JP2001291485A - Scanning electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a scanning electron microscope, in which secondary electrons can be detected even under a low vacuum, and an observation of a secondary electron image can be performed. SOLUTION: By a differential evacuation of a sample room and a corona ring room 16, where a corona ring 10 has been positioned, to make a degree of vacuum in a corona ring room higher, a sufficient voltage to accelerate the secondary electrons can be applied to the corona ring 10 without generating an electrical discharge. As a result, the secondary electrons that are generated by their radiation of an electron beam EB to the sample are collected by a collector 9 where voltage of 300 V has been applied, and they are collected in the vicinity of a central opening of a collector throttling 17 by an electric field of the collector throttling 17 where higher voltage than the collector potential has been applied. The collected secondary electrons are accelerated by the corona ring 10, and they collide with a scintillator 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing a low vacuum
The present invention relates to a scanning electron microscope capable of detecting secondary electrons and observing a secondary electron image.

[0002]

2. Description of the Related Art In a scanning electron microscope, an electron beam generated and accelerated from an electron gun is finely focused on a sample by a condenser lens or an objective lens, and secondary electrons and reflections generated by scanning of the electron beam are also observed. Electrons are detected, and this detection signal is supplied as an image signal to a cathode ray tube synchronized with scanning of an electron beam. As a result, a two-dimensional image of the sample is displayed on the cathode ray tube having persistence.

[0003]

In the above-mentioned scanning electron microscope, the degree of vacuum in the sample chamber is lowered (several Pa to several hundred P).
a) In addition, observation of a water-containing sample or the like mainly including living organisms whose surface shape changes in a high vacuum is performed. By the way, in a normal scanning electron microscope, it is general to detect secondary electrons or reflected electrons and display an image based on the detection signal.

[0004] When detecting secondary electrons, the detector collects secondary electrons from the sample with an umbrella called a collector to which a voltage of about 300 V is applied, and furthermore, a corona ring disposed around the sinterer. A high voltage of about 10 kV is applied to the second electrode, and the secondary electrons are accelerated by the high voltage and collide with the scintillator so that the scintillator emits light. The light emitted from the scintillator is multiplied by the photomultiplier tube, and the output signal of the photomultiplier tube is finally supplied to the cathode ray tube as a luminance modulation signal.

When such a secondary electron detector is introduced into a low-vacuum scanning electron microscope, a discharge occurs under a low vacuum due to the structure in which a high voltage as high as 10 kV is applied to the corona ring. It will be impossible.

For this reason, in a low-vacuum scanning electron microscope, observation of a backscattered electron image is mainly performed by using a backscattered electron detector which does not need to apply a high voltage. However, from the viewpoint of operability such as resolution and focusing, there is a strong demand for observation of a secondary electron image under a low vacuum.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to realize a scanning electron microscope capable of detecting secondary electrons even under a low vacuum and observing a secondary electron image. To be.

[0008]

A scanning electron microscope according to the first invention comprises an electron gun for generating and accelerating an electron beam;
A focusing lens for focusing the electron beam on the sample, a scanning unit for scanning the irradiation position of the electron beam on the sample, and a detector for detecting a signal obtained by irradiating the sample with the electron beam, In a scanning electron microscope equipped with a display means for displaying a sample image based on a detection signal of a detector, a means for maintaining a sample chamber in which a sample is placed at a lower degree of vacuum than a space above the sample chamber; A collector to which a relatively low voltage is applied to collect secondary electrons generated from the sample;
A high vacuum chamber maintained at a higher degree of vacuum than the sample chamber, and a relatively high voltage is applied in the high vacuum chamber to accelerate secondary electrons collected by the collector and collide with the scintillator. It is characterized by comprising an electrode and a photomultiplier tube for generating a detection signal based on light emission of the scintillator.

In the first invention, the space where the electrode to which a high voltage is applied, such as corona ring, is disposed at a relatively high vacuum level, and discharge is prevented to enable detection of secondary electrons. .

According to a second aspect of the present invention, in the first aspect, a stop having a minute opening is provided on the collector side of the high vacuum chamber in which the electrode to which a high voltage is applied is disposed, and a voltage higher than the collector voltage is applied to the stop. Is applied to further improve the detection efficiency of secondary electrons.

In a third aspect based on the second aspect, the surface of the collector aperture on the high true chamber side is formed of an insulating material to prevent discharge. In a fourth aspect based on the third aspect, the collector aperture is attached to the aperture holder, and the surfaces of the collector aperture, the aperture holder, and the high vacuum chamber wall on the high vacuum chamber side are formed of an insulating material.

In a fifth aspect based on the first aspect, the value of the high voltage applied to the electrode disposed in the high vacuum chamber is changed according to the degree of vacuum in the high vacuum chamber.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a main part of a scanning electron microscope according to the present invention, and FIG. 2 shows details of a secondary electron detector in FIG. In these figures, an accelerated electron beam EB generated from an electron gun (not shown) is finely focused on a sample 2 by a condenser lens (not shown) and an objective lens 1.

The sample 2 is placed in the sample chamber 3, and the sample chamber 3 is evacuated by the vacuum pump 4. The sample chamber 3 is configured so that a small amount of gas or air can be introduced by a variable leak valve 5.
An orifice stop 7 is provided near the sample chamber of the electron beam passage opening 6 of the objective lens 1. The orifice stop 7 has an opening with a very small diameter, and enables differential evacuation between the sample chamber 3 and the upper space of the objective lens 1.

A secondary electron detector 8 is provided in the sample chamber 3. The secondary electron detector 8 includes a collector 9 formed of a net-like material, a corona ring 10, a light guide 11,
It comprises a photomultiplier tube 12.

The collector 9 is connected to the power supply 13 from 250 to 3
A voltage of about 00 V is applied, and the corona ring 10
A high voltage of about 5 kV to 10 kV is applied from the power supply 14. A voltage for electron multiplication is applied to the photomultiplier tube 12 from a power supply 15.

The corona ring 10 has a corona ring chamber 16.
Inside. Corona ring room 10 and collector 9
A collector aperture 17 is provided between the two, and the aperture 17 is attached to an aperture holder 18.

The inside of the collector chamber 16 is configured to be evacuated by a vacuum pump 19. As a result, the inside of the sample chamber 3 and the inside of the collector chamber 16 are differentially evacuated by the collector throttle 17. A voltage of 400 V to 500 V higher than the collector potential is applied to the collector aperture 17 from the power supply 20. The operation of such a configuration will now be described.

First, the inside of the sample chamber 3 is evacuated by the vacuum pump 4, and the coloning chamber 16 is evacuated by the vacuum pump 19. Then, while monitoring the degree of vacuum in the sample chamber 3 with a vacuum gauge (not shown), the variable leak valve 5 is operated to introduce a small amount of an appropriate gas or air into the sample chamber 3, and A relatively low degree of vacuum of several Pa to several hundred Pa is set.

At this time, the upper space of the objective lens 1 (where the electron gun and the like are disposed) and the inside of the sample chamber 3 are differentially evacuated by the orifice diaphragm 7, and as a result, the upper space of the objective lens 1 is relatively high. At the vacuum level, the inside of the sample chamber 3 is maintained at a relatively low vacuum level.

Further, the corona ring chamber 16 is differentially evacuated, and a relatively high degree of vacuum (for example, 1 P
a) is maintained. Under such conditions, an electron beam EB is generated from an electron gun (not shown), and a condenser lens,
The electron beam EB is narrowly focused on the sample 2 by the objective lens 1. Further, the electron beam EB is two-dimensionally scanned on the sample 2 by a deflector (not shown).

Secondary electrons generated by irradiating the sample 2 with the electron beam EB are collected by a collector 9 to which, for example, 300 V is applied. The secondary electrons collected by the collector 9 are collected near the center opening of the stop 17 by the electric field of the collector stop 17 to which a voltage higher than the collector potential is applied. FIG. 3 shows this state, and the dotted line se is a secondary electron.

The corona ring 10 has a power source 14
For example, a high voltage of 5 kV is applied. As shown in FIG. 3, the potential based on the voltage application is set outside the collector aperture 17 (having a diameter of about 1 mm) outside (collector 9).
Side) to capture nearby electrons and accelerate them toward the scintillator. The accelerated electrons collide with the scintillator 21 to cause the scintillator to emit light.

The light of the scintillator passes through the light guide 11 and enters the photomultiplier tube 12. Photomultiplier tube 1
In 2, the incident light is converted into electrons, and the electrons are further multiplied. The multiplied electrons are detected, and the detected signal is taken out from the terminal 22. The signal at the terminal 22 is appropriately amplified and supplied to a display such as a cathode ray tube (not shown), so that a secondary electron image of the sample is displayed on the display.

As described above, in the above configuration, the sample chamber 3
And the colon ring chamber 16 in which the corona ring 10 is disposed is differentially evacuated to increase the degree of vacuum in the colon ring chamber, so that a sufficient voltage is discharged to the colon ring 10 to accelerate secondary electrons. Can be applied without the occurrence of.

For example, the inside of the coloning chamber 16 is 1-5P.
If it is about a, a voltage of 5 kV or more can be applied to the corona ring 10. In addition, the corona ring 10
Is preferably adjusted so as to be adjusted by the degree of vacuum in the corona ring chamber 16.

That is, when the degree of vacuum is high, the applied voltage is increased accordingly to increase the accelerating action of secondary electrons,
On the other hand, when the degree of vacuum is relatively low, the applied voltage is reduced to prevent the occurrence of discharge. Such an operation monitors the degree of vacuum in the corona ring chamber 16 with a vacuum gauge and adjusts the power supply 14 manually according to the degree of vacuum, or automatically controls the power supply 14 according to the degree of vacuum. Adjust the voltage value.

When the pressure in the sample chamber 3 is high (several P
a), the electrons accelerated by the electric field of the collector 9, the collector aperture 17, and the corona ring 10 collide with gas molecules in the sample chamber 3 and the like and cause an electron avalanche phenomenon, so that secondary electrons are further amplified. An effect also occurs. In the case of the net-shaped collector 9, the large amplitude of electrons at the collector 9 increases the probability that secondary electrons collide with gas molecules, and this effect further improves the detection efficiency of secondary electrons. Will do.

In the above configuration, each of the inner wall of the corona ring chamber 16, the inner wall of the aperture holder 18, and the inner wall of the aperture 17
As a preventive measure against electric discharge, it is desirable to use an insulating material. Since the potential is changed between the collector 9 and the collector aperture 17, the aperture holder 18 needs to be an insulating material.

Further, by making the collector diaphragm 17 a slide type or a shutter type, a secondary electron detector usable from high vacuum to low vacuum can be obtained. For this purpose, the voltage applied to the corona ring 10 is set to 0 to 10
It is desirable to be able to change in the range of kV.

Further, the outer shape of the collector aperture 17 can be increased, although it depends on the shape of the collector 9.
However, in this case, there is a limit to the size of the collector 9 simply because the electric field of the corona ring 10 does not reach the outer shape of the collector aperture 17. This limit is determined by the aperture diameter of the stop and the shape of the collector.

Further, although the shape of the collector 9 is flat as shown in the figure, by making it into a mortar shape, the opening diameter of the collector aperture 17 can be increased and the efficiency of detecting secondary electrons can be further improved. Can be. In addition, a coil is arranged in a mortar portion of a mortar-shaped collector, and the coil is disposed using a magnetic field.
In consideration of increasing the efficiency of capturing secondary electrons, the efficiency of detecting secondary electrons can be further increased.

Further, if an electrode having another potential is arranged outside the collector aperture 17, the detection efficiency of secondary electrons can be further improved. Note that the potential of this outer electrode needs to be lower than the collector throttle potential.

Furthermore, the power supply 13 for the collector 9 and the power supply 20 for the collector diaphragm can be shared by adjusting the voltage with a resistor or the like.

[0035]

As described above, in the first invention,
Because the space where the electrode to which a high voltage is applied such as corona ring is arranged is maintained at a relatively high degree of vacuum,
Discharge can be prevented and secondary electrons can be detected with high efficiency.

According to a second aspect, in the first aspect, a stop having a minute opening is provided on the collector side of the high vacuum chamber in which the electrode to which a high voltage is applied is arranged, and a voltage higher than the collector voltage is applied to the stop. Is applied, the detection efficiency of secondary electrons can be further improved.

In the third invention, in the second invention, since the surface of the collector diaphragm on the high true chamber side is formed of an insulating material, the effect of preventing discharge can be increased. According to a fourth aspect, in the third aspect, the collector aperture is attached to the aperture holder, and the collector aperture, the aperture holder,
Since the surface of the high vacuum chamber wall on the high vacuum chamber side is formed of an insulating material, the effect of preventing discharge can be further increased.

According to a fifth aspect of the present invention, in the first aspect, the value of the high voltage applied to the electrodes disposed in the high vacuum chamber is changed according to the degree of vacuum in the high vacuum chamber. , The optimum secondary electron detection efficiency can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main part of a scanning electron microscope according to the present invention.

FIG. 2 is a diagram showing details of a secondary electron detector in FIG. 1;

FIG. 3 is a diagram showing trajectories of secondary electrons.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Objective lens 2 Sample 3 Sample chamber 4, 19 Vacuum pump 5 Leak valve 6 Opening 7 Orifice 8 Secondary electron detector 9 Collector 10 Corona ring 11 Light guide 12 Photomultiplier tube 13, 14, 15, 20 Power supply 16 Corona ring Chamber 17 Collector aperture 18 Aperture holder 21 Scintillator 22 Terminal

Continued on the front page (72) Inventor Satoru Nemoto 2-6-38 Musashino, Akishima-shi, Tokyo Japan Electronic Technics Co., Ltd. F-term (reference) 5C033 KK01 NN01 UU04 UU06

Claims (5)

[Claims] An electron gun for generating and accelerating an electron beam;
A focusing lens for focusing the electron beam on the sample, a scanning unit for scanning the irradiation position of the electron beam on the sample, and a detector for detecting a signal obtained by irradiating the sample with the electron beam, In a scanning electron microscope equipped with a display means for displaying a sample image based on a detection signal of a detector, a means for maintaining a sample chamber in which a sample is placed at a lower degree of vacuum than a space above the sample chamber; A collector to which a relatively low voltage is applied to collect secondary electrons generated from the sample;
A high vacuum chamber maintained at a higher degree of vacuum than the sample chamber, and a relatively high voltage is applied in the high vacuum chamber to accelerate secondary electrons collected by the collector and collide with the scintillator. A scanning electron microscope comprising: an electrode; and a photomultiplier tube that generates a detection signal based on light emission of a scintillator. 2. The scanning electron microscope according to claim 1, wherein an aperture having a minute opening is provided on the collector side of the high vacuum chamber, and a voltage higher than the collector voltage is applied to the aperture. 3. The scanning electron microscope according to claim 2, wherein a surface of the collector diaphragm on the high true chamber side is formed of an insulating material. 4. The scanning electron microscope according to claim 3, wherein the collector diaphragm is attached to a diaphragm holder, and the surfaces of the collector diaphragm, the diaphragm holder, and the high vacuum chamber wall on the high vacuum chamber side are formed of an insulating material. . 5. The scanning electron microscope according to claim 1, wherein a value of a high voltage applied to an electrode disposed in the high vacuum chamber is changed according to a degree of vacuum in the high vacuum chamber.