JPH0917368A - Single magnetic pole type objective lens and scanning electron microscope - Google Patents

Abstract

PURPOSE: To provide a single magnetic pole type objective lens and a scanning electron microscope which are excellent in detecting efficiency of a secondary electron with high resolution. CONSTITUTION: An inside coil is wound inside a yoke 7, and an outside yoke 9 is wound outside the yoke 7. An exciting current is flowed to these inside coil 8 and outside coil 9. A sample 10 is arranged under a conical objective lens 6, and a secondary electron detector 11 is arranged along an inclination of the objective lens on the outside of the objective lens 6. The distribution of magnetic field intensity produced by the outside coil 9 permeates a little up to the sample 10, and a secondary electron (e) rises while rotating on the optical axis O. When the secondary electron (e) rises up to a certain degree along the optical axis, it is attracted in the secondary electron detector 11 direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-pole type objective lens most suitable for a scanning electron microscope and the like, and a scanning electron microscope excellent in secondary electron detection efficiency.

[0002]

2. Description of the Related Art In a scanning electron microscope and the like, various types of focusing lenses (objective lenses) at the final stage are used. Among them, a single-pole type objective lens has recently been receiving attention. Reference numeral 1 in FIG. 1 shows an example of such a single-pole type objective lens, and reference numeral 2 in FIG. 1A is a yoke. An exciting coil 3 is provided inside the yoke 2, and an exciting current is supplied to the exciting coil 3 from an objective lens power source (not shown).

An electron beam EB generated from an electron gun (not shown) is focused by an objective lens 1 composed of a yoke 2 and an exciting coil 3 and focused on a sample 4.
Secondary electrons generated by irradiating the sample 4 with the electron beam EB are detected by a secondary electron detector (not shown) arranged on the side of the objective lens 1. The secondary electron signal detected by the detector is supplied to the cathode ray tube synchronized with the scanning of the electron beam, and the secondary electron scanning image of the sample is obtained on the cathode ray tube.

[0004]

The objective lens 1 described above
The distribution of the magnetic field strength of is shown by B, and this distribution B shows a peak at the tip of the yoke 2. Further, as shown in the schematic view of FIG. 1B, the main surface M of the objective lens 1L is far away from the sample 4, and as a result, the aberration coefficient of the objective lens becomes large and the resolution of the obtained scanning image is high. Was bad.

FIG. 2 shows a state in which the sample 4 is tilted. In this figure, the configuration of the objective lens 1 is omitted, and the distribution B of the magnetic field strength of the objective lens and the sample 4 and secondary electron detection are shown. Vessel 5 is shown. The distribution B of the magnetic field strength does not reach the sample 4, and when the sample 4 is observed at a high inclination, most of the secondary electrons e emitted in the opposite direction of the secondary electron detector 5 are absorbed by the sample surface. Therefore, the secondary electron detector 5 cannot be reached. Therefore, the secondary electron detection efficiency is poor, and the portion of the inclined surface of the sample 4 becomes dark in the obtained scanning electron microscope image.

FIG. 3 shows the distribution B of the magnetic field strength when the exciting coil is wound outside the yoke of the objective lens.
In this case, the distribution B of the magnetic field strength approaches the sample 4. However, the secondary electron e generated by irradiating the sample with the electron beam EB is caught by the strong magnetic field of the magnetic field strength, rises along the optical axis O, and cannot be detected by the secondary electron detector 5. .

Further, when the distribution B of the magnetic field intensity reaches deeply to the structure (not shown) near the sample stage or the objective lens for fixing the sample 4, the magnetic material constituting the structure is magnetized. As a result, there is a problem that the obtained scanning electron microscope image is distorted.

The present invention has been made in view of the above circumstances, and an object thereof is to realize a single-pole type objective lens and a scanning electron microscope which have a high detection efficiency of secondary electrons with high resolution.

[0009]

A single-pole type objective lens according to the invention of claim 1 is a conical single yoke,
It is characterized by comprising an inner coil wound inside the yoke and an outer coil wound outside the yoke.

The single-pole type objective lens according to the second aspect of the present invention is characterized in that the electric currents in the same direction are passed through the inner coil and the outer coil. The single-pole type objective lens according to the invention of claim 3 is characterized in that currents are applied in opposite directions to the inner coil and the outer coil.

In the scanning electron microscope according to the invention of claim 4, the electron beam from the electron gun is finely focused on the sample by the objective lens, and the secondary electrons generated by the irradiation of the sample with the electron beam are detected as secondary electrons. In a scanning electron microscope in which a secondary electron image of a sample is obtained based on a detection signal by a detector, a single conical yoke as an objective lens, an inner coil wound inside the yoke, and a yoke A single-pole objective lens composed of an outer coil wound on the outer side of the objective lens is used, and the secondary electron detector is arranged on either the outer side or the inner side of the objective lens.

[0012]

The objective lens according to the present invention comprises a single conical yoke, an inner coil wound inside the yoke, and an outer coil wound outside the yoke. By bringing the lens closer to the sample, the aberration coefficient of the lens is reduced and the resolution is improved.

The scanning electron microscope according to the present invention has a single magnetic pole composed of a single conical yoke as an objective lens, an inner coil wound inside the yoke, and an outer coil wound outside the yoke. Type objective lens, the secondary electron detector is placed on either the outside or the inside of the objective lens, the magnetic field is slightly penetrated into the sample, and the secondary electrons generated from the sample are captured by the cyclotron motion. In the vicinity, the secondary electron is released from the cyclotron motion by the electric field of the secondary electron detector and attracted to the secondary electron detector.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 4 shows a single pole type objective lens 6 of the scanning electron microscope according to the present invention, and 7 is a single conical yoke constituting the objective lens. An inner coil 8 is wound around the inside of the yoke 7, and an outer yoke 9 is wound around the outside of the yoke 7. An exciting current is applied to the inner coil 8 and the outer coil 9 in the same direction from an exciting power source (not shown).

A sample 10 is arranged below the conical objective lens 6, and the sample 10 is constructed so that it can be arbitrarily tilted up to an angle θ. A secondary electron detector 11 is arranged outside the conical objective lens 6 along the inclination of the objective lens. The secondary electron detector 11 is configured so that a suction electric field for attracting secondary electrons can be generated on the front surface thereof.

Although not shown, an electron gun for generating an electron beam, a condenser lens for focusing the electron beam from the electron gun, and an electron beam on the sample 1 are provided above the objective lens 6.
A scanning coil and the like for two-dimensional scanning on 0 are provided. The operation of such a configuration will now be described.

When an exciting current is passed through the inner coil 8 and the outer coil 9 in the same direction, the direction of the magnetic flux produced by the inner coil 8 and the direction of the magnetic flux produced by the outer coil 9 coincide with each other, and the distribution of the magnetic field strength is made. Has the same sign, and the distribution of the magnetic field strength slightly penetrates into the sample 10.

FIG. 5A shows the structure of the objective lens 6 of FIG. 4 and the magnetic field strength distribution B. The magnetic field strength distribution B is shown in FIG.
Is a combination of the magnetic field created by the inner coil 8 and the magnetic field created by the outer coil 9. FIG. 5B shows a schematic diagram of the objective lens. The magnetic field strength distribution B is obtained by comparing the magnetic field lens 8L formed by the inner coil 8 and the outer coil 9
Objective lens 6 combined with magnetic field lens 9L made by
Formed by L. As a result, the main surface M of the objective lens 6L approaches the sample 10, the aberration coefficient of the objective lens 6 becomes small, and the resolution is improved.

Here, in FIG. 4, an electron gun (not shown)
The electron beam EB generated by the laser beam is finely focused on the sample 10 by the magnetic field generated by the objective lens 6. The secondary electrons e generated by irradiating the sample 10 with the electron beam EB are
It is attracted to the secondary electron detector 11 and detected by the suction electric field applied to the secondary electron detector 11.

The distribution of the magnetic field strength created by the outer coil 9 has slightly penetrated to the sample 10 as shown in FIG.
The secondary electrons e generated from the sample 10 undergo cyclotron motion due to the magnetic field and rise while rotating the optical axis O. When the secondary electron e rises to some extent along the optical axis, the attractive force of the secondary electron due to the attracting electric field applied to the secondary electron detector acts strongly near the surface of the sample 10, and the secondary electron e is the cyclotron. It is released from the motion and is attracted toward the secondary electron detector 11.

As a result, the secondary electrons e are efficiently detected by the secondary electron detector 11. The detection signal of the detector 11 is
Although not shown, the primary electron beam EB is supplied to the cathode ray tube in synchronization with the scanning, and the secondary electron image of the sample 11 is displayed on the cathode ray tube.

As described above, in the above-described embodiment, the resolution is improved, and the secondary electrons emitted in the opposite direction of the secondary electron detector 11 when the sample 10 is tilted at a high angle can be efficiently detected. Even at a high inclination, the inclined surface of the sample can be observed brightly.

FIG. 7 shows another embodiment of the present invention.
The same components in this embodiment and those in FIG. 4 are designated by the same reference numerals. The difference between this embodiment and the embodiment of FIG. 4 is that the direction of the current flowing through the inner coil 8 and the direction of the current flowing through the outer coil 9 are opposite to each other. With this configuration, the direction of the magnetic flux formed by the inner coil 8 and the direction of the magnetic flux formed by the outer coil 9 are opposite to each other, and the distribution B of the magnetic field strength has a reversed sign. It is possible to obtain the same effect as that of the configuration of No. 4.

[0024]

As described above, the single pole type objective lens according to the invention of claim 1 has a single conical yoke, an inner coil wound inside the yoke, and an outer coil wound around the yoke. Since the outer coil is rotated, the lens main surface of the objective lens can be brought closer to the sample, the aberration coefficient of the objective lens can be reduced, and the resolution can be improved.

The single-pole type objective lens according to the second aspect of the present invention allows currents to flow through the inner coil and the outer coil in the same direction, and the single-pole type objective lens according to the third aspect of the present invention includes an inner coil and an outer coil. A reverse current flow was applied to the outer coil. As a result, similarly to the first aspect of the invention, the lens main surface of the objective lens can be brought closer to the sample, the aberration coefficient of the objective lens can be reduced, and the resolution can be improved. Further, in the invention of claim 2, since the focusing action of the electron beam is performed by the inner coil and the outer coil, the amount of exciting current supplied to each coil can be reduced and the heat generation of the coil can be mitigated. .

In the scanning electron microscope according to the invention of claim 4, the electron beam from the electron gun is finely focused on the sample by the objective lens, and the secondary electron generated by the irradiation of the sample with the electron beam is detected as the secondary electron. In a scanning electron microscope in which a secondary electron image of a sample is obtained based on a detection signal by a detector, a single conical yoke as an objective lens, an inner coil wound inside the yoke, and a yoke A single-pole objective lens composed of an outer coil wound on the outer side of the objective lens was used, and the secondary electron detector was arranged on either the outer side or the inner side of the objective lens.

As a result, the magnetic field is slightly penetrated into the sample, the secondary electrons generated from the sample are captured by the cyclotron motion, and the secondary electrons are released from the cyclotron motion by the electric field of the secondary electron detector near the sample surface. It can be attracted to a secondary electron detector. Therefore, the detection efficiency of the secondary electrons can be increased, and even if the sample is tilted at a high angle, the sample surface opposite to the secondary electron detector can be observed brightly, and the SN ratio is high and the image quality is improved. An electronic image can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional single-pole type objective lens.

FIG. 2 is a diagram for explaining detection efficiency of secondary electrons when a sample is tilted.

FIG. 3 is a diagram for explaining the detection efficiency of secondary electrons when an outer coil is provided.

FIG. 4 is a diagram showing an embodiment of a single pole type objective lens according to the present invention.

FIG. 5 is a diagram showing a schematic view of the embodiment of FIG.

FIG. 6 is a diagram for explaining detection efficiency of secondary electrons when the sample is tilted.

FIG. 7 is a diagram showing another embodiment of a single pole type objective lens according to the present invention.

[Explanation of symbols]

 6 Objective Lens 7 Yoke 8 Inner Lens 9 Outer Lens 10 Sample 11 Secondary Electron Detector

Claims (4)

[Claims] 1. A single pole type objective lens comprising a single conical yoke, an inner coil wound inside the yoke, and an outer coil wound outside the yoke. 2. The single pole type objective lens according to claim 1, wherein currents in the same direction are passed through the inner coil and the outer coil. 3. The single pole type objective lens according to claim 1, wherein currents in opposite directions are applied to the inner coil and the outer coil. 4. An electron beam from an electron gun is finely focused on a sample by an objective lens, secondary electrons generated by irradiating the sample with the electron beam are detected by a secondary electron detector, and based on a detection signal. In a scanning electron microscope configured to obtain a secondary electron image of a sample, a conical single yoke as an objective lens, an inner coil wound inside the yoke, and an outer coil wound outside the yoke And a secondary electron detector configured to dispose a secondary electron detector on either the outside or the inside of the objective lens.