JPS5854783Y2 - scanning electron microscope - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a scanning electron microscope that efficiently allows secondary electrons generated from the surface of a sample to reach a detector, and achieves high resolution and high S/N.

In order to increase the resolution of a scanning electron microscope, attempts have often been made to reduce the distance between the main surface of the objective lens and the sample (hereinafter abbreviated as WD). that the probe diameter can be obtained;
Also, from the viewpoint of the secondary electron generation mechanism on the sample surface, the angle at which the sample is viewed becomes larger, that is, the depth of focus becomes shallower, so information from a wide area inside the sample is lost, and information from a relatively narrow area on the sample surface is lost. This is because image formation can be expected to be performed based on the information.

However, when the WD is reduced and the sample is placed on the main surface of the objective lens or inside the lens, the secondary electrons generated on the sample surface are blocked by the objective lens pole piece near the sample and the magnetic or electric field that exists there. This makes it difficult for the secondary electrons to efficiently reach the secondary electron detector.

To avoid this problem, a relay electrode is installed near the sample.
It has been proposed to apply an appropriate bias voltage to the relay electrode to cause secondary electrons generated on the sample surface to collide with the relay electrode, and to guide the secondary electrons generated at the relay electrode to a detector for detection. ing.

Although the above-mentioned difficulties can be considerably alleviated by means of using this relay electrode, there is a drawback that the amount of secondary electrons detected is still insufficient.

The present invention compensates for the drawbacks of the conventional technique of detecting secondary electrons through a relay electrode when the WD is reduced, and provides a high-resolution method that can increase the amount of secondary electrons reaching the secondary electron detector. The purpose is to provide a scanning electron microscope.

FIG. 1 is a diagram showing an example of a conventional scanning electron microscope that detects secondary electrons via a relay electrode when the WD is reduced.

1 is a primary (scanning) electron beam, 2 is an objective lens, 3 is a sample,
4 is a sample holder, 5 is a scintillator, 6 is a light guide, 7 is a secondary electron generated on the sample surface, 8 is a secondary electron generated on the relay electrode surface, 9 is a relay electrode, and 10 is an insulator.

In the example shown in FIG. 1, the sample 3 is placed at the main surface of the objective lens 2.

That is, WD=Qmm. A relay electrode 9 is provided for such a sample position, and an appropriate positive bias voltage EB is applied to the electrode to relay the secondary electrons 7 generated when the surface of the sample 3 is irradiated with the electron beam 1. The secondary electrons 8 generated on the surface of the relay electrode 9 by this collision are sent to the scintillator 5 (the surface of which is connected to the secondary acceleration power source Ep).
It was thought that a relatively large amount of secondary electrons could be detected by a relatively simple means of providing a relay electrode 9, by introducing a voltage of approximately +12 kV (applied with a voltage of approximately +12 kV).

However, in reality, it is desirable to increase the amount of secondary electrons that reach the scintillator 5, so in the present invention, a focusing electrode is placed along the path of the secondary electrons, especially between the relay electrode 9 and the scintillator 5. By applying a suitable bias voltage, the generated secondary electrons were efficiently guided to the scintillator.

FIG. 2 is a diagram showing one embodiment of the present invention.

In FIG. 2, 11 is an insulator, 12 is a focusing electrode, and other symbols are the same as in FIG. 1.

In this embodiment, the focusing electrode 12 is biased to the same potential as the relay electrode 9.

Note that when the secondary electrons 8 reach the scintillator 5, they are converted into light, which is passed through the light guide 6 and converted into a signal current in a photomultiplier tube (not shown).

FIG. 3 shows the case where the focusing electrode 12 is not provided (the case of the example shown in FIG. 1) and the case where the focusing electrode 12 is provided and biased to the same potential as the relay electrode 9 (the case of the embodiment shown in FIG. 2). ,
FIG. 3 is a diagram showing the relationship between bias voltage EB and photomultiplier tube output current.

The case without the focusing electrode is shown by ■, and the case where the focusing electrode 12 is provided is shown by ■.

The voltage applied to the focusing electrode 12 and the relay electrode 9 is approximately 3
It can be seen that in the case of 00■ or more, a signal current of about 2.3 times or more is obtained.

The equipment conditions when obtaining the results shown in Figure 3 were (a) acceleration voltage 25 kV, (b) probe current 2 x 10 = 1 A,
(C) Photomultiplier tube applied voltage was 600 V, (d) Tilt angle was 30°, and (e) WD=Qmm.

FIG. 4 shows another embodiment of the present invention, in which the focusing electrode 12 is cylindrical.

FIG. 5 is a diagram showing still another embodiment of the present invention, showing an example in which the focusing electrode 12 is shaped like a rectangular tube.

As explained above, the present invention makes it possible to detect a large amount of secondary electrons by simply providing a focusing electrode in addition to the relay electrode and applying a bias voltage of about 300 V or more to these electrodes. This made it possible to obtain high-resolution images with good S/N ratio.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of a conventional device provided with a relay electrode to detect secondary electrons when the WD is reduced, Fig. 2 is an example of an embodiment of the present invention, and Fig. 3 is a bias voltage The relationship between EB and photomultiplier tube output current is shown for the conventional example shown in Fig. 1 and the case of the embodiment of the present invention shown in Fig. 2. Fig. 4 shows the relationship between the EB and the photomultiplier tube output current. FIG. 5 is a diagram showing an embodiment of the present invention in which the focusing electrode is shaped like a rectangular tube. 1...Primary (scanning) electron beam, 3...Sample, 5...Scintillator, 7...Secondary electrons generated on the sample surface, 8... ...Secondary electrons generated on the surface of the relay electrode, 9...Relay electrode, 12.
...Focusing electrode.

Claims (1)

[Scope of utility model registration request] A relay electrode is provided near the sample, a bias voltage is applied to the relay electrode, and secondary electrons generated by scanning and irradiating the sample surface with the primary electron beam collide with the relay electrode,
In a scanning electron microscope in which a signal current is obtained by detecting secondary electrons generated at the relay electrode with a secondary electron detector, a focusing electrode is disposed along the path of the secondary electrons, and a focusing electrode is arranged along the path of the secondary electrons. A scanning electron microscope characterized in that a bias voltage of about 300 V or more is applied to the relay electrode.