JPH1012171A - Electron beam device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide by simple constitution an electron beam device capable of conducting the position correction and astigmatism correction of an electron beam caused by the variation of accelerating voltage. SOLUTION: The correction of astigmatism of an electron beam EB irradiated to a sample 4 is conducted by supplying astigmatism data from an X direction astigmatism correction data memory 16 and a Y direction astigmatism data memory 17 to astigmatism correction coils 11, 12 through astigmatism correction circuits 13, 14. Correction data corresponding to accelerated voltage is supplied to the astigmatism correction circuits 13, 14 from centering correction data memories 17, 18, and a centering correction signal is added to an astigmatism correction signal supplied to the astigmatism correction coils 11, 12.

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, such as a scanning electron microscope, which eliminates troublesome adjustment of astigmatism correction and corrects an axis shift corresponding to an acceleration voltage of an electron beam.

[0002]

2. Description of the Related Art In a conventional scanning electron microscope, a primary electron beam from an electron gun is finely focused on a sample by a condenser lens and an objective lens, and the primary electron beam is two-dimensionally scanned on the sample by a scanning coil. doing. Then, secondary electrons and the like generated by the irradiation of the sample with the electron beam are detected, and a detection signal is supplied to a cathode ray tube synchronized with the scanning of the electron beam to display a secondary electron image or the like on the cathode ray tube. I have.

In such a scanning electron microscope, if the primary electron beam has astigmatism, the primary electron beam cannot be focused finely on the sample, so that the astigmatism is corrected. FIG. 1 shows an arrangement of an astigmatism correction coil arranged on the optical axis of the primary electron beam.

FIG. 1A shows an arrangement of an astigmatism correction coil in the X direction. Xa and xb are arranged to face each other, and xc
And xd are also arranged to face each other. The pair of astigmatism correction coils xa and xb and the pair of astigmatism correction coils xc and xd
They are arranged 90 ° apart.

FIG. 1B shows the arrangement of the astigmatism correction coils in the Y direction. Ya and yb are arranged to face each other, and yc
And yd are also arranged to face each other. The pair of astigmatism correction coils ya and yb and the pair of astigmatism correction coils yc and yd are:
They are arranged 90 ° apart. The X-direction astigmatism correction coil and the Y-direction astigmatism correction coil are arranged in a state of being rotated by 45 °.

In FIG. 1A, a current flows through the astigmatism correction coils xa and xb. The magnetic field generated by the flow of the current causes the electron beam to operate so as to be focused, for example, in the optical axis direction. receive. A current flows through the astigmatism correction coils xc and xd, and the magnetic field generated by the flow of the current causes the electron beam to diverge, for example, from the optical axis direction.

In FIG. 1B, a current flows through the astigmatism correction coils ya and yb. The magnetic field generated by the flow of the current causes the electron beam to operate so as to be focused, for example, in the optical axis direction. receive. Further, a current flows through the astigmatism correction coils yc and yd, and the electron beam undergoes an operation of diverging from, for example, the optical axis direction due to a magnetic field generated by flowing the current.

[0008] In this manner, the correction of the astigmatism of the electron beam is performed. The current flowing through each coil is changed according to the size of the astigmatism. Corrected to a perfect circle.

[0009]

According to the above configuration,
The astigmatism of the electron beam is corrected. When the acceleration voltage of the electron beam is changed, the position of the electron beam passing through the astigmatism correction coil changes. Therefore, in the conventional scanning electron microscope, it is necessary to provide a deflection system for optical axis alignment in addition to the astigmatism correction coil, which has a problem that the configuration of the electron optical system becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of such a point, and an object of the present invention is to provide an electron beam capable of performing a position correction and an astigmatism correction of an electron beam by a change in acceleration voltage with a simple configuration. The realization of the device.

[0011]

An electron beam apparatus according to the first aspect of the present invention focuses an electron beam generated from an electron gun and accelerated by an electron lens, and two-dimensionally scans the electron beam on a sample. In such an electron beam apparatus, deflecting means for the electron beam facing along the optical axis of the electron beam is provided, and the deflecting means is supplied with the astigmatism correction signal of the electron beam, and the The present invention is characterized in that a signal for axis deviation correction according to the acceleration voltage is added.

According to the first aspect of the present invention, a correction signal for the axis deviation of the electron beam due to the change in the acceleration voltage is supplied to the deflection system for astigmatism correction together with the astigmatism correction signal.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 shows an example of a scanning electron microscope according to the present invention. Reference numeral 1 denotes an electron gun. An electron beam EB generated and accelerated from the electron gun 1 is applied to a sample 4 by a condenser lens 2 and an objective lens 3. Focused thinly. Further, the electron beam EB is two-dimensionally scanned on the sample 4 by a scanning signal supplied to the scanning coil 5.

Secondary electrons generated by irradiating the sample 4 with the electron beam EB are detected by the detector 6. The detection signal of the detector 6 is converted into a digital signal by the AD converter 7 and then supplied to the frame memory 8 for storage. The image signal stored in the frame memory 8 is
It is read and supplied to the DA converter 9. DA converter 9
The image signal converted into the analog signal by the above is supplied to the cathode ray tube 10 and displayed.

X along the optical axis of the electron beam EB
Direction astigmatism correction coil 11 and Y direction astigmatism correction coil 1
2 are arranged. An astigmatism correction current is supplied from the X astigmatism correction circuit 13 to the astigmatism correction coil 11 in the X direction.
The Y direction astigmatism correction coil 12 includes a Y astigmatism correction circuit 14.
Supplies an astigmatism correction current.

The X astigmatism correction circuit 13 is supplied with the X direction astigmatism correction data from the astigmatism correction data memory 15, and the Y astigmatism correction circuit 14 is provided with the astigmatism correction data memory 1.
6 supplies the Y-direction astigmatism correction data.

Further, the X-direction astigmatism correction circuit 13 is supplied with the X-direction centering correction data from the X-direction centering correction data memory 17, and the Y-direction astigmatism correction circuit 1
4 is supplied with Y-direction centering correction data from a Y-direction centering correction data memory 18.

Centering correction data memory 17, 1
8, a signal corresponding to the acceleration voltage of the electron beam is supplied from an acceleration voltage control circuit 19 of the electron gun 1, and centering correction data corresponding to the acceleration voltage is supplied from the memories 17 and 18 to the astigmatism correction circuits 13 and 14. Is done.

FIG. 3 shows details of the X-direction astigmatism correction circuit 13 and the X-direction astigmatism correction coils 11 (xa, xb, xc, xd). The astigmatism correction data from the X-direction astigmatism correction data memory 16 is supplied to the DA converter 20 and converted into an analog signal, and then added to the adders 21, 22, 23, and 24.
Supplied to

The output current of the adder 21 is supplied to the astigmatism correction coil xa via the driver amplifier 25. The output current of the adder 22 is supplied to the astigmatism correction coil xb via the driver amplifier 26. The output current of the adder 23 is supplied to the astigmatism correction coil xc via the driver amplifier 27. The output current of the adder 24 is
Is supplied to the astigmatism correction coil xd. Note that a signal corresponding to the current flowing through each coil is returned to the input side of each driver amplifier and configured to operate as a constant current source.

The first centering correction data for the astigmatism correction coils xa and xb from the centering correction data memory 17 is converted into an analog signal by a DA converter 29, and then supplied to an adder 21 and an inverter. After being inverted by 30, it is supplied to the adder 22.

The second centering correction data for the astigmatism correction coils xc and xd from the centering correction data memory 17 is converted into an analog signal by a DA converter 31 and then supplied to an adder 23 and an inverter. After being inverted by 32, it is supplied to the adder 24.

FIG. 3 shows the details of the X-direction astigmatism correction circuit 13 and the X-direction astigmatism correction coils xa, xb, xc, xd. The details of the point correction coils ya, yb, yc, yd have the same circuit configuration as in FIG. Further, astigmatism correction data signals are supplied as reference signals for the D / A converters 29 and 31, so that the outputs of the D / A converters 29 and 31 do not become larger than the value of the astigmatism correction data signal. . The operation of such a configuration will now be described.

When observing a secondary electron image, the electron beam EB from the electron gun 1 is narrowly irradiated on the sample 4 by the condenser lens 21 and the objective lens 3, and the electron beam EB is irradiated on the sample 4 by the scanning coil 5. Is scanned two-dimensionally.

Secondary electrons generated by irradiating the sample 4 with an electron beam are detected by a secondary electron detector 6.
The detection signal of the detector 6 is converted into a digital signal by the AD converter 7 and then supplied to the frame memory 8 for storage. The signal stored in the frame memory 8 is read out and passed through the DA converter 9 to the cathode ray tube 10.
, A secondary electron image is displayed on the cathode ray tube 10.

Now, the electron beam EB applied to the sample 4
Is corrected by using the astigmatism correction data from the X-direction astigmatism correction data memory 16. That is, the X-direction astigmatism correction data memory 16 stores the X-ray of the electron beam in advance.
Correction data for optimally correcting astigmatism in the direction is stored. The correction data is supplied to the DA converter 20 and converted into an analog signal, and then added to the adders 21, 22, 2
3, 24.

The output current of the adder 21 is supplied to the astigmatism correction coil xa via the driver amplifier 25, and the output current of the adder 22 is supplied to the astigmatism correction coil xb via the driver amplifier 26. As a result, the electron beam is focused, for example, in the center direction by the astigmatism correction coils xa and xb, and the output current of the adder 23 is supplied to the astigmatism correction coil xc via the driver amplifier 27. Is supplied to the astigmatism correction coil xd via the driver amplifier 28. As a result, the electron beam receives a force by the astigmatism correction coils xc and xd, for example, in a direction diverging from the optical axis. Therefore, the astigmatism of the elliptical or elliptical electron beam is corrected to make it almost a perfect circle.

When the accelerating voltage of the electron beam generated from the electron gun 1 is changed, the traveling direction of the electron beam changes, and an optical axis alignment (centering) operation of the electron beam is required. In this embodiment, electron beam centering correction data corresponding to the electron beam acceleration voltage is created and stored in the X-direction centering correction data memory 17 and the Y-direction centering correction data memory 18.

When the acceleration voltage of the electron beam generated from the electron gun 1 is set by the acceleration voltage control circuit 19, the first correction data from the X-direction centering correction data memory 17 is supplied to a DA converter 29 and converted into an analog signal. The converted data is supplied to the adder 21. The adder 21 adds the first correction data and the astigmatism correction signal, and supplies the added signal to the astigmatism correction coil xa via the driver amplifier 25.

Further, the first correction data from the DA converter 29 is inverted by the inverter 30 and supplied to the adder 22 to be added to the astigmatism correction signal. That is, the adder 22 substantially subtracts the first correction data from the astigmatism correction signal, and supplies the calculation result to the astigmatism correction coil xb via the driver amplifier 26. As a result, the electron beam is deflected by the astigmatism correction coils xa and xb according to the first correction data.

X direction centering correction data memory 1
The second correction data from 7 is supplied to the DA converter 31, converted into an analog signal, and supplied to the adder 23. The adder 23 adds the second correction data and the astigmatism correction signal, and supplies the added signal to the astigmatism correction coil xc via the driver amplifier 27.

Further, the second correction data from the DA converter 31 is inverted by the inverter 32, supplied to the adder 24, and added to the astigmatism correction signal. That is, the adder 24 substantially subtracts the second correction data from the astigmatism correction signal, and supplies the result of the operation to the astigmatism correction coil xd via the driver amplifier 28. As a result, the electron beam is deflected by the astigmatism correction coils xc and xd according to the second correction data.

The circuit configuration shown in FIG. 2 is for the astigmatism correction coils xa, xb, xc, xd, but a similar circuit is provided for the astigmatism correction coils ya, yb, yc, yd. I have. As a result, the astigmatism correction coils ya, yb,
Correction data corresponding to the acceleration voltage is also supplied to yc and yd, and the electron beam is deflected. With these two types of deflection systems, the axis deviation of the electron beam due to the change in the acceleration voltage is corrected. As a result, the electron beam always travels on a constant orbit regardless of the acceleration voltage.

As described above, in the present embodiment, the axis deviation of the electron beam due to the acceleration voltage is corrected by the deflection coil for the astigmatism correction without specially providing the deflection system for the centering correction of the electron beam. Can be.

Although the embodiment of the present invention has been described in detail, the present invention is not limited to this embodiment. For example, the present invention can be applied to a case where secondary electrons are detected but reflected electrons are detected to display a reflected electron image. Although the electromagnetic coil is used for correcting the astigmatism of the electron beam, an electrostatic deflector may be used. Furthermore, the scanning electron microscope has been described as an example, but the present invention can be applied to other electron beam apparatuses that scan an electron beam.

[0036]

The electron beam apparatus according to the present invention comprises means for deflecting an electron beam facing along the optical axis of the electron beam, and supplies an astigmatism correction signal for the electron beam to the deflecting means. Since the correction signal is added with the signal for correcting the axis deviation according to the acceleration voltage of the electron beam, the deviation of the axis of the electron beam due to the acceleration voltage should be specially provided with a deflection system for the centering correction of the electron beam. Instead, the correction can be performed by the deflection coil for astigmatism correction.

[Brief description of the drawings]

FIG. 1 is a diagram showing an arrangement of an astigmatism correction coil arranged on an optical axis of a primary electron beam.

FIG. 2 is a diagram showing an example of a scanning electron microscope according to the present invention.

FIG. 3 is an X-direction astigmatism correction circuit 13 and X-direction astigmatism correction coils xa, xb, xc, and X in the scanning electron microscope of FIG. 1;
It is a figure which shows the detail of xd.

[Explanation of symbols]

 Reference Signs List 1 electron gun 2 condenser lens 3 objective lens 4 sample 5 scanning coil 6 secondary electron detector 7 AD converter 8 frame memory 9 DA converter 10 cathode ray tube 11 X-direction astigmatism correction coil 12 Y-direction astigmatism correction coil 13, 14 Astigmatism correction circuit 15, 16 Astigmatism correction data memory 17, 18 Centering correction data memory 19 Acceleration voltage control circuit 20, 29, 31 DA converter 21, 22, 23, 24 Adder 25, 26, 27, 28 Driver Amplifier 30, 32 Inverter

Claims (1)

[Claims] In an electron beam apparatus, an electron beam generated and accelerated by an electron gun is focused by an electron lens, and the electron beam is two-dimensionally scanned on a sample, along an optical axis of the electron beam. An electron beam deflecting means is provided to supply an electron beam astigmatism correction signal to the deflecting means, and to add a signal for axial deviation correction according to the acceleration voltage of the electron beam to the astigmatism correction signal. The configured electron beam device.