JP3190922B2 - Scanning electron microscope - Google Patents

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 in which a sample is arranged in a magnetic field of an objective lens.

[0002]

2. Description of the Related Art A scanning electron microscope irradiates a sample with a finely focused electron beam, scans an irradiation position of the electron beam, detects secondary electrons generated from the sample based on the electron beam irradiation, The detection signal is supplied to a cathode ray tube synchronized with the scanning of the electron beam to display a secondary electron image. By the way, there is a scanning electron microscope in which a sample is arranged in a magnetic field of an objective lens. FIG. 1 shows a main part of such a scanning electron microscope, and 1 is an objective lens. A sample 2 is placed in an objective lens 1 and this sample 2
The primary electron beam EB narrowly focused is irradiated. Secondary electrons 3 are generated from the sample 2 by irradiating the sample 2 with the electron beam EB. The secondary electrons 3 are constrained by the magnetic field of the objective lens, travel spirally by cyclotron motion, and are extracted above the objective lens 1. A secondary electron detector 4 is disposed above the objective lens 1 at a distance from the optical axis of the electron beam, and a secondary electron capture voltage is applied to the secondary electron detector 4. The secondary electrons 3 extracted above the objective lens 1 along the optical axis are drawn toward the detector 4 by the electric field captured by the detector 4 and detected by the detector 4. The detection signal of the detector 4 is supplied to a cathode ray tube (not shown), and a secondary electron image of the sample is displayed on the cathode ray tube.

[0003]

When the sample 2 is a non-conductive material such as an insulating material or a semiconductor material, the surface of the sample is positively or negatively charged with irradiation of the sample. The degree of charge-up depends on the accelerating voltage of the primary electron beam, the material of the sample, etc., but the charge is mainly caused when the balance between the amount of secondary electrons and reflected electrons generated from the sample and the charge absorbed by the sample is lost. Up occurs. For example, if the secondary electron emission is too high in a certain area of the sample, the area will be charged up positively, and the secondary electrons generated in other areas will be recalled to the sample or directed to the secondary electron detector. Hinder. Conversely, when the number of secondary electrons emitted from the region irradiated with the primary electron beam EB is small and the negative charges remaining on the sample increase rapidly, the sample is negatively charged up. In that case, an incorrect deflection is given to the primary electron beam, or the trajectory of the secondary electron is affected.

When an insulator sample or a semiconductor sample is observed with a scanning electron microscope, the acceleration voltage of the primary electron beam is set to a low acceleration voltage of about 1 kV. On the other hand, it is often easy to take a charge, but the charge is often positively increased. When the sample is charged up in this way, the secondary electrons affected by the charge-up are guided to the detector 4 together with the secondary electrons not much affected by the charge-up, and are detected. As a result, the secondary electron image displayed on the cathode ray tube based on the detection signal becomes an image affected by charge-up.

[0005] The present invention has been made in view of such a point, and an object thereof is to observe a secondary electron image with little influence of charge-up even for a sample having poor conductivity. The realization of a scanning electron microscope.

[0006]

A scanning electron microscope according to the present invention irradiates a sample in an objective lens with an electron beam,
As a result, the secondary electrons generated from the sample are guided to the upper part of the objective lens by the magnetic field of the objective lens, and the secondary electrons are guided to the detector by the electric field of the secondary electron detector arranged apart from the optical axis above the objective lens. in the configuration with a scanning electron microscope to detect Te, along with arranging the hollow cylinder on the optical axis in proximity to the secondary electron detector, the electron beam optical axis
The length of the hollow cylinder in the direction along the length can be adjusted . Other scanning electron according to the invention
The microscope irradiates the sample in the objective lens with an electron beam,
As a result, the secondary electrons generated from the sample are converted to the objective lens magnetic field.
Therefore, the secondary electrons are guided to the upper part of the objective lens and the secondary electrons are
Of the secondary electron detector placed away from the optical axis above
A scanning device configured to guide detection to a detector by an electric field
In the scanning electron microscope, approached the secondary electron detector
Arranging a hollow cylinder on the optical axis and detecting the secondary electrons
So that the relative distance between the vessel and the hollow cylinder can be changed.
It is characterized by having achieved.

[0007]

The secondary electrons generated from the sample include those of various energies. When charge-up has occurred on the sample, at least secondary electrons having relatively high energy are less affected by the charge-up than low secondary electrons. The fact that it is not affected by the charge-up means that it contains a lot of information (for example, surface structure) of the sample, and if an image is formed based only on the unaffected secondary electrons, the accurate A secondary electron image of the sample can be observed. Therefore, in the scanning electron microscope according to the present invention, a hollow cylinder is arranged on the optical axis close to the secondary electron detector, and secondary electrons having relatively low energy are trapped in this cylinder and detected by the detector. To prevent that.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 shows an embodiment of the present invention,
The same parts as those of the conventional apparatus of FIG. 1 are denoted by the same reference numerals. In this embodiment, a hollow cylinder 5 is arranged on the electron beam optical axis close to the detector 4 above the objective lens 1. This cylinder is at ground potential. In such a configuration, as a result of irradiating the sample 2 with the primary electron beam EB, the secondary electrons 3 generated from the sample 2 travel in a spiral manner while performing a cyclotron motion while being constrained by the magnetic field of the objective lens 1. Extraction above the lens 1 is as described above. In this case, the trajectory of the secondary electron changes depending on the strength of the magnetic field. The secondary electrons 3a whose orbits are indicated by dotted lines in the figure have relatively high energy and rise with a large turning radius. The secondary electrons having a large radius of gyration are attracted by the trapping electric field of the detector 4 arranged away from the optical axis of the electron beam EB, and are incident on the detector 4 and detected.

On the other hand, the secondary electrons 3b having a low energy shown by a thin line rise with a small radius of rotation, enter the cylinder 5 at the ground potential, and are prevented from entering the detector 4. As a result, the detection signal of the detector 4 is based on secondary electrons having relatively large energy, that is, based on secondary electrons relatively unaffected by the charge-up of the sample 2, and such detection is performed. By guiding the signal to a cathode ray tube (not shown) and displaying the signal, it is possible to observe a scanning electron microscope image relatively free from the influence of charge-up.
In this embodiment, the charge-up state on the sample 2 changes depending on the material of the sample and the accelerating voltage. Therefore, it is effective that the relative distance (interval) between the hollow cylinder 5 and the detector 4 can be adjusted. That is, if the distance is changed, secondary electrons having higher energy can be made incident on the hollow cylinder 5, or only secondary electrons having lower energy can be made incident on the hollow cylinder 5. As a result, when the charge-up of the sample is large, the distance between the hollow cylinder 5 and the detector 4 is changed so that secondary electrons having higher energy are incident on the cylinder 5. Conversely, when the charge-up of the sample is small, the distance between the hollow cylinder 5 and the detector 4 is changed so that only secondary electrons of lower energy enter the cylinder 5. In this way, it is possible to always detect only secondary electrons that are less affected by charge-up depending on the state of charge-up of the sample.

FIG. 3 shows another embodiment of the present invention. In this embodiment, the hollow cylinder 5 is constituted by a first cylinder 5a and a second cylinder 5b outside the first cylinder 5a. The first and second cylinders 5a and 5b are in electrical contact with each other, and the second cylinder 5b is configured to be movable along the optical axis of the electron beam EB with respect to the first cylinder 5a. In such a configuration, the first and the second are changed according to the state of charge-up of the sample 2.
The length L of the cylinder 5 formed by the cylinders 5a and 5b is changed. In other words, if the length L of the cylinder 5 is increased, secondary electrons are more easily trapped by the cylinder 5, and L is increased when the amount of charge-up is large.

FIG. 4 shows another embodiment of the present invention.
The difference between this embodiment and the embodiment of FIG. 2 is that a low voltage is applied to the hollow cylinder 5 from the power supply 8. The power supply 8 is a variable power supply, and the voltage applied to the hollow cylinder can be changed according to the charge-up state of the sample 2.

[0012]

As described above, in the scanning electron microscope according to the present invention, the hollow cylinder is arranged on the optical axis close to the secondary electron detector, and the relatively low energy from the sample can be obtained.
Since the secondary electrons are trapped in this cylinder,
Even with a sample having poor conductivity, a secondary electron image with little influence of charge-up can be observed. Also try
The length of the hollow cylinder changes depending on the charge-up situation.
Can be changed. In addition, secondary electron detector and hollow
By changing the relative distance to the cylinder, the sample can be charged.
2 less affected by charge-up depending on up situation
Only the next electron can be detected.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main part of a conventional scanning electron microscope.

FIG. 2 is a diagram showing a main part of a scanning electron microscope according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a main part of a scanning electron microscope according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a main part of a scanning electron microscope according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Objective lens 2 Sample 3 Secondary electron 4 Secondary electron detector 5 Hollow cylinder 8 Variable power supply

Claims (4)

(57) [Claims] An electron beam is irradiated on a sample in an objective lens, and secondary electrons generated from the sample are guided to an upper portion of the objective lens by a magnetic field of the objective lens, and the secondary electrons are separated from an optical axis of the upper portion of the objective lens. in the configuration with a scanning electron microscope to detect guided to the detector by the electric field of the secondary electron detector disposed it is, while placing the hollow cylinder on the optical axis in proximity to the secondary electron detector, electronic Beam light
The length of the hollow cylinder in the direction along the axis can be adjusted
Scanning electron microscope, characterized in that the. 2. A sample in an objective lens is irradiated with an electron beam.
Then, the secondary electrons generated from the sample are
Field guides the upper part of the objective lens and the secondary electrons
Secondary electron detection located away from the optical axis above the lens
It is configured so that it is guided to the detector by the electric field of the
Approaching the secondary electron detector in a scanning electron microscope
A hollow cylinder on the optical axis, and the secondary electron
The relative distance between the detector and the hollow cylinder can be changed.
A scanning electron microscope characterized in that: 3. The hollow cylinder is held at a ground potential.
The scanning electron microscope according to claim 1 or 2 . 4. A voltage is applied to the hollow cylinder, and the voltage is applied to the hollow cylinder.
3. The scanning electron microscope according to claim 1, wherein the pressure value is arbitrarily changed .