JPH0535558Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement of an apparatus for obtaining a scanning electron microscope image using secondary electrons.

[Prior art] Recently, it has become possible to observe scanning electron microscope images using the electron beam irradiation system of a transmission imaging electron microscope.
A device with a secondary electron detector is used.

By the way, in such an apparatus, the secondary electron detector is arranged close to the optical axis Z in order to efficiently capture the secondary electrons generated from the sample. This is because the secondary electrons generated from the sample are aligned with the optical axis Z.
When the 2nd line rises in a spiral trajectory along the
This is to accelerate the secondary electrons toward the scintillator by applying the action of the electric field formed by the secondary electron capturing electrode provided in the secondary electron detector to the secondary electrons.

However, the electric field formed by the secondary electron trapping electrode gives irregular deflection and aberration to the electron beam for irradiating the sample. Therefore, in order to offset the effects of this incorrect deflection and aberration, axis alignment and astigmatism correction are performed, but even if such corrections are made, if the accelerating voltage is switched and used, the secondary electron The influence on the electron beam on the optical axis also changes depending on the electric field formed by the trapping electrode. Therefore, in the conventional device, adjustments such as axis alignment and astigmatism correction must be made every time the accelerating voltage is changed, resulting in a disadvantage that the operation becomes complicated.

[Purpose of the invention] The present invention aims to align the axis of the electron beam while keeping the influence of the electric field formed by the secondary electron capture electrode provided in the secondary electron detector substantially constant when the accelerating voltage is changed. The purpose is to simplify adjustment operations such as astigmatism correction.

[Structure of the invention] The structure of the invention includes a means for accelerating an electron beam taken out from an electron gun along the optical axis Z and irradiating the sample, a switching means for switching the accelerating voltage of the electron beam, and a means for accelerating the electron beam taken out from the electron gun along the optical axis Z to irradiate the sample. In an apparatus equipped with a secondary electron detector that guides and detects secondary electrons by its secondary electron trapping electric field, the detector position is moved to change the distance between the secondary electron detector and the optical axis Z. and means for driving the detection position moving means so that the influence of the secondary electron trapping electric field on the electron beam on the optical axis Z becomes substantially constant in conjunction with the switching of the acceleration voltage by the switching means. It is characterized by

[Examples] Examples of the present invention will be described below in detail based on the accompanying drawings.

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 2 is an enlarged view of the main parts thereof. In the figure, 1 is an electron gun for emitting an electron beam 2 along the optical axis Z, and 3 is a sample inserted approximately in the center of the gap between the objective lens upper magnetic pole piece 4 and the objective lens lower magnetic pole piece 5. . The electron beam 2 is two-dimensionally scanned on the sample surface of the sample 3 by a deflection coil (not shown), and secondary electrons 5 are generated from the sample surface. 6 is a secondary electron detector for detecting secondary electrons e generated from the sample 3. A detector holder 9 is vacuum-sealed and attached to the lens barrel 7 by a sealing member 8, and the secondary electron detector 6 is movably attached to the detector holder 9 while maintaining a vacuum. There is. 10 is a stepping motor for moving the secondary electron detector 6 in a direction perpendicular to the optical axis Z. Reference numeral 11 denotes a moving rod for moving the secondary electron detector 6, and a rack 12 is formed on the moving rod 11. 13 is a pinion fixed to the shaft of the stepping motor 10;
2 and pinion 13 are meshed with each other. Therefore, when the stepping motor 10 rotates, 2
The secondary electron detector 6 is configured to move in the optical axis Z direction or in the opposite direction. A secondary electron detector 6 for detecting the secondary electrons 5 is composed of a light pipe 15 having a scintillator 14 attached to its tip, an optical axis multiplier tube (not shown), etc. disposed at its rear end. . scintillator 14 at the tip of the light pipe
A conductive thin film is deposited on the front surface of the conductive thin film, and the conductive thin film is coated with a high positive voltage from a DC power source (not shown) together with a ring-shaped secondary electron capturing electrode 16 for capturing secondary electrons e. is applied. Further, a shield tube 17 having a ground potential is provided around the light pipe 15. Reference numeral 18 denotes a drive power source for driving the stepping motor 10, and the drive power source 18 is controlled based on a signal from a control circuit 20. This control circuit 20 includes an acceleration power source 19
A signal representative of the accelerating voltage is provided.

In the device configured as above, for example, when the accelerating voltage is switched to 100 KV, 50 KV, and 10 KV, the effect on the electron beam 2 by the secondary electron capturing electrode 16 is constant at each accelerating voltage. , the amount of movement of the secondary electron detector 6 based on the control of the control circuit 20 is set in advance. Therefore, when the electron beam 2 is accelerated by the acceleration power source 19 at, for example, 100 KV, the control circuit 20 controls the drive power source 18 based on the signal representing the acceleration voltage from the acceleration power source 19, and the stepping motor 10 Move the secondary electron detector 6 to the position A shown by the dotted line in FIG. The influence of the electric field on the electron beam 2 is controlled to be approximately constant. Therefore, even when the accelerating voltage is switched, the amount of deflection and the amount of astigmatism change of the electron beam 2 remain substantially constant, and adjustment operations such as axis alignment and astigmatism correction can be easily performed.

Note that the above is an example, and modifications are possible. In this embodiment, in order to move the detector in conjunction with switching of the accelerating voltage, a signal representing the accelerating voltage from the accelerating power source was supplied to the control circuit, but generally the average signal intensity from the secondary electron detector 6 is The higher the voltage, the lower the signal strength, so the control circuit 20
The detector may be moved in response to changes in the average signal strength.

[Effect of the device] As described above, the device irradiates the sample with an electron beam,
In the apparatus for obtaining a scanning electron microscope image using secondary electrons from the sample, the secondary electron trapping electric field is set so that the influence of the secondary electron trapping electric field on the electron beam on the optical axis Z becomes approximately constant according to switching of the accelerating voltage. By automatically moving the position of the electron detector, the amount of deflection and astigmatism of the electron beam are kept approximately constant,
A device is provided that facilitates adjustment operations such as axis alignment and astigmatism correction accompanying switching of acceleration voltage.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is an enlarged view of the essential parts of the embodiment of the apparatus shown in FIG. 1...electron gun, 2...electron beam, 3...sample,
4, 5... Objective lens magnetic pole piece, 6... Secondary electron detector, 7... Lens barrel, 8... Seal member, 9... Detector holder, 10... Stepping motor, 1
DESCRIPTION OF SYMBOLS 1...Moving rod, 12...Rack, 13...Pinion, 14...Scintillator, 15...Light pipe, 16...Secondary electron capturing electrode, 17...Shield tube, 18...Drive power source, 19... ...acceleration power supply,
20...Control circuit.

Claims (1)

[Scope of utility model registration request] A means for accelerating an electron beam taken out from an electron gun along an optical axis Z and irradiating the sample, a switching means for switching the accelerating voltage of the electron beam, and a means for capturing secondary electrons from the sample. In an apparatus equipped with a secondary electron detector that is guided and detected by an electric field, a detector position moving means for changing the distance between the secondary electron detector and the optical axis Z, and switching of the accelerating voltage by the switching means. A secondary electron detection device characterized by comprising means for driving the detector position moving means so that the influence of the secondary electron trapping electric field on the electron beam on the optical axis Z becomes substantially constant. .