JPS6093746A - Electron ray deflector - Google Patents

Abstract

PURPOSE:To enable signals from the sample to be easily analyzed by displaying the scanning angle by the coil current of the electron lens and the signal of the deflecting system. CONSTITUTION:The amplitude of the signal produced in an X-axis-deflecting-signal-producing circuit 7 is controlled by a microcomputer 10. The signal is also subjected to current amplification in an X-axis-deflecting circuit 5 to drive an X-axis deflecting coil 2. In the same way, the amplitude of the signal produced in a Y-axis-deflecting-signal-producing circuit 8 is controlled by a computer 10. The signal is alos subjected to current amplification in a Y-axis-deflecting circuit 6 to drive a Y-axis-deflecting coil 2. The standard voltage of an electron-lens- driving circuit 9 is controlled by a computer 10 to drive an electron lens 3. The scanning angle of electron rays is obtained by computing the coil current (Il) of the lens 3 and the currents (Ix) and (Iy) of the coil 2 by the computer 10 before being displayed on an angle displayer 11. By the mechanism mentioned above, the scanning angle is automatically displayed and it is possible to easily analyze the signal from a sample 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to improvement of an electron beam deflection device effective for observation of selected area diffraction images using a scanning electron microscope.

[Background of the invention]

In order to obtain a selected area diffraction image from a minute area of a sample using a scanning electron microscope, 1Ill of well-paralleled electrons are angularly scanned around the minute area of the sample targeted for analysis. Conventionally, the scanning angle was determined by observing a selected area diffraction image. However, there is a drawback in that even in the case of unknown or known diffraction images, it is necessary to compare them with a table containing the scanning angles of standard diffraction images.

[Purpose of the invention]

An object of the present invention is to provide an electron beam deflection device that automatically displays a scanning angle using a coil current of an objective lens and a signal of a deflection system.

[Summary of the invention]

According to the present invention, the scanning angle of a selected area diffraction image is calculated and displayed equally economically using the coil current of the electron lens and the signal of the deflection system.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure shows an example of controlling f(tU) of a nine-element deflection lens system using a microcomputer.

The signal generated by the X-axis deflection signal generation circuit 7 has an amplitude controlled by 1fflJ by the microcomputer lo, is current amplified by the X-axis deflection circuit 5, and drives the Xl1II deflection coil. Similarly, in the Y-axis deflection signal generation circuit 8, 32# I-
+ Ij4)1rf? I, r't M'
/W'-+Jff/'lItrIk The amplitude is controlled, the current is amplified by the Y-axis deflection circuit 6, and the Y-axis deflection coil is driven.

On the other hand, the electronic lens drive circuit 9 is operated by a microcomputer l.
The standard 'M working pressure is controlled from 0VC, and the electronic lens 3'i
I-drive.

The current of each deflection coil and electron lens is IxlIa+I
It is represented by the symbol t.

FIG. 2 is a diagram in which only the electron optical system portion of FIG. 1 is extracted.

The electron beam 1 is deflected by the deflection coil 2 and enters the electron lens 4 off-axis. Then, it is refracted by the refractive power of the electron lens 4 and irradiated onto one point on the sample 4.

If the current flowing through the coil in the 1iIII direction is i, , Ia, then
Expressed by CIi equation (1) in Figure 2! L.

C= K+ a (Il!2+IF")..."■
(1) Next, the focal length f of the 'nL child lens can be expressed as follows. Further, the relationship between the lens current It of the electron lens and the focal length f can be expressed as follows.

According to these formulas, the scanning angle θ (rad) is θ=ja
It becomes n-1-. In equation (4), Iz+Iy+It is controlled by a microcomputer and is known, and aF
i is a constant determined by the geometric method. Therefore, θ can be calculated by the microcomputer using equation (4) and displayed on the angle display 11. Furthermore, the formula (4
) in K1. 2) is unique to the device, and can be determined in advance by experiment.

In equation (4), the angle θ can be approximated as a small angle.

This has the effect that the scanning angle can be calculated more easily than equation (4).

Various methods can be considered for displaying the scanning angle.

The maximum scanning angle, the momentary scanning angle, or in the case of a scanning electron microscope, a scale and numerical values are displayed on the cathode ray tube (CR, T) used for image observation and photography.

The case where angular scanning is easily obtained using an electronic lens has been described above, but it will be explained next that angular display can be performed in the same way with a device having an aberration correction function when performing large angular scanning.

In Fig. 3, when the electron beam passes off-axis of the electron lens 3, if the Nariko lens current is kept constant, due to spherical aberration, there is a difference between A when it passes near the central axis and B when it passes far away. , the incident position on the sample differs, and the condition for angle scanning at one point on the sample is not satisfied. This is not a problem when the scan angle is small, but becomes a significant problem when it becomes large.

Various methods have been considered to correct this. For example, as shown in Figure 3, if the electron beam is incident on the electron lens as shown in B, if the current of the electron lens is reduced and the electron beam passes through the electron lens as shown in C, then the It is K that the light is incident on one point. In this case as well, the focal length f shown in equation (3) can be determined by K in exactly the same way by using the electron lens current It when the electron beam passes near the central axis, and the scanning angle θ can also be determined by equation (4 ) can be calculated.

〔Effect of the invention〕

As described above, according to the present invention, in a device that performs angular scanning using a deflection system and an off-axis part of an electron lens, the scanning angle is automatically displayed, and signals from a sample can be easily analyzed. effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
A diagram in which only the electron optical system part in Figure 1 is drawn out,
FIG. 3 is a diagram illustrating a phenomenon that occurs when the angle of angular scanning is widened.

Claims (1)

[Claims] 1. In an apparatus in which an electron beam is incident off-axis of an electron lens by a deflection system so that the electron beam scans an angle centering on a predetermined point on a sample, the coil current of the electron lens and the deflection are An electron beam deflection device characterized in that the scanning angle is displayed based on a system signal.