to the two photomultiplier tubes, and displaying the electron image and the cathodoluminescence image. 3. A scanning electron microscope according to claim 2, further comprising: means for switching each of the scanning electron microscopes. 4. The method according to claim 1, wherein said cathodoluminescent light is guided to a diffraction grating to selectively generate dispersed light and non-dispersed light, and detected by said cathodoluminescent light detector. The scanning electron microscope according to 2 or 3.