JPH08138601A - Scanning electron microscope - Google Patents

Abstract

PURPOSE: To easily make extremely low magnification observation high in image quality by a short-focus distance lens. CONSTITUTION: A primary electron beam 4 which is emitted from a negative electrode 1 by voltage V1 applied on the negative electrode 1 and a positive electrode 2 is accelerated by voltage Vacc applied on a positive electrode 3 and advances on a lens system of the rear stage. The primary electron beam 4 is finely converged on a sample 7 by a converged lens 5 and an objective lens 6, which are controlled by a lens control power supply 11, so as to be secondarily scanned on the sample 7 by deflection coils 8 and 9. Scanned signals of the deflection coils 8 and 9 are controlled by a deflection control circuit 13 according to observation magnification. And secondary electrons 21 generated from the primary electron beam irradiation point of the sample 7 are moved up around a magnetic field 20 of the objective lens 6 and detected by the secondary electron detector 17 so as to be changed into a secondary electron signal. The secondary electron signal and the scanned signals of the deflection control circuit 13 are input in an image display device 19 so that an expansion image (secondary electron image) of the sample is displayed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam apparatus, and more particularly to a scanning electron microscope suitable for enhancing the image quality in an extremely low magnification image.

[0002]

2. Description of the Related Art Conventionally, in a scanning electron microscope, in order to obtain high magnification and high resolution, a sample is placed in a lens magnetic field to shorten the focal length of the lens. Then, a secondary electron detector is arranged above the objective lens (electron source) to detect secondary electrons that are wound up by the magnetic field of the objective lens and proceed to the upper side to display an enlarged image of the sample. On the other hand, the distance (working distance) of the sample objective lens is set to 30 for low magnification observation.
Since it is used in a relatively long length of mm to 40 mm, there is a problem that the image quality is poor in image observation at an extremely low magnification. Therefore, in order to realize low magnification with a normal two-stage deflection type short focus lens, 25
The limit is 0 times. Further, in order to realize an extremely low magnification of several tens of times, there is a method in which the excitation of the objective lens is turned off or weakly excited and the deflection coil is used in one stage to increase the deflection amount on the sample. In this case, since the lens magnetic field is off or weakly excited, secondary electrons do not proceed to the secondary electron detector, and there is a problem of poor image quality of detection sensitivity.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a scanning electron microscope capable of improving the image quality of extremely low magnification observation in a state where the working distance for obtaining high resolution is relatively short.

[0004]

In order to achieve the above object, according to the present invention, two secondary electron detectors can be automatically selected when used at a normal high magnification and when used at an extremely low magnification. A switch is provided to change the position of the secondary electron detector. In order to obtain an extremely low magnification, secondary electrons are detected from a secondary electron detector arranged in the sample chamber (outside the objective lens). When the operator sets an extremely low magnification (for example, 250 times or less) for searching an observation field of view, the control circuit automatically switches the changeover switch to the secondary electron detector side.

[0005]

According to the above-mentioned characteristic structure of the present invention, the following operational effects can be obtained. That is, in the usual high-resolution observation that does not require extremely low magnification, the secondary electron wound by the conventional two-stage deflection and the lens magnetic field is detected by the secondary electron detector. To obtain extremely low magnification with a short focal length objective lens,
The control circuit switches to one-stage deflection and turns off the excitation of the objective lens. Then, the extremely low magnification state can be easily obtained. However, since the excitation of the objective lens is off, secondary electrons cannot be detected by the secondary electron detector due to the winding of the magnetic field. Therefore, when the magnification setting becomes extremely low, the control circuit automatically switches the secondary electron detector to the secondary electron detector side. Secondary electrons generated from the sample are efficiently detected by the secondary electron detector, and observation with high image quality can be performed at extremely low magnification.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a system diagram of an embodiment of the present invention. The primary electron beam 4 emitted from the cathode 1 by the voltage V1 applied to the cathode 1 and the anode 2 is accelerated to the voltage Vacc applied to the anode 3 and advances to the lens system in the subsequent stage.
The primary electron beam 4 is narrowed down to the sample 7 by the focusing lens 5 and the objective lens 6 controlled by the lens control power source 11, and the deflection coils 8 and 9 two-dimensionally scan the sample.
The scanning signals of the deflection coils 8 and 9 are controlled by the deflection control circuit 13 according to the observation magnification. On the other hand, the secondary electrons 21 generated from the primary electron beam irradiation point of the sample 7 are wound up by the magnetic field 20 of the objective lens 6, and the secondary electron detector 17
Detected and converted into a secondary electron signal. The secondary electron signal and the scanning signal of the deflection control circuit 13 are input to the image display device 19, and an enlarged image (secondary electron image) of the sample is displayed.

The winding ratio of the deflection coils 8 and 9 is such that the deflection fulcrum of the primary electron beam 4 is on the lens main surface of the objective lens 6 when the scanning signal of the deflection control circuit 13 flows through both deflection coils with the same current. Is set to. Deflection coil 9
Is provided with a one-stage changeover switch 14, and can be turned off by a changeover signal from the switch control circuit 12. Further, the objective lens 6 is also turned on / off by the exciting current selector switch 16.
You can turn it off. In addition to the secondary electron detector 17, 18 is arranged outside the objective lens 6. Then, the detector changeover switch 16 can select either the secondary electron detector 17 or 18. Changeover switch 14,
Both 15 and 16 can be controlled individually or by interlocking with the switch control circuit 12.

FIG. 2 is a system diagram showing an embodiment of the present invention. In this embodiment, the deflection trajectory (solid line and dotted line) of the primary electron beam 4 at extremely low magnification, the states of the changeover switches 14, 15 and 16, and the traveling state of the secondary electron 21 are shown. Usually, it is difficult to obtain an extremely low magnification with a working distance of high resolution observation. Therefore, the objective lens 6 is turned off by the exciting current switching switch 16. Then, the deflection coil 9 is turned off by the one-stage changeover switch 14 to perform the one-stage deflection, so that an extremely low magnification observation state can be easily obtained even at a short focal length. However, in order to obtain the extremely low magnification, the secondary electron 21 is not wound up by turning off the objective lens 6, so that it is not detected by the secondary electron detector 17. Therefore, when set to an extremely low magnification (for example, 250 times or less), the switch control circuit 12 automatically switches the detector changeover switch 15 to the secondary electron detector 18, so that the secondary electrons 7 generated from the sample 7 The secondary electron detector 18 efficiently detects it, and observation with extremely low magnification with high image quality can be performed.

[0009]

According to the present invention, very low magnification observation with high image quality can be easily performed with a short focal length lens.

[Brief description of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention.

FIG. 2 is a system diagram showing a deflection trajectory of a primary electron beam, a state of a changeover switch, and a traveling state of secondary electrons at an extremely low magnification.

[Explanation of symbols]

1 ... Cathode, 2, 3 ... Anode, 4 ... Primary electron beam, 5 ... Focusing lens, 6 ... Objective lens, 7 ... Sample, 8 ... Upper deflection coil, 9 ... Lower deflection coil, 10 ... Objective lens diaphragm, 11
... Lens control power source, 12 ... Switch control circuit, 13 ... Deflection control circuit, 14 ... One-stage changeover switch, 15 ... Detector changeover switch, 16 ... Excitation current changeover switch, 17, 18
... secondary electron detector, 19 ... image display device, 20 ... magnetic field, 2
1 ... Secondary electron.

Claims (2)

[Claims] 1. A focusing lens system for narrowing a primary electron beam to irradiate a sample and a two-stage deflector arranged on an optical axis for two-dimensionally scanning the primary electron beam on the sample. In a scanning electron microscope comprising an electron optical system including: and a display unit that detects a secondary electron generated from the sample and displays an enlarged image of the sample, a single-stage deflection switching operation and a sample chamber A scanning electron microscope characterized by using the operation of a secondary electron detector in conjunction with the magnification setting. 2. The scanning electron microscope according to claim 1, further comprising a control circuit for automatically switching in association with the magnification setting.