JPS59181449A - Two-step deflector for electron microscopes - Google Patents

Abstract

PURPOSE:To eliminate any change in the irradiating point of an electron beam to a sample in time of height and positional displacement in the sample or a variation in magnification as well as to make an accurate dark sight image observable, by installing a device capable of varying a ratio of a current or voltage to be fed to both of two-step deflectors according to the exciting strength of an objective lens. CONSTITUTION:A current for securing a necessary deflecting angle in a deflecting angle setting circuit 5 is set and fed to a shunt control circuit 6. This transferred current from the shunt control circuit 6 is halved into two parts with a fixed rate, and its one side is fed to a first deflecting coil 1 via an amplifier 7 while the other side is fed to a second deflecting coil 2 via an amplifier 8. The current value of an objective lens exciting power source 9 is designed to be variable for focusing. Signals in regard to the current value from this objective lens' power source 9 is fed to the shunt control circuit 6 and makes a shunt ratio of the current to be fed to both first and second deflecting coils 1 and 2 variable according to the value. With this constitution, even if the objective lens is varied whatsoever, such a two-step deflector as leaving the irradiating position of electron beams on a sample unchanged can be brought to fruition.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-stage deflection arrangement for use in transmission electron microscopes and the like.

For example, in a transmission electron microscope, it is often necessary to observe not only a bright field image of a sample but also a desired dark field image.

To observe the 11n field image, it is necessary to irradiate the electron beam at a predetermined angle θ (approximately 1) with respect to the optical axis. A two-stage deflection system is used. FIG. 1 is a diagram explaining the outline of a two-stage ft+a direction system, in which 1 is a first deflection coil, 2 is a second deflection coil, each having X and Y coils. The line can be deflected in any direction. The circular deflection coil is connected to a DC power source via a current shunt (not shown). 3 is an objective lens, and a sample 4 is placed inside the magnetic field of this objective lens.The electron beam generated in the electron beam irradiation system is
The electron beam is deflected by the deflection coil 1 of test without changing the sample irradiation position ('3I) It is necessary to change the irradiation angle to
, J2 is determined by the geometric relationship between the sample and both coils, as explained below.

The distance between the coil 1 and the second deflection coil 2 is 21, the distance between the second deflection coil and the sample is 9.2, and the distance between the first deflection coil and the sample is 21. 2. The deflection angle by the first deflection coil and the second deflection coil is approximately θ7. In the case of θ2, in order for the electron beam trial Terukawa fish not to change, Ω71θ1−Ω,';:0=Q2 (θ2−01)・(
1) must be (-Kffi. The formula j, (1+Q, 2) θ, -k. θ2-Ω, 0°, -, Q
2. /ku-θ, /θ2... (2>is 1
7. , the deflection angle of the electron beam Yσ0. , 02 is the excitation strength tlfJ+ of the first and second deflection coils, 1. Since it is proportional to J2, the above equation (2) is '12/Q, = J+ /J2 = const,
--・(3) Yell.

Therefore, conventionally, the excitation intensity of both deflection coils was J+.

The J2 ratio is fixed at the above Q2 /I2, but when the objective lens is strongly excited as is the case these days, the sample is inevitably drawn into the front magnetic field of the objective lens. Therefore, if the specimen is placed in the magnetic field of the objective lens,
The electron beam deflected J to the second stage 1-internal system is 6? of the objective lens. The sample is further deflected by the i-direction magnetic field (therefore, the final sample irradiation angle O is 1 including the deflection of the objective lens.
). Therefore, the objective 1 lens is changed when the sample is displaced in the height direction or for focusing the dotted line image with variable magnification, and therefore the intensity of the magnetic field in front of the objective lens 1'81 changes. As a result, the deflection angle due to the magnetic field changes, and the irradiation position on the sample changes. In a conventional two-stage deflection device, when the excitation intensity of the objective lens was varied for focusing tJ-, the ten electron beam spots were displaced according to the change. -J,
It interferes with the observation of precise dark-field images.

The present invention has been made in view of the above points, and its object is to provide a two-stage deflection device that can always irradiate a fixed point with an electron beam regardless of changes in the excitation intensity of the objective lens. .

The structure of the present invention is to install a two-stage electron beam deflector above a sample arranged in a magnet of an objective lens, and to supply current or voltage at a predetermined ratio to the two-stage deflector for C testing. An electron microscope configured to irradiate an electron beam at a predetermined angle to a target lens, the apparatus comprising means for varying the ratio of current or electric JT supplied to both deflectors in accordance with the excitation intensity of the objective lens. It is characterized by a two-stage deflection device for etc.

The present invention will be explained below based on the drawings.

Figure 2 shows that when the excitation strength a of the objective lens, that is, the excitation current, is changed, the two-stage deflection line ('1 is changed to 'rlA') of the equation (3) is changed.
5'F shows the relationship between the excitation strength (K) ratio of the first deflection coil and the second deflection coil. In the figure, the horizontal axis To represents the excitation current of the objective lens, and the vertical axis represents the ratio J2/Jl of the excitation strength J2 of the second deflection coil to the excitation strength WJ+ of the first deflection coil. It's Zurano. As can be seen from the figure, the excitation intensity ratio J 2 / J of the second and first deflections = 1 il with respect to the change in the excitation current of the objective lens.
+ indicates a change approximating a quadratic curve. Therefore, this relationship between J and U is measured in advance and C is set. When focusing the objective lens, depending on the current value, the current to be passed to the first deflection] and the current to be passed to the second deflection = the current to be passed to the second deflection are determined. If the ratio is shifted by [J-], there will be no displacement of the electron beam deflector.
A step deflection system will be obtained.

= 4- Fig. 3 (.1 is a block diagram of an embodiment of the present invention based on the above original 1jl'i, and the same symbols and months as in Fig. 1 indicate the same constituent members. 5 is a deflection angle setting The current is set to determine the required deflection angle (q), and the shunt control circuit 6
I can't stand it. The shunt control circuit divides the sent current into two parts at a constant conversion rate (one of which is sent to the first deflection coil 1 via the amplifier 7, and the other is sent to the second deflection coil via the amplifier 8).
Deflection of = 1 supply to il 2. 9 is an excitation power source for the objective lens, and its current value is variable for focusing.

A signal regarding the current value of the objective lens power supply hs + is sent to the sprout distribution flow control circuit 6, and the first
, the dividing ratio of the current supplied to the second deflection coil is varied. That is, when there is a relationship as shown in FIG. 2, the control circuit 6 approximates the curve with a certain function or a plurality of polygonal lines so that the shunt ratio is determined by the objective lens current value.
Roll from control 1 to . This makes it possible to realize a two-stage deflection device in which the irradiation position of the electron beam on the sample soil does not change no matter how the objective lens is varied.

Note that the above is one embodiment of the present invention, and various changes can be made in practical use. For example, we have shown the case where a loidal coil is used as the electron beam deflector, but the same effect 1':1 can be obtained not only when using such an electron beam deflector but also when using an electrostatic deflector. In the embodiment shown in Fig. 3, the excitation power source for the objective lens is 9J, and the control circuit 6 is connected to No. 18). In the lock, the branch control circuit 6 can be controlled by the -1 bicoater. Further, in the above embodiment, the current value was used depending on the excitation strength Yα of the objective lens, but if the magnetic field strength of the objective lens can be directly measured, it is better to use the magnetic field strength. Furthermore,
Although the above description is applied to the ++1 field image vA dormitory of a transmission electron microscope, it can be similarly applied to cases where scanning images are observed using the transmission electron microscope.

In this case, a scanning power source is used instead of the power source 5.

Since the two-stage deflection condition is always satisfied in the excitation bullet hole of the objective lens with the configuration as explained above, when the height position is changed or the magnification is changed in the first trial, the electron beam trial] irradiation point will not change, making it possible to observe precise dark-field images.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the outline of a conventional two-stage deflection system, FIG. 2 is a diagram for explaining the present invention in detail, and FIG. 3 is a block diagram of an embodiment of the present invention. 1: First deflection coil 2: Second deflection coil 3: Objective lens /' J Tsuka

Claims (1)

[Claims] A two-stage electron beam deflector is installed above the sample placed within the magnetic field of the objective lens. The apparatus for irradiating an electron beam at an angle is characterized by comprising means for varying the ratio of current or voltage supplied to both deflectors in accordance with the excitation intensity of the objective lens. Two-stage deflection device for covering electron microscopes, etc.