JPH035019B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for aligning an axis in an electron beam device capable of displaying an electron channeling pattern.

[Prior Art] As shown in FIG. 1, if the incident electron beam is angularly scanned in two directions θx and θy in a state where the irradiation point of the electron beam on the sample S is fixed at the incident point P,
Two lines parallel to the crystal plane are displayed on the display screen as loci of angles that satisfy the bragg condition. still,
OL indicates the objective lens. An image consisting of a set of two lines like this is called an electron channeling pattern, and by analyzing this electron channeling pattern, we can understand the crystal surface habit, grain boundaries, and crystal orientation relationships between different phases. Observation of this pattern has recently become widespread because it allows us to know the following. As mentioned above, angular scanning is necessary to obtain this electron channeling pattern, but in an apparatus that performs angular scanning by scanning the front focal plane of the objective lens with an electron beam, Due to the spherical aberration of the objective lens, the focal length F deviates by ΔF∝Cs(Xi ² +Yi ² )...(1). However, in equation (1), Xi, Yi
are the horizontal and vertical scanning signals flowing to the deflection coil for rocking the electron beam, and Cs is the spherical aberration coefficient of the objective lens. Therefore, when trying to obtain an electron channeling pattern in a minute area, a dynamic focus lens is provided near the objective lens, and the focal length is synchronized with the scanning of the electron beam by the amount given by equation (1). However, in order to maximize the correction effect of this dynamic focus lens, it is necessary to align the axes of the objective lens and the dynamic focus lens. Conventionally, this alignment is performed by mechanically moving a dynamic focus lens. By the way, when the excitation intensity of the objective lens is changed, the intensity of the deflection magnetic field by the lens changes, so alignment is required again, but as mentioned above, in the past, alignment was not done mechanically. Because it was getting old, the mirror had to be disassembled and aligned each time.
It was extremely troublesome.

SUMMARY OF THE INVENTION An object of the present invention is to solve these conventional drawbacks and provide an alignment method for an electron beam apparatus that can easily and accurately align an objective lens and a dynamic focus lens. .

[Configuration of the Invention] The present invention provides X-direction and Y-direction scanning signals Xi,
When Yi is supplied, Xi and Yi are supplied to the X and Y direction deflectors to scan the front focal plane of the objective lens with an electron beam, and the dynamic focus lens placed near the objective lens is supplied with Xi and Yi. By supplying a signal proportional to ² +Yi ² , the electron beam irradiation position on the sample is fixed and the electron beam is angularly scanned.
In the method for obtaining an electrochanneling pattern by guiding a detection signal accompanying the angular scanning to a display means, prior to obtaining the electron channeling pattern, scanning signals Xi and Yi are supplied to the X and Y direction deflectors, respectively. Then, a finely focused electron beam is scanned two-dimensionally on the sample, and a signal Xi ⁿ +Yi ⁿ is supplied to the dynamic focus lens, where n is a number of 2 or more, to perform the two-dimensional scanning. Observe the image displayed on the display means based on the accompanying detection signal, and adjust the deflection current of an alignment coil disposed in front of the objective lens so that an unblurred image area is located at the center of the display means. It is characterized by the fact that

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 2 is for showing an apparatus for carrying out the present invention. In the figure, 1 is an electron gun. After the electron beam EB from this electron gun 1 is focused by focusing lenses 2 and 3, it is passed through an objective lens. The light passes through the aperture 4 and enters the deflection system. The deflection system consists of the first stage scanning coils 5ax, 5ay for X (horizontal) and Y (vertical) direction scanning, the second stage scanning coils 5bx, 5by for X and direction scanning, and just outside the scanning coils 5ax, 5ay. The alignment coils 6ax, 6by are arranged immediately outside the first-stage alignment coils 6ax, 6ay and the scanning coils 5bx, 5by. These alignment coils 6ax, 6ay, 6
bx, 6by, deflection power supply 7ax, 7ay, 7bx, 7
It is designed to be able to supply a deflection current of more than by. The electron beam EB deflected by each scanning coil and alignment coil is irradiated onto a sample 10 through a dynamic focus lens 8 and an objective lens 9. 11X is a scanning signal generation circuit that generates a scanning signal in the X direction as shown in FIG. 3a;
The scanning signal from this scanning signal generation circuit 11X is sent to scanning coils 5ax and 5bx via a balance circuit 12X.
is supplied to. 11Y is a scanning signal generating circuit that generates a scanning signal in the Y direction as shown in FIG. There is. The X and Y direction scanning signals from the scanning signal generation circuits 11X and 11Y are also supplied to the scanning coils 13x and 13y of the cathode ray tube 13, so that the cathode ray tube 13 is scanned in synchronization with the scanning of the electron beam EB. It's getting old. Further, the scanning signals from the scanning signal generation circuits 11X and 11Y are sent to the squaring circuits 14X and 14X via switches Sx and Sy, respectively.
14Y is supplied. Square circuit 14X, 14
The output signal of Y is supplied to the adder circuit 15,
The output signal of the adder circuit 15 is sent to a variable amplification factor amplifier 16.
The light is supplied to the dynamic focus lens 8 via. Reference numeral 17 denotes an excitation power source for the objective lens 9, and an output signal from the excitation power source 17 is supplied to the objective lens 9 via an adder circuit 18. A current as shown in FIG. 3c can be supplied to this adder circuit 18 from a wobbler power supply 19 via a switch 20. 21 is a secondary electron detector, and the output signal from this detector 21 is supplied to the grid 13G of the cathode ray tube 13 via an amplifier 22 and an adder circuit 23. 24X is a comparison circuit, and this comparison circuit 24X is supplied with the X-direction scanning signal from the X-direction scanning signal generation circuit 11X and the signal from the potentiometer 25X.
A match pulse is generated when both signals match. Therefore, in response to the output signal from the potentiometer 25X, a bright line Lx as shown in FIG. 4a is displayed on the screen of the cathode ray tube 13, superimposed on the image. Similarly, 24Y is a comparison circuit, and this comparison circuit 24Y is supplied with the Y-direction scanning signal and the signal from the pollenciometer 25Y, and generates a matching pulse when both signals match. Therefore, the cathode ray tube 11
On the screen, a bright line as shown by Ly in FIG. 4a is displayed superimposed on the image.

In such a configuration, first, the focusing lens 3
After the excitation is made strong, the balanced circuit 12X,
12Y, the electron beam EB is deflected using the center of the objective lens 9 as a deflection branch, as shown by the dotted line in FIG. 2, thereby scanning the sample two-dimensionally to obtain a normal scanning image. Do it like this.
When the output signal from the detector 21 obtained in conjunction with this scanning is supplied to the cathode ray tube 13 via the amplifier 22, a secondary electron image of the sample 10 is displayed on the cathode ray tube 13. Therefore, the objective lens 9 is focused to display a sharp image. Next, after operating the potentiometers 25X and 25Y so that the intersection U of the bright lines Lx and Ly displayed on the cathode ray tube 11 is located at the center of the screen of the cathode ray tube 11 as shown in FIG. 4b, The sample 10 is moved to align the image D of a target object such as dust attached to the sample surface with the intersection U. Therefore, a wobbler current as shown in FIG. 3c is generated from the wobbler power source 19 to periodically change the focal length of the objective lens 9. As a result, the position of the image D of the target object rotates around the intersection U. Therefore, by adjusting the position of the objective diaphragm 4 so that the position of the target image D does not move, the axis of the objective lens 9 can be set at a position corresponding to the center of the screen. Next, the axis of the objective lens 9 and the dynamic focus lens 8 are aligned. For example, suppose that the axis Cd of the dynamic focus lens 8 is deviated from the axis Co of the objective lens 9 by a distance d as shown in FIGS. 5a and 5b. Therefore, first, turn off the switch 20 to cut off the supply of wobbler current from the wobbler power supply 19, so that the objective lens 9 is supplied with a steady excitation signal from the excitation power supply 17, and then close the switches Sx and Sy. X and Y direction scanning signals are supplied to square circuits 14X and 14Y. As a result, the X and Y direction scanning signals are Xi,
When Yi, the adder circuit 15 supplies the dynamic focus lens 8 with an excitation current proportional to Xi ² +Yi ² . Now, for simplicity, Yi
= 0, alignment coil 6
If alignment is not done by ax, 6ay, 6bx, and 6by, the electron beam EB moves on the sample 10 at the position indicated by the arrow E (corresponding to the center of the cathode ray tube screen), as shown in Figure 5a. However, as the electron beam EB scans in the X direction, the focal length of the dynamic focus lens 8 is changed in proportion to Xi ² , so the electron beam EB based on both lenses is scanned in the X direction. The focal point changes as shown by a quadratic curve R around an axis C shown by a two-dot chain line in FIG. 5a connecting the center of the objective lens 9 and the center of the dynamic focus lens 8. Therefore, on the screen of the cathode ray tube 13, only the area F at the edge of the screen is sharp and the other parts are blurred, as shown in FIG. The image will be displayed. Figure 4c
, D' and D'' indicate images of the target object that rotate vibrationally. Therefore, as the amplification factor of the variable amplification factor amplifier 16 is increased, this sharp region F as shown in FIG. The size of the target object D becomes narrower and it becomes possible to pinpoint the target object D in terms of location, and the movement of the target object D becomes even more rapid.
is moved mechanically to move the image D of the target object into the area F. Therefore, the image D of the target object is displayed sharply without rotation. Therefore, the deflection power supply 7ax,
7ay, 7b, and 7by to adjust the current supplied to the alignment coils 6ax, 6ay, 6bx, and 6by, as shown in FIG. make it match. In this state, the electron beam EB based on the dynamic focus lens 8 and objective lens 9 is
The focal point of the electron beam EB is
As shown by a quadratic curve R', the position on the sample corresponding to the center of the screen (indicated by arrow E) is on the axis C. Therefore, the electron beam EB has alignment coils 6ax, 6
ay, 6bx, and 6by cause the light to enter the objective lens 9 along the axis C, so that the axis of the objective lens 9 and the axis of the dynamic focus lens 8 can be made to coincide. Therefore, after the focusing lens 3 is weakly excited, the balance circuits 12X and 12Y are adjusted so that the electron beam
The focal point of EB is positioned on the front focal plane S of the objective lens 9. Therefore, when a signal proportional to Xi ² +Yi ² is supplied to the dynamic focus lens 8, each scanning coil receives a scanning signal Xi,
If Yi is supplied, the axes of the dynamic focus lens 8 and the objective lens 9 are aligned, so the spread of the electron beam irradiation point due to the spherical aberration of the objective lens can be corrected with high precision by the dynamic focus lens. , it is possible to display an electron channeling pattern by irradiating only an extremely small area with an electron beam.

In the above-described embodiment, when the axes of the dynamic focus lens and the objective lens are aligned, the signal supplied to the dynamic focus lens is used as a signal to be supplied to the dynamic focus lens when obtaining an electron channeling pattern. Although the signal to be supplied is used, for example, a signal obtained by adding the cube of the scanning signals in the X and Y directions may be added and supplied.More generally, when n is a number of 2 or more, Xi A signal of ⁿ +Yi ⁿ can be supplied.

Furthermore, in the above embodiment, the intersection of two bright lines was used as a mark to indicate the position on the screen, but it may also be a bright spot or a mark with a color that allows it to be distinguished from other image parts. Points etc. are also acceptable.

[Effect] As is clear from the above explanation, in the method based on the present invention, the axis of the objective lens and the axis of the dynamic focus lens can be easily and accurately aligned, so that When a dynamic focus lens is used to correct the spread of the electron beam irradiation point due to the spherical aberration of the objective lens, its effect can be fully demonstrated. Therefore, an electron channeling pattern can be displayed by scanning the angle of the electron beam while irradiating only an extremely small area with the electron beam.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining scanning of an electron beam to obtain an electron channeling pattern.
2 is a diagram illustrating an example of a device for implementing the present invention, FIG. 3 is a diagram illustrating output signals of each circuit element of the embodiment device shown in FIG. 2,
FIG. 4 is a diagram showing changes in the display screen of the cathode ray tube due to alignment work of the objective lens and dynamic focus lens, and FIG. 5 is an optical diagram for explaining the effects of the present invention. 1: Electron gun, 2, 3: Focusing lens, 4: Aperture,
5ax, 5ay, 5bx, 5by: scanning coil, 6ax,
6ay, 6bx, 6by: alignment coil, 7
ax, 7ay, 7bx, 7by: Deflection power supply, 8: Dynamic focus lens, 9: Objective lens, 1
0: Sample, 11X, 11Y: Scanning signal generation circuit,
12X, 12Y: Balanced circuit, 13: Cathode ray tube, 1
4X, 14Y: Square circuit, 15, 18, 23: Adder circuit, 16: Variable gain amplifier, 17: Excitation power supply, 19: Wobbler power supply, 20: Switch, 2
1: Secondary electron detector, 22: Amplifier, 24X, 2
4Y: comparison circuit, 25X, 25Y: potentiometer, C: composite axis of objective lens and dynamic focus lens, EB: electron beam, Lx, Ly: bright line, U: intersection of bright lines, D, D', D ″: Image of target object,
E: Arrow, S: Front focal plane.

Claims (1)

[Claims] 1 When the X-direction and Y-direction scanning signals are Xi and Yi, respectively, Xi and Yi are supplied to the X- and Y-direction deflectors to scan the front focal plane of the objective lens with the electron beam and to scan the front focal plane of the objective lens. By supplying a signal proportional to Xi ² + Yi ² to a dynamic focus lens placed nearby, the irradiation position of the electron beam on the sample is fixed, the electron beam is angularly scanned, and the detection signal accompanying the angular scanning is In the method of obtaining an electron channeling pattern by guiding the electrons to a display means, prior to obtaining the electron channeling pattern, scanning signals Xi and Yi are respectively supplied to the X and Y direction deflectors and focused narrowly on the sample. Scanning the electron beam two-dimensionally and supplying a signal Xi ⁿ +Yi ⁿ to the dynamic focus lens when n is a number of 2 or more, and displaying means based on the detection signal accompanying the two-dimensional scanning. A deflection current of an alignment coil disposed in front of the objective lens is adjusted so that an image displayed on the display means is observed and an unblurred image area is located at the center of the display means. Axis alignment method in electron beam equipment.